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Calhoun: The NPS Institutional Archive Theses and Dissertations Thesis Collection 1996-03 Application of pressure-sensitive paint in shock-boundary layer interaction experiments Seivwright, Douglas L. Monterey, California. Naval Postgraduate School http://hdl.handle.net/10945/7969

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Page 1: Application of pressure-sensitive paint in shock-boundary ... · Application of pressure-sensitive paint in shock-boundary layer interaction experiments Seivwright, ... Basedontheprincipleof

Calhoun: The NPS Institutional Archive

Theses and Dissertations Thesis Collection

1996-03

Application of pressure-sensitive paint in

shock-boundary layer interaction experiments

Seivwright, Douglas L.

Monterey, California. Naval Postgraduate School

http://hdl.handle.net/10945/7969

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DUDLEY KNOX LIBRARY

NAVAL POSTGRADUATE SCHOOL

MONTEREY CA 93943-5101

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NAVAL POSTGRADUATE SCHOOLMONTEREY, CALIFORNIA

THESIS

APPLICATION OF PRESSURE-SENSITIVEPAINT IN SHOCK-BOUNDARY LAYERINTERACTION EXPERIMENTS

by

Douglas L. Seivwright

March, 1996

Thesis Advisor: Raymond P. Shreeve

Approved for public release; distribution is unlimited.

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REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching

existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this

burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services,

Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and

Budget, Paperwork Reduction Project (0704-0188) Washington DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATEMarch 1996

REPORT TYPE AND DATES COVEREDMaster's Thesis

4. TITLE AND SUBTITLE APPLICATION OF PRESSURE-SENSITIVE

PAINT IN SHOCK-BOUNDARY LAYER INTERACTIONEXPERIMENTS

6. AUTHOR(S) Seivwright, Douglas L.

FUNDING NUMBERS

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Naval Postgraduate School

Monterey CA 93943-5000

PERFORMINGORGANIZATIONREPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORINGAGENCY REPORT NUMBER

1 1 . SUPPLEMENTARY NOTES The views expressed in this thesis are those of the author and do not reflect

the official policy or position of the Department of Defense or the U.S. Government.

12a. DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution is unlimited.

12b. DISTRIBUTION CODE

13. ABSTRACT (maximum 200 words)

A new type of pressure transducer, pressure-sensitive paint, was used to obtain pressure

distributions associated with shock-boundary layer interaction. Based on the principle of

photoluminescence and the process of oxygen quenching, pressure-sensitive paint provides a

continous mapping of a pressure field over a surface of interest. The data measurement and

acquisition system developed for use with the photoluminescence sensor was evaluated first

using an underexpanded jet blowing over a flat plate. Once satisfactory results were

obtained, the system was used to examine shock-boundary layer interaction in a blow-down

supersonic wind tunnel at Mach numbers of 1.4 and 1.7. Details of the measurement

technique, and discussion of the flow fields which were examined, are reported.

14. SUBJECT TERMS APPLICATION OF PRESSURE SENSITIVE PAINT IN SHOCK-BOUNDARY LAYER INTERACTION EXPERIMENTS

15. NUMBER OFPAGES 203

16. PRICE CODE

17. SECURITY CLASSIFI-

CATION OF REPORT

Unclassified

SECURITY CLASSIFI-

CATION OF THIS PAGEUnclassified

19. SECURITY CLASSIFI-

CATION OF ABSTRACTUnclassified

20. LIMITATION OFABSTRACT

UL

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. 239-18 298-102

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11

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Approved for public release; distribution is unlimited.

APPLICATION OF PRESSURE-SENSITIVE PAINT

IN SHOCK-BOUNDARY LAYER INTERACTION EXPERIMENTS

Douglas L. SeivwrightIf

Lieutenant, United States Navy

B.S., Embry-Riddle Aeronautical University, 1985

Submitted in partial fulfillment

of the requirements for the degree of

MASTER OF SCIENCE IN AERONAUTICAL ENGINEERING

from the

NAVAL POSTGRADUATE SCHOOLMarch 1996

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DUDLEY KNOX LIBRARYNAVAL POSTGRADUATE SCHOOLMONTEREY CA 93943-5101

ABSTRACT

A new type of pressure transducer, pressure-sensitive paint, was used to obtain

pressure distributions associated with shock-boundary layer interaction. Based on

the principle of photoluminescence and the process of oxygen quenching, pressure-

sensitive paint provides a continuous mapping of a pressure field over a surface of

interest. The data measurement and acquisition system developed for use with the

photoluminescence sensor was evaluated first using an underexpanded jet blowing

over a flat plate. Once satisfactory results were obtained, the system was used to

examine shock-boundary layer interaction in a blow-down supersonic wind tunnel

at Mach numbers of 1.4 and 1.7. Details of the measurement technique, and

discussion of the flow fields which were examined, are reported.

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VI

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TABLE OF CONTENTS

I. INTRODUCTION 1

A. DESCRIPTION OF THE CONCEPT 2

B. APPROACH TO THE PROBLEM 3

II. THEORY OF MEASUREMENT 5

A BACKGROUND 5

B. LUMINESCENCE 5

C. ABSORPTION AND EMISSION MECHANICS 6

1. Perturbation Theory 7

2. Spontaneous Emission 10

3. Triplet and Singlet States 10

4. Intramolecular Processes Involving Excited States 12

D. OXYGEN QUENCHING 16

E. MATHEMATICAL MODEL DEVELOPMENT 17

1. Temperature Effects 20

2. Aerodynamic Application 21

III EARLY DEVELOPMENT USING A FREE-JET APPARATUS 23

A APPARATUS AND FLAT PLATE ASSEMBLY 23

1. Freestream Flow Field ofthe Underexpanded Sonic Jet 27

a. Further Flow Field Studies 33

vii

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B. OPTICAL MEASUREMENT SYSTEM 41

1. Luminescence Coating 41

a. Reflective Backing 43

2. Illumination Source 43

a. Filters 45

3. Detection System 46

C. EXPERIMENTAL PROGRAM 48

1. Flat Plate Preparation 48

2. Experimental Procedure 49

3. Image Data Reduction 51

a. Image Processing 51

(1) Averaging 52

(2) Dark Current 54

(3) Registration 54

(4) Ratioing 63

b. Calibration 70

c. Field Pressure Map 77

IV APPLICATION TO SHOCK-BOUNDARY LAYERINTERACTION IN A SUPERSONIC WIND TUNNEL 83

A. DESCRIPTION OF FACILITY 83

1. Nozzle Blocks 86

a. Performance Evaluation ofthe Mach 1.7 Nozzle Blocks 86

viii

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B. INSTRUMENTATION 90

C. EXPERIMENTAL PROCEDURE 90

D. DISCUSSION AND RESULTS 94

V CONCLUSIONS AND RECOMMENDATIONS 103

APPENDLXA. RUSSELL-SANDERS COUPLING 107

APPENDLXB. LUMINESCENCE COATING CHARACTERISTICS 109

A. TEMPERATURE SENSITIVITY 109

B. PHOTODEGRADATION 110

C. TIME RESPONSE 112

D. COATING THICKNESS / INDUCTION PERIOD 112

APPENDIX C EPLX SOFTWARE SUMMARY 115

A IMAGE DATA ACQUISITION 115

B. IMAGE PROCESSING 120

1. Averaging 120

2. Subtraction 121

3. Registration 123

4. Ratioing 126

5. Thresholding 127

6. Pseudo-coloring 128

APPENDLXD. DARK CURRENT 131

ix

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APPENDIX E SUPERSONIC NOZZLE DESIGN PROGRAM 135

A. INVISCID CONTOUR SOFTWARE (Program char6) 136

1

.

Category 1 : Characteristic Lengths and Nozzle Types 137

2. Category 2: Nozzle Flow and Geometry Specifications 1 40

3. "outptl" Example and Description 143

B. MODIFICATION FOR VISCOUS EFFECTS (Program nbl6) ... 146

1. Category 1: Functional Modes 148

2

.

Category 2 : Flow Conditions and Nozzle Dimensions 151

3. File "outpt3" Format Description 155

C. PROGRAM LISTINGS 159

REFERENCES 179

INITIAL DISTRIBUTION LIST 183

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LIST OF FIGURES

Figure 1 Schematic Representation ofthe Pressure-Sensitive Luminescent

Coating Concept 3

Figure 2 Energy Level Diagram for the Representation ofFluoresence and

Phosphorescence 8

Figure 3 Energy Levels ofMolecular Excited States and Transitions

Between Them 13

Figure 4 Summary of Transition Types and Associated Rates 18

Figure 5 Schematic ofthe Underexpanded, Sonic Jet Nozzle and

Supporting Facility 23

Figure 6 Underexpanded Jet Nozzle Apparatus 24

Figure 7 Schematic ofthe Pressure Port Arrangement on the Plate Surface 25

Figure 8 Bracket and Model Assembly 26

Figure 9 Bracket and Model Assembly Mounted to the Face ofthe Sonic Jet 26

Figure 10 Sketch of Jet Structure Behind a Highly Underexpanded Nozzle 27

Figure 11 Underexpanded Free Jet at 65 psig Plenum Pressure 28

Figure 12 Flow Visualization and Pressure Distribution Across Flat Plate at 65 psig ...29

Figure 13 Flow Visualization and Pressure Distribution Across Flat Plate at 80 psig ...30

Figure 14 Flow Visualization and Pressure Distribution Across Flat Plate at 90 psig ...31

Figure 15 Flow Field Comparison Without (Top) and With (Bottom) the

Flat Plate 32

Figure 16 Flow Visualization at 30 psig 34

XI

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Figure 17 Flow Visualization at 38 psig 35

Figure 18 Flow Visualization at 65 psig 36

Figure 19 Details of Separation Bubble 37

Figure 20 Flow Visualization at 25 psig 39

Figure 21 Flow Visualization at 40 psig 39

Figure 22 Flow Visualization at 68 psig 40

Figure 23 Flow Visualization at 75 psig 40

Figure 24 Schematic ofPressure Measurement System 41

Figure 25 Excitation and Emission ofPlatinum Octaethylporphyrin 42

Figure 26 Modification ofFocusing Assembly of the Light Source 44

Figure 27 Spectral Response Curve for the COHU Camera Model 49 1 47

Figure 28a Single Image of the Underexpanded Jet Across the Flat Plate at 65 psig ...55

Figure 28b Graphical Representation of a Single Line of Pixels of a Single Image 56

Figure 29a Ten Averaged Images ofthe Underexpanded Jet Across the Flat Plate 57

Figure 29b Graphical Representation of a Single Line of Pixels of Ten Averaged

Images 58

Figure 30a One Hundred Averaged Images ofthe Underexpanded Jet/Flat Plate 59

Figure 30b Graphical Representation of a Single Line of Pixels ofOne Hundred

Images 60

Figure 31 Wind-On Image ofthe Underexpanded Jet at 65 psig Across a Flat Plate ...64

Figure 32 Wind-Offlmage for the 80 psig Condition 65

Figure 33 Three Dimensional Intensity Plot ofthe Surface ofthe Plate 66

xu

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Figure 34 Ratioed Image ofthe Wind-On and Wind-OffImages for the

Flat Plate/Jet Interaction 68

Figure 35 Result of a Ratioed Image Following Improper Registration Technique 69

Figure 36 Calibration Line of Pixels for the 65 psig Case Prior to Spatial Averaging ...72

Figure 37 Calibration Line of Pixels for the 65 psig Case After Spatial Averaging 73

Figure 38 Calibration Curve for the Underexpanded Jet/Flat Plate at 65 psig 74

Figure 39 Calibration Curve for the Underexpanded Jet/Flat Plate at 80 psig 75

Figure 40 Calibration Curve for the Underexpanded Jet/Flat plate at 90 psig 76

Figure 41 Graphical Representation ofthe Red, Green, and Blue Lookup Tables 78

Figure 42 Pressure Map of the Underexpanded Jet at 65 psig Across a Flat Plate 79

Figure 43 Pressure Map of the Underexpanded Jet at 80 psig Across a Flat Plate 80

Figure 44 Pressure Map of the Underexpanded Jet at 90 psig Across a Flat Plate 81

Figure 45 Schematic ofthe Supersonic Wind Tunnel and Supporting Facility 84

Figure 46 Supersonic Wind Tunnel Apparatus 84

Figure 47 Nozzle Blocks and Test Section Exploded View 85

Figure 48 Tunnel Pressure Distributions as a Result of Varying Rod Diameters 88

Figure 49 Cross-Sectional View ofthe Mass Bleed-Off System 89

Figure 50 Mass Bleed-OffTube Mounted in the Tunnel 89

Figure 51 Spectometer Results for the Optical Window 91

Figure 52 Instrumentation Setup for the Supersonic Wind Tunnel

Shock-Boundary Layer Experiment 92

Figure 53 Schematic ofthe Normal Shock-Boundary Layer Interaction 95

xm

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Figure 54 Mach 1 .4 Pressure Map of the Shock-Boundary Layer Interaction 96

Figure 55 Graphical Representation of the Pressure Distribution of the

Shock-Boundary Layer Interaction at Mach 1.4 97

Figure 56 Mach 1 . 7 Pressure Map ofthe Shock-Boundary Layer Interaction 98

Figure 57 Graphical Representation of the Pressure Distribution of the

Shock-Boundary Layer Interaction at Mach 1.7 99

Figure 58 Calibration Curve for the Mach 1 .4 Interaction 100

Figure 59 Calibration Curve for the Mach 1.7 Interaction 101

Figure Bl Luminescence Intensity as a Function of Temperature 110

Figure B2 Effect of Temperature on Coating Calibration Curve Ill

Figure B3 Illustrative Example ofthe Effect ofPhotodegradation

on Response Time Ill

Figure B4 Induction Period ofthe Luminescent Coating with Thicknesses

in Excess of 17 Micrometers 113

Figure C 1 "Main Menu" for EPIX Interactive Image Analysis Software 116

Figure C2 "Video Resolution" Sub-Menu 116

Figure C3 "Video Digitize/Display" Menu 117

FigureC4 "Motion Sequence Capture/Display" Sub-Menu 118

Figure C5 "Image Processing" Sub-Menu 122

Figure C6 "Two Image Arithmetic" Sub-Menu 123

Figure C7 "Pixel Peek, Poke and Plot" Sub-Menu 124

Figure C8 "Image, Copy, Resize, Rotate" Sub-Menu 125

Figure C9 "Contrast & Lookup Table" Sub-Menu 128

xiv

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Figure CIO "Define Lookup Table" Sub-Menu 129

Figure Dl Representation ofthe Effect ofDark Current on the Creation

of Charge 132

Figure El Illustrative Example ofthe Introductory Remarks for

Program "char6" 136

Figure E2 Schematic of Supersonic Nozzle Design by Method of

Characteristics 138

Figure E3 Example Showing the Format of File "outptl" 144

Figure E4 Nozzle Wall Correction for Boundary Layer 147

Figure E5 Example Showing the Format ofFile "outpt3" 156

xv

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XVI

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ACKNOWLEDGMENTS

I would like to take this opportunity to express my deep appreciation to those people

who have contributed to this seemingly endless endeavor. To Professor Raymond

Shreeve for his invaluable guidance and knowledge, and for instilling in me the qualities

that are necessary to successfully investigate the scientific unknown. To Rick Still for his

incredible technical expertise, creativity, and steadying influence. I thank Thad Best for

his support and sound judgment. Finally, I would like to thank my wife, Angelica, whose

patience, support, and encouragement has shown me that there is no obstacle that cannot

be overcome to attain your dreams and desires.

xvu

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I. INTRODUCTION

One of the major thrusts of military aircraft engine design is towards achieving higher

pressure ratios per compressor stage in order to reduce the number of stages and thereby

reduce engine weight. This requires higher aerodynamic loading on the blades, and/or

higher relative flow velocities over the blading. Where the relative Mach number is

supersonic, shock waves will occur in front of and within the blade passages. The

interaction of strong shocks with blade surface boundary layers can lead to high losses and

reduced turning. Thus shock-boundary layer interaction, and methods to alleviate its

attendant negative effects on compressor blade performance, warrant careful investigation.

It was the need to make surface pressure measurements in a model simulation of shock-

boundary layer interaction in a fan blade passage, which motivated the present study.

Currently, aerodynamic (surface) pressure measurements are made by installing a

prearranged distribution of pressure ports in a wind-tunnel model or prototype aircraft.

Since the installation of taps is an expensive process, the location and number oftaps is

normally predicated on a pre-selected area of interest. Obviously, this arrangement offers

little flexibility ifthe area of aerodynamic interest is broad and fine spatial resolution is

needed. Even with a substantially instrumented region, the information obtained is

spatially discrete. It is often difficult to decide where to position the taps before the model

is tested.

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Within the last six years, the Central Aero-Hydrodynamic Institute in Moscow, the

University ofWashington (with support from Boeing and NASA) and McDonnell Douglas

Aerospace have independently developed a new technique to measure surface pressures

which is based on photoluminescent coatings [Ref 1 through Ref 9]. The pressure-

sensitive coatings contain photoluminescent probe molecules. With the proper excitation

of light, the molecules luminesce with an intensity which is inversely proportional to the

local surface pressure. As a result, pressure-sensitive paints offer almost limitless spatial

resolution, in addition to being applicable to surface locations which may not be accessible

for pressure ports.

A. DESCRIPTION OF THE CONCEPT

Figure 1 illustrates the general concept of the method. A luminescent molecule

dissolved in an oxygen-permeable plastic resin is applied to a surface of interest. When

illuminated by ultraviolet radiation the coating luminesces with an intensity that depends

on the oxygen partial pressure seen by the active molecule. Thus the oxygen partial

pressure can be determined from the emitted light intensity and since the mole fraction of

oxygen in air is a known constant, the air pressure may then be readily calculated. The

result of this oxygen dependence is that the airflow-induced surface-pressure field (and the

corresponding oxygen partial-pressure field), gives rise to a luminescence intensity

distribution. The intensity field can be imaged using a video camera, the image digitized,

processed and stored on a computer. The end result is a map of the surface pressure field.

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/\UV Lamp

AIRFLOW ^

Camera /\VCR

<>/ Video Recorder

J Digitizer

J>J Computer

v _J Coating - Luminesceiit Emission

—* V

Figure 1. Schematic Representation ofthe Pressure-Sensitive Luminescent Coating

Concept1

The processing ofthe surface pressure image relies on a calibration curve for the coating

material, which is based on the Stern-Volmer relation. [Ref. 1: p. 34]

B. APPROACH TO THE PROBLEM

The present work was focused on the development of a working

pressure-measurement system, utilizing pressure-sensitive paints, for use in the Gas

Dynamics and Turbopropulsion Laboratories at the Naval Postgraduate School. Although

the system's initial application was tailored for use in the study of shock-boundary layer

interaction in a pilot transonic cascade wind tunnel, and subsequently in a larger

supersonic wind-tunnel, its use for other compressible flow studies was anticipated.

1

See Ref. 1, page 34, Figure 1

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The initial development was carried out using an existing flat-plate model in an

underexpanded sonic jet. This was an arrangement that would produce effects similar to

those to be measured in the tunnel, (i.e. shock waves impinging on a surface, creating a

near-discontinuity in a pressure distribution) but be visually unrestricted since no walls and

windows were present. Subsequently, measurements were made of the interaction ofthe

starting shock wave with the side-wall boundary layer in the test section of a blow down

wind tunnel. Results were obtained at M=1.4 and M=1.7 using different fixed nozzle

blocks. The blocks for M=1.7 were designed and built for the present study, and the

design is detailed in Appendix E.

In reporting the work, Section II first provides some preliminary background work

done in photoluminescent barometry in addition to the theory of photoluminescent

coatings. Section HI describes the development program using the sonic free-jet. Section

IV provides results of applying the system in the supersonic wind tunnel, and Section V

gives conclusions and recommendations. Since the system represents a powerful new tool

for two laboratories, the attempt has been made to include all information and details

necessary to both use and extend the present system.

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H. THEORY OF MEASUREMENT

A. BACKGROUND

Photoluminescence and the process of quenching by oxygen is a photo-chemical

interaction that is well documented and reasonably well-understood. In 1980, Peterson

and Fitzgerald first recognized its potential as a means to make qualitative assessments in

flow visualization studies [Ref. 3]. They reported on a technique in which fluorescent dye,

when applied to a surface and excited by a blue light, illuminated in varying degrees of

intensity, depending on the introduction of nitrogen or oxygen. When nitrogen was

injected through a wall static-pressure tap, a bright streak of luminescence, moving in the

direction ofthe surface flow, was observed. The nitrogen, in close proximity to the

fluorescent dye, reduced the effect ofthe quenching (by displacing the oxygen) and

allowed the intensity ofthe luminescence to increase. The introduction of oxygen, on the

other hand, enhanced the quenching process and decreased the luminescence, producing a

dark streak. This demonstrated that the concept of quenching could be used to acquire

surface pressure measurements.

B. LUMINESCENCE

According to the laws of thermodynamics, a system in an excited energy state due to

the absorption of radiation, must be such that the reverse process of emission of radiation

can occur. Ifno other process is available to allow the system to return to its initial state,

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then emission must take place. Light emission excited by light absorption is called

photoluminescence.

Luminescence is a broad term which encompasses both fluorescence and

phosphorescence. The basic, underlying difference between these two processes is the

time of emission with respect to the end of excitation; fluorescence has a relatively short

lifetime, approximately 10"9-10"7 seconds, whereas phosphoresence's lifetime persists for

lCTMO"2seconds. It is the phosphorescent emission that was used in the present work to

quantitatively measure the static pressure on a surface of interest.

C. ABSORPTION AND EMISSION MECHANICS

Quantum mechanics provides the necessary theoretical tools to describe the absorption

and emission processes of light that were previously unexplainable by wave theory

[Ref 10: p. 457]. Instead of considering light as a wave train of infinite length, the

radiation is instead composed of discrete photons (or quanta) whose energies are equal to

hv, where h is the universal Planck constant, 6.63 x 10"27 erg sec. The concepts of light

being consider as a wave train and that of discrete photons are linked in that the energy of

the quantum is proportional to the light excitation frequency, v . This led to the

hypothesis that radiation of frequency v could not be emitted or absorbed in arbitrary

amounts, but only in quanta of energy s = hv. During an emission process following light

absorption, less energy release by emission could occur, but would radiate at a lower

frequency.

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An absorbing molecule can exist in discrete, sharply defined levels in which transitions

between states occur in certain definite steps. The lowest of these states is the ground

state. States of higher energy are called excited states. There is a large number of

possible excited states, but usually only several ofthose ofthe lowest energy are produced

with visible or ultraviolet light. A simplistic description ofthe nature ofthese excited

states is that a single electron has been promoted from an orbital occupied in the ground

state to an orbital that is vacant while in the ground state.

Figure 2 illustrates several energy levels of an arbitrary molecule which are represented

by the horizontal lines. The vertical distance between two ofthese lines is proportional to

the corresponding difference in energy, hv; the level N represents the ground state. By

absorption of light frequency vnf the molecule is raised to the state F and ifno other

energy levels exist between N and F, the molecule can return to N only by re-emission of a

photon of light ofthe same frequency. Theoretically this is the simplest case of

photoluminescence; it is called "resonance radiation". However, if, as indicated in Figure

2, several other levels C, D, ... are located between N and F, other transitions to C, D, ...

can occur, resulting in the emission of spectral lines of frequency vfc, vfd, ... These

frequencies must be smaller than vfn and therefore photoluminescence can have no

greater frequency or shorter wave-length than the exciting light. [Ref. 1 1 : p. 2]

1. Perturbation Theory

For a molecule that absorbs or emits quanta of radiation under the influence of an

electric field, perturbation theory of quantum mechanics provides the theoretical model

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[-'

A1

A 1 1 j

ft1

i

A A• i

Ar

Mi i t

i i i

i ' i

;

i ?

I ; 1 |

ii

IVI

• i r\

1 i

-N'

! i .? 1 J1 2 3 4 5

N

1 . Resonance Radiation

2. Phosphorescence

3. Fluorescence

4. and 5. Anti-Stokes Fluorescence

Figure 2. Energy Level Diagram for the Representation ofFluorescence and

Phosphorescence2

that defines the physical interaction. The general solution of the wave equation for a

molecule in the presence of a perturbing field results in certain derived relations that

govern the changes ofthe molecule. One such outcome mandates that for radiation to be

absorbed and transition from a stable ground state of energy to an electronically excited

state of energy to occur, the frequency of the quantum must be proportional to the

difference in energy between the states, a situation previously discussed. Once this

condition is met, the probability ofthe transition is governed by the value ofthe transition

moment integral, a second corollary from the solution ofthe perturbed wave equation:

2Figure 2 is found in Ref 1 1, page 4, as Figure 2

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m = J*Fu M*F|dT

Here, ^u and*Fi are the total wave functions for the upper and lower states

respectively ( the wave functions result from the unperturbed solution ofthe Schrodinger

wave equation ) and M is defined as the dipole moment operator [Ref. 10: p. 583].

Evaluation of this integral determines the probability of an optical transition between two

states. Detailed analysis has shown that transitions are probable only between states

characterized by wave functions of a certain class. The results have been summarized in

the form of selection rules which are formulated in terms ofthe quantum numbers that

describe the electronic states involved [Ref 12: p. 51].

Perhaps the most important is the rule governing spin multiplicity. This states that

the spin of an electron must not change during an electronic transition. As will be seen

later, although from a theoretical standpoint transitions between states of different

"multiplicity" do not intercombine, in practice they are observed, but the probability is

usually much lower than an allowed transition. Thus, selection rules are good empirical

guides, but they are not inviolable. [Ref. 13: p. 36]

Although the selection rules considered have been based on the absorption and

emission of light by a molecule under the influence of a perturbing field, a second set of

selection rules similar to the first but derived under a different set of circumstances govern

radiationless processes. These processes, in addition to the spontaneous emission of light,

compete with the excited state of a molecule in depleting its acquired energy and allowing

it to return to its ground state.

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2. Spontaneous Emission

An excited state may undergo a third radiation-related transition to a lower state by

means of spontaneous emission, i.e., fluorescence and phosphorescence. In this process,

an excited species looses energy in a spontaneous manner in the absence of an electric

field. It is a random process: the rate-of-loss of excited species following a kinetic

first-order reaction. If a process follows first-order kinetics described by a rate constant

"k", the mean radiative lifetime, (the time x taken for the intensity to fall to 1/e of its initial

value), is given by

T=l/k

When a radiative transition occurs between states of similar multiplicity, it corresponds,

according to the selection rules, to an allowed transition. Such transitions are

characteristic of fluorescence emission having lifetimes equal to x = 10"8 seconds.

However, there are transitions in which x is much higher, 10'3seconds. When selection

rules suggest a low probability for a transition to occur, such as between states of different

multiplicity, the transition, though theoretically forbidden, can occur, but the process is

relatively slow. This is representative of phosphorescent emission. [Ref 10: p. 585]

3. Triplet and Singlet States

In the absence of a magnetic field, the energy of a single unpaired electron

characterized by its given values of "n" -(the principle quantum number) and "1" (the

azimuthal quantum number) must be further refined to explain the observed fine structure

of atomic spectra. The additional amount of energy that the spectroscopic evidence

10

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indicates is attributed to the interaction that occurs between the angular momenta from the

intrinsic spin and orbital motion of the electron. When several electrons within an atom

(or molecule) are present, the resultant orbit and resultant spin angular momenta

components can combine in several ways resulting in several energy levels for a single

configuration of an atom (or molecule). This interaction is known as Russell-Sanders

coupling, the result ofwhich is the "multiplicity" of energy levels that a given electron

configuration of an atom may possess. Thus, a single energy level for a given electron

configuration for an atom (or molecule) is referred to as singlet state, two energy levels as

a doublet, three energy levels a triplet, etc. [Ref. 14: p. 79] A more thorough discussion is

given in Appendix A.

Nearly all molecules have a ground-state electronic configuration in which the spin

of each electron is opposed to, or paired up with, the spin of another electron which

otherwise has the same spatial quantum numbers, a consequence ofthe Pauli exclusion

principle. In this instance the total angular momentum of each electron within the pair,

composed ofthe spin and orbital momenta, tend to cancel with each other . When all the

pairs of electrons within the molecule are considered, the net result is zero total angular

momentum (vector), producing a single energy level for the given electron configuration.

Molecules will have, in addition to a ground state that is usually a singlet state, a number

of excited states that also have all the electrons paired and that are, therefore, also singlet

states. [Ref. 15: p. 16]

11

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Whether or not the ground state is a singlet state for molecules with an even

number of electrons, there will be excited states in which a pair of electrons have their

spins in the same direction, giving the molecule a net total angular momentum (vector).

In this case, the coupling interaction results in three energy levels for the configuration,

and thus the designation triplet state.

Therefore, promotion ofan electron to an upper state can in principle give rise to

two types of energy states, the triplet and singlet, while still maintaining the same electron

configuration. Therefore, for every singlet state there is a corresponding triplet state, with

the triplet state displaying a lower energy level. Figure 3 illustrates the two types of

electronically excited states, where the spin orientations for each state are depicted as

arrows next to the appropriate state. The additional lines within each electronic state refer

to the various vibrational and rotational energy levels the molecule may acquire with the

absorption of energy.

4. Intramolecular Processes Involving Excited States

With the absorption of a quantum, a molecule is raised from a singlet ground to a

singlet excited state. The selection rules stipulate that the absorption of electromagnetic

radiation does not "unpair" the electrons of a molecule (transitions occur between states of

like multiplicity) thus preventing direct absorption of light from a singlet to a triplet state.

The molecule, having been raised to an upper vibrational level within the excited state,

begins to lose the excess vibrational energy by collisions with surrounding molecules. The

12

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-

*3

A

4

Internal

t

A

Conversion jl T

s,

10*V J'.-=1

jk

1 » J) Vibrational

V. Relaxation

4

3 io1^- 1

rTw

I .! 2

Internal ^/ Intersystem J I

Conversion N Crossing

r1 Si

5TSJPL-' ? 104 -10,2s-' c

J ^_ H 1r^ "If ^v ' o^ 1 s

i- JS

),_ «-

1

^/Vibrational .9 n 32 ^ *k, Oiipnrhino <» '

^s Intersystem <D '1

3 io1Vr S" I"? J r.rrxt:inn c *-

< u. C io"1-ioV 1 O if)

S a] I f Vibrational . . -s •

N Quenchina R A

itSo

\f f 10^1 ° 1

11

^o

Figure 3. Energy Levels ofMolecular Excited States and Transitions Between Them3

radiationless process of internal conservation then occurs whereby the molecule passes

from a low vibrational level ofthe upper state to a high vibrational level of a lower state

having the same total energy. Once internal conversion is complete, this cycle of events

repeats itself leading to the net result ofthe molecule falling to the lowest vibrational level

ofthe first excited singlet state as illustrated in Figure 3. [Ref. 15: p. 9]

At this point, the molecule may return to the ground state by one of three paths:

Si —> So (Internal conversion)

Si —> So + hv (Fluorescence)

Si —>Ti (Intersystem crossing)

Figure 3 is found in Ref 16, page 71, as Figure 5-1.

13

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The internal-conversion process, involved with the intramolecular energy transfer between

the first excited singlet and ground state, takes place at a much slower rate (109seconds)

as compared with the same process occurring between the upper excited singlet states to

the first excited singlet state (1012

seconds). The increase in inefficiency in energy transfer

is explained by the relatively large energy separation between S, and S as compared to

the energy differences between the upper excited states. This allows fluorescence (10'9to

10"7 seconds) and, with the combined effect ofthe spin-forbidden nature ofthe states, the

process ofintersystem crossing (109seconds) to effectively compete with the internal

conversion process.

When a molecule returns to the ground state via the first excited triplet state, it

undergoes a conversion process known as intersystem crossing. Intersystem crossing is a

non-radiative process between states of different multiplicity. It is theoretically forbidden

with regard to the formal selection rules, but in practice, these transitions do take place

(although with extremely low probability). This is made possible through the

"breakdown" ofthe spin-orbit coupling model discussed in Appendix A. In the absence

of magnetic or electric fields the total angular momentum ofthe molecule remains

constant, and the ability to discern between specific states such as singlet and triplet is

possible. However, when an electromagnetic field is present, though the total angular

momentum vector remains constant, the spin and oribital degrees offreedom become time

dependent, and it becomes meaningless to speak of specific states [Ref 16: p. 12]. This

ultimately leads to the mixing of states. The interaction is enhanced by heavier elements

14

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due to an increase ofthe magnetic field developed by the nucleus, as in the case of

platinum octaethlyporphyrin (PtOEP).

The lowest vibrational level of the lowest triplet state is generally situated at an

energy level below that ofthe lowest excited singlet state, but its upper vibrational levels

reach to the bottom ofthe singlet level, and intersystem crossing occurs with the molecule

crossing over to one ofthese upper vibrational levels ofthe lowest triplet state. From here

the molecule rapidly looses its excess vibrational energy and falls to near the lowest

vibrational level of the triplet state.

Again, the molecule may return to the ground state from this point by one ofthe

following paths:

Ti —» So (Intersystem Crossing)

Ti —> S + hv (Phosphorescence)

As before, it might be expected that the analogous process ofintersystem crossing from

the lowest vibrational level of the triplet state to the ground state would take place with

equal facility as the transition from Si —» Ti . In fact it is usually some 106- 10

9times

slower. If radiationless Ti -» S transitions occurred with rate constants of 10"8seconds,

the molecule would have no time to emitTi -» S phosphorescence by the spin-forbidden

radiative process. On the other hand, ifthe Si —> Ti intersystem crossing process were as

slow as that ofthe Ti —> S radiationless process, then it could -not compete effectively

with fluorescence. Phosphorescence would then be a rare phenomenon and the

photochemical behavior would be very different. The difference between the rates ofthe

15

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Si —> Ti and Ti —> S radiationless processes is, as was the case with internal conversion,

a function of the energy differences between S, and T, , and, T, and S .[Ref. 15: p. 41]

D. OXYGEN QUENCHING

The exceptionally long radiative lifetimes of molecules in the lowest triplet state make

them vulnerable to a variety of radiationless processes that deactivate the molecule,

allowing it to return to the ground state. As an example, they are very susceptible to

collisions with molecules, and in such cases may encounter molecules of a specific nature

which are particularly effective in removing excitation energy.

Previous reference was made to the fact that most molecules with an even number of

electrons have a ground state in which their electrons occupy orbitals in pairs. These

molecules were said to have singlet states. There are however some molecules containing

an even number of electrons for which the states of lowest energy have two unpaired

electrons occupying different orbitals. The most important ofthese is molecular oxygen,

ofwhich the ground state is a triplet. Molecular oxygen is very effective in removing

triplet excitation energy, and can act at exceedingly low concentrations. [Ref. 15: p. 36]

The energy transfer that takes place when an excited triplet PtOEP molecule collides

with a triplet oxygen results in a ground-state singlet PtOEP molecule and a singlet

excited oxygen molecule. The reaction is expressed as follows:

Ti + 32 -^S o +

1

2

The reaction occurs very rapidly but is consistent with the formal selection rules. It is this

bimolecular reaction that results in the quenching of the phosphorescence. The University

16

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ofWashington found that when PtOEP was embedded in an oxygen-permeable silicon

resin and subject to atmospheric pressure, the quenching reaction had a rate comparable to

that of phosphorescence. Variations in atmospheric pressure from to 1 atmospheres

demonstrated a suitable drop in phosphorescence yield ofPtOEP that would allow it to be

useful as a measurement tool in the study of static pressure changes in aerodynamic wind

tunnel testing. [Ref. 9: p. 18]

E. MATHEMATICAL MODEL DEVELOPMENT

Oxygen quenching ofluminescence by collisional deactivation ofthe emission process

is the basis for developing a prediction model. It is important to note that the end result of

this development, the Stem-Volmer relation, is strictly valid only for free molecules in

solution. However, it has been found that it describes accurately the quenching process

that occurs in the present situation. The basis for the present development is the work of

Parker [Ref. 15], which may be consulted for further details.

The development first begins with the definition ofthe triplet formation efficiency, <j>t ,

being the number oftriplet molecules formed per quantum of exciting light absorbed.

Assuming now that a system, illuminated with a beam of exciting light of constant

intensity, is in a photochemically steady state. The rate of population ofthe lowest excited

singlet state, S 1? is found to equal the rate of light absorption, I , and the rate offormation

of triplet molecules by crossing from Sj is equal to I <t>t

.

Figure 4 illustrates the rates ofthe various processes by which the triplet is produced

and consumed; these are represented in equation form as follows:

17

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9(7)

no12

)

1-T-kqW\

dd12

)

.-•' g

A(10-9

)

\ \m \ PA(10"4 \ (10-^ s

\to \10

+2) ^

to

10+2

) \

*oF§ n

(?)

II 2

f

(10-9

to

106 )

0*15)

Notes:

Key:

1

.

Radiative transitions are shown as full arrows.

2. Radiationless transitions are shown as dashed arrows.

a = absorbtion n = n' = internal conversion

f = fluorescence p= phosphorescence

m = g = g' = intersystem crossing

kQ[Ql = kq [q] = quenching

Figure 4. Summary of Transition Types and Associated Rates4

S ^ s 1 -» T

1

Rate = I a <t>t (Triplet Production)

Ti —> So + hv kp[T] (Phosphorescence)

Ti -» S + heat km[T] (Intersystem Crossing)

T, +q->S + q

T Thermal qA^iuiti^rv

kq[T][q] (Triplet Quenching)

ke[T] (Intersystem Crossing)Activation

The square bracketed [q] and [T] represent concentrations, [q] represents the

concentration of all quenching impurities in the system, kq [q] a composite pseudo

first-order rate constant for impurity quenching, and ke[T] represents the rate ofthermal

activation of triplet molecules back to the excited singlet level [Ref. 15: p. 87].

figure 4 is found in Ref 1 5, page 69, as Figure 23

18

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[T] represents the concentration of excited triplet molecules when the steady state has

been achieved. All processes so far considered in Figure 4, with the exception of light

absorption, are first-order reactions having rate constants equal to the reciprocals of the

lifetimes quoted.

Now consider, in addition to the previous statements and definitions made with respect

to the steady state ofthe system, that the rate of production of excited triplet molecules

(in stateT, ) is just balanced by their rate of disappearance via the various processes

discussed above. This can be expressed as

I a (|>t = (kp + km + kq [q]+ke)[T] (1)

Since the rate of emission of phosphorescence iskp [T] , the phosphorescence efficiency

<|>p is given by

<j>p= kp [T]/Ia (2)

Equation (1) may be solved for Iaand substituted into equation (2) to arrive at

4>p = kp <t>t / (kp + km + kq [q] + k e) (3)

In the absence of quenching agents affecting the removal of triplet excitation energy,

equation (3) gives, for the phosphorescence efficiency,

(f)°= kp(t)t/(kp+km +ke) (4)

Taking the ratio of equations (3) and (4):

$£% = 1 + kq [q] / (kp+ km + k e) (5)

or,

19

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d>£/(|>P=

l + K[q] (6)

where

K = x kq and l/x = (kp + km + ke) (7)

Equation (6) is known as the Stern-Volmer equation for quenching, and the constant K as

defined in equation (7) is referred to as the Stern-Volmer quenching constant.

For this particular application, the quenching impurity, [q], may be defined as

[q] - S Po 2 (8)

where S is the solubility of oxygen in the system and Po2 is the partial pressure of oxygen

in equilibrium with it. This leads to the relation

(|>p/(t>p= l+K /

Po2 (9)

Finally, by definition, the luminescence, I, is linearly proportional to the quantum yield

( <i>= photons emitted/photons absorbed) for a given quenching condition, (i.e.,I = I abs<i> )

,

where 1^ is the excitation light intensity by the luminescent species. Thus

Imax/I=l+K/

Po2 (10)

where Imax is the maximum possible value that occurs in the absence of a quencher.

1. Temperature Effects

The effect that temperature has on the efficiency of phosphorescence may lead to a

decrease in the intensity by several orders of magnitude over the range of 77° K to room

temperature. The effect results in the long lifetime of triplet states and the

correspondingly greater susceptibility to impurity quenching and intersystem crossing

[Ref. 15: p. 89].

20

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The rate constants for each of the intramolecular processes depend on temperature,

following the Arrhenius equation,

k = Ae-Ea/RT?

where k is the rate constant, A is the pre-exponential factor, Eais the activation energy, R

is the gas constant, and T is the temperature in degrees Kelvin [Ref 9: p. 20]. Hence, in

equation (10), 1, 1^ , and K are all functions oftemperature.

2. Aerodynamic Application

In order to apply the form ofthe Stern-Volmer relation presented in equation (10),

it would be necessary to purge the vicinity of the surface of interest of all oxygen in order

to determine 1,^ . In most cases of experimental work, this is impractical. A more

convenient approach is to manipulate the governing equation so that determination of1^

becomes unnecessary.

Equation (10) is first modified by noting that the oxygen partial pressure,Po2 , is

related to the air pressure, P, by Po2

= XP, where X is equal to the mole fraction of

oxygen. Equation (10) then becomes:

Imax/I=l+K/ XP (11)

In the method used in the present work, two images are taken. In the "flow-on"

case, the pressures are unknown. In the "flow-off" case, the pressure distribution is

constant on the surface and equal to atmospheric pressure. These conditions are

represented, respectively, as follows:

21

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WI=1+K'XP (12)

and Imax/I = l+K / XP (13)

where the subscript "o" denotes the value for the flow-off conditions. Dividing equation

(13) by equation (12),

I /I = (1 + K' X P)/(l + K' X P ) (14)

Rearranging,

I /I 1/(1 +K' X P ) + [(K' X P )/(l+ K' X P )](P/Po) (15)

which gives

I /I = A + B(P/P ) (16)

where,

A=l/(l+K'XP )andB = (K/

XPo)/(l+K/ XP ) (17)

A and B represent the coating sensitivity coefficients and are, in general, functions of

temperature for both wind-on and wind-off conditions. In the absence of a temperature

variation across the surface, A and B have the same value over the whole image. Notice

that A + B = 1 . This condition occurs only when the images of I and I are taken at the

same temperature. If any temperature variation is present between the two images, a

value other than one will result. [Ref 1: p. 34} Techniques discussed in Section 3 will

outline the procedures used for determining these coefficients.

22

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III. EARLY DEVELOPMENT USING A FREE JET APPARATUS

A. APPARATUS AND FLAT PLATE ASSEMBLY

A sonic-jet nozzle system located in the Gas Dynamics Laboratory (Bldg. 216) at the

Naval Postgraduate School was used in the initial experiments. A schematic ofthe facility

is illustrated in Figure 5. A photograph ofthe jet nozzle is shown in Figure 6.

Settling Chamber

(Plenum)

1" Diameter

Underexpanded Shrouded Vent

Jet Nozzle jo Atmosphere

TANKFARM

LABORATORY

COMPRESSOR ROOMFrom AtmosphereF<]

I.R. Reciprocating

Boost Pump150 psi

Elliot

Compressor

3 stg, Cent

0-150 psi

Decescant

Air Dryers

Figure 5. Schematic of the Underexpanded, Sonic Jet Nozzle and Supporting

Facility

23

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Figure 6. Underexpanded Jet Nozzle Apparatus

The flat plate used in the present work was a model designed and previously used for jet

interaction studies in the supersonic wind tunnel. The plate was made of stainless steel

with a leading edge diameter of 0.008 inches. Twelve ofthe existing pressure taps were

chosen as close to the centerline ofthe plate as possible. Figure 7 shows a schematic of

the surface ofthe plate showing the twelve taps relative to the centerline. The

pre-arrangement of the taps, in addition to discovering two plugged ports, required that

three offset taps be used to maintain near uniform spacing in the streamwise direction.

24

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6.375 in.

50 in. 0.25 in

3o 5o-I

0.25 in.|

1.0 in.

0.75 in

.^____2o—-o-o-o-^-6o-^b-5o--9o- 1

-°o---2o-k

H K31.0625 in. 0.4844 in. 0.7656 in. 0.25 in.

Epoxy Plug - 0.25 in 0.5 in.

O

0.5 in.

4.0 in.

Leading EdgeFlat Plate Schematic

Top View(Not to scale)

Figure 7. Schematic ofthe Pressure Port Arrangement on the Plate Surface

A simple bracket was made to mount the model so that the surface of the flat plate

become a radial plane, effectively dividing the axi-symmetric jet in half. The bracket and

model are shown in Figure 8 while Figure 9 illustrates this assembly mounted to the face

ofthe jet. Plate washers were placed on the mounting bolts to create a 1/4 inch gap

between the leading edge ofthe plate and nozzle face. This was necessary as it was found

that the jet would not properly form ifthe plate were installed with its leading edge at the

plane of the nozzle opening. Pneumatic pressure measurements were made using the

Scanivalve ZOC system developed by Wendland [Ref. 17].

25

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Figure 8. Bracket and Model Assembly

Figure 9. Bracket and Model Assembly Mounted to the Face of the Sonic Jet

26

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1. Freestream Flow Field of the Underexpanded Sonic Jet

The mechanics offormation and structure ofan underexpanded jet from a sonic

nozzle have been studied in detail by Adamson and Nicholls [Ref 18: p. 265]. A

schematic ofthe structure is illustrated in Figure 10.

InterceptingNoz?e Shock

Jet Boundary

Expansion FansNormal Shock

(MachDisc)

Figure 10. Sketch of Jet Structure Behind a Highly Underexpanded Nozzle5

The "Mach disc" within the free-jet offered an event that would produce a pressure

discontinuity similar to that ofthe starting-shock structure in the supersonic wind tunnel,

but without the visual restrictions imposed by thick test-section windows.

Using the schlieren technique, visualization studies ofthe flow field across the flat

plate were recorded. The data acquired using the pressure-sensitive paint on the flat plate

'Figure 10 is found in Ref. 18, page 265, as Figure 1

27

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could then be interpreted with reference to the flow structure. These studies began by

observing the underexpanded jet without the flat plate mounted to the jet nozzle. This

was done to provide a reference for changes in the flowfield as a result of the interaction

with the plate. Since the jet structure was axi-symmetric, it was anticipated that, with the

plate surface aligned along the centerline ofthe jet, the plate would simply isolate halfof

the jet structure. Figure 1 1 illustrates the jet structure without the flat plate installed at 65

psig plenum pressure. The flow proceeds from right to left.

Figure 11. Underexpanded Free Jet at 65 psig Plenum Pressure

The flat plate was then bolted to the nozzle face and several runs were made at

varying plenum pressures to record the shock structure. Three specific plenum pressures,

65, 80, and 90 psig were chosen as test points at which to compare pressure

measurements with data using the luminescent paint, and the schlieren images ofthe flow

field. The schlieren images of the three events and the corresponding pressure

measurements from the orfices along the flat plate are illustrated in Figures 12, 13, and 14.

28

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PRESSURE DISTRIBUTION ACROSSFLAT PLATE

20

w 15

I 10

oso

| (5)h

£(10)|-

(15)

Plenum Pressure of 65 psi

.

B /

/ VA

N\

\

\ S/ N ;

/ \

B ES

\j

!i

i . i

ai

0.2 0.4 0.6 0.8

(x/c) c = Length of plate (6.375 in.)

Figure 12. Flow Visualization and Pressure Distribution Across Flat Plate at 65 psig

(Flow is from left to right)

29

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PRESSURE DISTRIBUTION ACROSSFLAT PLATE

Plenum Pressure of 80 psi

20

O)X 10wfr3Ub.0)

2o (10)

M0)JCu (20)

(30)

BE—ra

/

F'i

i

i

m

\\

\P

\B\ /vB

i

0.2 0.4 0.6 0.8

(x/c) c = Length of plate (6.375 in.)

Figure 13. Flow Visualization and Pressure Distribution Across Flat Plate at 80 psig

(Flow is from left to right)

30

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PRESSURE DISTRIBUTION ACROSSFLAT PLATE

20

x 10

?I °

•S00)(A

|(20)

Plenum Pressure of 90 psi

- / \

i . i . i .

02 0.4 0.6 0.8

(x/c) c = Length of plate (6.375 in.)

Figure 14. Flow Visualization and Pressure Distribution Across Flat Plate at 90 psig

(Flow is from left to right)

31

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The images and the pressure measurement graphs have been aligned so that the pressure

changes seen on the graphs correspond to the events occurring on the plate surface.

As can be discerned from the schlieren images in Figures 12, 13, and 14, two

oblique shocks appear, a consequence ofthe plate being placed in the flow field. Figure

15 shows a comparison of the flow fields with and without the plate. The oblique shock

emanating from the leading edge ofthe plate can be explained as being due to the

underexpanded process the flow undergoes as it leaves the nozzle. The flow, as it exits

Figure 15. Flow Field Comparison Without (Top) and With (Bottom) the Flat Plate

the nozzle, is off-axis with respect to the centerline ofthe plate thus encountering the plate

at an incidence angle other than zero degrees. The flow in these images is from right to

left.

32

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The second oblique shock's structure gives the perception that it extends from the

surface ofthe plate to the jet boundary; however, closer examination of the two images in

Figure 15 shows that the oblique shock actually merges with the reflected shock (see

Figure 10) giving the erroneous illusion of a single entity. Of greater interest is the extent

ofthe oblique shock to the point of total suppression ofthe normal shock. The sensitivity

ofthe flow to the plate was much greater than first thought, and it was unclear what

events were taking place to justify the magnitude ofthe oblique shock. Additional study

seemed warranted.

a. Further Flow Field Studies

To visualize the flow, methanol was injected through the second pressure port

in the plate surface. Several light fixtures were placed around the plate to better illuminate

the injection area and to provide contrast between the background and flow field. A video

recorder was used to record the events.

Figures 16 through 18 show the sequence of events from selected frames of

the video at two different vantage points. In each set ofimages, the flow proceeds from

left to right.

In Figure 16, the plenum pressure was steady at 30 psig — the boundary layer

up to this point remained attached. At 38 psig, Figure 17 shows initial indications of

reversed flow at the center of the plate. In addition, 1/2 inch to the left of this point, a

pooling of methanol formed. This behavior indicated the presence of a bubble in which a

33

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Figure 16a. Flow Visualization at 30psig — Cross Flow View

Figure 16b. Flow Visualization at 30 psig — Acute View

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Figure 17a. Flow Visualization at 38 psig — Cross Flow View

Figure 17b. Flow Visualization at 38 psig — Acute View

35

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Figure 18a. Flow Visualization at 65 psig — Cross Flow View

Figure 18b. Flow Visualization at 65 psig ~ Acute View

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portion of the injected mass would be expected to stagnate near the separation point, as

the flow re-circulated within the bubble's boundaries. This is more clearly shown in the

schematic ofFigure 19. With increasing plenum pressure, the separation and recirculation

region ofthe flow field gradually moved downstream, eventually encompassing the

injection port, and allowing the alcohol to more clearly define the boundary ofwhat was

indicated to be a separation bubble.

Dividing Streamline r— Edge of Viscous Layer

Entrainment

Separation Point

777777777*

Reattachment Point

V7777777777Zero Velocity

Line

Figure 19. Details of Separation Bubble

To verify whether flow reattachment was in fact occurring downstream, a

second injection port, port number 5, was rigged to concurrently admit methanol into the

flow. Figures 20 through 23 show the sequence ofimages recorded in one such test.

Figure 20 shows that at 25 psig, attached flow was prevalent. At 40 psig, in

Figure 21, the injectant at the first port (port number 2) indicated the presence of reversed

37

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flow, while the injectant at the second port (port number 5) continued to indicate attached

flow. The vortex patterns are an indication of the pressure gradients that exist within the

bubble. In Figure 22, with the plenum pressure at 68 psig, the first sign of reversed flow is

evident at the second injection port, while Figure 23 shows the port fully immersed in

reversed flow at 75 psig.

The orientation of the plate relative to the centerline ofthe nozzle exit, and

thus the centerline of the flow, was found to be 89.7 degrees. Since alignment could

significantly influence the flow characteristics, the plate's inclination was changed to 90.3

degrees and the test runs were repeated. No dissimilarities between the results obtained at

corresponding plenum pressures were noted.

The evidence of reversed flow and reattachment strongly suggested the

presence of a closed separation bubble within the underexpanded jet when the plate was

present. The apparent extent ofthe bubble, reaching 3/8 to 1/2 inch above the plate, is

very surprising. However, it is consistent with the oblique shock in place of the normal

shock. Further data are needed, such as impact probe measurements, in order to fully

define the flow structure. For the present purpose, which was the investigation of

pressure sensitive paint, this was not needed.

38

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?*M?p$1&iFigure 20. Flow Visualization at 25 psig

Figure 21. Flow Visualization at 40 psig

39

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Figure 22. Flow Visualization at 68 psig

Figure 23. Flow Visualization at 75 psig

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B. OPTICAL MEASUREMENT SYSTEM

The measurement system was composed ofthree main components: (1) the

luminescence coating, (2) the illumination source, and (3) the luminescence detector and

associated data processing hardware and software. Each component is discussed

individually below. A schematic of the system used in conjunction with the free jet

apparatus is illustrated in Figure 24.

1. Luminescence Coating

The luminescence coating used in the present work was developed by the Chemistry

Department at the University ofWashington and was provided, as a sample, by the

NASA-Ames Research Center.

istnmented Flat

Rate

Pressire sensing lines

Sony Mont or

ta-

lma ge Display

386 PC with 4MEG VIDEOModel 1 2 Framegrabber Board

and Image Processing andAnalysis Software

MJIiprogrammer

Figure 24. Schematic ofPressure Measurement System

41

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The coating contained platinum octaethylporphyrin (PtOEP) as its active molecule.

PtOEP has characteristics of high luminescent quantum yield (-90%), short triplet life

(-100 micro seconds), and a high sensitivity to oxygen quenching

[Ref. 1: p.35]. Figure 25 shows the excitation and emission spectra for the molecule.

Excitation (absorption) peaks at 380 or 530 nm, whereas luminescence peaks at 650 nm.

The coating mixture consisted of the active molecule dispersed in a Genessee

GP-197 polymer-resin solution. The concentration was 0. 1 gm ofPtOEP per liter of

polymer resin [Ref. 19]. When the mixture was applied to the surface, the solvent

evaporated leaving a hard, thin film ofPtOEP dissolved in an oxygen-permeable polymer

[Ref. 9: p. 35]. Several undesirable characteristics associated with this coating are

described in Appendix B.

Excitation spectrum

Emission spectrum

300 £00 500 600

Wavelength (nm

)

700

Figure 25. Excitation and Emission ofPlatinum Octaethylporphyrin

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a. Reflective Backing

Before applying the luminescent coating to the surface, a white backing was

first applied. A significant improvement in luminescence performance was thereby gained

[Ref. 9: p. 32], allowing the camera to see a larger signal and an enhanced signal to noise

ratio.

The particular type of white paint used for this backing was an important

consideration. Kavandi [Ref 9: p. 33] found that some paints tend to darken after long

exposure to air and ultraviolet light. Krylon glossy-white spray paint (#1501) reportedly

offered the greatest resistance to this effect and was therefore used in the current work.

2. Illumination Source

McDonnell-Douglas [Ref. 6: p. 3] considered several types of illumination sources

to provide an adequate number of photons within the appropriate excitation wavelength of

the paint. The results showed that tungsten-halogen incandescent sources were the most

suitable in terms of compatibility and performance. Although the data in Figure 25 would

suggest that arc lamps emit more energy in the excitation range ofthe coating, they also

emit an EMF pulse that is damaging to CCD arrays. In addition, tungsten-halogen lamps

are extremely stable, with minimum intensity fluctuations, and any such variations will

directly effect the accuracy ofthe results. Consequently, an Oriel Corporation 1000W

quartz tungsten-halogen lamp, Model 66200, and the associated controller, Model 6405,

were selected for the present measurement system.

43

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Spatially-uniform illumination was also essential to reduce measurement errors.

(According to McDonnell-Douglas [Ref. 6: p. 4], this is especially true when the surfaces

are highly curved). Non-uniformity was found when the published procedures

[Ref. 20: p. 13] were followed to produce a collimated beam from the light source. The

procedure resulted in generating a focused image of the filament in the lamp. However,

by reversing the orientation of the barrel containing the lenses, a greater range of

adjustment was achieved. Figure 26 illustrates this modification, which made it possible to

produce a more uniform beam, although a slight degradation in spectral intensity was

noted.

Factory

lYW.WWF

WtWttWSOT,

Outer Sleeve

Modified

Barrel and Lenses

Assembly

amvwft

WAWWa:

Figure 26. Modification of Focusing Assembly ofthe Light Source

44

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a. Filters

The use of a broad-band light source mandated the use of filters to ensure

that the appropriate wavelength for excitation of the luminescence was allowed to pass

while blocking unwanted light. Unwanted light was that which would pass through the

narrow-band filter that was installed on the camera.

As Figure 25 shows, there are two wavelengths at which excitation ofthe

luminescent paint is optimum. Although either wavelength could have been used, the

380 nm wavelength was chosen because of its greater separation from the emission

wavelength of 650 nm. This also had the advantage, as discussed in [Ref 6: p. 5], of

allowing a filter with a more gradual cutoffto be used which would allow more light

energy to be utilized to excite the paint.

A combination of filters was used in the illumination system to isolate the

380 nm wavelength. The source beam first passed through a dichoric or cold mirror, Oriel

Model 66228, which had a spectral range of 350 - 450 nm and a cut-offfrequency of

550 nm [Cold mirrors are oriented at 45 degrees relative to the incoming beam from a

source. The infrared wavelengths are transmitted undeviated, while the ultraviolet

wavelengths are reflected through 90 degrees. This prevents the infrared from being

reflected back to the source and overheating the system.]

The source light was then directed through an Oriel interference filter, Model

57521, having a bandwidth of 70 nm centered at 400 nm. The filters were installed in a 90

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degree beam turner and mirror holder, Oriel Model 66246, which was fitted to the lamp

housing.

Finally, the camera used to record the emitted luminescent energy from the

paint had a 650 ran interference filter with a 70 nm bandwidth, Oriel Model 57610,

mounted over its lens to block out all other frequencies.

3. Detection System

Luminescent data were acquired using a COHU Model 4910 high performance,

monochrome, low-intensity CCD camera and transferred to a framegrabber board in a

80386 PC using an R-59 coaxial cable. The camera was fitted with a Cosmicar 16 mm,

f71 .4 lens. To ensure the output signal would be linearly proportional to light intensity

received, the camera was configured with the gamma set equal to one and the automatic

gain control (AGC) disabled [Ref. 2: p. 3342]. The camera's spectral response, as shown

in Figure 27, shows that its relative response at 650 nm is approximately 65%.

The camera produced a frame every 1/30 of a second and thus was limited to

recording pressure fluctuations at rates less than 30 Hz. [A simple test to determine ifthe

illumination system was bleeding over into the detection system was to illuminate an

unpainted surface (i.e., no luminescent paint) and then direct the camera towards this

surface to see if any spurious light was being detected. None should be present].

The analog output signal from the camera was initially digitized using an IDEC

Supervision 16 framegrabber board residing in a 80386-based PC. The raw data were

then reduced and analyzed using "Image Pro Plus" analysis and processing software.

46

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1

SENSOR SPECTRAL RESPONSE

9

.8

uj .7

to22 .6to

* ,

5 .4

.3

2

1

r////

400 500 600 700 800 900 1000

WAVE LENGTH (NM)

Figure 27. Spectral Response Curve for the COHU Camera Model 4910

However, this hardware/software combination was extremely limited in application

resulting in long data acquisition periods and time-consuming data reduction. Because of

the characteristic degradation ofthe luminescent coating, the accuracy of the data was

questionable.

The initial hardware/software combination was replaced with a much more versatile

Epix 4MEG Video Model 12 framegrabber board and software which included image

analysis and processing programs. The spatial resolution ofthe framegrabber was

operator adjustable, thus a balance between sampling resolution and the board's memory

storage could be tailored to a given application. For the underexpanded-jet and flat-plate

work, the spatial resolution was set to 752 x 480, the highest resolution setting. The

gray-level resolution of the board was 8-bits.

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C. EXPERIMENTAL PROGRAM

1. Flat Plate Preparation

The surface of the flat plate was cleaned with acetone, ensuring the removal of all

oils and dirt. Fine wire was then inserted into each ofthe pressure ports to prevent paint

from entering the holes. The white Krylon undercoating was then applied in a series of

three to four thin coats, allowing four to five minutes between coats. Ten minutes after

applying the last coat, the fine wires were removed from the ports. This was necessary to

prevent the paint from drying on the wire. [Significant portions ofthe undercoating could

be removed from around the pressure port when extracting a wire to which the paint had

hardened]. At this point, the white undercoating was allowed to dry for one hour.

Prior to the application ofthe pressure-sensitive paint, the fine wires were

re-inserted into the ports. The luminescent coating was then applied to the surface using a

standard hobby airbrush. The nitrogen supply in the Gas Dynamics Laboratory was used

as the pressure source for the airbrush (instead of shop air) as it offered a contaminant-free

pressure source. With a properly adjusted airbrush and a good painting technique,

continuous application ofthe luminescent coating to the surface could be achieved until

the surface was "suitably" covered. Although Kavandi et al [Ref. 2:p. 3343] refers to

normal coating thickness as being in the range of 5 to 15 micrometers, it was both

impractical and unnecessary to measure the coatings to determine ifthe paint fell within

these prescribed limits. The approach used in the present work was simply to observe

when the pigment of the pressure-sensitive paint seemed insensitive to further application,

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and that the texture ofthe surface appeared smooth. Several attempts were necessary to

develop the technique and the judgement in applying the luminescent coating. Three to

four minutes after the completion ofthe coating, the fine wire were removed. Once the

model was installed for testing, sufficient time had elapsed for the coating to have properly

cured. Note that it was important to avoid touching the painted surface at any time since

body oils could adversely affect the behavior ofthe luminescent coating.

2. Experimental Procedure

Setting the video resolution for the framegrabber to the maximum (752 x 480)

resulted in 1 1 frame buffers being available to store for image data. The controlling

software for the framegrabber was capable of capturing a sequence of images, digitizing

them, and storing each image of the sequence in consecutive image buffers, the number of

buffers used in the sequence (from one up to the number of available buffers) being

specified by the operator. Because ofthe limitation of collecting only 1 1 images for each

execution ofthe sequence algorithm, and the fact that averaging one hundred images was

desirable to obtain noise-free data, for each of the wind-on and wind-off conditions, ten

runs were executed. (10 frame buffers vice 1 1 buffers were utilized). Since the

underexpanded free jet was a steady and repeatable event, this method of collecting data

was a feasible solution for the limited memory ofthe frame-grabber board.

The data for the wind-off condition was collected first. The flat plate was

illuminated with the tungsten-halogen light source while the laboratory lights were turned

off, preventing any spurious wavelengths from entering the camera and offsetting the

49

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image data. A real-time image of the plate was displayed on the image monitor so that the

camera output could be adjusted for the best quality picture using a combination of focus,

manual gain, and lens iris. Manual gain was necessary because of the low light condition,

but care had to be exercised because with an increase in gain there was an accompanying

increase of noise introduced into the image. The shutter speed for the camera was set to

off.

After the first sequence of images was captured and stored in the frame buffers, the

light source was switched off to minimize the degradation to the paint. The light source

was such that the line voltage applied to the lamp housing was adjustable; however, power

was ultimately controlled with an on/off switch. Thus, the same illumination intensity was

maintained each time the lamp was turned on.

The ten images were averaged together to form a single image. The single image

was saved to a floppy disk. The light source was again switched on in preparation for the

second sequence of images, allowing time for the luminescent coating to reach its

maximum intensity. (This is referred to as the "induction period", which is explained in

Appendix B). The second sequence of images was then captured and stored, and the

tungsten-halogen lamp shut-off. The images were averaged to give a single image and

again saved to floppy disk. This routine was executed until ten averaged images for the

wind-off condition had been saved to floppy disk. Each sequence of capturing the data

took less than one minute.

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The procedure for obtaining images for the wind-on condition was similar. With

the light source on and the plate properly illuminated, the underexpanded-jet apparatus

was started. Once the desired pressure was set using the plenum control valve, and the

pressure was stabilized, the imaging sequence was executed. When the software had

completed its routine, the jet was shutdown and the light source turned off. The jet

apparatus was equipped with a shutoffvalve so that the jet could simply be turned on and

offwithout disturbing the setting of the plenum control valve. This ensured repeatability

ofthe event for each sequence of 10 images.

It is important to note that throughout these events, the camera and light source had

to remain fixed, spatially, with respect to the plate. In addition, no adjustments of any

kind could be made to the instruments or equipment. Any deviations would introduce

errors into the results.

Conventional pressure data were obtained concurrently with the luminescent paint

data using the CALSYS2000 data acquisition system [Ref. 17]. Twenty samples per port

using a data collection rate of 33 Hz were obtained and averaged together. These pressure

data would be used later in the calibration process. Ambient pressure and temperature

were also recorded.

3. Image Data Reduction

a. Image Processing

Several image-processing techniques were used to manipulate the data in

order to obtain the desired result. The techniques are described individually below.

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Appendix C provides a summary of the steps used in operating the EPIX software for

acquiring, processing, analyzing, and reducing the data.

Round-off error from the image processing routines was a concern. To

ensure against loss of accuracy due to round-off error, the system hardware had to be

capable of doing at least 16 bit arithmetic. The EPIX frame grabber board was capable of

conducting 32-bit operations. When the image was processed, the 8-bit intensity values

for each pixel in the image were first converted to 32 bit words. Once the processing was

complete, the modified values of each pixel were converted back to an 8-bit format for

display. Ifthe mathematical operations were conducted with anything less than 16-bit

precision, all significant digits would be truncated.

(1) Averaging. The emission of photons from any source is a random

process following a Poisson distribution, and the number of photogenerated carries

collected in a potential well of the camera array (see Appendix D for an explanation on the

operation of a CCD camera) in time "t" is thus a random variable. The standard deviation

of this random variable is referred to as photon (shot) noise. This noise is a fundamental

limitation in all imaging applications since it is a property of light itself, not ofthe image

sensor.

By averaging a sequence of images, the signal-to-noise ratio of the data

has been found to be significantly improved. This process has the effect of reducing the

scatter in the luminous intensity measurement [Ref. 6:p. 8]. McDonnell-Douglas [Ref 6]

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has found that as few as eight images averaged together showed a marked reduction of

noise on the signal.

The reason for choosing one hundred images for each of the wind-on and

wind-off conditions was the prior experience in the work conducted by NASA-Ames, the

University ofWashington, and McDonnell-Douglas. In each case, one hundred images

was adopted in all work done to date.

The ten averaged images of the wind-off condition were loaded into ten

frame buffers ofthe EPDC framegrabber board. As with the initial averaging ofthe raw

image data, the ten buffers were averaged together to form a single image. This single

image, a result of averaging one hundred "raw" images together, was then saved to floppy

disk. The corresponding wind-on images were averaged in a similar manner, and the

resultant image saved with its wind-ofif counterpart.

The procedure used in averaging the data in the present work was slightly

different than used at NASA-Ames, the University of Washington, and McDonnell-

Douglas. In those cases, one hundred images were collected and then averaged in one

step. In the present work, ten averaged images were averaged to form the final image.

Again, this is a result of the limited memory available on the frame grabber board.

However, since each image has a random distribution of data associated with it, the

averaging technique used will have little effect on the outcome ofthe result.

The significance of image averaging can be seen in Figures 28 through 30.

In each figure, an image and a graphical distribution along a single line of pixel values in

53

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the image is shown. Figure 28 shows a single raw image of the wind-on condition at 80

psig. Figure 29 shows the effect of averaging ten wind-on images together and Figure 30

shows one hundred images averaged together. In each figure, an image and a graphical

distribution along a single line of pixel values in the image are shown

(2) Dark Current. Appendix D details what dark current is and how it affects

the storage of photogenerated carriers in the potential well of a photo-sensitive array

element. The effect ofthe dark current on an image is that it produces an offset in which

the zero incident light condition does not correspond to the zero grey level. To correct

for this offset, a "dark" image was acquired and then subtracted from the wind-off and

wind-on conditions.

To acquire a dark image, a lens cover was placed on the lens prohibiting

any light from striking the CCD array, and then an image was acquired. One hundred

images were taken and averaged as was done with the wind-on and wind-off conditions.

A dark image was generated after each of the wind-on runs. Analysis ofthe dark current

image showed that 1 to 2 grey levels were present, which were the levels subsequently

subtracted from the wind-off and wind-on images.

(3) Registration. When a pixel-to-pixel comparison oftwo images ofthe

same object field taken from the same sensor at different times is desired, it is necessary

to spatially register the images to correct for relative translational shifts, rotational shifts,

and geometrical distortions. In the general case, this is accomplished in the software

54

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Figure 28a. Single Image ofthe Underexpanded Jet Across the Flat Plate at 80 psig

55

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56

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Figure 29a. Ten Averaged Images of the Underexpanded Jet Across the Flat Plate

57

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58

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Figure 30a. One Hundred Averaged Images ofthe Underexpanded Jet /Flat Plate

59

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-255"=7

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Figure 30b. Graphical Representation of a Single Line of Pixels ofOne Hundred

Averaged images

60

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using a pair of transformation equations relating the new coordinates to the old

coordinates. An example set of transformation equations, termed the affine projection,

are

x' = (an x + a12y + a

13)/(a

31x + ^y +1)

and

y' = (a^x + a22y + a^a^x + 3^+1)

where x,y are the old coordinates and x',y' are the new coordinates. The eight unknown

coefficients in the two equations can be determined if the coordinates offour points, called

control points, can be determined from each ofthe two images involved. [Ref 21:p. 71]

In the jet/plate interaction experiment, the stiffness ofthe plate was

expected to be sufficient to withstand the forces imposed on it by the jet so that any

deformation that did occur would be insignificant, making registration unnecessary.

However, comparison ofthe wind-on and wind-off images showed that the plate did

experience a horizontal translation when the jet was on. It was found that the thrust

produced by the jet caused a deformation in the structure supporting for jet apparatus.

Thus, the jet apparatus and flat plate in combination experienced a displacement relative to

the camera.

Examination ofthe wind-off and the corresponding wind-on images

showed that for the 65 and 80 psig cases , the images had shifted one pixel width in the

direction of the thrust, and two pixel widths for the 90 psig case. The image-registration

algprithm in the EPDC software was found to be unsuitable for this correction. In

61

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addition, the lack of "natural" features on the plate to serve as control points did not allow

the use of the software. [When the object lacks such features and image registration is

anticipated, artificial marks such as black circles can be distributed on to the surface.

In the present case, registration was not expected to be needed, the plate was not so

equipped]

The registration between the wind-off and wind-on images was a

relatively simple issue involving rigid body motion in one dimension. For this particular

situation the images were aligned using the "Copy and Shift Image" function in the EPIX

software which allowed an image to be shifted in its buffer up or down, left or right by an

operator- specified number of pixels. The registration scheme was accomplished by first

loading the wind-on and wind-off images into consecutive image buffers. The wind-on

condition was considered the "warped" image and the wind-offimage the "reference"

image to which the warped image would be registered. A cursor overlay was

simultaneously displayed on the image monitor with the wind-offimage. The cursor was

adjusted so that its horizontal character overlaid the pressure ports along the centerline of

the plate while the vertical character of the cursor overlaid the pressure ports along the

vertical centerline ofthe plate. The cursor remained fixed relative to the screen ofthe

monitor; this served as a reference for comparison of object feature location when shifting

between the wind-on and wind-off buffers. The wind-on image was then shifted relative

to the vertical-cursor character until the vertical centerline pressure ports were overlaid by

the vertical cursor character. When complete, the images were considered registered.

62

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The accuracy of using this approach was judged to be similar to that of

registration software since the registration software normally requires the operator to

manually locate the control points in each image. In addition, since the body moved

relative to the light source, consideration must be given to whether changes in brightness

were due to the pressure variations, or were caused by the motion of the plate.

McClachlan et al [Ref. 22:p. 3] indicate that this is of greatest concern when model

deflections and distortions are extreme. Since the flat plate motion consisted of rigid body

translation, the magnitude ofwhich was extremely small, this concern was considered to

be insignificant.

(4) Ratioing. While the reason for ratioing the wind-offimage with the

wind-on image was to satisfy the Stern-Volmer relation and produce a pressure map, there

were other benefits which arose from the procedure. In Figure 31 it is easy to discern the

gross features ofthe pressure distribution in the wind-on image. The ratioing process had

the affect of enhancing the finer detail in the image that would otherwise be too subtle for

detection. [Ref. 7:p. 7]

Examination ofthe wind-offimage in Figure 32 shows the evident

brightness variations from point to point across the surface. This was due to a

combination of differences in illumination, paint thickness variations, and features in the

model itself. Figure 33 shows a three dimensional graphical representation ofthe wind-off

intensity values across the surface ofthe plate. This illustrates the variations that exist

across the plate. The result of ratioing was the elimination of these non-uniformities.

63

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Figure 31. Wind-on Image ofthe Underexpanded Jet at 80 psig Across a Flat Plate

64

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Figure 32. Wind-off Image for the 80 psig Condition

65

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+&s'r?

Figure 33. Three Dimensional Intensity Plot of the Wind-off Condition of the Plate

66

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The "Ratio Image Operation" under the "Two Image Arithmetic" menu of

the EPIX software formed the weighted ratio of corresponding pixels. The operation is

mathematically expressed as

(cO * PixB + cl)/(c2 * PixA + c3)

where the coefficients cO, cl, c2, and c3 are modifiable. For the current work, PixA was

designated the wind-on image while PixB, the wind-off image. In addition, the coefficient

cO was assigned the value of 100 while the coefficients cl, c2, and c3 were assigned the

values 0, 1, respectively. The reason for assigning cO the value of 100 was

to scale the resultant ratioed intensity map such that differences ofthe grey values between

neighboring pixels could be discerned.

Figure 34 illustrates the ratioed image for the underexpanded jet across

the flat plate at 65 psig plenum pressure. The importance of proper registration ofthe

wind-on and wind-of images prior to ratioing cannot be overstated. To illustrate the effect

ofimproper registration, the images used to form the resultant image in Figure 34 were

modified where the wind-on condition was shifted an additional five pixel widths in the

direction ofthe thrust. The result of ratioing these two images is shown in Figure 35. A

reduction in fine details, as compared to Figure 34, is clearly evident.

67

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Figure 34. Ratioed Image of the Wind-off and Wind-on Images for the Flat Plate

/Jet Interaction at 80 psig

68

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Figure 35. Result of a Ratioed Image Following Improper Registration Technique

69

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b. Calibration

Two methods were available to calibrate the intensity ratio map, the intent of

which was to obtain the sensitivity coefficients for the Stern-Volmer equation and

establish the pressure map.

The first method, termed "a prior", involved calibrating a paint sample in a

controlled pressure and temperature chamber. Using the data obtained from the chamber,

and knowing the temperature ofthe model surface, the appropriate values for the

Stern-Volmer coefficients could be found [Ref 7:p. 7].

The second method, termed "in situ", which was the method employed in the

present work, used the pressure obtained using a conventional pressure tap in the model

surface and compared this with the intensity from the luminescent paint adjacent to the

tap. Using data from a number oftaps, the sensitivity coefficients were obtained by a

least-squares linear fit. The coefficients A and B, being functions only oftemperature,

were good over that portion of the surface which was at the same temperature as the area

containing the pressure taps. [Ref. 7:p. 10]

The approach used to produce pressure data from the ratioed image was

similar to that used by Kavandi [Ref. 9:p. 94]. This entailed averaging the data from five

adjacent rows of pixels near the pressure taps to produce a single row of data. (This, has

the effect of averaging a total of five hundred images together.)

To do this, the ratioed image was loaded five times into consecutive frame

buffers of the frame-grabber board. Each successive image was then vertically offset by

70

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one pixel row with respect to the previous image, i.e., the first image remained

unmodified, the second image was shifted one pixel row down in its frame buffer with

respect to the first image, the third image shifted two pixel rows down with respect to the

first image, etc. The five buffers were then averaged. Each row of pixels in the resultant

image, with the exception ofthe first five and the last five rows ofthe image, was then an

average ofthe corresponding row in each ofthe five images. A row of pixels close to the

pressure taps was then selected to serve as calibration data. Figure 36 shows the data

from the selected line of pixels for the flat plate in the underexpanded jet at 80 psig, prior

to averaging with four adjacent lines of pixels. Figure 37 shows the data for the same line

after the averaging procedure. [It is noted that the "spike" on the left side ofthe graph is

due to paint that has separated from the leading edge ofthe plate]. From an examination

ofFigure 36 and Figure 37 it can be concluded that the five-row averaging procedure had

the effect of reducing the noise level in the distribution with negligible effect on the

distribution itself.

The calibration curves that resulted from plotting intensity values against the

measured surface pressure at jet stagnation pressures of 65, 80 and 90 psig, are shown in

Figures 38, 39 and 40, respectively. All data were obtained using the line of pixels and the

line of pressure taps along the centerline ofthe jet. Two separate linear fits are shown in

each ofthe figures. This was done when it was realized that the data were poorly

represented by a single curve, and that large variations in temperature over the surface of

the plate was the probable cause. It is possible that the groups of points which correlate

71

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255-. . < ; ; ^ ; > ^

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Figure 36. Calibration Line of Pixels for the 80 psig Case Prior to Spatial Averaging

72

Page 104: Application of pressure-sensitive paint in shock-boundary ... · Application of pressure-sensitive paint in shock-boundary layer interaction experiments Seivwright, ... Basedontheprincipleof

255- : : : : ; y.

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Figure 37. Calibration Line of Pixels for the 80 psig Case After Spatial Averaging

73

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Calibration Curve For The UnderexpandedJet Nozzle Across A Flat Plate

(65 psig Plenum Pressure)

100

r 80ace

Pressure (P/Po)

Figure 38. Calibration Curve for the Underexpanded Jet/Flat Plate at 65 psig

74

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Calibration Curve For The UnderexpandedSonic Jet Across A Flat Plate

(80 psig Plenum Pressure)

120

110 -

100-

Pressure (P/Po)

Figure 39. Calibration Curve for the Underexpanded Jet/Flat Plate at 80 psig

75

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Calibration Curve For The UnderexpandedSonic Jet Across A Flat Plate

(90 psig Plenum Pressure)

100

90

>. 80

CO

cCD

c

70 -

60 -f——H——i——i—•—i—'—i——i—•""

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Pressure (P/Po)

Figure 40. Calibration Curve for the Underexpanded Jet/Flat Plate at 90 psig

76

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linearly are from regions of similar surface temperatures. However, the complexity of the

flow over the plate surface, with a three-dimensional separation contained within it, makes

the estimation of surface-temperature distribution very difficult. These results clearly

indicate the need to measure surface temperature ifin-situ calibration is to be used.

a Field PressureMap

Pseudo-coloring (or "false coloring") of a gray scale image was used to

accentuate areas of an image that are not easily discerned by the eye. This was

accomplished by providing an assignment ofamounts of red, green and blue to a

corresponding value of intensity in the gray-scale image. Through the use of look-up

tables, the software allowed specification of linear ramps, logarithmic curves, polynomials,

gamma correction, inversion and transposition in a pattern or sequence of a non-specific

nature. For a gray-scale image the index value is synonymous with its intensity value.

Reference 23 may be consulted for further information concerning the manipulation of

lookup tables. The color map or sequence that was developed for the present work is

shown in Figure 41 . The constants A and B represent the minimum and maximum index

values ofthe interval over which the color map was defined. All other index values were

assigned the pixel value ofzero in the color map. The minimum and maximum index

values were found by conducting a histogram on the gray-scale image which gave a

breakdown ofthe pixel intensity values and the frequency of occurrence in the image. The

intensity values associated with the pressure-sensitive paint images are usually grouped in

an interval between the to 255 index value range.

77

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255Red Green Blue

y\

CO #/r i \

j

\*P 9/ NSbc <£/ j

\> &/X*c

j \ / ^w

j

\ /

D B

Figure 41. Graphical Representation ofthe Red, Green, and Blue Lookup Tables

The constant C represents the mid-point of this interval. The constants D and E were

varied to obtain the desired bandwidth ofthe green lookup-table input which influenced

the mid portion ofthe color spectrum.

The final pressure maps for the 65, 80, and 90 psig plenum conditions are

given in Figures 42, 43, and 44 respectively. Although quantitative information is not

available, the results in Figures 42, 43, and 44 show good qualitative agreement with their

schlieren counterparts in Figures 12, 13, and 15 respectively.

78

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Figure 42. Pressure Map of the Underexpanded Jet at 65 psig Across a Flat Plate

79

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Figure 43. Pressure Map of the Underexpanded Jet at 80 psig Across a Flat Plate

80

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Figure 44. Pressure Map of the Underexpanded Jet at 90 psig Across a Flat Plate

81

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IV. APPLICATION TO SHOCK-BOUNDARY LAYER INTERACTION IN A

SUPERSONIC WIND TUNNEL

A. DESCRIPTION OF FACILITY

The supersonic wind tunnel, located in Bldg. 216 ofthe Gas Dynamics Laboratory

[Bldg. 216] at the Naval Postgraduate School, was of the blow-down type. Supply air

was produced by the same supporting facility as the underexpanded sonic jet apparatus. A

schematic ofthe tunnel and supporting facility is shown in Figure 45 while Figure 46

shows a photograph ofthe wind tunnel.

Air to the tunnel, from a maximum pressure of 300 psi, was controlled by a pneumatic

control valve. The control valve used a diaphragm actuator. Regulated instrument air

from the supply system was routed to one side ofthe diaphragm and the controlled

pressure, from a tap on the plenum, was connected to the other. This allowed precise

control ofthe plenum pressure. A pressure gauge installed on the plenum provided

pressure readout.

The plenum chamber was cylindrical with an internal diameter of approximately 20

inches. With the exception of a splash plate mounted perpendicular to the flow near the

entrance of the chamber, the plenum was empty. The flow exited the chamber through a

contraction and circular-to-rectangular transition section, into the convergent-divergent

83

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Plenum ChamberBlock Valve

Confection and

Circular to

Rectangular Transition

Exhaust Section

o

Pneumatic Plenum

Control Valve

8000

cult.

o300 psi

TANKFARM

Nozzle Blocks

and

Test Section

LABORATORY

COMPRESSOR ROOMFrom Atmosphefelr<

I.R. Reciprocating

Boost Pump150 psi

Elliot

Compressor

3stg, Cent

0-150 psi

Decescant

Air Dryers

Figure 45. Schematic ofthe Supersonic Wind Tunnel and Supporting Facility

Figure 46. Supersonic Wind Tunnel Apparatus

84

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nozzle. The nozzle and test section,shown schematically in Figure 47, were comprised of

a set oftwo (interchangeable) aluminum blocks forming the contour and two flat plates

forming the side walls and enclosing the constant-width section.

The test section was nominally four inches in width and four inches in height. Six-inch

diameter circular glass windows on each side ofthe test section provided optical access.

Two small gate valves were mounted on each ofthe side walls just downstream ofthe test

section. They were used to allow "bleed" and thus control back pressure in order to

position the "starting" normal shock in the test section. The flow exited the test section

into an exhaust duct which vented to the atmosphere outside the building.

Side Wall

Nozzle Blocks

Side Wall

Optical Access

1

.

Subsonic Section

2. Supersonic Nozzle

3. Test Section

Figure 47. Nozzle Blocks and Test Section Exploded View

85

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1. Nozzle Blocks

The interchangeable pairs of nozzle blocks were each designed to produce a specific

Mach number in the test section. For the present study, two Mach numbers, 1 .4 and 1.7,

were used, since this was the range ofMach number of interest in the proposed study of

control of shock-boundary layer interaction. A set of blocks for M=l .4 existed.

However, it was necessary to design and manufacture a set of blocks to provide M=l .7.

The program described in Appendix E was used to derive the contour for the M=l .7

nozzle. The new blocks were otherwise similar to the existing blocks and were

manufactured to the original dramings using the new contour.

a. Performance Evaluation ofthe Mach 1. 7Nozzle Blocks

To evaluate the new nozzle blocks, several runs at varying plenum pressures

were conducted. A series of pressure taps along one side ofthe tunnel allowed pressure

data to be collected. The taps extended approximately four inches upstream ofthe nozzle

throat and downstream to the entrance ofthe test section. A metal blank containing

additional taps was installed in place of one ofthe test section windows to measure

pressures through the test section. One tap downstream of the test section measured the

pressure of the exiting flow.

The data acquired indicated that the normal shock associated with the nozzle

starting process rapidly passed through the test section into the exhaust duct as soon as

the operating pressure ratio decreased below the first critical condition. Unlike with the

M=l .4 blocks, the bleed valves on the sides ofthe tunnel could not be used to position the

86

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shock. It was realized that some form ofblockage would have to be introduced into the

passage at some point downstream of the test section in order to "set" the shock in the test

section.

The mounting points for the gate valves, which were located three inches

downstream ofthe test section and were aligned such that their centerlines coincided with

each other, were adapted so that circular rods ofvarying diameter could be installed

across the tunnel. A total of four rods was used. Operating the tunnel at 75 psi plenum

pressure, the static pressure distribution was recorded for each configuration. The effect

of rod diameter on shock position is clearly seen in Figure 48.

The 3/8 inch diameter rod was found to place the shock just prior to the test

section. To position and control the shock precisely in the center ofthe test section, a

means ofbleeding offmass flow was developed. The solid rod was replaced by a 3/8 inch

outside diameter tube. A series of 1 1/64 inch holes was drilled through the tube wall, in a

line along its 4-inch length. The tube was then mounted between the gate valves with the

holes aligned with the flow. This arrangement allowed a controlled mass flow to pass

through the holes into the tube and out ofthe tunnel via the gate valves. The gate valves

could be adjusted to vary the amount of outgoing mass, thus moving the shock to the

desired position in the test section. A schematic ofthis arrangement is shown in Figure 49

while Figure 50 shows a photograph ofthe bleed-off tube mounted in the tunnel.

87

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Pressure Distribution

Mach 1.7 (75 psi

Along Tunnel Wall

Plenum Pressure)

-o No Rod

•4 0.675 inches

-— 0.502 inches

• 0.375 inches

-— 0.3125 inches

Distance (inches)

Figure 48. Tunnel Pressure Distributions as a Result of Varying Rod Diameters

88

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Tunnel Cross-SectionNozzle Block-

>\

',

,i

Gate Valve

Side Wall'

/

Side Wall

ooooooooooo

\AL

Gate Valve

3/8" Dia. Tube

with

11/64" Holes

Nozzle Block

Figure 49. Cross-Sectional View ofthe Mass Bleed-Off System

Figure 50. Mass Bleed-Off Tube Mounted in the Tunnel

89

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B. INSTRUMENTATION

The metal blank, containing eleven pressure taps, and used as described above to

measure the pressure distribution in the test section, was used as the model surface on

which to observe the interaction between the starting normal shock and the nozzle

boundary layer using pressure-sensitive paint. The metal blank was installed on one side

ofthe test section and a six inch glass window was installed on the other. Concern for the

spectral transmittance ofthe glass window led to an analysis ofthe glass for the range of

350 nm to 700 nm using a spectrometer. The results of the test, shown in Figure 51,

indicated that the transmittance levels were satisfactory for the current work.

The optical measurement system was the same as was used for the underexpanded jet

study described in chapter three. A schematic ofthe setup is shown in Figure 52.

C. EXPERIMENTAL PROCEDURE

It was found that the shock-boundary layer interaction in the test section was

inherently unsteady. This precluded the use ofthe procedure outlined in chapter three for

acquiring the wind-on data. That method required the event of interest to be steady and

repeatable, thus enabling one hundred images to be taken over a series often runs. The

approach taken for the unsteady process was simply to create as many image buffers as

possible for a single sequence, and to execute this sequence in the shortest period of time.

90

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#1 m

Figure 51. Spectrometer Results for the Optical Window

91

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Pressure Measurement set-up Shock-Boundary Layer Interaction Studies

Gas Dynamics Laboratory

Figure 52. Instrumentation Setup for the Supersonic Wind Tunnel, Shock-

Boundary Layer Experiment

The maximum number ofimage buffers that could be created for image capture was a

function ofvideo resolution. To maximize the number of available buffers it was

necessary to minimize the video resolution. To accomplish this, the camera was focused

on the test section so that the surface of the metal blank was clearly displayed on the video

monitor. The video resolution was set at maximum (752 x 480) at this point. With the

video resolution menu displayed on the computer screen, the parameters controlling the

numbers of pixels and pixel lines were iteratively decreased until the camera's field ofview

shown on the video monitor exhibited only the test surface, the rest ofthe field ofview

being deleted. The resulting resolution was 600 pixels per line and 340 lines ofvideo or

600 x 340 (assuming "Interlace: Use Distinct (2) Fields?" is active) which allowed 21

image buffers to be available for image capture. Since McDonnell-Douglas [Ref 6: p. 8]

92

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had shown that averaging data from as few as eight images significantly reduced the noise

on the signal, it was concluded the 2 1 images would be sufficient.

The period required for a sequence to be completed was based on the time interval

specified between consecutive samples, the shortest interval being 1/30 of a second. Since

a video frame was generated every 1/3Oth of a second by the camera, the total time to

execute a sequence containing 21 image buffers was 1 .37 seconds.

The experiment began with the Mach 1 .4 blocks installed in the tunnel. Using the

shadowgraph technique, the normal shock was positioned in the test section by adjusting

the backpressure through the gate valves, while the plenum pressure was set at 30 psi.

When the valves were properly adjusted the tunnel was shut down, the metal window

blank with pressure sensitive paint applied was installed, and the camera and illumination

system were located eight inches away from the optical glass window. A real-time image

ofthe test section was displayed on the image monitor, and the parameters to execute the

desired sequence described above, were input into the computer. A cover was placed

over the test section to prevent photodegradation ofthe paint, the light source was turned

on and allowed to "ramp up" and stabilize. The wind tunnel was then started, the plenum

pressure set at 30 psi, and the laboratory lights were turned off. The wind-on data were

captured while pressure data were taken simultaneously using the CALSYS2000 data

acquisition system. Twenty samples per port were taken at a sampling rate of 10,000 Hz.

Three such runs were conducted. Between each run, wind-off and dark-current images

were collected. Temperatures for the tunnel and the test plate were not available.

93

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The Mach 1 . 7 nozzle blocks were then installed with the mass bleed-off system

described earlier. With the plenum pressure set at 70 psi the shadowgraph was again used

to position the normal shock. With the test plate installed, three runs were conducted in a

similar manner to that described for the M=l .4 blocks. The data were post-processed

using the techniques described in chapter three.

D. DISCUSSION AND RESULTS

The flow structure expected to be produced by the interaction between a normal shock

and a turbulent boundary layer is shown schematically in Figure 53. The

pressure-sensitive paint technique was to be used to measure the surface pressure through

the interaction region. Previous work by Perretta [Ref. 24] involved a study of the flow

across the shock structure shown in Figure 53, and the resulting separation, for the given

M=1.4 tunnel configuration used in the present study.

For the M=l .4 case, the pressure map obtained is shown in Figure 54. It can be seen

that the interaction was nearly two-dimensional. To illustrate the distribution of the

pressure rise, a line of pixel intensity values taken along the plate is shown in Figure 55.

The profile resembles those ofKooi [Ref. 25 :p. 30-8] for turbulent boundary layer

separation on a flat plate due to normal shock interaction. The steepest slope ofthe curve

indicates the start of the interaction, according to Kooi's work. The separation point can

be identified as that point in the curvature where either a discontinuity in the curvature

94

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Flow

Boundary Layer

Normal Shock

Free Shear Layer

Lamda Foot

777777777777777777777177777777777777777777777777777

Separation Bubble

Figure 53. Schematic ofthe normal shock-boundary layer interaction

exists or the degree of change in curvature is much less compared to that ofthe start of

the interaction, indicating a much slower rise in pressure. From the distribution ofthe

intensity values, this point is difficult to determine. This can be attributed to oscillations of

the normal shock, and the pressure-sensitive paint's poor dynamic response to these

changes, causing an averaging effect and eliminating changes in curvature from the curve.

Also, the time to execute the data collection sequence was much longer than the

oscillation period of the shock, adding to the error in the results. The absence of a plateau

in the intensity distribution suggests that the separation region was very short.

In the case ofM=l .7, the determination of separation is more definite. The pressure

map is shown in Figure 56 while the corresponding streamwise line of pixel-intensity

95

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Figure 54. Mach 1.4 Pressure Map of the Shock-Boundary Layer Interaction

96

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255-

24023©-228-210-200-iyw-1fl0-

170-* 160-Z 158-flS 140-* 130-_, 120-oi 118-* 10O-

88-70-eo-

48-30-20-

*i i i i i i::::::::::::::::::::::::::::

:::::::m* fc-j, .t<i*luJLjf

-i

i ,**»*»JudtfZ.]

L... ,,J _.^T 1 i L —

|

inpljIMHlll*^**^*^

I z z z " z

*

7cI 100 SO0 200 400 500 £00

X Coordinate

1I

751

Figure 55. Graphical Representation ofthe Pressure Distribution ofthe Shock-

Boundary Layer Interaction at Mach 1 .4

values is displayed in Figure 57. The intensity curve here shows a definite plateau, a

region of nearly constant pressure, which is an indication of an extended length of

separation. This region corresponds to the area illustrated by the narrow green band in

the pressure map ofFigure 56.

The calibration curves for the M=l .4 and M=l .7 data are given in Figures 58 and 59

respectively. In contrast to the calibration curves developed for the underexpanded jet/

flat plate data, areas of similar temperature are more easily identified in the

shock-boundary layer experiment. The data points upstream and downstream ofthe

normal shock have been linearly approximated separately since there was a near

97

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Figure 56. Mach 17 Pressure Map of the Shock-Boundary Layer Interaction

98

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255J

240-230-iaaa-210-200-lSO-180-170-

« 1GB«. iao-t 140-9 130-^ 130V 110-* 100-

oe-70-60-FR-4030-20-

il

_^»l|i.r...

: lyw1*"

::: kii.A_^-i^l^^, . ,

:

,fJWWy.

Ill ! !izi i i

.

: 1 : ': i

>V. r—

--

,

— ,- - T- ,.. i |

O 10O 298 30© 400 300 600 TZ

X Coonftinate

Figure 57. Graphical Representation ofthe Pressure Distribution of the Shock-

Boundary Layer Interaction at Mach 1.7

discontinuity in temperature and heat transfer at the shock impingement location. There is

seen to be a change in the sensitivity ofthe paint to pressure change which occurs at the

shock. The paint is more sensitive downstream ofthe shock, which is consistent with the

occurrence of higher temperature.

99

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Calibration Curve For The Shock-Boundary

Layer Interaction In The Supersonic Windtunnel

(Mach 1.4 -- 30 psig Plenum Pressure)

130

120 -

^ 110

"5

100 -

After Shock

Before Shock

1.2

Pressure (P/Po)

Figure 58. Calibration Curve for the Mach 1 .4 Interaction

100

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Calibration Curve For The Shock-Boundary

Layer Interaction In The Supersonic Windtunnel

(Mach 1.7 - 75 psig Plenum Pressure)

200

180After Shock

160 -

140

120 -

100

Pressure (P/Po)

Figure 59. Calibration Curve for the Mach 1.7 Interaction

101

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V. CONCLUSIONS AND RECOMMENDATIONS

The pressure-sensitive paint (PSP) technique offers a flexible and convenient method

for measuring surface static pressures in aerodynamic testing. Its most significant feature

is the non-intrusive manner in which it provides a mapping of a continuous pressure field

over a surface. Because of its detailed spatial resolution (when compared to conventional

pressure taps), a complete picture of the events occurring on the surface is available,

including details not necessarily anticipated prior to testing. It appears to be highly

suitable as a technique to use to validate results calculated using computational fluid

dynamics (CFD). In the present study, pressure-sensitive paint was applied successfully in

two experimental configurations involving shock-boundary layer interaction. The

conclusions drawn from the present application are relevant to any first-time application of

the technique.

The luminescent technique, although conceptionally simple, required learning. It was

important to understand the entire process, including each of the components comprising

the pressure measurement system (paint, optics, camera, software), the limitations ofthe

system (particularly ofthe luminescent paint), and the interpretation ofthe measurements

through calibration, before meaningful data were acquired. Several attempts to progress

through the entire process were found to be necessary. Thus, the initial experimental

arrangement (a flat plate immersed in an underexpanded jet) served well as a test bed for

building experience before more complicated experimental geometries were attempted.

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The components that comprised the current measurement system were adequate for

initial experience, system development, and measurements. However, in order to make

highly quantitative measurements routinely, some refinements are recommended. The

camera and the digitizer combination are, by far, the most critical components in the PSP

measurement system. The accuracy and precision of the measurements is highly

dependent upon the dynamic range and signal-to-noise ratio ofthese components. The

camera and digitizer used had a grey-scale resolution of eight bits giving a dynamic range

of 256: 1. Since many measurements, such as in shock-boundary layer interaction

experiments, may generate changes in the luminescent intensity as little as two percent, it

is crucial that the camera and digitizer be sensitive enough to these changes and to assign a

gray-scale value that is appropriate for the given intensity level. Recommendations from

NASA Ames Research Center and McDonnell Douglas have suggested a minimum of 14

bits for gray level resolution.

With a relatively low signal being detected, the signal-to-noise ratio at high light levels

is limited by the photon shot noise. The accuracy ofmeasurement is contingent upon the

highest possible full-well potential ofthe CCD element, which requires a minimum

generation of dark current. Active cooling ofthe CCD array would maximize the

signal-to-noise ratio ofthe array. Such developments in CCD cameras can be expected

[For example, Princeton Instruments Inc. currently offers a Penta Max camera that uses

air circulation to cool its CCD array, which achieves -45 degrees Celsius]. Similarly,

104

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system noise can be reduced by combining the digitizer with the camera, thereby reducing

electrical noise, and then feeding the signal directly into a memory buffer in the computer.

The EPEX 4Meg Model 12 frame grabber and memory buffer and its associated

software was limited in data collection. Since the board was limited to capturing only 1

1

images per sequence (assuming maximum resolution), the acquisition of one hundred

images was far to slow to avoid inaccuracy ofthe results due to photodegradation ofthe

paint. The EPIX 48Meg Model 12 frame grabber, for example, would provide the ability

to capture up to 132 images per sequence. Not only would this reduce or eliminate the

error associated with photodegradation, but image processing time would be significantly

reduced. Data acquisition speed is mandatory in experiments in which the flow is not

completely steady.

A similar issue concerns the present image-processing software. Designed for general

applications, it is not the most efficient, or the most suitable, for the PSP applications.

Although single-function algorithms such as registration software to spatially align two

images together, to compensate for temperature sensitivity and apply the calibration to the

data, and routines to pseudo-color the results must be written, consideration should be

given to automating the entire process, from acquisition of the data to production ofthe

calibrated pressure field map.

The temperature sensitivity ofthe paint and its effect on the results is a major concern

if pressure measurements are to be made in the compressible flow regime. To accurately

measure the pressures on a surface, it will be necessary to know the surface distribution of

105

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temperature so that the calibration curves can be adjusted accordingly. Although

temperature measurements could be made using thermocouples, this approach raises the

same issues as those associated with using pressure taps to make pressure measurements.

A possible solution is to use, concurrently, a high-performance infrared camera to record a

high-resolution, continuous image ofthe temperature distribution on the surface. Since

the results from infra-red cameras are produced using a digital process similar to that used

in PSP, it is possible that the techniques could be combined to produce a temperature-

compensated pressure map.

Finally, the applicability of the present technique to more complicated model

configurations with more limited optical accessibility ofthe surface of interest, has yet to

be attempted here. The combination of curved surfaces with significant temperature

variations, and with limited optical access, will provide a significant challenge to the

successful quantitative use ofPSP.

106

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APPENDIX A. RUSSELL-SANDERS COUPLING

Associated with the angular momentum of an electron is a magnetic moment. When

the electron is placed in a magnetic field, the interaction ofthe field with the magnetic

moment ofthe electron causes the angular-momentum vector to precess about the

direction ofthe external field, much the same way a toy top precesses in a gravitational

field. However, in contrast to the top, which can have an infinite number ofmomentum-

vector orientations with respect to the field direction, the angular-momentum vectors of

the electrons in an atom (or molecule) are allowed only certain orientations. The solutions

ofthe Shrodinger equation dictate permitted orientations; not every orientation is allowed.

The only allowed directions are those at which the components ofthe angular momentum

along the direction defined by the magnetic field have certain quantized values. This

behavior is called space quantization. [Ref. 10:p. 491]

Each orientation ofthe momentum vector with respect to the external field direction

corresponds to a unique energy state. Since the angular motion ofthe electron is

equivalent to an electromagnet, the energy of the interaction between the magnetic

moment it possess and an external field can be expressed asE = u, H cos , where H is the

strength ofthe external field, is the angle between the field and momentum vector, and

H is the magnetic moment. [Ref. 26:p. 25]

Now consider what happens when a single unpaired electron is not in the presence of a

magnetic field. Here, the orbital angular momentum ofthe electron creates the magnetic

107

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field, defining a specific direction in space. Thus the angular momentum associated with

the intrinsic spin of the electron is oriented with respect to this magnetic field. According

to space quantization principles, the spin angular-momentum vector of the electron can

have two orientations with respect to the direction defined by the magnetic field; this

corresponds to the doublet line structure observed for the spectra of an atom, and is the

basis for the spin quantum number (+1/2 and -1/2) assigned to the electron. [Ref 26:p.27]

In an atom with several electrons, the orbits are usually oriented first with respect to

each other, giving a resultant orbital magnetic moment. Similarly, there is a resultant spin

moment which is oriented with respect to the resultant magnetic field due to the orbital

motion. With space quantization, the resultant spin vector may have several orientations,

each corresponding to a different energy level. Thus, the atom (or molecule) may have

several energy levels for a single configuration. [Ref. 27:p. 79] These multiple energy

levels for a single configuration of an atom (or molecule) is the basis for Russell-Sanders

coupling which impacts the multiplicity of state that an atom or molecule can possess.

108

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APPENDIX B. LUMINESCENCE COATING CHARACTERISTICS

The luminescent coating used in the present work possessed several undesirable

characteristics ofwhich the user must be aware if accurate results are to be obtained. A

summary ofthese is presented below. For a more in-depth discussion, the reader may

refer to the references mentioned.

A. TEMPERATURE SENSITIVITY

The photoluminescence process is temperature sensitive by nature. The coating used

in the present work exhibited a non-linear response, and intensity decreased with

increasing temperature. This response at a constant pressure is shown graphically in

Figure Bl. [Ref l:p36] The temperature dependence has a significant effect on the

calibration curves of intensity vs. pressure. As is shown in Figure B2a, the variations in

slope can be significant [Ref. l:p. 62].

An interesting property displayed by the calibration curve for the coating is the

condition where the coating-sensitivity coefficients add to unity (i.e. A + B = 1, in the

Stern-Volmer equation). This occurs when the data taken for I and I are taken at the

same temperature. Ifthis is not the case, the coefficients add to other than one,

A + B * 1 . The consequences are illustrated in Figure B2. In Figure B2(a) only the 23.7°

C curve exhibits the property that A + B = 1 while the 50 and 6 °C calibration curves were

calculated with I and I at different temperatures. In Figure B2(b), the 50 and 6° C

109

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ho — [>i

< i ' i > i

i

120 ^-fo-.

Intensity

a>

oo

o

o

o

o

—En.

40 ^"&?-i_

20 . i i I i 1 i I i^xir

10 20 30 40

Temperature ( °C

}

50

Figure Bl. Luminescence Intensity as a Function of Temperature [From Ref. 1 :p. 36]

calibration curves have been replotted using data for both I and I obtained at similar

temperatures. Clearly, the slope and zero intercept have been significantly altered. [Ref.

l-P-37]

B. PHOTODEGRADATION

When subjected to ultraviolet light, the luminescent coating undergoes

photodegradation, resulting in a decrease of its response with time of exposure. A

representative example of this is shown in Figure B3 where intensity is plotted as a

function oftime of exposure. In this case the coating lost 46% of its response after one

hour of exposure. [Ref. l:p. 36 ]

110

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Figure B2. Effect ofTemperature on Coating Calibration Curves [From Ref. lp: 37]

(a). I for Curve Measured at 23.7° C(b). I for Curve Taken at its Respective Temperature

1 On_. L

1

1 ' 1i

-

, {

0.9 —

0.8 1 ™1

|o.7

~ 0.6Ljs

-

5 l 1 I 1 i

^^n

10 20 30 L0

Time(min)50 60

Figure B3. Illustrative Example ofthe Effect ofPhotodegradation on

Response Time [From Ref. lp:36]

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C. TIME RESPONSE

The luminescent coating used in the present work has been found to exhibit a time

response on the order of 1 second limiting measurements of pressure fluctuations to no

greater than 1 Hz. [Ref 8: p. 3]

This limitation is not a characteristic of the active molecule. In theory, the time

response ofthe coating to pressure transients may be as fast as the decay of luminescence.

For platinum octaethylporphyrin this is approximately 0. 1 milliseconds. The problem lies

with the polymer matrix in which the active molecule is embedded. By limiting the rate of

oxygen diffusion, the polymer slows the optical response to surface pressure fluctuations.

[Ref. l:p. 41]

D. COATING THICKNESS / INDUCTION PERIOD

Kavandi [Ref. 9:p.86] has conducted tests to determine if film thickness has any effect

on calibration results. Over the range of 5.5 micrometers to 17 micrometers, consistent

with normal application, no significant variations were noted. However, a noticeable lag,

or "induction period", existed between the time excitation light was turned on and the time

that the detected luminescence reached maximum intensity. The period ofmaximum

intensity was observed to be in the range of30 to 45 seconds and it is therefore advisable

to allow this period to elasped before taking data. A graph of absolute intensity as a

function oftime following exposure to the exciting light is shown in Figure B4. [Ref.

9:p.89]

112

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22fl-

210-

"3> 200-

03

190-

G

5180<

170-

() 20

i i —

40 60

Time (seconds)

—t 1

80

Figure B4. Induction Period of the Luminescent Coating with Thicknesses in

Excess of 17 Micrometers [From Ref 9:p. 89]

113

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APPENDIX C. EPK SOFTWARE SUMMARY

This appendix outlines the software steps used in acquiring, processing and reducing

image data. All information discussed here may be found in [Ref. 23]. The appendix is

intended to serve as a user guide but is not meant to be a substitute for the EPEX user's

manual. The user's manual is vital to developing a sound understanding of the software in

order to be able to use it to its fullest extent. The data acquisition and image processing

system is set up such that the menus and commands are displayed on the computer

monitor while the images are displayed on the Sony image monitor.

A. IMAGE DATA ACQUISITION

The main menu for the EPIX 4MEMMIPTOOL software is shown in Figure CI

.

Prior to data collection, the video resolution is set. Selecting "Video Resolution" from the

main menu, the video resolution sub-menu will be displayed as in Figure C2. Check to

insure that the "Interlace: Use Distinct (2) Fields ?" is set to "ON". The sampling

resolution is considered next and it is application dependent. The sampling resolution sets

the size ofthe video window displayed on the image monitor, allowing the selection of a

smaller field ofview. The maximum resolution is 752 pixels per line by 480 lines per

frame or image (Two fields make up one frame; however the number of lines selected is

based on each field, the maximum number being 240. For both fields to be active, the

interlace function must be on). Upon setting the desired sampling resolution, the

115

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4M1P

V2.84MEG VIDEO Image Acquisition, Display, Processing, AnalysisCopyright (C) 1984-1993 EPIX, Inc. All rights reserved

! COMMAND »

> Video Formats> Video Resolution

> Video Digitize/Display> Motion Sequence Capture/Display> Special Operations & Modes

> Contrast & Lookup Tables> Pixel Peek, Poke & Plot> Image Zoom & Pan

> MIPX Scripts> Custom Menu

|< Quit Menu

? Help Key Usage> Image Test Patterns & Sequences

> Image Processing> Image Printing> Image File Load/Save

> Image Measurements> Paint, Draw & Text Overlay> Feature Finders

> DOS Escape> Obscure Menus

Figure CI. "Main Menu" for EPIX Interactive Image Analysis Software

> Video Resolution

! COMMAND » |< Quit Menu

! Interlace: Use Distinct (2) Fields ? ON

! Horz: Pixels Sampled per Line 752

! Horz: Pixel Width 1

! Horz: Left Edge 8" Horz: Right Edge 761

! Horz: Set L/R Centering ON

! Horz: Set Max Samples per Line OFF

! Vert: Lines Sampled per Field

! Vert: Line Height

! Vert: Top EdgeVert: Bottom Edge

! Vert: Set Top/Bot Centering! Vert: Set Max Samples per Fie

2401

240

ONd OFF

{Variable Sampling (Pixel Width or Line 1

jlHorz: Width Multiple at Edge 1

!Horz: Width Unaffected Center 1

leight) Parameters:

IVert: Height Multiple at Edge'.Vert: Height Unaffected Center

1

1

Split Digitize/Display Screen Parameter!

! Horz: Division Position 2

! Horz: Division Spacing 8

! Vert: Division Position! Vert: Division Spacing

2

Pixels in each Image 360960 |~ Image Buffers in Memory 11

Figure C2. "Video Resolution" Sub-Menu

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number of frame buffers available for capturing images is displayed in the lower right

corner ofthe menu. For 752 x 480 resolution, 1 1 frame buffers are available. After

setting the resolution, return to the main menu by selecting "Quit Menu".

From the main menu, select the "Video Digitize/Display"; this menu is shown in Figure

C3. Select the function "Digitize", the result ofwhich is a real-time video display ofthe

camera's field ofview. Adjustments to the camera can be performed, such as focus, gain,

iris setting, etc., to achieve the desired image. When complete, return to the main menu;

the real-time image will remain displayed on the monitor.

Next select the "Motion Sequence Capture/Display" sub-menu; this menu is illustrated

in Figure C4. The first step here is to choose the length ofthe sequence, and which

buffers are to be used, by selecting the sequence starting and ending buffers. For example,

> Video Digitize/Display

! COMMAND » < Quit Menu

! Toggle Current Mode! Display [**]

! Current Image Buffer 1

! Digitize C ] ! Image Memory Bit Write Mask xOO! Blank Video [ ] ! Camera Control Mode xOO! Stop Video Timing [ ]

! Set Genlock in Display OFF Switch Video after Odd Field ( )

! Set Genlock in Digitize ON Switch Video after Even Field (**)

Switch Video after Any Field ( )

> Split Screen Modes

Figure C3. "Video Digitize/Display" Menu

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> Motion Sequence Capture/Display

! COMMAND »

Sequence Starting BufferSequence Ending Buffer

> Trigger Options

1

11

< Quit Menu

Available Image Buffers

! Current Image Buffer

11

1

! Digitize Sequence. Period: 4

! Display Sequence. Period: 6

! Digitize w. Sample Redisplay Sequence. Period: 60

! Digitize Continuous, Circular Sequence. Period: 4

! Reorder Circular Sequence

! Average Image Sequence

> Repeated Digitize/Display Cycles (MIPX)

Figure C4. "Motion Sequence Capture/Display" Sub-Menu,

in the flat plate/jet interaction work only 10 ofthe 1 1 burTers were used; thus the starting

buffer was set to 1 and the ending buffer to 10.

The time interval between consecutive samples is then set with the "Digitize Sequence.

Period:" function. The period is based on units ofvideo fields if the video is not interlaced

(1/60 sec) or video frames ifthe video is interlaced (1/30 sec). The COHU camera was

set internally to send an interlaced image to the frame-grabber board. Since the incoming

signal to the board is interlaced, the software can be programmed using the interlace

function to store either an image with both fields ofthe image (interlaced) or an image

with a single field (non-interlaced). With the "Interlace: Use Distinct (2) Fields ?" set to

active, the period will be based on units offrames. For the jet/plate interaction experiment

collection, the period was set to the default value of4 frame periods between each

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captured image or 4/30 = 2/15 of a second between each captured image. For the

supersonic wind tunnel experiment the period was set to 1 or 1/30 of a second between

each captured image.

One note concerning this function; to enter the desired period, the mouse or arrow

keys are first used to position the cursor on the function. The period is entered using the

numeric keys, the program responding to the entry by "highlighting" it red. The entry is

then entered into memory by either strobing the left mouse button or striking the "enter"

key. This action, however, also starts the execution ofthe algorithm for sequence image

capture. When complete, all designated buffers will contain a captured image. Ifthe

image buffer used to display the real-time image lies between the starting and ending

sequence buffers, it too will contain a captured image. Therefore, until the desired event

is being displayed on the monitor in the real-time format, the entry for the period should

not be strobed or the above sequence of events will have to be repeated to redisplay the

real time image. It is, of course, not necessary to display a real-time image to capture a

sequence of images. By simply re-strobing the "Digitize Sequence. Period:" a new set of

images is stored in the designated buffers. Displaying a real-time image ofthe desired

event on the monitor is simply a matter of choice.

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B. IMAGE PROCESSING

1. Averaging

The procedure outlined in Chapter III for data collection of the wind-on, wind-off,

and dark-current conditions involved executing the above-described steps ten times, i.e.,

ten images per sequence, executing the motion-sequence algorithm ten times, for a total of

one hundred images. After each sequence run, the images in the designated buffers were

averaged together to form a single image. This was done by strobing the function

"Average Image Sequence" in the "Motion Sequence Capture/Display" sub-menu. The

averaged image is stored in the buffer designated as the starting sequence buffer.

The hard drive ofthe 80386 PC used in the present work contained software

applications used in other research, which presented inadequate memory space for image-

data storage. Therefore, all data was transferred from the frame-grabber board to floppy

disk. The command to store data to disk is found in the main menu and is designated as

"Image File Load/Save". From the resulting sub-menu, select the option "File Load/Save,

TiffFormat w. AOI". The sub-menu for this option is brought up onto the computer

screen. Position the cursor on the option, "Save Image to File. Name", and type "b:

filename.tif. Striking the "enter" key will bring up the menu "Select IMAGE BUFFER

and/or AREA OF INTEREST" to appear; select the option "Image Area Of Interest: Full

Image". The image will then be sent to the floppy. "Full Image" refers to the image size

that is set in the "Video Resolution" sub-menu; thus ifthe image resolution is set to 752 x

480, this will be the image size that is stored on the disk.

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Once ten averaged images have been saved to disk, they can be loaded back into ten

frame buffers on the frame-grabber board using "Image File Load/Save" function. Again,

select "File Load/Save, TiffFormat w. AOI" and then position the cursor on "Load Image

from File . Name:". Type "b.filename.tif and strike "enter". In the "Select IMAGE

BUFFER and/or AREA OF INTEREST" sub-menu, select "Image Area Of Interest: Full

Image" and strike "enter". The image will be loaded into the current image buffer. The

current image buffer is selected by simply toggling the Pg Up/Pg Dn keys.

With all ten averaged images loaded into the frame grabber, return to the main

menu and select the "Motion Sequence Capture/Display" function. Insure the "Sequence

Starting and Ending Buffers" reflect the sequence of buffers that the averaged images are

stored in (See Figure C4). This complete, the images are averaged together using the

"Average Image Sequence" option, the resultant image being stored in the buffer

designated the sequence-starting buffer. This image represents either the wind-on and

wind-offimages that will eventually be ratioed or the averaged dark-current image that

must first be subtracted from these two images. The three resultant images are again

stored on floppy disk.

2. Subtraction

The averaged wind-on, wind-off, and dark-current images are loaded back into

consecutive buffers of the frame-grabber board using the steps for loading files that were

discussed above. From the main menu select "Image Processing", from which the image-

processing sub-menu is displayed on the screen as in Figure C5. Choose the "Two Image

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Image Processing

! COMMAND >> |< Quit Menu

> Histogram Displays |> Moments & Center of Mass

> TMS320 Resident Operations> TMS320 Loadable Operations

> Simple Pixel Operations> Image Copy, Resize, Rotate> Two Image Arithmetic> Spatial Filters> Edge Detectors> NxN Operations> Miscellaneous Operations

> Morphological Operations> Transform (FFT) Operations> Image Interlace Modification> Equalization & Normalization> Two Image Normalizations> 32 Bit Integration> Image Sequence Operations

> Image Processing Modes1

Figure C5. "Image Processing" Sub-Menu

Arithmetic" option, which sub-sequently displays the options available for conducting

operations involving two images, this menu being illustrated in Figure C6. Four

subtraction options may be selected; the option "Abs(PixB - PixA)" was used in the

present work, where the absolute value of an intensity value is taken if it is less than zero.

When this function is selected, the "Select IMAGE BUFFER and/or AREA OF

INTEREST" for PixA menu is displayed. Before selecting anything from this sub-menu,

ensure that the current-image buffer that is being displayed on the image monitor is that

containing the dark current image; this represents PixA. From the "Select IMAGE

BUFFER and/or AREA OF INTEREST" menu, choose the option "Full Area of Interest:

Full Image". When this step has been completed, the "Select IMAGE BUFFER and/or

AREA OF INTEREST" for PixB is displayed. Here, ensure the current image buffer

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> Two Image Arithmetic

! COMMAND » |< Quit Menu

! Add Images: PixB <- PixB + PixA MOD 256

! Add Images: PixB <- Min(Pix + PixA, 255)

! Subtract Images: PixB <- 128+(PixB-PixA)/2

! Subtract Images: PixB <- PixB - PixA MOD 256

! Subtract Images: PixB <- Max(PixB - PixA, 0)

! Subtract Images: PixB <- Abs(PixB - PixA)

! AND Images: PixB <- PixB & PixA

! Exclusive OR Images: PixB <- PixB o PixA

! Average Images: PixB <- (PixA + PixB) / 2

! Product Images: PixB <- (cO*PixA+d) * (c2*PixB+c3) / c4

"Product Coefficient: cO 1 "Product Coefficient: c3

"Product Coefficient: d "Product Coefficient: cA

'Product Coefficient: c2 1

64

! Ratio Images: PixB <- (cO * PixB + d) / (c2 * PixA + c3)

"Ratio Coefficient: cO 1 "Ratio Coefficient: c2

"Ratio Coefficient: d "Ratio Coefficient: c3

1

! Function on Images: PixB <- f(PixB, PixA). Expression:

! Unlnsert Images: If (PixB = PixA) PixB < 0. Eps #:

! Insert Images: If (PixB == 0) then PixB <- PixA

Figure C6. "Two-Image Arithmetic" Sub-Menu

being displayed on the monitor is either the wind-on or wind-off image; this represents

PixB. Again select "Full Area of Interest: Full Image" from the sub-menu. Execution will

begin, the modified image residing in the frame buffer that originally contained PixB.

Conduct this operation on both the wind-on and the wind-off images.

3. Registration

Registration of images will be unique to every application. As discussed in Chapter

III, the registration procedure between the wind-on and wind-off images for the jet/flat

plate interaction involved solid body motion, a relatively simple registration problem.

Registration between images that involve more complex scenarios such as translational

shifts, rotational shifts, and geometric distortions, will require more complicated software

procedures than were used here.

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If the extent of distortion between the images is simply solid body translation, then

the following procedure can be used: Load the wind-on and wind-off images into

consecutive buffers. From the main menu, select the "Pixel Peek, Poke & Plot" option,

this sub-menu is shown in Figure C7. When this menu is displayed, the cursor will be

overlaid on the image monitor, and can be controlled with the left button on the mouse is

depressed. The cursor coordinates remain the same as the image buffer is changed,

allowing examination of feature registration among image sequences. Thus using the

wind-offimage as the reference image, the vertical and horizontal characters of the cursor

are aligned on a feature or control point that is distinctive in both images. By shifting back

and forth between the buffers containing the images, using the Pg Up/Pg Dn keys and not

disturbing the cursor location, an indication ofthe magnitude of distortion is obtained.

> Pixel Peek, Poke & Plot

! COMMAND >> < Quit Menu

• Cursor X Coordinate 230 ! Current Image Buffer 3

! Cursor Y Coordinate 99 ! Device/Unit Selected! Pixel Value at Coordinate 72

Peeking Within Image Buffers: Peeking Across Image Buffers:! Pixel Peek 17x17, X-Y ! Pixel Peek 17x17, B-Y

! Pixel Plot, Line (X) ! Pixel Peek 17x17, X-B! Pixel Plot, Column (Y) ! Pixel Plot, Suffers (B)

! Pixel 3-D Plot, X-Y

Figure C7. "Pixel Peek, Poke and Plot" Sub-Menu

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Return to the main menu and select "Image Processing", followed by the option "Image

Copy, Resize, Rotate"; this sub-menu is shown in Figure C8. The function "Copy & X,Y

Shift" copies an image , shifting the image left or right and up or down in its buffer. The

Left(-X) Right(+X) Shift parameter specifies the number of pixels the image is to be

shifted left or right; the Up(-Y) Down(+Y) Shift parameter specifies the number of pixels

the image is to be shifted up or down. When the parameters have been entered, strobe the

"Copy & X,Y Shift" function using the left button ofthe mouse or the "enter" key.

(Ensure that the wind-on image is in the current image buffer prior to this step). The

"Select IMAGE BUFFER and/or AREA OF INTEREST" for image A menu will appear

from which the "Image Area of Interest: Full Image" option is selected; when this is done

the "Select IMAGE BUFFER and/or AREA OF INTEREST" will re-appear for image B

> Image Copy, Resize, Rotate

! COMMAND »

! Copy Image

! Copy & X,Y Shift' Left(-X) Right(+X) Shift:' Up(-Y) Down(+Y) Shift:

! Copy & Skew Left/RightSkew at Top Edge:Skew at Bottom Edge:

< Qui t Menu

Copy 8 Flip Left/Right

Copy £ Flip Top/Bottom

Copy & Flip Top/Bottom & Left/Right

! Copy & Skew Up/DownSkew at Left Edge:

Skew at Right Edge:

Following operations require nonover lapping source and destination:

! Copy & Resize w. Bilinear Interpolation! Copy & Resize w. Nearest Neighbor Interpolation

Interpolate: Top->Up [**]

Interpolate: Top->Down [ ]

Interpolate: Top->Left [ ]

Interpolate: Top->Right [ ]

Interpolate: Top Flipped NO

! Copy & Resize w. Linear Area Interpolation! Copy & Resize w. Gaussian Area Interpolation

! Copy & Resize w. Pixel ReplicationPixel Replication, X 2 I

Pixel Replication, Y 2

! Copy & Rotate w. Bilinear Interpolation. Angle:! Copy & Rotate w. Nearest Neighbor Interp. Angle:

Rotation Correction for Aspect Ratio (X/Y):

45.0

45.02.33

Figure C8. "Image, Copy, Resize, Rotate" Sub-Menu

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where again the option "Image Area of Interest: Full Image" is chosen. When this

selection is made the operation will then be executed. The current image buffer containing

the wind-on image will be replaced with the modified wind-on image. Return to the "Pixel

Peek, Poke & Plot" sub-menu and use the cursor to determine if the wind-on and wind-off

images are properly registered. Several iterations may be necessary until the images are

aligned.

4. Ratioing

With the images correctly registered, the ratioing process can now be executed, i.e.,

the wind-offmay be divided by the wind-on images. Proceed to the "Two Image

Arithmetic" sub-menu as previously done when the dark current image was subtracted

from the wind-on and wind-off images. Under the "Ratio Images" option, set the ratio

coefficients, that are used for "gain and offset", as follows: cO = 100 (or 128), cl = 0, c2 =

1, c3 = 0. Next strobe the "Ratio Images" function which will cause the "Select IMAGE

BUFFER and/or AREA OF INTEREST" menu for PixA to be displayed. Ensure the

current image buffer is displaying the wind-on image. Select "Image Area of Interest: Full

Image". This will cause the "Select IMAGE BUFFER and/or AREA OF INTEREST" to

be re-displayed for PixB . Now shift the buffer containing the wind-offimage such that it

becomes the current image buffer. Again select "Image Area of Interest: Full Image".

The ratioing process will then commence replacing the image designated as PixB, i.e., the

wind-off image, with the modified image.

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5. Thresholding

A black background is usually added to the ratioed image to provide contrast and

enhancement to the resultant image. From the main menu chose "Image Processing" and

then the option "Simple Pixel Operations". Under the function "Threshold Pixel Values"

set the values as follows:

- Threshold: Lowbound

- Threshold: Highbound 255

- Threshold: NewValue

Strobe the "Threshold Pixel Values" function with the left mouse button; the "Select

IMAGE BUFFER and/or AREA OF INTEREST" menu will appear. The boundary shape

ofthe painted surface depicted in the ratioed image will dictate which area of interest to

select for this image processing operation, i.e., "Interactive Rectangular", "Interactive

Elliptical", "Interactive Freehand", and "Interactive Polygon". The area of interest

includes the area ofthe image that the painted surface does not occupy; for the flat plate,

since the sides were parallel to the image axis, the "Interactive Rectangular Region" was

selected as the region of interest. The area ofthe flat plate image not occupied by the

plate was broken down to four areas of interest, that is, the area above the plate, below

the plate, left ofthe plate, and to the right ofthe plate. Using the mouse with the right

button depressed, these areas were outlined individually with the cursor. Once the areas

had been outlined, the thresholding process was executed.

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6. Pseudocoloring

To add false coloring or pseudocoloring to the gray-scale image, select the

"Contrast & Lookup Tables" option from the main menu. This menu is illustrated in

Figure C9. Each ofthe primary colors, red, green, and blue are set by selecting the

"Numerically Set & Show" option for the individual colors. The option displays the

sub-menu illustrated in Figure CIO. Using the function "Set Partial Linear Ramp" any

configuration of linear ramps may be constructed. A graphical display of the inputs can be

shown on the computer screen by selecting the "Plot Table" option in the menu illustrated

in Figure CIO.

> Contrast & Lookup Tables

! COMMAND » |< Quit Menu

! Number of Lookup Table Sets 1

! Current Lookup Table Set 1

> Numerically Set & Show: Red Table> Numerically Set & Show: Green Table> Numerically Set & Show: Blue Table

> Interactive Contrast & Color: Center> Interactive Contrast & Color: Black

, Width, Depth

Level, Contrast

> File Load/Save of RGB Set.....

Figm$ C9. "Contrast & Lookup Table" Sub-Menu

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i

> Define Lookup Table

! COMMAND » |< Quit Menu

! Set Linear Ramp! Set Log Curve! Set Exp Curve! Set Gamma Curve, Gamma

! Set as f(C). Expression:

1.00

! Set Partial Linear Ramp"Starting Coordinate"Starting Value"Ending Coordinate"Ending Value

255

255

! Complement/Invert Table

! Transpose Table

? Show Table

? Plot Table

! Save Lookup Table to File.» Load Lookup Table from File.

Name:Name:

Figure CIO. "Define Lookup Table" Sub-Menu

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APPENDIX D. DARK CURRENT

Thermal generation of electrons or "dark-current" is a naturally-occurring consequence

of using semiconductor devices for photo reception. To understand dark-current effects

on pressure-sensitive paint measurements, it is necessary to review the operation of a

charged-coupled device (CCD). A schematic illustration of a CCD is shown in Figure Dl.

Consider a single CCD electrode in Figure Dl . Absent the application ofa bias to the

gate electrode, a uniform distribution of holes or majority carriers exists in the p-type

semiconductor. As a positive voltage is applied to the gate, the holes are repelled from

the semiconductor immediately beneath the gate, forming a depletion layer or potential

well. An increase in the voltage causes the depletion region to extend further down into

the bulk semiconductor, causing an increasing positive potential known as a surface

potential to exist at the semiconductor and insulator (oxide) interface. Eventually a gate

bias is reached at which the surface potential becomes so positive that the minority carriers

(in this case electrons) are attracted to the surface where they form an extremely thin but

very dense inversion layer. [Ref 28:p. 6 ]

In image-sensing applications ofCCD's, the minority carriers are generated when

photons entering the silicon substrate excite the valence electrons of the material into the

"conduction band", becoming free electrons. The electrons are then collected under the

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READOUT REGISTER CLOCKS

#1 o-

&2 O-

^3°"

LIGHT SPOT-^ PHOTON ENERGYGATE OXIDE

UsINVERSION LAYER

\

I

yOUTPUT DFFUSION

COD ELECTRODES /

POTENTIAL WELL

P-TYPE SILICON SUBSTRATE

G00X°eeQ

Desired event : well filled with

electrons as a result of photon energy GO9 00 00/000©

Well "off-set' due to "Dark Current"

Figure Dl. Representation of the Effect ofDark-Current on the Creation of Charge

electrode ofthe applied bias. The number of electrons under the electrode within a given

period oftime is proportional to the local light intensity.

In addition to the photoelectric effect described above, free electrons can also be

produced by thermal energy, ofwhich the rate of generation increases exponentially with

temperature for a pure semiconductor. Thus, the presence ofthermally generated minority

carriers limits the maximum possible usefulness ofthe potential well by displacing optically

generated carriers. This produces an "offset" in the measurement image such that the

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zero-incident light level does not correspond to a zero gray-level pixel index. Thus, the

dark image must be removed from the measurement images. To do this, a dark image is

acquired by prohibiting any light from striking the CCD array and sampling an image.

Several ofthese images are taken and time averaged together. This is necessary because

dark current generation tends not to be uniform over a whole array. The resulting

averaged dark current is then eliminated from the measurement images using image

processing techniques discussed in Chapter m.

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APPENDIX E. SUPERSONIC NOZZLE DESIGN PROGRAM

Software for the design of two-dimensional supersonic nozzles was acquired from the

Naval Surface Warfare Center (NSWC), White Oak, Maryland. The software package is

comprised oftwo programs; the first program is concerned with establishing the

isentropic contour of the nozzle while the second corrects for the viscous effects ofthe

fluid and adjusts the contour accordingly.

Support documentation for the software from a user's standpoint is not available. In

addition, the early fortran code is not well structured, making it difficult to interpret the

algorithm and follow its logic. It is difficult to recognize many ofthe variables, and there

are no comment statements. However, enough information has been deduced such that

the program may be operated effectively. The intention of this appendix is to document

what is now known about the software.

Modifications have been made to the original software primarily involving the manner

in which program input entries are made and data storage accomplished. Originally, the

program was designed to access punch-card readers and magnetic-tape drives for data

input and output management. Entries are now made directly to the program through

interactive software in a format that is more flexible and user friendly. Output data are

stored in a file structure compatible with hard drive systems. A listing of the modified

software is given in Section C ofAppendix E.

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A. INVISCID CONTOUR SOFTWARE (Program chart)

The program "char6" generates the isentropic contour of the supersonic nozzle using

the method of characteristics. Initiation of the program will depend on the filename

assigned to the object code at the time of compiling and linking ofthe source code. Once

started, the program first displays an introductory summary as shown in Figure El . As

indicated by these remarks, the storage ofthe output data is currently limited to the data

for one run. A successive run will overwrite the data storage files from the previous run.

Entries made by the user through the interactive sequence ofprompts for input data

have been sub-divided into two categories; the first category identifies the "characteristic"

lengths and nozzle type that will be used to define the configuration; the second specifies

dimensions and flow characteristics to which the nozzle will be designed.

U.S. NAVAL ORDANCE LABORATORY, WHITE OAK, MARYLAND

COMPUTER PROGRAM FOR THE DESIGN OF TWO-DIMENSIONAL SUPERSONIC NOZZLES

PARTI

THE ISENTROPIC CORE OF THE NOZZLE

INTRODUCTION:

This program uses the method of characteristics to determine the contour of a two-dimensional

isentropic core of a supersonic nozzle. The program requires two sets of inputs; one that

provides the general characteristic lengths and nozzle types that will be used to describe the

nozzle; the second set outlines the specific flow characteristics and geometric lengths that the

contour will be designed to. The program is currently limited to one output file; in other words

successive runs will overwrite data generated on previous runs.

Figure El. Illustrative Example ofthe Introductory Remarks for Program char6

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1. Category 1: Characteristic Lengths and Nozzle Types

1

.

INPUT A DESCRIPTION OF THE PROJECT

Allows a short summary ofthe project to be recorded as part ofthe final output

summary. The description is limited to 80 characters.

2. INDICATE TYPE OF NOZZLE, 1-SHORT, 2-REGULAR, 3-EXPONENTIAL

Provides the option of choosing a specific contour shape. The methodology the

program uses to generate the contour begins by first determining the centerline

Mach number distribution based on the choice of contour. The method of

characteristics is then used in conjunction with the centerline distribution in

determining contour geometry.

3. INDICATE THROAT OR EXIT HEIGHT TO BE READ, 1-EXIT,

2-THROAT

Irrespective which is used; the program calculates the option not selected using

simple isentropic relations. Both heights are employed in the program in

computing the contour.

4. INDICATE CHARACTERISTIC HORIZONTAL LENGTH TO BE READ,1-EXIT LENGTH, 2-START OF TEST RHOMBUS

Refer to Figure E2 for clarification ofthe horizontal lengths discussed. The exit

length is defined as the distance between the nozzle throat and the nozzle exit.

The characteristic network created by the method of characteristics is such that

the last two characteristic lines in the grid complete the expansion process by

turning the flow parallel to the centerline ofthe nozzle and thus expanding it to

the desired test section Mach number. These two characteristic lines can also be

thought of as forming halfof an imaginary rhombus as shown in Figure E2. This

is known as the test section rhombus. The distance between the nozzle throat

and the intersection formed by the two characteristic lines defines the horizontal

length referred to above.

5. INDICATE OUTPUT, 1-STEP-BY-STEP, 2-WALL POINTS ONLY

Generally, the approach used in applying the method of characteristics can be

summarized in a three step process: Step 1 ~ the determination ofthe

characteristic lines in the xy space using

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Test Section Rhombus

Initial Data Line

Start of Test Rhombus

Exit Length

Figure E2. Schematic of Supersonic Nozzle Design by the Method of Characteristics

(£W=tan(9±u)

where 9 is the angle between the streamline ofthe flow and the horizontal and

[i is the angle between the streamline and the characteristic line; Step 2 ~ the

determination ofthe compatibility equations

9 + v(M) = const = K_9 - v(M) = const = K+

(along the right characteristic)

(along the left characteristic)

where again 9 is the angle between the horizontal and the streamline, and, v(M)

is the Prandtl-Meyer function, the compatibility equations holding along the

characteristics; Step 3 — the solution of the compatibility equations point by

point along the characteristics.

Note: The initial data line used in starting the computation

ofthe method of characteristics in this program begins with

the assumption that the sonic line at the throat is straight. Apoint AM downstream ofthe sonic line along the centerline

Mach number distribution is chosen as the initial point for the

characteristics procedure. With the combination of this

initial point , the centerline distribution, and the radius of

curvature at the throat, the method of characteristics is carried

out in a marching fashion.

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Choosing the option step-by-step will instruct the program to include in the final

output all "steps" used in calculating the characteristic net, including local data

pertaining to the nodal points comprising the turning angle, the x and y coordinates

ofthe grid points and the Mach number. If in turn the option "wall points only" is

exercised, the data associated with the grid points that decide the contour or wall

geometry are included in the final output.

Once the last selection for the first category of inputs is chosen and the "enter" key is

subsequently struck, the selections made are then displayed in the following format:

NOZZLE = SHORT (REGULAR, EXPONENTIAL)

HEIGHT TO BE READ = EXIT (THROAT)

LENGTH TO BE READ = LENGTH TO EXIT (LENGTH TO RHOMBUS)

OUTPUT FORMAT = STEP-BY-STEP (WALL POINTS)

The question, "Are input values correct?, 1-Yes, 2-No", follows immediately, allowing the

opportunity to make changes to the inputs if necessary. Selecting "Yes" causes the

following menu to be displayed:

INPUT VALUES TO BE CHANGED (1, 2, 3, 4):

1- TYPE OF NOZZLE: A. SHORT, B. REGULAR, C. EXPONENTIAL

2 - HEIGHT TO BE READ: A. EXIT, B. THROAT

3 - LENGTH TO BE READ: A. EXIT, B. TEST RHOMBUS

4 - TYPE OF OUTPUT: A. STEP-BY-STEP, B. WALL POINTS ONLY

By selecting a value from one to four a sub-menu ofthe descriptors to the right ofthe

colon ofthe input chosen is listed. For example, selecting the value of2 (Height to be

read) from the above menu yields

1 - EXIT, 2 - THROAT

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prompting a choice of height designation. After hitting the "enter" key, the program will

again display the first-category input selections, showing the latest modifications. An

opportunity to make additional alterations is also afforded when the question, "Any other

changes?, 1-Yes, 2-No", immediately follows. Selection of "No" initiates the sequence of

events for data input associated with the second category.

2. CATEGORY 2: NOZZLE FLOW AND GEOMETRY SPECIFICATIONS

Commencement ofthe sequence of prompts for the second category of inputs is

denoted by the statements

"THE NEXT SET OF INPUTS SPECIFY FLOW CHARACTERISTICS ANDSPECIFIC GEOMETRY DIMENSIONS FOR THE NOZZLE"

***** PLEASE UTILIZE DECIMAL POINTS FOR THESE INPUTS *****

It is necessary to use decimal points when specifying numeric data; the program is

formatted to read the input data in scientific notation, though numeric values may be

entered into the program as real numbers. If a decimal point is not explicitly stated, the

exponent field in the scientific notation format will reflect this with zeros, resulting in an

ambiguous input. Thus, if the real number "14" is the desired input, it must be entered as

" 14"; this results in the scientific notation representation "0. 14000E+02". If the number

is entered as "14", the resulting representation will be "0. 14000E+00".

The inputs for the second group are outlined as follows:

1. INPUT RATIO OF SPECIFIC HEATS

Self-explanatory.

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2. INPUT TEST SECTION MACH NUMBER

The Mach number of the uniform flow that is required at the exit plane ofthe

nozzle.

3. INPUT EXIT LENGTH (INCHES) OR INPUT BEGINNING OF TESTRHOMBUS (INCHES)

The choice made in the first category of inputs concerning the horizontal length will

dictate which prompt will be displayed. Refer to Figure E2.

4. INPUT HALF HEIGHT OF EXIT (INCHES) OR INPUT HALF HEIGHT OFTHROAT (INCHES)

Again dependent on the selection made in the first category of inputs with

reference to the height to be read.

5. INPUT RADIUS OF CURVATURE AT THROAT (INCHES)

Self-explanatory.

6. INPUT MULTIPLICATIVE FACTOR FOR "X" INCREMENT

Influences the spacing between consecutive contour points. A range between 1 .0

(representing 150 points to describe the contour) to 0.5 (representing 400 points) is

available.

Note: Generation ofthe cubic centerline Mach number distribution,

which is associated with the regular nozzle contour, is dependent

upon the result of a "feasibility expression" involving the second

category values input by the user. Ifthe outcome ofthe expression

does not fall into a pre-determined interval, the program halts

execution and displays the message,

*** CUBIC CENTERLINE MACH NO DISTRIBUTION IS

NOT APPROPRIATE FOR INPUT GIVEN ***

At this point, the program must be re-initialized and the process of

re-entering the input started over. One ofthe input values, gamma,

test section Mach number, exit length or length to test rhombus, exit

or throat height, or the radius of curvature, or a combination thereof

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must be changed such that the compatibility requirements set forth by

the feasibility expression are satisfied.

When the data for the multiplicative factor has been entered and the "enter" key struck the

second category of inputs are displayed in the following fashion:

GAMMA = 0. 14000E+01

SMT = 0.17000E-K)1

XEXXT = 0.11500E+02

YTHEX = 0.19500E+01

RCT = 0.11500E+01

DELMUL = 0.70000E+00

ARE INPUT VALUES CORRECT ?, 1 - YES, 2 - NO

where

GAMMA = Ratio of specific heats

SMT = Test section Mach number

XEXXT = Exit length or length to the beginning of test

rhombus depending on the choice in first category

of inputs

YTHEX = Half height of exit or halfheight of throat depending

on the choice in the first category of inputs

DELMUL = Multiplicative factor for "x" increment

As in the first category of inputs, the option to make changes to the input data is

available. When changes are desired a listing ofthe input descriptors is displayed:

INPUT VALUE TO BE CHANGED: 1 - GAMMA, 2 - SMT,3 - XEXXT, 4 - YTHEX, 5 - RCT, 6 - DELMUL

A selection will exhibit a directive prompting the user to input the new value. For

example, choosing gamma (1) results in,

INPUT NEW VALUE FOR GAMMA

Fulfilling this and subsequently striking the "enter" key causes the second category of

inputs to be re-displayed showing the recent modifications. Additional changes may also

be conducted at this point if necessary.

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Ifthe second category of inputs have been reviewed with satisfaction, the program will

begin calculation ofthe isentropic contour at this point. Conclusion ofthe routine is

indicated by the remarks,

OUTPUT ISENTROPIC DATA FOR NOZZLE CONTOURSTORED IN FILENAME "outptl"

DATA FROM THIS FILE TO BE USED IN THE VISCOUSPROGRAM "nbl6.f ' IS STORED IN FILENAME "outpt2"

The file "outptl" contains a systematic breakdown ofthe data calculated by the program

which are then available to the user for review. A complete explanation and an example of

the format are presented in the following section. The file "outpt2" contains the data that

are to be utilized in the program "nbl6" and are in a format that is convenient for file

processing.

3. "outptl" EXAMPLE AND DESCRIPTION

Figure E3 shows the format in an example ofthe file "outptl ". It has been

sub-divided into it's major components and labeled for reference below.

1

.

Introductory Header - Self-explanatory.

2. Descriptive Comments - Refers to the comments made in the first category

of inputs when prompted by the program for a description ofthe project.

3. User Inputs - Encompasses all the inputs into the program made by the user.

The input identifiers associated with the first category of inputs are defined

as follows:

INDSR = Nozzle Type

INDYTH = Characteristic Height (Throat or Exit)

INDXTE = Characteristic Length (Exit or Test Rhombus)

INDOUT = Output Mode (Step-by-Step or Wall Points)

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US NAVAL ORDANCE LABORATORY. WHITE OAK, MARYLAND

COMPUTER PROGRAM FOR THE DESIGN OF TWO-DIMENSIONAL SUPERSONIC NOZZLES

PARTI

THE ISENTROPIC CORE OF THE NOZZLE

1 7 MACH NOZZLE

INTRODUCTORYHEADER

.DESCRIPTIVE

COMMENTS

INPUT DATACARD NO. 1 INDSR = 2

INDYTH = 1

INDXTE = 1

INDOUT = 1

INDCAL =

INDTAP =

INDCRD =

CARD NO. 2 GAMMA = 14000E+01

SMT= 0.17000E+01

XEXXT = 11500E+02

YTHEX= 019800E+01RCT= 011500E+02

DELMUL = 70000E+00

NOZZLE PARAMETERS

MACH NO. YTH YEX1T XEXIT XT

017000E+01 0.14803E+01 O.19800e+01 011500E+02 0.87780E+01

RCT B0.11500E+02 0.3S425E+00

USERINPUTS

NOZZLEPARAMETERS

CENTERLINE MACH NUMBER DISTRIBUTION USING CUBIC EQUATION

N X MACH NO.

1 534600E-03 0.1 0001 OE+01

2 0.732600E-03 0100014E+01

3 0.930600E-03 0.10001 7E+01

CENTERLINEDISTRIBUTION

CHARACTERISTICS MANIPULATION ( 'INTERPOLATED WALL VALUES)

K X(1NCHES) Y(INCHES) MACH NO. STREAM ANGLE3 0.629684E-03 0.6428261 E-02 O.OOOOOOE+OO 0136713E-04

2 0.828632E-03 0.5607560E-02 O.OOOOOOE+OO 0156680E-04

3 0718964E-03 0.1198140E-01 O.OOOOOOE+OO 0.293399E-04

METHOD OFCHARACTERISTIC

RESULTS

FINAL OUTPUT TO PART I, ISENTROPIC CORE CONTOURI X(INCHES) Y(INCHES) CL MACH NO WALL MACH NO WALL ANGLE RAD OF CURV (IN)

1 0.435619E+00 0.149273E+01 107887E+01 0.114198E+01 0.220395E+01 O.OOOOOOE+OO

2 0.462758E+00 0.149380E+01 108359E+01 0.114598E+01 0.228777E+01 188330E+02

3 0.490391E+00 0149492E+O1 0.108838E+01 0.1150O3E+01 0.237073E+01 O193154E+02

Figure E3. Example Showing the Format of File "outptl"

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ENDCAL, INDTAP, and INDCRD are no longer user-accessible. These

variables were used in the original software and controlled the medium to be

used to record the output data, i.e., magnetic tape or punch cards. The

variables have been "hardwired" in order to accommodate the current

software modifications for data output management.

The input descriptors for the second category of inputs have been previously

defined.

4. Nozzle Parameters - These include, in addition to those dimensions

supplied by the user, the "related" values calculated by the program using

isentropic relationships or simple geometric relations. Thus, given the input

ofthe throat height the program calculates the exit height ,or, given the

horizontal length from the throat to the exit plane the program calculates the

length from the throat to the test rhombus. The parameters are defined as,

Mach No. = Nozzle exit Mach number

YTH = Halfheight ofnozzle throat

YEXIT = Half height of nozzle exit

XEXIT = Length between nozzle throat and exit

XT = Length between nozzle throat and test rhombus

RCT = Radius of curvature at throat

* B = Indicates result of "Feasibility Expression"

* Note: The result of the feasibility expression, to determine

ifthe cubic centerline Mach number distribution maybe calculated with the given nozzle dimensional inputs,

must fall in the interval -2.0 < B < 1 .0.

5. Centerline Mach Number Distribution - Denotes the centerline location

(relative to the throat) and corresponding Mach number. The function used

to generate the distribution, i.e., cubic, exponential, etc., is dependent upon

the choice of nozzle type (regular, exponential, short).

6. Method of Characteristic Results - Describes the characteristic manipulation

used to generate the wall values along the contour.

N = Characteristic line (From left to right)

L = Nodal points along characteristic line

X (inches) = X-coordinate of nodal point

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Y (inches) Y-coordinate of nodal point

Mach No. = Local Mach number at nodal point

Stream angle = Local velocity angle at nodal point with

respect to the horizontal

7. Contour Output - Final output of the isentropic core.

X(INCHES) = X - coordinate of isentropic core

Y(INCHES) = Y - coordinate of isentropic core

CL MACH NO. = Centerline Mach number

WALL MACH NO. = Mach number along contoured wall

WALL ANGLE = Wall angle relative to centerline

RAD. OF CURV. (IN) = Radius of curvature

B. MODIFICATION FOR VISCOUS EFFECTS (Program nbl6)

The program "nbl6" modifies the contour ofthe nozzle to account for the boundary

layer formation. Originally, this software considered the boundary layer effects along the

contour ofthe nozzle only and neglected the effects that would be caused with the

addition of side walls. To compensate for this deficiency in correcting for boundary layer

displacement, the approach used by Demo [Ref. 29: p. 24] was employed. The

assumption is made that the displacement thickness is the same on both contoured and

side walls. The viscous displacement effects on all surfaces are then summed together and

evenly distributed between the two contour surfaces only, as illustrated in Figure E4.

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Boundary Layer

Growth

Corrected

Contour

B

Ay

Figure E4. Nozzle Wall Correction for Boundary Layer

Thus, the total displacement area ofthe entire nozzle cross-section is compensated by

modifying only the contoured walls, allowing the side walls to remain flat and parallel.

The displacement required to the inviscid contour was calculated using the expression

where 5* = displacement thickness, B = nozzle width, and y = half height ofthe contour.

This equation has been incorporated into the software. The final output, discussed later,

was modified to reflect this change.

The data-output management structure, as before, is limited to storing data for one

run. A successive run will overwrite the data stored from the preceding run.

Input into the program is supplied by both the output from "char6" (i.e., file outpt2)

and the user using an interactive presentation similar to that discussed above for the

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inviscid contour. The first category of inputs consists of a series of functional mode

selections concerned with the thermal and velocity boundary layer behavior. The second

category is comprised of numerical input prompts for flow conditions and nozzle

dimensions.

1. CATEGORY 1: FUNCTIONAL MODES

The functional modes establish the desired profile behavior that the velocity and

thermal boundary layers will undergo while traversing the length ofthe nozzle. The

modes are outlined below.

1 . INDICATE WHERE THE BOUNDARY LAYER CALCULATIONWILL TAKE PLACE, 1. ALONG CENTERLINE ONLY, 2. ALONGTHE WALL ONLY, 3. BOTH THE CENTERLINE AND THE WALL

Specifying the first option results in the message,

************************************ CENTERLINE PARAMETER INPUT DATA *

indicating that all input into the program from this point will pertain to

the effects of the boundary layer along the nozzle centerline. Selection

ofthe second option displays

************************************ WALL PARAMETER INPUT DATA *

***********************************

indicating further inputs will apply to the effects ofthe boundary layer

along the nozzle contoured walls. Option three effectively causes

the program to run twice, once for the effects along the centerline

followed by a run associated with the boundary layer effects along the

contoured walls. The final output for option three is consolidated as

a single output vice individual outputs for each run.

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2. INDICATE BOUNDARY LAYER MODE BEGINNING AT NOZZLETHROAT, 1. STRICTLY LAMINAR, 2. STRICTLY TURBULENT,3. LAMINAR-TRANSITION-TURBULENT

Self-explanatory.

3. INDICATE WALL TEMPERATURE FOR NOZZLE, 1. CONSTANTTEMPERATURE, 2. ADIABATTC WALL, 3. TEMPERATUREDISTRIBUTION ALONG NOZZLE TO BE INPUT BY PROGRAMUSER

Wall temperature is assumed only along the contour ofthe nozzle. Since

the boundary layer displacement thickness for the entire cross-section of

the nozzle is a function ofthe displacement thickness generated along the

contour, it can be thought of that the temperature distribution exists both

on the contour and side walls.

4. INDICATE THE CHARACTERISTIC PARAMETER ON WHICHTRANSITION WILL BE BASED, 1. REYNOLDS NUMBER, 2. "X"

DISTANCE FROM THE THROAT

The transition mode only becomes active ifthe laminar-transition-

turbulent selection ofthe boundary layer mode is chosen. The point

oftransition from laminar flow to turbulent flow may be based upon a

horizontal distance "x" relative to the nozzle throat and along the

centerline or a Reynolds number in which the momentum thickness of

the boundary layer is used as the characteristic length

The last entry made for the mode options is followed by a listing ofthe selections to

verify the settings:

B.L. MODE = LAMINAR (TURBULENT, LAM-TRANS-TURB)

WALL TEMP. MODE = CONSTANT (ADIABATIC, USERDEFINED)

*TRANSITION PARAMETER = REYNOLDS NUMBER ("X"

DISTANCE)

B.L CALCULATION = CENTERLINE ONLY (WALL ONLY,BOTH CENTERLINE AND WALL)

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"ARE INPUT VALUES CORRECT?, l-YES,2-NO

*Note: Displayed only if B.L. Mode = Lam-Trans-Turb

If a mode is incorrectly set or a change is desired, "no" is subsequently chosen, resulting in

a modification menu:

INPUT VALUE TO BE CHANGED (1,2,3,4):

1. B.L. MODE: A. LAMINAR, B. TURBULENT, C. LAM-TRANS-TURB

2. WALL TEMP. MODE: A. CONSTANT, B. ADIABATIC, C USER DEFINED

3. B.L CALCULATION: A. CENTERLINE, B. WALL, C. CENTERLINEAND WALL

*4. TRANSITION: A. REYNOLDS NUMBER, B. "X" TRANSITION

*Note: selection of the transition mode with the B.L. Modeset other than B.L. Mode = Lam-Trans-Turb will result in

the message, "Transition parameter not required for inputs

given".

The mode to be modified is selected from the menu list, which in turn causes a sub-listing

ofthe options to which the mode may be set to be displayed. For example, ifthe

boundary layer mode is to be changed, its selection from the modification menu would be

followed by,

1 LAMINAR, 2. TURBULENT, 3. LAM-TRANS-TURB

A choice ofone ofthe available options sets the mode and then causes a re-display of all

the modes and their current status;

B.L. MODE = LAMINAR

WALL TEMP MODE = CONSTANT

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TRANSITION PARAMETER = REYNOLDS NUMBER

B.L. CALCULATION = WALL ONLY

"ANY OTHER CHANGES?, 1-YES, 2-NO"

Other modifications may be done at this point in a sequence similar to that discussed

above. If no other changes are required or ifthe modes initially set were correct, the

series ofprompts for the second category of inputs will be initiated.

2. CATEGORY 2: FLOW CONDITIONS AND NOZZLE DIMENSIONS

The second category ofinputs includes the numerical data associated with the flow

conditions, and additional dimensions ofthe nozzle, which will be made clear below. The

onset ofthe second set of inputs is denoted by the message

* * * PLEASE UTILIZE DECIMAL POINTS FOR THE FOLLOWING INPUTS * * *

followed by the first prompt for information. Decimal points are necessary for the

numeric inputs for the reasoning previously explained.

Most ofthe input prompts are self-explanatory and require no elaboration. Those

prompts requiring explanation or having relevant comments will be summarized following

the prompt.

1. INPUT REYNOLDS NUMBER FOR TRANSITION(Reynolds number based on momentum thickness ofboundary layer)

Displayed only ifthe boundary layer mode is set to B.L. Mode =

Lam-Trans-Turb and the transition indication mode set to Transition

Parameter = Reynolds Number.

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2. INPUT TRANSITION DISTANCE FROM THE THROAT IN FEET

Displayed only if the boundary layer mode is set to B.L Mode =

Lam-Trans-Turb and the transition indication mode is set to Transition

Parameter = "X" Distance From Throat.

3. INPUT MOMENTUM THICKNESS OF BOUNDARY LAYER AT THETHROAT IN FEET

A value of 1.0E-5 feet is suggested.

4 INPUT STAGNATION PRESSURE IN LBS/IN2

5 INPUT TOTAL TEMPERATURE OF SUPPLY MEDIUM IN DEGREES R

6. INPUT TEMPERATURE OF THE WALL IN DEGREES R

Displayed only ifthe wall temperature indication mode is set to Wall

Temp. Mode = Constant.

7. INPUT THE EXTENSION LENGTH OF NOZZLE PAST THE EXIT IN

INCHES AS DEFINED FOR THE ISENTROPIC CORE

The nozzle contour may be extended past the exit plane ofthe nozzle,

as defined by "char6", if, for instance, a test section is to be added.

Assumes uniform duct flow.

8. INPUT INCREMENT OF "X" IN INCHES FOR EXTENSION LENGTH TOINTERPOLATE CONTOUR OF NOZZLE

Establishes the horizontal distance between consecutive points that

describe the contour ofthe extension length.

9 INPUT WIDTH OF NOZZLE

10. INPUT RATIO OF SPECIFIC HEATS

1 1

.

INPUT EXPONENT FOR VISCOSITY-TEMPERATURE RELATION

For air, this is (o=) 0.76.

12. INPUT MOLECULAR WEIGHT OF GAS SUPPLY (AIR = 28.97)

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13. INPUT SPECIFIC HEAT OF GAS IN BTU/LB-DEG-R (AIR = 0.24)

14. INPUT PRANDTL NUMBER FOR GAS (AIR = 72)

Following the conclusion ofthe last prompt, a listing of all the input descriptors and the

values assigned to them is displayed:

*REYNOLDS NUMBER = 0.50000E-02

*"X" TRANSITION = 0.60000E+01

MOMENTUM THICKNESS = 0. 10000E-04

STAGNATION PRESSURE = 0.47500E+02

STAGNATION TEMPERATURE = 0.68000E+02

**WALL TEMPERATURE = 0.72000E+02

EXTENSION LENGTH PAST NOZZLE EXIT = 0. 12000E+02

INCREMENT "X" FOR EXTENSION = 0.65000E+00

WIDTH OF NOZZLE = 0.40000E+01

GAMMA = 0. 14000E+01

VISCOSITY-TEMP. EXPONENT = 0.76000E+00

MOLECULAR WEIGHT OF GAS = 0.28970E+02

SPECIFIC HEAT = 0.24000E+00

PRANDTL NUMBER = 0.72000E+00

"ARE INPUTS CORRECT?, 1-YES, 2-NO"

*Note: Displayed only ifboundary layer mode is set to B.L.

Mode = 3 and the transition indication mode is set to

either Transition Parameter = Reynolds Number or

Transition Parameter = "X" Distance from Throat

**Note: Displayed only it the wall temperature indication

mode is set to Wall Temp. Mode = Constant

Ifthe option is exercised to change any ofthe input values, the user will be presented with

the following menu:

INPUT VALUE TO BE CHANGED (1,2,3,4,5,6,7,8,9,10,1 1,12,13):

1 TRANSITION PARAMETER2. MOMENTUM THICKNESS AT THROAT3 STAGNATION PRESSURE4. TOTAL TEMPERATURE5. WALL TEMPERATURE

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6 EXTENSION LENGTH OF NOZZLE7. "X" INCREMENT FOR EXTENSION LENGTH8 WIDTH OF NOZZLE9. RATIO OF SPECIFIC HEATS10 VISCOSITY-TEMPERATURE EXPONENT11. MOLECULAR WEIGHT OF GAS12. SPECIFIC HEAT (Cp) FOR GAS13 PRANDTL NUMBER

Selection from the menu generates a prompt for the new information to be input for the

chosen descriptor. Upon entering the new value and striking the "enter" or "return" key,

the list containing the input descriptors and their assigned values will be re-displayed

exhibiting the latest changes and soliciting further modifications.

If at this point no other changes are desired and ifthe wall temperature indication mode

is set to an option other than Wall Temp. Mode = Temperature Distribution Input By

User, the program will proceed to calculate the modified contour according to the inputs

given. Ifthe user has elected to enter a defined temperature distribution along the nozzle

contour, the following sequence ofprompts can be expected:

INDICATE THE NUMBER OF TEMPERATURE POINTSTO BE ENTERED. THREE OR MORE POINTS AREREQUIRED OR PROGRAM WILL TERMINATE THE DATAOUTPUT PRIOR TO COMPLETION.

INPUT THE "X" LOCATION FOR POINT NUMBERRELATIVE TO THE THROAT

INPUT TEMPERATURE IN DEGREES R FOR POINTNUMBER

The second and third statement are repeated until the number of points designated in the

first statement have been entered. When the last point is entered, the program proceeds in

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its calculation ofthe modified contour. Completion of the routine is denoted by the

message,

PROGRAM RUN COMPLETE OUTPUT DATATRANSFERRED TO FILE "outpt3"

3. FILE "outptf" FORMAT DESCRIPTION

Figure E5 illustrates an example ofthe format used for the output file "outpt3".

Again it, as before, has been sub-divided into it's major components and labeled as

follows:

1. Functional Modes

*INDINP = 2

*INDPRG=1

ENDMO = 2 (Boundary Layer Mode) where 1 = Laminar,

2 = Turbulent, 3 = Lam-Trans-Turb

ENDTW = 1 (Wall Temperature Mode) where 1 = Constant Temp.,

2 = Adiabatic, 3 = User Defined Distribution

INDTR =1 (Transition Indication Mode) where 1 = Transition at

Reynolds Number, 2 = Transition at "X" Length

*INDCF = 1

INDOUT =

*Note: Indicates values are hardwired into the program and

are no longer user accessible

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IIC*NP = 2

IM)PRG= 1

INCMO - 2

INDTW = 1

INDTR =

INDWC = 3

INOCF = 1

NDOUT =

TRCON= 00O0OOOE*00THZERO = 0.1000006-O4

PO = 7260O0E+O2

TO = 0.8200006*03

TWU1 = 5300006*03

XTE>*> = 2650006*02

a 6250006-01

functionalMODES

xFLOW CONDITIONS> AND NOZZLEDIMENSIONS

CARD 3

X(IN)

0.318238E+003330826+00

3480896*00

WUL DATA *

Y(IN)

0.142340E*01

0.1423866+01

0.1424346+01

GAMMA = 1400006+01

OMEGA 0.7600006+00

V\OTE 0.2900006*02

OP = 0.2400006*00

PR = 0.72QOO0E*O0

XINC = 0.0000005*00

M0.1119796*01

0.1123526*01

0.1127266*01

"» OUTPUT CODE—

X(IN) S(IN) Y(IN) M REU1/FT)

U6<FT/SeC) MUE<PSEaFT2) RH06(PS6C2/Fr4) TE(R) TW(R)

DB-TA(IN) THETA(IN) DELSTAR(IN) H TWTO

DPDS(PrtT2) DMDS<1/FT) DUDS(1/SEO

q(Btlyft2/S6C) ha(btu/ft2secr) n

DTHDS TALWAL(Pn=T2)

R6TH PE/PO

TAD(R) TE/TO

TWTAD TAD/TO

CF BETATH

0.189944E+O4 0374381E-060.348474E-HX 0.300135E-01

POINT NO. 1

0.2637556*02 0.2639875+02 0.1886006*01 0.17O00OE+O1 0.1205076*08 0.3007756*05 0.2025936*00

0.2375206-02 0.5196456+03 5300006+03 0.788847EJB 0.6337146*00

0.5408966-01 0.1602516*01 0.8463416*00 0.6718666*00 0.9820096*00

0000006*00 0000006*00 0000006+00 100080E-C2 8576296*01 2000866-02 0000006*00

0.1123876+O2 O434220E-O1 0.7530406*01

0.3073686+O2

POINT NO. 2

0.2643805*02 0.264612E*02 1398005+01 0.1700006*01 1205075+08 0.3014Q36+O5 2025836*00

01899446*04 03743815-08 237520E-02 05196456*03 5300006*03 7888475*03 06337146*00

0.3492556+00 0.3007616-01 0.5421066-01 0.1802456*01 0.6463416*00 0.6718666*00 09620096*000.0000006*00 00000006*00 0O30000E+O0 1000476-02 8573*66*01 0.2000956-02 0.0000006*00

0.1123976*02 0. 4342206-01 0.7532256*00

0.3079536*02

XIINOESl

0.3182386*00

0.3330826*00

03480896*00

D6LSTAR( INCHES)

0.1979016-03

02804796-03

0.3532886-03

• WALL R6SULTS

YCOR6*D6LSTAR0.1423606*01

0.1424146*01

0.1424706+01

MWALL DELTAY YCORE+DELTAY0.1119796*01 0.3387286-03 0.142374E+01

0.1123525*01 0.4801216-03 01424346+010.1127266*01 0.8048276-03 01424956+01

Figure E5. Example Showing the Format of File "outpt3"

156

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2. Flow Conditions and Nozzle Dimensions

TRCON = 0.000000E+00

THZERO = 0.100000E-04

PO - 0.726000E+02

TO = 0.820000E+03

TWALL = 0.520000E+03

XTEND = 0.265000E+02

DL = 0.625000E-01

GAMMA = 0. 140000E+01

OMEGA = 0.76000E+00

WATE = 0.290000E+02

CP = 0.240000E+00

PR = 0.720000E+00

XINC = 0.000000E+00

(Reynolds number value or "x" length

depending on the option set in the

Transition Indication Mode)

(Momentum thickness at nozzle throat)

(Stagnation pressure)

(Stagnation temperature)

(Wall temperature when INDTW = 1)

(Extension length past nozzle exit plane)

(Increment in "x" ofextension length)

(Ratio of specific heats)

(Viscosity-Temperature exponent)

(Molecular weight ofgas)

(Specific heat ofgas)

(Prandtl number)

(Not applicable; hardwired value)

3. Input Data from "outpt2" - Data generated from the inviscid contour

software "char6".

4. Output Code - Constitutes the flow properties along the contour ofthe

nozzle calculated by "nbl6" for each set of coordinates that define the nozzle

contour.

X(IN)

S(IN)

Y(IN)MREL(1/FT)

RETH

x - coordinate of contour point

Contour length

y - coordinate of contour point

Mach number along contour

REL = (pUE)/uReynolds Number; RETH = (REL)(THETA)

157

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PE/POUE(FT/SEC)

MUE (PSEC/FT2)

RHOE (PSEC2/FT4)

TE(R)TW(R)TAD(R)TE/TODELTA (IN)

THETA(IN)DELSTAR (EST)

HTW/TOTW/TADTAD/TODPDS (P/FT2)

DMDS (1/FT)

DUDS (1/SEC)

DTHDS

TAUWAL (P/FT2)

CF

Q (BTU/FT2/SEC)

HA(BTU/FT2-SEC-R)

Static Pressure / Total Pressure

Velocity

Absolute Viscosity (u)

Density (p)

Static Temperature

Wall Temperature

Adiabatic Wall Temperature

Static Temperature / Total Temperature

Boundary Layer Thickness (8)

Momentum Thickness (Q)

Boundary Layer Displacement (5*)

Form Factor (H = 570 )

Wall Temperature / Total Temperature

Wall Temperature / Adiabatic Wall Temperature

Adiabatic Wall Temperature / Total Temperature

Change in pressure with respect to surface

distance

Change in Mach number with respect to surface

distance

Change in velocity with respect to surface

distance

Change in momentum thickness with respect to

surface distance

Wall shear stress (Tw)

Friction Coefficient

Local rate of heat transfer

Convection heat transfer coefficient

5. Final Results - Modified contour output as calculated by "nbl6"

X (INCHES) x - coordinate of modified contour

DELSTAR (INCHES) Boundary layer displacement thickness

YCORE+DELSTAR

MWALL

DELTAY

Modified contour accounting for boundary

layer growth on contoured wall only

Mach number at the wall

Modified displacement thickness as

determined by the equation modeled by

Demo [Ref 28: p.24].

158

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YCORE+DELTAY Modified contour accounting for the

boundary layer effects contributed by the

side walls

C. PROGRAM LISTINGS

Listings are given as follows:

1. Program "char6"

2. Program Hnbl6"

159

Page 197: Application of pressure-sensitive paint in shock-boundary ... · Application of pressure-sensitive paint in shock-boundary layer interaction experiments Seivwright, ... Basedontheprincipleof

Program "char6"

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160

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Program "char6" (cont.)

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Program "char6" (cont.)

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LIST OF REFERENCES

1. Kavandi, J.L., Callis, J.B., Gouterman, M., Green, G., Khalil, G, Burns, D. and

McLachlan, B.G., "Surface Pressure Field Mapping using Luminescent Coatings",

Experiments in Fluids, v. 14, pp. 33-41, 1993.

2. Kavandi, J.L., Callis, J.B., Gouterman, M., Khalil, G., Wright, D., Green, E.,

Burns, D. and McLachlan, B.G., "Luminescent Barometry in Wind Tunnels", Rev. Sci.

Instruments, Vol. 61, No. 5, pp. 3340-3347, November 1990.

3. Peterson, J.I. and Fitzgerald, R.V., "New Technique of Surface Flow Visualization

Based on Oxygen Quenching ofFluoresence", Rev. Sci. Instruments, Vol. 51,

pp.670-671, May 1980.

4. Vollan, A. and Alati, L., "A New Optical Pressure Measurement System", 14th

International Congress on Instrumentation in Aerospace Simulation Facilities

(ICIASF), Paper No. 10, Rockville, Md., October 1991.

5. Morris, M.J., Donovan, J.F., Kegelman, J.T., Schwab, S.D., Levy, R.L. and Crites,

R.C., "Aerodynamic Applications ofPressure-Sensitive Paint", ALAA Paper No.

92-0264, 30th ALAA Aerospace Sciences Meeting, Reno, Nevada, January 1992.

6. Morris, M.J., Benne, M.E., Crites, R.C. and Donovan, J.F., "Aerodynamic

Measurements Based on Photoluminescence", AIAA Paper No. 93-0175, 3 1th AIAAAerospace Sciences Meeting, Reno, Nevada, January 1993.

7. McLachlan, B.G., Bell, J.H., Kennelly, R.A., Schreiner, J.A, Smith, S.C, and Strong,

J.M., "Pressure-Sensitive Paint Use in the Supersonic High-Speed Oblique Wing(SHOW) Test", AIAA Paper No. 92-2686, 10th AIAA Applies Aerodynamics

Conference, Palo Alto, Ca., June 1992.

8. McLachlan, B.G., Bell, J.H., Espina, J., Gallery, J., Gouterman, M., Demandante,

C.G.N, and Bjarke, L., "Flight Testing of a Luminescent Surface-Pressure Sensor",

NASA Technical Memorandum 103970, October 1992.

9. Kavandi, J.L., Luminescence Imagingfor Aerodynamic Pressure Measurements,

Doctoral Thesis, Chemistry Department, University of Washington, 1990.

10. Moore, W.J., Physical Chemistry, Prentice Hall, Inc., 1962.

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Pringsheim, P., Fluorescence and Phosphorescence, Interscience Publishers, 1949

12. Calvert, J.G and Pitts, J.P. Jr., Photochemistry, John Wiley and Sons, Inc., 1966.

13. Wayne, R.P., Photochemistry, American Elsevier Publishing Company, Inc., 1970.

14. Rice, O.C., Electronic Structure and Chemical Binding, Dover Publications, Inc.,

1969.

15. Parker, C.A.., Photoluminescence ofSolutions, Elsevier Publishing Company, 1968.

16. Cundall, R.B. and Gilbert, A., Photochemistry, Appleton-Century-Crofts, 1970

17. Wendland, R.A., Upgrade and Extension of the Data Acquisition Systemfor

Propulsion and Gas Dynamics Laboratories, M.S.A.E. Thesis, Naval Postgraduate

School, Monterey, California, June 1992.

18. Adamson, T.C. Jr. and Nicholls, J.A.,"On the Structure of Jets From Highly

Underexpanded Nozzles Into Still Air", J. Aero/Space Sciences, Vol. 26 No. 1, 1959.

19. James H. Bell, (Private Communication) NASA Ames, Moffet Field, CA., January

1994.

20. Instruction and Operating Manuals, Quartz Tungsten Halogen Lamp Housing

Model 66186 andLamp ControllerModel 6405, Oriel Corporation, 1992.

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Hord, M.R., Digital Image Processing ofRemotely SensedData, Academic Press,

1982.

22. McLachlan, B.G., and Bell J.H., "Image Registration for Luminescent Paint Sensors",

ALAA Paper No. 93-0178, 31stAerospace Sciences Meeting and Exhibit, Reno,

Nevada, January 1993.

23. User's Manual, EPIX4MP - 4MPTOOL Interactive Image Analysis Software, EPDCIncorporated, 1993.

24. Perretta, DA., Laser Doppler Velocimetry Measurements Across A Normal Shock In

Transonic Flow, M.S.A.E. Thesis, NavaL Postgraduate School, Monterey, California,

March 1993.

25. Kooi, J.W., "Experiment on Transonic Shock-Wave Boundary Layer Interaction",

Advisory Groupfor Aerospace Research andDevelopment (AGARD),AGARD-CP-168, pp. 30-1, 30-10, November 1975.

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26. Sebra, D.K., Electronic Structure and Chemical Bonding, Blaisdell Publishling

Company, 1964.

27. Rice, O.K., Electronic Structure and Chemical Binding, Dover Publications, Inc.,

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28. Beynon, J.D.E. and Lamb, D.R., Charge-CoupledDevices and Their Applications,

McGraw-Hill, 1980.

29. Demo, Jr., W.J., Cascade Wind Tunnelfor Transonic Compressor Studies, M.S.A.E.

Thesis, Naval Postgraduate School, Monterey, California, June 1978.

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