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Experimental Aerodynamic Analysis of a Plug Nozzle for Supersonic Business Jet Application. John Tapee Dr. John Sullivan. CAD Model. Schlieren. Installed Hardware. Static Pressures. Shadowgraph. Dynamic Pressures. Introduction/Overview. Experimental static test of plug nozzle - PowerPoint PPT Presentation
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Experimental Aerodynamic Analysis of a Plug Nozzle for Supersonic Business Jet Application
John TapeeDr. John Sullivan
2
CAD Model Schliere
n
Shadowgraph
Static Pressures
Dynamic Pressures
Installed Hardware
Introduction/Overview• Experimental static test of plug nozzle• Research carried out under Task 7c of the Supersonic Business Jet program (SSBJ)• Purpose:
– Characterize behavior, especially low nozzle pressure ratio (NPR) unsteady effects– Provide basis for CFD comparison & evaluation
• Test geometry derived from Gulfstream’s High-Flow Bypass concept– Designed for sonic boom mitigation– High-flow bypass region avoids thick engine nacelle that would create strong shock wave– Zero-energy-added stream; only intent is to reduce losses– Plug nozzle design chosen for easy integration with this concept
3Gulfstream High-Flow Bypass Concept [Conners, 2008]
Flow
Flow
0, upstreamNPRPP
Background• Plug nozzles are altitude-compensating• Free jet boundary expands to match
local ambient pressure– For NPRs below design, avoids
overexpansion– For NPRs at and above design, behaves
like standard C-D nozzle• Shocks/expansions are the mechanisms
that enable altitude-compensation– Consider thrust as integral of surface
pressure over projected area– Pressure plot at right shows better
performance for plug at low NPR• Can truncate plug to get net increase in
performance• Plug design has also been shown to be
less noisy [Dosanjh, 1986; Stone, 2000]
4
Surface Pressures at Low NPR for Plug and C-D Nozzle
Plug Nozzle at NPR < NPRdesign [Hagemann, 1998]
[Ruf, 1997]
Background• Similar studies have been performed for conical, truncated, and contoured plugs• Images shown here taken from tests conducted by Verma at India’s National
Aerospace Labs• Both plugs are conical, not contoured• Design NPR ≈ 7.8, both images at NPR = 2.57
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[Verma, 2008][Verma, 2008]
Model Geometry
Notable Geometry Differences
• No high-flow bypass stream• Shroud wall thickness increased for
structural soundness and machinability• Subsonic convergent angle increased• Hot/cold flow split introduced• New strut design for rig compatibility and
instrumentation pass-through
7
Flow
Flow
Gulfstream High-Flow Bypass Concept [Conners, 2008](reproduced with permission)
Test Geometry No geometry modifications to supersonic stream – flow behavior should be similar to full scaleDark Gray = Rig Hardware
Light Gray = Plug Nozzle Hardware
• Design nozzle pressure ratio (NPR) of 6.23• Scale = 0.155
– Based on available mass flow• Unmixed core & bypass airstreams• Constructed from stainless steel (hot parts) and aluminum (cold parts)• Swappable aluminum and glass shrouds for pressure measurement and internal flow
visualization, respectively• Hollow struts for instrumentation pass-through
Model Geometry Overview
8
HOT
COLD
COLD
HOT6.811 in
11.579 in
“Shroud” “Plug” or
“Centerbody”
Facility and Instrumentation
Test Facility
10
• Used new dual-stream, co-annular nozzle rig developed under SSBJ Task 7b• Simulates typical turbofan engine exhaust
– Unheated bypass stream– Vitiated core stream
• Blowdown facility capable of test times on the order of several minutes [Trebs, 2008]
• Condition-monitoring temperature and pressure measurements throughout• Total temperature & pressure rakes provide nozzle feed conditions
Mass-averaged nozzle pressure ratio (NPR) defined as:
where total pressures are averaged over space, not time
Instrumentation• Static Pressure Taps
– Focused primarily on axial resolution (best is 0.5”)• High-frequency Sensors
– Kulite Pressure Transducers– Accelerometers– Used Welch’s method to pull power spectral density from raw data
• High-speed Schlieren/Shadowgraph
11
Pressure Measurements
12
Angle Reference(looking upstream)
High-frequency Transducers
• Omitted taps marked (P19, P29, S15)• Primary static measurement along
+45° row (blue, 0.5” spacing)– 20 taps on plug– 12 taps on shroud
• Additional taps for azimuthal variation– 10 on plug– 9 on shroud
Flow Visualization• Schlieren
– Sensitive to 1st derivative of density in direction perpendicular to knife edge
– Most tests with vertical knife edge– Images external section of nozzle– Considerable background noise
• Shadowgraph– Sensitive to 2nd derivative of density, non-
directional– Implemented due to schlieren limitations with
glass shroud– Images almost entire nozzle (from about 1”
downstream of throat)– Image processing technique applied to reduce
effect of glass imperfections on image
13
x
Original Result
Sample Full-Range Visualization
Schlieren• Playback at actual speed• NPR range: 1.0 – 5.5
Shadowgraph• Playback at 1/10th speed• NPR range: 1.0 – 2.5
14
NOT SYNCHRONIZED
Tip Vibration Analysis• Two methods of analysis:
1. Track intensity of individual pixel near centerbody edge• Pixel choice important• Not that sensitive to noise in schlieren images
2. Track tip location• Provides amplitude as well as frequency• Quite sensitive to noise in schlieren images
15
Method #1
Track intensity value from chosen pixel
Method #2
Tip (track x,y coordinates)
Centerline
Vertical Centers
Tip Vibration Results
16
• Sample case: Hot fire, NPR 2.03, shadowgraph imaging
• Tip deflection plots show maximum amplitude of roughly 0.015 in– Less than one pixel
• Dominant frequency at 18 Hz• Similar power spectra for each method
Method #2: Tip TrackingMethod #1: Pixel Intensity
y de
flect
ion
(in)
x de
flect
ion
(in)
Tip Vibration Results• Schlieren images of high-NPR hot fire tests show
thermal growth of centerbody (corresponds to ΔT of about 75°F over 5 seconds)
• Vibration magnitude (and frequency) independent of NPR
17
Tip is difficult to detect in some schlieren images
Hot, 4.47
y de
flect
ion
(in)
y de
flect
ion
(in)
Hot, 6.12Cold, 2.56
Cold, 1.74 (Shadowgraph)
Selected Test Cases
Tests• Total of 57 successful tests
– Conducted from Jan. 28, 2009 through Feb. 23, 2009– 22 steady-state hot, NPRs of 1.77 to 6.12– 30 steady-state cold, NPRs of 1.26 to 5.75– 5 cold flow sweeps
• For hot fires, temperature varied between 600 °F and 1200 °F– Insufficient control of fuel flow to reduce this variation
• Concentrated on low NPRs ( < 3.0 )– Region of concern for unsteady characteristics
19
Case Type NPR Core Temp (°F)
1 Cold 3.73 n/a
2 Cold 1.59 n/a
3 Hot 2.50 660
4 Hot 6.12 870
Selected Cases
Case #1:Cold Flow, NPR 3.73
• Flow fairly steady• No substantial peaks in power spectrum• Little asymmetry in pressure distribution
– x/L = 0.52• Black/yellow diamonds indicate suspect data
– Possible leak or geometry error
20
Playback at 1/10th speed
Case #2:Cold Flow, NPR 1.59
• Shock location very unsteady• Unsteadiness shown in dynamic transducers
– Peak oscillation at 200 Hz• Almost no asymmetry in pressure distribution
21
Playback at 1/10th speed
Image at NPR 1.74
Case #3:Hot Fire, NPR 2.50
• Axial position reasonably steady• No specific frequency peaks, just broadband
oscillations below 200 Hz• Somewhat asymmetric at shock (x/L = 0.38)
22
• Shadowgraph: Cold, NPR 2.45• Playback (both) at 1/10th speed
Case #4:Hot Fire, Cruise Condition
• Actual NPR = 6.12 (cruise target is 6.23)• Difficult to capture hot fire schlieren due to
refractive index gradients• Fairly steady – frequency range > 1kHz
shows combustion frequencies• Little asymmetry (x/L = 0.52 again)
23
Playback at 1/10th speed
Detailed Data Comparisons & Additional Analysis
Cold 3.70 (approx.)
Hor
izon
tal K
nife
-Edg
e
Cold 3.73
Vert
ical
Kni
fe-E
dge
Cold 2.45 Shadowgraph
Shock Structure
• Classic lambda shock forms on both plug and shroud wall
• Large region of separation on plug• Higher NPRs setup classic diamond-shock pattern in
exhaust• Schlieren and Shadowgraph techniques integrate
along the optical path – for axisymmetric flow, this results in “phantom” shock patterns (dotted lines)
25
LEGEND
Cold Flow Schlieren
26
NPR 1.40 NPR 1.88* NPR 2.23
NPR 3.06 NPR 3.73 NPR 5.75
*discussed in detail later
Hot Fire Schlieren
• At cruise, shroud trailing edge shock lies right at theoretical plug tip
• Quality schlieren images harder to obtain during hot fires due to combustion products and temperature gradients
• Mixing layer between hot core and cold bypass streams not very clear due to light path integration issue
27
NPR 2.50 NPR 3.48
NPR 4.47 NPR 6.12
[Rossmann, 2001]
v1, ρ1
v2, ρ2
Sample Expected Mixing Layer Image
Mixing Layer Edge
Low-NPR Shadowgraph
• Optical properties of glass shroud prevented schlieren use
• More detail visible in cold flow• After 1st hot fire, some
condensed liquid accumulated on the shroud’s inner surface, forming a visualization of shock location at the wall typical of oil flow
28
Hot, NPR 2.03 Hot, NPR 2.39 Hot, NPR 2.93
Cold, NPR 2.14 Cold, NPR 2.45
CFD Schlieren Comparison
• Phantom normal shock train– No shock reflection or separation on plug– “Wavy” shape of apparent shocks is uncharacteristic of normal shocks
• Axisymmetric CFD shows that a large separation region does exist and that the faint normal shocks do not extend all the way to the plug surface
29
Cold Flow, NPR 1.88Hot Fire, NPR 2.03 (courtesy Dheeraj Kapilavai)
High-Speed Schlieren
• Cold Flow 2.11• Recorded at 6000 fps• Playback at 10 fps (1/600th speed)
• Shock oscillation visually observed– Period of 17 frames– Equivalent to 353 Hz
• Very good match with dynamic pressure transducers
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Steady Pressures: Experimental Comparisons
• Can clearly see shock locations, separation regions• Black/yellow diamonds indicate suspect data points• Primary difference between hot & cold operation is position of shock along
plug– Caused by temperature difference of roughly 800-1000°F
31
*only viewing 45° taps
Separation
Shocks
Steady Pressures: CFD Comparisons
• Fluent analysis with coarse unstructured grid for sizing– No dedicated boundary layer gridding
• Most glaring difference is axial shock location• Conclusion: flow is dominated by boundary layer and separation
– This CFD does not resolve the boundary layer well• Comparison near throat shows why two pressure taps are suspect
32
CFD – solid linesExperimental – discrete data points
Cold Flow Kulites• Substantial pressure
oscillations at NPRs ≤ 2.25 due to shock movement
• Dominant frequency = 200-400 Hz
• Unsteady behavior beyond dynamic transducers for NPR ≥ 2.59
33
Hot Fire Kulites• Frequency peaks in same
200-400 Hz range, not as evident as with cold flow
• Spectrum for f > 1000 Hz caused by combustion instabilities
• 60 Hz noise seen in many hot fire tests
• Near NPR 2.50, wide band of pressure oscillation frequencies, but no distinct peaks (repeatable during 3 distinct tests)
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Flow Structure Jump atNPR ≈ 2.05
• Abrupt change in flow behavior & shock train at NPR of roughly 2.05• Shows distinct asymmetry in 2nd structure• (Recorded at 100 fps, playback at 1/10th speed)
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Flow Structure Jump atNPR ≈ 2.05
• Pressure distributions show this structure change• Shock abruptly moves aft along plug (and forward along
shroud) as NPR slowly increases past 2.05
36
• Flow structure change visible in pressure histories as well– Each line reflects pressure at tap
indicated by similarly colored diamond• Overall, shows decrease in pressure
fluctuations in 2nd structure• NPR plot below shows no abrupt
change in feed conditions
Flow Structure Jump atNPR ≈ 2.05
37
Time window for pressure histories
Conclusions
Summary & Conclusions
Summary• A derivative of Gulfstream’s high-flow bypass nozzle has been designed and manufactured to fit
the new nozzle rig at HPL.• A series of experimental tests of this nozzle has been successfully conducted in close
partnership with our sponsors.• Instrumentation suite allowed collection of steady-state pressure profiles and unsteady flow
characteristics• Used a combination of schlieren and shadowgraph methods to enhance understanding of
nozzle flow physics
Conclusions• At cruise (NPR = 6.23), nozzle performs well• At NPRs between 2.5 and 6, flow is relatively steady
– Shock/boundary layer interaction and separation along plug and shroud• At NPRs between 1.0 and 2.5, flow is unsteady
– Dominated by boundary layer and separation characteristics on plug
39
• Variable geometry will be necessary for a production system (this was expected but is still worth noting)
• Truncate Plug– Literature indicates that additional compressions and/or expansions that would occur would
remain within the plume and have little effect on the external flow field– Reduce/eliminate any tip vibration and reduce manufacturing complexity– Weight savings → possible net performance gain
• Shorten Shroud– Incorporate better altitude-compensating behavior– Reduce/eliminate massive separation along plug– Simple modification to existing geometry
• Use focused schlieren– Combat the “phantom” shocks created by the light path integration issue– Would also reduce sensitivity to background noise
Recommendations
40
Gulfstream Shroud Extension
[Hagemann, 1998]
Questions?
References1) Tim Conners. Gulfstream Aerospace Corporation. Presentation to Rolls-Royce, 23 January
2008. Images reproduced with permission.2) Adam Trebs. Biannular Airbreathing Nozzle Rig Facility Development. Master’s thesis, Purdue
University, August 2008.3) S.B. Verma. Performance Characteristics of an Annular Conical Aerospike Nozzle with
Freestream Effect. In 44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, July 2008.
4) G. Hagemann, H. Immich, and M. Terhardt. Flow Phenomena in Advanced Rocket Nozzles – the Plug Nozzle. In 34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, July 1998.
5) J. H. Ruf and P. K. McConnaughey. The Plume Physics Behind Aerospike Nozzle Altitude Compensation and Slipstream Effect. In 33rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference, July 1997.
6) D.S. Dosanjh and I.S. Das. Aeroacoustics of Contoured Plug-Nozzle Supersonic Jet Flows. In AIAA 10th Aeroacoustics Conference, July 1986.
7) James R. Stone, Eugene A. Krejsa, Ian Halliwell, and Bruce J. Clark. Noise Suppression Nozzles for Supersonic Business Jet. In 36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, July 2000.
8) Tobias Rossmann, M. Godfrey Mungal, and Ronald K. Hanson. Acetone PLIF and Schlieren Imaging of High Compressibility Mixing Layers. In 39th AIAA Aerospace Sciences Meeting and Exhibit, January 2001.
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