AEROTHERMODYNAMICS AND

TURBULENCE17 March 2011

John D. Schmisseur

Program Manager

AFOSR/RSA

Air Force Office of Scientific Research

AFOSR

Distribution A: Approved for public release; distribution is unlimited . 88ABW-2011-0805

2

Speed is the essence of war. Take advantage of the

enemy's unpreparedness; travel by unexpected routes and

strike him where he has taken no precautions. -Sun Tzu

Speed and Range Change the Game

March 4, 1944: P-51 Mustangs

escort B-17 Flying Fortress bombers

in the daylight bombing of Berlin

The first time your bombers came over Hanover

escorted by fighters, I began to be worried.

When they came with fighter escort over Berlin

- I knew the jig was up. - Hermann Göring

Responsive

Reusable

Boost for

Space

(FCC)

We are still seeking the advantage of superior Speed and Reach

X-51

High-Speed Weapon Prompt Global Strike

3

Hypersonic: The Most Challenging Flight Regime

Hypersonic: High-speed flow

regime where energy transfer

between the flow and

thermodynamic and chemical

processes becomes significant

There are many scientific

challenges to understanding

and modeling the Hypersonic

environment and related

technologies

hn

RotationalVibrational Electronic Reactions

Gas Thermophysics

Shock-Dominated Flows

Boundary Layer Physics

Hypersonics is Not:

• a scientific discipline

• defined by Mach > 5

• anything Scramjet Powered

Development of Hypersonic Capabilities Requires the Integration

of Contributions from a variety of Scientific Disciplines

Supersonic Combustion

High-Temperature

Materials

Gas-Surface Interactions

4

Challenges and Opportunities

High-Speed Flight Environments Cannot Be

Duplicated in Ground Facilities• thermochemical state and noise environment

unknown

• flight data required to guide ground test and

simulations

Unprecedented Insight Into Critical

Phenomena• driven by large-scale computing and optical

diagnostics

There is No Mature Industry Base for

Hypersonic Systems

• opportunity to rapidly transition science

breakthroughs for integration into emerging

systems!

Sodium Fluorescence of Boundary Layer, H. Hornung, CalTech

DNS of SBLI

P. Martin, U. Maryland

5

NAME: John D. Schmisseur

Aerothermodynamics

Hypersonics and Turbulence

BRIEF DESCRIPTION OF PORTFOLIO:

Identify, Model and Exploit critical

physical phenomena in turbulent and

high-speed flows

• emphasis on energy transfer

Sole DoD basic research program in this area

SUB-AREAS IN PORTFOLIO:

• Boundary Layer Physics

• Shock-Dominated Flows

• Gas Thermophysics

• Gas-Surface Interactions

• Turbulence and Transition

2011 AFOSR SPRING REVIEW2307/A Aerothermodynamics and Turbulence

Partners

National Hypersonic

Foundational Research

Plan

Joint Technology

Office -

Hypersonics

Assessment of

SOA and Future

Research

Directions

Jet Noise

Tech

Transition

Arnold

Engineering

Development

Center

6

Outline

Outline

• Big Picture

• Scientific Strategy

and Highlights

• Jet Noise

• Shock Boundary Layer

Interactions

• Laminar-Turbulent

Transition

• Energy Transfer in

High-Enthalpy Flows

Take-Away

• Time of Great Opportunity

• Advance aerothermodynamics

via new tools

• Transition advancements to

impact emerging capabilities

• Exploiting large-scale simulations

to address key science challenges

• Drawing on expertise from other

disciplines – materials and chemistry

• Establishing the sound scientific

basis to revolutionize how we

consider high-speed systems

Incre

asin

g M

ach n

um

ber

7

• Disturbances trigger instabilities

which drive breakdown to turbulence

• Roughness

• Freestream Perturbations

• Particles

• Significant mixing “energizes”

layer – results in increased

surface drag and heat transfer

• High Mach: Turbulent heat

transfer is 3-7X greater than laminar

• Smooth variation in

wall-normal profile

Boundary Layer Image from Hornung, Cal Tech

Laminar Transitional Turbulent

Three Boundary Layer Statesd -thickness

Energ

y

Wavenumber

Turbulent

Energy

Spectrum

~ d-1

~ h-1

Kolmogorov

Scale

ModeledResolved • RANS - Reynolds-

Averaged Navier-Stokes

• “Turbulence Models”

• All scales modeled

• DES & Hybrid

• Mixed RANS and LES

• LES – Large-Eddy

Simulation

• Large scales resolved

• Small scales modeled

• DNS – Direct Numerical

Simulation

• All important scales

modeled

• “Numerical

Experiment”

Eng.

Tool

First

PrinciplesIncreasing Fidelity and Cost

Modeling Turbulent Flows

RANS LES DNS

Heat Transfer on a 7-deg. Cone,

Mach =10 Holden, CUBRC

Laminar

Turbulent

Turb. Models

challenged

Laminar, equilibrium flows

are simulated with confidence

Review: Boundary LayersViscous Region Determines Surface Conditions

8

Characterizing the Influence of Turbulence On Complex Flowfields

Inviscid

Shock

SBLIs Can be

Unsteady

M >1

Incoming Turbulent

Boundary Layer

Bifurcated

Shock Foot

Shock/Turbulent Boundary

Layer Interaction(Rizzetta and Visbal, AFRL/RBAC)

Separation • due to adverse

pressure gradient

Reattachment• extreme conditions

“Bubble”

Characterization and Control of

Turbulence in Jets(D. Gaitonde, Ohio State U.)

x (cm)

HeatT

ran

sfe

rR

ate

(Watt

/cm

2)

0 4 8 12 160

10

20

30

40

50

60

70

80Experiment

1024 x 512 simulation

Heat

Transfer

M >> 5

Inlet

Distortion

Effects

Efficiency

Goal: understand role of turbulence in

generation and propagation of noise

identify >> model >> control

“Noise issue delays Eglin JSF basing decision”

Air Force Times – Nov 2008

“F-35 is twice as loud as the F-15”

• Complex turbulent processes play a critical role in determining the

macroscopic flow features

• Judicious choice of modeling approach is key to economically resolving

key dynamic phenomena - LES appears to be optimal trade-off today

Research Partners

9

Critical Phenomena: Crackle

High-fidelity turbulence simulation

tools integrated with nonlinear

propagation theory to identify root

mechanisms of jet crackle

J. Freund, U. of Illinois

• Distinguishing feature of sound from high-

thrust engines on fighters and rockets

• Mechanisms are unclear, particularly

source of its peculiar signature

Model flow that emits crackle-like shocks being interrogated to study

mechanisms: near-field nonlinear wave steepening observed

Reproduced in

turbulence

simulations

M = 1.25

M = 1.25

Near-field sound, grad (u)

vorticity,

curl (u)

Direct Numerical

Simulation (DNS)

10

Exploring the Impact of Jet Actuation

High-fidelity numerical simulations

provide new insight into complex

dynamics resulting from actuation

D. Gaitonde, M. Samimy/ Ohio State U.

• Large-Eddy Simulation used to

characterize effect of plasma filament

actuators

• Results reveal influence of excited

structures on jet mixing and diffusion

x

8 1

2

3

45

7

6

Plasma actuators at 8 circumferential stations

thermally excite local flow – replaces frequently-

utilized sawtooth trailing edge

Each actuator

excites two vortex

pairs

First simulations

to reveal hairpin-

like structures in

high-speed jet

head

*

* John Glenn Chair in Mech and Aero Eng

11

Exploring the Impact of Jet ActuationD. Gaitonde, M. Samimy/ Ohio State U.

Actuation scheme

preferentially excites

structures that effect

jet lateral spreading

First (flapping)

mixed mode

(m=+/-1)

- Alternating sides

8 1

2

3

45

7

6

m=+/-1 (flapping plane)

m=+/-1 (non-flapping plane)

No excitationSimulation ExperimentEnhanced spreading in

flapping plane is result of

interaction of ring vortices of

alternating inclination

12

Courtesy Kei Lau, Boeing

Shock/Boundary Layer Interactions (SBLIs)Ubiquitous Challenge to Development of High-Speed Capabilities

Courtsey: R. Baurle, NASA

Directed EnergyMinimize Gas Laser

Diffuser Length

Air VehiclesInlet Performance Optimization

PropulsionIsolator Stability and Unstart Control

Air Vehicles- Extreme Loads

Air VehiclesNovel Inlet Configurations

x (cm)

Hea

tTra

nsf

erR

ate

(Wat

t/cm

2)

0 4 8 12 160

10

20

30

40

50

60

70

80Experiment

1024 x 512 simulation

Heat Transfer

M >> 5Shock/Boundary Layer

Interactions are a Critical

Challenge for All High-Speed

Capabilities Based on Air-

Breathing Propulsion

At Least 5 AFRL research groups

focus their efforts on this key

phenomena

AFRL Experiment Explores

Structural Response Due

to Dynamic Shock

Interactions

Joint effort of Air Vehicles

and Propulsion DirectoratesT. Eason and M. Spottswood, AFRL/RB

J. Donbar and M. Brown, AFRL/RZ

AFOSR as Catalyst: In-House Workshop Coordinates Previously Disconnected Efforts

Mach 2

Compliant

Panel

Shock

Generator

Impinging

Shock

PSP and TSP for

full field

aerodynamic

and thermal loads

DIC for full field

structural response

Adjustable

shock

generating

wedge

200 300 400 500 600 700 800 90010-3

10-2

10-1

100

101

102

103

Frequency (Hz)

Spectral Response of Panel 0 deg

4 deg

6 degPreliminary

Results

13

Model-Free Simulations of Mach 3 Shock / Turbulent Boundary

Layer Interactions Provide Physical Insight for Development

of Reduced Order Models M. Pino Martin, U. of Maryland

High-Fidelity Simulations Provide Insight Into Underlying Physics

Isosurface of magnitude

of density gradient

Simulations used as test bed to explore

• the dynamics of unsteadiness

• the role of turbulent structures

• development of large-eddy simulation models

Much lower Reynolds Number than Experiments

Coherence between shock motion in the freestream and two wall-pressure signals in the incomngboundary layer.

Weak correlation implies low frequency unsteadiness is not driven by incoming boundary layer

“Snapshots” reveal separation region is not function of shock position

14

HIFiREHypersonic International Flight Research Experimentation

AFRL/Australian DSTO

Collaborative Effort for Flight

Research Exploring Critical

Fundamental Phenomena

International Partnership Provides Opportunity to Collect

Flight Data on SBLI Unsteadiness

Flight 1

Dynamic

measurements of

unsteady SBLI

Integrating All Resources

Experiment Computation

Flight Research

Wind Tunnel

Schlieren

Tunnel Expt - Dolling and Murphy

Note: Dissimilar Scales

Preliminary Results: First flight data

for unsteady SBLIs reveals low-

frequency unsteadiness comparable to

that observed in wind tunnels

15

InstabilityAcoustic

Absorption

diffusive

transport of

chemical energy

transport of

thermal

energy

surface

heat

transfer

Surface Heat

Transfer

Equation

Changing the Research ParadigmAn Opportunity for Transformation

Current culture: Please

compute this accurately

so we can try to develop

a new material to handle

the thermal load

Control the gradient

via boundary layer

management

Improve models

for energy

transfer

New Paradigm: How can we actively control energy transport to

minimize surface heat transfer?

Control T via

energy

management

Reliable models for Gas-

Surface Interactions

Philosophy: these phenomena are too complex to be “predicted”• Exact conditions in applications of interest will be unknown

• Must understand behavior of dominant modes that govern physics

• Estimation methods will be built based on the probability that various modes dominate

16

Laminar-Turbulent Transition

Turbulent Flow

Laminar Flow

Radiated Acoustic Waves

“Quiet” Flow• Flight-like disturbance

environment

AFOSR has championed the development of critical research capabilities

Conventional tunnels:

noise corrupts

transition experiments

Quiet tunnels: allow

natural disturbance

growth – “flight-like”

Challenges• Measuring and computing

instabiliites ~ 1x10-6 of mean

• realistic surfaces

Transformation• Estimation tools based on semi-

empirical methods are changing the game

Partners

Image Modified from Original by Dan Reda, 1979

Roughness

Freestream

Disturbances

Disturbances trigger instabilities which drive breakdown to turbulent stateImage: Hornung,

Cal Tech

Conventional 3rd order upwind method

KE conserving method Energy conserving

numerics allow improved

resolution of fine-scale

fluctuations

Candler, U. Minnesota

Quiet Tunnels at

Purdue and Texas A&M

Data from Dist. Along Surface

Heat Flux

(W/cm2)N-Factor (Growth

Exp.)Trans.

N=5.5

Measured Transition Location

N-Factor

Correlation

Reθ

Me

Estim

ate

d T

ran

sitio

n L

oca

tio

n

Semi-Empirical Estimation Methods

Collapse Data from Multiple Facilities

17

Exploring the Effect of Roughness on Laminar-Turbulent Transition

• Measurements in thick laminar wall boundary layer allow

increased spatial resolution, Mach 6 freestream

Joint Experimental-Computational Effort

Yields First Detection of Roughness-

Induced Instability at High Mach NumbersB. Wheaton and S. Schneider / Purdue U. - NASA/OSR

M.Bartkowicz and G. Candler / U. Minn - OSR/NSSEFF

DNS of Cylinder in

Tunnel Wall

Boundary Layer

• 21 kHz signal first seen in experiments

• Computations reproduced instability

and identified source

• Later experiments verified presence of

instabilities predicted by computations

at source

18

Supersonic flow impacts

the upper edge of the

roughness

Temperature contour on centerline

Exploring the Effect of Roughness on Laminar-Turbulent Transition

Numerical Schlieren image on

centerline

Numerical Simulations Identify Source

of Roughness-Induced InstabilityM.Bartkowicz and G. Candler / U. Minn

B. Wheaton and S. Schneider / Purdue U.

Experiment confirmed prediction

of 21 kHz disturbance upstream

of roughness element

Unsteady jet forms,

creating unsteadiness in

upstream vortex structure

Pressure gradient causes

fluid to accelerate away

from the high pressure

region

Disturbances created upstream then travel downstream and grow

19

Creating New Testing Capabilities

Recent-Developed Basic Research

Methods Rapidly Transitioned to

Revolutionize Ground Test of Major

National ProgramsJ. Lafferty/ AEDC,

G. Candler/ U. Minn.

and S. Schneider / Purdue

Integrated Computations and Experiments provide unprecedented insight into

sources and impact of critical aerothermodynamic phenomena

U. Minn. AEDC

Falcon HTV-2

High-Fidelity

Numerical

Methods yield

detailed insight

into physics

Innovative fluctuation

measurements - PurdueTemperature-Sensitive Paint

provides global heating

AEDC Tunnel 9

PrimaryTest

Article

Low-Frequency Acoustic Pitot Probe

High-FrequencyAcoustic Pitot Probe

Purdue /SandiaTransition Cone

Hemisphere Heat-Transfer Probe

Temperature Sensitive

Paint

Auxiliary Model

SupportFocused schlieren image of BL transition obtained on 7° transition cone

at Mach 10, Re/L = 2.0×106/ft

20

x (cm)H

eatT

ran

sfe

rR

ate

(Watt

/cm

2)

0 4 8 12 160

10

20

30

40

50

60

70

80Experiment

1024 x 512 simulation

Experiment

Numerical Simulation

NitrogenAir, 4.5 Mj/kg Air, 15.2 Mj/kgAir, 10.4 Mj/kg

Increasing Internal EnergyPredictions Fail

as Chemical

Complexity

Increases

(Re)Establishing the Thermochemical Basis for Numerical Simulations of High-Enthalpy Flows

All Graphics Courtesy

G. Candler, U. Minn.

Kinetic rates used in CFD are

based on outdated shock-tube data

Park (1988): the “good”

model

Hanson and Baganoff

(1972): Dissociation rates

inferred from end-wall

pressure measurements in

a shock tube.

Opportunity: utilize

modern diagnostics and

numerical methods to

develop accurate kinetic

rate models

• improve CFD capabilities

• need help from

chemistry

Partners

Inferred

rates

depend on

the flow

model used

to interpret

the data

Experiments and Simulations have shown that separation zone size is influenced by kinetic rates

• quality of numerics is demonstrated in Nitrogen case

• only variable in the above simulations is complexity of air thermochemistry

21

MURI: Fundamental Processes in High-Temperature Hypersonic Flows

University of Minnesota, Penn State University, Montana State University, University of Arizona, and University of Buffalo

Approach

Graham V. Candler, Don Truhlar, Adri van Duin, Tim Minton, Deborah Levin

Tom Schwartzentruber, Erica Corral, Dan Kelley and Paul DesJardin

•Use detailed quantum mechanics to develop

accurate force fields for key processes

•Train reactive force field for MD simulations

of post-shock wave flows and gas-surface

interactions

•Extend to continuum models with DSMC

models and state-specific simulations

•Perform experiments at all scales to provide

validation data for model generation

Molecular Dynamics

High-Fidelity,

Large-Scale

CFD

MURI Explores Molecular scale

Kinetic Processes to Advance

Simulation of Vehicle Scale

Phenomena

Integration of Aerothermodynamics,

Chemistry and Materials Research to

develop advanced models for gas-surface

interactions

Reaction Dynamics

Experiments

Reactive

Force FieldsMaterial Surface Effects

22

Physically Accurate Boundary Conditions for Gas-Surface Interactions

Molecular Dynamics Simulations

Enable Finite-Rate Surface

Catalysis Model T. Schwartzentruber, U. of Minnesota

O

recombination

on SiO2Super-

Catalytic

Non-

Catalytic

- Finite Rate

Ceramic (SiO2-

based) materials

often weakly

catalytic. Here, heat

flux increases by

only 1%.

Activation energy required for

recombination O+Os -> O2+[s]

• Catalytic heating is typically estimated via

limiting assumptions (non-catalytic vs. super-

catalytic) – can vary 30%-300% in heat flux

• New model solves a set of one-step chemical

reaction equations at each wall element in a

simulation – facilitates analysis via Molecular

Dynamics

• Result is much better CFD model for gas-

surface interactions that is consistent with

fundamental chemistry

23

Modeling of Recombination in Hypervelocity High-Enthalpy Facilities

Energy Bin Model Accounts for

Excited States in Simulations of

High-Enthalpy FlowsG. Candler and J.D. Kelley

U. of Minnesota

• Popular two-temperature (T, Tv)

model ignores electronic,

rotational states

• Fail with increasing flow enthalpy

• Energy Bin model combines

rotational and vibrational states

in common bins

• Two modeled excited O2 states

are populated by recombination

• Will dissociate again more readily

• Approach favors recombinaton

at higher internal energy levels

Run 85 ρ (kg/m3) T

(K)

% O2

[X]

% O2

[a]

Velocity

(m/s)

Park TTv

Model

9.24 x 10-4 586 66.5 0 4080

Energy Bin

Model

9.50 x 10-4 276 64.2 0 4010

Energy Bin

+ O2[a]

9.73 x 10-4 358 60.8 4.7 4080

Computed conditions in CUBRC LENS 10.1 MJ/kg, 43.30% Total O2

Multiple v,J states present in an energy bin

24

Measurement of Nonequilibrium Processes

• Raman signal is analyzed to

measure population of each

vibrational quantum state

• Point measurement of vibrational

and rotational/translational

temperatures in less than 200 psec

sampling time

• enables time-resolved

measurement in very short

duration facilities.

• System is robust and easily

transportable.

Psec CARS* Diagnostic

Allows Measurement of

Vibrational Energy

Content in High Enthalpy

N2 and Air Flows W. Rich, W. Lempert, and I. Adamovich

Ohio State

N2Pulser

Electrodes

DC sustainer

Electrodes Injector

Optical

Extensions

Nozzle

Throat

*Picosecond Coherent Antistokes Raman Scattering

Mach 5 Plasma

Wind Tunnel

Tv = 1100

+/- 100 K

Tv = 2150

+/- 150 K

Single Shot

CARS Spectra

Pulser Only Pulser + Sustainer

Temporal evolution of Tv

during sustainer

discharge pulse, 3.5 kV

DC, 300 Torr N2.

25

Exploring Transition Control Via Energy Transfer to Internal Modes

Transition Delay Resulting from CO2

Injection in Boundary Layer Provides

Potential Mechanism for Control

I . Leyva, AFRL/RZ

J. Shepherd and H. Hornung, Cal Tech

CO2 Injection

From Hornung, H.G., Adam, P.H., Germain, P., Fujii, K., Rasheed, A., “On

transition and transition control in hypervelocity flows,” Proceedings of the

Ninth Asian Congress of Fluid Mechanics, 2002

CO2 Transition Re* is about 4X that of

Air and N2

CO2

Air & N2

CO2

Air

Acoustic

Absorption

2nd Mode

Instability

(Acoustic)

For CO2 internal energy and acoustic

instability modes overlap

Curves for 3 total enthalpy values

26

Porous Injector Results (10 MJ/kg): CO2 Delays Transition

Zero injection

Transition at

Re = 4.12 x 106

Ar injection at 11.6 g/sec

Transition at

Re = 2.88 x 106

Exploring Transition Control Via Energy Transfer to Internal Modes

CO2 injection at 11.6 g/sec

Laminar Flow past

Re = 5.22 x 106

No

n-d

ime

nsio

nal

He

at

Tra

nsfe

r(S

t)

Reynolds Number based on distance from nose tip

Turbulent

Heating

Correlations

Laminar Heating

Measured Heat TransferTransition Transition

Laminar

27

Summary

Outline

• Big Picture

• Scientific Strategy

and Highlights

• Jet Noise

• Shock Boundary

Layer Interactions

• Laminar-Turbulent

Transition

• Energy Transfer in

High-Enthalpy

Flows

Take-Away

• Challenge: understanding energy transfer via

turbulence and thermochemistry

• Opportunity: Use optical diagnostics and

high-fidelity simulations for deep insight

Identify >> Model >> Exploit

• Trend: leverage chemistry and materials

disciplines to improve insight into

aerothermodynamic processes

• Partners: NASA, Sandia, ONR, DARPA, AEDC

• Transitions: Revolutionized Test and Demo

programs via high-fidelity methods for

estimating and measuring aero-heating

• Transformation Opportunity: Energy

management in high-speed flows may change

the game for thermal management12 highlights, 11 lead PIs

~ 1/3rd of the portfolio

M > 1

M > 2

M > 4

M > 8