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The Role of Density Gradient in Liquid Rocket Engine Combustion Instability Amardip Ghosh Aerospace Engineering Department University of Maryland College Park, MD 20742 Advisor - Kenneth Yu Sponsors- NASA CUIP (Claudia Meyer) NASA/DOD. Liquid Rocket Engine (LRE). Combustion Chamber

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The Role of Density Gradient in Liquid Rocket Engine Combustion Instability Amardip Ghosh

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The role of density gradient in liquid rocket engine combustion instability amardip ghosh

The Role of Density Gradient in

Liquid Rocket Engine Combustion Instability

Amardip Ghosh

Aerospace Engineering Department

University of Maryland

College Park, MD 20742

Advisor - Kenneth Yu

Sponsors- NASA CUIP (Claudia Meyer)

NASA/DOD


Liquid rocket engine lre

Liquid Rocket Engine (LRE)

Combustion Chamber

With Shear Coax Shower Head

Shear Coaxial Injector

SSME – LOX / LH2

Arianne 5 – LOX / Kerosene

Soyuz – LOX / Kerosene

Ghosh, 2008 PhD


Combustion instability

Combustion Instability

Onset of Instability

Stable Combustion

Combustion Instability

  • Large amplitude pressure oscillations (Reardon, 1961)

  • Increased heat transfer rates to the combustor walls (Male, 1954)

  • Increased mechanical loading on the thrust chamber assembly

  • Off Designoperation of entire engine

  • CatastrophicFailures

Ghosh, 2008 PhD


Scope of present work

Scope of present work

  • Correlations Exist

  • Injector Geometry

  • Outer Jet Momentum

  • Outer Jet Temperature

  • Recess

  • Hydrocarbon Fuel

  • Lacking

  • Physics Based Mechanisms

  • Predictive Capability

  • Recognized as a key element controlling LRE stability margins

  • Rich Physics

    • Reacting Interface

    • Hydrodynamic Instabilities

      • Kelvin Helmholtz

      • Rayleigh Taylor

      • Richtmyer Meshkov

    • Chamber Acoustics

      • Baroclinic Interactions

Ghosh, 2008 PhD


Recent work

Recent Work

Ghosh, 2008 PhD


Technical objectives

Technical objectives

  • To better understand the physical mechanisms that play key role during the onset of combustion instability in liquid rocket engines (LRE).

    • What leads pressure perturbations (p’) to couple with heat release oscillations (q’)

      • Hydrodynamic Modes

      • Jet and Wake Modes

      • Chamber Acoustics

      • Heat Release

      • Coupling between two or more of the above

  • To model the relative importance of various flow-field parameters affecting flame acoustic interaction in LREs

    • Fuel-Oxidizer Density Ratio

    • Fuel-Oxidizer Velocity Ratio

    • Fuel-Oxidizer Momentum Ratio

    • Fuel composition

  • To build experimental database for CFD code validation

Ghosh, 2008 PhD


Experimental apparatus and techniques

Experimental Apparatus and Techniques

  • Two-Dimensional Slice of Shear-Coax Injector Configuration

    • Turbulent Diffusion Flames

    • Central O2 Jet

    • Outer H2 Jet

    • Inert Wall Jet at Boundary

    • Transverse Acoustic Forcing

  • Flow Visualization

    • Phase-Locked OH* Chemiluminescence

    • Phase-Locked Schlieren/Shadowgraphy

    • High Speed Cinematographic Imaging

  • Measurement Devices

    • Static Pressure Sensors (Setra)

    • Dynamic Pressure Sensors (Kistler)

    • ICCD Camera (DicamPro)

    • Photomultiplier Tube

    • Hotwire

    • High Speed Camera

Ghosh, 2008 PhD


Experimental apparatus and techniques1

Experimental Apparatus and Techniques

  • Instrumentation

    • Signal Generator

    • Amplifier

    • Oscilloscope

    • LabView based VIs

  • Firing Sequence (Reacting Flow Cases)

    • H2-O2-H2 tests

    • O2/N2-H2-O2/N2 test

    • H2/Ar-O2/He-H2/Ar tests

    • H2/Ar/He-O2-H2/Ar/He tests

    • H2/CH4-O2-H2/CH4 tests

Ghosh, 2008 PhD


Preliminary flame acoustic interaction tests

Preliminary Flame-Acoustic Interaction Tests

Ghosh, 2008 PhD


Acoustic characterization using broadband forcing

Acoustic Characterization using Broadband Forcing

  • Acoustically excited response using band-limited (< 5000Hz) white noise

  • Dynamic pressure

  • Spectral analysis using FFT (400 spectra averaged).

  • Non-reacting and reacting environments.

Ghosh, 2008 PhD


Acoustic characterization using broadband forcing1

Acoustic Characterization using Broadband Forcing

Ghosh, 2008 PhD


Non reacting flow experimental results

Non-reacting Flow Experimental Results

  • Quarter-wave mode of the oxidizer post (longitudinal)

    • Insensitive to the density ratio

    • Insensitive to the sensor locations

  • Three-quarter-wave mode of the chamber (longitudinal)

    • Sensitive to the density ratio

    • Relatively insensitive to the sensor location

  • Quarter-wave mode of the chamber (transverse)

    • Sensitive to the density ratio

    • Insensitive to the sensor location

f2

f1

f3

f0

f2

f1

f3

f0

Ghosh, 2008 PhD


Modeling resonance in variable density flowfields

Modeling Resonance in Variable Density Flowfields

  • Complete Reaction Model

    • Consider variation in speed of sound through heterogeneous media consisting of fuel, oxidizer, and equilibrium products

  • Jet-Core Mixing-Length Model

    • Assign two different length scales in the streamwise direction -- incompletely-mixed near-field region defined by jet-core length (Ln~6D) and fully-mixed far-field region consisting of the equilibrium products

    • Near-field mixture fraction determined by velocity ratio

  • Transverse Entrainment Model

    • Oxidizer entrainment depends on cross-flow momentum ratio (i.e., ratio between transverse pressure force and total injection momentum)

    • Average mixture fraction depends on the momentum ratio

Far-Field:

Near-Field:

Ghosh, 2008 PhD


Comparison of isothermal case data

f3

T/4

f2

L/4

f1

O/4

Comparison of Isothermal Case Data

  • Resonance at f1

    • Longitudinal first-quarter wave mode of the oxidizer post

    • Well predicted

  • Resonance at f2

    • Longitudinal three-quarter wave mode of the chamber

    • Adequately predicted by various models

  • Resonance at f3

    • Transverse first-quarter wave mode of the chamber

    • Under-predicted by complete reaction model (implies the fuel content is actually higher than the equilibrium approximation)

Ghosh, 2008 PhD


Acoustic excitation of density stratified non reacting flows

Acoustic Excitation of Density Stratified Non-Reacting Flows

Ghosh, 2008 PhD


Acoustic excitation of density stratified non reacting flows schlieren results for helium jet

Acoustic Excitation of Density Stratified Non-Reacting Flows - Schlieren Results for Helium Jet

He (18m/s)

He (18m/s)

Air

6m/s

Baseline

ReAir (Center Jet)~ 7000

234 Hz

Phase = 0o 90o 180o 270o

Ghosh, 2008 PhD


Acoustic excitation of density stratified non reacting flows schlieren results for helium jet1

Acoustic Excitation of Density Stratified Non-Reacting Flows - Schlieren Results for Helium Jet

He (18m/s)

He (18m/s)

Air

6m/s

400 Hz

ReAir (Center Jet)~ 7000

625 Hz

Phase = 0o 90o 180o 270o

Ghosh, 2008 PhD


Acoustic excitation of density stratified non reacting flows schlieren results for helium jet2

Acoustic Excitation of Density Stratified Non-Reacting Flows - Schlieren Results for Helium Jet

He (18m/s)

He (18m/s)

Air

6m/s

771 Hz

ReAir (Center Jet)~ 7000

1094 Hz

Phase = 0o 90o 180o 270o

Ghosh, 2008 PhD


Hydrodynamic modes hot wire experiments

Hydrodynamic Modes - Hot Wire Experiments

  • Wake Mode Instability

  • Jet Preferred Mode

Wake Mode Frequencies

F1 = 1134 Hz

F2 = 756 Hz

F3 = 378 Hz

Jet Preferred Mode Frequencies

Ghosh, 2008 PhD


Hydrodynamic modes hot wire experiments1

Hydrodynamic Modes - Hot Wire Experiments

Probe

Air

6m/s

He

18m/s

He

18m/s

  • Low Quality Resonant Response

  • f1 = 429.7 Hz, f2 = 869.4 Hz,f3=1289.3 Hz

  • Forced Response Closely Follows Natural Response.

ReAir (Center Jet)~ 7000

Ghosh, 2008 PhD


Hydrodynamic modes excitation of wake mode

Hydrodynamic Modes– Excitation of Wake Mode

He (18m/s)

He (18m/s)

Air

6m/s

429.7 Hz (Wake Mode Excitation)

ReAir (Center Jet)~ 7000

Phase = 0o 90o 180o 270o

Ghosh, 2008 PhD


Reacting flow experiments characteristic flame acoustic interactions

Reacting Flow Experiments Characteristic Flame-Acoustic Interactions

H2

H2

O2

Ghosh, 2008 PhD


Reacting flow experiments characteristic flame acoustic interactions1

Reacting Flow Experiments Characteristic Flame-Acoustic Interactions

300 Hz

1150 Hz

Phase = 0o 90o 180o 270o

Ghosh, 2008 PhD


Asymmetric excitation for the h2 o2 h2 flame baroclinic vorticity as a potential mechanism

Asymmetric Excitation for the H2-O2-H2 flame Baroclinic Vorticity as a potential mechanism

Ghosh, 2008 PhD


Effect of density gradient reversal

Effect of Density Gradient Reversal

Ghosh, 2008 PhD


Effect of density ratio variations

Effect of Density Ratio Variations

  • Fix velocity ratio constant at 3 and at stoichiometric H2-O2 ratio

  • Vary density ratio by mixing inert gas

Ghosh, 2008 PhD


The role of density gradient in liquid rocket engine combustion instability amardip ghosh

Effect of Density Ratio Variations Instantaneous OH* Chemiluminescence(Acoustic Forcing Characteristics Held Constant at 1150Hz;12.5W)

Ghosh, 2008 PhD


The role of density gradient in liquid rocket engine combustion instability amardip ghosh

Chapter 5 - Effect of Density Ratio Variations Ensemble Averaged OH* Chemiluminescence(Acoustic Forcing Characteristics Held Constant at 1150Hz;12.5W)

Ghosh, 2008 PhD


Measurements of flame wrinkling amplitude

Measurements of Flame Wrinkling Amplitude

  • Quantifying the special extent of flame wrinkling from time-averaged OH*-chemiluminescence data

Ghosh, 2008 PhD


Effect of density gradient on flame acoustic interaction

Effect of Density Gradient on Flame-Acoustic Interaction

  • Time-Averaged Measurement of Flame Wrinkling Thickness

    • Fixed OH Ratio, Velocity Ratio, Acoustic Forcing Amplitude

    • Variable Density by Ar or He Dilution

Ghosh, 2008 PhD


Effect of heat release variations

Effect of Heat Release Variations

  • Use noble gas to dilute fuel and oxidizer streams while keeping the velocities constant

  • Gradual change in heat release with dilution

  • O2/He and H2/Ar combination

    • Exponential change in density ratio

    • Ideal for isolating the density effect

  • O2/Ar and H2/He combination

    • Little change in density ratio

    • Ideal for studying the effect on chemistry

Ghosh, 2008 PhD


The role of density gradient in liquid rocket engine combustion instability amardip ghosh

Effect of Heat Release VariationsUnder Constant Forcing, Constant Heat Release, Different Density Ratios

  • Acoustically Forced

    • Heat Release: 15 kW

    • 6% Dilution by Mole

    • Density Ratio: 7.0 (left) and 15.2 (right)

  • Unforced

    • Heat Release: 15 kW

    • 6% Dilution by Mole

    • Density Ratio: 7.0 or 15.2

Ghosh, 2008 PhD


Effect of jet momentum variations

Effect of Jet Momentum Variations

  • Use noble gas to dilute fuel and oxidizer streams while keeping the velocities constant

  • Exponential change in Density Ratio with dilution

  • O2/He and H2/Ar combination

    • Exponential change in density ratio

    • Linear increase in outer jet momentum

    • Linear Increase in total jet momentum

Ghosh, 2008 PhD


Effect of jet momentum variations acoustic excitation 1150 hz 15 8 watts

Effect of Jet Momentum VariationsAcoustic Excitation – 1150 Hz, 15.8 Watts

  • Case 1

    • Outer Jet Momentum :0.0055 kg.m/s2

    • Inner Jet Momentum : 0.0047 kg.m/s2

    • Density Ratio: 8

  • Case 2

    • Outer Jet Momentum :0.0055 kg.m/s2

    • Inner Jet Momentum : 0.0036 kg.m/s2

    • Density Ratio: 2

Ghosh, 2008 PhD


Rayleigh taylor growth rate

Rayleigh Taylor Growth Rate

  • Richtmyer-Meshkov Instability

  • Rayleigh-Taylor Instability

g

Rayleigh-Taylor Instability Youngs (1984)

Richtmyer-Meshkov Instability Sunhara et al. (1996)

Ghosh, 2008 PhD


Rayleigh taylor growth rate1

Rayleigh Taylor Growth Rate

  • Classical Rayleigh-Taylor mode instability analysis yields wavelength-dependent growth rate

  • Intermittent fluid acceleration by pressure waves is used instead of gravitational acceleration

Ghosh, 2008 PhD


Parametric studies dimensional analysis for the shear coax injector problem

Parametric Studies. Dimensional Analysis for the Shear-Coax Injector Problem

δ(x)=|ro- ri |,

where I(x,r) satisfies

Imax(x)-I(x,ro)=Imax(x)-I(x,ri)=0.9[Imax(x)-Ibackground(x)]

Ghosh, 2008 PhD


Parametric studies effect of density ratio

Parametric Studies. Effect of Density Ratio

  • Time-Averaged Measurement of Flame Wrinkling Thickness

    • Fixed OH Ratio, Velocity Ratio, Acoustic Forcing Amplitude

    • Variable Density by Ar or He Dilution

Ghosh, 2008 PhD


Parametric studies effect of velocity ratio

Parametric Studies. Effect of Velocity Ratio.

Ghosh, 2008 PhD


Parametric studies effect of velocity ratio1

Parametric Studies. Effect of Velocity Ratio

  • OH* Chemiluminescence Imaging

    • Uf/Uo : 3.02, 3.36, 3.64, 4.01,4.51, 5.03, 5.27

    • Density Ratio: 8

Ghosh, 2008 PhD


Parametric studies effect of velocity ratio2

Parametric Studies. Effect of Velocity Ratio

  • Time-Averaged Measurement of Flame Wrinkling Thickness

    • Fixed OH Ratio, Density Ratio, Acoustic Forcing Amplitude

    • Variable Velocity Ratio by He Addition to outer Jet

Ghosh, 2008 PhD


Parametric studies effect of momentum change

Parametric Studies. Effect of Momentum Change

Ghosh, 2008 PhD


Parametric studies effect of momentum change1

Parametric Studies. Effect of Momentum Change

  • Case A

  • Case B

Increase in Outer Jet Momentum

Velocities fixed (Velocity Ratio ~ 3)

Decrease in Oxidizer Fuel Density Ratio (6 - 2)

Increase in Outer Jet Momentum

Densities Fixed (Density Ratio ~ 8)

Increase in Fuel Oxidizer Velocity Ratio (3 - 5.3)

Ghosh, 2008 PhD


Parametric studies effect of momentum change2

Parametric Studies. Effect of Momentum Change

  • Case A

    • Fixed Densities

    • Outer Jet Velocity is Increased

  • Case B

    • Fixed Velocities

    • Density Ratio is Decreased

Ghosh, 2008 PhD


Parametric studies effect of chemical composition

Parametric Studies. Effect of Chemical Composition.

Ghosh, 2008 PhD


Parametric studies effect of chemical composition1

Parametric Studies. Effect of Chemical Composition

Lifted flame using only methane as fuel (a) OH* average (b) CH* average (c) OH* instantaneous (d) CH* instantaneous

50% methane and 50% hydrogen flame subjected to acoustic excitation. (a) OH* average (b) CH* average (c) OH* instantaneous (d) CH* instantaneous

Ghosh, 2008 PhD


Parametric studies effect of chemical composition2

Parametric Studies. Effect of Chemical Composition.

  • Time-Averaged Measurement of Flame Wrinkling Thickness

    • Fixed Density Ratio ~ 6

    • Fixed Velocity Ratio ~ 3

    • Fuel Composition is varied.

Ghosh, 2008 PhD


The role of density gradient in liquid rocket engine combustion instability amardip ghosh

Chapter 5- Parametric Studies .Dependence of Flame-Acoustic Interactionon Density Ratio, Velocity Ratio, HC Mole Fraction

Fuel mixture ratio

(methane mole fraction)

Density ratio

Velocity ratio

y = 0.022 exp(5.1 x)

y = -3.5 x + 3.6

y = -0.87 x + 2.3

Ghosh, 2008 PhD


Simultaneous measurement of pressure and heat release oscillations

Pressure Oscillation

OH* Oscillation

Simultaneous Measurement of Pressure and Heat Release Oscillations

Density Ratio = 14.5

Density Ratio = 3

Ghosh, 2008 PhD


Oh chemiluminescence oscillations

OH* Chemiluminescence Oscillations

  • Photomultiplier Measurements

  • Forcing Frequency = 1150 Hz

f = 1150 Hz

Ghosh, 2008 PhD


Oh chemiluminescence oscillations1

OH* Chemiluminescence Oscillations

  • Photomultiplier Measurements

  • Forcing Frequency = 1150 Hz

f = 1150 Hz

Ghosh, 2008 PhD


Oh chemiluminescence oscillations2

OH* Chemiluminescence Oscillations

  • Photomultiplier Measurements

  • Forcing Frequency = 1150 Hz

Low FrequencyResponse

Ghosh, 2008 PhD


Oh chemiluminescence oscillations3

OH* Chemiluminescence Oscillations

  • Photomultiplier Measurements

  • Forcing Frequency = 1150 Hz

Low FrequencyResponse

Ghosh, 2008 PhD


Vortex pairing and excitation of secondary frequencies

Vortex Pairing and Excitation of Secondary Frequencies

  • High-Speed Imaging Results

    • Framing Rate – 1000 fps

  • Density Gradient

    • Vorticity Generation at Forcing Frequency

  • Velocity Gradient

    • Vortex Pairing and Merging

    • Deviation from Forcing Frequency

  • Dynamic Interactions

  • Amplification of small disturbance by flame-acoustic coupling

Ghosh, 2008 PhD


Secondary evidence of rt instability

Secondary Evidence of RT instability

RT unstable

Ghosh, 2008 PhD


Density tailoring for reduction of flame acoustic interaction possible control strategy

Density Tailoring for Reduction of Flame Acoustic Interaction - Possible Control Strategy

Ghosh, 2008 PhD


Summary and conclusions

Summary and Conclusions

  • Model shear-coaxial injector flames were acoustically forced from transverse direction to characterize the flame-acoustic interaction during the onset of combustion instability. Qualitative characterization of flame response under acoustic excitations revealed :

    • Flame response depends on frequency and amplitude of forcing

    • Acoustic Modes Setup in the Combustor

    • Interactions differ if responding to travelling waves or standing waves

    • Depends on the nature and orientation of acoustic media in the volume of interest.

  • Density Ratio between fuel and Oxidizer was identified as a critical parameter affecting flame Acoustic Interactions.

    • It was shown that small acoustic disturbances could be amplified by flame-acoustic coupling, leading to substantial modulation in spatial heat release fluctuation for flame fronts with large density ratios.

Ghosh, 2008 PhD


Summary and conclusions1

Summary and Conclusions

  • A New Physical Mechanism (Intermittent Baroclinic Vorticity) based on density ratio between fuel and Oxidizer was identified as a key mechanism in LRE Combustion Instability.

    • This kind of mechanism involving intermittent baroclinic torque arising from the interactions between misaligned pressure and density gradients has never been reported in liquid rocket engine instability studies.

  • Parametric Studies were conducted. Effects of density ratio, velocity ratio, and fuel mixture fraction on flame-acoustic interaction were studied by systematically changing each parameter while holding others constant.

    • The amount of flame-acoustic interaction was most sensitive to changes in density ratio. Similar changes in velocity ratio and fuel mixture ratio produced relatively smaller effects.

    • Density ratio affected flame-acoustic interaction by changing the amplitude of periodically applied baroclinic torque on the mixture interface. The observed dependence on density ratio was exponential.

    • Increasing the outer jet velocity reduced the amount of interaction almost linearly. This effect was attributed to the decrease in acoustic energy per mass flow rate.

    • Increasing the methane mole fraction also reduced the amount of interaction linearly. This effect was attributed to the reduction in total heat release rate which affected the amplification mechanism.

Ghosh, 2008 PhD


Summary and conclusions2

Summary and Conclusions

  • Non-linear response in flame-acoustic interaction.

    • Flame forced at 1550 Hz responded not only at 1150 Hz but also at a substantially lower frequency.

  • Model development.

    • Well-stirred reactor based Model.

    • Jet mixing length based Model.

    • Acoustically driven entrainment Model.

Ghosh, 2008 PhD


Significance of this work

Significance of this Work

  • The possible existence of a new mechanism in the initiation of Combustion instabilities in liquid rocket engines has been identified.

    • This kind of mechanism involving intermittent baroclinic torque arising from the interactions between misaligned pressure and density gradients has never been reported in liquid rocket engine instability studies.

  • Instead of modifying the acoustic boundary conditions to control the amplitude of acoustic oscillations, new control strategies based on tailoring the density field inside the combustor can now be attempted.

    • Improve the stability margin of the combustor

    • Decrease the growth rate of instabilities even when initiated.

Ghosh, 2008 PhD


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