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RANS CFD Simulations of Scramjet Flow Path Transients

Logan P. Riley, Robert J. Yentsch, Datta V. Gaitonde

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Overview •  Personal Background • Motivation • HIFiRE-2 Program

– Mode-Transition –  Experiments

• HIFiRE-2 CFD Studies – Computational Approach –  Steady Operation Simulations – Mode-Transition Simulations

•  Looking Ahead • Closing Remarks

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Special Thanks:

Dr. Michael Brown, AFRL/RQ Dr. Jeffrey Donbar, AFRL/RQ Dr. Mark Gruber, AFRL/RQ

Dr. Mark Hagenmaier, AFRL/RQ Mr. Kevin Jackson, AFRL/RQ

Dr. Jiwen Liu, Taitech, Inc.

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Personal Background • B.S. Mechanical Engineering

– University of Akron – May 2012 – Minor in applied mathematics

•  PhD Aerospace Engineering – The Ohio State University – Fall 2013-Fall 2017 (Expected) – Graduate Course Work

›  Hypersonic flows ›  Advanced air-breathing propulsion ›  Compressible CFD ›  Turbulence

• Research interests – Scramjet flow paths – Hypersonic roughness-induced

boundary-layer transition

• Awarded DAGSI Fellowship – Begins: Fall 2014 – Mentor: Dr. Jeff Donbar

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Motivation • Scramjets

– Military applications – Access to space – High-speed transport

• Challenges – Chemistry – SBLI

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Interest: transition between ramjet and scramjet operation

Forebody/Inlet: Compression

Isolator: Contains shock train

Expansion: Thrust

Injectors: Combustion

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HIFiRE-2 Program • Hypersonic International Flight

Research Experiment • Objective: study HC-fueled

combustion during mode-transition (M=6à8) •  Successful flight test May 2012

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Reproduced from Jackson et al., 2011

http://www.nasa.gov/topics/aeronautics/ features/hifire.html

Extensive ground tests in addition to flight test

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HIFiRE-2 Program

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Reproduced from Jackson et al., 2011

Image reproduced with permission from Jackson et al., 2011

http://www.nasa.gov/topics/aeronautics/ features/hifire.html

Primary emphasis on discovery, not demonstration

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http://www.nasa.gov/topics/aeronautics/ features/hifire.html HIFiRE-2 Program

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Wikipedia

Reproduced from Jackson et al., 2011

Wikipedia

Mode-Transition

What are the physics of mode-transition?

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HIFiRE-2 Experiments Ground (HDCR) Configuration Flight Configuration

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Reproduced from Jackson et al., 2008 Reproduced from Gruber et al., 2008

Difference in inlet geometry significantly affects flow field

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HIFiRE-2 Experiments Ground (HDCR) Configuration Flight Configuration

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Reproduced from Jackson et al., 2008 Reproduced from Gruber et al., 2008

Primary (x8)

Secondary (x8)

Outboard

Inboard

Outboard

144 static pressure ports 19 surface thermocouples

4 heat flux gauges

Ground test pressure data used for validation

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Computational Approach • URANS with CFD++ code by METACOMP, Inc. • Taitech-Princeton Ethylene combustion (TP2) model • Hybrid structured/unstructured grids, O(2.5M) cells

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How do differences in geometry (ground versus flight) affect flow field?

How does mode transition occur?

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Steady, Dual-Mode Operation

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Good agreement between steady dual-mode/scramjet simulations and experiment

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Mode-Transition: Physics

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Ma0>1 Mac<1

Dual-Mode Shock train

Boundary layer separation caused by pressure rise

Combustion

Ma0>1 Ma0>Mac>1

Scramjet-Mode Shock train Supersonic flow

throughout Combustion

Pres

sure

Axial position

Scramjet-Mode pressure rise downstream of injectors

Dual-Mode pressure rise in isolator section

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Mode-Transition: HDCR Geometry

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Mode-transition characterized by loss of flame-holding in inboard primary-injectors

Does this occur in flight?

Dual-Mode Scramjet-Mode

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Mode-Transition: Flight versus Ground Geometries

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Low energy region near centerline preserves inboard PI flame-holding in flight

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Mode-Transition: Flight versus Ground Geometries

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Gaitonde et al., 2003

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HDCR Scramjet-Mode Operation

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Transient B.C. simulation

Steady B.C. simulations

Although the steady-operation simulations better reflect the actual progression of the experiment, the mode-transition simulation results better match the experimental data

Tare Fueled

Dual-Mode Scramjet-Mode

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Looking Ahead: Investigation of Scramjet Unstart • DAGSI Fellowship (Fall 2014) under mentorship of Dr. Jeff Donbar • Unstart adversely affects engine performance

– Want to capture large scale transients ›  Identify precursors to unstart ›  Quantify SBLI sensitivity to variations in fuel input

– Understanding transient behavior will facilitate development of control systems to limit unstart

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Can unstart be anticipated by measuring away from the wall?

Can quantities other than pressure be used to predict unstart?

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Looking Ahead: Future Work

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AFRL Direct Connect Rig

HIFiRE-2 HDCR

Evaluate unstart detection techniques

Unstart in dual-mode operation

HIFiRE-2 Mode-Transition

Validate with exp. work of Cabell et al. 2011

Build on exp. work of Donbar et al. 2010

Full flight test geometry

Rapid fuel flow perturbations

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Summary • Mode-transition CFD studies completed for HIFiRE-2

– Model parameters validated against ground test data – Loss of flame-holding affected by SBLI/geometry – Difference in predicted HDCR scramjet-mode behavior between:

›  Steady-operation (static B.C.) ›  Mode-transition (transient B.C.)

• Work beginning on the transients associated with unstart – Probe flow away from wall to identify precursors – Application to developing better fuel control systems

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Q&A

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