RANS CFD Simulations of Scramjet Flow Path Transients...Evaluate unstart detection techniques...
Transcript of RANS CFD Simulations of Scramjet Flow Path Transients...Evaluate unstart detection techniques...
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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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