Dr. Kei Lau is an expert in aerothermodynamics and hypersonic vehicle design. He has extensive experience with theoretical and experimental analysis techniques as well as computational fluid dynamics and thermal analysis. His work has focused on issues like boundary layer transition and thermal protection system design for programs such as the National Aero-Space Plane. High-fidelity simulation tools are needed to reduce uncertainty in hypersonic vehicle design, including computational fluid dynamics, conjugate heat transfer analysis, and finite element structural analysis.

1. Aerothermodynamics and
Hypersonic Vehicle Design
Excerpt from Fundamentals of Hypersonic Flight Short Courses
Kei Y. Lau, PhD

2. Name: Kei Y. Lau, PhD
Key Technical Field: Aerothermodynamics, hypersonics, thermal technology
Assignment since 2008: F/A-18 Thermal Design/Technology Lead
Biography:
Dr. Kei Lau is a Boeing Technical Fellow and a nationally known expert in
aerothermodynamics and hypersonic vehicle design. He studied under Prof. E.R.G.
Eckert, Ephraim M. Sparrow, Suhas V. Patankar and Prof. Richard Goldstein (advisor)
at University of Minnesota where he received his doctorate degree in Thermodynamics
and Heat Transfer. He has expertise that ranges from theoretical to experimental,
fundamental flow physics to applied CFD and hypersonic vehicle design to basic
thermal analysis and heat transfer. He was instrumental in resolving the controversial
issue of boundary layer transition in SCRAMJET flowpath during the NASP program.
His recent assignments include Shuttle return to flight, SCRAMJET technology
demonstration programs such as HyFly and X-51. He served often as peer review panel
member in DoD and NASA programs and was frequent speaker at AFRL/AFOSR
workshops. From 2003 to 2011, he served as AFOSR Fluid Panel member to evaluate
annual grant proposals for Fluid Control and Hypersonic portfolio (Portfolio Manager,
Dr. John Schmisseur).
Presenters

3. 17 August 2016 | 3
Aerothermodynamics and Hypersonic Vehicle Design
Aerothermodynamic Design Starts with The physics of high
speed flight
Hypersonic Vehicle Design Overview
The vehicle airframe archetiture
The thermal management challenge
Current SOTA examples
The Engineering of High Speed
The standard aerothermal-thermal design process
Define the external aerothermal environment
Flow and solid model interaction
The multi-discipline design
High Heat Flux Component Design (Leading Edge)

4. 17 August 2016 | 4
What Is Aerothermodynamics
The process of applying analytical and
expermental techniques to quantify the complex,
hypervelocity thermal environment surrounding
the air and space vehicle
Importance of Efficient Aerothermal Design
Minimize TPS Weight and Reduce Burn-through Risk
Reduce Aerodynamic Drag and Increase Control Authority
Optimize Thermal Management Design
Increase Launch Flexibility and Entry Cross Range
Reduce TOGW by Optimizing Structural Weight and
Minimizing Cyrogenic Fuel Boil-off

5. 17 August 2016 | 5
Regions Of Strong Viscous Interactions
• Shock/Shock and Shock/Boundary Layer
Interaction are Important Factors in Determining
Aerodynamic Heating Rates

6. 17 August 2016 | 6
Aerothermal Loads Has 1st Order Impact on
TPS Weight Optimization
Heating distribution Effects
Thermal expansions at joining components
Stress induced by emperature gradients in &
between components
Distortion by pressure/thermal gradients
Viscous Interaction Effects
Shock/boundary layer interaction
Corner flow
Fin gap heating
Inlet Shock and Vortex
Impingement Causes
Heating to Increase locally
and downstream
Free Shear Flow Increases Heating
Corner Flow Increases Heating
Fin Shock Increases Heating
Fully Turbulent Flow Analysis Will Not Predict Accurate Thermal Gradient
Fully Turbulent Flow Analysis Has Excessive TPS Weight Panelty

7. 17 August 2016 | 7
Hypersonic Boundary Layer Transtion
• Many Factors Influence Boundary Layer Transition
• M, Re, a
• Wall Temperature
• Lateral Curvature
• LE/nose Bluntness
• Pressure Gradient
• Roughness
• M, Re, a
• Wall Temperature
• Lateral Curvature
• Longitudinal Curvature (Gortler)
• Pressure Gradient
• Roughness
• Shock-BL Interaction
• Bluntness/Entropy
Swallowing
• Transpiration
Cooling
• Curvature
• Relaminarization
• Roughness
• M, Re, a
• Bluntness
• Attachmentline
• Upstream Contamination
• Tail Deflection
• Shock-BL Interaction
• Roughness
• Nonequilibrium
• Relaminarization
• Acoustics
• Film Cooling
• Nonequilibrium
• Free Shear Layer
• Acoustics
• Pressure Gradient
Inside Scramjet
• Shock-BL Interaction
• Acoustics
• Fuel Injection
• Separation
Kei Y. Lau, “Hypersonic Boundary Layer Transition – Application to High Speed Vehicle Design”, AIAA Paper 2007-0310.

8. Challenges With Hypersonic
and Reentry Vehicles
Objective
Minimize the risk to future vehicle programs through the proactive establishment of high
temperature structures and materials technologies focusing on environmental durability and
manufacturing
Two recurring issues preventing the success of hypersonic and reentry programs
High temperature structures and materials environmental durability
High temperature structures and materials manufacturing (Note: Manufacturing refers to the
fabrication of advanced hardware, not an assembly line for hundreds of airplanes per year.)
Two different situations occur
High temperature structures and materials issues were recognized early in the program and
became a major risk reduction effort
High temperature structures and materials issues were not recognized as a problem and
became a major cost, schedule, and performance hit
Two key points
A state-of-the-art material is not the same as a state-of-the-art structure
TRL is a strong function of cycles, temperature, pressure, loads, etc.
 Thermal-structural issues are an/the “Achilles heel” of hypersonic and reentry
vehicles. CMC’s are an enabling solution for this problem. (Note: CMC’s refers to a
generic “family” of CMC’s, potentially including C/C, C/SiC, SiC/SiC, SiC/C, et. al.)
David E. Glass, NASA Langley Research Center

9. 17 August 2016 | 9
The structures and materials challenges in most of these
cases can be divided into two major categories
Environmental durability
Oxidation resistance
Life prediction
NDE (field “OK to fly”)
Manufacturing
Affordable (cost & schedule) manufacturing techniques
Assembly
Delamination
Critical flaw
Tolerances
Vehicle integration
Material property databases
Design of efficient and producible structures
Environmental Durability and Manufacturing

10. High-Fidelity Discipline Analysis Tools Required
to Reduce Design Uncertainty and Risk
High-fidelity tools must also be automated
and wrapped in order to support MDA/MDO
Continued increases in computer speed
(Moore’s Law) will soon permit practical
application to conceptual design
CFD for aerodynamics, aero-heating, loads and
propulsion
Conjugate thermal analysis
Finite element structural analysis
Flight dynamics simulation and control system
analysis
Computational electromagnetic analysis for
communication

11. Typical Thermal Analysis Approach
Sequential
Processes
Using
Individual
Tools &
Modules
FEM Modeling
Convert FEM into
Thermal Analysis
Model
External
Surface Grid
Generation
Trajectories
External Surface
Geometry
External Heat Flux
Baseline
Configuration
(CAD Model)
Finite Difference
Thermal Analysis
(SINDA)
ENGR
Methods
(MINIVER)
CFD
(DPLR)
Aeroheating
Aerothermal
WTT
FEM Thermal Model
Thermal
Analysis
Input
Material
Properties
Nodal Temperature
Distribution
Structural
Thermal
Loads
Component
Local Thermal
Environments
ENGR
Methods
(MINIVER)
CFD
(DPLR)
Aeroheating
Aerothermal
WTT

12. 17 August 2016 | 12
Unique Aerothermal Test Facility
Schematic Diagram of the CUBRC LENS I
and LENS II Shock Tunnels
Schematic Diagram of the
Shock Tunnel Operation

13. Hypersonic Heat Transfer CFD Requirements
Current SOTA required structured or semi-structured grid
Efficient gridding system
Domain decomposition (non-pointed matched or overset grid) allowed
efficient use of grid
Automatic domain decomposition to capture strong flow interference
such as protuberance heating and shock interaction
Grid adaptation to adequately resolution shock boundary, viscous
boundary and near wall region
Higher order turbulence modeling
SST (Mentor) model sufficient for general application
Spalart model showed better result in separated flow
Develop hybrid scheme using LES (largescale Eddy Simulation) to
capture strong flow interference such as protuberance heating and
shock interaction
Efficient nonequilibrium thermo-chemical models
AF Unified Flow Solver (UFS) initiative is for long term

14. 17 August 2016 | 14
Popular CFD Solver: DPLR Method
Data-Parallel Line-Relaxation (DPLR) Method:
Structured multi-block, finite-volume formulation
Various flux evaluation methods
Solve linearized system of equations along lines normal to
surface:
Allows huge time steps: CFL = 106
Convergence independent of grid stretching
Fully couple finite-rate chemistry
Fully parallel
Wide variety of nonequilibrium thermo-chemical models:
5, 8, 11-species air, etc
Vibrational nonequilibrium
Wall catalysis, radiative equilibrium, etc
Designed for High-quality heat transfer solutions
Method was designed for hypersonic and re-entry flows
Developed by Dr. Michael Wright of NASA/Ames
Unstructured Grid CFD is near term future
US3D from U of Minnesota/NASA Ames
FUN3D from NASA/Langley
6.0
Pull-up after reentry
Temperature (°F)
1,000 6,2005,8005,0005,4004,6004,2001,8001,400 2,6002,200 3,0003,4003,800

15. External TPS Ablation Modeling
1-D ablation code: AESOP-STAB v.3
CMA derivative with turbulent blowing model
3-D ablation code: CHAR
Orion program uses above developed at NASA/JSC
Similar tools available from NASA/AMES
17 August 2016 | 15

16. Inputs for Ablation Modeling Need Material Test
Thermal & ablation material properties, needed for both Virgin &
Char states of material:
Thermal Conductivity
Specific Heat
Hemispherical Emissivity
Solar Absorptivity
Additional properties (for ablation process)
Arrhenius Decomposition Coefficients
Heat of Decomposition
Heat of Combustion
Heat of Vaporization
Pyrolysis gas specific heat as a function of temperature and pressure
Pyrolysis gas enthalpy as a function of temperature and pressure
B’ Char as a function of temperature, pressure and B’ Gas
Virgin elemental composition
Char elemental composition
Enthalpy at the char (or ablating) surface
Physical Properties
Virgin Density
Charred Density
17 August 2016 | 16

17. Full Trajectory Aeroheating Mapped to Thermal Model
A mapping tool automatically maps aero-heating results
generated from the aero-heating module to the 3-D thermal
model
The mapping tool reduces the overall design cycle time and
most importantly reduces user errors
Time = 28
sec
Time = 28
secFigure 63a MINIVER heating result Figure 63b Mapped 3-D thermal model
Kei Y. Lau and 4 others, “The Aerothermal, Thermal and Structural Design Process and Criteria for the HIFiRE-4 Flight Test
Vehicle”, AIAA Paper 2012-5842.

18. Air Loads and Temperatures Mapped to FEM
3-D temperature thermal model
completed and mapped to the FEM
model
Load Case: Max Thermal Gradient
CFD Model vs Applied
Pressure to 3D FE Model
Load Case: Mach 5.67,
Alpha 25°, Elevon -6.25°
Kei Y. Lau and 4 others, “The Aerothermal, Thermal and Structural Design Process and Criteria for the HIFiRE-4 Flight Test
Vehicle”, AIAA Paper 2012-5842.

19. 17 August 2016 | 19
Component Level Thermal Modeling - TIK
Chassis Temperature limit = 185°F
Power dissipation = xxx W
Component mass ~ yy.0 lb
Heat sink included
Insulation required = 0.zz” Min-K
TIK Thermal Environment for Trajectory 2
0
100
200
300
400
500
600
700
0 100 200 300 400 500 600
Time (s)
Temperature(°F)
Aft Payload Bay Air
Mouting Location
Generic Test Instrument Kit Example

20. 17 August 2016 | 20
High Heat Flux Component Design (Leading Edge)
Tungsten
Nosecap
Inconel®
Isolator
Fitting
(TPS over
Isolator Not
Shown)
Nosetip hot
Interface reference
Manage airframe
interface

21. 17 August 2016 | 21
Modeling and Simulation Summary
Optimal high speed system design requires highly coupled analyses
with reliable data infrastructure and high fidelity/high efficiency
analysis tools
Conceptual, PDR design phase
Mechanism based correlations from relevant historical database
Conventional engineering tools (CMA/STAB, MASCC, MINIVER, BLIMPK)
Limited use of CFD based tools for parametric trade studies
Component (TPS, airframe) CDR design phase
Extensive use of CFD based tools, including stability analysis
New test database (Ground and/or flight)
New material characterization data
Ablation modeling as needed
Loosely coupled flow and thermal analysis
System CDR design phase
Conjugate heat transfer analysis – CFD flowfield, radiation, TPS thermal
response, structural thermal response
System qualification test

22. Leverage AFRL/Academia Team Resources
The STAR (STability Analysis for Reentry) team was initially formed in
2004 at the request of AF/DARPA program managers concerned about
deficiencies in the state-of-the-art in laminar-turbulent transition
estimation methods utilized for the design of advanced technology
demonstrators
Graham Candler, U. Minnesota – Large scale, high-fidelity computational fluid dynamics
Steven Schneider, Purdue U. – Quiet tunnel experiments
Helen Reed, Texas A&M – Stability analysis
Roger Kimmel, AFRL – Transition experiments, flight research
Evaluate fault tree node #1.3: Inlet Flowfield Modeling/Transition
o Review inlet ramp transition data from Purdue Mach 6 Quiet Tunnel test
o Conduct cowl boundary layer stability analysis with flight freestream conditions
(University of Minnesota)
o Review CUBRC heat transfer data on full-scale X-51 model
o Analyze impact to pressure from delayed transition on the cowl
o Analyze likelihood of turbulent transition for scenario of laminar boundary layer reaching
body shock reflection impinging on cowl surface
17 August 2016 | 22

23. 17 August 2016 | 23
High-Fidelity Discipline Analysis Tools Required
to Reduce Design Uncertainty and Risk
High-fidelity tools must also be automated and
wrapped in order to support MDA/MDO
Continued increases in computer speed (Moore’s
Law) will soon permit practical application to
conceptual design
CFD for aerodynamics, aero-heating, loads and propulsion
Conjugate thermal analysis
Finite element structural analysis
Flight dynamics simulation and control system analysis
Computational electromagnetic analysis for communication
blackout