cei extraction of boundary layer characteristics from fluent results
TRANSCRIPT
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Extraction of Boundary Layer Characteristics from Fluent Results
Fluent 2005 CFD Summit, Dearborn, MI
Kent P. Misegades, CEI Inc., Apex, NC
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Background & Real Flow Visualization
Traditional Visualization of CFD results
Boundary Layer Characterization
Boundary Layer Characteristic Extraction
Other Techniques
Future Work
Topics
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Subject: Viscous, High-Speed, Compressible Flows
Slender bodies & wings at low angle-of-attack
High Reynolds numbers, thus thin boundary layers
Shock / boundary layer interaction significant
BL thickness and flow distortion in engine inlets
Extensive laminar flow may exist, thus BL transition critical
Background
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Background
Lockheed-Martin HCV
Aerion SSBJ
Advanced Aircraft with Extensive Laminar Flow
SAI SSBJ
Boeing 787
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High-Fidelity Fluent CFD Aerodynamic Simulations
Accuracy now comparable to legacy lab aero codes
Dense meshes needed for turbulence models & shocks
Boundary layers for RANS+SA models are well resolved
DNS, LES, DES all produce far more detail than RANS
Traditional post-processing ignores rich data in results
We need to return to basics & real flow visualization
Background
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Real Flow Visualization
Laminar BL Separation and Turbulent BL Reattachment, M. Selig, UIUC
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Real Flow Visualization
Boundary Layer Surface Flow using Paint Dots, Flometrics
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Real Flow Visualization
Schlieren Photographs, NASA
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Real Flow Visualization
Shadowgraph of Spacecraft Model, NASA
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Fluent Test CaseGeometry: ONERA M6 Wing
Mesh: 884,736 hexahedra
Reynolds Number: 11.34 million
Freestream Mach Number: 0.84
Angle of Attack: 3.07 degrees
Fluent 6.2 results courtesy Thomas
Scheidegger, Fluent Inc.
All images created using EnSight 8.0
from CEI, Inc.
CFD Visualization
M > 1
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Simple TechniquesResults displayed on model surfaces & clip planes
• Velocity, Cp, density, Mach number, etc.
Derived variables
• total pressure, vorticity, entropy, helicity, etc.
Velocity profiles
• qualitatively depicts BL profiles, thickness, separation, etc.
Isosurfaces
• total pressure, sonic (Mach=1), vorticity, entropy, etc.
CFD Visualization
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CFD Visualization
Surface Pressure Pressure on Clip Plane
Total Pressure on Clip Plane Mach Number on Clip Plane
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Sophisticated TechniquesRegions of Reverse flow
• Streamwise velocity at a small offset distance from a surface
Surface-Restricted Traces
• Oil flow analog, particle traces in laminar sublayer
Lines of BL Separation and Attachment
• Singularities on surface
Shock surfaces & Dilitation Contours
Schlieren & Shadowgraph simulation
CFD Visualization
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CFD Visualization
Offset Velocity Magnitude Offset Vx
Surface-Restricted Traces Surface Traces and Offset Velocity
Reverse Flow
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CFD Visualization
Lines of BL Separation (green)
Lines of BL Attachment (magenta)
Shock Surface Extraction
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CFD Visualization
Velocity Profiles under BL Separation Bubble
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CFD Visualization
Schlieren Simulation (|∇∇∇∇·�|) Shadowgraph Simulation (∇∇∇∇2�)
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BL Characterization
Boundary Layers on an Airfoil, NASA
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Classical Boundary Layer Characteristics
See: Abbott & von Doenhoff, Theory of Wing Sections
Thickness (δδδδ): distance at which u = 0.99 x U
Displacement thickness (δδδδ*): how BL displaces flow
Momentum Thickness (ΘΘΘΘ): loss of momentum in BL
Shape Factor (H = δδδδ* / Θ)/ Θ)/ Θ)/ Θ): separation tendency
Skin Friction Coefficient (Cf): viscous drag, transition
BL Characterization
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BL “Health” Indicator: Total Pressure Loss
• Total pressure drops due to viscosity and shocks
• Isosurface of 95% freestream Ptotal indicates BL growth
• Distance from surface to this 95% isosurface is desired
Boundary Layer Transition
• Of increasing importance for DNS, LES, DES results
• Involves anaysis of variables at BL edge
BL Characterization
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Incorporated in EnSight 8.x from CEI
Classical BL Characteristics• Thickness, δ, determined by proprietary edge-finding
algorithm developed at CEI
• δ* and Θ are 1-D integrals computed on surface nodes
• Shape Factor is simply H = δ* / Θ
• Cf is computed on surface
• Numerically intensive computations for irregular grids
• All characteristics available as surface variables
BL Characteristic Extraction
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BL Characteristic Extraction
BL Thickness, δδδδ BL Displacement Thickness, δδδδ*
BL Momentum Thickness, ΘΘΘΘ Shape Factor, H
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Elevated surfaces of BL characteristics
“Distance to value” variable on surfaces
Variables on edge of boundary layers
BL transition indicators
Animations of all techniques for transient flows
Other Techniques
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Other Techniques
Elevated Surface of δδδδ Elevated Surface of δδδδ
Contour of 95% Ptotal� Distance to 95% Ptotal�
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Other Techniques
BL Thickness, δδδδ Distance to 95% Ptotal�
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Further Validation against DPW-I & II DLR models
Flow separation detection & reporting
Laminar/turbulent area ratios
Drag breakdown
Interactive velocity profiling
Smart flow mapping with GPS-like decluttering
Faster methods, better defaults & filters
Future Work
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DPW-I DLR-F4
Pressure
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DPW-I DLR-F4
Boundary Layer Thickness
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DPW-I DLR-F4
Distance to 95% Ptotal�
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Thank You
Boeing Commercial Airplane Company, for supporting this work
Fluent Inc., for use of FLUENT and providing example datasets
Boeing 787