Background & Real Flow Visualization. Traditional Visualization of CFD results.
Boundary Layer Characterization. Boundary Layer Characteristic Extraction.
Extraction of Boundary Layer Characteristics from Fluent Results Fluent 2005 CFD Summit, Dearborn, MI Kent P. Misegades, CEI Inc., Apex, NC
… analyze, visualize, communicate
Topics Background & Real Flow Visualization Traditional Visualization of CFD results Boundary Layer Characterization Boundary Layer Characteristic Extraction Other Techniques Future Work … analyze, visualize, communicate
Background 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 … analyze, visualize, communicate
Background
Boeing 787
Lockheed-Martin HCV
Aerion SSBJ
SAI SSBJ
Advanced Aircraft with Extensive Laminar Flow … analyze, visualize, communicate
Background 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 … analyze, visualize, communicate
Real Flow Visualization
Laminar BL Separation and Turbulent BL Reattachment, M. Selig, UIUC … analyze, visualize, communicate
Real Flow Visualization
Boundary Layer Surface Flow using Paint Dots, Flometrics … analyze, visualize, communicate
Real Flow Visualization
Schlieren Photographs, NASA … analyze, visualize, communicate
Real Flow Visualization
Shadowgraph of Spacecraft Model, NASA … analyze, visualize, communicate
CFD Visualization Fluent Test Case Geometry: ONERA M6 Wing Mesh: 884,736 hexahedra Reynolds Number: 11.34 million Freestream Mach Number: 0.84 Angle of Attack: 3.07 degrees M>1
Fluent 6.2 results courtesy Thomas Scheidegger, Fluent Inc. All images created using EnSight 8.0 from CEI, Inc. … analyze, visualize, communicate
CFD Visualization Simple Techniques Results 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. … analyze, visualize, communicate
CFD Visualization
Surface Pressure
Total Pressure on Clip Plane
Pressure on Clip Plane
Mach Number on Clip Plane … analyze, visualize, communicate
CFD Visualization Sophisticated Techniques Regions 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 … analyze, visualize, communicate
CFD Visualization Reverse Flow
Offset Velocity Magnitude
Surface-Restricted Traces
Offset Vx
Surface Traces and Offset Velocity … analyze, visualize, communicate
CFD Visualization Shock Surface Extraction
Lines of BL Separation (green) Lines of BL Attachment (magenta)
… analyze, visualize, communicate
CFD Visualization
Velocity Profiles under BL Separation Bubble … analyze, visualize, communicate
CFD Visualization
Schlieren Simulation (|∇ ∇· |)
Shadowgraph Simulation (∇ ∇2 ) … analyze, visualize, communicate
BL Characterization
Boundary Layers on an Airfoil, NASA … analyze, visualize, communicate
BL Characterization Classical Boundary Layer Characteristics See: Abbott & von Doenhoff, Theory of Wing Sections Thickness (δ δ): distance at which u = 0.99 x U Displacement thickness (δ δ*): how BL displaces flow Momentum Thickness (Θ Θ): loss of momentum in BL Shape Factor (H = δ* / Θ): Θ) separation tendency Skin Friction Coefficient (Cf): viscous drag, transition … analyze, visualize, communicate
BL Characterization 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 … analyze, visualize, communicate
BL Characteristic Extraction 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 … analyze, visualize, communicate
BL Characteristic Extraction
BL Thickness, δ
BL Momentum Thickness, Θ
BL Displacement Thickness, δ*
Shape Factor, H … analyze, visualize, communicate
Other Techniques 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 … analyze, visualize, communicate
Other Techniques
Elevated Surface of δ
Elevated Surface of δ
Contour of 95% Ptotal
Distance to 95% Ptotal … analyze, visualize, communicate
Other Techniques
BL Thickness, δ
Distance to 95% Ptotal
… analyze, visualize, communicate
Future Work 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 … analyze, visualize, communicate
DPW-I DLR-F4
Pressure … analyze, visualize, communicate
DPW-I DLR-F4
Boundary Layer Thickness … analyze, visualize, communicate
DPW-I DLR-F4
Distance to 95% Ptotal … analyze, visualize, communicate
Thank You
Boeing 787
Boeing Commercial Airplane Company, for supporting this work Fluent Inc., for use of FLUENT and providing example datasets … analyze, visualize, communicate
