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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