Exa Contribution to DPW-6 using a Lattice-Boltzmann Method

16-17 June 2016 Washington, DC

Benedikt König, André F.P. Ribeiro, Ehab Fares Exa GmbH, Stuttgart, Germany

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LBM Classical CFD

Numerical Method Lattice Boltzmann Method

Results

Continuum Equations

Discrete Approximation

Numerical Integration

Discrete Statistical Approximation

of Particle Movements

Advection and Collision of Particle Distributions

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Numerical Method Lattice Boltzmann Method - Properties

Discretization – Inherently unsteady – Limited set of discrete particle velocities

Turbulence Modelling – Compute coherent, anisotropic structures – Model universal, isotropic structures – Two equation k-ε model (extended RNG)

Grid Approach – Automatic Cartesian grid generation – Wall function

New Transonic Capability

Schematic view only, not representative of transonic LBM model

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Numerical Method Computational Mesh

Tiny Medium X-Fine

Resolution (cells / MAC) 968 1280 1693

Voxels [106] 89 196 438

CPUh [10³] 2.8 7.2 31

Wallclock on 360 cores [h] 8.1 21 45

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Numerical Method Application of LBM vs RANS

Geometry

Un

stea

din

ess

RANS

LBM

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Exa DPW-6 Results Case 2 Grid Convergence – Forces

Corrected for CL≠0.5

Simulations run at α=2.75° (fixed)

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Exa DPW-6 Results Case 2 Grid Convergence – Drag Difference

Drag increment WBNP -WB: +23 d.c. (Extrapolated)

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Exa DPW-6 Results Case 2 Grid Convergence – WB Spanwise Lift

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Exa DPW-6 Results Case 2 Grid Convergence – WB Spanwise Pitching Moment

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Exa DPW-6 Results Case 2 Side-of-Body Separation – medium resolution

~ 50mm

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Exa DPW-6 Results Case 2 Pylon Separation – medium resolution

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Exa DPW-6 Results Case 2 Grid Convergence – Pressure Distributions

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Exa DPW-6 Results Case 3 Polar Study – Pressure Distributions

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Exa DPW-6 Results Case 3 Polar Study – Pressure Distribution at α=4°

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Exa DPW-6 Results Case 3 Polar Study – Pressure Distributions

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Exa DPW-6 Results Case 3 Polar Study – Lift and Drag

Additional data points run for JAXA Second Aerodynamics Prediction Challenge (APC-II, https://cfdws.chofu.jaxa.jp/apc/) at Re=1.5x106

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Beyond DPW-6 Buffet Plane Visualization at α = 4.87°

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Beyond DPW-6 Buffet Iso-Surface Visualization at α = 4.87°

Iso-surface Cpt = 0

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Beyond DPW-6 Pressure Fluctuations at α = 4.87°

Measurement data from JAXA Second Aerodynamics Prediction Challenge (APC-II, https://cfdws.chofu.jaxa.jp/apc/)

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Beyond DPW-6 Pressure Fluctuations at α = 4.87°

Measurement data from JAXA Second Aerodynamics Prediction Challenge (APC-II, https://cfdws.chofu.jaxa.jp/apc/)

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Summary

New transonic Lattice-Boltzmann available – Breakthrough technology for LBM – Current version still beta-stadium

Absolute drag sensitive to resolution – Refinement shows convergence towards CFD consensus – Drag increment (WBNP-WB) well captured

Significant flow unsteadiness found for α ≥ 3.5°

Beyond drag prediction: Buffet prediction