ICMMES-2004-68

Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.

Dr.-Ing. Norbert Grün Aerodynamics Simulation International Conference for Mesoscopic Methods in Engineering and Science Braunschweig, Germany July 26-29, 2004

BMW Group Dr. Norbert Grün International Conference for Mesoscopic Methods in Engineering and Science,

July 26-29, 2004


Outline

– PowerFLOW key features

– CFD simulation process

– Validation examples

– Various applications

– Conclusion


July 26-29, 2004


PowerFLOW Key Features

– Lattice-Boltzmann Method.

– Transient simulation.

– Low Re-#: Direct simulation without model assumptions.

– High Re-#: VLES (Very Large Eddy Simulation) in the fluid. Boundary Layer modeled by an extended log-law (accounting for longitudinal and crossflow pressure gradients).

– No manual meshing required: Automatic volume discretization using cubic cells (lattice) of different size (variable resolution).

– Automatic decomposition for parallel processing.

– Stable solutions.


July 26-29, 2004


CFD Simulation Process

CAD/CAS Model CATIA/ALIAS

Clay Model POLYWORKS

Simulation Model (Surface Facetization)

ANSA, QUICKMESH, THINK3, ...

1-5 Days

Simulation PowerFLOW

1 Day

Postprocessing PowerVIZ

Result

Shape Modification

of CAD/CAS Data

Morphing of the

Surface Mesh (PowerCLAY)

Turnaround

2-6 Days


July 26-29, 2004


CFD Process: Geometry Input

The surface

facetization

represents the

geometry only.

It does not set

the resolution

for the simulation.

Depending on the

level of detail up to

2-3 million facets

are used.


July 26-29, 2004


CFD Process: Modular Assembly

The complete

configuration may

be composed of

any number of

components.

Components may

be arranged in an

arbitrary fashion

and also intersect

each other.


July 26-29, 2004


CFD Process: Automatic Discretization

Typical voxel counts

for external aerodynamic

cases range from 20-80

milion cells.

Geometry representation

embedded in a lattice of

cubic cells (with different

levels of resolution).


July 26-29, 2004


CFD Process: Transient Simulation

100,000 Timesteps

(1 Timestep = 4.7 10-6 sec.)

No explicit convergence criterion, user monitors key quantities to decide when to stop the simulation.

Averaging Window


July 26-29, 2004


Validation Models (Scale 1:2.5).

5series touring

Open Convertible

5series Limousine with/without Mirror


July 26-29, 2004


Validation: Aerodynamic Forces

CZ2

0.114 0.105

CZ1

0.067 0.070

PowerFLOW 3.4: 0.252

CX

BMW Windtunnel: 0.252

CZ1

CZ2

-0.038 0.009 -0.027 0.006


CX



July 26-29, 2004


Validation: Surface Pressure Distribution

Top Centerline (Geometry not to scale)

PowerFLOW Experiment

Bottom Centerline (Geometry not to scale)


July 26-29, 2004


Validation: Near Surface Flow Topology


July 26-29, 2004


Validation: Wake Velocity Magnitude

Hot Wire Anemometry

PowerFLOW 3.4


July 26-29, 2004

0,300

0,320

0,340

0,360

0,380

0,400

0,420

0,440

Serie LT Sport

Cx *

A

Windkanal

(Aschheim)

PowerFLOW


Validation: Motorcycles (Windshield Variations)

Hot Wire Measurement PowerFLOW

Serie

LT

Sport


July 26-29, 2004


Analysis of Drag Generation

-0,06

-0,04

-0,02

0,00

0,02

0,04

0,06

0,08

0,10

0,0 0,1 0,3 0,4 0,5 0,6 0,7 0,9 1,0

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,400,0

Cx(x) Verteilung

Cx(x) Integral


CX



July 26-29, 2004


Analysis of Lift Generation

-0,03

-0,02

-0,01

0,00

0,01

0,02

0,03

0,0 0,1 0,3 0,4 0,5 0,6 0,7 0,9 1,0

-0,40

-0,30

-0,20

-0,10

0,00

0,10

0,200,0

Cz(x) Verteilung

Cz(x) Integral

CZ1 CZ2

0.011 0.013 0.143 0.123

PowerFLOW 3.4

BMW Windtunnel


July 26-29, 2004


Visualization: Transient Surface Pressure


July 26-29, 2004


Visualization: Near Wall Streamlines


July 26-29, 2004


Visualization: 3D Streamlines

Colors represent Near Surface Velocity Distribution


July 26-29, 2004


Visualization: Transient Flow Field Slices


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Visualization: Time Averaged Flow Field Slices


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Visualization: Transient Isosurface Cpt=0

For Cpt=0 the total pressure loss is equivalent to the dynamic free stream pressure


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Visualization: Time averaged Isosurface Cpt=0

Isosurface sweeping from high to low total pressure losses


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Visualization: Transient Isosurface VX=0

Reverse flow (Vx<0) inside the isosurface


July 26-29, 2004


Applications: NASTRAN Interface (Structure)

Select parts per PID

Match NASTRAN parts

with the PowerFLOW model

PLOADs [N/mm2]

on the PowerFLOW model

Map area loads onto

the NASTRAN model

Forces on

individual parts


July 26-29, 2004


Applications: ABAQUS Interface (Heat Transfer)

Mapping heat transfer coefficients

from a PowerFLOW simulation

onto an ABAQUS structure model


July 26-29, 2004


Applications: Motorsports Aerodynamics

Total

Aerodynamic

Force

Velocity Magnitude

Static Pressure Total Pressure Streamlines

Static Pressure


July 26-29, 2004


Applications: Motorsports Aerodynamics

Total

Aerodynamic

Force

Velocity Magnitude


July 26-29, 2004


Applications: Underhood Flow


July 26-29, 2004


Applications: Motorcycles - Transient Flow Field


July 26-29, 2004


Applications: Electronics Cooling

Goals: qualitatively – Heat Transfer Distribution

quantitatively – Surface Temperatures

Heat Transfer Coefficient

Velocity Magnitude


July 26-29, 2004


Conclusions

Short preprocessing phase due to automatic meshing. Capability to handle complex geometries. Steep learning curve due to ease-of-use. Does not require a numerics expert. Optimization loops still slower than the wind tunnel. Hardware requirements high for rapid turnaround.

Thank you for your attention.



July 26-29, 2004

ICMMES-2004-68

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