1. 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

2. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 2
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Outline
– PowerFLOW key features
– CFD simulation process
– Validation examples
– Various applications
– Conclusion

3. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 3
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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.

4. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 4
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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

5. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 5
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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.

6. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 6
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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.

7. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 7
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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).

8. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 8
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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

9. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 9
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Validation Models (Scale 1:2.5).
5series touring
Open Convertible
5series Limousine with/without Mirror

10. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 10
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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
PowerFLOW 3.4: 0.276
CX
BMW Windtunnel: 0.292

11. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 11
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Validation: Surface Pressure Distribution
Top Centerline
(Geometry not to scale)
PowerFLOW
Experiment
Bottom Centerline
(Geometry not to scale)

12. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 12
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Validation: Near Surface Flow Topology

13. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 13
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Validation: Wake Velocity Magnitude
Hot Wire Anemometry
PowerFLOW 3.4

14. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 14
0,300
0,320
0,340
0,360
0,380
0,400
0,420
0,440
Serie LT Sport
Cx*A
Windkanal
(Aschheim)
PowerFLOW
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Validation: Motorcycles (Windshield Variations)
Hot Wire Measurement
PowerFLOW
Serie
LT
Sport

15. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 15
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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
0,40
0,0
Cx(x) Verteilung
Cx(x) Integral
PowerFLOW 3.4: 0.371
CX
BMW Windtunnel: 0.382

16. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 16
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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
0,20
0,0
Cz(x) Verteilung
Cz(x) Integral
CZ1
CZ2
0.011 0.013
0.143 0.123
PowerFLOW 3.4
BMW Windtunnel

17. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 17
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Visualization: Transient Surface Pressure

18. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 18
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Visualization: Near Wall Streamlines

19. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 19
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Visualization: 3D Streamlines
Colors represent Near Surface Velocity Distribution

20. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 20
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Visualization: Transient Flow Field Slices

21. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 21
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Visualization: Time Averaged Flow Field Slices

22. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 22
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Visualization: Transient Isosurface Cpt=0
For Cpt=0 the total pressure loss is equivalent to the dynamic free stream pressure

23. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 23
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Visualization: Time averaged Isosurface Cpt=0
Isosurface sweeping from high to low total pressure losses

24. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 24
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Visualization: Transient Isosurface VX=0
Reverse flow (Vx<0) inside the isosurface

25. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 25
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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

26. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 26
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Applications: ABAQUS Interface (Heat Transfer)
Mapping heat transfer coefficients
from a PowerFLOW simulation
onto an ABAQUS structure model

27. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 27
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Applications: Motorsports Aerodynamics
Total
Aerodynamic
Force
Velocity Magnitude
Static Pressure Total PressureStreamlines
Static Pressure

28. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 28
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Applications: Motorsports Aerodynamics
Total
Aerodynamic
Force
Velocity Magnitude

29. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 29
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Applications: Underhood Flow

30. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 30
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Applications: Motorcycles - Transient Flow Field

31. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 31
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
Applications: Electronics Cooling
Goals: qualitatively – Heat Transfer Distribution
quantitatively – Surface Temperatures
Heat Transfer Coefficient
Velocity Magnitude

32. BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004
Page 32
Industrial Applications of a Lattice-Boltzmann Code in Vehicle Aerodynamics.
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.

33. Thank you for your attention.
Industrial Applications of a
Lattice-Boltzmann Code
in Vehicle Aerodynamics.
BMW Group
Dr. Norbert Grün
International
Conference for
Mesoscopic
Methods in
Engineering
and Science,
July 26-29, 2004