VKI-RVAD-2005-BMW-Presentation
-
Upload
norbert-gruen -
Category
Documents
-
view
52 -
download
0
Transcript of VKI-RVAD-2005-BMW-Presentation
Application of aLattice-Boltzmann Code inAutomobile and MotorcycleAerodynamics.
Dr.-Ing. Norbert GrünAerodynamics Simulation
Lecture Series on Road Vehicle Aerodynamicsvon Karman Institute for Fluid Dynamics, BrusselsMay 30 – June 03, 2005
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 2
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Outline
� Aerodynamic Development Process
� Physics Overview
� Simulation Process
� Validation Examples
� Various Applications
� Conclusion
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 3
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
CFD in the Aerodynamic Development Process
Simultaneous Usage of Experimental & Virtual Tools
Serial Development PhaseConcept Phase
Prototypes100%
Windtunnel Model
CFD-Models
A
C
D
F
CC
F
A
B
C
D
E
F
Styling-Freeze
Styling–Competition
A
C
D
F
CC
F
A
B
C
D
E
F
40%Windtunnel Models
CFD-Models
Proportion-Studies
CFD-Models
Sty
ling
Pro
cess
Aer
oA
naly
sis
Too
ls
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 4
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Requirements on CFD as a Productive Tool
• Accuracy (∆CD <±0.005, ∆CL <±0.010), at least for trends
• Geometry input preparation minimized
• Ability to handle complex geometries (underhood & underbody)
• Deliver results in a reasonable timeframe (over night)
• Easy to use (by non-numerics specialists)
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 5
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
CFD Resources
285
222
95
48
248
253
0
50
100
150
200
250
300
1997 1998 2000 2001 2002 2004 2005
Tot
alN
umbe
rofP
roce
ssor
s
SUNSUN
SGI
2 x SGI
(95+127)
1 x SGI
(127)
2 x HP
(je 63)
SUN
1 x SGI
(160)
2 x HP
(je 63)
decicated PowerFLOW servers
Number of Processors
Speed-Up
Efficiency onParallel Computers
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 6
New Goal :
• Construct simplified microscopic description (mesoscopic)that still contains the essential micro-physics to achievedesired macroscopic behaviour.
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Motivation for Lattice-Boltzmann Methods (LBM)
Microscopic______________
Mesoscopic______________
Macroscopic
Microscopic______________
Mesoscopic______________
Macroscopic
Kinetic Theory
Lattice Methods
Navier-Stokes
Kinetic Theory
Lattice Methods
Navier-Stokes
• Simulate fluid at microscopic level since the physics is simplerand more general than macroscopic, continuum (PDE) approach.
• However, complete reproduction of molecular dynamicsis much too expensive (today and also in the „near“ future).
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 7
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
LBM vs. Traditional CFD Methods
Real FluidFree molecules in continous space
Kinetic TheoryMicroscopic particles (Boltzmann Equation)
Real FluidFree molecules in continous space
Kinetic TheoryMicroscopic particles (Boltzmann Equation)
Traditional CFD Methods___________________________
Chapman-Enskog ExpansionStatistical Method applied to real gases
Navier-Stokes EquationsConservation of Mass, Momentum and Energy
Numerical MethodsDiscrete Approximation of
Partial Differential Equations
Traditional CFD Methods___________________________
Chapman-Enskog ExpansionStatistical Method applied to real gases
Navier-Stokes EquationsConservation of Mass, Momentum and Energy
Numerical MethodsDiscrete Approximation of
Partial Differential Equations
Lattice-Boltzmann_________________________________
Simulation of Particle Dynamics
• No integration of partial differential eqn.
• Movement & collisions conservemass, momentum and energy
• No numerical instabilities
Lattice-Boltzmann_________________________________
Simulation of Particle Dynamics
• No integration of partial differential eqn.
• Movement & collisions conservemass, momentum and energy
• No numerical instabilities
ResultsFluid dynamic quantities at discrete points in space and time
ResultsFluid dynamic quantities at discrete points in space and time
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 8
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Basics of Kinetic Theory
Boltzmann Equation ),,(),,(),,(),,( tcxCtcxfctcxft
tcxfdt
d rrrrrrrrr =∇⋅+∂∂=
Describes the rate of change of the velocity distribution function due to nonequilibrium
Velocity Distribution Function ),,( tcxfrr
Gives the number of particles at time t per unit volume in phase space around x and c
Collision Term C satisfies the necessary conservation laws
∫ = 0)()( cdcCcrrrξ
Mass
Momentum
Energy
1)( =crξ
ccrr =)(ξ
2
2
1)( cc
rr =ξ
Describes fluid behaviour using the interactions of air molecules
∫= cdtcxftxrrrr
),,(),(ρDensity
∫= cdctcxftxutxrrrrrr
),,(),(),(ρMomentum
∫ −= cductcxftxErrrrrr 2))(,,(),(Energy
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 9
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Basics of Lattice Methods
Replace the continuous velocitydistribution function by a discreteset of particle velocities defined ona lattice of equal shaped cubic cells
Vtxiftxintcxf ∆≡→ ),(),(),,(rrrr
},...,1;{ miicc =∈ rr
Particle dynamics is now described by the Lattice Boltzmann Equation
),(),(),( txiCtxintticxinrrr +=∆++
The collision operator C determines if a lattice systemproduces a physically meaningfull fluid behaviour
During an elementary time interval particles can only hop fromone center of a cell to one of the m near neighbouring cellsaccording to their velocity
)1(=∆txr
ticx ∆+ rr
icr
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 10
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Macroscopic Quantities
• Macroscopic quantities, such as density, pressure, velocity, etc.are computed by statistical methods from the state vectors
DENSITY
MOMENTUM
ENERGY
• Higher order moments (Energy Flux, Stress Tensor)are also available locally (do not involve derivatives)
∑=j
j txntx ),(),(rrρ
∑=j
jj txnctxu ),(),(rrrrρ
[ ]∑ •=j
jjj txnccmtxE ),(),( 21 rrrr
0=urρ 0≠u
rρ
Vector lengthdenotes numberof particles movingin that direction
m
TkVRMS 3= ≈ 1000 m/s for oxygen at 20° C
Particle velocities can be much higherthan the resulting macroscopic velocity
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 11
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Transport Coefficients in Lattice Methods
Kinetic Theory allows to compute viscosity and thermal conductivityfrom the velocity distribution function !
TD
Da MFPMFP
2+== λλνThe molecular viscosity depends on themean free path between collisions andthe speed of sound (temperature).
Viscosity is set by adjusting the relaxation parameter of the collision operator
{ }( )
( ) jceqjc
eqjjcj
jjjjj
nn
nntxn
txnCtxntcxn
ωωω
−+=−−=
+=++
1
),(
),(),()1,(r
rrrr
Lattice-Boltzmann Equation
Viscosity is reduced by reducing the meanfree path or equivalently the timebetween collisons
Collision frequency for2<cω 0>Lattcν
cω/1
−=
2
11
cT ων
Chapman-Enskog Expansion
−+=
2
11
2
2
c
D
T ωρλ
Viscosity Thermal Conductivity
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 12
Simple 2D Model with 4 directions and 3 speeds
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Concept of Particle Models
• The fluid is composed of a very large number of particles(not molecules, this is a mesoscale model)
• Particles are only allowed to move in certain directions on the latticewith limits on how far they can get in a single time step (their speed)
• The state of the fluid is represented by the number njiof particles moving with speed (energy) j in direction i
1
PossibleDirections
2
3
4
Particle withspeed 1 indirection 4
Particle withspeed 1 indirection 4
Particle withspeed 2 indirection 3
Particle withspeed 2 indirection 3
A model allowing 3 speeds(0,1,2) and 4 directions re-presents the particle popu-lation by 9 state vectors nji
n0 ( = n01 = n02= n03= n04)n11 , n12 , n13 , n14n21 , n22 , n23 , n24
State vectors are integers !Particle with speed 0
Particle with speed 0
The maximum number of particles per statedepends on the number of bits for state vectors !
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 13
• Repetition evolves time (t -> t+1) and forms an inherently transient solver
• The process of evolving ( solving ) the update equation is inherentlyparallel (computationally efficient) and stable (computationally robust)
is the collision operator that exactly conserveslocal mass, momentum and energy
jC
• Also drives local distribution to equilibrium (entropy maximized)neq
j
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Fluid – Fluid Interaction
• Dynamics in the fluid consists of two steps : MOVE & COLLIDE
• Update equation { }),(),()1,( txnCtxntcxn jjjjj
rrrr +=++
Time tTime t+1
n1
n2
n‚2
n‘1
Example : Mass Conservation
n'1 + n'2 = n1 + n2
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 14
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Fluid – Surface Interaction
Facets
Solid Body
Voxels
Surfels
Automatic discretization
The intersection of voxels with the facetsrepresenting solid bodies creates surfelswhich define the computational surfaceresolution.
In each timestep surfels gather and scatterparticles, altering their momentum accordingto the boundary conditions
Surface forces depend on the momentumexchange between fluid and wall
VinVout
Specular Reflection
Vtin
Vnin
Vtout
Vnout
Vin Vout
Bounce Back Reflection
Slip ConditionNormal component invertedTangential component unchanged
Momentum balance →→→→ normal force only
No Slip ConditionNormal component invertedTangential component inverted
Momentum balance →→→→ normal & tangential force
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 15
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Reynolds-Number Regimes
Regime Reynolds Number PowerFLOW__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Low Re < 10,000 Direct SimulationTransitional 10,000 < Re < 100,000 currently not applicableHigh Re > 100,000 Boundary Layer Simulation
approximate values,actual values problem dependent
Regime Reynolds Number PowerFLOW__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Low Re < 10,000 Direct SimulationTransitional 10,000 < Re < 100,000 currently not applicableHigh Re > 100,000 Boundary Layer Simulation
approximate values,actual values problem dependent
Solid Wall Solid Wall
Modeled Flow
Direct SimulationUsing a large number of voxels theboundary layer is resolved down to the wallwith zero velocity at the wall.Particles are bounced back from the wallexactly canceling their momentum.
Boundary Layer SimulationThe presence of the wall is modeled by ashear stress at the slip surface.Particles loose momentum at the slip surfaceaccording to the (modified) law of the wall.
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 16
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Turbulent Wall Model
( ) Byu += ++ ln1
κ
Assumption: Universal velocity profile of a turbulent2D boundary layer with dp/dx=0
++ = yu
:505for ≤≤ +y
:5for ≤+y
0.5
4.0
≈≈
B
κ
τu
uu =+
υτu
yy =+
ρτ
τwu =
PowerFLOW Extension:
• include the effect of a longitudinal pressure gradient
∂∂+=→ ++++
x
pfAAyUyU 1mit)/()(
The wall model provides the wall shear stressto alter the momentum of scattered particles.
wτ
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 17
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Approaches to Turbulence Modeling
Dissipation
dl LLength
ν/2dl UL /Time
Turbulent Scales
4/3Re/ ≈dlLRange
( ) ( ) 2/12 Re/// ≈νdlULRange
RANS = Reynolds AveragingAll scales of motion are described by statistical methods (time averaged )
LES = Large Eddy SimulationAlle Skalen werden berechnetmodeled computed via modified unsteady Navier-Stokes equations
Filter Width (Grid Size)
DNS = Direct SimulationAll scales of motion in space and time are computed
VLES = Very Large Eddy Simulation
modeled computed unsteady
Coherent anisotropic eddiesUniversal eddies
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 18
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
CFD Simulation Process
CAD/CAS ModelCATIA/ALIAS
CAD/CAS ModelCATIA/ALIAS
Clay ModelPOLYWORKS
Clay ModelPOLYWORKS
Simulation Model(Surface Facetization)
ANSA, QUICKMESH, PowerWRAP, ...
1-5 Days
Simulation Model(Surface Facetization)
ANSA, QUICKMESH, PowerWRAP, ...
1-5 Days
SimulationPowerFLOW
1 Day
SimulationPowerFLOW
1 Day
PostprocessingPowerVIZ
PostprocessingPowerVIZ
ResultResult
Shape Modificationof CAD/CAS Data
Shape Modificationof CAD/CAS Data
Morphing of theSurface Mesh
(PowerCLAY)
Morphing of theSurface Mesh
(PowerCLAY)
Turnaround
2-6 Days
Turnaround
2-6 Days
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 19
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
CFD Process: Geometry Preparation (Wrapping)
Complete STL Data(imperfect facetization)
� Gaps & holes� Overlaps & intersections� Interior details
Wrap
Wrapped Surface Facetization(ready for simulation)
� Water-tight single solid� Controlled granularity� Interior details removed
Preparation time reducedfrom days to hours !
Complete Set of CAD Data
Export or
facetize withoutcleanup or de-featuring
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 20
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
CFD Process: Geometry Morphing
Modification of the surface facetization instead of changing the CAD datawhich would require a re-facetization.
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 21
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
CFD Process: Geometry Input
The surfacefacetizationrepresents thegeometry only.
It does not setthe resolutionfor the simulation.
Depending on thelevel of detail up to2-3 million facetsare used.
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 22
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
CFD Process: Modular Assembly
The completeconfiguration maybe composed ofany number ofcomponents.
Components may be arranged in anarbitrary fashion and also intersect each other.
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 23
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
CFD Process: Automatic Discretization
Voxels(Fluid Cells)
Solid Body
Facets(G
eometry)
Surfels
(Surface
Elements)
Typical voxel countsfor external aerodynamiccases range from 20-100milion cells.
Geometry representationembedded in a lattice ofcubic cells (with differentlevels of resolution).
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 24
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
CFD Process: Simulation Timestep
� Simulations are always run in transient mode
� The physical time per timestep is determined by resolution and test conditions
[ ]epsec/timestV
xMaa
V
xVt LatticeLattice
∞∞
∆⋅⋅=∆⋅=∆
� Strictly there is no room left for the user to control the timestep
� Artificially elevating the Mach number increases the time step
� Example:
mmxepsec/timesttMaCT
smV
210515.020
/506
=∆⋅=∆⇒=⇒°=
=−
∞
∞
That means 1 secondof physical time requires 200,000 timesteps
Using Ma=0.30instead of Ma=0.15cuts the run time in half !
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 25
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
CFD Process: Transient SimulationNo explicit convergence criterion, user monitors key quantities to decide when to stop the simulation.
100,000 Timesteps
(1 Timestep = 4.7 10-6 sec.)
Averaging Window
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 26
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Validation Models (Scale 1:2.5).
5series touring
Open Convertible
5series Limousine with/without Mirror
Calibration Motorcycle
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 27
Application of a Lattice-Boltzmann Code in Road 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
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 28
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Validation: Surface Pressure Distribution
Top Centerline(Geometry not to scale)
PowerFLOWExperiment
Bottom Centerline(Geometry not to scale)
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 29
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Validation: Near Surface Flow Topology
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 30
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Validation: Reynolds Effect
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 31
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Validation: Motorcycles (Windshield Variations)
0,300
0,320
0,340
0,360
0,380
0,400
0,420
0,440
Serie LT Sport
Cx
*A
Windkanal(Aschheim)
PowerFLOW
Hot Wire MeasurementPowerFLOW
Serie
LT
Sport
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 32
Application of a Lattice-Boltzmann Code in Road 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
0,400,0
Cx(x) Verteilung
Cx(x) Integral
PowerFLOW 3.4: 0.371
CX
BMW Windtunnel: 0.382
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 33
Application of a Lattice-Boltzmann Code in Road 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
0,200,0
Cz(x) Verteilung
Cz(x) Integral
CZ1
CZ2
0.011 0.0130.143 0.123
PowerFLOW 3.4
BMW Windtunnel
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 34
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Visualization : Transient Surface Pressure
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 35
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Visualization : Near Wall Streamlines
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 36
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Visualization : 3D Streamlines
Colors represent Near Surface Velocity Distribution
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 37
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Visualization: Transient Isosurface V X=0
Reverse flow (Vx<0) inside the isosurface
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 38
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Visualization : Transient Flow Field Slices
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 39
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Visualization : Transient Isosurface C pt=0
For Cpt=0 the total pressure loss is equivalent to the dynamic free stream pressure
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 40
Application of a Lattice-Boltzmann Code in Road 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
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 41
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Applications: ABAQUS Interface (Heat Transfer)Mapping heat transfer coefficients
from a PowerFLOW simulation
onto an ABAQUS structure model
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 42
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Applications: Detail Optimization (Mirror)
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 43
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Applications: Underhood Flow
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 44
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Applications: Motorcycles - Transient Flow FieldNear Surface Velocity
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 45
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Applications: Motorcycles - Transient Flow FieldReverse Flow (V x<0)
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 46
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Applications: Motorcycles - Transient Flow FieldDifferent Windshields
TouringTouring StandardStandard
SportSport
Helmkraft
StandardStandard
TouringTouring SportSport
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 47
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Applications: Motorcycle Acoustics
Punkt 92
0
20
40
60
80
100
120
140
10 100 1000 10000
Hz
dB(A
)
Experiment Berechnung_grob
Punkt 101
0
20
40
60
80
100
120
140
10 100 1000 10000
Hz
dB(A
)
Experiment Berechnung_grob
Punkt 110
0
20
40
60
80
100
120
10 100 1000 10000
Hz
dB(A
)Experiment Berechnung_grob
� Small timesteps enable high sampling rates forpressure and velocity fluctuations.
� The upper frequency limit is determined by thebackground noise of the Lattice-Boltzmann method.
� The lower frequency limit depends on the physical time(number of periods) covered by the simulation.
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 48
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Applications: Electronics Cooling
Goals: qualitatively – Heat Transfer Distribution
quantitatively – Surface Temperatures
Heat Transfer Coefficient
Velocity Magnitude
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 49
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Applications: Windtunnel Design
BMW GroupDr. Norbert Grün
Lecture Series onRoad VehicleAerodynamics
VKI, Brussels
May 30-June 3, 2005
Page 50
Application of a Lattice-Boltzmann Code in Road Vehicle Aerodynamics.
Conclusion
+ Maturity level sufficient for external aerodynamics
+ Short preprocessing phase due to automatic meshing.
+ Capability to handle complex geometries(underhood/underbody).
+ 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.
- Thermal management capabilities still under development.