drivaer -aerodynamic investigations for a new realistic ... · • road = moving wall •...
TRANSCRIPT
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DrivAer - Aerodynamic Investigations for a New
Realistic Generic Car Model using ANSYS CFD
Thomas Frank(*), Benedikt Gerlicher(*), Juan Abanto(**)
(*) ANSYS Germany, Otterfing, Germany(**)ANSYS Inc., Lebanon, NH, USA
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October 31, 2013 22013 Automotive Simulation World Congress
Contents
• The DrivAer Benchmark by TU Munich, Institute of Aerodynamics and Fluid Mechanics− Investigated DrivAer car model variants
• The meshing process• CFD investigations for the DrivAer fastback car:
− F_S_woM_wW− F_D_wM_wW
• Comparison to TU Munich wind tunnel data• Cross-comparison of ANSYS CFX and ANSYS Fluent• Summary & Outlook
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October 31, 2013 32013 Automotive Simulation World Congress
Objectives
• Automotive AerodynamicsValidation of ANSYS CFD
• Generic reference model with modern car geometry
• Investigation of meshing process and technologies for contemporary and complex car body geometry− Including wheels− Including mirrors− Including detailed floor with exhaust system
• Validation of ANSYS CFX & ANSYS Fluent• Comparison to TU Munich wind tunnel data• Turbulence model validation and data comparison
���� steady/transient SST and SAS-SST
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October 31, 2013 42013 Automotive Simulation World Congress
DrivAer GeometryDevelopment of the DrivAer model by TU Munich
BMW 3 Series
Limousine
Audi A4
Limousine
Courtesy by TU Munich, Inst. of Aerodynamics
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October 31, 2013 52013 Automotive Simulation World Congress
DrivAer GeometryDevelopment of the DrivAer model by TU Munich
BMW 3 Series
Limousine
Audi A4
Limousine
DriveAer Car Body
Courtesy by TU Munich, Inst. of Aerodynamics
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October 31, 2013 62013 Automotive Simulation World Congress
DrivAer GeometryDevelopment of the DrivAer model by TU Munich
Total length 4613mm
Total width 1820mm
Total height 1418mm
Wheelbase 2786mm
Track width front 1520mm
Track width back 1527mm
Courtesy by TU Munich, Inst. of Aerodynamics
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October 31, 2013 72013 Automotive Simulation World Congress
Testcase Description - GeometryDevelopment of the DrivAer model by TU Munich
Rear end
Underbody
Mirrors
Wheels
Courtesy by TU Munich, Inst. of Aerodynamics
Naming conventions
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October 31, 2013 82013 Automotive Simulation World Congress
Testcase Description - GeometryDevelopment of the DrivAer model by TU Munich
Rear end
Underbody
Mirrors
Wheels
Courtesy by TU Munich, Inst. of Aerodynamics
Naming conventions
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October 31, 2013 92013 Automotive Simulation World Congress
Testcase Description - GeometryDevelopment of the DrivAer model by TU Munich
Rear end
Underbody
Mirrors
Wheels
Courtesy by TU Munich, Inst. of Aerodynamics
Naming conventions
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October 31, 2013 102013 Automotive Simulation World Congress
Testcase Description - GeometryDevelopment of the DrivAer model by TU Munich
Rear end
Underbody
Mirrors
Wheels
Courtesy by TU Munich, Inst. of Aerodynamics
Naming conventions
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October 31, 2013 112013 Automotive Simulation World Congress
Experimental Facility and Data
• The experimental data is provided by the Institute of Aerodynamics and Fluid Mechanics, TU Munich
• Experiments are performed in a wind tunnel includin g a moving belt @ 1:2.5 model scale
Courtesy by TU Munich, Inst. of Aerodynamics
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October 31, 2013 122013 Automotive Simulation World Congress
Test Case ConditionsModel Scale 1:2.5
Inlet velocity 40 m/s
Air Temperature 20℃
Air Pressure 1.013 bar
Air Density 1.2047 kg/m3
Reference Length (Length of car model) 1.84 m
Resulting Reynolds number 4.87*106
Ground velocity 40 m/s
Courtesy by TU Munich, Inst. of Aerodynamics
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October 31, 2013 132013 Automotive Simulation World Congress
Experimental UncertaintiesAlso DrivAer experiments are carried out with care, the data are subject to the following uncertainties :• Blockage of the TUM wind tunnel cross sectional are a is rather
high for the car model• Existent pressure gradient over the length of the m easurement
section of the wind tunnel• Efficiency of boundary layer scoop• Necessity to take into account rolling friction and aerodynamic
effects from rotating wheels and tire rim design; b ut tires are not connected to the weights (i.e. C D and C L measurement system)
• Disturbance from model support system (MSS) and whe el supports on car aerodynamics
• Influence from interaction of the rolling road syst em (RSS) with not moving side floor of the wind tunnel
• General measurement errors of applied measurement technologies (weights, pressure transducers)
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October 31, 2013 142013 Automotive Simulation World Congress
Investigated DrivAer Car Models
E_S_woM_woWEstate_
Smooth underbody_
without Mirrors_
without Wheels
F_S_woM_wWFastback_
Smooth underbody_
without Mirrors_
with Wheels
F_D_wM_wWFastback_
Detailed underbody_
with Mirrors_
with Wheels
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October 31, 2013 152013 Automotive Simulation World Congress
Investigated DrivAer Car Models
E_S_woM_woWEstate_
Smooth underbody_
without Mirrors_
without Wheels
F_S_woM_wWFastback_
Smooth underbody_
without Mirrors_
with Wheels
F_D_wM_wWFastback_
Detailed underbody_
with Mirrors_
with Wheels
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October 31, 2013 182013 Automotive Simulation World Congress
Geometry & Computational Domain
Dimensions of the Bounding Box
Model scale 1 : 1 1 : 1
Total length 10L 46.13 m
Total width 11B 20.02 m
Total height 8H 11.34 m
Model Scale to Car Size 1:1
Inlet velocity 16 m/s
Air Temperature 20℃
Air Pressure 1.013 bar
Air Density 1.2047 kg/m3
Reference Length (Car Length) 4.6
Resulting Reynolds number 4.87*106
Ground velocity 16 m/s
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October 31, 2013 192013 Automotive Simulation World Congress
Meshing Process
• Meshing process using:− ANSYS DesignModeler 14.5− ANSYS TGrid in Fluent 14.5
ANSYS DM
Geometry
Cleanup
TGrid Meshing
IGES CAD
Geometry
ANSYS DM
.agdb Geometry
Export
TGrid
Tet/Prism
Mesh Export
ANSYS CFX
ANSYS Fluent
TGrid 14.5 :
CAD-import
conformal tesselation
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October 31, 2013 202013 Automotive Simulation World Congress
Geometry Clean -up
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October 31, 2013 212013 Automotive Simulation World Congress
F_D_wM_wW: Computational Mesh2• Full 3d model ���� SAS-SST• ~110 Mill. Cells• Four refinement zones• 20 Inflations on the car• 15 Inflations on the road• y+<1 on the car body• MRF-Zones for the rims
(MRF=Moving Reference Frame)
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October 31, 2013 222013 Automotive Simulation World Congress
Connection between road and wheels
Mesh Generation
Tire Surface
Road Surface
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October 31, 2013 232013 Automotive Simulation World Congress
• Road = Moving wall
• Rotational boundary condition on tire
• MRF-Zones at the rims (Moving Reference Frame)
Setup for Road & Wheels
RIMS MRFINTERFACE
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October 31, 2013 242013 Automotive Simulation World Congress
ANSYS TGrid Meshing Details
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October 31, 2013 252013 Automotive Simulation World Congress
Simulation Matrix
Timestep Mesh 1 Mesh 2Mesh 2 Full
Domain
Steady SST ∆t = 0.1ms
Steady SST ∆t = 1 ms
Steady SST ∆t = 10 ms
Transient SST ∆t = 1 ms
Transient SAS-SST ∆t = 1 ms
Transient SAS-SST ∆t = 0.2 ms
– ANSYS CFX investigation – ANSYS Fluent investigation
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October 31, 2013 262013 Automotive Simulation World Congress
Investigation Results F_S_woM_wW
F_S_woM_wW - Fastback_Smooth underbody_without Mirrors_with Wheels
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October 31, 2013 272013 Automotive Simulation World Congress
F_S_woM_wW : Comparison of Drag
∗∗∗∗ - Simulation did not totally converge within the given coefficient loops
Averaged over 60s 1500 time steps 1440 time steps 2000 time steps 6382 time steps
∗∗∗∗
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October 31, 2013 282013 Automotive Simulation World Congress
ANSYS CFD, SAS-SST – CD Histories
CD, Experiment =0.2519
CD, mean, Fluent=0.2684
CD, mean, CFX =0.2834
Experimental data by courtesy of TU Munich, Inst. o f Aerodynamics
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October 31, 2013 292013 Automotive Simulation World Congress
ANSYS CFD, SAS-SST –Cp at Symmetry Plane y=0mm (top)
Experimental data by courtesy of TU Munich, Inst. o f Aerodynamics
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October 31, 2013 302013 Automotive Simulation World Congress
ANSYS CFD, SAS-SST –Cp at Symmetry Plane y=0mm (bottom)
Experimental data by courtesy of TU Munich, Inst. o f Aerodynamics
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October 31, 2013 312013 Automotive Simulation World Congress
ANSYS CFD, SAS-SST –Cp at z=0.15m
z=0.15m
Experimental data by courtesy of TU Munich, Inst. o f Aerodynamics
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October 31, 2013 322013 Automotive Simulation World Congress
Comparison of Q -Criterion
URANS SST
Δ t=0.001s
2,942 Timesteps
=> 2.942s
SAS-SST
Δ t=0.001s
High Resolution
1,000 Timesteps
=> 1s
Q criterion level = 0.0005
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October 31, 2013 332013 Automotive Simulation World Congress
Comparison of Q -CriterionANSYS Fluent
ANSYS CFX
Fluent, SAS-SST
Δt=0.2 ms
15000 time steps
3.0 s total time
CFX, SAS-SST
Δt=0.2 ms
14419 time steps
2.884s total time
Q criterion level = 0.0005
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October 31, 2013 342013 Automotive Simulation World Congress
Vortex Structure from Transient Simulation, SAS -SST, ∆∆∆∆t=0.2ms
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October 31, 2013 352013 Automotive Simulation World Congress
Vortex Structure from Transient Simulation, SAS -SST, ∆∆∆∆t=0.2ms
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October 31, 2013 362013 Automotive Simulation World Congress
Investigation Results F_D_wM_wW
F_D_wM_wW - Fastback_Detailed underbody_with Mirrors_with Wheels
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October 31, 2013 372013 Automotive Simulation World Congress
ANSYS CFD, URANS SST & SAS -SST – CD Histories –
CD, Experiment =0.2927
CD, mean, Fluent=0.3114
CD, mean, CFX =0.3158
Experimental data by courtesy of TU Munich, Inst. o f Aerodynamics
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October 31, 2013 382013 Automotive Simulation World Congress
ANSYS CFD, SAS-SST –Cp at Symmetry Plane (top)
Experimental data by courtesy of TU Munich, Inst. o f Aerodynamics
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October 31, 2013 392013 Automotive Simulation World Congress
ANSYS CFD, SAS-SST –Cp at Symmetry Plane (bottom )
Experimental data by courtesy of TU Munich, Inst. o f Aerodynamics
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October 31, 2013 402013 Automotive Simulation World Congress
ANSYS CFD, SAS-SST –Cp at z=0.15m (left)
Better agreement
between CFD and data for
CP extracted from the left
side of the car
z=0.15m
Experimental data by courtesy of TU Munich, Inst. o f Aerodynamics
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October 31, 2013 412013 Automotive Simulation World Congress
ANSYS CFD, SAS-SST –Cp at z=0.15m (right)
z=0.15m
Experimental data by courtesy of TU Munich, Inst. o f Aerodynamics
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October 31, 2013 422013 Automotive Simulation World Congress
ANSYS CFX, URANS SST, ∆∆∆∆t=0.2ms– Asymmetric wake –
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October 31, 2013 432013 Automotive Simulation World Congress
ANSYS CFX, URANS SST, ∆∆∆∆t=0.2ms– Asymmetric wake –
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October 31, 2013 442013 Automotive Simulation World Congress
ANSYS CFX, URANS SST, ∆∆∆∆t=0.2ms– Asymmetric wake –
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October 31, 2013 452013 Automotive Simulation World Congress
ANSYS Fluent SAS -SST, ∆∆∆∆t=0.2ms– Q-Criterion Isosurfaces –
Q criterion level = 0.0005
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October 31, 2013 462013 Automotive Simulation World Congress
ANSYS Fluent SAS -SST, ∆∆∆∆t=0.2ms
Lambda-2 criterion level = 0.01
Bottom view of F_D_wM_wW
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October 31, 2013 472013 Automotive Simulation World Congress
ANSYS Fluent SAS -SST, ∆∆∆∆t=0.2ms
Lambda-2 criterion level = 0.001
Bottom view of F_D_wM_wW
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October 31, 2013 482013 Automotive Simulation World Congress
Summary & Conclusions
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October 31, 2013 492013 Automotive Simulation World Congress
Summary & Outlook
• Simulating the DrivAer car is first of all a meshing challenge!
• Established a meshing process, where ANSYS TGridin Fluent 14.5 and direct CAD model tessellation was applied
• Three different DrivAer cars meshed and simulated���� (U)RANS SST and SAS-SST comparison
• Applied feasible amount of CFD best practice relate d investigations:− mesh and timestep dependence− iteration error ���� convergence− steady vs. transient− (U)RANS vs. scale-resolving turbulence modeling
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October 31, 2013 502013 Automotive Simulation World Congress
Summary & Outlook (cont.)
• CFD predicted slightly higher C D values in comparison to data− Influence from wind tunnel geometry− Quite high blocking ratio for this large model in T UM wind tunnel− Influence from road simulator vs. entirely moving r oad (CFD)
���� Desirable to have PIV data for flow field compariso n
• Good and very consistent comparison between ANSYS C FX and ANSYS Fluent for investigated DrivAer car models
• Further streamlining and refinement of the ANSYS TG rid in Fluent based meshing process possible���� e.g. longer extension of refined zones behind the ca r
• Reasonable good agreement for C Pvalue comparison to data
• Influence from the model support system (MSS) on C P on the top of the car roof observable
• Differences at point of vortex impingement in the rear of the car
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October 31, 2013 512013 Automotive Simulation World Congress
Questions?
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October 31, 2013 522013 Automotive Simulation World Congress
References
1. http://www.aer.mw.tum.de/abteilungen/automobilaerod ynamik/drivaer/
2. http://www.cfd-online.com/Wiki/DrivAer_Model
3. A. Heft, T. Indinger, N. Adams: “Experimental and Numerical Investigation of the DrivAer Model” , ASME 2012, July 8-12, 2012, Puerto Rico, USA, FEDSM2012-72272
4. A. Heft, T. Indinger, N. Adams: “Introduction of a New Realistic Generic Car Model for Aerodynamic Investi gations” , SAE 2012 World Congress, April 23-26, 2012, Detroit , Michigan, USA, Paper 2012-01-0168
5. P. Nathen: “Investigation of the Complex Turbulent Flow around a Generic Vehicle” , MSc Thesis, TU Munich, Inst. Aerodynamics and Fluid Dynamics, April 2012