Validation of a novel open source software suite against an extensive data set of automotive aerodynamics test cases

1. VALIDATION OF A NOVEL CAE
SOFTWARE SUITE AGAINST AN
EXTENSIVE DATA SET OF
AUTOMOTIVE AERODYNAMICS
TEST CASES
Angus Lock
Head of Aerodynamics
Auto Research Center

2. Streamline Solutions | Who We Are
AUTO RESEARCH CENTER
Automotive Engineering R&D, Wind
Tunnel, 7-Post & Gearbox Rig
ENGYS
CFD Engineering, MDO, Open Source
Software Development, User Support
STREAMLINE SOLUTIONS
Joint
Venture
www.arcindy.com www.engys.com

3. Streamline Solutions | Open Source
• Streamline Solutions
have built an end to
end open source CFD
process
• Scripting, geometry
clean-up and
creation, morphing,
meshing, solving,
optimization and post-
processing are all
conducted using open
source tools

4. What Is ELEMENTS?
• CAE tool with embedded best practices for
automotive applications
• Based on HelyX Core
• Extension of ESI OpenFOAM® library
• Beta repository available within 3-6 months
• Up-to-date upgraded within 6-12 months
• Fully supported via GUI and setup tool
• 2 major releases per year
• Up to 4 minor releases (issue resolution)
• Currently based on latest OpenFOAM-2.1.x
• 2.2.x based release scheduled for Q3 2014
© 2013 STREAMLINE SOLUTIONS. All rights reserved.

5. CFD Modelling | Mesh Setup
• Base mesh scaled by overall
vehicle dimensions
• Leak/crack detection and fixing
• Hex dominant mesh
• Automatic feature edge capturing
• Improved surface snapping
• Full projection of near-wall layers
to inlets, outlet, symmetry planes
• Surface-based cell-spacing
• Volumetric refinement boxes and
buffer layer refinement
• Stagnation and wake zone
refinement tailored to vehicle type
• Mesh size 50-80 million cells

6. CFD Modelling | Solver Setup
• Transient DDES formulation
• Spalart-Allmaras model with wall functions
• Robust first/second-order blending for advection
scheme based on CFL and near-wall distance
• Run time is scaled by vehicle length and free-
stream velocity
• Multiple time-steps (coarse and fine)
• Reduced overall memory usage
• Improved scaling for parallel processors
© 2013 STREAMLINE SOLUTIONS. All rights reserved.

7. CFD Modelling | Post-Processing
• Automated, batch driven co- and post-processing:
– Contour plots of U, p, tauw, Unw fields
– Isosurfaces of Ptot
– Averaged CD and CL, Cp
– Force development plots
– HTML / WEBGL reporting C:/Users/alock/Desktop/motorBike/test.html

8. Validation | Vehicle Types
• 100+ different vehicle types:
– Sedan
– Hatchback
– Estate
– SUV
– Sportscar
– Streamliner
– Nascar
– Indycar
– Light Duty Truck
– Heavy Duty Truck
© 2013 STREAMLINE SOLUTIONS. All rights reserved.

9. Validation | Parametric Changes
• Fixed Ground
• 5-belt Moving Ground
• Single Belt Moving
Ground
• Yaw Angle
• Ride Height
• Test Speed
• Vehicle Modifications
(e.g. Open or Closed
Cooling, Spoiler on/off,
Underbody Panels on/off)

10. Validation | ARC Wind Tunnel
• Max Wind Speed : 50 m/s
• Max Road Speed: 50 m/s
• Nozzle Size: 2.3 m x 2.1 m
• Contraction Ratio: 4.8 : 1.0
• Moving Belt Size: 3.4 m x 1.7 m
• Boundary Layer Thickness: 1mm
• Main Fan Motor Power: 320 kW
• Primary BL Motor Power: 80 kW
• Secondary BL Motor Power: 19 kW
• Rolling Road Motor Power: 120 kW
Rapid prototyping, workshops &
office space
Moving ground, scale-model wind tunnel
Vehicle dynamics 7-post rig

11. Validation | Aerodynamic Balance
• Models are mounted in the tunnel by means of an overhead sting
• The 6-component balance is contained within the model
• Secondary balance for tractor-trailer

12. Validation | Instrumentation
• 128 pressure channels to allow for evaluation of surface
pressures from around the model
• Cooling mass-flow measurement by a grid of up to 14 vane type
anemometers

13. Validation | Flowfield Comparison
• Extensive work was
conducted to compare
flow field structure
• The figures below
illustrate the correlation
between the CFD
predictions and wind
tunnel data for the
DrivAer models (SAE
2012-01-1068)
13

14. Validation | Flowfield Comparison
14
Upper surfaces Lower surfaces
• Comparison of centerline pressures on fastback

15. Validation | Flowfield Comparison
15
Experiment CFD
• Comparison of surface pressures on fastback windshield

16. Validation | Flowfield Comparison
16
Experiment CFD
• Comparison of surface pressures on fastback windshield

17. Validation | Flowfield Comparison
17
Experiment CFD
• Comparison of surface pressures on fastback windshield

18. Validation | Flowfield Comparison
18
Experiment CFD
• Comparison of surface pressures on fastback windshield

19. Validation | Flowfield Comparison
19
Experiment CFD
• Comparison of surface pressures on fastback windshield

20. Validation | Results
CD CLF CLR
1 DRIVAER Estate n/a 40% SingleBelt 2.40%
2 DRIVAER Fast n/a 40% SingleBelt -0.41%
3 DRIVAER Notch n/a 40% SingleBelt 0.41%
4 Sedan 1 open 100% 5 Belt 0.67% -0.67% -6.56%
open 40% SingleBelt 0.00% -7.19% 4.45%
closed 40% SingleBelt 1.74% -2.48% 4.61%
5 Sedan 2 open 100% 5 Belt 0.00% -1.87% -0.37%
blanked 100% Fixed 1.57% -26.38% 9.84%
6 Sedan 3 closed 100% Fixed 2.35%
open 40% SingleBelt 0.32% -2.27% -2.27%
closed 40% SingleBelt 2.03% -1.35% 2.03%
7 Estate1 open 40% SingleBelt -0.32% 11.04% 26.62%
8 Estate2 open 100% 5 Belt -0.95% -3.81% -3.17%
9 Hatchback1 open 40% SingleBelt 3.09% 7.21% 19.75%
10 Hatchback2 open 100% 5 Belt 2.18% -22.55% 12.00%
11 SUV 1 open 40% SingleBelt 0.81% 6.59% -16.76%
12 NASCAR 1 40% SingleBelt 2.22%
13 NASCAR 2 open 40% SingleBelt -1.25% -32.67% -10.47%
14 Sem i-Truck1 open 12.5% SingleBelt 0.19%
15 LightTruck1 open 20%% SingleBelt -0.38% -5.09% -10.38%
1.2% 9.37% 9.24%AverageErrorM agnitude
Scale
Ground
Sim ulation
CoefficientsVehicleNo. VehicleM odel
Grille
(open,
closed,
blanked)
W ind TunnelData Elem ents
CD CLF CLR
21 Sem i-Truck2 open 0.000 0.125 SingleBelt 0.19%
open 0.000 0.125 SingleBelt -1.13%
open 6.000 0.125 SingleBelt 2.63%
open 6.000 0.125 SingleBelt 3.45%
open 6.000 0.125 SingleBelt 3.45%
open 0.000 0.125 SingleBelt 2.25%
open -6.000 0.125 SingleBelt 4.85%
open 9.000 0.125 SingleBelt 2.50%
open -9.000 0.125 SingleBelt 3.13%
open 9.000 0.125 SingleBelt 0.00%
open 9.000 0.125 SingleBelt 2.06%
22 LightTruck2 open 0.000 0.125 SingleBelt -0.38% -5.09% -10.38%
open 6.000 0.125 SingleBelt 2.69% -0.36% -17.95%
open 3.000 0.125 SingleBelt 1.47% -3.87% 14.73%
23 Sem i-Truck3 open 0.000 0.125 SingleBelt 0.57%
open 3.000 0.125 SingleBelt 4.13%
open 6.000 0.125 SingleBelt 4.98%
open 9.000 0.125 SingleBelt 1.11%
24 Sem i-Truck4 open 0.000 0.125 SingleBelt 5.86%
2.5% 3.11% 14.35%
Yaw
AverageErrorM agnitude
Scale
Ground
Sim ulation
CoefficientsVehicleNo. VehicleM odel
Grille
(open,
closed,
blanked)
W ind TunnelData Elem ents
• Target is a best practice that
delivers drag coefficient errors
less than 2% for passenger cars,
and 4% for heavy trucks.

21. Conclusions
• The result of this project is a set of best practices that
consistently delivers drag coefficient error magnitudes
less than 2% for passenger cars, and 4% for heavy
trucks.
• The CFD results have been heavily validated in a range
of wind tunnels, and for a variety of different vehicle
shapes.
• For typical mesh sizes of 50-80 million cells, running on
144 cores, turnarounds of 16-24 hours are the median.
This is considered to be extremely competitive when
compared to other commercial CFD codes.