nafems americas elements presentation

VALIDATION OF A NOVEL CAE SOFTWARE SUITE AGAINST AN

EXTENSIVE DATA SET OF AUTOMOTIVE AERODYNAMICS

TEST CASESAngus Lock

Head of AerodynamicsAuto Research Center

Streamline Solutions | Who We Are

AUTO RESEARCH CENTER

Automotive Engineering R&D, WindTunnel, 7-Post & Gearbox Rig

ENGYSCFD Engineering, MDO, Open

SourceSoftware Development, User

Support

STREAMLINE SOLUTIONS

Joint Venture

www.arcindy.com www.engys.com

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

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.

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

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


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

Validation | Vehicle Types • 100+ different vehicle types:

– Sedan– Hatchback– Estate– SUV– Sportscar– Streamliner– Nascar– Indycar– Light Duty Truck– Heavy Duty Truck


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)

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

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

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

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

Upper surfaces Lower surfaces

• Comparison of centerline pressures on fastback


15

Experiment CFD

• Comparison of surface pressures on fastback windshield


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Experiment CFD



17

Experiment CFD



18

Experiment CFD



19

Experiment CFD


Validation | ResultsCD CLF CLR

1 DRIVAER Estate n/ a 40% Single Belt 2.40%

2 DRIVAER Fast n/ a 40% Single Belt -0.41%

3 DRIVAER Notch n/ a 40% Single Belt 0.41%

4 Sedan 1 open 100% 5 Belt 0.67% -0.67% -6.56%

open 40% Single Belt 0.00% -7.19% 4.45%

closed 40% Single Belt 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% Single Belt 0.32% -2.27% -2.27%

closed 40% Single Belt 2.03% -1.35% 2.03%

7 Estate 1 open 40% Single Belt -0.32% 11.04% 26.62%

8 Estate 2 open 100% 5 Belt -0.95% -3.81% -3.17%

9 Hatchback 1 open 40% Single Belt 3.09% 7.21% 19.75%

10 Hatchback 2 open 100% 5 Belt 2.18% -22.55% 12.00%

11 SUV 1 open 40% Single Belt 0.81% 6.59% -16.76%

12 NASCAR 1 40% Single Belt 2.22%

13 NASCAR 2 open 40% Single Belt -1.25% -32.67%-10.47%

14 Semi-Truck 1 open 12.5% Single Belt 0.19%

15 Light Truck 1 open 20%% Single Belt -0.38% -5.09% -10.38%

1.2% 9.37% 9.24%Average Error Magnitude

ScaleGround

Simulation

CoefficientsVehicle No. Vehicle Model

Grille (open, closed,

blanked)

Wind Tunnel Data Elements

CD CLF CLR

21 Semi-Truck 2 open 0.000 0.125 Single Belt 0.19%

open 0.000 0.125 Single Belt -1.13%

open 6.000 0.125 Single Belt 2.63%




open -6.000 0.125 Single Belt 4.85%


open -9.000 0.125 Single Belt 3.13%



22 Light Truck 2 open 0.000 0.125 Single Belt -0.38% -5.09% -10.38%

open 6.000 0.125 Single Belt 2.69% -0.36% -17.95%

open 3.000 0.125 Single Belt 1.47% -3.87% 14.73%






2.5% 3.11% 14.35%

Yaw

Average Error Magnitude

ScaleGround

Simulation

CoefficientsVehicle No. Vehicle Model

Grille (open, closed,

blanked)

Wind Tunnel Data Elements

• Target is a best practice that delivers drag coefficient errors less than 2% for passenger cars, and 4% for heavy trucks.

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.