'PowerFLOW' CFD solver helps Dodge Motorsports

The aerodynamics team accelerated its work with CFD, advanced visualisation and scale-model wind-tunnel development to augment traditional full-scale tunnel and on-track testing.

A 3/8-scale clay model of the Intrepid was produced and tested in the scale-model wind tunnel at the DaimlerChrysler Technical Center in Auburn Hills, MI. After several additional scale-model tests, the first full-scale prototype was tested at the Lockheed-Martin wind tunnel in Marietta, GA. Once the development team was satisfied with the general body design, the full-size and scale prototypes were digitized with laser scanners and reverse-engineered into CAD body surfaces for further development.

The first step for the team was to ensure the validity of CFD aerodynamics results by comparing them to those from wind-tunnel testing. The team's goal was to see a coefficient of drag within 5 percent, a coefficient of lift within 10 percent, and balance, or lift distribution, within 5 percent.

Simulations using the Lattice-Boltzmann-based 'PowerFLOW' solver were run on Silicon Graphics 'Origin 2000' supercomputers. The development team used 'EnSight' software from CEI to visualise the CFD results.

"It is very difficult to visualize the airflow streams under a ground vehicle, or under its hood, during a traditional scale or full-size wind-tunnel test," said Jean-Michel Esclafer de la Rode, a product engineer at DaimlerChrysler. "Visualisations help us better understand the aerodynamics of ground-effects on both our production and race vehicles."

DaimlerChrysler used EnSight to generate and animate large sets of streamlines around the car to depict airflow patterns. Surface visualisations and vector clips made patterns readily visible to the development team. Areas of high and low pressure depicted in the visualisations were used to determine cooling opening locations, separated wake regions, and other aerodynamic characteristics. Three-dimensional streamlines were shown underneath the car as a typical 'horseshoe' vortex that trails a vehicle.

The DaimlerChrysler team found a close correlation between CFD and wind-tunnel results, providing the confidence needed to use computational testing for real-world simulations.