Machine Design

3D CAD, CFD give NASCAR shop a winning edge

<strong>Gillett Evernham Motorsports</strong>, in Statesville, N.C., credits 3D CAD and CFD for giving its team the hundredths of a second advantage often needed to win a race. CFD Manager Chris Woodward says CFD is fairly new to the firm and to NASCAR as a whole.

Catia V5 from Dassault Systemes in Woodlands Hills, Calif. is the 3D CAD, and Gillett uses CFD solvers from several different programs.

“Catia includes a lot of backand- forth translators, so it communicates efficiently with downstream programs,” says Woodward. “When it comes time to mesh the CAD model, we use software that directly imports Catia files so there is no need to use a third-party file format. This helps streamline our workflow.”

The shop focuses mostly on external aerodynamics. “For example, we often compare different body configurations for underbody flow,” says Woodward. “We select the best solution from CFD and import the mesh file for that model back into Catia. The model is regenerated from the mesh file to facilitate the design change.”

Typically, the firm scans a whole car, imports the point cloud into Catia, and then builds a model directly from the point data. “Our models tend to be large. The number of cells in a mesh is one way to measure size of a CFD model. Obviously, the more cells, the more accurate the solution. But the limiting factor is hardware. Right now, we can run maybe 50 million cells. With hardware continually getting cheaper, we think we will solve models 10 times that size in the next two or three years.”

Expectations are that CFD will replace the traditional wind tunnel. “Besides flow, the software optimizes car components for drag, downforce, lift-to-drag ratio, side force, and aerodynamic loads and moments,” Woodward says. “Because CFD shows how air moves around a race car, it allows better design for specific purposes. For example, it’s important to reduce drag for a superspeedway car. But for a short-track car, it makes more sense to optimize cooling in the grille and brakes.”

The Car of Tomorrow spec that NASCAR is moving to next year tightly regulates race-car bodies. “So a lot of underbody flow will need to be studied,” says Woodward. “And where previous cars had a spoiler, the new car has a wing, one of many variables to investigate. But studying them must be done in an intelligent manner. That’s where the experience of team engineers, aerodynamicists, and guys building the cars come in.”


Results of a CFD program show external aerodynamics of a particular body configuration. Catia V5 provided the original 3D CAD model.

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