Alternative Simulation Methods for Assessing Aerodynamic Drag in Realistic Crosswind 2014-01-0599

The focus of evaluating yaw characteristics in automotive aerodynamics has been primarily with regards to the effects of crosswind on vehicle handling. However, changes to drag that the vehicle experiences due to prevalent on-road crosswind can also be significant, even at low yaw angles. Using wind tunnel testing, it is possible to quickly determine the static yaw performance of the vehicle by rotating the vehicle on a turntable to different yaw angles during a single wind tunnel run. However, this kind of testing does not account for dynamic crosswind effects or non-uniform crosswind such as with natural on-road turbulence.

Alternatively, numerical simulations using computational fluid dynamics (CFD) can be used to evaluate yaw performance. In this paper, Exa's PowerFLOW is used to examine two alternative methods of simulating aerodynamic performance in the presence of realistic on-road crosswind for the Tesla Model S sedan. These methods provide reduced computational cost compared to simulating a full range of static yaw angles. The first is dynamic vehicle yaw, which rotates the vehicle similar to a wind tunnel turntable during the transient simulation. The second method uses a high onset turbulence level that provides a more realistic on-road wind condition by including non-uniform velocity fluctuations representing natural turbulence from wind. Results are compared to those obtained using the traditional methodology with static yaw sweeps for characterizing performance in crosswind.