The Aerodynamic Development of the Tesla Model S - Part 2: Wheel Design Optimization

Aerodynamic efficiency plays an increasingly important role in the automotive industry, as the push for increased fuel economy becomes a larger factor in the engineering and design process. Longitudinal drag is used as the primary measure of aerodynamic performance, usually cited as the coefficient of drag (CD). This drag is created mostly by the body shape of the vehicle, but the wheel and tire system also contributes a significant portion. In addition to the longitudinal drag created by the body and wheels, rotational drag can add an appreciable amount of aerodynamic resistance to the vehicle as well. Reducing power consumption is an especially vital aspect in electric vehicle (EV) design. As the world's first luxury electric sedan, the Tesla Model S combines a premium driving experience with an electric drivetrain package that allows for unique solutions to many vehicle subsystems. The Model S has been developed from its inception with a focus on minimizing aerodynamic drag from all components. To that end, a wheel that reduces aerodynamic power loss was investigated. Exa's PowerFLOW CFD simulation software helped to expedite the design cycle, from force and moment values to qualitative flow visualization. PowerFLOW's proven Lattice-Boltzman solver and inherent transient nature provide accurate results and unique insight into the aerodynamic characteristics of each design not produced by other CFD solvers. The sliding mesh capability was also included to more closely represent the actual physics at work around the wheel. Ultimately, a new wheel was developed which greatly reduces aerodynamic power consumption.