Investigation of Aerodynamic Wheel Designs on a Passenger Car at Different Cooling Air Flow Conditions

Passenger cars represent the largest part of all means of personal transportation today. Thus, it is important to work towards reduced energy consumption of cars if a sustainable mobility is to be achieved. This involves many aspects of vehicle engineering; one of them being aerodynamics. This study focuses on aerodynamic drag and the contributions from the wheels at different cooling air flow configurations. Wheels and wheel housings are important for the overall aerodynamic drag on passenger cars. It has been shown that as much as 25% of the aerodynamic drag originates from these components. Therefore, it is desirable to understand the flow structures related to the wheels and wheel housings, and how they interact with other important flow regions. This paper presents an investigation of the effects of wheel designs on aerodynamic drag at different cooling air flow configurations on a sedan type passenger car. Comparisons between numerical simulations and wind tunnel measurements are made for some of the configurations as well. Several additional wheel configurations were investigated numerically to further investigate the flow structures at the front and rear wheels. The numerical results show that the effects of radial wheel covering varied noticeably with cooling air flow configuration. In two of the configurations this resulted in a net drag increase with closed cooling air inlets. The best configuration with closed cooling air inlets generated an overall drag reduction of 29 drag counts compared with the numerical baseline with open cooling air inlets. In addition to the obvious drag reduction of closing the cooling air inlets, the main reasons for the additional decrease was limiting the drag increase at the front stagnation region and positive interference effects along the underbody and vehicle base.