Wing-Diffuser Interaction on a Sports Car 2011-01-1433

Amongst the aerodynamic devices often found on race cars, the diffuser is one of the most important items. The diffuser can work both to reduce drag and also to increase downforce. It has been shown in previously published studies, that the efficiency of the diffuser is a function of the diffuser angle, ground clearance and most importantly, the base pressure. The base pressure of a car is defined by the shape of the car and in particular the shape at the rear end, including the rear wheels. Furthermore, on most race cars, a wing is mounted at the rear end. Since the rear wheels and wing will influence the base pressure it is believed that, for a modern race car, there could be a strong interaction between these items and the diffuser.

This work aims to systematically study the interaction between the rear wheels and wing; and the diffuser of a contemporary, sports car type, race vehicle. The work was carried out using computational fluid dynamics and the geometry, that the study was based on, was the Lotus Evora Type 124 CUP car. The car carried detailed chassis components and a complete cooling system. In the study, the diffuser angle was varied over several inclinations, ranging from 3 to 12 degrees. Furthermore, the height of the wing over the “rear deck” of the car was also varied.

It was found from the study that the vertical position of the wing over the rear deck of the car had no significant influence on the flow through the diffuser, at the wing heights tested and vice versa, the diffuser showed only little influence on the flow past the rear wing. The diffuser however, had an influence on the base pressure and most importantly; on the downforce generation. At increasing diffuser angles the base pressure was reduced and consequently the downforce was increased.