Development and performance evaluation of undertray diffusers during racing manuevers

Abstract

A potential to develop the monocoque and diffuser on the Chalmers Formula Student (CFS) car, as to increase its downforce, was identified by CFS. Downforce is the downward aerodynamic lifting force that is obtained when a pressure difference is created between the top and bottom of the car. This effect is crucial for the grip of the car in driving scenarios like cornering, accelerating and braking. With more downforce, accelerating and braking can be done faster, and higher speeds can be maintained in cornering. The objective of this project is to develop a methodology for modeling of aerodynamic forces during different racing maneuvers of a CFS car. These new methods are purely computational. Further, the methods are used in the development of a new diffuser concept. This is done with the aim of providing CFS with knowledge and proof-of-concept of the implementation of a new diffuser, which could increase aerodynamic performance of the car. It was shown that straight ahead driving, braking, and cornering were the most critical driving scenarios. These were used to perform three types of simulations. Different diffuser designs were simulated based on these scenarios. It was further shown that the following parameters had an effect on aerodynamic performance: the expansion angle of the diffuser, the starting point of the diffuser, the radius of the diffuser throat, and the implementation of strakes and side floors. Differences in the performance robustness of the different designs were observed. Two diffusers provided the greatest downforce: one with a 13° expansion angle and the other with a 19° expansion angle. The diffusers were in other regards identical. Lastly, the 13° diffuser was chosen as the best contending design, due to its robust performance in each of the simulated driving scenarios.