An experimental study of automotive underbody diffusers

Aerodynamics has always been a driving force in motorsport and road vehicle design and development, and continues to play an important role. A significant advancement in race car aerodynamics was the development of the vehicle underbody to produce downforce, in particular the implementation of the diffuser. This thesis concentrates on the performance flow mechanisms found in simple rear diffusers commonly seen in motorsport applications. There is little published work on these mechanisms, especially the influence of the more commonly used multiple-channel diffusers

Experimental study of multiple-channel automotive underbody diffusers

Underbody diffusers are used widely in race car applications because they can significantly improve the cornering capacity of the vehicle through the generation of a downforce. They are also likely to have a wider role in reducing the drag in road vehicles as it becomes increasingly important to reduce emissions of carbon dioxide. This paper reports on a wind tunnel investigation, using a simplified bluff body model, into the effect of splitting a simple plane diffuser into multiple channels. Tests are reported for a range of diffuser geometries suitable for road and race car applications. The results for the lift, the drag, and the incremental changes to the lift-to-drag ratio are reported and discussed in terms of the underbody pressures. While broadly similar trends to the single-channel plane diffuser are seen in the multiplechannel diffuser configurations, it was found that the effect of increasing the number of channels depended on the flow regimes present in the plane diffuser. At angles just above the plane diffuser optimum, where the flow is partially separated, the multiple-channel configurations give large improvements in the downforce with minimal increase in the drag, significantly extending the performance envelope. The pressure maps indicate that the gains occur through improved diffuser pumping and pressure recovery in both the inner and the outer channels