Aerodynamics of a Convex Bump on a Ground-Effect Diffuser

Abstract

A ground-effect diffuser is an upward-sloping section of the underbody of a racing car that enhances aerodynamic performance by increasing the downforce, thus improving tire grip. The downforce generated by a diffuser can be increased by geometric modifications that facilitate passive flow control. Here, we modified a bluff body equipped with a 17deg diffuser ramp surface (the baseline/plane diffuser) to introduce a convex bump near the end of the ramp surface. The flow features, force, and surface pressure measurements determined in wind-tunnel experiments agreed with previous studies but the bump favorably altered the overall diffuser pressure recovery curve by increasing the flow velocity near the diffuser exit. This resulted in a static pressure drop near the diffuser exit followed by an increase to freestream static pressure, thus increasing the downforce across most of the ride heights we tested. We observed a maximum 4.9% increase in downforce when the modified diffuser was compared to the plane diffuser. The downforce increment declined as the ride height was gradually reduced to the low-downforce diffuser flow regime.

Parametric, response surface, and adjoint optimizations of the underbody diffuser of a generic ground vehicle

“…When geometric modification between these two models is examined (see Figure 6) inward curved surface of the diffuser section is the usual suspect of this variance. A similar case is presented in the investigation by Ehirim, 41 and it is stated that curved surface modification close to the diffuser exit can alter the shape of the straight-line airflow to a curved flow and the flow curvature introduces a pressure rise on the diffuser. Freestream underneath the body is restricted which causes a reduction in the asymmetric flow between the underbody and upperbody.…”

Study of the Effect of Vertical Airfoil Endplates on Diffusers in Vehicle Aerodynamics

“…Thereby, there is a clear trade-off of ground interaction and underbody upsweep mechanisms which depends on the ride height. An additional drag component is also generated by this augmented flow and at small ride heights it can totally cancel the underbody upsweep advantage of reducing drag [24].…”