Aerodynamics of a Convex Bump on a Ground-Effect Diffuser

作者：Ehirim O H; Knowles K; Saddington A J^*; Finnis M V

来源：Journal of Fluids Engineering-Transactions of the ASME, 2018, 140(9): 091102.

DOI：10.1115/1.4039518

• aerodynamics
• ground-effect diffuser
• convex-surface
• pressure-recovery
• downforce

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 17 deg 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.