Ehirim, ObinnaKnowles, KevinSaddington, Alistair J.Finnis, Mark V.2018-12-122018-12-122018-04-19Ehirim OH, Knowles K, Saddington AJ, Finnis MV. (2018) Aerodynamics of a convex bump on a ground-effect diffuser. Journal of Fluids Engineering, Volume 140, Issue 9, 19 April 2018, Article number 091102; Paper No: FE-17-16250098-2202https:doi.org/10.1115/1.4039518http://dspace.lib.cranfield.ac.uk/handle/1826/13720A 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° 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.enAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/aerodynamicsground-effect diffuserconvex-surfacepressure-recoverydownforceArticle22120087