Open-Wheel Aerodynamics: Effects of Tyre Deformation and Internal Flow

Abstract

Competitive performance of an F1 race car relies upon a well designed and highly developed aerodynamic system. In order to achieve this, total understanding of the downstream wake of exposed rotating wheels is essential. Components such as bargeboards and indeed much of the front wing are developed to provide pressure gradients and vortex structures to influence the wheel wake, ensuring high energy mass-flow to the sensitive leading edge of the underfloor and eventually the rear wing.

Wind tunnel testing of model-scale deformable tyres has become a common occurrence in F1 in recent years although there is a significant lack of available literature, academic or otherwise, as to their use. This work has studied in detail the aerodynamic consequences which occur from the varying sidewall bulge and contact patch region making use of several techniques. These include scanning rotating tyre profiles under load, static contact patch size measurements, five-hole pressure probe wake measurements, particle image velocimetry (PIV) and load-cell drag measurements. CFD simulations utilising two industrial codes have also been performed to support the experimental work. Coordinates representing tyre profiles under a range of on-track conditions are available for other researchers to use as a basis for CFD studies.

The work presented here includes a full range of representative on-track axle heights which far exceed the more conservative range usually tested in an industrial setting for longevity reasons. The most sensitive parameters for aerodynamic testing of wheels have been identified. For development of a full car, in decreasing order of priority, the following must be correctly matched to the realistic scenario: axle height, yaw condition (without glycerol - often used to reduce friction at the expense of a compromised tyre profile), camber angle, detailed internals, high inflation pressure, through-hub flow rate and least significantly the rotation of the internal brake rotor.

The study of through-hub flows revealed that the external aerodynamic effect of the brake scoop inlet varies significantly with the amount of internal restriction. The pumping effect of the brake rotor was measured to be negligible compared to the restrictive effect of its internal passages and that leads to an effect known as inlet spillage with a negative cooling drag trend, whereby the drag of the wheel assembly decreases with increased through-hub flow.