A study of the time-resolved structure of the vortices shed into the wake of an isolated F1 car wheel

This paper describes the flow about a smooth isolated wheel rolling steadily along a plane surface. The shape chosen is typical of those used for Formula 1 racing cars, and it is fitted with an inflatable tyre to ensure that an appropriate contact patch geometry is realised. Single-pass PIV is used to obtain instantaneous records of the velocity field around the wheel, and examples of the detailed wake structure are presented. The evolution of the vortices generated by the wheel and shed into the wake is studied for a range of yaw angles up to 6°. It is shown that the structure of the wake for the unyawed wheel fluctuates considerably, switching between distinct states where a dominant lower ground vortex is observed on either the left or the right side of the wake or a third state where a symmetrical pair of vortices forms. Yawing the wheel, even by as little as 2°, which will frequently arise in practical situations due to cross winds or steering the vehicle, biases the flow towards the leeside which inhibits the switching. In such a case, a stable dominant leeside lower ground vortex is formed and the wake structure changes significantly. The origin of the ground vortex formation ahead of the wheel is identified as vorticity coming from the boundary layer generated on the front face of the tyre and not the “jetting phenomenon” as is widely assumed.