The aerodynamic characteristics of an exposed racing car wheel
The aerodynamics of an exposed racing car wheel have been analysed using experimental and computational (CFD) techniques. A 40% full-scale pneumatic tyre/wheel assembly was used for the experimental investigations and the exact geometry was replicated in the CFD model. The wheel had an aspect ratio of 0.53 and the tests were conducted at a Reynolds number, based on the wheel diameter, of 2.5 x 10 . Both rotating and stationary wheels were tested with moving and fixed ground-planes, respectively. The experiments were conducted using new and existing methods of data acquisition and analysis. A non-intrusive radio telemetry system was successfully designed and developed that enabled surface static pressure data to be transmitted from a rotating wheel to a local PC. Other experimental techniques included the use of particle image velocimetry (PIV) and a pneumatic non-embedded five-hole pressure probe to investigate the flow-field about the wheel. The early flow separation, which is a characteristic of the rotating wheel, was observed in the surface static pressure distributions and PIV velocity fields. Lift and drag forces were found to decrease as a result of wheel rotation, which agreed with the work of other investigators, and the mechanisms responsible for such force reductions are postulated. The wake structures were investigated and showed weaker streamwise vorticity for the rotating wheel compared to the stationary wheel. The most important and remarkable aspect of this work was the experimental observation and subsequent CFD prediction of the rear jetting flow mechanism whose existence was previously theoretically predicted by another investigator. The PIV velocity fields clearly show the rear jetting phenomenon and this is further corroborated by a negative pressure peak in the surface pressure distributions on the wheel centreline. The effects the rear jetting phenomenon has on the wake mechanics, and hence the forces acting on the rotating wheel, are postulated.