Search Results

Rally cars are frequently operated at high speeds on loose road surfaces and significant slip angles are achieved when cornering. A wind tunnel test procedure is presented which allows those slip angles to be accommodated whilst maintaining contact between the tires and the wind tunnel's moving ground plane. It is shown that as the slip angle is increased both the drag and lift increase whilst the centre of pressure moves rearwards. Simulations are presented which evaluate the effect of those aerodynamic changes upon the overall performance of the car over a rally stage.

Flow unsteadiness has been investigated experimentally for two idealised model geometries including the Ahmed form. Several techniques were used including twin hot-wire probes located at different positions in the wake and a frequency domain correction method for pneumatic tubing. Levels of periodicity in the wakes and on the surfaces of the models have been examined using spectral analysis techniques. Unsteadiness was found to originate from movement of the closed separation bubble at the end of the large radii at the front of the models and from vortex shedding when large radius curved rear surfaces are present.