A Parametric Study of Automotive Rear End Geometries on Rear Soiling

The motivation for this paper is to consider the effect of rear end geometry on rear soiling using a representative generic SUV body. In particular the effect of varying the top slant angle is considered using both experiment and Computational Fluid Dynamics (CFD). Previous work has shown that slant angle has a significant effect on wake shape and drag and the work here extends this to investigate the effect on rear soiling. It is hoped that this work can provide an insight into the likely effect of such geometry changes on the soiling of similarly shaped road vehicles. To increase the generality of results, and to allow comparison with previously obtained aerodynamic data, a 25% scale generic SUV model is used in the Loughborough University Large Wind Tunnel. UV doped water is sprayed from a position located at the bottom of the left rear tyre to simulate the creation of spray from this tyre. Having a single source of contamination simplifies the configuration of both experimental tests and simulations. It also improves analysis by allowing the soiling pattern from only one wheel to be seen in isolation. In order to provide further insight into the flowfield and its interaction with the spray CFD simulations are also performed at the same scale. A Detached Eddy Simulation approach is used, specifically the Spalart Allmaras formulation of the IDDES CFD model. Lagrangian particle tracking is used to model the dispersed phase. This CFD methodology has been found to give good agreement for soiling pattern with experiment for baseline cases.