Investigations on the optimization of the flow around wheels and wheel arches have been carried out. The significance of realistic wheel modeling in CFD simulations has been demonstrated. Furthermore, we have presented in this paper four different areas which after detailed analysis turned out to be suitable for optimization measures for reducing the aerodynamic drag of a passenger car. Two optimization measures have been presented in detail. The investigations of the first optimization measure show again how important rotating wheels and ground simulation are for wind tunnel measurements. Whereas the measure developed by using CFD could not be verified in the BMW wind tunnel without moving floor the results of the FKFS wind tunnel with ground simulation and rotating wheels show a very good agreement with the CFD results. With this optimization measure we confirmed the existence of a jet which was identified by analyzing the CFD flow field. This jet has been deflected by an obstacle. The consequence was a pressure reduction on the wheel-cavity surface behind the wheel and a benefit of 4 drag counts. The identified jet is an excellent example for the relevance of CFD simulations. In the wind tunnel the identification would be almost impossible without the previous knowledge gained through CFD. Moreover we have used CFD for developing aerodynamically optimized rims with reduced resistance torque due to aerodynamic forces. The critical region where the spoke merges into the wheel rim bed exhibits the highest pressure levels in combination with the largest lever arm. Roll-drag test bench measurements have been conducted to verify the effect of the optimized rim styling. The results showed that optimized rims can significantly reduce the required power for wheel rotation. This power saving is equivalent to a drag reduction of 3-4 % for modern passenger cars. In conclusion, our approach showed how important CFD is for a detailed understanding of the complex flow field around the wheels and wheel arches. It is possible to consider and optimize sub regions in detail separately. Those measures with minimum destructive interference can be safely combined.
New directions in the optimization of the flow around wheels and wheel arches
Neue Richtungen bei der Optimierung der Umströmung von Fahrzeugrädern und Radhäusern
2008
12 Seiten, 10 Bilder, 10 Quellen
Conference paper
English
New Directions in the Optimization of the Flow Around Wheels and Wheel Arches
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