Investigation of Wheel Housing Flow on Heavy Trucks

Licentiate thesis, 2009

Increasing fuel prices and demands for reductions of emissions have led to a considerably increased interest in developing more efficient vehicles. Besides designing more efficient power units with lower fuel consumption and emission levels it is possible to increase the total efficiency of the vehicle by aerodynamic optimization. It is well known that aerodynamic drag becomes the dominant part of the total driving resistance of heavy trucks at velocities above 80 km/h. The drag from the underbody, including wheels and wheel housing, constitutes a significant proportion of the total aerodynamic drag of heavy vehicles. An accurate simulation of the underbody boundary conditions, including rotating wheels and moving ground, has turned out to be of great importance in the minimising of the aerodynamic drag. In this study the flow around the front wheels of a heavy truck has been investigated. A long-haulage truck geometry with a fully detailed underbody was used and the flow was simulated using Computational Fluid Dynamics. The vortex structures originating from the wheel rotation were identified and it was shown that the major part of the incoming flow to the front wheel housings entered from below the bumper skin and from inside the engine compartment. As the flow approached the wheel it was highly yawed, and this led to an asymmetric flow around the wheel where the largest outflow from the wheel housing was located behind the wheel. An investigation of different wheel housing design parameters were performed in order to reduce the drag of the vehicle, and it was found that changes in the wheel housing geometry had a significant impact on the local flow field and force distribution. The relation between aerodynamic drag and wheel housing volume corresponded to previous studies and showed that a smaller wheel housing volume will result in reduced drag. It was also shown that implementing wheel housing ventilation had a potential for reducing the drag and by careful design this can be improved even further.