WHEEL STRUT INTERFERENCE

Paper i proceeding, 2006

To fine tune the aerodynamic properties of road going vehicles the flow along the underbody is of outmost importance. Hence moving ground facilities has been introduced. In full-width mono-belt facilities the test vehicle is most often suspended over the ground plane by a sting system. To mount the wheels, two possibilities exist. The designer of the wind tunnel model is faced with the choice to have the wheels on or off the model. The first option gives the most satisfying boundary conditions from a fluid dynamics point of view, however, the designer will face the problem of creating a frictionless chassis suspension system for the model. The ”wheels off” type does not require such complex system but unfortunately creates a non-realistic flow due to the presence of so called wheel struts that carries the wheels. In the present work a numerical study of the flow around a ”wheels off” model has been conducted. The study was performed to quantify how the presence of the wheel struts would affect the flow field and hence how this influence flow related measurements made on the model. The work has been done using a commercial CFD-code, running a standard k-epsilon model on a tet-dominated mesh, counting roughly 6.5 million cells. As expected the flow field in the vicinity of the wheels is affected due to the extra vorticity introduced by the struts. The modified pressure field alters the drag and of further significance is the influence from the wheel struts on the underbody flow field. It is shown that care must be taken in studies of underbody and later underhood flows, using a ”wheels-off” configuration.