4 Three-Dimensional Velocity Measurements in Model Car Wakes

Abstract

The wakes of three car models with different rear shapes were investigated, first with a combination of 9 Pitot-tubes and afterwards with a 2-Dimensional LDV-system. By combination of both data types and utilizing software on a workstation, the data was visualized in form on quasi three-dimensional streamline graphs. These graphs showed a structural correspondence between the vortices of either the fastback shape and the sedan shape, differences only occurred in their location and extent: two opposite rotating longitudinal vortices developed out of the flow around the car body, leaving a relatively small reverse flow area directly behind the car. Comparing these flow fields with that of the wagon-shaped car the wake differs substantially: the longitudinal vortices are almost not existing, whereas a large reverse flow area mainly caused by the underbody flow of the car developed.