Drag-reducing underbody flow of a heavy vehicle with side skirts

Abstract

Aerodynamic drag reduction in heavy vehicles is a very interesting research topic that is relevant for both the industries and the environment. The underbody flow induces considerable drag as it passes through the underside of heavy vehicles and interacts with rolling wheels and other underbody structures. Nonetheless, the drag caused by such an underbody flow has received less research attention, compared with those attributed to forebody and base body flows. Side skirts are one of the most effective drag-reduction devices to control the underbody flow. They consist of straight panels curtaining the space between the front and rear wheels. However, the mechanisms of underbody flow modified by side skirts have yet to be fully understood. In this study, the drag reduction underbody flow of a scaled-down 15-ton truck model attached with two different types of side skirts was quantitatively visualized through wind tunnel tests. Results show that the straight-type side skirt and the flap-type side skirt significantly change the flow structures under the vehicle model, reducing drag coefficient by 3.1 and 6.1 %, respectively. Furthermore, flow characteristics in the underbody of the vehicle model with and without side skirts are investigated using a PIV technique to understand the associated drag-reduction mechanism.