Numerical Investigation of Aerodynamics of Vehicle Underbody with Overset Grid System.

Recently, the shapes of not only upperbodies but also underbodies of vehicles have been improved in order to reduce aerodynamic drag of vehicles. Since it is impossible to flatten the whole underbody, we need to find an effective method to reduce the drag by partial refinement of underbody shape. In this study, using computational fluid dynamics (CFD), we have investigated the relation between the locations of the obstacles attached to the underbody and the change in drag and obtained a good way of drag reduction.

Because the shape of a vehicle is very complicated, we have employed an overset grid system. We noted a notch-back-type vehicle with a flat underbody, in which square-section cylinders are set at various locations on the underbody as obstacles. In the case studies, we can change the location of the obstacle easily using the overset grid system. Computational results reveal that the drag tends to increase when the obstacle is located around the front axle or behind the rear axle. The results suggested the underbody shape for smaller drag and made it possible to obtain an effective way of improving the underbody shape.
�@