Investigation of flow structures in different body types contributing to drag change due to crosswind

To reduce aerodynamic drag during real world driving, it is important to consider the effect of crosswinds. In this study, we investigated the differences in flow structures between an SUV and a notchback to understand the mechanism behind the difference in yaw angle dependence of Cd value when a quasi-steady yaw angle is applied. In this study, simulations and wind tunnel tests were performed for the SUV and the notchback with yaw angles of 0°, 2°, and 5°. The indicator of flow structure analysis were crossflow and total pressure, and the results of wind tunnel tests and simulations were visualized, focusing on rear wake. In addition, iso-surfaces and path lines around the vehicle were visualized in detail, using the results of simulations. These results revealed the differences in flow structures depending on the body type. In the case of the notchback, the main vortex at yaw angle zero is behind the C-pillar. When a yaw angle is applied, this becomes stronger on both the leeward and windward sides. On the other hand, in the case of the SUV, the main vortex at yaw angle zero is located at the rear bumper corner, and when a yaw angle is applied, the vortex becomes stronger on the leeward side, but weaker on the windward side. This difference in vortex structure could explain the difference in yaw angle dependence of Cd value between the notchback and the SUV. When the yaw angle increased, the notchback had a larger change in Cd than the SUV, because the vortex was strengthened both leeward side and windward side.