Investigation of Flow Structures in Different Body Types Contributing to Drag Change Due to Crosswind

<div class="section abstract"><div class="htmlview paragraph">To reduce aerodynamic drag during real-world driving, it is essential to consider the effects of crosswinds. The yaw angle dependence of aerodynamic drag is known to vary based on the vehicle body type; however, there are limited studies on the physical mechanisms underlying this difference, particularly through detailed visualizations of the flow structure and its response to yaw angles. This study investigates the differences in flow structures between an SUV and a notchback to understand the mechanism responsible for the variation in yaw angle dependence of <i>C<sub>D</sub></i> under quasi-steady yaw angle conditions. Numerical simulations and wind tunnel tests were conducted for both the SUV and the notchback at yaw angles of 0°, 2°, and 5°. Crossflow and total pressure were employed as indicators for visualizing the flow structure, with a focus on the wake behind the vehicle in the visualizations of the wind tunnel tests and simulations. Additionally, isosurfaces of the crossflow velocity magnitude and streamlines around the vehicle were visualized based on the simulation results. These visualizations revealed body-type-dependent differences in flow structures. For the notchback, the main vortex at a yaw angle of zero was generated behind the C-pillar, strengthening on both the leeward and windward sides as the yaw angle increased. In contrast, for the SUV, the main vortex at a yaw angle of zero originated from the rear bumper corner, becoming stronger on the leeward side but weaker on the windward side under yaw angle conditions. This variation in the yaw angle response of the main vortex structure explains the difference in yaw angle dependence of <i>C<sub>D</sub></i> between the two body types. As the yaw angle increases, the notchback exhibits a more pronounced increase in <i>C<sub>D</sub></i> than the SUV due to the vortex strengthening on both the leeward and windward sides.</div></div>