LES on the Effect of Vehicle Motion and Driver Response on Aerodynamic Drag under Wind Fluctuations
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In aerodynamic design aimed at improving automotive fuel efficiency, conventional CFD analyses have been conducted with a fixed vehicle attitude using uniform flow conditions or steady flow conditions with a fixed yaw angle. However, these analyses fail to capture the spatiotemporal nonuniformity of natural winds or variations in vehicle motion, and may differ from the aerodynamic drag experienced under actual driving conditions. Therefore, CFD-based evaluation of aerodynamic characteristics under unsteady conditions that model real-world driving environments including vehicle motion, driver response, and wind fluctuations has become crucial. In this study, an aerodynamic-vehicle motion coupled analysis framework using “CUBE”, a LES-based fluid analysis software developed by RIKEN and Kobe University, and “Project Chrono”, an open-source vehicle motion analysis software is adopted. This framework is further improved to enable realistic aerodynamic simulations by applying modeled fluctuating winds based on natural wind characteristics are applied to the vehicle, thereby reproducing an unsteady flow field with time-varying wind direction and velocity. This study shows that, under unsteady wind conditions representative of real-world driving environments, vehicle motion and driver response have a significant effect on aerodynamic drag characteristics.
