Aerodynamic Characteristics of Overtaking Bus under Crosswind: CFD Investigation

The presence of other vehicles, travelling together on the road, highly contributes to the condition on the realistic air flow direction. The position alteration of other vehicles generates different airflow direction which is unpredictable experienced by the vehicle under investigation. It considerably affects the stability of a vehicle having large size of the body. The purpose of the study was to investigate the aerodynamic response of a detailed bus model in overtaking process with the interference of crosswind. Fluidic simulation was performed to investigate the air flow behavior imposed on the bus by means of Computational Fluid Dynamics (CFD) analysis. A scaled bus model was used in the simulation with the different positions representing the buses during the overtaking process. The coefficient X/L was introduced to realize the vehicle position during the overtaking process. The results discussed the alteration of drag force coefficient, lift force coefficient, side force coefficient, during the position on overtaking process. The resulting turbulence kinetic energy around the bus was also discussed by comparing the case without crosswind and when the yaw angle was 30°. The most prominent aerodynamic forces alteration occurs when the overtaking process was at X/L=1. Further explanation about the pressure coefficient at the surface of the bus and the area around the vehicle was investigated at this position. The accuracy of numerical results calculation was verified by comparing the result of simulation and experimental testing of Cd and Cl with the percentage of deviation 0.37% and 2.90% respectively.