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Relationships between vehicle's high speed stability during a steering action and following aerodynamic coefficients have already been reported in the past: coefficients for time-averaged aerodynamic lift, yawing moment, side force and rolling moment. In terms of the relationships, however, we have occasionally experienced different high speed stability during steering input even with identical suspension property and almost the same aerodynamic coefficients. A vehicle during high speed cornering shows complex behavior due to unsteady air flow around the vehicle and unintentional steering input from a driver. So it is supposed that the behavior is too complex to be fully described only with those aerodynamic coefficients. Through on-road test [1] and CFD analysis [2,3,4], we have studied unsteady aerodynamic characteristics around a vehicle for pitching motion during straight-line high speed driving.

Experiment and CFD have been performed to clarify the distribution of wind noise sources and its generation mechanism for a production vehicle. Three noise source identification techniques were applied to measure the wind noise sources from the outside and inside of vehicle. The relation between these noise sources and the interior noise was investigated by modifying the specification of underbody and front-pillar. In addition, CFD was preformed to predict the noise sources and clarify its generation mechanism. The noise sources obtained by simulation show good agreement with experiment in the region of side window and underbody.

A road vehicle’s cornering motion is known to be a compound motion composed mainly of forward, sideslip and yaw motions. But little is known about the aerodynamics of cornering because little study has been conducted in this field. By clarifying and understanding a vehicle’s aerodynamic characteristics during cornering, a vehicle’s maneuvering stability during high-speed driving can be aerodynamically improved. Therefore, in this study, the aerodynamic characteristics of a vehicle’s cornering motion, i.e. the compound motion of forward, sideslip and yaw motions, were investigated. We also considered proposing an aerodynamics evaluation method for vehicles in dynamic maneuvering. Firstly, we decomposed cornering motion into yaw and sideslip motions. Then, we assumed that the aerodynamic side force and yaw moment of a cornering motion could be expressed by superposing linear expressions of yaw motion parameters and those of sideslip motion parameters, respectively.