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The main purpose of this paper is to reveal the drag reduction mechanism of single-channel rear diffuser on the vehicle aerodynamic drag and to obtain the relationship between the structure parameters of rear diffuser and the vehicle aerodynamic drag. The influence of the single-channel rear diffuser on the aerodynamic drag is studied using the Reynolds-averaged method with the 25° slant Ahmed model. The accuracy of the numerical method is validated by means of a wind tunnel test. The aerodynamic performance of the Ahmed model with different vertical diffuser angles, lateral diffuser angles, and channel widths is discussed. The results demonstrate that the vortex location will be influenced by the vertical diffuser angle, and with the vortex core approaching to the model, the aerodynamic drag will increase. The aerodynamic drag reaches the minimum value with a vertical diffuser angle of 10.46°. Moreover, the aerodynamic drag decreases with increasing channel width. Finally, the aerodynamic drag can be reduced by 5.3%, when the vertical diffuser angle, lateral diffuser angle, and channel width are 10.46°, 0°, and 351 mm, respectively.

Mathematical model and computer aided simulation techniques have been used to predict and analyse the steering stability of high-speed vehicles. A new vehicle dynamics simulation model, based on considering the roll motion of suspensory mass of the vehicle and the effect of side winds, has been established in this paper. The model is able to simulate the transient state of a vehicle under side winds and to analyse the steering stability and veering character of the vehicle. Some simulation results are presented and discussed.