S.Y. Cheng

Effects of Transient Aerodynamics on Vehicle Stability: A Large Eddy Simulation analysis

The present study investigated the extent to which the results obtained from simple bluff body model, regarding pitching stability, can be applied to real vehicle aerodynamics. The investigation was carried out using a large eddy simulation method with vehicle-motionairflow dynamic coupling capability. The aerodynamic damping coefficient and mechanism obtained from realistic sedan-type vehicle model cases are found similar to the one for simple body model cases. These agreements deduce that the use of simple body model in automotive aerodynamic research is justifiable.

Transient Analysis of Pitching Stability of Sedan-type Vehicle Models using Large-Eddy Simulation

Large eddy simulation was used to investigate the pitching stability characteristic of sedan-type vehicle. In the simulation, small scale simplified vehicle models which represent the sedan car of different pitching stability characteristics were used. Results of stationary cases are compared with wind tunnel measurements for validation, and good agreement is attained. To analyze the dynamic response of the vehicle models, forced-sinusoidal-pitching oscillation is imposed and the resulting pitching moment is phase averaged for analysis. Vehicle model of higher pitching stability is found to exhibit two-dimensional flow structure above the central region of its trunk deck, whereas vehicle model of lower stability is associated with strong cross flow and upwash circulatory flow structure. The formation of these two distinct flow patterns is primarily affected by the rear pillar vortices. Finally, the aerodynamic dumping mechanism is discussed based on the phased-averaged results.