非定常来流对汽车气动升力瞬态特性的影响

Effects of Unsteady Stream on Transient Characteristics of Automotive Aerodynamic Lift

采用大涡模拟与风洞试验相结合的方法,研究了非定常来流下汽车气动升力瞬态特性的变化规律,分析了来流速度脉动频率对气动升力的影响,讨论了对气动特性产生影响的物理机制。模拟计算结果表明:来流速度的脉动频率对升力系数有很大影响;来流以短周期脉动时,升力系数近似呈正弦规律变化;来流以长周期脉动时,升力系数先增大后减小,随后趋于平稳振荡。研究结果表明:尾部流场结构在很大程度上影响气动升力的大小和方向,速度脉动变化引起上下部压差变化进而导致升力变化。

An approach of combining the large eddy simulation and wind tunnel experiment was employed to study the variation of transient characteristics of automotive aerodynamic lift under the unsteady stream. The effects of velocity perturbation frequencies on aerodynamic lift were analyzed and the physical mechanism contributing to the variation on the aerodynamic characteristics was discussed. Simulation results show that velocity perturbation frequencies have a great impact on lift coefficient. Specifically,in terms of short period oscillating stream,lift coefficient changes in accordance with sinusoidal curve. With respect to the long period oscillating stream, however, lift coefficient firstly increases and then decreases. Finally, it tends to stable oscillation. The primary analysis shows that trail flow field structure largely affects the magnitude and direction of the aerodynamic lift. Additionally,the change of velocity perturbation leads to the change of pressure difference between upper and lower of the body, thereby giving rise to the change of aerodynamic lift.