车身俯仰运动时流场的迟滞现象研究

通过LES模拟某轿车在行驶时车身发生俯仰运动的流场瞬态变化过程, 车身俯仰运动规律为正弦波动，正弦波动的斯特劳尔数为0.13.利用风洞实验验证了该方法的准确性，比较瞬态与准静态模拟结果发现两者变化规律相差很大，说明采用准静态模拟无法真实体现汽车实际行驶时的气动性能.从瞬态模拟结果可以发现车身在最高和最低位置时存在滞后，说明流场在俯仰运动过程中存在迟滞效应.并通过Q-准则可视化车身周围的瞬态流场，从空间和时间上更加深入地了解车身周围复杂流场的瞬态流动.
This paper studied the transient flow-field response of a simplified vehicle pitching around its front axle. The transient numerical solver employed is based on the large-eddy simulation. The sinusoidal -pitching motion was imposed on the model, and the Strouhal number was 0.13. The numerical method was validated with wind-tunnel experiments. The change rule of the results between transient simulation and quasi-steady simulation is quite large. It has been found that the quasi-steady simulation cannot reproduce the aerodynamics performance of vehicle driving on road. It has also been found that, from the transient simulation results, there is a time lag at the extreme position, which suggests that the flow-field has hysteresis effects. The complex flow-field of transient flow around the road vehicle was thoroughly understood from the space and time through the Q-criterion to identify the coherent structures of the flow.