直背式轿车起动过程中气动现象的研究

Study of aerodynamic characteristics of fastback car in starting process

用计算流体力学方法对直背式轿车起动过程中的非定常外流场进行了数值模拟,采用k-ε湍流模型及一阶迎风格式计算出两种加速度下气动阻力和阻力系数.结果表明起动过程中气动阻力有较为显著的增加,并在起动后很短时间内达最大值.当汽车行驶平稳时,阻力趋于某一定值.阻力系数在起动过程中急速下降,起动结束后变化平缓,也趋于某一定值.起动过程中,车尾部逐渐形成旋涡,汽车头尾部压差逐渐变大,行驶平稳后,压差变小.

The unsteady flow field of a fastback car during starting process was simulated numerically with Computational Fluid Dynamics（CFD）method. The aerodynamic drags and drag coefficients under two starting accelerations were calculated using k-ε turbulent model and the first order upwind scheme. The results show that the aerodynamic drag increased significantly in the starting process and reached a maximum value in a very short period after starting. When the car ran steadily,the drag tended towards a constant value. The drag-coefficient decreased rapidly during starting and became steadily after completion of starting. In the process of staring, wake vortex formed gradually and the pressure difference between the front and back of the car became bigger. After running steadily, the difference became smaller.