Abstract: In order to improve the accuracy of numerical simulation of vehicle external flow field, the characteristic size parameters of boundary layer mesh were optimized and the influence of each parameter on the simulation results was analyzed. On the basis of MIRA square-back model, the thickness of the first boundary layer, the total thickness of the boundary layer and the number of layers in the boundary layer were selected as the design variables for the experimental design. The drag coefficient Cd and the lift coefficient Cl were taken as the optimization targets to carry out the multi-objective optimization. According to the Pareto diagram of response value Cd and Cl, the effect of design variables and response values was explored. Finally, the Cd,Cl and velocity flow field calculated by wind tunnel test and optimized by numerical simulation were compared. The results show that the interaction effect between the thickness of the first layer and the total thickness of the boundary layer has the greatest effect on Cd, and the single factor effect of the number of boundary layers and the total thickness of the boundary layer has a great effect on the Cl. After optimization, the calculation error of Cd and Cl is reduced, and the consistency of velocity flow field display with PIV experiment is improved greatly.

Key words: vehicle engineering, vehicle external flow field, CFD, boundary layer, optimization design

摘要： 为了提高汽车外流场数值模拟计算的精度，对边界层网格特征尺寸参数进行优化设计，分析各参数对模拟结果的影响。在MIRA直背车型基础上，选取第一层边界层厚度、边界层总厚度和边界层层数为设计变量进行实验设计，以阻力系数Cd和升力系数Cl为优化目标进行多目标优化，依据响应值Cd和Cl的Pareto图探究各设计变量与响应值的效应影响，最后将风洞试验和优化后数值模拟计算的Cd、Cl及速度流场情况进行对比。结果表明：第一层边界层厚度与边界层总厚度的交互效应对Cd影响最大，边界层层数和边界层总厚度的单因素效应对Cl影响较大；优化后，Cd和Cl的计算误差减小，速度流场显示与PIV实验的一致性亦得到较大改善。

关键词: 车辆工程, 汽车外流场, 计算流体力学, 边界层, 优化设计