The connection between the result of numerical simulation of aerodynamic drag coefficients of hatch back and the number of grids was analyzed. In order to find a grid method to obtain the accurate solution, fast back MIRA model was chosen. By increasing the grids around the model and at the rear of the model, the drag coefficients of different gird methods, different methods of grid refinement and different number of grids were obtained, and then they were compared with the wind tunnel test results. The results show that after refining grid, the structure of vortex in the wake of the model can be captured clearly. The drag coefficient reduces with the number of grids. The independent results about the drag coefficient and the number of grid can be obtained when the numbers of grid are over lOmillion. Meanwhile, there is a deviation between the drag coefficient tested by wind tunnel and the number of grid -independent solution.%研究两厢车气动阻力系数的数值解与网格的关系,存在精度不高的问题.针对MIRA快背式模型,为了找到计算两厢车模型气动阻力较为精确的网格方案,通过对四面体网格和混合网格分别进行汽车整体加密及汽车尾部加密,得到MIRA快背式模型在不同网格形式、不同加密方式、不同网格数下的阻力系数,然后和试验结果进行对比.结果表明:加密后的网格能够很好地捕捉到MIRA快背式模型的尾部涡结构.阻力系数随着网格数增加而减少.当得到阻力系数与网格数无关的解时,网格数均超过1000万.同时,数值计算得到的阻力系数与网格数无关的解,与试验数据存在误差.
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