The grid strategy of high reliable numerical simulations for aerodynamic performance of high-speed trains

Based on numerical studies on an elliptic cylinder in ground effect and the turbulent boundary layer on a flat plate, a new criterion to arrange the surface tangential grid and a new method to predict the dimension of the first-layer grid normal to wall are proposed for RANS simulations of high-speed trains. Using the proposed grid strategy, a numerical comparison is implemented for a CRH3-like model, and a numerical validation is performed for a simplified model experiment in 90° crosswind. It is indicated that: the wall tangential grid scale can be parameterized by the grid-to-radius ratio, which stands for the ratio of the tangential grid size to the local curvature radius on a wall surface. When the grid-to-radius ratio is less than 0.2, the surface pressure distribution agrees well with experimental results. Using the proposed equation of normal grid sizes for RANS with the wall function method, the dimension of the first-layer grid normal to wall can be predicted for the computational error of viscous drag less than 5%. The criteria for tangential gird scales and normal grid sizes can be applied both in crosswind and non-crosswind environments. The total amount of grid points can be effectively controlled and computational results with acceptable precision can be obtained by RANS.