An algorithm study of three-dimensional DSMC simulation based on two-level Cartesian coordinates grid structure

Combining Cartesian grids of high computational efficiency with precise description of unstructured triangular cells on vehicle geometry surfaces, the DSMC numerical simulation method based on two-level Cartesian coordinates meshes is presented in this paper. Level-I grids which referred as background cells created by uniform Cartesian grids in computational regions. Level-II grids are separate collision and sampling cells which are the division of background cells into sub-cells during the adaptation procedure according to the local flow gradients. The molecular collision pairs are selected in sub-cells to produce nearest neighbor collisions. The calculated aerodynamic coefficients of Orion configuration from free molecular flow to transitional flow have good agreements with DS3V and DAC codes. The reliability and validity of current technical scheme and its code are verified by the comparisons. The computational results of flow field and surface aerodynamic parameters are also analyzed and they have better regularity.