Proper Cell Dimension and Number of Particles Per Cell for DSMC

Different opinions still exist on some basic principles of DSMC method, such as the proper grid dimension and the proper number of particles in a cell. In this paper DSMC simulation of Poiseuille flow is made to evaluate the dependence of simulation results on cell dimension and number of particles per cell. In the simulation process a self adapting block structured grid system is employed to make sure that the number of particles per cell is constant. The simulation covers both slip flow regime and transition flow regime and each regime covers both high pressure and low pressure. Our simulation results indicate that the number of particles per cell and scaling factor exert little influence on simulation result for both slip flow and transition flow when the number of particles per cell surpasses 5, but the dimension of cell influences the accuracy of result obviously. The error caused by cell dimension decreases as the diminish of cell dimension. It is concluded that in the DSMC method it is necessary to make sure that the cell is less than 1/2 of molecular mean free path.