Proper cell dimension and number of particles per cell for DSMC

The Direct Simulation Monte Carlo (DSMC) method models fluid flows using simulation particles which represent a large number of real molecules in a probabilistic simulation to solve the Boltzmann equation. Different opinions still exist on some basic understandings of the controlling factors of DSMC method, such as the proper grid dimension and the proper number of particles in a cell. In this contribution, DSMC simulation of Poiseuille flow was carried out to evaluate the dependence of simulation results on cell dimension and number of particles per cell. In the simulation process a self-adaptive block-structured grid system was employed to guarantee that the number of particles per cell is constant. The simulation covers both 2D and 3D, slip flow regime and transition flow regime, and for each regime, covers both high pressure and low pressure cases. Our simulation results indicate that the number of particles per cell and scaling factor have little influence on simulation result for both slip flow and transition flow when the number of particles per cell is greater than 5, but the dimension of cell influences the accuracy of results significantly. The error caused by cell dimension decreases with the decrease of cell dimension. It is concluded that in the DSMC method it is necessary to ensure that the cell is less than 1/2 of molecular mean free path.