A grid-independent particle pairing strategy for DSMC

A new particle pairing strategy is presented for the Direct Simulation Monte Carlo (DSMC) method. By combining Nearest Neighbour (NN) and Quad Tree Sort (QTS) algorithms, this modified DSMC method becomes largely independent of grid cell size. Therefore, the method possesses considerable advantages in terms of coupling with other grid-based methods in comparison to classical DSMC methods, which have to resolve the mean free path in each cell. The Green–Kubo theory is used to estimate the effects of cell size on transport coefficients. First, the Green–Kubo theory is reviewed for the calculation of the viscosity coefficient as a function of cell size in the classical DSMC method. Next, this theory is extended to the case of using the Nearest Neighbour pairing strategy. Plane Couette flow simulations are used to demonstrate the success of the new particle pairing strategy in becoming independent of the cell size.