DSMC Calculation of Vortex Shedding behind a Flat Plate with a New Intermolecular Collision Scheme

The generation of vortices for the flow past a flat plate is calculated by the DSMC method. The new intermolecular collision scheme and the conventional one are compared with respect to their allowable cell dimension. In the condition of Re=50, when using the conventional scheme, the vortex behind an inclined flat plate becomes weak with increasing the cell dimension beyond the mean free path, and finally the structure of vortex is smeared out. In the new scheme, on the other hand, the strength of the vortex does not weaken even with the cell length being ten times the mean free path. At Re=200, the new scheme can produce the vortex shedding behind a flat plate with the cell dimension of 20λ for the inclined plate, or 12λ in the case of a normal plate to the flow direction, although the conventional one cannot. The new intermolecular collision scheme is verified effective for unsteady flows such as vortex shedding.