  Recently, the DSBGK method (note: the original name DS-BGK is changed to
DSBGK for simplicity) was proposed based on the BGK equation to reduce the
stochastic noise in simulating rarefied gas flows at low velocity, in which the
deviation from equilibrium state is small making the traditional DSMC
simulation time-consuming due to the dominance of noise in transient results.
In both DSMC and DSBGK simulations, the simulated molecules move into and out
of cells randomly and frequently. Consequently, the transient information of
molecules in each particular cell contains significant noise. The DSMC method
uses the transient values of molecular variables to compute the cell's
variables (including number density, flow velocity and temperature) and so the
stochastic noise in its cell's variables is remarkable particularly in the case
of low velocity. In the DSBGK simulation, the increments rather than the
transient information of molecular variables are used to update the cell's
variables based on the mass, momentum and energy conservation principles of
intermolecular collision process. This updating scheme significantly reduces
the noise in cell's variables of DSBGK simulations because the molecular
variables are updated smoothly by the extrapolation of acceptance-rejection
scheme and so their increments contain low noise. The detailed comparisons of
algorithms and results between the DSMC and DSBGK methods are given here.
Several benchmark problems are simulated to verify the DSBGK method by
comparison with the DSMC method as criterion.
