  The present study addresses the challenge of enhancing computational
efficiency without compromising accuracy in numerical simulations of vacuum gas
dynamics using the direct simulation Monte Carlo (DSMC) method. A technique
termed "fixed particle per cell (FPPC)" was employed, which enforces a fixed
number of simulator particles across all computational cells. The proposed
technique eliminates the need for real-time adjustment of particle weights
during simulation, reducing calculation time. Using the SPARTA solver,
simulations of rarefied gas flow in a micromixer and rarefied supersonic
airflow around a cylinder were conducted to validate the proposed technique.
Results demonstrate that applying the FPPC technique effectively reduces
computational costs while yielding results comparable to conventional DSMC
implementations. Additionally, the application of local grid refinement coupled
with the FPPC technique was investigated. The results show that integrating
local grid refinement with the FPPC technique enables accurate prediction of
flow behaviour in regions with significant gradients. These findings highlight
the efficacy of the proposed technique in improving the accuracy and efficiency
of numerical simulations of complex vacuum gas dynamics at a reduced
computational cost.
