  The direct simulation Monte Carlo (DSMC) method is a widely used stochastic
particle approach to solving the Boltzmann equation. However, its computational
cost remains a major drawback, which can be attributed to statistical errors
when handling flows with low Mach numbers. Thus, many studies have focused on
variance reduction to reduce the computational cost. One approach is the
deviational particle (DP) method, which focuses solely on modeling deviations
from the equilibrium state. The DP method has been implemented in the
low-variance deviational simulation Monte Carlo (LVDSMC) method, which has
proven effective for monatomic gas simulations but faces limitations when
extended to polyatomic gases. In this study, we present a practical DP method
for polyatomic gas simulations that combines the LVDSMC method with the
Larsen-Borgnakke (LB) model, which introduces a group reduction algorithm for
the inelastic collision process. Numerical experiments demonstrated that the
proposed method efficiently and accurately simulates flows across a relatively
broad range of non-equilibrium values. Remarkably, the variance was reduced to
about 5% that of the DSMC method.
