Particle-based hybrid and multiscale methods for nonequilibrium gas flows

Abstract

Over the past half century, a variety of computational fluid dynamics (CFD) methods and the direct simulation Monte Carlo (DSMC) method have been widely and successfully applied to the simulation of gas flows for the continuum and rarefied regime, respectively. However, they both encounter difficulties when dealing with multiscale gas flows in modern engineering problems, where the whole system is on the macroscopic scale but the nonequilibrium effects play an important role. In this paper, we review two particle-based strategies developed for the simulation of multiscale nonequilibrium gas flows, i.e., DSMC-CFD hybrid methods and multiscale particle methods. The principles, advantages, disadvantages, and applications for each method are described. The latest progress in the modelling of multiscale gas flows including the unified multiscale particle method proposed by the authors is presented.

Entropic Fokker-Planck kinetic model

“…Motivated by recent studies pointing out to the lack of H-theorem and practical deficiency of the cubic-FP model in accurately resolving shock profiles [33,34], the objective of this work is to derive a mathematically rigorous FP framework which offers two features: consistency of moment relaxations and H-theorem.…”

An efficient algorithm of the unified stochastic particle Bhatnagar-Gross-Krook method for the simulation of multi-scale gas flows

“…One of the strategies to overcome this difficulty is combining the continuous and kinetic methods. For example, the CFD-DSMC hybrid method [3][4][5] implements the CFD solver and direct simulation Monte Carlo (DSMC) method in different regions. Another example is the general synthetic iterative scheme (GSIS) [6] developed recently, which is solved by the CFD and discrete velocity method (DVM) together in the whole region but at different levels.…”

Competition of natural convection and thermal creep in a square enclosure

“…Theoretically, DSMC is valid for the whole flow regimes, as it can be regarded as a particle simulation method of solving Boltzmann equation based on the kinetic theory. However, it is required that the cell sizes and time steps in DSMC need to be smaller than the mean free path and mean collision time, respectively 29 . Therefore, the application of DSMC to the continuum regime is computationally too expensive to accessible.…”