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.

中文翻译：

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非平衡气流的基于粒子的混合和多尺度方法

在过去的半个世纪中，各种各样的计算流体动力学（CFD）方法和直接模拟蒙特卡洛（DSMC）方法已分别广泛并成功地分别应用于连续和稀疏区域的气流模拟。但是，它们在现代工程问题中处理多尺度气流时都遇到困难，整个系统在宏观范围内，但非平衡效应起着重要作用。在本文中，我们回顾了为模拟多尺度非平衡气流而开发的两种基于粒子的策略，即DSMC-CFD混合方法和多尺度粒子方法。描述了每种方法的原理，优点，缺点和应用。