In this paper, we extend the unified gas-kinetic wave-particle (UGKWP) methods to the multi-species gas mixture and multiscale plasma transport. The construction of the scheme is based on the direct modeling on the mesh size and time step scales, and the local cell’s Knudsen number determines the flow physics. The proposed scheme has the multiscale and asymptotic complexity diminishing properties. The multiscale property means that according to the cell’s Knudsen number the scheme can capture the non-equilibrium flow physics when the cell size is on the kinetic mean free path scale, and preserve the asymptotic Euler, Navier-Stokes, and magnetohydrodynamics (MHD) when the cell size is on the hydrodynamic scale and is much larger than the particle mean free path. The asymptotic complexity diminishing property means that the total degrees of freedom of the scheme reduce automatically with the decreasing of the cell’s Knudsen number. In the continuum regime, the scheme automatically degenerates from a kinetic solver to a hydrodynamic solver. In the UGKWP, the evolution of microscopic velocity distribution is coupled with the evolution of macroscopic variables, and the particle evolution as well as the macroscopic fluxes is modeled from a time accumulating solution of kinetic scale particle transport and collision up to a time step scale. For plasma transport, the current scheme provides a smooth transition from particle-in-cell (PIC) method in the rarefied regime to the magnetohydrodynamic solver in the continuum regime. In the continuum limit, the cell size and time step of the UGKWP method are not restricted by the particle mean free path and mean collision time. In the highly magnetized regime, the cell size and time step are not restricted by the Debye length and plasma cyclotron period. The multiscale and asymptotic complexity diminishing properties of the scheme are verified by numerical tests in multiple flow regimes.

中文翻译：

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统一的气体动力学波粒方法IV：多种物种的气体混合物和等离子体传输

在本文中，我们将统一的气体动力学波粒法（UGKWP）扩展到多物种气体混合物和多尺度等离子体传输。该方案的构建基于网格大小和时间步长比例的直接建模，而本地单元格的Knudsen数决定了流动的物理性质。所提出的方案具有递减复杂度的多尺度性质。多尺度性质意味着，根据单元格的Knudsen数，当单元格大小处于动力学平均自由程尺度时，该方案可以捕获非平衡流物理场，并在以下情况下保留渐近的Euler，Navier-Stokes和磁流体动力学（MHD）单元的大小在流体动力学尺度上，并且比粒子平均自由程大得多。渐近复杂度减小的特性意味着该方案的总自由度会随着像元的Knudsen数的减少而自动减少。在连续状态下，方案自动从动力学求解器退化为流体动力学求解器。在UGKWP中，微观速度分布的演化与宏观变量的演化是耦合的，并且从动力学尺度粒子传输和碰撞的时间累积解到时步尺度对粒子演化以及宏观通量进行建模。对于等离子体传输，当前方案提供了从稀疏状态下的胞中粒子（PIC）方法到连续谱状态下的磁流体动力学求解器的平稳过渡。在连续极限中，UGKWP方法的像元大小和时间步长不受粒子平均自由程和平均碰撞时间的限制。在高度磁化的情况下，细胞大小和时间步长不受德拜长度和等离子回旋周期的限制。该方案的多尺度和渐近复杂度递减性质已通过在多种流动状态下的数值试验得到了验证。