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arXiv 1003.4127math.NAcs.NA
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ES-BGK 模型的渐近保持格式

An Asymptotic Preserving Scheme for the ES-BGK model

University of Wisconsin-Madison(威斯康星大学麦迪逊分校)

Francis Filbet, Shi Jin

AI总结:

针对 ES-BGK 动力学方程,提出一种隐式-显式时间离散格式,通过显式处理对流项、隐式处理松弛项克服刚度,并证明在平均自由程趋于零时格式渐近保持欧拉极限,且无需非线性迭代求解器。

摘要:

本文研究了 ES-BGK 动力学方程初值问题的时间离散格式。由于小平均自由程或松弛时间引起的非线性刚性碰撞(源)项,数值求解这些方程具有挑战性。我们研究了一种隐式-显式(IMEX)时间离散化,其中对流项显式处理,而松弛项隐式处理以克服刚度。我们首先展示了如何显式求解隐式松弛,然后渐近证明当平均自由程趋于零且数值时间步长固定时,该时间离散化将密度分布驱动至局部麦克斯韦分布。这自然地在欧拉极限下形成了一个渐近保持格式。如此设计的格式不需要对隐式松弛项进行任何非线性迭代求解器。此外,即使由克努森数确定的小尺度在数值上未被解析,它也能捕捉宏观流体动力学(欧拉)极限。我们还证明了如果粘性和热传导被数值解析,该格式与可压缩纳维-斯托克斯方程一致。几个一维和二维空间的数值例子被用来展示该格式的预期行为。

英文摘要:

In this paper, we study a time discrete scheme for the initial value problem of the ES-BGK kinetic equation. Numerically solving these equations are challenging due to the nonlinear stiff collision (source) terms induced by small mean free or relaxation time. We study an implicit-explicit (IMEX) time discretization in which the convection is explicit while the relaxation term is implicit to overcome the stiffness. We first show how the implicit relaxation can be solved explicitly, and then prove asymptotically that this time discretization drives the density distribution toward the local Maxwellian when the mean free time goes to zero while the numerical time step is held fixed. This naturally imposes an asymptotic-preserving scheme in the Euler limit. The scheme so designed does not need any nonlinear iterative solver for the implicit relaxation term. Moreover, it can capture the macroscopic fluid dynamic (Euler) limit even if the small scale determined by the Knudsen number is not numerically resolved. We also show that it is consistent to the compressible Navier-Stokes equations if the viscosity and heat conductivity are numerically resolved. Several numerical examples, in both one and two space dimensions, are used to demonstrate the desired behavior of this scheme.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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