瑞利不稳定区的剪切盒模拟
Shearing box simulations in the Rayleigh unstable regime
摘要：
研究了两种不同剪切$q=2.1, 4.2$（$q = - d\lnΩ/ d\ln r$）值下纯流体动力学和磁流体动力学（MHD）区域中Rayleigh不稳定流的稳定性，并与Keplerian情形$q=1.5$进行了比较.我们发现，$q>2$制度是不稳定的流体动力学和MHD极限（与初始弱磁场）。在这种情况下，速度波动主导的磁场波动。相反，在$q<2$（磁旋转不稳定性（MRI））制度的磁波动占主导地位。这突出了两个不同的路径MHD湍流暗示的两个制度，这表明在$q>2$制度的不稳定性产生主要的速度波动，导致磁波动，与因果关系相反的$q<2$ MRI不稳定制度。我们还发现，磁场的相关性是越来越本地化的剪切力的增加，在瑞利不稳定制度。在计算MHD方程中不同项的空间平均值随时间的演化时，我们发现$q>2$区域主要是由涨落中的非线性项所控制，而对于$q<2$，线性项起着更重要的作用。
英文摘要：
We study the stability properties of Rayleigh unstable flows both in the purely hydrodynamic and magnetohydrodynamic (MHD) regimes for two different values of the shear $q=2.1, 4.2$ ($q = - d\lnΩ/ d\ln r$) and compare it with the Keplerian case $q=1.5$. We find that the $q>2$ regime is unstable both in the hydrodynamic and in the MHD limit (with an initially weak magnetic field). In this regime, the velocity fluctuations dominate the magnetic fluctuations. In contrast, in the $q<2$ (magnetorotational instability (MRI)) regime the magnetic fluctuations dominate. This highlights two different paths to MHD turbulence implied by the two regimes, suggesting that in the $q>2$ regime the instability produces primarily velocity fluctuations that cause magnetic fluctuations, with the causality reversed for the $q<2$ MRI unstable regime. We also find that the magnetic field correlation is increasingly localized as the shear is increased in the Rayleigh unstable regime. In calculating the time evolution of spatial averages of different terms in the MHD equations, we find that the $q>2$ regime is dominated by terms which are nonlinear in the fluctuations, whereas for $q<2$, the linear terms play a more significant role.
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