Stratorotational instability in MHD Taylor-Couette flows
Stratorotational instability in MHD Taylor-Couette flows
复制标题
MHD Taylor-Couette 流中的平旋不稳定性
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
D. Shalybkov
中科院分区：
文献类型：
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作者：
G. Ruediger;D. Shalybkov
目标。考虑了具有稳定轴向密度分层和指定方位磁场的耗散泰勒-库埃特流的稳定性。方法。对于绝缘圆柱体和导电圆柱体，都找到了具有环形磁场、密度分层和微分旋转的线性化 MHD 方程的全局非轴对称解。结果。对各种间隙宽度的流体动力学计算表明，诸如开普勒旋转之类的平面旋转定律相对于 SRI 总是不稳定的。然而，准银河系旋转定律对于较宽的间隙是稳定的。无电流环形磁场对 SRI 的影响在很大程度上取决于磁普朗特数 Pm：Pm > 1 支持 SRI，Pm < 1 则抑制 SRI。对于过于平坦的旋转定律，当流体动力 SRI 停止时，存在向环形磁场与微分旋转结合产生的不稳定性的平滑过渡。首次在存在轴向密度梯度的情况下计算了这种非轴对称方位角磁旋转不稳定性（AMRI）。如果圆柱体之间的磁场不是无电流的，那么泰勒不稳定性也会发生。在存在差异旋转和密度分层的情况下，从非磁性离心不稳定性到磁性泰勒不稳定性的转变被证明是复杂的。最引人注目的是密度分层导致的稳定域的“膨胀”：很小的旋转就已经稳定了磁场以对抗泰勒不稳定性。
Aims. The stability of the dissipative Taylor-Couette flow with a stable axial density stratification and a prescribed azimuthal magnetic field is considered. Methods. Global nonaxisymmetric solutions of the linearized MHD equations with toroidal magnetic field, density stratification, and differential rotation are found for both insulating and conducting cylinders. Results. Hydrodynamic calculations for various gap widths show that flat rotation laws such as the Kepler rotation are always unstable against SRI. Quasigalactic rotation laws, however, are stable for wide gaps. The influence of a current-free toroidal magnetic field on SRI strongly depends on the magnetic Prandtl number Pm: SRI is supported by Pm > 1 and it is suppressed by Pm < 1. For rotation laws that are too flat, when the hydrodynamic SRI ceases, a smooth transition exists to the instability that the toroidal magnetic field produces in combination with the differential rotation. For the first time this nonaxisymmetric azimuthal magnetorotational instability (AMRI) has been computed in the presence of an axial density gradient. If the magnetic field between the cylinders is not current-free, then the Tayler instability occurs, too. The transition from the nonmagnetic centrifugal instability to the magnetic Tayler instability in the presence of differential rotation and density stratification proves to be complex. Most spectacular is the “ballooning” of the stability domain by the density stratification: already a small rotation stabilizes magnetic fields against the Tayler instability.