强环向磁场扭折型不稳定性引起的涡旋粘性和湍流Schmidt数
Eddy viscosity and turbulent Schmidt number by kink-type instability of strong toroidal magnetic fields
摘要：
考虑到具有不同旋转速率的导电圆柱之间的近均匀环向场的稳定性，探讨了非轴对称磁不稳定性传输角动量和混合化学物质的潜力。假设圆柱体之间的流体是不可压缩的，并且具有均匀的密度。用线性理论计算了m=1时的中性稳定映射。刚性旋转必须是亚阿尔夫文旋转才能允许不稳定，而对于具有负剪切力的差异旋转，也存在具有超阿尔夫文旋转的不稳定域。磁不稳定性的旋转淬灭是最强的磁普朗特数Pm=1，并成为弱得多的Pm不等于1。不稳定性导致的有效角动量输运对于次旋转（超旋转）是向外（向内）的。由此产生的磁致涡流粘度超过微观值的10-100倍。这只适用于超阿尔文流;在强场极限下，数值仍然小得多。同样的不稳定性也会通过它的涨落来抑制化学物质的浓度梯度。相应的扩散系数始终小于磁致涡动粘度。施密特数的顺序为30被发现的有效粘度和扩散系数的比率。磁不稳定性传输的角动量比它混合化学物质的角动量多得多。
英文摘要：
The potential of the nonaxisymmetric magnetic instability to transport angular momentum and to mix chemicals is probed considering the stability of a nearly uniform toroidal field between conducting cylinders with different rotation rates. The fluid between the cylinders is assumed as incompressible and to be of uniform density. With a linear theory the neutral-stability maps for m=1 are computed. Rigid rotation must be subAlfvenic to allow instability while for differential rotation with negative shear also an unstable domain with superAlfvenic rotation exists. The rotational quenching of the magnetic instability is strongest for magnetic Prandtl number Pm=1 and becomes much weaker for Pm unequal 1. The effective angular momentum transport by the instability is directed outwards(inwards) for subrotation(superrotation). The resulting magnetic-induced eddy viscosities exceed the microscopic values by factors of 10-100. This is only true for superAlfvenic flows; in the strong-field limit the values remain much smaller. The same instability also quenches concentration gradients of chemicals by its nonmagnetic fluctuations. The corresponding diffusion coefficient remains always smaller than the magnetic-generated eddy viscosity. A Schmidt number of order 30 is found as the ratio of the effective viscosity and the diffusion coefficient. The magnetic instability transports much more angular momentum than that it mixes chemicals.
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