The angular momentum transport by unstable toroidal magnetic fields
The angular momentum transport by unstable toroidal magnetic fields
复制标题
不稳定环形磁场的角动量传输
DOI：
10.1051/0004-6361/201424060
复制
发表时间：
2015
影响因子：
6.5
通讯作者：
Tereshin
中科院分区：
文献类型：
--
作者：
Rüdiger;Gellert;Tereshin
我们证明了与非线性磁流体动力学（MHD）的代码，角动量可以传输，因为磁不稳定性的环向场的影响下的差分旋转，以及由此产生的有效粘度可能是足够高的，以解释几乎刚体旋转观察到的辐射恒星核心。我们只考虑静止的，无电流的场，并且只考虑那些提供最大粘性数值的旋转速率和磁场振幅的组合。我们发现，有效分子粘度的无量纲比率，νT/ν，线性增长的雷诺数的旋转流体乘以磁普朗特数的平方根，这是近似为1所考虑的红亚巨星星星KIC 7341231。对于所考虑的磁雷诺数的区间-这是由非线性MHD代码的数值约束-磁普朗特数有显着的影响的相对重要性的贡献的雷诺应力和麦克斯韦应力的总粘度，这是磁占主导地位的只有为Pm <$0.5。我们还发现磁化等离子体表现为非牛顿流体，即，所得的有效粘度取决于旋转定律中的剪切。因此，差旋的衰减时间取决于它的剪切，并且在恒星核自旋下降的过程中变得越来越长。
We demonstrate with a nonlinear magnetohydrodynamic (MHD) code that angular momentum can be transported because of the magnetic instability of toroidal fields under the influence of differential rotation, and that the resulting effective viscosity may be high enough to explain the almost rigid-body rotation observed in radiative stellar cores. We only consider stationary, current-free fields, and only those combinations of rotation rates and magnetic field amplitudes which provide maximal numerical values of the viscosity. We find that the dimensionless ratio of the effective over molecular viscosity,νT/ν, linearly grows with the Reynolds number of the rotating fluid multiplied by the square-root of the magnetic Prandtl number, which is approximately unity for the considered red subgiant star KIC 7341231. For the interval of magnetic Reynolds numbers considered – which is restricted by numerical constraints of the nonlinear MHD code – the magnetic Prandtl number has a remarkable influence on the relative importance of the contributions of the Reynolds stress and the Maxwell stress to the total viscosity, which is magnetically dominated only forPm≳ 0.5. We also find that the magnetized plasma behaves as a non-Newtonian fluid, i.e., the resulting effective viscosity depends on the shear in the rotation law. The decay time of the differential rotation thus depends on its shear and becomes longer and longer during the spin-down of a stellar core.