Electromotive force and large-scale magnetic dynamo in a turbulent flow with a mean shear.
Electromotive force and large-scale magnetic dynamo in a turbulent flow with a mean shear.
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平均剪切湍流中的电动势和大型磁发电机。
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
N. Kleeorin
中科院分区：
文献类型：
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作者：
I. Rogachevskii;N. Kleeorin
研究了导电流体非旋转湍流中剪切大尺度运动对平均电动势的影响。它表明，在均匀的发散自由湍流的α效应不存在，然而，平均磁场可以产生，即使在非旋转的湍流与强加的平均速度剪切由于“剪切电流”效应。平均速度剪切导致湍流磁扩散的各向异性。的平均磁场（卡帕效应）的梯度张量的对称部分相关的电动势的贡献被发现在非旋转湍流与平均剪切。kappa效应和湍流磁扩散降低了平均磁场的增长率。结果表明，当背景湍流（无平均速度切变）的能谱指数小于2时，可以产生平均磁场。剪切电流效应的研究使用两种不同的方法：τ近似（Orszag三阶闭合程序）和随机微积分（路径积分表示的感应方程的解决方案，Feynman-Kac公式，和Cameron-Martin-Girsanov定理）。天体物理的应用所获得的结果进行了讨论。
An effect of sheared large-scale motions on a mean electromotive force in a nonrotating turbulent flow of a conducting fluid is studied. It is demonstrated that in a homogeneous divergence-free turbulent flow the alpha effect does not exist, however a mean magnetic field can be generated even in a nonrotating turbulence with an imposed mean velocity shear due to a "shear-current" effect. A mean velocity shear results in an anisotropy of turbulent magnetic diffusion. A contribution to the electromotive force related to the symmetric parts of the gradient tensor of the mean magnetic field (the kappa effect) is found in nonrotating turbulent flows with a mean shear. The kappa effect and turbulent magnetic diffusion reduce the growth rate of the mean magnetic field. It is shown that a mean magnetic field can be generated when the exponent of the energy spectrum of the background turbulence (without the mean velocity shear) is less than 2. The shear-current effect was studied using two different methods: the tau approximation (the Orszag third-order closure procedure) and the stochastic calculus (the path integral representation of the solution of the induction equation, Feynman-Kac formula, and Cameron-Martin-Girsanov theorem). Astrophysical applications of the obtained results are discussed.