Dynamo action in complex flows: the quick and the fast
Dynamo action in complex flows: the quick and the fast
复制标题
复杂流程中的 Dynamo 动作：快速且快速
DOI：
10.1017/s002211200800044x
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发表时间：
2008
影响因子：
3.7
通讯作者：
F. Cattaneo
中科院分区：
文献类型：
--
作者：
S. Tobias;F. Cattaneo
我们考虑由湍流和相干结构混合组成的速度场的运动发电机问题。对于这些流，发电机增长率由具有大磁雷诺数但周转时间长的大流结构与具有低磁雷诺数但周转时间短的小流结构之间的竞争决定。我们引入快速发电机的概念，即在其临界磁雷诺数的某个（小）邻域内达到最大增长率的发电机。我们认为，如果相干结构是快速发电机，则可以通过观察那些具有空间和时间尺度的流结构来预测总体发电机增长率，使得它们的磁雷诺数略高于临界值。我们通过研究 2.5 维发电机作用来对这个想法进行数值测试，该作用允许考虑极端参数值。所需的速度由给定频谱的湍流和长寿命涡流（相干结构）的混合组成，通过求解主动标量方程获得。通过使用光谱过滤，我们证明了发电机作用的尺度与理论预测的一致。
We consider the kinematic dynamo problem for a velocity field consisting of a mixture of turbulence and coherent structures. For these flows the dynamo growth rate is determined by a competition between the large flow structures that have large magnetic Reynolds number but long turnover times and the small ones that have low magnetic Reynolds number but short turnover times. We introduce the concept of a quick dynamo as one that reaches its maximum growth rate in some (small) neighbourhood of its critical magnetic Reynolds number. We argue that if the coherent structures are quick dynamos, the overall dynamo growth rate can be predicted by looking at those flow structures that have spatial and temporal scales such that their magnetic Reynolds number is just above critical. We test this idea numerically by studying 2.5-dimensional dynamo action which allows extreme parameter values to be considered. The required velocities, consisting of a mixture of turbulence with a given spectrum and long-lived vortices (coherent structures), are obtained by solving the active scalar equations. By using spectral filtering we demonstrate that the scales responsible for dynamo action are consistent with those predicted by the theory.