Scaling laws in decaying helical hydromagnetic turbulence
Scaling laws in decaying helical hydromagnetic turbulence
复制标题
衰减螺旋水磁湍流的标度定律
DOI：
10.1002/asna.200510365
复制
发表时间：
2002
影响因子：
0.9
通讯作者：
A. Brandenburg
中科院分区：
文献类型：
--
作者：
M. Christensson;M. Hindmarsh;A. Brandenburg
本文研究了自由衰减三维MHD湍流中磁场相干长度xi、能量E_M和磁螺旋度H的增长和衰减规律。我们表明，在一定的假设下，磁功率谱的自相似性意味着xi~t^{1/2}。这又意味着磁螺旋度以H~t^{-2s}的形式衰减，其中s=（xi_{diff}/xi_H）^2，根据扩散长度尺度xi_{diff}和螺旋度功率谱定义的长度尺度xi_H。相对磁螺旋度保持恒定，意味着磁能以E_M~t^{-1/2-2s}衰减。参数s与磁雷诺数Re_M成反比，Re_M在自相似区是常数。
We study the evolution of growth and decay laws for the magnetic field coherence length xi, energy E_M and magnetic helicity H in freely decaying 3D MHD turbulence. We show that with certain assumptions, self-similarity of the magnetic power spectrum alone implies that xi~t^{1/2}. This in turn implies that magnetic helicity decays as H~t^{-2s}, where s=(xi_{diff}/xi_H)^2, in terms of xi_{diff}, the diffusion length scale, and xi_H, a length scale defined from the helicity power spectrum. The relative magnetic helicity remains constant, implying that the magnetic energy decays as E_M~t^{-1/2-2s}. The parameter s is inversely proportional to the magnetic Reynolds number Re_M, which is constant in the self-similar regime.