Evolution of magnetic fields in freely decaying magnetohydrodynamic turbulence.
Evolution of magnetic fields in freely decaying magnetohydrodynamic turbulence.
复制标题
自由衰减磁流体动力湍流中磁场的演化。
DOI：
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发表时间：
2007
影响因子：
8.6
通讯作者：
L. Campanelli
中科院分区：
文献类型：
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作者：
L. Campanelli
研究了自由衰减磁流体动力学湍流中磁场的演化。通过将Navier-Stokes方程拟线性化，在拟正规近似下解析求解了诱导方程。我们发现，如果磁场不是螺旋的，则磁能和关联长度分别随时间演化为E（B）与t（-2（1 +p）/（3+p））成正比，xi（B）与t（2/（3+p））成正比，其中p是初始幂律谱的指数.在螺旋的情况下，磁螺旋度几乎是守恒量，并迫使磁能和相关长度按比例缩放为E（B）与（logt）（1/3）t（-2/3）成比例，xi（B）与（logt）（-1/3）t（2/3）成比例。
We study the evolution of magnetic fields in freely decaying magnetohydrodynamic turbulence. By quasilinearizing the Navier-Stokes equation, we solve analytically the induction equation in the quasinormal approximation. We find that, if the magnetic field is not helical, the magnetic energy and correlation length evolve in time, respectively, as E(B) proportional to t(-2(1+p)/(3+p)) and xi(B) proportional to t(2/(3+p)), where p is the index of initial power-law spectrum. In the helical case, the magnetic helicity is an almost conserved quantity and forces the magnetic energy and correlation length to scale as E(B) proportional to (logt)(1/3)t(-2/3) and xi(B) proportional to (logt)(-1/3)t(2/3).