Simulations of nonhelical hydromagnetic turbulence
Simulations of nonhelical hydromagnetic turbulence
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DOI：
10.1103/physreve.70.016308
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发表时间：
2004-07-01
影响因子：
2.4
通讯作者：
Dobler, W
中科院分区：
文献类型：
--
作者：
Haugen, NEL;Brandenburg, A;Dobler, W
在多达256个处理器和1024（3）个网格点上使用大规模模拟研究了非螺旋磁流体强迫湍流。磁普朗特数在1/8和30之间变化，尽管在大多数情况下它是1。当磁雷诺数是基于反强迫波数，发电机作用的临界值被证明是约35磁普朗特数的单位。对于小的磁普朗特数，我们发现临界磁雷诺数的增加而减少磁普朗特数。对于运动学区域，确认了磁能的Kazantsev k（3/2）谱，即，当非线性效应仍然是不重要的，当磁普朗特数是统一的。在非线性区域，能量预算收敛大雷诺数（约1000），使我们的参数约70%是动能和约30%是磁能。能量耗散率收敛到30%粘性耗散和70%电阻耗散。Elsasser变量的二阶结构函数给出了k（-5/3）谱的证据。尽管如此，三维谱接近k（-3/2），但我们认为这是由于瓶颈效应。瓶颈效应被证明是同样强大的磁湍流和湍流，但它是弱得多，通常在实验室湍流研究的一维光谱。其他阶次的结构函数指数由She-Leveque公式很好地描述，但速度场的间歇性明显小于Elsasser变量，磁场的间歇性大于Elsasser变量。
Nonhelical hydromagnetic forced turbulence is investigated using large scale simulations on up to 256 processors and 1024(3) mesh points. The magnetic Prandtl number is varied between 1/8 and 30, although in most cases it is unity. When the magnetic Reynolds number is based on the inverse forcing wave number, the critical value for dynamo action is shown to be around 35 for magnetic Prandtl number of unity. For small magnetic Prandtl numbers we find the critical magnetic Reynolds number to increase with decreasing magnetic Prandtl number. The Kazantsev k(3/2) spectrum for magnetic energy is confirmed for the kinematic regime, i.e., when nonlinear effects are still unimportant and when the magnetic Prandtl number is unity. In the nonlinear regime, the energy budget converges for large Reynolds numbers (around 1000) such that for our parameters about 70% is in kinetic energy and about 30% is in magnetic energy. The energy dissipation rates are converged to 30% viscous dissipation and 70% resistive dissipation. Second-order structure functions of the Elsasser variables give evidence for a k(-5/3) spectrum. Nevertheless, the three-dimensional spectrum is close to k(-3/2), but we argue that this is due to the bottleneck effect. The bottleneck effect is shown to be equally strong both for magnetic and nonmagnetic turbulence, but it is far weaker in one-dimensional spectra that are normally studied in laboratory turbulence. Structure function exponents for other orders are well described by the She-Leveque formula, but the velocity field is significantly less intermittent and the magnetic field is more intermittent than the Elsasser variables.