Intermittency and geometrical statistics of three-dimensional homogeneous magnetohydrodynamic turbulence: A wavelet viewpoint
Intermittency and geometrical statistics of three-dimensional homogeneous magnetohydrodynamic turbulence: A wavelet viewpoint
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DOI：
10.1063/1.3628637
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发表时间：
2011-09
影响因子：
2.2
通讯作者：
K. Yoshimatsu;K. Schneider;Naoya Okamoto;Yasuhiro Kawahara;M. Farge
中科院分区：
文献类型：
--
作者：
K. Yoshimatsu;K. Schneider;Naoya Okamoto;Yasuhiro Kawahara;M. Farge
本文用正交小波分解方法研究了无平均磁场的三维不可压缩均匀磁流体湍流的尺度相关统计和几何统计。流动计算的直接数值模拟与傅立叶谱方法在分辨率5123和单位磁普朗特数。尺度相关的二阶和高阶统计的速度和磁场允许量化的能量谱的空间波动，平坦度，和概率分布函数在不同的尺度方面的不稳定性。不同的尺度相关的相对螺旋度，例如，动力学、交叉和磁相对螺旋度产生关于不同尺度依赖场之间的对准的几何信息。在每个尺度上，发现速度和磁场之间的对准比这里考虑的其他对准更明显，即，速度和涡量之间的尺度相关对准，磁场和其矢势之间的尺度相关对准，以及磁场和电流密度之间的尺度相关对准。最后，统计尺度相关的分析欧拉和拉格朗日加速度和相应的时间导数的磁场进行。据发现，拉格朗日加速度并没有表现出显着更强的阻力比欧拉加速度相比，在流体动力学湍流的拉格朗日加速度比欧拉加速度表现出更强的阻力。磁场的欧拉时间导数比磁场的拉格朗日时间导数更具间歇性。
Scale-dependent and geometrical statistics of three-dimensional incompressible homogeneous magnetohydrodynamicturbulence without mean magnetic field are examined by means of the orthogonal wavelet decomposition. The flow is computed by direct numerical simulation with a Fourier spectral method at resolution 5123 and a unit magnetic Prandtl number. Scale-dependent second and higher order statistics of the velocity and magnetic fields allow to quantify their intermittency in terms of spatial fluctuations of the energy spectra, the flatness, and the probability distribution functions at different scales. Different scale-dependent relative helicities, e.g., kinetic, cross, and magnetic relative helicities, yield geometrical information on alignment between the different scale-dependent fields. At each scale, the alignment between the velocity and magnetic field is found to be more pronounced than the other alignments considered here, i.e., the scale-dependent alignment between the velocity and vorticity, the scale-dependent alignment between the magnetic field and its vector potential, and the scale-dependent alignment between the magnetic field and the current density. Finally, statistical scale-dependent analyses of both Eulerian and Lagrangian accelerations and the corresponding time-derivatives of the magnetic field are performed. It is found that the Lagrangian acceleration does not exhibit substantially stronger intermittency compared to the Eulerian acceleration, in contrast to hydrodynamic turbulence where the Lagrangian acceleration shows much stronger intermittency than the Eulerian acceleration. The Eulerian time-derivative of the magnetic field is more intermittent than the Lagrangian time-derivative of the magnetic field.