Diffusion and dispersion of passive tracers: Navier-Stokes vs. MHD turbulence
Diffusion and dispersion of passive tracers: Navier-Stokes vs. MHD turbulence
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被动示踪剂的扩散和色散：纳维-斯托克斯与 MHD 湍流
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
A. Busse
中科院分区：
文献类型：
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作者：
W. Müller;A. Busse
基于高分辨率直接数值模拟，对均匀、宏观各向同性Navier-Stokes（NS）和非螺旋磁流体动力学（MHD）湍流中的湍流扩散和对色散进行了比较。MHD和NS系统之间的显着差异被观察到的对色散特性，特别是在MHD湍流的分离速度的强烈减少相比，NS的情况下。结果表明，在MHD湍流中，平均对色散在τd <$$> t <$10 τd（τd为Kolmogorov时间）处变慢，这是由于拉格朗日示踪剂的相对速度与局部磁场的一致性造成的。NS和MHD湍流中的湍流单颗粒扩散没有显着差异。在最小的耗散结构附近的流体粒子的轨迹被发现是特征不同的，虽然在这项工作中调查的统计数据，这些罕见的事件有一个可以忽略不计的影响。
A comparison of turbulent diffusion and pair-dispersion in homogeneous, macroscopically isotropic Navier-Stokes (NS) and nonhelical magnetohydrodynamic (MHD) turbulence based on high-resolution direct numerical simulations is presented. Significant differences between MHD and NS systems are observed in the pair-dispersion properties, in particular a strong reduction of the separation velocity in MHD turbulence as compared to the NS case. It is shown that in MHD turbulence the average pair-dispersion is slowed down for τd ≲ t ≲ 10τd, τd being the Kolmogorov time, due to the alignment of the relative Lagrangian tracer velocity with the local magnetic field. Significant differences in turbulent single-particle diffusion in NS and MHD turbulence are not detected. The fluid particle trajectories in the vicinity of the smallest dissipative structures are found to be characteristically different although these comparably rare events have a negligible influence on the statistics investigated in this work.