Generation of Solenoidal Modes and Magnetic Fields in Turbulence Driven by Compressive Driving
Generation of Solenoidal Modes and Magnetic Fields in Turbulence Driven by Compressive Driving
复制标题
压缩驱动湍流中螺线管模式和磁场的产生
DOI：
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发表时间：
2020
影响因子：
4.9
通讯作者：
Heesun Yoon
中科院分区：
文献类型：
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作者：
J. Lim;Jungyeon Cho;Heesun Yoon
本文对压缩驱动下的流体动力学（HD）和磁流体动力学（MHD）湍流进行了数值模拟，研究了螺线线速度分量和小尺度磁场的产生。我们主要研究了平均磁场（B0）和音速马赫数（Ms）的影响。在压缩驱动湍流中，螺线管比（即螺线管与动能之比）和磁能密度对Ms的依赖关系已经建立，但对B0的依赖关系尚未建立。我们还考虑了两种不同的驱动方案的相关时间尺度的强迫向量：有限相关驱动和三角洲相关驱动。我们的研究结果如下。首先，当我们确定B0的值时，饱和后的螺线管比随着增大而增大。当B0较小时，磁场的产生也有类似的趋势。其次，当我们固定值时，当B0不强时，HD和MHD模拟结果相似的螺线管比（例如，MA≥5，其中MA为alfv<s:1>马赫数）。当MA > 5时，比值增大。粗略地说，饱和后的磁能密度与ms无关，是B0的线性递增函数。第三，螺线线速度分量的产生对数值分辨率不敏感，但磁能密度的产生是轻度敏感的。最后，在初始条件相同的情况下，有限相关驱动产生的螺线形速度分量和小尺度磁场分量总是大于delta相关驱动。我们还分析了涡度方程，以理解为什么更高和B0产生更大数量的螺线线速度分量。
We perform numerical simulations of hydrodynamic (HD) and magnetohydrodynamic (MHD) turbulence driven by compressive driving, to study the generation of solenoidal velocity components and the small-scale magnetic field. We mainly focus on the effects of mean magnetic field (B0) and the sonic Mach number (Ms). The dependence of solenoidal ratio (i.e., ratio of solenoidal to kinetic energies) and magnetic energy density on Ms in compressively driven turbulence is already established, but that on B0 is not yet. We also consider two different driving schemes in terms of the correlation timescale of forcing vectors: a finite-correlated driving and a delta-correlated driving. Our findings are as follows. First, when we fix the value of B0, the solenoidal ratio after saturation increases as increases. A similar trend is observed for generation of magnetic field when B0 is small. Second, when we fix the value of , HD and MHD simulations result in similar solenoidal ratios when B0 is not strong (say, MA ≳ 5, where MA is Alfvén Mach number). However, the ratio increases when MA ≲ 5. Roughly speaking, the magnetic energy density after saturation is a linearly increasing function of B0 irrespective of Ms. Third, generation of the solenoidal velocity component is not sensitive to numerical resolution, but that of magnetic energy density is mildly sensitive. Finally, when initial conditions are same, the finite-correlated driving always produces more solenoidal velocity and small-scale magnetic field components than the delta-correlated driving. We additionally analyze the vorticity equation to understand why higher and B0 yield a larger quantity of the solenoidal velocity component.