论文标题
由压缩驾驶驱动的湍流中的螺线管模式和磁场的产生
Generation of Solenoidal Modes and Magnetic Fields in Turbulence Driven by Compressive Driving
论文作者
论文摘要
我们通过压缩驾驶驱动的流体动力学（HD）和磁性水力动力学（MHD）进行数值模拟，以研究螺线管速度成分和小规模磁场的研究产生。我们主要关注平均磁场（$ B_0 $）和声音马赫数（$ M_S $）的影响。我们还考虑了强迫向量的相关时间尺度上考虑两种不同的驾驶方案：有限相关的驾驶和与三角洲相关的驾驶。前者的相关时间尺度比后者具有更长的相关时间尺度，该时间尺度与大涡流额相当。我们的发现如下。首先，当我们修复$ b_0 $的值时，饱和度后的螺线管速度组件的水平随着$ m_s $的增加而增加。当$ B_0 $很小时，观察到磁场的产生类似趋势。其次，当我们修复$ M_S $，HD和MHD仿真的值时，当$ B_0 $ $ \ lyseSim $ 0.2（或$ \ sim $ 5的Alfven Mach数量）时，导致螺线管组件的水平相似。但是，当$ b_0 $ $ \ gtrsim $ 0.2时，水平会增加。粗略地说，饱和后的磁能密度是$ b_0 $的线性增加功能，而不论$ m_s $。第三，螺线管速度成分的产生对数值分辨率不敏感，但磁能密度的分辨率有些敏感。最后，当初始条件相同时，有限相关的驾驶总是会产生比三角相关驱动的螺线管速度和小规模的磁场成分。我们还分析了涡度方程，以了解为什么更高的$ m_s $和$ b_0 $产生大量的螺线管速度组件。
We perform numerical simulations of hydrodynamic (HD) and magnetohydrodynamic (MHD) turbulence driven by compressive driving to study generation of solenoidal velocity component and small-scale magnetic field. We mainly focus on the effects of mean magnetic field ($B_0$) and the sonic Mach number ($M_s$). We also consider two different driving schemes in terms of correlation timescale of forcing vectors: a finite-correlated driving and a delta-correlated driving. The former has a longer correlation timescale of forcing vectors, which is comparable to large-eddy turnover time, than the latter. Our findings are as follows. First, when we fix the value of $B_0$, the level of solenoidal velocity component after saturation increases as $M_s$ increases. A similar trend is observed for generation of magnetic field when $B_0$ is small. Second, when we fix the value of $M_s$, HD and MHD simulations result in similar level of the solenoidal component when $B_0$ $\lesssim$ 0.2 (or Alfven Mach number of $\sim$ 5). However, the level increases when $B_0$ $\gtrsim$ 0.2. Roughly speaking, the magnetic energy density after saturation is a linearly increasing function of $B_0$ irrespective of $M_s$. Third, generation of solenoidal velocity component is not sensitive to numerical resolution, but that of magnetic energy density is mildly sensitive. Lastly, 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 $M_s$ and $B_0$ yield larger quantity of the solenoidal velocity component.
