激波与多个磁化云团相互作用的数值模拟
Numerical Simulations of a Shock Interacting with Multiple Magnetized Clouds
摘要：
我们对冲击波与两个或三个圆柱形云组相互作用进行了二维绝热磁流体动力学（MHD）模拟。我们研究了附近的云的存在如何影响这种相互作用的动态，并探讨了由此产生的差异和相似之处，在每个云的演变。从这项小规模研究中获得的理解将有助于解释具有许多10或100个云的系统的行为。我们观察到各种各样的行为在相互作用的研究，这是依赖于云的初始位置和方向和强度的磁场。我们发现：i）一些云沿着它们的场线被拉伸，而另一些云被它们的场线限制; ii）上游云可能加速通过下游云（尽管磁张力可以阻止这种情况）; iii）当云相互“弹射”过去时，它们也可能改变它们在激波传播方向上的相对位置; iv）由于下游云处于上游云的背风面，下游云可能受到一些保护，不受迎面而来的气流的影响; v）当附近有相邻的云时，云压缩和再膨胀的循环通常较弱; vi）云物质中的等离子体$β$可以随着云彼此碰撞而迅速变化，但是$β$的低值总是暂时的。这项工作与多相区的研究有关，在多相区中，快速、低密度的气体与致密的云相互作用，例如在星周气泡、超新星遗迹、超级气泡和银河风中。
英文摘要：
We present 2D adiabatic magnetohydrodynamic (MHD) simulations of a shock interacting with groups of two or three cylindrical clouds. We study how the presence of a nearby cloud influences the dynamics of this interaction, and explore the resulting differences and similarities in the evolution of each cloud. The understanding gained from this small-scale study will help to interpret the behaviour of systems with many 10's or 100's of clouds. We observe a wide variety of behaviour in the interactions studied, which is dependent on the initial positions of the clouds and the orientation and strength of the magnetic field. We find: i) some clouds are stretched along their field-lines, whereas others are confined by their field-lines; ii) upstream clouds may accelerate past downstream clouds (though magnetic tension can prevent this); iii) clouds may also change their relative positions transverse to the direction of shock propagation as they "slingshot" past each other; iv) downstream clouds may be offered some protection from the oncoming flow as a result of being in the lee of an upstream cloud; v) the cycle of cloud compression and re-expansion is generally weaker when there are nearby neighbouring clouds; vi) the plasma $β$ in cloud material can vary rapidly as clouds collide with one another, but low values of $β$ are always transitory. This work is relevant to studies of multi-phase regions, where fast, low-density gas interacts with dense clouds, such as in circumstellar bubbles, supernova remnants, superbubbles and galactic winds.
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