On the Hydrodynamic Interaction of Shock Waves with Interstellar Clouds. II. The Effect of Smooth Cloud Boundaries on Cloud Destruction and Cloud Turbulence
On the Hydrodynamic Interaction of Shock Waves with Interstellar Clouds. II. The Effect of Smooth Cloud Boundaries on Cloud Destruction and Cloud Turbulence
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DOI：
10.1086/501530
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发表时间：
2005-11
期刊：
影响因子：
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通讯作者：
F. Nakamura;C. McKee;R. Klein;R. Fisher
中科院分区：
文献类型：
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作者：
F. Nakamura;C. McKee;R. Klein;R. Fisher
采用局部自适应网格加密技术和轴对称Goddom流体动力学格式，研究了光滑云边界对定常平面激波与星际云相互作用的影响。还进行了三维计算以证实二维结果。我们发现，光滑的云边界显着影响云的形态和延缓云的破坏。激波通过后，由于在光滑的云边界上产生的速度梯度，形成了一个急剧的密度跳跃。我们将这种密度跳跃称为“滑动面”，因为速度平行于其表面被剪切。由于Kelvin-Helmholtz和Rayleigh-Taylor不稳定性，滑动面的形成导致完全的云破坏。我们构造的云阻力和涡度生成的分析模型，比较以及与数值结果。由不稳定性形成的小碎片具有显著的速度分散性，其速度分散性为环境激波速度的10%-20%。它们可能与最近由Stanimirović和Heiles观测到的小型冷H I云有关。速度色散对区域尺寸的依赖性，即所谓的线宽-尺寸关系，被认为是时间依赖性的。在早期阶段，线宽-尺寸关系或多或少是平坦的，因为开尔文-亥姆霍兹不稳定性产生了显著的小尺度波动。在后期阶段，小尺度波动趋于衰减，导致线宽随尺寸增加。讨论了冲击压缩引发引力不稳定的可能性。我们证明了只有当辐射激波（γ < 4/3）不太强且非热运动很弱时，才能在初始均匀云中诱发引力坍缩。
The effect of smooth cloud boundaries on the interaction of steady planar shock waves with interstellar clouds is studied using a local adaptive mesh refinement technique with an axisymmetric Godunov hydrodynamic scheme. A three-dimensional calculation is also done to confirm the two-dimensional results. We find that smooth cloud boundaries significantly affect cloud morphology and retard cloud destruction. After shock passage, a sharp density jump forms due to velocity gradients generated in the smooth cloud boundary. We refer to this density jump as a "slip surface" because the velocity is sheared parallel to its surface. The formation of a slip surface leads to complete cloud destruction because of the Kelvin-Helmholtz and Rayleigh-Taylor instabilities. We construct analytic models of cloud drag and vorticity generation that compare well with the numerical results. Small shreds formed by the instabilities have significant velocity dispersions of 10%-20% of the ambient shock velocity. They could be related to the small cold H I clouds recently observed by Stanimirović & Heiles. The dependence of the velocity dispersion on region size, the so-called line width-size relation, is found to be time-dependent. In the early stages, the line width-size relation is more or less flat because of the significant small-scale fluctuations generated by the Kelvin-Helmholtz instability. In the later stages, the small-scale fluctuations tend to damp, leading to a line width that increases with size. The possibility of gravitational instability triggered by shock compression is discussed. We show that gravitational collapse can be induced in an initially uniform cloud by a radiative shock (γ < 4/3) only if it is not too strong and nonthermal motions are weak.