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A comparison of shock-cloud and wind-cloud interactions: the longer survival of clouds in winds

机译:冲击云和风云相互作用的比较:云中风的存活时间更长

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摘要

The interaction of a hot, high-velocity wind with a cold, dense molecular cloud has often been assumed to resemble the evolution of a cloud embedded in a post-shock flow. However, no direct comparative study of these two processes currently exists in the literature. We present 2D adiabatic hydrodynamical simulations of the interaction of a Mach 10 shock with a cloud of density contrast χ = 10 and compare our results with those of a commensurate wind-cloud simulation. We then investigate the effect of varying the wind velocity, effectively altering the wind Mach number Mwind, on the cloud's evolution. We find that there are significant differences between the two processes: 1) the transmitted shock is much flatter in the shock-cloud interaction; 2) a low-pressure region in the wind-cloud case deflects the flow around the edge of the cloud in a different manner to the shock-cloud case; 3) there is far more axial compression of the cloud in the case of the shock. As Mwind increases, the normalized rate of mixing is reduced. Clouds in winds with higher Mwind also do not experience a transmitted shock through the cloud's rear and are more compressed axially. In contrast with shock-cloud simulations, the cloud mixing time normalized by the cloud-crushing time-scale tcc increases for increasing Mwind until it plateaus (at tmix ≃ 25 tcc) at high Mwind, thus demonstrating the expected Mach scaling. In addition, clouds in high Mach number winds are able to survive for long durations and are capable of being moved considerable distances.
机译:通常认为,高温高速风与致密冷分子云的相互作用类似于震后流中嵌入的云的演化。然而,目前在文献中没有对这两个过程的直接比较研究。我们提出了Mach 10冲击与密度对比为χ= 10的云相互作用的2D绝热流体动力学模拟,并将我们的结果与相应的风云模拟结果进行了比较。然后,我们研究了改变风速,有效改变风马赫数Mwind对云的演化的影响。我们发现这两个过程之间存在显着差异:1)传递的冲击在冲击-云相互作用中更加平坦; 2)风云箱中的低压区域以与冲击云箱不同的方式使云边缘周围的气流偏转。 3)在受到冲击的情况下,云的轴向压缩更大。随着Mwind的增加,标准化的混合速率会降低。 Mwind较高的风中的云也不会通过云的后部传递冲击,并且会在轴向受到更大的压缩。与冲击云模拟相反,通过压云时间尺度tcc归一化的云混合时间会增加,以增加Mwind直到在高Mwind达到平稳状态(tmix≃25 tcc),从而证明了预期的Mach缩放。此外,高马赫数风中的云能够长期生存,并且能够移动相当远的距离。

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    Goldsmith, KJA; Pittard, JM;

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  • 年度 2017
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  • 正文语种 en
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