We report three-dimensional hydrodynamical simulations of shocks (${\cal M_{\rm shock}}\geq 4$) interacting with fractal multicloud layers. The evolution of shock-multicloud systems consists of four stages: a shock-splitting phase in which reflected and refracted shocks are generated, a compression phase in which the forward shock compresses cloud material, an expansion phase triggered by internal heating and shock re-acceleration, and a mixing phase in which shear instabilities generate turbulence. We compare multicloud layers with narrow ($\sigma_{\rho}=1.9\bar{\rho}$) and wide ($\sigma_{\rho}=5.9\bar{\rho}$) log-normal density distributions characteristic of Mach $\approx 5$ supersonic turbulence driven by solenoidal and compressive modes. Our simulations show that outflowing cloud material contains imprints of the density structure of their native environments. The dynamics and disruption of multicloud systems depend on the porosity and the number of cloudlets in the layers. `Solenoidal' layers mix less, generate less turbulence, accelerate faster, and form a more coherent mixed-gas shell than the more porous `compressive' layers. Similarly, multicloud systems with more cloudlets quench mixing via a shielding effect and enhance momentum transfer. Mass loading of diffuse mixed gas is efficient in all models, but direct dense gas entrainment is highly inefficient. Dense gas only survives in compressive clouds, but has low speeds. If normalised with respect to the shock-passage time, the evolution shows invariance for shock Mach numbers $\geq10$ and different cloud-generating seeds, and slightly weaker scaling for lower Mach numbers and thinner cloud layers. Multicloud systems also have better convergence properties than single-cloud systems, with a resolution of $8$ cells per cloud radius being sufficient to capture their overall dynamics.

中文翻译：

---

星系流出中的激波-多云相互作用 - I. 具有对数正态密度分布的云层

我们报告了与分形多云层相互作用的冲击 (${\cal M_{\rm Shock}}\geq 4$) 的三维流体动力学模拟。激波-多云系统的演化包括四个阶段：产生反射和折射激波的激波分裂阶段，前向激波压缩云物质的压缩阶段，由内部加热和激波再加速触发的膨胀阶段，以及剪切不稳定性产生湍流的混合阶段。我们比较了具有窄 ($\sigma_{\rho}=1.9\bar{\rho}$) 和宽 ($\sigma_{\rho}=5.9\bar{\rho}$) 对数正态密度分布特征的多云层由螺线管和压缩模式驱动的马赫 $\大约 5$ 超音速湍流。我们的模拟表明，流出的云材料包含其原生环境密度结构的印记。多云系统的动态和中断取决于层中的孔隙率和小云的数量。与多孔“压缩”层相比，“电磁”层混合更少，产生的湍流更少，加速更快，并形成更连贯的混合气体壳。类似地，具有更多小云的多云系统通过屏蔽效应淬灭混合并增强动量传递。扩散混合气体的质量加载在所有模型中都是有效的，但直接密集气体夹带效率非常低。稠密气体只存在于压缩云中，但速度很低。如果相对于冲击通过时间进行归一化，演化显示了冲击马赫数 $\geq10$ 和不同的云生成种子的不变性，对于较低的马赫数和较薄的云层，缩放比例略弱。多云系统还具有比单云系统更好的收敛特性，每个云半径 8 美元的单元分辨率足以捕捉其整体动态。