Abstract The mechanism of the generation and evolution of the air-core vortex formed between a free surface and a horizontal flow intake is investigated using large-eddy simulation of two-phase flows, with the air-water interface captured by a coupled level-set and volume-of-fluid method. The simulation provides a detailed description of the flow features of the air-core vortex formation. Based on the simulation data, the flow patterns and the underlying vorticity dynamics at different stages of the vortex formation are analyzed. It is found that the development of the air-core vortex is associated with the evolution of the vertical component of the vorticity. Analyses of the vorticity evolution dynamics reveal the fundamental mechanism of the air-core vortex generation, which is the amplification of the free-surface vertical vortices due to the vertical stretching effect above the intake associated with the pipe suction. Initially, weak vertical vortices caused by the spanwise disturbance of streamwise flows are randomly distributed near the surface and are enhanced by the stretching effect. Then, these randomly distributed vortices interact with each other and evolve into a dominant vortex, which eventually draws air into the intake and creates a fully-developed air-core vortex. The mechanism responsible for maintaining the fully-developed air-core vortex is still the vertical stretching effect in the core. The tilting from streamwise and spanwise vortices to vertical vortices, albeit large in the presence of the fully-developed vortex, nearly cancel each other and has negligible influence on sustaining the vortex.

中文翻译：

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进气流中空心涡演化机制的数值研究

摘要 利用两相流的大涡模拟研究了自由表面和水平流入口之间形成的空心涡的产生和演化机制，气水界面由耦合水平集捕获。和流体体积法。模拟提供了对空心涡形成的流动特征的详细描述。基于模拟数据，分析了涡流形成不同阶段的流动模式和潜在涡度动力学。发现空心涡的发展与涡量垂直分量的演化有关。涡度演化动力学分析揭示了空心涡生成的基本机制，这是由于与管道吸力相关的进气口上方的垂直拉伸效应导致的自由表面垂直涡流的放大。最初，由流向流动的展向扰动引起的弱垂直涡在地表附近随机分布，并被拉伸效应增强。然后，这些随机分布的涡流相互作用，演变成主导涡流，最终将空气吸入进气口，形成一个完全发展的气芯涡流。负责维持完全发展的空心涡旋的机制仍然是核心中的垂直拉伸效应。从流向和展向涡旋到垂直涡旋的倾斜，尽管在完全发展的涡旋存在下很大，