Wei Wangru, Xu Weilin, Deng Jun, Tian Zhong, Zhang Faxing
State Key Lab of Hydraulic and Mountain River Engineering, Sichuan University, Chengdu, 610065, China.
Sci Rep. 2019 Jul 29;9(1):11008. doi: 10.1038/s41598-019-46883-5.
The air bubble entrainment and self-aeration phenomena in free-surface water flows reveal a rich interplay of fundamental science and engineering, and the size distribution of the entrained bubbles enhances the air-water gas flux, improves the gas transfer, and influences the cavitation erosion protection in high-speed flows. In the present study, we investigate the bubble-formation mechanism of free-surface air entrainment and the related microscopic bubble scale in the laboratory. This paper provides a quantitative description of bubble entrainment. The entrapment deformation of the local free surface over a period follows a power-law scaling and entrains a bubble when the entrapped surface becomes enclosed in the unstable movement period. Both the size scale and shape character of the entrapped free surface determine the size and skewness of the distribution of the air bubble. The entrapment deformation process confirms that the instability behaviour of the local air-water interface results in the onset of bubble entrainment. Further research is necessary to elucidate the instability criterion dominated by the interface instability and promote a new understanding of multiphase flow generation and development.
自由表面水流中的气泡夹带和自曝气现象揭示了基础科学与工程学之间丰富的相互作用，夹带气泡的尺寸分布增强了气水气体通量，改善了气体传输，并影响高速水流中的空蚀防护。在本研究中，我们在实验室中研究了自由表面空气夹带的气泡形成机制以及相关的微观气泡尺度。本文提供了气泡夹带的定量描述。一段时间内局部自由表面的捕获变形遵循幂律缩放，当捕获表面在不稳定运动期被封闭时夹带一个气泡。捕获自由表面的尺寸尺度和形状特征都决定了气泡分布的尺寸和偏度。捕获变形过程证实了局部气水界面的不稳定性行为导致了气泡夹带的开始。有必要进行进一步的研究以阐明由界面不稳定性主导的不稳定性准则，并促进对多相流产生和发展的新理解。
