明渠水流自掺气发展区水气结构分析

Analysis of air-water structure in self-aerated developing region of open channel flows

为研究明渠水流自掺气发展区内水气结构特征,采用针式掺气流速仪对自掺气发展区内气泡尺寸与数量进行了试验研究,比较了气泡尺寸与数量随自掺气发展的变化规律,结果显示,同一水流断面上,随着掺气浓度的减小,气泡弦长尺寸分布范围与弦长平均值逐渐减小,掺气区内小尺寸气泡在数量上占有较大的比例,而大尺寸气泡则在含气量上占有较大的比例,分析认为从水面附近高掺气浓度区至自掺气区域底缘低掺气浓度区,明渠自掺气水流水气结构发展过程为"水面变形为主—水面变形与个体空气泡共存—个体空气泡",为进一步研究明渠自掺气形成机理提供了一定的参考。

To investigate the air-water structural characteristic of the self-aerated developing zone in the open channel flow,the bubble size and quantity changes with the self-aeration development were evaluated experimentally,using a double-tip conductivity probe. The results showed that the distribution range of bubble chord length and mean chord length decrease gradually with reduced air concentration in the same flow cross-section; within the self-aerated zone,small-sized bubbles dominate quantitatively while large-sized bubbles have a large portion in terms of air content. It was believed from analysis that from the area at high air concentration near the water surface to the one at low air concentration at the bottom of the self-aerated zone,the development process for the air-water structure of self-aerated flow is predominant surface deformation-coexistence of surface deformation and individual bubbles- individual bubbles,which will be helpful for further study on formation mechanism of self-aeration in open channel flows.