Abstract We performed laboratory experiments on bubbly channel flows using silicone oil, which has a low surface tension and clean interface to bubbles, as a test fluid to evaluate the wall shear stress modification for different regimes of bubble migration status. The channel Reynolds numbers of the flow ranged from 1000 to 5000, covering laminar, transition and turbulent flow regimes. The bubble deformation and swarms were classified as packing, film, foam, dispersed, and stretched states based on visualization of bubbles as a bulk void fraction changed. In the dispersed and film states, the wall shear stress reduced by 9% from that in the single-phase condition; by contrast, the wall shear stress increased in the stretched, packing, and foam states. We carried out statistical analysis of the time-series of the wall shear stress in the transition and turbulent-flow regimes. Variations of the PDF of the shear stress and the higher order moments in the statistic indicated that the injection of bubbles generated pseudo-turbulence in the transition regime and suppressed drag-inducing events in the turbulent regime. Bubble images and measurements of shear stress revealed a correlated wave with a time lag, for which we discuss associated to the bubble dynamics and effective viscosity of the bubble mixture in wall proximity.

中文翻译：

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过渡区硅油水平流道中气泡对壁面剪应力的修正

摘要 我们使用具有低表面张力和清洁气泡界面的硅油作为测试流体对气泡通道流进行了实验室实验，以评估不同气泡迁移状态的壁面剪切应力改性。流动的通道雷诺数范围从 1000 到 5000，涵盖层流、过渡和湍流流态。气泡变形和群被分类为填充、薄膜、泡沫、分散和拉伸状态，基于气泡的可视化，因为体积空隙率发生了变化。在分散状态和薄膜状态下，壁面剪切应力比单相状态降低了 9%；相比之下，壁面剪切应力在拉伸、填充和泡沫状态下增加。我们对过渡和湍流状态下壁面剪应力的时间序列进行了统计分析。剪切应力的 PDF 变化和统计中的高阶矩表明，气泡的注入在过渡区产生了伪湍流，并在湍流区抑制了诱导阻力事件。气泡图像和剪切应力的测量显示了具有时滞的相关波，为此我们讨论了与壁附近气泡混合物的气泡动力学和有效粘度相关的波。