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Wall shear stress modified by bubbles in a horizontal channel flow of silicone oil in the transition region

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Title: Wall shear stress modified by bubbles in a horizontal channel flow of silicone oil in the transition region
Authors: Oishi, Yoshihiko Browse this author →KAKEN DB
Murai, Yuichi Browse this author →KAKEN DB
Tasaka, Yuji Browse this author →KAKEN DB
Keywords: Bubbly flow
Drag reduction
Turbulent flow
Wall shear stress
Issue Date: Dec-2020
Publisher: Elsevier
Journal Title: International journal of heat and fluid flow
Volume: 86
Start Page: 108748
Publisher DOI: 10.1016/j.ijheatfluidflow.2020.108748
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.
Rights: © <2020>. This manuscript version is made available under the CC-BY-NC-ND 4.0 license
Type: article (author version)
Appears in Collections:工学院・工学研究院 (Graduate School of Engineering / Faculty of Engineering) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 田坂 裕司

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