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Wall shear stress modified by bubbles in a horizontal channel flow of silicone oil in the transition region
被引：0
作者：
Oishi, Yoshihiko
[1
]
Murai, Yuichi
[2
]
Tasaka, Yuji
[2
]
机构：
[1] Division of Production Systems Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran,Hokkaido,050-8585, Japan
[2] Laboratory for Flow Control, Faculty of Engineering, Hokkaido University, N13W8, Sapporo,Hokkaido,060-8628, Japan
关键词：
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. © 2020 Elsevier Inc;
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