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Rainbow-Color Imaging Of Microbubbles Strongly Clustering In A Turbulent Boundary Layer

Y. Murai, D. Saitoh, H. J. Park, Y. Tasaka

Laboratory for Flow Control, Faculty of Engineering, Hokkaido University, Japan

Rainbow-color volumetric illumination for visualizing 3D microbubble distributions was examined in order to find microbubble clustering in a spatially developing turbulent boundary layer. The color coding was defined according to the wall unit from 0 to 200, straddling viscous-sub layer, buffer layer and log-law region. This allowed understanding where the microbubbles were accumulated or diffused within the boundary layer. The results showed microbubble clouding in the low-speed streak regions along the viscous sublayer, clustering into cores of streamwise vortices ejected into the buffer layer, and intermittent exhaust of the clusters toward the log-law region. Furthermore, correlation of these behaviors with local Reynolds shear stress event (ejection, sweep) was found with quadrant analysis of the liquid velocity vector data obtained by PIV.

20th Edition
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