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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Flow structures and the dynamics in the wake of a bubble rising close to a vertical wall




Abstract

In the case of a rising bubble at moderate Reynolds numbers of an order of 100, it is known that it follows an oscillatory path, which is attributed to the vortex dynamics in the wake. The presence of the vertical wall, common situations in most gas-liquid flows in industry, will modify the bubble wake significantly and its dynamics. In the present study, we investigate the wall-induced flow structures around a rising bubble while varying the distance between the wall and the bubble, measured at horizontal and vertical planes with two-phase particle image velocimetry. Experiments are conducted in a cubic water tank filled with quiescent water and the considered Reynolds and Weber numbers of a bubble are 750 and 3.3, respectively, indicating that the reference bubble rises in a plane zigzag path. When the bubble collides the vertical wall, it is found that the distance between counter-rotating streamwise vortices in the wake increases and the secondary vortex appears, which is responsible for the retarded bubble oscillation, which is supported by the weakened vorticity generation around the bubble after the bubble-wall collision. As the distance to the wall increases, the bubble motion becomes close to that of reference bubble and the bubble wake changes as well. While reconstructing the three-dimensional vortices in the wake behind the bubble, finally we develop a new model for the convection velocity of the wake vortices.

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