Interaction and ordering of bubbles levitated in vortical flow

Abstract

Interaction of suspended bubbles with the flow and with other bubbles is encounted in numerous ground-based natural and technological processes and plays essential role in space applications. In experiments conducted on board spacecraft, bubbles remain suspended for a long time while at normal gravity they tend to rise due to buoyancy. However, in intensive flow bubbles may be trapped by vortices and maintain their vertical position, exhibiting the behavior similar to microgravity conditions. This type of behavior was observed e.g. bubble motions in the Couette-Taylor flow. Air bubbles injected to the viscous fluid sheared in a Couette device form a highly ordered structure. In a short time scale, the bubbles are getting entrapped in the secondary rotating flow of the Taylor vortices and are pushed to the center streamline of the vortex defying buoyancy. During a longer time scale the inertial interaction between the bubbles in the primary shear flow drives the bubbles away from each other. Equal size bubbles eventually assume an ordered string with equal separation distances between all neighbors. This phenomenon repeats itself regardless of the number of bubbles in the flow. Hence, doublets will assume opposite positions, triplets will form a triangle, four bubbles will arrange in a square and so on. We present visualizations, measurements and a model inviscid 2D analysis