Near-wall bubble migration and wake structure in viscous liquids

Abstract

The migration and wake structure of a single bubble in a viscous medium near a vertical wall have been experimentally investigated using a two-camera orthogonal shadowing method combined with a particle image velocimetry system. The effects of bubble size, liquid properties, and migration modes on the motion of a near-wall bubble and its wake structure are discussed. It is shown that, unlike migration in pure water, collisions between bubbles and walls are rare in viscous liquids. As viscosity increases, the mobility of the bubble near the wall changes from 3D to 2D and finally exhibits 1D motion with only one degree of freedom. While 1D motion is dominated by viscous forces, 2D migration is influenced by both wall effects and viscous forces, while 3D migration is primarily affected by bubble size. After analyzing the wakes produced by different factors, it was found that the wakes generated by mobile bubbles in three dimensions exhibit similar shedding patterns to Karman vortex streets, while two-dimensional wakes show stronger continuity. The average topological flow field structure of the bubble wake is obtained through periodic phase averaging, and the effect of different factors on the evolution of near-wall bubble wakes is analyzed.