Experimental Investigation on the Dynamic Characteristics of Bubble-in-Chain Near a Vertical Wall

Abstract

The motion of near-wall bubble-in-chain, which is a crucial aspect of the study of near-wall bubble flows, involves not only the wall effect but also the interactions between bubbles. However, there have been few studies on this topic. In this study, we investigated the motion of near-wall bubble-in-chain using a dual-camera orthogonal shadow method and tracked bubbles using image processing and feature matching techniques. Considering both the wall effect and bubble generation frequency, we discussed the statistical characteristics, motion modes, dynamic characteristics, and energy evolution of bubbles. The results demonstrate that an increase in bubble generation frequency leads to a greater deviation of bubble trajectories from the wall and an increase in trajectory amplitude while weakening the suppression of bubble speed by the wall. Furthermore, changes in both bubble equivalent diameter and drag coefficient reveal how bubble generation frequency affects their shape stability during motion as well as regulation by the wall effect. The drag coefficient decreases with increasing Reynolds number for bubbles; however, an increase in bubble generation frequency broadens its distribution range. Additionally, it is evident that the wall effect significantly impacts drag characteristics for bubbles: uncollided bubbles experience increased drag coefficients with greater distance from the wall while collided bubbles exhibit decreased drag coefficients. In cases of high generation frequency, the conversion of kinetic energy to surface energy during bubble collisions, especially the enhancement of the peak of surface energy, indicates an increase in the bubble’s energy storage capacity and energy conversion efficiency. The findings not only enhance comprehension of behavior exhibited by near-wall bubbles but also offer a novel perspective for regulating near-wall bubble flows in industrial applications.