Bubbles Near a Vertical Wall: Experimental Investigation and Flow Analysis

The motion of bubbles near a solid vertical wall and the resulting induced flow field were experimentally investigated using the shadow method and particle image velocimetry (PIV). The study analyzed how bubble generation frequency and initial distance from the wall affect the average velocity distribution of bubbles and the characteristic parameters of the bubble-induced flow. The results demonstrate that a wall's presence can both decelerate and accelerate the movement of a bubble chain. This dual effect diminishes with increasing distance from the wall, and a higher bubble generation frequency can alleviate the slowing effect. The induced flow field near the wall generates secondary vortices, formed due to the wall's influence and the accumulation of leading-edge vortices from bubbles on the wall, especially at medium and low generation frequencies. However, at high generation frequencies, their formation is not solely attributable to these factors. Instead, it is primarily due to secondary induction within the bubble-induced flow, with the wall predominantly compressing the flow field. Additionally, proper orthogonal decomposition (POD) analysis reveals the impact of different bubble generation frequencies on induced flow characteristics. High-frequency bubbles exhibit a stronger flow-inducing capability, but in such cases, the subsequent bubble tends to disrupt the flow structure established by its predecessor, leading to a more uniform distribution of energy throughout the induced flow field.