Influences of the wall distance and initial shape on the dynamic behaviors of near-wall bubbles

Abstract

The phenomenon of buoyancy-driven bubbles near a fluid-solid interface is common in both natural settings and industrial processes, such as oil and gas exploration and production. The intricate dynamics of bubbles are profoundly shaped by their interactions with adjacent solid walls. In this study, a direct numerical simulation of bubbles rising near a wall is conducted using the volume of fluid method. The motion behavior and wake vortex structure of bubbles with three types of migration trajectories (linear, zigzag, and spiral) are analyzed. The influences of the initial shape and wall distance of the bubbles on their motion trajectory, rising velocity, and wake structure is investigated. The results show that the presence of a nearby wall obstructs the diffusion of eddies across a bubble surface, and the repulsive force induced by the wall increases as the distance between the bubble and the wall decreases. Remarkably, at a dimensionless wall distance of 0.6, a change in the lateral lift direction triggers a collision between a zigzagging bubble and the wall, consequently setting the bubble into a bouncing motion mode. In the case of spiral-moving bubbles, proximity to the wall enhances the likelihood of oscillations within the bubble's migration trajectory along the x-y plane while maintaining stability along the z-y plane. While variations in the initial aspect ratio of bubbles have marginal impacts on the migration paths of linear and zigzagging bubbles, the initial shape affects the migration trajectory of spiral bubbles to some extent. The bubble migration trajectory first experiences oscillations when the initial deformation reaches its maximum.