Investigation of the bubble dynamics between two parallel plates within confined spaces

The present paper investigates the bubble dynamics between two parallel plates within the confined spaces. Based on the high-speed photography experiments, the bubble typical collapse morphologies and splitting phenomena are observed under the constraint of the parallel plates. The influence of the plate spacing on the bubble centroid movements and collapse jets are quantitatively analyzed. Based on the Kelvin impulse theoretical model, flow velocity and Kelvin impulse distributions during the bubble oscillation process are investigated and compared with the experimental results. The conclusions are given as follows: (1) Three bubble splitting phenomena are identified at symmetric positions between two parallel plates: vertical split, radial expansion, and horizontal split. The difference in the transverse and longitudinal contraction velocities of the bubble interface leads to the different splitting phenomena. (2) Four collapse morphologies are identified at asymmetric positions: semi-cylindrical, triangle-shaped, bulb-shaped, and ellipse-shaped collapses. (3) As the bubble moves away from the symmetric position, its jet velocity continues to increase, and the bubble centroid displacement first increases and then decreases.