Unequal splitting phenomenon of cavitation bubbles near rigid boundaries within a narrow gap

The present work investigates the unequal splitting of cavitation bubbles near rigid boundaries within a narrow gap. Based on high-speed photographic experiments, the typical phenomenon of unequal bubble splitting is shown, and the parametric partitions of unequal bubble splitting in proximity to a cylinder and a flat wall are presented. Based on the Kelvin impulse theory, the underlying physical bubble-splitting mechanisms are explored. In addition, the impacts of the main parameters on the unequal splitting are quantitatively analyzed. The main conclusions are as follows. (1) Under different cylinder–bubble distances, the bubble splits into three typical cases: an upper larger part and a lower smaller part, two equal-sized parts, and an upper smaller part and a lower larger part. (2) The unequal bubble splitting is caused by the inconsistencies between the directions of the bubble-collapse jet and the centroid movement. (3) As the cylinder radius and the cylinder–wall distance increase, the bubble splitting shifts from case 1 to case 3, suggesting the cylinder effect increases and the flat-wall effect decreases.