Competing boundary effects on bubble collapse jets near a semi-submerged cylinder

The present paper conducts a systematic analysis of the bubble dynamic behaviors in the vicinity of a semi-submerged cylinder. A theoretical model for the bubble oscillation near the semi-submerged cylinder is established. The influence of the semi-submerged cylinder on the liquid velocity, jet, and impulse characteristics is qualitatively and quantitatively investigated. Furthermore, the jet attraction region and the impulse-dominated region are delineated. The main conclusions are outlined below: (1) The jet direction can be effectively predicted by the direction of the maximum liquid velocity on the bubble interface. Among the factors affecting the liquid velocity, the free surface dominates the liquid velocity contribution over approximately 70% of the parametric range, whereas the cylinder dictates the rest. (2) The bubble collapse jets are classified into the jet pointing towards the cylinder and the jet not pointing towards the cylinder. The impulse attraction region of the cylinder is confined to a relatively small area in its vicinity, correlating with the cylinder radius and spanning approximately 1.1 times its cross-sectional area. (3) The impulse contributed by the cylinder and the free surface are opposite in direction, and a region of minimum impulse intensity and highest impulse sensitivity is present directly below the cylinder.