Collapsing behavior of a spark-induced cavitation bubble near the air bubble attached to the tube nozzle

Air entrainment has been proved to be an effective method to weaken the cavitation damage. The objective of this paper is to apply high-speed photography and schlieren optical method to investigate the collapse behavior of cavitation bubble near the air bubble. The corresponding data such as bubble collapse time, collapse position and the velocity of collapse jet are analyzed. Results are presented for a cavitation bubble generated directly above an air bubble under a wide range of dimensionless standoff distances. The results show that (1) four distinctive patterns are identified by the collapse direction of the cavitation bubble and the interaction between the cavitation bubble and the air bubble. (2) The dynamic features of the cavitation bubble at collapse stage vary evidently at different patterns, including the collapse direction, high-speed jet and shock waves. (3) Compared with the cases that the cavitation bubble does not merge with an air bubble, the velocity of collapse jet and the intensity of shock waves are extremely smaller when the cavitation bubble merging with the air bubble. Investigating the influence of air bubble on the cavitation bubble has great significance to understand the mechanism of air entrainment to reduce cavitation damage.