Experimental and theoretical analysis of water exit of a supercavity

Supercavitation flow means that an underwater body moves in a vapour or gas cavity instead of water. This paper presents an experimental research on water exit of a fully developed supercavity by highspeed photography. It is found that, when the underwater supercavitating vehicle approaches free surface, the supercavity collapses; after that, the vehicle generates a new supercavity which collapses again in air after the vehicle brings it out of the water surface. Sometimes, the supercavity has no time to collapse in water but is carried by the vehicle into open air, where the supercavity collapses. A theoretical model is given to estimate the collapsing time of a supercavity. Besides, through comparing the measured cavity shape parameters with Logvinovich’s and Savchenko’s semi－empirical formulas, both agreement and disagreement are found.