Physical Investigation of a Cavitation Vortex Collapse

Abstract

Most of severe cavitation erosion of hydraulic machines are found to be associated with the collapse of transient cavitation vortices downstream of a leading edge cavity. The dynamics of such a type of cavitation is studied in a Cavitation Vortex Generator (CVG). By producing the cyclic growth and collapse of a single cavitation vortex, this device provides a way to investigate the mechanisms involved in the final stage of the vapour cavity collapse. The observations of vapour structures and emitted shock waves are based on high-speed visualisations (up to $2 10^6$ frames/s) which are obtained by using a shadowgraph video system. Luminescence sources which are emitted during the collapse are visualised by using an intensified camera. By adjusting a short exposure time of 500 $ns$ before shock waves are captured, this allows the time of minimum cavity volume and position to be estimated. This paper presents the complex physical mechanisms of cavitation vortex collapse which have been pointed out with these simultaneous visualisations.