Experimental investigations on the flow structure and turbulence of the propeller tip vortex at different cavitation states

Abstract

In a previous series of open water tests for a certain marine propeller, we kept decreasing the advance coefficient and observed the propeller tip vortex going through a process from non-cavitating to cavitating and back to non-cavitating but micro-bubble-filled conditions. This process provides an excellent opportunity for investigating the flow structure and the turbulence associated with the tip vortex under different statuses of cavitation. Particle image velocimetry technique is used to measure the instantaneous velocity distributions at six experimental conditions parameterized with the advance coefficient and the cavitation number. The results show that the mean circulation (or mean kinetic energy) of either the cavitating or the micro-bubble-filled tip vortex is greater than that of the singlephase (liquid) counterpart, whereas the turbulent kinetic energy associated with the tip vortex has an opposite trend. These phenomena imply that extraordinary kinetic energy sources/transfers within the flow exist due to interactions between the vapor and the liquid phases of the tip vortex fluid.