Tip vortex cavitation at incipient conditions of a confined elliptic hydrofoil*

LES of a confined elliptic hydrofoil is performed at Re=900000 under incipient conditions. A polydisperse model is used to track the concentration of bubbles of different sizes, and to investigate the effects of water quality on inception. It was found that inception is strongly dependent on the amounts of nuclei in the freestream. When the flow is deplete of nuclei, inception is an intermittent event confined to a position very close to the hydrofoil's tip. However, when the flow is rich in nuclei, a larger portion of the tip vortex cavitates, as well as part of the suction side very close to the leading edge of the hydrofoil. Probability density functions revealed that cavitation occurs in any region experiencing a pressure field lower than vapor pressure when the flow is rich in nuclei, while extremely low values of pressure (usually kPa of tension) are required to make a flow deplete of nuclei cavitate.