An experimental study on the impact behavior of cavitation inside tip clearance of a hydrofoil

Tip clearance cavitation is one of the most common cavitation phenomena exist on duct propellers,pumps and some hydraulic turbines,which may lead to erosion of the components.Due to the influence of the nearby wall,cavitation inside the tip clearance is more complicated than other cases without interaction.So far,the understanding about the impact mechanism of tip clearance cavitation is still limited.In this paper,to obtain the impact behavior of tip clearance cavitation,a high-speed camera was used to capture the cavitation behavior inside the tip clearance of a hydrofoil,and surface paint coating peeling method was applied to show the impact region.Results indicated that cavitation around the tip of the hydrofoil was composed of a tip separation cavity and a tip leakage vortex cavity,and the one with contribution to impact was the tip separation cavity.Through the comprehensive analysis of the paint peeling region and dynamic behavior of tip separation cavity,the impact was found to be related to the local collapse and rebound of the cloud cavitation shed from the attached part.In addition,the influence of tip clearance size on the behavior of tip clearance cavitation was also investigated.As the tip clearance size increased,the tip separation cavity tended to transfer from sheet cavitation to vortex cavitation.These findings can provide a sound basis for evaluating the erosion risk arising from the tip clearance cavitation.

Study of tip vortex cavitation inception and vortex singing

Tip vortex cavitation(TVC)is an important cavitation phenomenon in marine propeller.The formation and evolution of tip vortex cavitation are hot topics consistently both in engineering application and mechanism research.In this paper some recent studies on tip vortex cavitation inception and the noise of tip vortex cavitation evolution are presented.The effects of both flow field and water qualities on tip vortex cavitation inception are considered by experiments and numerical simulations.The results show that besides the average minimum pressure in the vortex core the turbulence fluctuation and water qualities including air content and nuclei distribution have great influence on tip vortex cavitation inception.Based on the idea of first nucleus cavitating in tip vortex core new prediction formula for tip vortex cavitation inception is proposed.The synchronous technique of high speed video observation and noise measurement are adopted to study the development of tip vortex cavitation.S-type total noise characteristics are obtained when cavitation number from low to high.Vortex singing is found in the case where the tip vortex cavitation just before leaves the tip region.The excited mechanism of vortex singing is proposed by analyzing the wave propagation on the interface of vortex cavity.