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.