Experiment investigation of the tip vortex cavitation around a pitching hydrofoil

Abstract

Experimental research was carried out to investigate the characteristics of tip vortex cavitation (TVC) caused by tip vortex in an oscillating hydrofoil. Shanghai Shipping and Research Institute's looped cavitation tunnel served as the site of the experiments. The hydrofoil used as the test was NACA (National Advisory Committee for Aeronautics) 63820. Two high-speed cameras, one torque sensor, and six hydrophones were employed to capture the cavitation patterns, the torque exerted on the hydrofoil, and the cavitation noise, respectively. The cavitation flow under static angle of attack (AoA) and the dynamic AoA have all been investigated in order to have a better knowledge of the differences between the TVC surrounding these two conditions. The AoA of 8.5°, 10°, and 14.5° and the AoA range of 1.8°–16° were selected for the static condition research and the dynamic condition study, respectively. A tip vortex flow was created between the tip of the stationary hydrofoil and the ceiling of the tunnel test section. To investigate the impact of the cavitation number on the growth of TVC surrounding the pitching hydrofoil, various pressure environments were built up. As for the experiment environment, cavitation numbers 2.47, 2.00, and 1.66 were used. The results indicate: (1) under static conditions, decreasing cavitation and increasing AoA lead to increased stability and topological complexity of TVC. (2) Comparing and analyzing cavitation patterns during the ascending, static, and descending processes reveal that the strongest cavitation intensity during the descending process, followed by static conditions, with the least intensity during the ascending process. (3) The frequency properties under pitching motion include those of each static AoA condition, although the acoustic characteristic of higher AoA has a stronger influence on that of dynamic condition.