Numerical investigation of cavitation induced noise and noise reduction mechanism for the leading-edge protuberances

Cavitation leads to an increase in noise for high-speed ships, propellers, etc., which exacerbates ocean noise pollution. The objectives of this paper are to investigate the sound generation mechanism of cavitation noise and explore the noise reduction mechanism for the leading-edge protuberances. The large eddy simulation (LES) and the Zwart cavitation model were used to predict the unsteady cavitating flow around the National Advisory Committee for Aeronautics (NACA) 0012 baseline hydrofoil and the modified hydrofoil with the leading-edge protuberances. The load noise was predicted using the Ffowcs Williams-Hawkings (FW-H) acoustic simulation method from the flow field results, while the cavitation noise was calculated using the Sound radiation theory for spherical cavity. The noise reduction characteristics were analyzed in combination with the evolution characteristics of cavities and vortices. The leading-edge protuberances prevent the formation of large-scale shedding vortices, significantly reducing the pressure fluctuation amplitude on the suction surface of the hydrofoil. The flow instability and cavity collapse become the major sources of noise when cavitation occurs. Cavitation not only leads to an increase in radiated noise but also affects the characteristic frequency of noise. The modified hydrofoil effectively suppresses the formation and development of cavities, reducing cavitation instability. The modified hydrofoil can effectively reduce monophonic noise in low-frequency bands, resulting in a reduction of approximately 10.5 dB in peak monophonic noise. The high-frequency broadband noise between 300 and 500 Hz is reduced by approximately 7.58 dB. This research provides a reference for noise reduction optimization of hydraulic machinery.