Experimental investigation of tip vortex cavitation noise under static and dynamic states

Abstract

Tip vortex cavitation (TVC) stands as a primary source of underwater radiated noise, garnering significant attention in the relevant fields due to its early manifestation in propellers and broad frequency spectrum. Although some meaningful experimental and numerical research concerning TVC noise has been implemented, a comprehensive understanding of TVC noise properties still remains elusive. This study delves into the acoustic characteristics of TVC through cavitation experiments of hydrofoil and jet pump and signal processing tools, including frequency-domain analysis, time-frequency representation, and signal demodulation. Comparative analysis between static and dynamic states of the test hydrofoil and the test jet pump reveals several insights into TVC noise. First, the acoustic characteristics of TVC primarily encompass multiple low-frequency characteristic peaks below 300 Hz alongside an overall increase in the high-frequency domain. Second, the oscillating hydrofoil at a cavitation number of 2.00 exhibits two distinct frequency bands caused by cavity volume variation and cavity resonance of TVC at 190–280 and 360–400 Hz, which shift toward the lower frequency region with larger TVC sizes. Finally, the periodic oscillation of hydrofoil or the rotational motion of impeller induces a modulation effect on TVC noise, with spectral correlation (SC) identifying two dominant carrier bands within 100–400 Hz.