Experimental Investigation of Cavitation-Induced Acoustic Noise from Marine Propellers

Ship-induced acoustic noise can be treated as a measure of environmental impact of marine transportation industry, where, if present, cavitation is often the dominant noise source. Quantitative prediction of emitted noise levels requires detailed characterization of cavitation regimes associated with operation of marine propellers. We conducted an experimental campaign in a pressurized cavitation tunnel, following the experimental standards of the International Towing Tank Conference (ITTC). The experiments were designed to reproduce various cavitation regimes that are expected to occur during operation of a typical four-bladed propeller of a tanker ship. The measurements were conducted under steady inflow conditions, which eliminated the effects of the hull wake and shaft inclination in order to provide a first set of simplified cases for validation of numerical methodologies, before moving to more complex conditions. We obtained stroboscopic photographic images of the cavitation event, measurements of propeller loads, and high-resolution acoustic pressure levels across a broad frequency spectrum. The distinct regimes of bubble cavitation, sheet cavitation, and tip vortex cavitation were created experimentally in varying combinations, along with a reference case of cavitation suppression. For each considered cavitation regime, we identified the corresponding dominant frequencies and levels of the acoustic noise. The experiments will validate the propeller cavitation noise model that is used to guide ship hybrid electric propulsion system design and operation control to reduce ship induced ocean noise.