Multi-domain characterization of propeller cavitation noise using spectral-coherence-weighted synchronous modulation spectrum for quantifying rotation-synchronous modulation

This study investigates how cavitation-regime transitions reorganize the broadband and rotation-synchronous components of propeller noise. A five-bladed model propeller was tested in a cavitation tunnel under uniform inflow at fixed rotational speed and advance coefficient, while the cavitation number was reduced from non-cavitating to tip-vortex, sheet, and sheet/cloud conditions. Hydrophone signals were acquired synchronously with high-speed imaging and analyzed using spectral analysis, short-time Fourier transforms, and a spectral-coherence-weighted synchronous modulation spectrum to identify the carrier bands supporting blade-rate modulation and their evolution with cavitation regime. As cavitation intensified, acoustic energy increased persistently in 2–5 kHz and 30–80 kHz, whereas a marked reduction appeared in 5–30 kHz when sheet/cloud cavitation became dominant and tip-vortex cavitation weakened. Rotation-synchronous modulation was supported mainly by 2–10 kHz carriers and shifted towards lower carrier frequencies under stronger cavitation, while radiation above 30 kHz became more intermittent. The results show that cavitation development reorganizes the spectral and modulation structure of propeller noise rather than amplifying all frequency bands uniformly. These conclusions are limited to a model-scale propeller under uniform inflow; extension to full-scale propellers or non-uniform wakes requires consideration of scale effects, wake-induced unsteadiness, and altered cavitation dynamics.