Non-stationary acoustic characteristics of cavitation-induced noise from a marine propeller operating under non-uniform inflow

Cavitation-induced acoustic emissions from marine propellers operating in non-uniform wake fields exhibit highly complex, non-stationary behaviors. This study investigates the spatiotemporal evolution and cyclostationary characteristics of cavitation noise from a composite high-skew propeller. By employing a phase-resolved high-speed visualization and hydroacoustic synchronized measurement system, the physical coupling between various cavitation structures and their acoustic signatures is analyzed across distinct cavitation regimes. In the time domain, a phase-based signal decomposition combined with excess kurtosis tracking reveals a fundamental transition in the acoustic emission mechanism: from pure rotational noise, to isolated impulsive shocks, to dense continuous shocks, and ultimately to highly structured periodic energy bursts. In the frequency domain, a pronounced regime-dependent redistribution of acoustic energy is identified. Notably, fully developed cloud cavitation triggers a massive concentration of acoustic energy in low-frequency blade-synchronous components, simultaneously accompanied by an anomalous energy attenuation in the 4–40 kHz mid-to-high frequency band. To decode the underlying modulation mechanisms, a simplified acoustic source propagation model is proposed. First- and second-order cyclostationary analyses, utilizing the cyclic mean spectrum and spectral coherence, demonstrate that the non-uniform wake acts as a periodic gating mechanism. The results reveal a non-monotonic evolution of amplitude modulation and cross-frequency coupling, fundamentally linking the stochastic nature of transient cavitation dynamics to the deterministic cyclostationarity of propeller rotation. These findings provide new physical insights into the modulation-driven acoustic response of cavitation under realistic wake conditions and contribute to a deeper understanding of cavitation noise generation mechanisms in marine propellers.