Unsteady loading and tip-vortex instability of a propeller under coupled oblique inflow and cavitation

Propellers in oblique inflow exhibit pronounced thrust/torque fluctuations and premature tip-vortex instability, while cavitation further intensifies the unsteadiness. Focusing on a four-bladed right-handed PC456 propeller, high-fidelity simulations are performed using stress-blended eddy simulation coupled with the Zwart–Gerber–Belamri cavitation model across multiple operating conditions. A multi-scale time-frequency framework—connecting a full-propeller and single-blade responses with radial-strip decomposition and moving trailing-edge probes—is established to elucidate how oblique inflow and cavitation jointly govern loading and the evolution of coherent tip-vortex structures. Results indicate that oblique inflow breaks loading symmetry and strengthens phase modulation of single-blade responses at the shaft frequency, whereas the aggregate spectrum of the full propeller is dominated by the blade-passing frequency. Cavitation clamps local suction-side pressure near vapor pressure, shifts loading from the tip toward mid-span, and introduces high-frequency pressure pulses; in combination with oblique inflow, this yields a composite spectral signature in which low-frequency phase modulation is superimposed with cavitation-induced high-frequency pulses. Under joint action, tip-vortex coherence is lost earlier, and breakdown occurs sooner; in the far wake, the dominant frequency of the turbulent-kinetic-energy spectrum shifts toward approximately one-half to one-quarter of the blade-passing frequency, evidencing a pronounced low-frequency drift.