Effects of flow incidence on propeller underwater radiated noise

This paper presents an analysis of the noise generated by a marine propeller in oblique flow, by using a detached eddy simulation for the flow field modeling, and the Ffowcs Williams and Hawkings equation for hydroacoustics. The study aims to expand the understanding of noise generation from a propeller under moderate blade loading subjected to lateral flow, which simulates an idealized off-design condition like a steady-state maneuvering. Hydroacoustic results in the time and frequency domains are compared with those predicted under straight flow conditions, highlighting differences and similarities in the noise field properties. In oblique flow, a novel noise-generating mechanism, arising from complex interactions between blade(s) root vortex and the hub vortex, is identified and its impact on the radiated sound discussed as well. The investigation reveals that noise propagation toward the far-field is predominantly influenced by nonlinear acoustic effects associated with wake dynamics. It is proven that the status of far-field propagation is reached much earlier in drifting than in axial flow conditions and that the presence of the lateral flow makes the propeller noisier. This yields an overall sound pressure level distribution dominated by tonal harmonics upstream and broadband components downstream of the rotor disk, contrasting with axisymmetric configuration where the broadband component prevails throughout.