Propagation and sources of linear noise generated by an underwater propeller under nonuniform inflow
Phys. Rev. Fluids 10, 114802 – Published 5 November, 2025
DOI: https://doi.org/10.1103/v3lq-xwgm
Abstract
This study examines the propagation characteristics and sources of linear noise generated by an underwater propeller, employing a tailored formulation of the Ffowcs Williams–Hawkings equation. The simplified formulation enhances efficiency of the noise calculations by assuming uniform propagation times for noise sources located at different points on the blade surface. Comparisons of the predicted noise under uniform and nonuniform inflow conditions show that azimuthally varying inflow significantly amplifies the overall sound pressure level across most emission angles. Notably, the noise directivity and decay rates exhibit substantial changes, particularly within the propeller disk plane. These variations are primarily attributed to the amplification and dominant contribution of blade passing frequency (BPF) loading noise. An equivalent emission point acoustic model, derived from the simplified formulation, offers intuitive insights into the propagation behavior and source distribution of the loading noise. In the near field, the noise radiation is determined by variations in both radiation distance and blade forces. The predominant BPF tone arises from elements associated with different harmonics of the blade force, with interference among these elements causing azimuthally asymmetric noise radiation under the nonuniform inflow condition. In the far field, the noise spectrum is governed solely by the force derivatives, and the force fluctuations under nonuniform inflow only amplify the BPF tones, as interblade interference suppresses components at other frequencies. Regarding the noise source distribution, the near-field BPF tone and far-field broadband noise under the uniform inflow primarily originate from the root of the blade suction side and the blade trailing edge, respectively. Under the nonuniform inflow condition, the dominant BPF tone in both near and far fields is driven by the interaction of azimuthally varying inflow with the leading edges of the blades.
