Hydrodynamic noise and noise source characteristics of an upstream hydrofoil and propeller system

The upstream hydrofoil and propeller system (UHPS) is not only a major source of hydrodynamic noise in underwater vehicles but also a classic problem in fundamental fluid mechanics. This paper employs large eddy simulation and the Ffowcs Williams–Hawkings equation to study the influence of hydrofoil incidence angle on the hydrodynamic noise of the UHPS. The flow-field and acoustic prediction methods are validated. By identifying the noise sources in the system, the mechanisms linking the evolution of noise sources and far-field noise are revealed. As the hydrofoil incidence angle increases, the permeable surface noise of the UHPS increases significantly, mainly in the low-frequency range. The maximum increase reaches 6.40 dB, while the direction of maximum radiation shifts from 180° to 170°. The low-frequency energy of both the dipole and quadrupole noise is enhanced. This increase arises from two mechanisms. First, the increase in dipole noise sources is primarily caused by the amplification of near-wall pressure fluctuations on the propeller blade at shaft frequency (fs), blade passing frequency (fbp), and their harmonic frequencies. Second, the increase in wake noise sources is attributed to both the amplification of turbulent energy in the hydrofoil wake and the enhanced interference between the hydrofoil tip vortices and the propeller wake. Overall, this study reveals new physics mechanisms by which increasing the hydrofoil incidence angle strengthens the interaction of the hydrofoil and propeller, leading to enhanced pressure fluctuations on the blades and propeller wake distortion. These effects redistribute the dominant noise sources, intensifying far-field noise of the UHPS.