Bio-inspired serrated hydrofoil: Vortex–pressure interactions and noise suppression mechanisms

The study of biomimetic structures in the fields of acoustics and fluid mechanics is of great significance, as they can mimic and exploit the efficient flow-control mechanisms found in nature to enhance the performance of fluid machinery, reduce energy losses, and achieve noise reduction. In this work, the application of biomimetic hydrofoils to underwater flow-induced noise suppression is investigated. The NACA66 (National Advisory Committee for Aeronautics) hydrofoil is selected as the baseline model, and its trailing edge is modified into a serrated shape to explore the corresponding hydrodynamic and acoustic characteristics. Large eddy simulation (LES) combined with the permeable surface Ffowcs Williams and Hawkings (FW-H) equation is employed, and the results confirm that the biomimetic structure can effectively suppress flow-induced noise. The serrated trailing edge of the biomimetic hydrofoil guides the formation of local vortices, effectively delaying boundary-layer separation, reducing turbulence intensity in the wake region, and shifting the onset of flow separation downstream, thereby enhancing flow stability. The serrated structure also reduces pressure loss. Compared with the baseline hydrofoil, the lift coefficient of the biomimetic design increases by 3.9%, while the drag coefficient rises by 4.4%. This indicates that the modified hydrofoil proposed in this study effectively improves hydrodynamic performance, thereby enhancing its engineering application prospects in equipment with stringent requirements for lift characteristics and flow control capabilities. Compared with the baseline hydrofoil, the biomimetic design exhibits a remarkable noise reduction effect at a monitoring radius of 15 m. At the monitoring point, the noise sound pressure level (SPL) is mainly concentrated in the low- to mid-frequency range, while the high-frequency SPL remains relatively low. A comparison of the SPL between the biomimetic and baseline hydrofoils at the same receiving point shows that the biomimetic hydrofoil achieves a significantly lower SPL in the low- to mid-frequency band. The maximum difference in the dominant frequency SPL reaches 15 dB. These results demonstrate that optimizing the trailing-edge shape of the hydrofoil can, within a certain range, improve its hydrodynamic performance and acoustic characteristics. This provides new insights into low-frequency noise suppression for underwater propulsors and theoretical support for noise reduction design in underwater propulsors and fluid machinery.