Predicting the hydroacoustic signature of ducted tidal turbines: A computationally efficient BEM/FW-H approach

초록

Ducted horizontal axis tidal turbines offer substantial power gains of 30%+ over conventional open-rotor designs, but their effect on the underwater acoustic environment remains unquantified. This paper addresses this critical knowledge gap by applying a coupled numerical framework to systematically analyze the hydroacoustic performance of ducted turbines. The methodology combines a hydrodynamic Boundary Element Method (BEM) with a Full Wake Alignment (FWA) scheme to predict unsteady blade and duct loading, the Ffowcs Williams-Hawkings (FW-H) acoustic analogy to compute blade-radiated tonal noise (blade-passing frequency and harmonics), and a Boundary Integral Equation (BIE) to model acoustic scattering by the duct. The FW-H formulation captures thickness and loading sources while omitting quadrupole sources associated with turbulent noise. The framework is rigorously validated against experimental data for open-rotor configurations and high-fidelity Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations for the ducted case. The results reveal the duct's dual acoustic role, amplifying axial sound pressure levels (SPL) while shielding lateral noise. The proposed method shows reasonable agreement with URANS with over a 10x computational speedup, validating its efficiency and accuracy. The findings indicate that the trade-off between hydrodynamic performance and acoustic signature is not a simple penalty but a complex redirection of energy that can be engineered.

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