Numerical investigation on the hydrodynamics and wake characteristics of ducted and bare tidal turbines under wave conditions

This study uses computational fluid dynamics to compare the hydrodynamics and wake characteristics of a bare turbine versus a ducted turbine under wave conditions. By developing and validating a coupled wave-current numerical model, this study systematically analyses the influence of wave and submergence depth on the loadings, power output, and wake evolution of both turbines. The results show that the ducted turbine achieved a higher average power output and effectively suppressed the fluctuations in rotor thrust and power. Across the investigated cases, the ducted turbine achieves an average power coefficient about 65%-69% higher than the bare turbine, with a more evident advantage at higher wave heights. Concerning the wake characteristics, compared to the bare turbine, the near-wake diameter of the ducted turbine increased by approximately 60%, exhibiting a more pronounced velocity deficit, with a maximum difference of approximately 40% at 2D downstream. However, its wake recovered faster, exceeding the bare turbine's wake recovery level by 8D downstream. Furthermore, the influence of waves on wake recovery was limited, improving the recovery rate by approximately 8% within the parameter range of this study. The findings indicate that the ducted turbine provides superior overall performance in wave environments; however, its structural design must prioritise the dynamic loads induced by waves. This study provides theoretical insights and data support for the design and array arrangement of ducted turbines in complex marine environments.