Wave-induced surge effects on the hydrodynamic performance and wake dynamics of a side-by-side floating tidal turbine array

The wake interaction between adjacent floating tidal stream turbines is crucial for reducing the footprint and energy losses. In this paper, numerical simulations are conducted on a side-by-side twin-turbine array under wave-current conditions. The analysis focuses on transient power trajectories, hydrodynamic loads, and three-dimensional wake topologies. The results reveal that both the mean and fluctuation of performance coefficients increase with wave height and frequency. A lateral spacing of 1.5 times the rotor diameter (1.5D) produces a negligible mutual induction effect on the individual wake trajectories. However, the spatial distribution of the wake velocity becomes highly non-uniform under wave action, exhibiting distinct wake interference and fusion further downstream. Due to this asymmetric induction, the inner blade-tip vortices exhibit higher vorticity intensity than the outer ones. Furthermore, a three-dimensional proper orthogonal decomposition analysis reveals that the low-order conjugate mode pairs capture most of the fluctuation energy, indicating that large-scale coherent vortex shedding is strongly associated with the wave frequency. Wave height primarily affects the turbulent fluctuation intensity, whereas wave period determines the axial wavelength and spatial survival distance of downstream vortices. These results clarify the coupled effects of wave-induced surge and turbine rotation on floating tidal turbine arrays.