Research of the roll motion on hydrodynamic performance and wake interaction of a side-by-side tidal stream turbine array

In floating tidal turbine farms, the global wake interaction affects the ecological footprint, hydrodynamic performance, and the project's investment return. In this paper, a computational fluid dynamics model with advanced overset mesh techniques investigates the response of a side-by-side tidal turbine array under roll and current. The predicted power coefficients are confirmed against experiments, showing a relative error of 2.37% at the rated TSR = 3.9. The variations of the hydrodynamic load and wake of the turbines are investigated in terms of the roll period and amplitude. The results show that the roll results in the interaction between the two parallel turbines, and the load and wake are simultaneously affected by the adjacent turbine and the roll motion. Specifically, platform roll introduces dual-frequency fluctuations arising from rotor rotation and platform motion, while the mean power (CP ≈ 0.34) and thrust (CT ≈ 0.81) coefficients remain nearly constant. Complex interactions occur between the blade tip vortices in the wakes. The vortex instabilities relate to the roll motion, increasing the recovery of momentum in the wake, while also creating a more unstable inflow for potential downstream turbines.