Wake of a floating wind turbine model under roll motion

Abstract The development of floating offshore wind turbine (FOWT) technology facilitates the exploration of deep-ocean wind resources. Meanwhile, there are still open questions on how the structural response will affect the performance of floating turbines and wind farms. Based on wind tunnel experiments, this study investigated the effects of roll motion on the wake characteristics of a floating wind turbine model. Various roll dynamics, differing from roll frequency and amplitude (in the ranges of 0 – 4 Hz and 0 – 15°, respectively), were tested and compared. The results showed that roll motion can accelerate wake recovery and increase the wake turbulence intensity of the floating wind turbine. Spectral analyses revealed the wake periodicity imposed by the cyclic roll motions. Wake meandering was found to have a dominant frequency that was the same as the roll frequency, and was enhanced by the roll motion of the turbine, especially in the spanwise direction. As a result, the lateral wake growth rate increased with increasing roll frequency or amplitude, while wake growth in the vertical direction was less affected. The Gaussian wake model was applied to predict the wake of a FOWT in roll motion. The results showed that the model underestimated the wake deficit in all roll cases, and failed to depict the wake shape (especially in cases with relatively high roll frequency or amplitude), highlighting the importance of considering roll dynamics in floating wind turbine wake model development.