LAUSR

Abstract The capacity of offshore wind power has increased recently because of the emerging environmental and social problems in onshore wind turbines. A floating offshore wind turbine (FOWT) system experiences the additional six-degree-of-freedom (6DoF) motions caused by both wind and wave loads. These motions are associated with the distortion of the wake structure and the oscillation of aerodynamic performance. This study focused on the unsteady wake characteristics of FOWTs. A nonlinear vortex lattice method (NVLM) was coupled with a vortex particle method (VPM) and used for simulation of the NREL 5-MW wind turbine undergoing periodic motions. Translational (heave, sway, and surge) and rotational (yaw, pitch, and roll) motions were imposed on the wind turbine, and the displacements of the floating platform were defined as a sinusoidal function. Significant variations in the thrust force and power output were observed for the streamwise motions. In addition, the platform motions affected the wake evolution strongly, thus resulting in periodic deformation of the wake structure and the rapid breakdown of helical wake vortices for all motions. A discussion of the current study could facilitate in understanding the wake-induced phenomena and the unsteady wake behavior of FOWTs.