Sea waves-wind interaction and offshore wind turbine's implications

Understanding how sea-waves interact with the atmospheric boundary layer is necessary to predict the impact on offshore wind turbines both in terms of power production and loads on the blades. In this study, sea waves are simulated as moving sinusoidal waves. Large Eddy Simulations (LES) are performed with different values of the ratio between wave speed (U_wave) and hub-height wind velocity (U_hub). Four different cases are reproduced with U_wave/ U_hub = [0, 0.4, 0.6, 0.7]. The sinusoidal waves are reproduced in the LES with the Immersed Boundary Method. 

In the first set of LES the wind turbine wasn’t considered. Due to the wave motion, the drag of the moving waviness significantly decreases respect to the reference case with  U_wave/ U_hub = 0. As a consequence, a reduction in the shear exponent of the mean velocity profile is also observed. A similar behavior is observed for the turbulence intensity at the hub height. Further increasing the wave speed from U_wave/ U_hub = 0.44 to U_wave/ U_hub = 0.7 only moderately reduces the turbulent intensity. 

In the second set of simulations, a wind turbine was included using the previous set of simulations as precursors. The effect of sea waves-wind interaction on offshore wind turbine performance will be discussed during the presentation.