Investigation on the Effect of Resolving Waves Motion in the Simulation of Offshore Wind Farms

Offshore Wind Turbines (WTs) are characterized by heights that fall within the Atmospheric Boundary Layer (ABL). In ABL the flow is characterized by specific turbulence scales and velocity profile. The motion of the sea surface can influence turbulence in the surface layer, thereby impacting wake dynamics and recovery. In this study, we explore the role of wave modeling in the wake interaction between two wind-oriented IEA 15 MW reference WTs, modeled using the Actuator Line Method (ALM). Two hybrid LES-RANS simulations are carried out, one with a flat sea and the other with swell wave motion, imposed by a dynamic computational grid. Turbulence modelling relies on k-ω SST IDDES model, enabling the resolution of the large-scale turbulence associated with wind fluctuations and turbine wakes. The Kaimal velocity spectrum is here applied to generate stochastic velocity fluctuations superimposed as a time-dependent boundary condition to a neutrally stratified ABL velocity profile. Results showed that wind-aligned waves can induce an alternating up- and down-wash effect up to 50 meters from the sea surfaces, behaving as a modification (reduction) of the aerodynamic roughness. This effect is more evident in the wake flow. Analysing the performance of the downwind rotor, a 0.5% difference in power production is observed for the case with resolved waves motion.