Analysis of wake effects on global responses for a floating two-turbine case

Abstract

While most existing modeling and analysis of floating wind turbines (FWTs) considers isolated systems, interactions among multiple FWTs arranged in an array have received little attention. In this study, two 10 MW semi-submersible FWTs, separated by 8 rotor diameters (D) in the wind direction, are simulated with an ambient wind speed of 10 m/s and in moderate wave conditions using FAST. Farm to investigate the effects of wakes on global responses. Synthetic inflow is generated using three methods: the Kaimal turbulence model, 1) without and 2) with spatial coherence in the lateral and vertical velocity components, and 3) the Mann turbulence model (where spatial coherence in all three dimensions is inherent to the model). The first method results in negligible wake meandering, a relatively uniform wake deficit, while the second and third methods result in meandering of the upstream turbine's lateral wake center at the downstream turbine's rotor plane of up to approximately 1D and 1.5D, respectively. The slow meandering behavior of the upstream turbine's wake resulted in increased low-frequency platform motions for the downstream turbine. Yaw motions were especially susceptible to wake meandering as the standard deviation of the downstream turbine's yaw motion increased by 28.0 % for the second method and 11.3 % for the third method. Increased low-frequency response in structural loading was also observed. Wake effects led to between 2 % and 30 % greater fatigue damage at the top of the tower for all three methods and at the base of the tower for the second method. However, other results were found to be sensitive to the blade-passing frequency.