The impact of platform motion on the aerodynamic characteristics of floating offshore wind turbine arrays

Floating offshore wind turbines (FOWTs) are gaining increasing attention within the industry. In this paper, the impact of platform motion on the aerodynamic characteristics of the FOWT array is numerically investigated. A high-fidelity numerical tool with the Computational Fluid Dynamics (CFD) method is further developed based on the open-source CFD toolbox OpenFOAM by coupling the Actuator Line Model. Three turbines with different arrangements based on tandem and staggered layouts are simulated. Significant wake interactions are observed by investigating the flow field around the downstream region, the velocity and turbulence variation due to the wake interaction has been studied. The capacity factor of the total system of a tandem layout is 50% in the most common scenarios, while it is 92% for the staggered layouts. The motion of the turbine, due to the floating platform, has a minor influence on the time-averaged power output but significantly influences the power fluctuation. In gridded layouts, the downstream FOWT can have up to 25% higher fluctuation amplitude than fixed one, while for staggered layouts, this can reach 80% in the most critical case. The flow field also indicates that strong wind turbulence reduces the impact of platform motion on power fluctuations, especially for the third turbine, with the most significant wake interaction. By analyzing the power output and the platform motion, it is found that the pitch and surge motion of the OC4 platform have an opposite influence on the power output. Thus, a coupled model considering both degrees of freedom is necessary.