A Large Eddy Simulation Study of Turbine Pitch Motion Effects on Power Generation in Fully Developed Floating Wind Turbine Arrays

Abstract

Interactions between floating wind turbines and the marine atmospheric boundary layer affect turbine wakes and power output. This study examines the impact of turbine representations and platform pitching motion on power predictions for aligned floating wind turbine arrays. Large-eddy simulations (LES) are performed for a fully developed wind turbine array boundary layer with periodic streamwise and spanwise boundary conditions and moving surface drag (MOSD) at the bottom surface. A proposed power-curve-aware extension of the conventional actuator disk model (PCADM) is compared with the traditional constant coefficient actuator disk model (CCADM), which is valid in principle only during Region 2 operation. Harmonic pitching motion matched to a representative ocean wave frequency is prescribed for IEA 15MW turbines mounted on the UMaine VolturnUS-S platform. Results demonstrate that the CCADM produces unphysical power overshoot when relative velocities induced by harmonic pitching periodically exceed rated speed, while the PCADM eliminates these unrealistic excursions from the actual turbine operating range. Various wind-wave conditions and relative pitching motions for an aligned farm with PCADM turbines are analyzed, including in-phase, opposite-phase, and incommensurate-phase row-to-row relative turbine motion. Results reveal that, depending on operational regions, turbine pitching motion can either increase or decrease mean turbine power output. Among the relative phases considered, in-phase motions produce larger fluctuations at the farm scale due to stronger turbine-turbine correlations. These findings highlight the importance of accounting for turbine motion and associated changes in operational regions when modeling turbine and wind farm power production in LES of offshore floating wind farms using actuator disk representations.