A Large Eddy Simulation Study of Turbine Pitch Motion Effects on Fully Developed Floating Wind Farm Boundary Layers

Interactions between arrays of floating wind turbines and the marine atmospheric boundary layer greatly affect wind farm wakes interactions and power output. These interactions and the turbine level power output can be greatly affected by turbine platform motion. In this work we focus on the effects of platform pitching on the power output of an array of turbines. We simulate an array of floating turbines that are limited to pitching motion in a Fully Developed Wind Turbine Array Boundary Layer (FD-WTABL) using large eddy simulation (LES) with periodic streamwise and spanwise boundary conditions. A PI pressure gradient controller is used to maintain target velocity at the top of the computational domain. The Moving Surface Drag Model (MOSD) of Ayala et al (2024) is applied at the bottom surface. Turbine pitch is prescribed as a harmonic motion matched to ocean wave frequency, with defined amplitude and phase. An inertia-induced lag is incorporated via an exponential time filter applied to the disk-averaged velocity based on an imposed timescale. The turbine/platform system is modeled based on actuator disk representation (ADM) of the IEA 15MW reference turbine mounted on the UMaine VolturnUS-S reference platform. We compare various relative pitching motions including in-phase, opposite phase and incommensurate phase motions. LES results reveal that the resulting wind-wave-wake interactions can affect average large-scale flow properties such as the vertical profile of the mean velocity, especially at and below turbine heights. Turbine pitching can also lead to power variations, which are important to account for in studies of floating wind energy.