Exploring unsteady dynamics of turbine rotor aerodynamics and wakes under surge and pitch

Expanding offshore wind energy is essential for meeting international decarbonization goals. At many high wind resource locations, deep water requires the use of floating offshore wind turbines (FOWTs). In realistic ocean conditions, wind and waves induce unsteady kinematic turbine motions, such as surge and pitch, which in turn result in unsteady inflow conditions to the rotor. This unsteady inflow affects forcing, loading, and power production of individual rotors. However, current models to predict rotor aerodynamics are based on steady or quasi-steady approximations that do not hold in all regimes of turbine motion. In this study, we perform large eddy simulations of turbines across a wide range of unsteady surge and pitching motions, and quantify modeling errors in mean power when compared to the LES across the rotor thrust coefficient, as well as the frequency and amplitude of the motion. Turbine motion also affects downstream flow by altering the morphology and recovery of turbine wakes. Modal analysis reveals modifications to the wake dynamics and structure that are triggered by the unsteady forcing and kinematics of the turbine in motion. Improving the modeling of both rotor and wake behavior under realistic FOWT motions is crucial for developing control strategies and optimizing the design and control of floating wind turbines and floating wind turbine arrays.