Nonlinear Wake Dynamics of a Model Floating Offshore Wind Turbine Under Pitch and Roll Motions

Abstract Floating offshore wind development requires an improved understanding of wake dynamics influenced by platform motions. Pitch and roll motions significantly influence wake behavior, especially in low to moderate turbulence, affecting downstream turbines. This study employs an improved delay detached eddy simulation (IDDES) with a blade-resolved approach to analyze the wake characteristics of a floating offshore wind turbine (FOWT) subjected to harmonic pitch and roll motions. Using a sliding interface approach, turbine rotation, and oscillatory dynamics are modeled. Considering only the turbine rotor, the wake dynamics of the moving and stationary cases are compared. The simulation results show good agreement with the available experimental data, confirming their validity. The results show that platform motions increase wake unsteadiness, enhance turbulence mixing, and accelerate far-wake recovery through coherent flow structures. Larger motion amplitudes lead to earlier onset of wake structures - 34% for pitch and 42% for roll - increasing turbulence and velocity deficit. Probability density functions of the wake reveal that roll motion significantly broadens the lateral wake, increasing turbulence. In contrast, pitch motion results in a more balanced and stable wake displacement in both lateral and vertical directions.