Unsteady aerodynamic fluctuations and wake recovery of a floating offshore wind turbine subjected to yaw motions

The impact of yaw motions on the unsteady aerodynamic performance and wake behavior of floating offshore wind turbines (FOWTs) is critical to the feasibility of their deep-sea deployment. To investigate these influences, a computational fluid dynamics (CFD) model was employed to study the aerodynamic performance and wake characteristics of a FOWT under prescribed yaw motions with various amplitudes and frequencies. The numerical model was validated through comparisons of aerodynamic performance metrics and wake velocity profiles, especially showing deviations of less than 2% in the power coefficient (Cp) at the examined tip speed ratio (TSR). Based on frequency-domain analysis, an aerodynamics decomposition model via Fourier expansion was developed and validated, which incorporates a constant term from uniform inflow, velocity-induced damping, and acceleration-induced additional mass terms and provides the foundation for fast aerodynamic predictions. Quantitative analyses of the average aerodynamic performance and fluctuation ratios under yaw motion were conducted. The results indicated that variations in mean aerodynamic performance was negligible across the investigated yaw motion parameters. However, yaw-induced aerodynamic fluctuations of Cp and axial thrust coefficient (Ct) warranted attention for stable power generation, particularly at larger yaw amplitudes regardless of frequency. Furthermore, uneven blade pressure distributions led to significant near-rotational-frequency fluctuations. Regarding wake properties, greater yaw amplitude and higher yaw frequency promoted faster average wake velocity recovery, with average wake velocity recovery exhibiting higher sensitivity to yaw frequency.