Numerical analysis of aerodynamic performance of a floating offshore wind turbine under pitch motion

Abstract

The aerodynamic performance of wind turbines is essential to evaluate their electricity-generating capability. Compared with the wind turbines with traditional fixed structures, the aerodynamic performance of floating offshore wind turbines (FOWTs) is affected by the additional platform motion, especially for the pitch motion. In view of this, the computational fluid dynamics (CFD) method with the improved delayed detached eddy simulation (IDDES) is applied. Before the numerical simulation, the CFD model of the redesigned 1:50 scale rotor from NREL 5 MW wind turbine is verified with the available experimental data and numerical comparison. Then, the aerodynamics of the FOWT under the harmonic pitch motion with different periods and amplitudes is investigated. It is shown that the aerodynamic performance of the FOWT is sensitive to these parameters of the pitch motion. First, amplitudes of the rotor thrust and torque decrease with the increment of the pitch period. In particular, the wake interference phenomenon is the most evident when the pitch period is short and the pitch amplitude is high, which may compensate some energy to the rotor. In addition, amplitudes of the rotor thrust and torque increase with the increment of the pitch amplitude. Also, the stall phenomenon happens when the pitch amplitude is high, which may impact FOWTs’ aerodynamic performance adversely. Finally, the rotor power increases under the periodic pitch motion, especially by decreasing the period or increasing the amplitude. It is concluded that the pitch motion of the platform will change the aerodynamic performance of a wind turbine and should be taken into consideration during design procedure.