Abstract

With the increasing of rated power of offshore wind turbines, the blade is becoming longer and slender. This leads to the significant structural deformation of the wind turbine blade and further make the aerodynamic responses of offshore wind turbines unsteady. Moreover, the change in wind turbine aerodynamics will alter the coupled performance of floating offshore wind turbines because of strong interference effects between the wind turbine and the floating platform. In the present work, a coupled aero-hydrodynamic analysis model for floating offshore wind turbines considering blade deformation is established. The actuator line technique is applied to calculate the aerodynamic loads and reproduce the turbine wake. The structural dynamic equations and the finite element method are used to obtain the blade deformation. Coupling effects between the aerodynamic responses of wind turbine and the structural deformation of blade are taken into consideration. In addition, the hydrodynamic responses of floating platform and mooring system are predicted by in-house CFD code naoe-FOAM-SJTU. The aeroelastic module is firstly validated by the previous numerical results. Then coupled aero-hydrodynamic responses of a spar-type floating offshore wind turbine under combined wind-wave loads are analyzed in detail using the proposed analysis model. It is found that the average aerodynamic loads including rotor power and thrust decrease and the fluctuation amplitude of aerodynamic power increases when the blade deformation is considered. The blade deformation shows small effects on the wake velocity, while it has significant effects on the blade structural bending moments.

Introduction

With the rapid development of the offshore wind industry, the wind turbine mounted on floating structures have gradually become the trend of offshore wind turbines (Rodrigues et al., 2015). Under wind-wave-current loads, there are strong interactions between the wind turbine and the floating platform. The aerodynamic loads transformed via tower affects the motion responses of floating platform, and the six-degree-of-freedom platform motions alter the inflow condition of wind turbine and influence the aerodynamic performance in return (Shen et al., 2018). Moreover, the blades of offshore wind turbines are becoming larger and slenderer in order to improve the efficiency of power generation and reduce the operating costs (Ederer, 2014). This leads to the significant structural deformation of the wind turbine blade and further makes the coupled aero-hydrodynamic responses of floating offshore wind turbines (FOWTs) more complicated. To further understand the performance of floating offshore wind turbine under combined wind-wave loads, it is necessary to investigate the influence of blade deformation on the coupled aero-hydrodynamic responses.

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