Load Reduction on Offshore Wind Turbines by Aerodynamic Flaps

Abstract

This paper focuses on load reduction by implementing controllable trailing-edge flaps on an offshore wind turbine (OWT) supported on different fixed bottom structures in various water depths. The benchmark NREL 5-MW offshore horizontal axis wind turbine is used as a reference. This work utilizes the wind turbine simulation tool FAST with coupled stochastic aerodynamic-hydrodynamic analysis for obtaining the responses. The flap is controlled using an external dynamic link library through PID controller. Blade element momentum (BEM) theory and Morison equation are used to compute the aerodynamic and hydrodynamic loads, respectively. BEM theory is presently modified to account for unsteady effects of flaps along the blade span. Variation in force coefficients is shown due to unsteady effects of flaps. The present analysis results show reduction up to 8–29% in blade loads for the turbine with different support structures on implementing controllable trailing edge flaps. Also, an influence of blade load reduction on tower base and nacelle is shown. Tower loads are calculated considering aerodynamic and hydrodynamic loads individually. This study can form the basis for evaluating the performance for large-scale fixed offshore wind turbine rotors.