Experimental evaluation of fatigue in wind turbine blades with wake effects

Abstract

Large investments in the implementation of wind turbines were made in the last decades, which increased the importance of this source in the national electricity systems. The management of this asset can strongly benefit from the development of cost effective monitoring strategies. These may contribute to the extension of the lifespan of existing wind turbines, to the reduction of insurance costs by reducing the operation risk and to the optimization of the design, leading to an increase in the competitiveness of this energy source. This paper is dedicated to the implementation and validation of tools to assess the fatigue condition of wind turbine blades from strains measurements with a set of fiber optic strain gages installed at the blade roots. It describes the data processing needed to obtain accurate experimental estimations of the bending moments applied to the blade roots and the procedure to obtain the accumulated fatigue damage. The instrumentation of two wind turbine rotors aligned with the most frequent wind direction allowed quantifying the interaction between neighboring wind turbines and its effect on fatigue life consumption. The paper presents unique experimental data simultaneously collected in two 1.8 MW wind turbines of an onshore wind farm during 14 months that permitted a very clear illustration of wake effects on fatigue consumption.