Investigation of the effect of off-axis spar cap plies on damage equivalent loads in wind turbines with superelement blade definition

Abstract

The effect of off-axis plies in the spar caps of a wind turbine blade on the damage equivalent loads in a wind turbine system is investigated. The use of off-axis plies in the spar caps is exploited for load alleviation in the whole turbine system through the bending-twisting coupling induced due to off-axis plies. Fatigue damage equivalent load is used as the metric to assess the effect of off-axis ply placement in the spar caps of the turbine blade on the load alleviation in the whole wind turbine system. In the initial phase of the study, known sectional beam properties of NREL’s 5MW turbine blade are utilized in an inverse design framework, and a reference blade is designed such that sectional beam properties of the 3D blade design approximately match the sectional beam properties of NREL’s 5MW turbine blade. In order to appropriately account for the effect of off-axis plies on the bending-twisting coupling potential, dynamic superelement of the blade is created and introduced into the multi-body dynamic model of the wind turbine system. For the purposes of the study, a 5 MW multi-body wind turbine model is generated in Samcef Wind Turbine environment, and multi-body dynamic simulations of the wind turbine system are performed for the power production load case with the constant wind the normal turbulence model as the external wind loadings. Time history results of aeroelastic simulations are used to calculate damage equivalent loads at the selected monitor points in the wind turbine system, and conclusions are inferred with regard to the effectiveness of the off-axis spar cap plies in the blade structure in load alleviation and possible drawbacks of the use of off-axis plies in the spar caps. Results show that in the overall, with the use of off-axis plies in the main spar caps of the blade, damage equivalent loads associated with the critical force or moment components can be reduced in the wind turbine system.