Study of Bend to Twist Coupling of Composite Laminates for Passive Load Alleviation of a Wind Turbine Blade

Abstract

One of the biggest challenges wind turbines in low speed wind regions (sudden extreme wind speeds) face, is bearing the sudden and excessive loads caused by typhoons and tropical cyclones in the region. The extreme turbulence and rapid change in the wind direction and speeds are the major causes of wind turbine failures. This leads to blade pitch angle error in the traditional pitching mechanism used for load alleviation, causing large responses in terms of rotor thrust and generator torque. This can potentially lead to fatal accidents. Hence, passive load alleviation techniques are gaining ground, bend to twist coupling of anisotropic composite laminates in particular. The induced twist when the laminate is under bending loads helps reduce excessive loads in the structure. This concept can be applied to the blades of the stalled wind turbines to withstand extreme loads. Previous research findings support this hypothesis and show that eliminating the pitching subsystems can help create lighter blades that require less maintenance. In this study, five single-ply and five two-ply laminates are analysed using a MATLAB program to determine their bending-twisting coupling coefficients, strains and stresses under an applied moment. For our loading condition, the study seems to indicate that the addition of the 25° ply is optimal in terms of reducing the stresses by twisting. Further work is required in order to understand the effect of the number of plies, ply architecture, different cross-sections, etc. on the bend-twist coupling of composite structures so as to incorporate it into a wind turbine blade spar.