Long-term fatigue reliability enhancement of horizontal axis wind turbine blade

The enhancement of fatigue life of ultra-large horizontal axis wind turbine blade using longitudinal stiffening is the theme of this work. For this purpose, a tendon made of shape memory alloy is used along the longitudinal axis of blade, which is modelled in aeroelastic spinning finite element framework. The force developed in the tendon acts against the deformation where the material is modelled using Liang and Rogers constitutive relationship along with the principles of thermodynamics. The fatigue design follows the guidelines provided in internationally recognised codal provisions. The blade responses are simulated using aeroelastic loads obtained from blade element momentum theory. These dynamic responses are utilised to evaluate the longitudinal stress in the extreme fibre over the blade profile. Then, short-term and long-term damages are evaluated using rainflow matrix obtained from these stresses. Finally, the reliability of blade against fatigue failure is investigated. The numerical analysis presented in this study clearly demonstrates the performance of the longitudinal stiffening in combination with pitch angle on the fatigue life of the blade.