Aeroelastic stability evaluation of bend-twist coupled composite wind turbine blades designed for load alleviation in wind turbine systems

摘要

Wind turbine blades for turbines with large rotor diameter tend to be very flexible in order to remain weight and cost effective. Bending-twisting coupling induced in big composite wind turbine blades is one of the passive control mechanisms which is exploited to alleviate loads incurred due to the flexing of the blades. In the present study, aeroelastic stability characteristics of bend-twist coupled blades, designed for load alleviation in wind turbine systems, is investigated to check whether the bending twisting coupling significantly affects the aeroelastic stability characteristics of the blades or not. For this purpose, different full GFRP and hybrid GFRP and CFRP bend-twist coupled blades are designed for load reduction purpose for a 5 MW wind turbine model that is set up in a wind turbine multi-body dynamic code that uses non-linear beam blade definition and allows bend-twist coupling. For the study of aeroelastic stability characteristics of the blades, overspeed analysis of the wind turbine system is performed without using any blade control and applying slowly increasing wind velocity. Time responses of the torsional and the flapwise bending deformation of the blades obtained in the overspeed analysis are processed to predict the flapwise bending-torsion flutter wind and rotational speeds and the flutter frequencies. Flutter analysis results show that hybrid GFRP and CFRP bend-twist coupled blades have lower flutter speeds compared to the baseline and the bend-twist coupled GFRP blade.