Abstract
Usage of composite materials in wind turbine blades is a passive mechanism to alleviate fatigue loads besides the reduction in the mass of the wind turbine system. Off-axis plies in bend-twist coupled (BTC) blades account for the passive fatigue load reduction by reducing the effective angle of attack of blade sections. Reduction in fatigue loads is generally represented by damage equivalent load ratios. In the present study, multibody aeroelastic analyses are performed for wind turbine systems for the underrated, rated and the overrated turbulent wind speeds. It is shown that load reduction can be achieved for the whole range of wind speeds with the usage of bend-twist coupled blades at the cost of power loss at underrated wind speeds which is unacceptable. Thus, the main concern of the present study is first to make performance study of wind turbines with bend-twist coupled blades at underrated wind speeds and then to overcome the power loss while still achieving reduction in damage equivalent loads by the proper modification of the pre-twist variation of the bend-twist coupled blades together with the generator torque curve across whole range of wind speeds. This study has been performed utilizing the same pitch control settings in region 2 to examine the mere effect of pretwist modification on the power performance of the wind turbine and on the damage equivalent loads.
Highlights
Larger wind turbines with longer blades are needed in order to produce more energy from wind
Damage equivalent loads in the wind turbine system reduce across the whole range of wind speeds with the use of bend-twist coupled blades, at the underrated wind speeds, power loss occurs due to the torque reduction which cannot be compensated by the pitch controller because of the minimum pitch limit
Power loss at the underrated wind speeds is compensated by modifying the pretwist variation of the reference blade in the outboard 32.8 m where bending twisting coupling is induced through the off-axis spar cap plies as described previously
Summary
Larger wind turbines with longer blades are needed in order to produce more energy from wind. With bend-twist coupled blades, passive twist control can be achieved and this can be used to alleviate loads in wind turbine blades. With the bend-twist concept, the increase in the angle of attack due to the twisting of the blade caused by the aerodynamic loading can be compensated by the proper placement of the off-axis layer through the wind turbine blade. Damage equivalent loads in the wind turbine system reduce across the whole range of wind speeds with the use of bend-twist coupled blades, at the underrated wind speeds, power loss occurs due to the torque reduction which cannot be compensated by the pitch controller because of the minimum pitch limit. There has been several studies in the literature on the load reduction in wind turbine systems through the use of bend-twist coupled blades.
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