Research On Bend-twist Coupling Characteristics Of Large Composite Wind Turbine Blade

With the increasement of the blade size, the deformation effect of is remarkable with its large flexibity and the loads become larger with its large quality. Wind turbine blades with bend-twist coupling characteristic bend and twist at the same time under wind load. Through the reasonable design, the bend-twist coupling blade can lower the impact load on the blade and broad the wind speed scope that wind turbine operating normally. The generating mechanism of bend-twist coupling phenomenon and description method of bend-twist coupling charactertistics are researched in this paper. Furthermore, the bend-twist coupling charactertistics are researched from the angle of analytical, experimental and numerical solution. A 5MW wind turbine blade with bend-twist coupling characteristic is designed. The main research and results of the paper are as follows:(1) The bend-twist coupling effect is explained from the angle of material coupling and structure coupling. The nodal displacement method is presented to discribe the bend-twist coupling characteristic. The bend-twist coupling vector and equivalent bend-twist coupling coefficient are defined in this method. The nodal displacement method looks the bend-twist coupling coefficient as integral property and includes the material coupling and structure coupling. The research of mechanism of bend-twist coupling effect production and the discription method provide a basis for research of bend-twist coupling characteristic for wind turbine blade.(2) Constitutive equation of composite plate beam that simplified from wind turbine blades is given with the classical laminate theory. The bend-twist coupling phenomenon is explained from the angle of material coupling. The analytical solution of bend-twist coupling vectors and equivalent bend-twist coupling coefficient for cantilevered laminated beam are deduced. The effect of material coupling and length coupling to bend-twist coupling characteristic are researched through the lay up and coupling area. The research results are compared with traditional cross-section stiffness method.(3) Two kinds of laminated plates are designed and fabricated, they are the uniform symmetric laminated plate with different ply orientation and the un-uniform laminated plate with different coupling area. The bend-twist coupling characteristic of the two kinds of laminted plates are tested with the suspension line method. Tensile testings which have the same material with the laminated plates are fabricated and its mechanicas mechanics performance parameters are got. The numerical solution of deformation and bend-twist coupling coefficients for the two laminated plates are calculated with finite element model according mechanic property parameter and size. The numerical solution is compared with the experimental results. The results show that the nodal displacement method can describe the bend-twist coupling characteristic reasonably and accurately. Also, the experiment of bend-twist coupling characteristic have verfied the analytical solution.(4) The influence of warping effect, location of webs, number of webs, material coupling and spar type on blade section coupling are researched with the cross-section properties calculation method. A bend-twist coupling characteristic calculation method of wind turbine blade based on beam-shell finite element model is given. The effect of material coupling and structure coupling to bend-twist coupling characteristic for wind turbine blade spar are researched with the bend-twist coupling characteristic calculation method. The results show that warping effect, presence of web and spar type on blade section coupling effect has a great influence on the cross-section properties. The effect of location and number of webs, material coupling to bend-twist coupling characteristic can be negligible. The displacement calculation method given in the bend-twist coupling characteristic calculation method has a high accuracy and effciency. The research of bend-twist coupling characteristic of wind turbine blade’s spar provide a basis for research of bend-twist coupling characteristic for wind turbine blade.(5) The analysis software of modal and bend-twist coupling characteristic for wind turbine blade is writed using the bend-twist coupling characteristic calculation method based on beam-shell finite element model. A 5MW wind turbine blade is designed and the parametric bend-twist coupling blades are established using the 5MW wind turbine blade as baseline. The bend-twist coupling characteristics of these parametric bend-twist coupling blades are calculated with the software and the optimized model is got among these blades. The static and dynamic characteristics of the optimized 5MW bend-twist coupling blade under normal operating conditions are calculated. The results show that the bend-twist coupling blade can produce larger torsion deformation, the influence of rotating speed on the dynamic characteristic for bend-twisting coupling blades are same with non-bend-twist coupling blade.