Research On The Aerodynamic Performance Calculation And Structural Design Of Large-scale Wind Turbine Rotor Blade

The renewable energy has greatly developed in recent years due to the crisis of fossil energy and environment. As a type of environment-friendly and inexhaustible energy, wind energy went into its golden time of development in 80s, 20th century. China, as a large consumer of energy, wind power has got quick development in recent years with the state's support. But the MW-class wind turbine technologies almost are all imported because of the deep gap between China and west countries with advanced wind power technology, especially rotor blade, which is one of the key components of wind turbine. With the support of Beijing FRP company and aid of National "11th five-year" Scientific Support Plan (2006BAA01A09), researches were focused on the aerodynamic performance calculation and structural design of rotor blade on the basis of the existing imported blade. The main achievements are as follow:(1) The aerodynamic performance was defined by power, thrust, torque and their corresponding coefficients. In this paper, by the use of blade element and momentum theory and in combination with the research results finished by our predecessors, a relatively complete calculation model for the aerodynamic performance of rotor blade is built with the consideration of rotor solidity (blade number), pitch angle, zone angle, tilt angle and blade width, thickness, yaw angle etc. Matlab codes adopted the iterative algorithm are generated and the influences of these factors on the aerodynamic performance are analyzed. Also, detailed analyses on the distribution of axial and tangential induction factors and the blade element power along the whole blade are performed. Analyses above show that solidity and pitch angle have a great effect on the aerodynamic performance while blade width and thickness affect little and the existences of zone and tilt angle will lead reduction of aerodynamic performance of rotor blade.(2) An entire set of method of large-scale blade analysis is completed by using finite element software, and also an effective approach of building the FE model of composite blade with complex aerodynamic shape and internal laminate structure is investigated. And then directly use software to calculate the sectional stiffness approximately, the results from which are identical with the theoretical ones. Compared with theoretical method, FE method is easy and convenient, especially applied at rigidity calculation of composite structures with irregular cross section. Theoretical investigation is made on blade dynamic behavior (modal analysis), approximate computation equation of blade natural frequency is derived. Modal analysis shows that the first mode happens in flapwise direction and the second in edgewise direction. High order mode shapes are getting complicated, which are mixed mode. It is clear that bigger strains occur In the region of blade root and station with maximum chord length. In the buckling analysis, it is found that blade tip area is one part that maybe easily be buckled.(3) Study work is carried out on the structure design, which is one of the key design of blade, the preliminary structural design theory is achieved. Based on the section-design principle, structural is redesigned with the same external shape as the existing blade by using classical laminate theory and Euler-Bernoulli beam theory. Structure study shows that theoretical design is not the final design, it is important to combine with FE analysis to check and modify repeatedly, through which final structural schedule will be determined. Through comparison of blade weight, stiffness at flapwise and tip deformation with the existing blade, the approach in this paper is reasonable, except the stability.(4) Feasibility of FRP replaced by GRP in spar cap to introduce bend-twist couple design is investigated. First Parametric study of bend-twist design is implemented and then finds out the main controlling parameterα, and then makes an approximation of value range of this parameter from theoretical and numerical aspects. Bend-twist coupling design can be implemented from several aspects, such as geometrically or by using unbalanced off axis fibers oriented at an angle with respect to the primary loading direction. The latter is preferred in this paper and the oriented angles are 0°, 10°, 15°and 20°.respectively. Analysis and comparison work between the blades with different design approach are done and shows that the performance of blade structure is getting higher designed by bend-twist coupling.