Study On The Key Theory Of Wind Turbine Blade And Dedicated Airfoils

As a clean energy, wind power attracts more and more attention around the world. Blade is one of the most important components of the wind turbine, which cost up to 20% of the whole machine. Furthermore, wind turbine power performance and its load characteristics are influenced by the designing of the airfoils and blade distribution. Therefore, it is necessary to develop the new theory and methodology for the wind turbine dedicated airfoils and blade design. These works will play a very important role both in theoretical and industrial application.To study the inherence of airfoil profiles and blade shapes, the dissertation proposes a study entitled"Study on key theory of wind turbine blade and dedicated airfoils", sponsored by National Natural Science Foundation of China (No: 50775227) and Natural Science Foundation of ChongQing (No: CSTC, 2008BC3029). Based on the analyzing the design theory of wind turbine blade and airfoils, the new method of"Shape function"for two-dimensional airfoil representation and"Shape function/Distribution function"for three-dimensional blade representation are presented. By combining functional analysis conception, multidisciplinary design optimization ideas, concurrent and collaborative design theory and methods, a series of wind turbine blades and dedicated airfoils are developed. Finally,wind tunnel experiments for new airfoil are carried out. In this dissertation, the main work and results are summarized as follows:①The geometric similarities of two-dimensional airfoils have been discussed. Based on the conformal transformation and series theory, a novel parametric representation method-"Shape function"for airfoils was developed. The airfoil design space and shape control equations were studied. The research showed that the airfoils which generated by"Shape function"method was able to cover a near circle design space. This method broke through the inherent limitation of traditional airfoil model, and could use a function to express the airfoil shape exactly. The method transformed the shape optimization to the parameters optimization and the design method of airfoil profiles for wind turbines is broadened.②Results of the parametric representation of more than thirty wind turbine airfoils are shown to illustrate the evaluation processes and to demonstrate the rate of convergence of the geometric and aerodynamic characteristics. The coordinates and aerodynamic performance of approximate airfoils is rapidly close to the target airfoil corresponding to the increasing orders of polynomial. The lowest orders of different airfoils parametric representation are presented. This approach provided a basic theory for the topological study of wind turbine airfoil profiles.③Based on the"Shape function"method and multi-disciplinary design optimization ideas, this paper dealt with multi-objective shape optimization (maximize the lift/drag ratio both in free and fixed transition), design variables (coefficients of shape funtion) and constraints (control function, the requirement of aerodynamic, structural and acoustic disciplinary) related to the profile design of a wind turbine dedicated airfoil shape. The multi-objective optimization model for two dimensional airfoil profile design was established by taking to the weighted averages of sub-objectives for the different wind farmer condition. A series of wind turbine dedicated airfoils were developed by applying the improved multi-objective genetic algorithm. This approach broke the limitation in current design method of airfoil design, and presented a new method for the wind turbine dedicated airfoil design.④A universal method for three-dimensional blade integration-"Shape function/Distribution function"was presented based on the two-dimensional airfoil Shape function and the analyzing of the blade distributions of airfoils, chord and twist angle. This method was able to represent all the details of blade shape including the airfoil shape functions and distribution, chord distribution and twist distribution. An actual wind turbine blade was well represented by using this parameterization method. The universal integration method for three-dimensional blade provided a sound basis for the wind turbine blade shape optimization. This could potentially be used to solve the problems of other three-dimensional shape integration.⑤Three-dimensional blade shape optimization was studied based on the functional thought and series theory. By using the blade Shape function and Distribution function, the blade geometrical shape optimization was transformed to the functional optimization. The blade shape and distributing characteristics could be controlled by adjusting the series coefficients. The shape functional optimization can be gained by varying the coefficients of polynomial series, which also can be used to solve the general three-dimensional blade shape optimization problem. Aimed at maximizing the annual energy generation in constant and variable speed operation condition respectively, assigned the coefficients of the blade distribution function as variables.Based on the wind turbine aerodynamics, the wind turbine blade shape optimization model was established by using the new WT series airfoil in the major power generating region of the blade. Two types of rated power of 2.3 MW wind turbine blades with high power coefficient were developed. This blade optimization method provided a reliable theoretical basis for developing efficient wind turbine blade and also put a new example for impeller type fluid machinery design.⑥Wind tunnel experiments for WT180 were carried out both in clean and roughness condition in the 3.0m×1.6m low-speed wind tunnel and three kinds of Reynolds number (2.0×106, 3.0×106, and 4.0×106) were chosen during the tests. The testing verified the high lift/drag ratio and high maximum lift coefficient for the WT180 and the airfoil was found to be very insensitive to leading edge roughness. Like most wind turbine airfoils, the scope of lift coefficient increased and the drag coefficient decreased with increasing Reynolds number both in the clean configuration and in the situation with roughness at the leading edge. Comparisons of the RFOIL prediction and experimental results generally show good agreement. The wind tunnel experiments comparison were carried out between new airfoil and advanced RIS? airfoil, the result demonstrated that the WT180 airfoil show a superior aerodynamic performance than RIS? airfoil. The novel design theory and methodology for wind turbine dedicated airfoil and blade design proposed in this paper is verified by the wind tunnel experiments. This has a great significance for developement of new blade and its industrial application.