Research On Large-scale Wind Turbine Blade Structure Design Method

As an important part of green energy, wind power has been getting more and more attention in the world. Wind turbine blades are the main components of wind turbines, and their design and manufacturing technology are regarded as the key to wind turbine research and development. The researches on blade structure design are still faced with big challenges in China; therefore, a thorough study on relevant basic theories and techniques is of great significance to commanding the core techniques of wind turbines and improving our capacity for independent innovation. In the above context, a study featuring the design of wind turbine blade structure and relevant techniques is carried out in this dissertation.With theoretical analysis on the design of wind turbine blades, the author probes into the aerodynamic coefficients, structural parameters, definitions of relevant coordinates and the common aerodynamic design methods involved in wind turbine blade design. On the basis of analyzing the structure of wind turbine blades, the features of different blades are compared and the differences in bearing structure design between blades of strong spar and those of weak ones are studied. Besides, the author also conducts a strength analysis for laminated classic composite plates and applies the replacement methods of Beam theory into blade bearing structure design.Load calculation lays a foundation for wind turbine blade design. With a research on wind features, this dissertation offers an engineering calculation model involving wind turbulence such characteristic quantities as wind speeds, directions and intensity of a short period. This model can also be used for calculating random aerodynamic loads. Analyzing the main load calculating methods, description model of wind conditions, and system operating state, the author studies the combination conditions for wind system operating state and the external wind regime, and determines the minimum load design that may cover all the conditions for wind system operation. In addition, the author researches the timing simulation method, and conducts an analysis over the random components-contained maximum load with statistical extrapolation methods and the Gumbel distribution model, and finally generates the method for calculating the ultimate load of blade.With a comprehensive application of the classic laminated plate theory, the replacement design methods of Beam theory and some empirical formulas, a design method for the main load structure of blade is established, a testifying procedure is produced, a case analysis calculation is conducted, and the validity of design methods is justified. The calculation results show that both the way to design the blade structure layering with the theory of laminated classic composite plates and the method to calculate the thickness of blade laminated plates are feasible, the design method of Beam theory is more convenient and it can also lay a foundation for calculating composite layers, and the results obtained from rigidity design of replacement methods of Beam theory are closer to the real situation, which shows that the rigidity condition is one of the key constrained conditions in large-scale wind turbine blade structure design. As for the issue of blade structure optimization, the author builds a spar structure optimization model which takes into account of the curve and shear stress.As for the problem that the aerodynamic design and the structure design were conducted separately in the past, this dissertation offers an analysis of the overall influence of blade thickness, solidity and the torsion angle on aerodynamic and structure functions, and provides a balance design of aerodynamic and structure with reasonable distribution of extending airfoil shape of blade. This method initiates the concept of the structure coefficient ofк, and divides the large-scale blades into inner circles featuring structure requirements and out circles catering for aerodynamic requirements. The inner circles adopt the blunt trailing edge airfoil type to improve the structure strength and stiffness of the blade, while the out circles take the thin airfoil type with sound aerodynamic functions, to properly resolve the conflict between blade aerodynamic and structure. For the location design of the pitch center, this dissertation studies the blade torque load and produces a design scheme of coinciding the pitch center and the center of gravity in the cross section of blade. It can help reduce the blade torque load in operation.