피로수명을 고려한 1 MW급 수평축 고효율 풍력터빈 블레이드의 공력 및 구조 설계에 관한 연구

Abstract

The mankind have used wind energy resource in various methods for several thousand years. The oldest use of wind resource was a sailer, we found the old literature about the windmill in China and Egypt, and according to the literature, it describes the ancient people had used it from three thousand years before. In other words, the technology of the wind turbine system has a long and firm historical foundation. The wind turbine system technology has a disadvantage of low efficiency of the system and little quantity of power generation because totally depend on wind resource but the cheapest technology which uses one of new and reusable energy resources. However, the world was the necessity of clean energy became important while faces the crisis of energy and the environmental problems due to excessive consumption of fossil fuel. Many countries intensively invest the experience and knowledge using wind power in the past, they have achieved a great result and utilization of the system from small sized power generation to the MW class. These results entails the commercialization, and many countries have been working on research to increase demand even though they have inconvenience in use than the existing energy source. The output of the wind turbine system has characteristic become larger in proportion to the square of the blade diameter, it frequently used in the MW class. The wind turbine system is rapidly grows the recent 10 years in mainly Germany, Denmark and America, etc. In advanced countries the wind power industry has been supported by government for the growth and spread. Vestas, Enercon, Repower, GE Wind and around 3 ~ 5 MW class large wind turbines have been developed and is being produced by commercial or prototype , 6 MW class or are under development. Comparing with the advanced countries, the scale of the Korea wind turbine system market is very small, but continuously grows to the supporting policy of renewable energy by the Korea government. The research has been started from the early of the 1990s and the development of technology of 750 kW, 2 MW and 3 MW class respectively for the blade for the wind turbine system was completed and in the commercialization and demonstration and currently is promoted the development of 5 MW class of blades. As the Wind Turbine blade used by composite materials, its structural strength, rigidity, fatigue life and economic efficiency, etc was greatly improved. Composite materials of the blade for the wind turbine system include glass/epoxy, carbon/epoxy and wood/epoxy, etc but glass/epoxy has generally used because it is economic efficiency, excellent performance and light. Wind turbine blade aerodynamic shape was used the NACA series or the improved SERI series in the past, but in recently specifically developed airfoil for wind turbine blade. In this study, for the establish the lightweight design method for large scale wind turbine blade considering fatigue life, performed aerodynamic and structural design for 1 MW class blade, lightweight design method was newly suggested. The low wind speed as possible was determined as rated wind speed in the scope that the diameter of blade was not excessively increased. The NACA 63-421 airfoil was selected to compare and analyze airfoils for the wind turbine system in order to select the airfoil whose the characteristics of Reynolds number, maximum lift coefficient, stall angle of attack, maximum lift coefficient over drag coefficient ratio, maximum thickness, etc are comparatively good. Chord length with a blade shape and the twisting angle distribution of the blade were determined by designing the basic shape according to the Strip Theory using the momentum theory and the blade factor theory together were determined, and a method to design the optimum receiving angle to obtain the high efficiency was adopted. After designing the wind turbine system known through literatures to verify the feasibility of the aerodynamic design suggested in this study, we performed the comparison and analysis with the experimental results suggested in literatures. A structural design was performed by using the Netting Rule and the Rule of Mixture Design Method by applying the Glass/Epoxy-Foam sandwich composite materials with low price and light weight. For the analysis of the structural, stress, displacement, buckling and frequency problems due to bending load were considered by using the Finite Element Method. Finally, using the Spera’s empirical equations about the manner of S-N linear damage method and cyclic load, th durability which was required for twenty years was examined.