A Study On The Performance Of Vertical Axis Wind Turbine With Expandable Blades Based On The Structure Of Savonius Turbine

In recent years, with the increasing demand on energy for social development and people’s lives, conventional energy sources such as coal, oil are over exploited and used, which not only leads to serious environment pollution, but also makes the problem of energy exhausted growing worse. Therefore, the development and utilization of renewable energy has become a long-term development strategy of the country. Wind energy is one mature renewable energy, wind turbine performance and power efficiency have the direct impact on the using and development of wind power. Because the difficultly of designing, manufacturing and installation of horizontal axis wind turbine, the blades are more sensitive for wind direction and attack angle, and the start up wind speed of the wind turbine requires higher, people have not given up researching and developing on the vertical axis wind turbine. In this dissertation, two new types of wind turbine based on Savonius wind turbine with rectifier and airfoil blades are proposed. Research on the performance analysis and optimization of structural parameters are conducted on the new proposed structures.In this dissertation, the variation of the flow around the rotor and the torque characteristic of Savonius wind turbine are simulated by Fluent software. By analyzing the variation of static torque coefficient and its impact on performance of start-up of the wind turbine, the variation of dynamic torque coefficient and its impact on the utilization of wind turbine. The existing problems of the performance of Savonius wind turbine are illustrated in this dissertation.Flow field of the Savonius wind turbine under different conditions of tip speed ratio has been studied. The variation of the flow field and its impact on Savonius wind turbine has been analyzed. The reasons that the wind energy utilization of Savonius wind turbine is very low have been drawed. All of these preliminary work provides theoretical support for the improvement of Savonius type wind turbine.Two improved schemes for Savonius wind turbine are proposed in which adding the rectifier outside the wind turbine rotor and using airfoil blades instead of the Savonius wind turbine curved blades. The influence of rectifier structural parameters and curved baldes structural parameters on the wind turbine flow field have been studied. Through the simulating calculation, structural parameters of rectifier such as the rectifier diameter ratio and the inclination angle of the rectifier board have been obtained. And the structural parameters of curved blade such as the number of blades, the length of the blade chord and inclination angle of the blade which has great impact on the wind energy utilization coefficiency of the wind turbine have been obtained.Geometrical model of airfoil blade instead of curved blade of wind turbine and its rotating scheme in the flow are established in which the symmetric airfoil NACA0012 was chosen. The stress analysis of airfoil blades in the flow field are calculated. And the wind speed factor of the model is calculated by application of stream tube method. Parameters such as airfoil blades unilateral open angle, revolution angle of the rotor while blades are opening or closing which have effects on the coefficiency of wind energy utilization are calculated. Finally various parameters of airfoil blades influence on the coefficiency of wind energy utilization are calculated by software. The calculation results are used to analyze the feasibility of the geometrical model calculations.One test system for measuring the aerodynamic performance of improved Savonius wind turbine is designed. The aerodynamic performance of the Savonius wind turbine with new airfoil blades is tested by this system. The influence of different structural parameters on the performance of the wind turbine is analyzed. The results of the experiment are compared with the calculation results. Reasons of the error are analyzed the and suggestions are put forward for improvement.In summary, this dissertation presents two improved Savonius wind turbine with rectifier and airfoil blades. The coefficiency of wind energy utilization of these two kinds of wind turbine is improved compared with the Savonius wind turbine. The improved wind turbine with the rectifier and airfoil blades still have great performance on the self starting up compared with other wind turbines. At the same time, the wind turbine blades have the same cross section in the height direction. The blades can be produced by the form of straight blades which can reduce the cost of manufacturing of the blades. The improved wind turbines are not only suitable for medium and large wind farms, but also suitable for relatively poor wind energy areas.