Aerodynamic Performance Analysis For Variable Pitch Vertical Axis Wind Turbine

Vertical axis wind turbine does not need to yaw into flow direction and provides some distinct advantages over horizontal axis wind turbine, including simple structure and low noise. Therefore, it has been regarded as an attractive solution for many domestic and aboard scholars, and thus investigations have been carried out and more concern have been paid on the core issue of maximizing performance coefficient, starting performance of wind turbine and transient loads etc.With faultiness of theory and research methods for the vertical axis wind turbine, it is therefore especially insignificant to study computational fluid dynamics, which is an effective research method. In addition, not only can it indicate some analysis from the macro, but also allows us to acquire micro characteristics including transient flow field distribution and instantaneous forces and torques etc, which are important practical values for wind turbine research.Numerical simulation methods are used to develop wind turbine performance of wind turbine in this paper. It is gradual process from part to whole, from static to dynamic and from fixed pitch to variable pitch wind turbine.Firstly, principles of variable pitch vertical axis wind turbine are introduced, then performance of lift and drag of airfoil under static conditions are presented with various Reynolds number, and equal airfoil is selected at the same time. Based on mathematical model derived from VAWT, dynamic analysis has been carried out to get knowledge of the general relationship between performance of airfoil and wind turbine blades at different quadrants. According to the aerodynamic airfoil dates, variable pitch law has been obtained by the methods of multiple stream tube models.Secondly, basic ideas of numerical simulation have been introduced, with the help of basic principles of fluid to solve the numerical simulation problems of vertical axis wind turbine appeared in the calculation. From the comparative analysis of two-dimensional and three-dimensional of fixed pitch wind turbine and variable pitch wind turbine, it shows that simulation results are very sensitive to Y+parameter. Then it is crucial to find out the sensitivity of the results affected by other numerical factors, as well as solving the accuracy problem of the calculation. At last, we provide power performance, tangential force and axis force as well as lift-drag characteristics from experiments to verify the reliability of calculation.Thirdly, mechanical analysis and aerodynamic model of fixed pitch wind turbine have been conducted, and then a number of conditions are calculated by sliding meshes to focus on how the layouts of wind turbine affect its performance. From a macro point of view, analysis of geometric parameters have been carried out, including numbers of blade, chord length, wind speed and radius. Especially, more efforts have been devoted to the influences of torque and power caused by pitch angle of wind turbine. While the relationship, at different pitch angle and tip speed ratio, among instantaneous efficiency, instantaneous overall efficiency, stall angle, beta limit, effective angle of attack and the azimuth etc, have been determined by microanalysis. In addition, we indentify causal association between votex and power performance of wind turbine.Finally, mechanical analysis and aerodynamic model of variable pitch wind turbine have been built, and dynamic grid programs have been debugged. UDF methods about variable pitch laws of wind turbine have been proposed by the methods of a variety of dynamic region with unchanged topology of grids. Besides, comparison of advantages and disadvantages of different methods has been implemented to provide convenience for variable pitch wind turbine research. Meanwhile, investigations of three cases concerning a certain wind speed and rotational speeds are carried out, such as a certain wind and changed tip speed ratio, a certain tip speed ratio and synchronous changed wind speed and rotational speed. Macro analysis of power performance and power output for variable pitch wind turbine have been carried out, as well as the tangent force and axis force and torque around rotation shaft at different azimuth angle in the view of microscopic. A comparison between them shows that variable pitch wind turbine not only can enhance power performance but also improve the starting performance and reduce the pulse frequecy of the blade. Therefore, investigations of aerodynamic performance have been conducted by coupling lift-drag characteristics and the flow field aroud the variable-pitch wind turbines.