A Study Of Stall Characteristic Of Wind Turbines

The aerodynamic characteristic of the wind turbine is the core content of the wind turbine engineering. Good aerodynamic performance of wind turbine can not only obtain high power factor, and achieved good economic benefits, but also in security and reliability and reducing environmental noise pollution, etc. With the popularity of megawatt wind turbine, it need to study more reliable aerodynamic loads prediction method and calculation model of wind turbine impeller design and accurate performance calculations because the rotor diameter increases. The accuracy of these estimates methods and calculation model depend on the study of the wind turbine stall characteristics.This thesis concentrated studying the common wind turbine airfois and wind turbine units of National 973 Project and its field testing. And refer the foreign disclosed airfoil experimental data and research material, it would respectively study on the static stall, dynamic stall and 3D rotation effect based on the combination of theoretical analysis, numerical calculation and field experiment. The research results helped to establish a load forecast model for wind turbine, and provided some technical reference to the structure design and theoretical research for large wind turbine.The main contents and achievements of the research are as follows:1)Compared with the 2D wind tunnel test datum,it verified with the turbulence model SST k-ω for transition could research the airfoil aerodynamic performance accurately.And numerical calculation was carried out on the NACA44 XX series airfoils by using the calculation model. Research was mainly focused on the influence of the stall characteristics on the Reynolds number, the thickness and the surface roughness of the airfoils. The size and position of the relative thickness of airfoils had great influence on the stall characteristics of the airfoils. And the height of 0.5mm was the key to influence the flow separation on the airfoil surface. Using the numerical cacalation studied the NACA4412 airfoil and its trailing edge modification of the blunt trailing edge and Gurney,it concluded that the airfoils of blunt trailing modified by 2% chord had superior stall characteristics and low noise, but had unstable torque characteristic.2) Using the unstructured dynamic grid technology and its deformation, the the-sis researched the stalling characteristics of S809 airfoil with the pitch motion around the aerodynamic center, and analyzed the average angle of attack, oscillation amplitude and frequency conversion effects on airfoil stall characteristics. By contrasting the lift and resistance coefficient hysteresis curve for pitching motion state and static of airfoils, it found that there was small difference between static and dynamic state at mall angle range.But at stall zone, there was significant difference between the two states. In the process of dynamic rose, the maximum lift coefficient of airfoil is higher than the static value. However, with the decrease of angle of attack, the lift coefficient is close to the static values in the process of leaning. Through the analysis of airfoil flow field and changing process of the trailing vortex,it would be found that there was a close relationship between the development of dynamic stall and the unsteady separation and interference of eddy current.3) Numerical studies was used to study the aerodynamic characteristics of vertical axis wind turbines by sliding mesh method. It determined the vertical axis wind turbines impeller in the azimuth range of dynamic stall condition and interior fluid field through analysis of the different airfoil types, thicknesses and compaction degrees, and got some important conclusions for the tip speed ratio to the performance impact of vertical axis wind turbine.4) A lot of wind turbine aerodynamic performance experiment was carried out with the aid of the field experiment platform of the National 973 Project. By comparing the wind turbine blade surface pressure distribution characteristics of parking and rotating conditions, it found that there was obvious difference in different working conditions, and there was large fluctuation of the rotate blade surface pressure distribution. Especially in the blade root, pressure distribution was disorder. It explained that there was strong airflow separation on the surface of the wind turbine blades.5) 3D numerical simulation was carried out for the experimental units based on the LES algorithm. And the calculated results were compared with the field experiments and 2D numerical. After analysised the results, it considered that the stall delay model considered the effect of rotation and c/r and other factors on the stall characteristics of wind turbine, so the stall characteristics of wind turbine blade rotating process could be simulated well. The calculation results was more closed to the experimental data. But the calculated results were still quite different from the experimental results at turbines root.It need correct the calculation model in the aerodynamic performance prediction for the 2D calculation ignoring the factors of flow around the hub.This thesis studied of the stall characteristics of wind turbines combined the the-oretical analysis, numerical calculation and field experiment,and optimized the calculation models. It provided some technical references to promote the development of aerodynamics wind turbine and research and development level of wind turbine blades.