Investigation On Three-Dimensional Aerodynamic Characteristics Of Wind Turbine Airfoils With Blunt Trailing Edge

With the development of large-scale wind turbine, the contradiction between aerodynamic characteristics and structural properties of the blade has become increasingly prominent. The advantage of structure and aerodynamic performance of the wind turbine blade with blunt trailing edge provides an effective method to solve the problem that various domestic wind resource characteristics such as wind farms with low wind speed or in high altitude, or in typhoon areas are very common in China. Compared with the conventional airfoil, the three-dimensional aerodynamic characteristics of the blunt trailing edge airfoil will change greatly due to the changing of trailing edge shape, but there is a lack of research results currently. Based on this, the author took a blunt trailing edge blade of 100 kW designed by our research group as an object of study, investigated the aerodynamic characteristics of this blade by combining the computational and experimental methods, and studied the three-dimensional aerodynamic characteristics of the blunt trailing edge airfoils by inverse BEM method. The main works are as follows:Firstly, the reliability of the CFD method to simulate blunt trailing edge blade is validated by comparing CFD results with the wind farm experimental results and BEM results. Detail analysis on CFD results shows that there is an obvious span-wise flow in the root of the blunt trailing edge blade. When the pitch angle is 0° and the tip speed ratio is smaller, the three-dimensional effect is more obvious. Comparison between blunt and sharp trailing edge blade shows that the aerodynamic performance of blunt trailing edge airfoils is better than that of sharp trailing edge airfoils in the same span-wise location, which makes the aerodynamic characteristics of the blade of blunt trailing edge becoming better. The power coefficient of blunt trailing edge blade is about 6.64% higher than that of sharp trailing edge blade.Secondly, experimental investigation of blunt trailing edge airfoils was carried out to study the two-dimensional aerodynamic performance of blunt trailing edge airfoils, and to verify the numerical methods used in this paper. Measurements were conducted on airfoils DU91-W2-250, DU91-W2-250₆, and DU91-W2-25010 with the relative thickness of 25% but different trailing thickness. The aerodynamic characteristics data of these three airfoils are acquired, which shows that the life coefficient linearly increases with the angle of attack before stall. The stall occurs at high angle of attack, when the drag coefficient undergoes a rapid growth after the slow growth. With the increase of the Reynolds number, the angle of attack at stall for the airfoil decreases so that the stall speeds up.. With the increase of trailing edge thickness, the lift coefficient of airfoil, the maximum lift coefficient, and the drag coefficient increase. And stall also delays. After experiments, the aerodynamic performance of airfoils is calculated by CFD and Rfoil methods. The comparison with the experiment results indicates that the results calculated by CFD agree better with the experiments than the Rfoil results, and shows that the influence of trailing edge thickness on the aerodynamic performance is in coincidence with the experiment results. The two-dimensional CFD method for blunt airfoil simulation is considered as reliable.Finally, three dimensional flow field information of blunt airfoils was obtained from the CFD results of blunt trailing edge blade of 100 kW by inverse BEM, which was then compared to the aerodynamic characteristics from 2-D calculation of airfoils. In this paper, the difference between 3-D aerodynamic performances of airfoil and 2-D aerodynamic performances of airfoil and the reason for the difference were analyzed. Comparison of the aerodynamic parameters shows that the aerodynamic performance of airfoil in 3-D simulation is better than that in 2-D simulation.. The maximum lift coefficient of airfoil is increased, the drag coefficient is reduced, and the stall is delayed compared to 2-D aerodynamic parameters. By analyzing the low field of the airfoil the author found that the separation zone of airfoil in 3-D case was less than that in 2-D case when the angle of attack is the same, and so the separation was delayed by 3 dimensional effects. Through analyzing the order of the flow equation, the results show there is obvious the aerodynamic characteristics of blunt trailing edge airfoil are better, spanwise flow at the inboard section of blade, which has a direct relationship with the convection item, Coriolis force and centrifugal force. The increase of them accounts for the difference between three-dimensional aerodynamic characteristics and two-dimensional aerodynamic characteristics. The local radius and inflow angle of attack have an important influence on the difference.