The Investigation On Aerodynamic Characteristics Of Thick Airfoil And The Exploration Of The Airfoil Stall Mechanism For Wind Turbines

Wind energy has developed rapidly in the last10years all over the world. To satisfy the particular developing requirement of wind energy and alleviate the contradiction, coming with large wind turbines, between aerodynamics characteristics and structural characteristics, a lot of series of airfoils for wind turbine have been designed. Although a mountain of work on aerodynamics study has been done, considering the unique wind energy environment, it is important to design airfoils to satisfy the development of large wind turbines in China. Before the design effort, there are three problems which should be considered:(1) the effect of thickness and Reynolds number on aerodynamics characteristics of wind turbine airfoils;(2) the accuracy and error of the common numerical simulation methods, which used in thick blunt airfoils for wind turbines;(3) the exploration of the airfoil stall mechanism for wind turbines.To figure out the effect of thickness and Reynolds number on aerodynamics characteristics, this article uses the Transition SST k-ω turbulent model to simulation flow around the DU airfoils and analysis the changing trend on aerodynamics characteristics. The thickness of chose airfoils is from21%to40%. Considering the engineering application, the range of Reynolds number is1×106～6×106. To learn the high Reynolds number effect, in the case for21%thickness airfoil, the rang of Reynolds number extends to1×106～10×106. The results show that thickness and Reynold number have a complicated impact on aerodynamics characteristics.(1) In high Reynolds number, maxium C1/Cd decrease with the increase of Reynolds number.(2) With the increasing of thickness and Reynolds number, the slopes of lift coefficients increase before stall and the aerodynamics characteristics change gently near stall.(3) The effect of thickness on aerodynamics characteristics decreases with the Reynolds number increasing, while the effect of Reynolds number increases with the thickness increasing.To investigate the accuracy and error of common numerical simulation methods for wind turbine, when applied to thick blunt airfoils, we focus on CAS-W1-450and analysis the result of CFD、Xfoil and Rfoil with the experiment data. Comparing the computation of Xfoil and Rfoil with different N, which helps modeling transition of the boundary, we find that setting N around5is much suitable considering the fact and error of the results. In this part, it has been worked out that the result of all these three methods matches the experiment data well. But from the point of computational stability and accuracy, the CFD matches best, Rfoil next, Xfoil last.Finally, for the exploration of the airfoil stall mechanism for wind turbine, we use large eddy simulation to simulate the flow around the DU93-W-210airfoil and try to learn how the laminar bubbles affect the flow. The result shows that:there are some laminar bubbles attached on both sides of the airfoil. These bubbles, where the vortex structure grows and turbulent fluctuation increases, enhance the flow instability. The appearance of the laminar bubbles on leading edge makes the flow field unstable, accelerates the flow separation progress and contributes to the generation of airfoil stall. The impact of the bubbles is quite small with small angle of attack. When the angle of attack increases, the size and location of the bubbles play a great role on the flow field, especially the bubbles on the suction side.