Aerodynamic Analysis And Optimization Of Airfoil Of Low Wind Velocity And Long Blade Wind Turbine

In recent years,as China’s three northern regions(Northeast,Northwest,North China)and other high wind speed areas have become more and more serious problems of abandon wind,the development and utilization of wind energy gradually turned to low wind speed areas with large power demand.The area of low wind speed resources that can be used in China accounts for about68% of the total area of wind energy resources that can be developed in the country.The development and utilization of low wind speed wind energy resources has become one of the key directions for the development of wind power generation in China.Compared with foreign countries,there is still a certain gap in the core technology of wind turbines.The development of the airfoil blade airfoil and the aerodynamic shape design of the blade are mostly dependent on foreign countries,and the introduction of the airfoil and lack of key technologies,which seriously restrict the independent research and development level of China’s wind turbine equipment.In particular,there is a lack of independent intellectual property rights in the design and research of airfoil-specific airfoil families.Therefore,it is of great significance to carry out the theoretical research on the aerodynamic shape design of the special airfoils and blades for wind turbines to improve the independent R&D level of wind power equipment in China and actively develop wind energy resources.This paper focuses on the conditions of low wind speed,and studies the flow and optimization of the airfoil surface of a wind turbine as follows:(1)Analyze the flow characteristics of the airfoil surface and investigate the boundary layer transition and fluid separation phenomena.According to the Prandtl separation criterion,the necessary and sufficient conditions for the separation of the airfoil surface of the wind turbine are proposed.For the actual viscous flow described by the N-S equation,the behavior of the actual viscous flow around the separation point of the airfoil surface is analyzed to obtain the relative positions of the separation flow line,the zero u line,and the zero vortex line,that is,the zero u line of the over-separation point.The slope is 2/3of the slope of the separation streamline.The slope of the zero vortex at the separation point is 1/3 of the slope of the separation streamline.(2)Based on the Reynolds-averaged Navier-Stokes equations,the blade airfoil is numerically simulated and the aerodynamic performance of the airfoil is calculated.The aerodynamic performance of the airfoil under low wind speed was calculated by FLUENT software.The pressure distribution,velocity distribution and fluid separation of the airfoil surface were calculated.As the Reynolds number decreases,the viscosity effect of the boundary layer increases,which increases the frictional resistance of the airfoil surface,thereby increasing the airfoil drag coefficient and decreasing the lift-to-drag ratio.At large angles of attack,the airfoil stalls and the trailing edge forms a separate stream.The pressure after separation is basically equal to the pressure at the separation point.After the separation,the differential pressure resistance increases,resulting in a sharp increase in the airfoil drag coefficient.(3)A positive design method is used to combine the numerical optimization method with the aerodynamic performance of the airfoil.The optimization method uses the optimization function in the MATLAB optimization tool and uses XFOIL software to calculate the aerodynamic performance of the airfoil.Through the establishment of MATLAB/XFOIL interface,using MATLAB automatically call XFOIL program,and the results of the calculation into MATLAB.For the optimization of the airfoil with low wind speed,the airfoil profile is parameterized by the modified Hicks-Henne function method with the airfoil lift-drag ratio as the optimization goal.The basis function coefficient of the Hicks-Henne type function is design variable.The optimized airfoil application XFOIL software calculates its aerodynamic performance and verifies the correctness of the optimization results.