Research On Aerodynamic Characteristics Of Wind Turbine Airfoil Based On Circulation Control

With the development of China’s economy and the improvement of industrialization technology,the demand for energy production is increasing.The ensuing environmental pollution problem is also imminent,and it is urgent to seek new energy to replace traditional energy and transform the energy structure.As a new small energy machine,vertical axis wind turbines have extremely broad application prospects.As the main components of energy conversion,blades determine the power generation efficiency and load characteristics.Due to the low efficiency of wind power generation,it is necessary to study the improvement of wind turbine blade airfoil.Circulation control technology is a very popular flow control technology,which is derived from the Coanda Effect.Its principle is to make use of the wall effect of the fluid on the curved surface,so as to effectively control the flow separation of the fluid,regulate the flow field and improve the aerodynamic characteristics.This paper proposes a method of using circulation control airfoil.Based on numerical simulation and experimental,it studies the aerodynamic characteristics and flow field structure visualization to investigate the application of circulation control airfoil.The main research contents and results are as follows:In the numerical simulation part,the two-dimensional k-ω SST turbulence model was used to preliminarily screen the jetting position,provides a theoretical basis for the next research.Furthermore,the large eddy simulation is used to calculate the circulation control airfoil of the optimal jetting position scheme.The calculation results are presented in more detail by using the vortex recognition method of swirling strength.In the test part,based on the wind tunnel platform of Xihua University,a physical model of the circulation control airfoil was made for the wind tunnel test.Six-component strain-gauge balance was used to measure the lift-drag coefficient of circulation control airfoil at different Reynolds Numbers,and the development law of lift-drag coefficient with the angle of attack was studied.The pressure data of airfoil are extracted by pressure scanning valve,which can directly reflect the pressure distribution at different positions.The jetting position of L=70%c performs well before and after the airfoil stall.In general,the closer jetting position to the separation point,the control effect better.Compared with the k-ω SST turbulence model,the large eddy simulation does not perform the averaging process on the airfoil near wall which can accurately capture the separation and reattachment of the airfoil suction surface flow,and the trailing edge vortex shedding,vortex band swing,dissipation and other flow patterns.The swirling strength identification method can effectively ignore the interference of the strong shear layer in the process of vortex identification and express the rotation characteristics of the vortex.The circulation control method has the remarkable effect of increasing lift and reducing drag,and has the obvious improvement to the airfoil flow field structure.The jetting flow breaks the back flow vortex at the trailing edge of the airfoil and forms a laminar flow attached to the airfoil wall,which effectively restrains the separation vortex in the nearby flow field and reduces the separation area.The local high-energy flow is disturbed by the viscous effect of the fluid,which is coupled with the main flow and affects the surrounding flow field,so that it has the same energy and gradually improves the global flow.Jetting causes the expansion of the negative pressure area,and then increases the pressure difference with the pressure surface,forming a greater lift.But the energy injected by jetting is not the higher the better.Generally speaking,the effect of circulation control is the best when the jetting speed is close to the incoming wind velocity.If the energy is too small,it will not work.If the energy is too large,it will overcorrect the flow field.