Experimental Study On Influence Of Airfoil Concavity On Aerodynamic Noise Of Wind Wheel

With the rapid development of distributed wind power industry,more and more wind turbines are installed in the area near the load center.However,the aerodynamic noise produced by wind turbine in operation has seriously affected the normal life of local residents,and has become an important factor hindering the development of decentralized wind power.Therefore,how to reduce the aerodynamic noise of wind turbine has become an urgent problem.Through the analysis of the generating mechanism of wind turbine aerodynamic noise,it is found that reducing the wind shear effect and the interaction between turbulence and blade can effectively reduce the aerodynamic noise of wind turbine.In the past research of the research group,it was found that the airfoil concave blade can improve the structural performance and aerodynamic performance of the blade.Therefore,based on the existing research,this paper explores the influence of airfoil concave on the low-frequency and high-frequency noise of wind turbine.In addition,the reasons for the influence of airfoil concave on the low-and high-frequency noise and the position of sound source are analyzed from the two directions of blade structure field and blade surface flow field respectively.In view of the impact of airfoil concave on the low-frequency and high-frequency noise of the wind wheel,this paper uses a 60-channel acoustic array system to collect noise from the original airfoil blade and airfoil concave blade,and uses the optimal acoustic holography and beamforming method.The processing and analysis of low-frequency and high-frequency noise found that under the same conditions,the airfoil concave change can significantly reduce the low-frequency noise of the wind wheel,and the noise reduction effect gradually increases with the increase of the number of times of the rotating fundamental frequency doubling.At the same time,the influence of the airfoil concave change on high-frequency noise is mainly concentrated in the 1000 ～ 1500 Hz frequency band.The influence of the airfoil concave change on the average sound pressure level of high-frequency noise gradually increases with the increase of wind speed,when the wind speed v = 9m / s,the average sound pressure level of the airfoil concave variable blade can be reduced by about 3.48%.In addition,it was found that the airfoil concave change can move the position of the high-frequency noise source to the tip of the blade,and the amount of movement can be up to 6.25%.In order to explore the cause of low-frequency noise of wind turbine caused by airfoil concave,based on the mechanism of low-frequency noise,this paper analyzes the static and dynamic natural frequencies of the original airfoil blade and airfoil concave blade,and found that after airfoil concave,the natural frequency and damping ratio of the blade can be increased,and then the stiffness of the blade can be improved,so that the vibration intensity of the blade can be reduced when the blade is subjected to the same aerodynamic load,resulting in the reduction of the compression and expansion of the blade to the surrounding fluid,thus reducing the low-frequency noise.In order to explore the reason of the influence of airfoil concave change on the high-frequency noise and the position of the sound source of the wind turbine,according to the mechanism of high-frequency noise,this paper starts from the flow field,through the high-frequency noise at the position of the maximum sound source of the blade,the flow field of the original airfoil blade and each section of the airfoil concave blade is photographed,and through the analysis of the influence of airfoil concave on the axial Reynolds stress and the axial pulsation speed,it is found that under the higher wind speed,the concave of airfoil can effectively delay the transition from laminar flow to turbulent flow,thus weakening the interaction between turbulent boundary layer and blade surface and trailing edge,and reducing the high-frequency noise.Through the analysis of the radial time average velocity of each chord section,it is found that after the airfoil concave changes,the fluid on the suction surface of the blade can converge in the groove,increase the radial time average velocity in the groove,and induce the fluid to move towards the blade tip,which results in the maximum sound source position of high-frequency noise moving towards the blade tip.