Noise Reduction Of Horizontal Axis Wind Turbine Blade Based On Owl’s Wing

With the rapid development of wind power industry,wind turbine is developing in the direction of increasing rated power,increasing blade length and wind farm location close to the city.Since,the aerodynamic noise of wind turbine blades has been widely concerned.With the development of bionics,scientists began to imitate the characteristics of biology to solve engineering problems.Owl birds have the ability of "silent flight",which provides a way of thinking for the design of wind turbine blades.In this paper,the characteristics of the sawtooth at the end of the wings of owl are extracted to construct the bionic leaves with low noise.At the same time,the method of combining numerical simulation with experimental measurement is often used to study the aerodynamic problems of horizontal axis wind turbine blades.Therefore,the paper mainly uses the method of combining large eddy simulation and BEM acoustic model to study the noise reduction mechanism of horizontal axis wind turbine blades and blades with tail edge serrations,The model experiment shows that the blade has remarkable noise reduction effect.Firstly,the blade of NACA4412 airfoil is used as the standard blade.The sawtooth structure of the tail feathers at the end of the owl wing is extracted,and the parameters of the sawtooth structure are determined according to the geometric similarity principle,among which,the sawtooth width λ is 5～10mm,and the height of 2h is 12.5～20mm.Based on the standard blades,9 groups of bionic blades with serrated tail edge structure were designed.The influence of saw tooth parameters on the aerodynamic noise of horizontal axis wind turbine blades was analyzed by orthogonal experiment.The results show that the tail edge serration structure can effectively reduce the noise of horizontal axis wind turbine blades,with noise reduction of 2.52-9.75 db,the height of serration16 mm,the width of the serration of 6mm and 70% of the layout,and the influence of sawtooth width on the aerodynamic noise is great,The noise reduction decreases with the increase of the width of the saw tooth.Secondly,the blade of horizontal axis wind turbine bears a certain aerodynamic load.When the wind speed is 8m / s,the strength of standard blade and bionic blade is analyzed based on the finite element method.The results show that the stress distribution at the root and leading edge of the blade is large.Under the same wind load,on the basis of ensuring the strength of the blade,the position and magnitude of the maximum equivalent stress of the bionic blade are basically consistent with that of the standard blade.At the same time,using commercial software ANSYS fluent 19.2 and virtual.Lab to analyze the velocity,pressure and vortex structure distribution of standard blade and bionic blade by using large eddy simulation model under rated power.The simulation results show that the aerodynamic performance of bionic blade is better than that of standard blade,and the serrated structure affects the pressure distribution on the blade surface and the shedding frequency of vortex structure,and then affects the noise.The boundary element method(BEM)is used to calculate the aerodynamic noise of the standard blade and bionic blade of horizontal axis wind turbine.The sound directivity,sound pressure level distribution and sound pressure nephogram of the standard blade and bionic blade of horizontal axis wind turbine are analyzed.The results show that: at the same distance,the sound pressure at different monitoring points is different,which indicates that the noise source has obvious dipole characteristics,and the sound pressure level distribution of sound directivity conforms to this characteristic;The sound pressure level at the center of the horizontal axis wind turbine decreases with the increase of the distance,and the maximum sound pressure of the bionic blade is about 8.3db lower than that of the standard blade;In the X0 Z plane sound pressure nephogram,the sound pressure radiation is spherical,and the radial sound pressure level is greater than the axial sound pressure level.The sound pressure along the blade source is proportional to the radial distance,and the sound pressure at the blade tip is the largest.The reason of sawtooth structure noise reduction is that the frequency of trailing edge vortex shedding and the dissipation speed of vortex cluster in the wake are accelerated,which makes the aerodynamic noise of bionic blade lower than that of standard blade.Finally,the noise test of S6 wind turbine blade and bionic wind turbine blade is carried out.The experimental results show that the edge serrated structure can change the size and movement of vortex around the blade,and can effectively reduce the noise of S6 wind turbine blade,the noise reduction rate is 8.83%,and the power loss is 1.15%.In this paper,the low-noise serrated trailing edge blade constructed by bionic idea is used to reduce the aerodynamic noise of wind turbine,which can provide the basis for the subsequent methods to suppress the aerodynamic noise.