Studies On The Characteristics Of Aerodynamic Noise And The Noise Reduction Mothods For Wind Turbine Blades

With the large-scale of wind turbine generators and large-scale construction of wind farms,the influence of wind turbine on the environment become the issue that people pays close attention to generally.Aerodynamic noise of wind turbine generators blade is one of the more prominent issues.Research of wind turbine blade aerodynamic noise generation mechanism and denoise method becomes a hotspot in the reserch of wind turbine blades.Aiming at the two problems to carry out research work,using computation fluid dynamics(CFD)method,combine with the acoustic analogy method,aerodynamic noise characteristics of typical wind turbine airfoil is studied and corresponding denoise method is proposed.Then the aerodynamic noise characteristics and denoise method of wind turbine blade is studied.Firstly,with a blunt trailing edge airfoil as the research object,respectively,BPM and CFD/FW-H method were used on the airfoil aerodynamic noise characteristics,and the calculated values were compared with the experimental values,to verify the credibility of CFD/FW-H and BPM model.Simulation results of CFD/FW-H and BPM in high frequency region are very close,and both with experimental values are in good agreement,but CFD/FW-H calculation results is better than that of the BPM calculation results in the low frequency region.Three turbulence computation method(URANS,DES,LES)are selected for airfoil calculations.found that three kinds of turbulence computation method for airfoil sound pressure level basic frequency consistent,and the sound pressure level basic frequency is almost the same.The calculated frequency is lower than the experimental frequency,but the peak of sound pressure level is not much different.Among three kinds of calculation methods,DES calculation results are more close to the experimental value,while LES calculation results in high frequency region is larger than experimental value.In the flow field the changing of sound pressure with pressure is related,the basic frequency of sound pressure pulsation and that of pressure pulsation is basically the same,and the high order harmonic frequency is basically the same.At the downstream of the airfoil,the basic frequency of the sound pressure spectrum was basically the same at different space points.On the basis of verification and validation,the method of CFD/FW-H was used to research of airfoil aerodynamic noise characteristics on airfoil attack angle and airfoil trailing edge thickness,reveals the relationship between airfoil blunt trailing edge aerodynamic noise and trailing edge shedding vortex.Study found that airfoil dynamic noise sound pressure level does not vary monotonically with attack angle,but was first decreased and then increased.Airfoils sound pressure level decreases with the increase of the radius distance,at different distance of radius,the airfoil noise directivity distribution shows dipole shape.At the small attack angle,airfoil noise directivity on the top and bottom surface shows the symmetrical distribution along the chord line.And at the large attack angle,noise basically shows symmetric distribution along incoming flow.The noise at airfoil trailing edge is significantly greater than leading edge noise,but the leading edge noise and trailing edge noise are less than the top and bottom surface noise.Aerodynamic noise sound pressure level does not change monotonically with the attack angle,the sound pressure level vary with the attack angle is firstly reduced then increased.The conventional airfoil at small attack angle,sound pressure level distribution shows low frequency characteristic,and at large attack angle,shows broadband characteristics.While the blunt trailing edge airfoil sound pressure distribution shows low frequency characteristic.Blunt trailing edge airfoil at small attack angle,the sound pressure level is greater than the conventional airfoil,while at large attack angle,acoustic pressure level is almost the same.Secondly,according to the airfoil aerodynamic noise characteristics,two typical wind turbine airfoil as the object,the method of CFD/FW-H was used,reveal the denoise mechanism of vortex generators,got the Interference flow field of concentrated vortex and separation vortex,and effect law of concentrated vortex noise and separation vortex noise on aerodynamic noise of balde and airfoio.Found that the vortex generators on airfoil noise are slightly different laws at different attack angles.At small attack angle the vortex generators can reduce the airfoil aerodynamic noise,at large attack angle,the vortex generators also can reduce the airfoil aerodynamic noise,but in some other attack angles,vortex generators will increase the airfoil aerodynamic noise.For clean airfoil,at small attack angle,airfoil noise distribution shows low frequency characteristics,at large attack angle shows broadband characteristics.For the airfoil with vortex generators,at all attack angles,the noise distribution shows low frequency characteristics.Finally,a wind turbine blade as the research object,using the CFD/FW-H method to study aerodynamic noise characteristics of different position of blade airfoil,and three-dimensional aerodynamic noise characteristics of wind rotor.The study found that the minimum sound pressure level and relative thickness of airfoil is an inverse correlation,but after airfoil stall,sound pressure level and airfoil thickness is little relevant,But on the whole,large thickness of airfoil sound pressure level is slightly larger.For a typical airfoil,the noise intensity does not change linearly with the attack angle.The sound pressure level vary with the lift drag ratio is similar,and the attack angle of the minimal sound pressure level and attack angle of maximum lift drag ratio is closely related,but not completely corresponding.In three dimensional blade noise directivity distribution,at blade inner spanwise,the sound pressure level at blade leading edge and trailing edge is greater than that at top and bottom surfaces.While at blade outer spanwise,noise directional distribution is similar to airfoil,and the sound pressure level at blade leading edge and trailing edge is less than that at top and bottom surfaces.At the leading edge and trailing edge of blade,the noise shows broadband characteristics,while at upper and lower surfaces,the noise shows low frequency characteristic.At blade inner spanwise,the noise shows low frequency characteristic,and at blade outer spanwise,the noise showes broadband characteristics.On this basis,research on aerodynamic noise influence laws on three kinds of vortex generator structure(triangle,trapezoid,rectangular)is performed.The results show that three kinds of vortex generators structure can delay flow separation,improve the aerodynamic performance of blade.Butrectangular vortex generators increases the sound pressure level of blade,while trapezoid and triangle vortex generators can reduce the sound pressure level,and the triangle vortex generators decrease the aerodynamic noise to the greatest extend.So the best optimal denoise effect is triangle vortex generators.