Research On The Influence Of Pitch Angle On The Aerodynamic Noise Of Wind Turbines

Wind energy,as a new type of green energy,has gradually occupied an important position in the global energy structure,and wind power generation has become the main form.In order to prevent the blade from colliding with the tower in the actual operation of horizontal axis wind turbine,there is usually a pitch Angle.The pitch Angle has a complex effect on wind turbine performance and noise due to its influence on wind inflow Angle and blade stress.Too small or too large pitch Angle will lead to the increase of wind shear and aerodynamic load,thus causing noise problems.The influence of stage pitch Angle on aerodynamic noise of wind turbines has not been thoroughly studied.Therefore,it is very important to study the influence of pitch Angle on aerodynamic noise of wind turbine.The large eddy simulation turbulence model combined with the acoustic equation was used to numerically simulate the flow field and sound field of horizontal axis wind turbine under different pitch angles,analyze the pressure changes,velocity characteristics and vorticity distribution of blade surface of wind turbine under different pitch angles,and explore the influence law of pitch Angle on wind turbine flow field.On the basis of the flow field,monitoring points were arranged and acoustic equations were used to study the mean change of sound pressure pulsation,spectrum characteristics of radiated sound and propagation law of radiated sound under different pitch angles.The comparison of the concurrent flow curves and the sound effects come from conclusions on the fluid dynamics of fluid dynamics,we can gain a better understanding of the overall system dynamics.The significance of various factors affecting the aerodynamic noise of wind turbines was analyzed,and a better operating condition was determined to provide reference for the operation of wind turbines under pitch state.The main research contents and conclusions are as follows:(1)Large eddy turbulence model was used to simulate the wind turbine flow field,and the influence law of different pitch angles on the wind turbine flow field was explored.The output power fluctuates periodically at different pitch angles.With the increase of pitch Angle,the sweep area of the wind wheel decreases,and the energy absorbed by the wind wheel becomes less.The output power of the wind wheel first increases and then decreases.With the increase of pitch Angle,the axial velocity loss decreases,the diffusion area of the central vortex increases,and the vorticity intensity increases.Therefore,the aerodynamic performance of the blade surface is the best when the pitch Angle is 3°.(2)The acoustic field of wind turbine is calculated based on acoustic equation,and the influence law of different pitch angles on aerodynamic noise of wind turbine is studied.The mean value of sound pressure pulsation at different pitch angles is distributed along the radial direction of the blade,and the peak value is mainly concentrated around 0.57R-0.86 R.With the increase of pitch Angle,the sound pressure level and sound power spectrum density reach the highest value at the fundamental frequency,and there is an obvious diffusion of energy.The sound pressure level increases as a whole,and the rise amplitude of aerodynamic noise becomes larger.With the increase of frequency,the sound power spectrum density shows a trend of decreasing gradually,which is the attenuation of acoustic signal in the linear propagation process.The aerodynamic noise propagates axially and spanwise in the presence of pitch Angle,which is similar to that in the absence of pitch Angle.The position of the maximum sound source moves from the middle of the blade to the tip with the increase of pitch Angle.A The amplitude increase of sound pressure level is the smallest when the wind turbine under the weight is at 3° pitch Angle,so it is concluded that3° pitch Angle is the best pitch Angle.(3)Using orthogonal test method to analyze the significance of aerodynamic noise factors and determine the better operating conditions.According to the range analysis method and variance analysis method,the significant order of aerodynamic noise of wind turbine is wind speed>pitch Angle>rotate speed,and the significant order of output power wind speed>rotate speed>pitch Angle.According to the principle of " take the best level for significant influencing factors and any level for insignificant factors",The optimal orthogonal combination can be obtained as 3° pitch Angle,10m/s wind speed and 887r/min.