Study On The Influence Of Blade Tip Structure Change On The Aerodynamic Noise In The Near Wake Region Of A Wind Turbine Under Yaw

At present,the dual carbon strategy has become the theme of global development,and wind power generation has received extensive attention,among which improving the efficiency of wind energy utilization and reducing aerodynamic noise are the current research focuses of wind turbines.In this paper,the double fork blade wind turbine with tip structure is designed by using Wilson design method.The blade fork angles designed are 0°,30° and 60° respectively.Under the rated working condition of 5m/s incoming wind speed and 600r/min rotating speed,numerical calculations are carried out for wind turbines with different tip structures at 0°,10°,20° and 30° yaw angles to analyze their flow field and sound field characteristics,and wind tunnel tests are used to verify the reliability of numerical calculations.The main research contents and conclusions are as follows:(1)By using S825 airfoil and Wilson method,unmodified blade and blade with double fork tip structure are designed.The designed blade wind turbine is divided into watersheds,and a certain included angle is set between the outer watersheds and the inner watersheds to simulate the yaw angle.After that,unstructured grid is divided for the constructed watershed,and wind turbine is numerically calculated in the simulation software based on the incompressible N-S equation and the large eddy simulation turbulence model to obtain the aerodynamic performance of the wind turbine under yaw and the aerodynamic noise of the wind turbine under yaw.(2)The numerical results are used to analyze the aerodynamic performance of the wind turbine under yaw.It is found that in the range of0～30°yaw,the blade pressure difference,output power and wind energy utilization coefficient of the double fork tip structure wind turbine decrease with the increase of yaw angle.When the yaw Angle is constant,for the above parameters,the double fork tip structureθ=60°is better than the double fork tip structureθ=30°is better than the double fork tip structureθ=0°.The blade with double fork tip structure disperses the incoming flow into two vortices.Its principle is similar to that of a diffuser,which has the effect of wind gathering,making it easier for incoming flow to pass through the wind turbine,thus improving the efficiency of wind energy utilization.To sum up,under the yaw angle of 0～30°,the double fork tip structureθ=60°wind turbine has the best aerodynamic performance.(3)The numerical calculation results are used to analyze the aerodynamic noise of the wind turbine under yaw.It is found that the blade is the sound source.The mean distribution of its sound pressure fluctuation and the sound pressure levels at different radial distances determine that the position with the largest contribution to the aerodynamic noise sound source is between 0.75 R and R at the blade radial distance.The fundamental frequency calculated theoretically is basically consistent with that shown in the spectrum diagram.Taking the maximum sound pressure level corresponding to the fundamental frequency as the noise value,the variation law of the radial noise and the axial noise in the wake region is analyzed.It is found that the aerodynamic noise of each wind turbine increases first and then decreases along the blade span direction.The larger the yaw angle is,the closer the maximum sound pressure level in the wake area is to the rotation axis.At the position close to the wind turbine,the aerodynamic noise value of each wind turbine reaches the maximum,and then decreases gradually along the direction of the rotation axis.At any yaw Angle,the maximum noise value of the double fork tip structure θ=0°wind turbine is larger than that of the double fork tip structure θ=30° wind turbine is larger than that of the double fork tip structure θ=60° wind turbine.Therefore,under the yaw Angle in this range,the double fork tip structure blade can effectively reduce the aerodynamic noise in the wake area,and the larger the fork angle,the better the noise reduction effect.(4)The wind tunnel test obtained the three-dimensional velocity distribution of the wind turbine wake area flow field.It was found that within the range of 0～30° yaw,along the blade span direction,the radial velocity of each blade wind turbine showed a fluctuation trend of first increasing,then decreasing,and then increasing.The tangential velocity showed a fluctuation trend of first decreasing,then increasing.And the axial velocity showed a trend of increasing.Wind tunnel test results show that at any yaw angle,the maximum noise value of the double fork tip structure θ=0° wind turbine is larger than that of the double fork tip structure θ=30° wind turbine is larger than that of the double fork tip structure θ=60° wind turbine,and the larger the yaw angle is,the closer the position of the loudest pressure level is to the rotation axis.There are some errors between the experimental results and the numerical simulation results,but the development trend is consistent,which verifies the reliability of the numerical calculation.In this paper,the aerodynamic performance and aerodynamic noise of wind turbines with different blade tip structures under yaw are analyzed and compared to study the impact of blade tip structure changes under yaw on the aerodynamic noise near the wake area of wind turbines,and the reliability of numerical calculation is verified by experimental tests,providing data support and experimental verification for the low-noise design of small wind turbine blades.