Study On The Correlation Mechanism Between Vibration And Noise Coupling Characteristics Of Wind Turbine Caused By Blade Tip Structure Change

In order to reduce the vibration and noise of wind turbines,a double-fork blade tip structure modification design scheme for horizontal-axis wind turbines is proposed,and the wind turbine modal test,vibration characteristics test,aerodynamic noise test,and vibration and noise coupling characteristics test were carried out.It is used to explore the influence of the change of blade tip structure on the coupling characteristics of vibration and noise of wind turbines.(1)Use Wilson design method and select S825 airfoil to design the unmodified blades and doublefork blade tip structure blades with different blade angles,and use 3D printing technology to manufacture the blades,and test the external characteristics of the blades in the wind tunnel laboratory.The test results shown that the double-fork blade tip structure can improve the output power and wind energy utilization coefficient of the wind turbine in the low wind speed section and the middle wind speed section of 3～9 m/s,and the double-fork blade tip structure can make the wind turbine output power is 4.59%to 8.91%higher than the unmodified wind turbine,and the wind energy utilization coefficient is 4.58%to 9.17%higher than the unmodified wind turbine.Among them,the double-fork blade tip structure-3 wind turbine has the best output power and wind energy utilization coefficient.(2)The modal test and vibration characteristics test of wind turbine were carried out.The modal test results shown that the double-fork blade tip structure can increase the second-to-fourth order natural frequency and damping ratio of the wind turbine,and has a small effect on the natural frequency and damping ratio of the tower.The vibration characteristics test results show that double-fork blade tip structure can reduce wind wheel disc effect,first and second order vibration acceleration amplitude and tower first and second order axial and radial vibration acceleration amplitude,and adjust the trend of the vibration frequency curve of the wind wheel and the tower,make the wind wheel leave the resonance zone faster,and the speed corresponding to the resonance point of the wind wheel can be adjusted,increase the wind wheel resonance margin.Among them,the effect of reducing the amplitude of vibration acceleration and improving the resonance characteristic is the best with double-blade blade tip structure-3 blades.(3)The wind turbine aerodynamic noise test was carried out.The test results shown that under different working conditions,the double-fork blade tip structure can reduce the maximum sound pressure level corresponding to the rotating fundamental frequency and the sound pressure level corresponding to the blade tip vortex shedding frequency.Under rated operating conditions,the double-fork blade tip structure can reduce the maximum sound pressure level corresponding to the rotating fundamental frequency by 4.06%to 8.41%,and can reduce the sound pressure level corresponding to the blade tip vortex shedding frequency by 5.67%to 9.94%.Among them,the double-fork blade tip structure-3 blade has the best noise reduction effect.(4)A coupling characteristic test of wind turbine vibration and aerodynamic noise was carried out.The test results shown that under the condition that the centrifugal force load of the wind turbine is unchanged and the aerodynamic load law is increased,the disc effect,the first and second-order vibration frequencies,the maximum sound pressure level corresponding to the rotating fundamental frequency,and the sound pressure level corresponding to the blade tip vortex shedding frequency of wind wheel remain basically unchanged.Under the condition that the aerodynamic load of the wind turbine is unchanged and the law of centrifugal load is increased,the disc effect,the first and second-order vibration frequencies,the maximum sound pressure level corresponding to the rotating fundamental frequency,and the sound pressure level corresponding to the blade tip vortex shedding frequency of wind wheel also increase regularly,indicating that wind turbine vibration is directly proportional to aerodynamic noise.According to the above analysis,it can be concluded that the change in the structure of the blade tip affects the coupling characteristics of wind turbine vibration and noise:the double-fork blade tip structure can reduce the vibration of the wind turbine and the aerodynamic noise of the wind turbine.Among them,the double-fork blade tip structure-3 blades have the best vibration and noise reduction effects.It is found that the angle of the blade tip of the double-fork blade tip structure is the main factor affecting the vibration and noise reduction effect.The angle of the blade tip is in the range of 0～90°,and the larger the angle,the greater the vibration and noise reduction effects of the wind turbine.The research results provide a new idea for the optimization design of aerodynamic structure of wind turbine blades.