Numerical Study On Near-Field Rotating Noise Of Wind Turbine

Aiming at the rapid development of decentralized wind power industry,the aerodynamic noise generated during the operation of wind turbine seriously affects the normal life of local residents.The rotating noise energy produced by the wind rotor is higher.At present,it is popular to find out the causes of aerodynamic noise in the operation of wind turbine and take corresponding measures to reduce the noise effectively.Rotating noise generated by wind turbine during operation is mainly divided into the following two categories: One is the noise generated when the observation point is disturbed by the rotating blade,which acts as the sound source to propagate in the medium;the other is the noise generated when the blade interacts with the airflow around the tower and produces periodic pulsation,which acts as the sound source to the observation point.In order to further explore the correlation characteristics between the flow field and the sound field during the operation of the wind turbine,the near-field rotating noise of the wind turbine is studied as follows.Based on the certain correlation between pressure pulsation and sound pressure,the loudest energy position of the rotation plane of the whole machine and the single wind turbine model was explored and the correlation between sound field and flow field was further found.The sound field monitoring points were arranged on the rotating plane,and it was found that during the rotating process of the wind turbine,the sound pressure level of the single wind turbine model was larger near the blade radial radius 0.77R-0.83 R,while the sound pressure level of the whole machine model was the largest at the blade radial radius 0.71 R at the measuring points 0°and 180°,and the sound pressure level was the largest at the blade radial radius 0.83 R at the measuring points 120°and 300°.In the analysis of the loudest energy position in the rotating plane of the wind turbine,it is found that the acoustic field of the wind turbine model has a certain lag compared with the flow field due to the interference of the tower,and the lag azimuth is about 30°.By analyzing the distribution of the pressure pulsation at the measuring point of the tower side in the negative direction of y axis and the azimuth angle of the wind rotor rotation of the sound pressure level,and comparing the azimuth angle of the first peak of the two,it is found that the sound pressure level of the sound field lags behind the pressure pulsation of the flow field at y=-0.1 m,y=-0.3 m,y=-0.5 m and y=-0.7 m lag respectively22°,5°,9°与 18°.The flow characteristics of the rotation plane at the position with the loudest energy were investigated.From the overall vortex structure distribution,it was found that the vortex structure lifted at the position with the loudest energy on the blade surface.From the distribution of high and low speed zones,it is found that the position of the loudest energy on the blade surface is affected by the flow from the leading edge to the trailing edge and the flow from the leading edge to the leading edge in two opposite directions.By analyzing the pressure distribution of the loudest energy position along the inlet direction at different chordal positions,it is found that at the chordal direction y=0.02 m,the low-speed fluid jets to the high-speed fluid region of the outer layer,and at the radial direction of 0.8R,the pressure of the inner layer near the blade surface is higher than that of the outer layer.At the position of y= 0.02 m and y= 0.01 m in the chord direction,there is an obvious phenomenon of vortex structure lifting,and the corresponding radial positions of the blades are 0.8R and 0.7R,0.75 R respectively.Based on the flow characteristics of the loudest energy position of the rotating plane,the SPL and pressure pulsation analysis results of the measuring points at the side of the tower during the rotating process of the wind turbine were analyzed.It was found that the SPL amplitude increased first and then decreased during the moving process from the blade root to the blade tip,and the amplitude reached the maximum at y=-0.5m.Similarly,the amplitude of the pressure pulsation reaches the maximum at y=-0.5m,and the slope of the pulsation values of the peak and trough is the largest at this point.The research on the flow field and sound field of wind turbines can provide ideas for noise reduction in blade design,and also provide ideas for subsequent studies on the flow field and sound field under different working conditions.