Research On Characteristic And Noise Reduction Method Of Aerodynamic Noise From Wind Turbine Blades

In order to ensure the national energy safety, protect the ecological environment, and promote the sustainable development of the society and economy, the Chinese wind power industry is rapidly developed in recent years. Because of the restriction of grid consumptive capability, the applications of large-scale wind turbine are expanded to the areas that have abundant wind resource and developed economy. For the population is densely in these areas, the aerodynamic noise of the wind turbine would have an effect on the inhabitants near the wind plant. It has drawn the interest of the researchers.In this thesis, the velocity field and the pressure field of a kind of 2 MW wind turbine blade model are numerically simulated with the FLUENT software. Based on the aerodynamic acoustics theory, the aerodynamic noise from the wind turbine blades can be predicted. The single parameter method is used to analyze the effect of the operation parameters on the aerodynamic noise, such as wind flow speed, rotate speed and pitch angle. The results show that:(1) Under the rating conditions, the airflow speed distribution on the wind turbine blade surface shows that the speed is gradually increased from the blade root to the blade tip, and it has reached a maximum speed at the blade tip. The pressure gradient change of the wind turbine blade surface shows that the pressure is gradually increased from the blade leading edge to the blade trailing edge, the static pressure and the total pressure changes dramatically. The static pressure change is the major factor to produce the aerodynamic noise. As the distance is increased from the rotor rotating plane to the individual monitoring-station, the noise sound pressure level of the individual monitoring-station is decreased. The attenuating range along the rotational axis is getting less and less, and even to be flat. In parallel to the Y-axis direction, the radiated noise near the zone of the blade tip is large, and its attenuation range is also large.(2) As the wind speed and rotating speed are increased, the airflow speed and pressure on the wind turbine blade surface are also increased. The rotating speed has a greater effect on the airflow speed and the pressure gradient. As the deviation between the rotor speed and the rated speed has increased, the region that the dynamic pressure changes intensely moves from the blade tip to the maximum blade chord position. When the pitch angle is increased from 0 to 10 degree, the airflow speed and pressure gradient on the wind turbine blade surface has increased, but the change ranges are small. It is indicated that the blade pitch angle has less effect than other parameters. When the blade pitch angle has increased to 15 degree, the airflow speed and pressure gradient on the wind turbine blade surface have changed slightly lower. With the change of wind speed, rotating speed and pitch angle, the change trends of the noise sound pressure from the monitoring station are consistent with the rating conditions. The rotating speed has a great effect on the noise sound pressure level.Based on the above analysis, several methods to reduce the aerodynamic noise from the wind turbine blades are proposed:(1) Reducing the rotating speed of the wind turbine blade appropriately can effectively reduce the pressure value of the wind turbine blade surface. Thereby it can reduce its aerodynamic noise, especially the noise from the wind turbine blade trailing edge. Studies have shown that aerodynamic noise of the studied 2MW model can reduce the overall sound pressure level 1 ~ 2dB, as the rotating speed decreases under the rated speed 1rpm.(2) Reducing the blade pitch angle appropriately at the rated wind speed can effectively reduce the aerodynamic noise from wind turbine blades.Based on the simulation of the velocity and pressure field, and the prediction of the sound field of the wind turbine blades, several methods to reduce the aerodynamic noise from the wind turbine blades are proposed. It can provide theoretical reference to reduce the aerodynamic noise from the wind turbine blades, and promote the large-scale wind turbines applications in residential areas.