Study On Aero-Acoustics Of Wind Turbine Blade

As the fast development of wind power industry, the unit capacity of wind turbine grows binger and bigger, and also of the wind turbine blades. As a result, the radiated noise grows fast. The existing analysis shows that aerodynamic noise is the main noise source of modern large-scale wind turbines, and the aerodynamic noise level is approximately proportional to the 5th power of tip speed. The blade flexibility enlarges as the wind turbine blade enlarges, and results in aero-elastic problems and then induces additional noise.In order to satisfy the request of environmental noise, the design speed of wind turbine is controlled within a certain range. As a result, wind energy utilization coefficient is far from the optimal value. If the aero-acoustics of wind turbine blades can be reduced and the rotation speed increases, the wind energy will be utilized more fully. Besides, if the rotation speed increases as the blades noise reduces in the blades design process, the blade solidity can be reduced, and also the blade weight and the cost.The author research the radiated noise of a 2.5 MW wind turbine using the BPM airfoil self noise semi-empirical formula and Amiet turbulent inflow semi-empirical formulas.The results of prediction and experiment are in good agreement. The research of inflow wind speed indicates that, wind turbine radiated noise is mainly influenced by rotation speed, and the influence of inflow wind and sheer-wind are small. Besides, the position of biggest noise is located at 80-95% in spanwise. For the observer in the ground, the result of the blade position where there is the biggest radiated noise is agreed with the experiment.The radiated noise of large thickness airfoil with blunt trailing-edge designed by IET, CAS is researched. As the inflow speed is small, the main noise is separation stall noise; while it is large, the main noise is blunt trailing-edge noise.In addition, in order to research the aero-acoustics caused by unsteady movement of blades deeply, noise prediction model of moving airfoil is established and validated numerically. Noise source formula of moving monopole in 2D FW-H equation is deduced in frequency domain, and the radiated noise is calculated using the formula. The result shows that the monopole acoustic source intensity caused by unsteady moving airfoil is more than the dipole acoustic source intensity caused by unsteady loads of airfoil surface.Then, the unsteady flow field and sound filed of moving airfoil are studied. For the plunging and pitching airfoil with unsteady inflow, the coefficients of lift and drag increase as the moving frequency increases, and also the radiated sound intensity. The coefficients of lift and drag with turbulent inflow are more than what are with steady inflow while the airfoil plunging frequency is small. However, the coefficients of lift and drag with turbulent inflow are similar to what are with steady inflow while the airfoil plunging frequency is more than 0.5 Hz. This may be due to the change of vortex structure in the wake, resulting in effects of vortex structure change exceeding turbulent inflow. The results are similar for the airfoil pitch.