The Design And Application Of Wind Turbine Airfoil Considering The Aerodyamic Noise

With the large-scale wind turbine development, the noise problem can not be ignored any more. As the intensity of acoustic noise is approximately proportional to the tip speed up to the fifth power, the tip speed of wind turbine is often limited by manufacturer in some degree, this shortcoming obviously restricts the efficiency of wind turbine, how to optimize the noise performance of wind turbine become a vital issue that must be solved immediately. The airfoil with excellent aerodynamic performance and low noise level can make a breakthrough in wind turbine blade design that is been limited by rotor speed because of the noise. The airfoil theory, the aerodynamic design theory of wind turbine and some basic knowledge of noise are firstly explained in this paper. And then, the kinds of airfoil self-noise and the generation mechanisms for each noise source are also analyzed. A feasible method of airfoil optimization is presented, to establishe a foundation for airfoil aerodynamic noise optimization and its application in the blade design.In order to obtain wind turbine airfoils with high lift-to-drag ratio and low noise level, the aerodynamic noise is introduced into the wind turbine airfoil design process. To evaluate the airfoil aerodynamic noise level, the airfoil self-noise model is studied and the NASA self-noise model based on extensive field and tunnel experiments is applied to model the airfoil aerodynamic noise. With the airfoil profile described by using shape function perturbation method, taking the aerodynamic characteristics as the performance constraint and the relative thickness of airfoil as the shape constraint, a noise optimization method is set up with the objective to satisfy the lowest self-noise level. In the design process, XFOIL is applied to get the boundary layer parameters and evaluate the airfoil aerodynamic performance. By combining the flow field solver and the direct optimization method, and applying the improved complex method to carry out the search iterations, a MATLAB based optimization program is developed. Taking NACA4415 as the original airfoil, applying the developed program to carry out the optimum design under working conditions with different Reynolds number, airfoils with high aerodynamic performance and low noise level are obtained.The original and optimized airfoils are applied to 5KW horizontal axis wind turbine blade design respectively. Glauert optimization theory is used to the blade aerodynamic shape simple design. Based on airfoil self-noise theory, using finite element thought to predict the entire blade noise, both aerodynamic performance and noise level are compared between the blade using the original airfoil and the blade using the optimized airfoil, the result shows that the optimized blade maintains a good aerodynamic performance and has a improved noise performance at the same time. The feasibility of the research method discussed in this thesis is demonstrated.