An aeroacoustic analysis of wind turbines

This paper describes computational aeroacoustic methods that are being applied to predict the noise radiated by wind turbines. Since the wind turbine noise problem is very challenging, only some of the important noise sources and mechanisms are being considered. These are airfoil self-noise, the effects of blade rotation, and the propagation of sound over large distances. Two aspects of airfoil self-noise are being studied. The first is the relatively low frequency noise generated by deep stall and the second is trailing edge noise. The noise associated with blade rotation includes the effects of blade rotation on the blade aerodynamics, incoming gusts, incoming atmospheric turbulence and wind shear. The unsteady flow simulations are coupled to the radiated noise field with the permeable surface Ffowcs Williams - Hawkings formulation. For long-range noise propagation predictions, methods based on solutions of the linearized Euler equations or the Parabolic Equation approximation are discussed. Alternative methods for the implementation of boundary conditions for the propagation studies are also included.