Noise Propagation Issues in Wind Energy Applications

Abstract

The prediction of noise emitted from operating wind turbines is important to planners in order to avoid the possibility of surpassing the allowable limits close to residential areas. To this end, the wave equation is solved, taking into account the atmospheric and ground characteristics that affect sound propagation. In the present paper, a ray tracing methodology capable of performing axisymmetric calculations of the sound field around an isolated source is used. The methodology simulates all the main physical mechanisms that influence sound propagation and performs calculations for the whole range of acoustic frequencies. In the case of more sources, a quasi-3D calculation is implemented, superposing the contributions from all sources. Application to single wind turbines is validated with available measurements. The effect of various parameters such as ground impedance, temperature, humidity, turbulence, and wind velocity is investigated for an isolated wind turbine as well as for wind parks. It is shown that ground and atmospheric absorption are important at the low and high frequency ranges, respectively. In flat terrain cases, simple propagation models may also give satisfactory predictions of the overall sound pressure levels. However, in complex terrain cases, the wind velocity and the relief of the topography can significantly affect noise propagation, suggesting the necessity for using sophisticated propagation models, such as the current one.