| As wind continues to become a more prevalent source of energy, concerns over the proximity of wind turbines to residential areas will grow. Densely populated Europe has already encountered this problem and the United States is beginning to experience it. One of the main concerns about wind farms is the radiation of acoustic noise. Although some noise is caused by the gearbox and generator, it is the wind turbine blades that produce the strongest sources of noise on modern turbines. To aid in the design of quieter wind turbine blades, diagnostic tools are required to assess the components of wind turbine noise during operation in the field. Single microphone techniques have been employed in the past, but they are unable to distinguish between the potentially large number of sources of noise. Furthermore, very low signal-to-noise ratios can result from single microphones due to wind noise. An array of microphones can be used to provide a high resolution, high signal-to-noise ratio diagnostic tool. Acoustic arrays have been used for decades in the analysis of aeroacoustic noise, mainly on aircraft. Recently, acoustic arrays have been applied to the study of wind turbine noise. This thesis describes research performed on the design of a 32-microphone acoustic array for wind turbine noise analysis. The work is a cooperation between the National Renewable Energy Laboratory (NREL) and the University of Colorado. The array has been successfully tested on a 100 kW wind turbine at NREL in Boulder, Colorado and was used to analyze acoustic noise generated from the blades of a 100 kW turbine in Bushland, Texas in cooperation with Sandia National Laboratories during 2009 and 2010. |
