2019 Volume 40 Issue 1 Pages 40-48
Wind turbine noise (WTN) generally has amplitude modulation (AM) components, which often cause psychological annoyance in residential areas around the power generation plant. To investigate the directivity of AM sound generated from a wind turbine, field measurements have been performed under various wind conditions. Some receiving points were set circularly around a single wind turbine, and meteorological and associated wind turbine operational data were collected along with corresponding acoustic data. The method for extracting the AM components from the analyzed sound pressure levels at 100 ms intervals is based on the ideas of the F-S method. The results revealed a distinguishable directivity pattern of the strength of the AM components contained in WTN. The magnitudes of AM sound become lower in the downwind directions and highest in the direction approximately 60° relative to the front of the nacelle. In addition, the strength distributions of the AM components at distances of up to 200 m from the turbine were examined. It was found that almost all the magnitudes of AM sound still remained above 2 dB at a distance of even 200 m, whereas the A-weighted sound pressure levels decreased with increasing propagation distance.