Infrasound and low-frequency noise from wind turbines

Abstract

Infrasound, low-frequency noise (ILFN) and amplitude modulation of the noise are known to disturb some residents living near wind farms. However, the mechanisms responsible for ILFN and amplitude modulation are not well understood. In an attempt to shed some light on these mechanisms, acoustic measurements were taken close to a wind farm, at residences located two or more kilometres from the nearest turbine in a wind farm and in an anechoic chamber using a scale-model, electrically-driven, wind turbine. The measured spectra reveal distinct peaks at the frequencies corresponding to the blade-pass frequency and its harmonics, and the characteristics of these peaks are remarkably similar for field and laboratory measurements, indicating that the zero mean flow simulation is a good representation of an actual wind turbine. Near field acoustic holography measurements on the scalemodel turbine confirm that tonal components at the frequencies corresponding to the blade-pass frequency and its harmonics are generated as a result of blade-tower interaction, suggesting that it is likely to be an important mechanism of infrasound generation for industrial wind turbines. Inaccuracies in the assumed location of sources of noise generated by a wind turbine affect the accuracy of community noise predictions. This is because the source height affects the distance from the turbine beyond which sound rays arrive at the receiver having been reflected from the ground more than once, thus reducing the attenuation with distance from the turbine.