Wind turbine low frequency and infrasound propagation and sound pressure level calculations at dwellings.

Stephen E Keith,Gilles A Daigle,Michael R Stinson

doi:10.1121/1.5051331

Stephen E Keith, Gilles A Daigle + Show 1 more

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https://doi.org/10.1121/1.5051331

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Abstract

This study was developed to estimate wind turbine low frequency and infrasound levels at 1238 dwellings in Health Canada's Community Noise and Health Study. In field measurements, spectral peaks were identifiable for distances up to 10 km away from wind turbines at frequencies from 0.5 to 70 Hz. These measurements, combined with onsite meteorology, were in agreement with calculations using Parabolic Equation (PE) and Fast Field Program (FFP). Since onsite meteorology was not available for the Health Canada study, PE and FFP calculations used Harmonoise weather classes and field measurements of wind turbine infrasound to estimate yearly averaged sound pressure levels. For comparison, infrasound propagation was also estimated using ISO 9613-2 (1996) calculations for 63 Hz. In the Health Canada study, to a distance of 4.5 km, long term average FFP calculations were highly correlated with the ISO based calculations. This suggests that ISO 9613-2 (1996) could be an effective screening method. Both measurements and FFP calculations showed that beyond 1 km, ISO based calculations could underestimate sound pressure levels. FFP calculations would be recommended for large distances, when there are large numbers of wind turbines, or when investigating specific meteorological classes.

Highlights

Infrasound produced by wind turbines can be comparable to natural infrasound (Turnbull et al, 2012)
Predictions verified by measurements show that under common meteorological conditions wind turbine noise can be measurable at 10 km downwind of wind turbines
The downwind infrasound propagation is more favorable than a 6 dB decrease in sound pressure level (SPL) per doubling of distance, i.e., in class W3S5 which is estimated to occur on average 1.8(0.5) h a night in the area of the Health Canada study

Summary

Introduction

Infrasound produced by wind turbines can be comparable to natural infrasound (Turnbull et al, 2012). The previously indicated studies suggest that there may be some cases with sustained propagation that is more favorable than spherical spreading (a 6 dB decrease per doubling of distance) over land. This is not a common option in most commercially available sound propagation models, which were primarily developed for A weighted sound pressure level (SPL) from low sources (like vehicles), and for short propagation distances (up to 1 km). There are methods that allow results that may be comparable to a 3 dB decrease in SPL per doubling of distance (i.e., cylindrical spreading): The Swedish calculation method (SEPA, 2012), but only for conditions over water; and Nord2000 (Plovsing, 2006a,b)

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