Delivering a thumping, grinding, mechanical cacophony, industrial wind turbines drive neighbours nuts. But, as a recent study from Flinders University in South Australia has found, there’s a reason why wind turbine noise is so much worse after dark.

The pulsing, thumping nature of wind turbine noise – which relates to blades passing the tower – is referred to as ‘amplitude modulation’ (AM). And it’s the peaks and troughs in sound pressure levels that makes living with wind turbine noise a daily misery for thousands around the world.

But changes in humidity, temperature, atmospheric pressure, wind speed and direction all have a part to play in how the wind industry’s victims get to experience AM in the range of other unnatural noises generated by these things.

Over the last four years, Dr Kristy Hansen and her PhD candidate Duc Phuc Nguyen have been researching the complex nature of the noise from wind turbines that’s driven dozens of South Australians mad in their homes and, in too many cases, out of them, for good.

Their latest results show that, as the wind industry’s long-suffering victims already know, wind turbine noise gets worse after the sun goes down. Coincidentally, when most people are trying to seek a little rest and respite within their homes.

Wind turbine night noise
Techxplore
Flinders University
18 August 2021

Diurnal and seasonal variation of AM characteristics. (a) Diurnal variation of AM prevalence. Thicker lines are the average trend over the year for three locations. Light lines indicate the trend for each month. Credit: Adelaide Institute for Sleep Health, Flinders University

Flinders University experts are using machine learning and other signal processing techniques to characterize annoying noise features from wind farms.

The new studies find that ‘amplitude modulation’ (AM) from wind turbines is likely to be heard by neighboring residents up to five times more often than during day-light hours, depending on wind direction, season and wind farm distance.

For the first time, the research led by Flinders University Ph.D. candidate Duc Phuc (‘Phuc’) Nguyen and acoustic expert Dr. Kristy Hansen has combined long-term monitoring of wind farm noise with machine learning and available knowledge to quantify and characterize AM in wind turbine noise.

“We found that the amount of amplitude modulation present during the daytime versus night-time varies substantially occurring two to five times more often during the night-time compared to the daytime,” says Nguyen.

“The noise seems to worsen after sunset when amplitude modulation can be detected for up to 60% of the night-time at distances around 1 km from a wind farm.

“At greater than 3 km, amplitude modulation also occurs for up to 30% of the night-time.”

The Wind Farm Noise Study, based at the Adelaide Institute for Sleep Health at Flinders University, is investigating noise characteristics and sleep disturbances at residences located near wind farms.

Dr. Hansen says the directional nature of wind turbine noise means residents living in downwind and crosswind conditions are likely to be more disturbed by wind turbines.

“We found that AM occurs most often during these wind directions,” she says. “Using these recent advances in machine learning, we have been able to develop an AM detection method that has a predictive power close to the practical limit set by a human listener”.

“This includes the noise that increases and decreases as the blades rotate, or AM, including a ‘swoosh’ sound, which further contributes to the negative effects of wind turbine noise.

“These studies advance our ability to measure and monitor the noise from wind turbines that is likely to be more annoying than other noise types at the same level.”

The studies were published in Applied Acoustics and Measurement.


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September 10, 2021