Falmouth Wind Turbine Noise Confirmed DEC 2011

Wind Turbine Noise and Air Pressure Pulses

Wind turbines emit noises and air pressure pulses from:

– machinery noise in the nacelle
– rhythmic/pulsating trailing edge noise from the blades (“blade swish”) as they slice through the air at up to 200 mph
– irregular, low frequency noise (LFN) and infrasound air pressure pulses from the blades due to in-flow air turbulence
– LFN and infrasound air pressure pulses at the blade-tower-passage frequency and its harmonics.

At 350 m (1,148 ft) the audible sound emitted by:

– a well-behaving wind turbine with no in-flow turbulence and low wind shear is about 35 dB(A); often during daytime when the sun is warming the ground and air.
– a badly-behaving wind turbine with in-flow turbulence and/or high wind shear up to 55 dB(A); often during nighttime when a stable atmosphere forms.

This compares with rural nighttime noise of 20-40 dB(A) and urban residential nighttime noise of 58-62 dB(A).

The wind speeds and directions upstream of a wind turbine vary due to terrain effects, such as hillyness and ridge lines, objects on the surface of the terrain, such as buildings and trees, daytime thermal effects and upwind wind turbines.

During daytime, as a large blade rotates, it encounters air at various speeds and directions which produces a combination of sound effects, i.e., rhythmic/pulsating blade swish about 3 dB(A) above the steady aerodynamic noise, and a steady rhythm of LFN and infrasound air pulses.

During nighttime, the daytime thermal effects are minimal which causes the air speeds and directions to become more varied and the atmosphere to become more stratified, background noise is less causing the various sound effects (aerodynamic noise, rhythmic/pulsating noises, rhythmic LFN and infrasound air pulses) to be noticeably more intense than during the daytime. The daytime blade swish noise becomes a nighttime clapping, beating, or thumping noise.

As the 3-bladed rotor turns at 15 to 20 rpm at higher wind speeds, a blade reaches the top about 45 to 60 times per minute, or 0.75 to 1.0 Hz. At lower wind speeds the frequencies are less.

The air pressure pulses have audible components (20 to 500 Hz with peak amplitudes at about 200 to 500 Hz) and inaudible components (0 to 20 Hz with peak amplitudes at about 0.75 to 1.0 Hz). The pulses travel great distances, a mile of more, for large, utility-size wind turbines.

The wind speeds and directions downstream of a wind turbine are similar to the vortices leaving the ends of airplane wings, except they all rotate in the same direction. When the wind direction aligns with the ridge direction of the wind turbines, the downwind turbines will have a degraded performance of up to 20 to 30 percent, i.e., a reduced CF, due to wake turbulence, and they will be noisier, and they will have increased wear and tear.

The title of this article is irresponsible. A more accurate title would have been:

Quick, single home study funded by a wind turbine opponent seems to confirm Falmouth Turbine health impacts

Frankly, I find this study to be intriquing. It’s interesting because it found elevated infrasound effects indoors (much greater than outdoors). This suggests that sound waves from turbines cause homes to vibrate to produce secondary infrasound. If I was in authority in Falmouth I’d see if the study could be reproduced.

But a study done in a single home over a single day and a half is far, far short of a serious study. It’s intriging but it didn’t come close to justifying the article title here.