Question about Wind Turbines

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By Cathy MacLellan on 4 April 2007 - 5:01pm

I just had a long conversation with a reporter and he was commenting on studies that indicate medical issues (headaches, depression) related to low frequency (inaudible?) noise emitted by wind turbines. Is anyone familiar with this? I thought I would ask here before spending hours on the internet sorting through the various opinions there.
Cathy in Waterloo

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Turbine noise widely reported

Submitted by Donald Fletcher on 6 April 2007 - 11:21am.

Lambton Kent Middlesex EDA (SW Ontario)
Have youu ever experienced the sound a helicopter makes, that whup whup whup as teh blades rotate?

Some families have found wind turbine noise so disrupting that they discussed building a berm or wall to protect the house and yard. Then there is that very audible noise some turbines make when the blade starts to furl. turn out of the wind or come back into it. Props that feather rather than furl do not have this noise.

Then you look at brand names for consumer wind machines, like whisper. The manufacturers have started to sell quiet. None of them are any noisier than a labouring diesel generator.

Some turbines also produce irritating bearing noise. This can be eliminated with electro-magnetic bearlings. (This is not a low frequency noise.)

Wind machines like any other machines have noise factors that diminish as the lnverse square of the distance from the machine, so that installation very close to housing or any place people are, can be avoided. But of course cutting noise at source has a pronounced effect.

Next, a barrier at 45 degrees will deflect noise directly up and so protect those beyond it..

Because these nuisances have been reported so widely we have to give some credence to the need to ensure that the next installation will not . By the way, sounds that are inaudible take a bit of detection, as in if a windmill in a forest makes noise that nobody can hear, is it really making a noise?

Lambton Kent Middlesex EDA (SW Ontario)

Turbine noise

Submitted by Cathy MacLellan on 6 April 2007 - 1:00pm.

Thanks Donald - yes I'm very aware of the helicopter-like noise of small turbines, and the more gentle "shwosh" of the really large ones, but this idea of inaudible low frequency "noise" is what I was trying investigate.

compression decompression principle

Submitted by Donald Fletcher on 6 April 2007 - 5:43pm.

Lambton Kent Middlesex EDA (SW Ontario)
When air is compressed and then decompressed we get a shock wave that travels through the air. We call it sound when the outgoing wave is heard, but even the passing of a car sends a bow wave of comptession and a transom wave of decompression. HIgh speed aircraft, just below the sound barrier, are creating a save that we can not hear but can measure. Only when it gets up to the sound barrier speed will it act like a sonic wave in all respects.
An aircraft propeller may be breaking the sound barrier. Any high speed propeller tip may be making a compression decompression disturbance in the air as the tip speed gets close to the sound barrier.

We get more power from a given mass of propeller as it goes faster, so there is a reason for building wind turbines that come close to making a noise. But because of public opposition we have to make sure that the machines we build are not going to offend with harmful noise., feather the prop rather than allow it to become noisy at high speed, I suppose.

Lambton Kent Middlesex EDA (SW Ontario)