Noise level of various mill types

[Ungrounded Lightning Rod]

I've been trying to decide what sort of mill to make, and noise level is significant for me.

At the rural site I have occasional very high winds, and neighbors within a few hundred feet.  (The suburban site is your typical '50s ticky-tacky suburb spacing, though it has reliable lake-effect evening winds, so it would likely only have toys and prototypes.)

My impression is that high TSR HWAT blades produce a lot of noise at high windspeeds, especially if they start stalling out or overspeeding on their way to feathering in high winds.  (It was the recent comparison to "sounding like a helicopter" in such situations that got me thinking about it.)

For HWATs I expect the noise mechanisms are:

 - Vortex peeling from the whole blade during stall.

 - Vortex peeling from blade tips.

 - Vortex peeling from blade trailing edges if not properly streamlined.

 - Low-frequency "thrumming" from the variation of the decelleration of the wind by the blades as they turn.

With VWATs I get the impression that a Savonius might be a lot quieter due to the low TSR, and that a Darrius might sound more like a HWAT since they have similar tip speeds (though the "egg-whisk" designs don't have the tip vortices).

But not yet having actually MADE and HOISTED any of these devices, and not having easy access to any active sites, I don't have a subjective feel for the noise levels involved.

I realize most of you folks probably haven't used noise meters on your mills, so your results won't be directly comparable.  But a lot of you have built and hoisted a lot of mills, visited more of 'em.  And I bet there are experts out there, too.  I'd like to tap this knowlege base.

So how about it?  What are your impressions of the noise of various designs and implementations of them?  Especially of the various homebrew-blade HWAT designs that have been discussed here.  And has anybody who'se built a Sandi Savonius got an impression of that?

[Flux]

I don't know how VAWT's compare on noise, but it normally related to TSR and rotational speed.

In general high TSR's are noisy and most propellers become more noisy as their operating TSR goes above the design value.

Noise is worse when running at an angle to the wind, when furling or yawing.

Down wind blades are more prone to "thumping" due to tower shadow.

If you keep to a TSR of 6 or lower, keep the speed down towards stall in high winds and keep the tips thin and the trailing edges sharp, you should be ok on most sites.

If noise is a problem it could be wise to use an alternator large enough to hold things down towards stall at the furling point.

A prop with TSR 10 at runaway is frightening. A good well made prop TSR 5 could be quiet enough to be masked by general wind noise at high winds.

There may be tricks you can do with the shape of the tips that would also help, perhaps others have some experience of this.

If you are in a very turbulent wind site  VAWT might offer some advantage but I have no experience.

Hope this is a start, lets see what others think.

Flux

[DanB]

I would think that noise from HAWT designs is an issue if...

 - they are very fast, or overspeeding

 - the blades are too flexible

When the alternator is a bit too powerful, and the blades stall at higher wind speeds (which has been the case with lots of my machines at least untill they've been adjusted) - I find they are very quiet.  I dont think blades stalling is a noise issue, blades overspeeding is though.

I dont find any of the machines we've put up to be noisy (at least not very noisy) when furling.  The most noise I hear is a quiet whooshing sound and the quiet growl of the alternator.

Air 403's are very noisy!- I suspect because the blades are very flexible and they flutter.  They also run at a very high TSR.

A nice, slow TSR, rigid wooden blade should run very quietly I think if the alternator is reasonably well matched.

[John II]

I have witnessed a 2 blade 16' whirl Wind windcharger( now discontinued ) sound like a helicopter from 1/2 mile away, when a gust would over speed it. It made the extremely loud helicopter noise when the gust let up.I own a whisper H-900 it's fairly quit.

From all the reading I have done for the past 15 years...I hear that Bergy units are fairly noisy because they use a non true airfoil.I have heard that Jacobs are extremely quiet.

From all of my reading, it seems that 3 or more blade units are usually more quiet than two blade units. Normally, the more blades the quieter they are. Also the slower the prop speed the more quit they usually are.

I understand that low wind windchargers are usually quieter than ones that are designed for high wind speeds.

For instance... I suspect that the AWP wind turbine featured in Home Power Magazine (which can be read on line) on page 82 of their August-September 2004 issue would be incredibly quite. see the following URL's for this particular unit.

http://www.homepower.com

http://www.africanwindpower.com

http://www.abundantre.com

John II  

(S.W. Missouri)

[Victor]

Hi John,

"From all the reading I have done for the past 15 years...I hear that Bergy units are fairly noisy because they use a non true airfoil.I have heard that Jacobs are extremely quiet."

 The Bergey XL.1 is quieter than the Whisper H-40 up to around 40mph. above that windspeed there are short bursts of flutter from both in my experience with the Whisper fluttering before the Bergey. The two  Bergey  machines now have new highly developed airfoils. The Excel 10kw second generation blades were much quieter than the originals and the third generation is supposedly  extremely quiet. I will be installing a set of these next month for a client.

 I think the Jacobs machines owe their quietness to low tip speeds (around 5/1 on the DC machines and 7/1 on the AC units)and the fact that they feather instead of furl for overspeed protection.

Victor

Aerofire Windpower