ideas wanted - we need to reduce noise on our new wind generator

[Robin1958]

(blank)

[rossw]

The Jaycar units are almost identical to the one I got - except mine is a 3m dia, 1000 watt job.

It too had the same problem - it'd scream like a banshee in high wind.

I took to it with my angle-grinder and removed the square end, and re-shaped the back of the blades to bring it back to something aproaching an airfoil shape with a sharp trailing edge instead of the square back. Also fixed the leading edge, sanded the whole thing back smooth, filled all the holes with epoxy filler, resanded and painted it with a few cans of quick-drying outdoor paint.

It made a substantial difference. Let me know if you want photos...

[Robin1958]

Hi,

Some photos would be very useful, thank you

Robin

[gizmo]

Those cheap windmills should come with ear plugs. Or at least Jaycar

should mention the noise problem in their advertising.

Wrote an article about a few modifications to those blade here...

http://www.thebackshed.com/Windmill/articles/ChineseBlades.asp

There are two modifications, one to gain some power and the other to reduce the noise.

Glenn

[rossw]

The end of the blade, and the trailing edge were like this:




and

The first rough pass with the angle grinder took it to:

After some hand sanding, and the first coat of paint (but before I'd wet-and-dry cut it back)

[Capt Slog]

Wasn't there someone on the board who mistakenly 'cleaned up' a set of blades? He took a ridge off the back of the blade thinking that this would make it quieter, it had the exact reverse effect.  He ended up putting the ridge back by applying a piece of line down the back of the blade.

(for some reason I couldn't add this post as a comment to the original)

[electronbaby]

Please see my post:

http://www.fieldlines.com/story/2007/3/28/205619/172

This might help you. This method (if placed in the right spot) could help with noise on any prop.

It might take some experimenting.

Good luck :-)

[Ungrounded Lightning Rod]

Electronbaby's link, above, points to the article with the information on removing the ridge (oops) and putting one back on with metal duct tape(?) and monofiliment (whew!).

[Ungrounded Lightning Rod]

On reshaping the tip.

As I understand it, changing the tip profile like the "20 mm" illustration near the end of your article is half of forming a particularly good tip profile ala (Sandia?).  (Except the curve should end up tangent to the straight portion of the leading edge, and it appears to form an angle in the ilustration..)

The other half is to bring the end of the blade down to a knife edge.  The "leading corner" starts out like a ball where the curve leaves the leading edge, then blends into the sharp end of the blade.

The point of this is to change how the wind that's trying to "run around the end of the blade" (from the high-pressure front to the low-pressure back) behaves.  With a rounded end it just runs around the end smoothly, depowering the outer few inches of the blade.  With the edge, the wind jumps off the tip in a jet, and by the time it gets turned around the blade has moved on.  So the pressure difference on the end of the blade is maintained, as is the lift that pressure difference creates.  The end of the blade retains full power - which is very significant, because it has more swept area per unit of length than any other part of the blade.  So even a small improvement makes a lot of power.

Another way to look at it is that the jet off the bladetip pushes the tip vortex farther out, effectively lengthening the blade.  It's doing much the same thing as a wingtip fin at right angles to the blade (like the "wing keel" on some fixed-keel sailboats designed for shallow water capability or easy trailering), but without the added air friction.

[Ungrounded Lightning Rod]

I have no idea how that wingtip change would affect sound...