Didn't realise that windmill blades are serrated

Took the weans a walk away up the back of The Three Towns in Ayrshire where they are installing these big bad boys.

GreyShack 46 points 3 years ago

They disrupt the trailing edge eddies - which is what causes any noise - and so make them quieter. They are often fitted in areas where sound might be a particular issue.

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kev 12 points 3 years ago

I can't hear the word eddies without thinking Hitchhiker's Guide

"Eddies," said Ford, "in the space-time continuum."

"Ah," nodded Arthur, "is he. Is he."

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Trail 3 points 3 years ago

So why don't my CPU/case fans have serrated edges as well? Because they are too small?

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GreyShack 5 points 3 years ago

Because they are too small?

Could be. As is said so often: physics doesn't scale. Trailing edge eddies may not be the major source of the noise in this anyway - since these are pushing air not being pushed by it.

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Trail 3 points 3 years ago

Yeah that makes sense I guess.

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Siamanguel 4 points 3 years ago

Some do, e.g. Noctua: https://noctua.at/en/vortex-control-notches

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Finnbot 2 points 3 years ago

They are surrounding a farm with hunners of cows in multiple fields, so I wonder if the noise is quite scary for them, hence efforts to make them quieter. Or the farmer insisting. Are they usually quite loud?

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Gormolius 1 point 3 years ago

Trailing edge you say? So not designed to mince up birds, that's a relief.

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kitonthenet 2 points 3 years ago

Oh they’ll still mince birds, just with the blunt side

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GreyShack 8 points 3 years ago

Most of the bird deaths are not actually physical strikes - it is a result of the massive change of air pressure as the blades pass at speed. Evidently painting one of the blades black - or some contrasting colour - keeps a lot of the birds well away.

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tessellatedtangerine 1 point 3 years ago

do they pass out? does it affect their breathing? this is very interesting to me

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juusukun 13 points 3 years ago

Unless if they be milling grain those are turbines if I'm not mistaken

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Finnbot 4 points 3 years ago

Aye but doesn't sound as quaint though, does it?

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juusukun 3 points 3 years ago

True, maybe they could be both? They should have little mill yer own grain stations at the bottom lol

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erusuoyera 2 points 3 years ago

I guess a lot of grain mills use electric motors now, so in a way they are.

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P_Nuts 9 points 3 years ago

Helps them chop up birds better

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Transcendant 9 points 3 years ago

Huh, TIL. Had no idea they were serrated either.

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MoltenBoron 6 points 3 years ago

brb

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Finnbot 1 point 3 years ago

Look at the size of those bad boys!

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RoadieRich 6 points 3 years ago

It reduces the turbulence at the trailing edge, reducing noise. Bernouli's principle dictates that part of the force on the blade is due to the airflow on each side moving at different speeds, if the crashed into each other all at once, you'd get a lot of turbulence, and hence noise. The serrations ensure that the two flows meet over a longer distance, reducing said turbulence.

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pbkoden 3 points 3 years ago

Same reason you see chevrons on the back of some modern turbofan engines

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buhala 5 points 3 years ago

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sideone 4 points 3 years ago

Is it true they make noise?

We have some quite close (a few miles away) and I've cycled right past them. I've never heard anything from them.

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greyscale 1 point 3 years ago

Riding my moped past these and I can tell you they make swooping noises, especially if they're aimed 90 degrees to you. These windmills are quite small and old, however, and are quite low. Its a bit intimidating seeing something that massive moving that fast, that close.

They make a rainbow though

Apparently one collapsed recently

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1nk 4 points 3 years ago

As others have said, mostly about noise reduction. There's actually work looking whether the same concept could be developed for electric aircraft.

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thegiddystitcher 4 points 3 years ago

There's something oddly disturbing about this fact. I don't like it!

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Mister_Haste 2 points 3 years ago

The Bird-Slurry 3000 is almost complete!

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