UKCasual @lemmy.world Finnbot @lemmy.world 1y ago

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.

26 comments

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.
- 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."
- Trailing edge you say? So not designed to mince up birds, that's a relief.
  
  Oh they’ll still mince birds, just with the blunt side
- So why don't my CPU/case fans have serrated edges as well? Because they are too small?
  
  Some do, e.g. Noctua: https://noctua.at/en/vortex-control-notches
  
  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.
- 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?
Unless if they be milling grain those are turbines if I'm not mistaken
- Aye but doesn't sound as quaint though, does it?
  
  True, maybe they could be both? They should have little mill yer own grain stations at the bottom lol
- I guess a lot of grain mills use electric motors now, so in a way they are.
Helps them chop up birds better
Huh, TIL. Had no idea they were serrated either.
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.
- Same reason you see chevrons on the back of some modern turbofan engines
I'm sure that makes sense for some reason but all I can think of is giant comb.

Is it true they make noise? Or were they not running at the time?
- 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.
There's something oddly disturbing about this fact. I don't like it!
brb
As others have said, mostly about noise reduction. There's actually work looking whether the same concept could be developed for electric aircraft.
The Bird-Slurry 3000 is almost complete!

26 comments