Ok, Paul,
I've learnt something.
Paul Taylor said:
"On Wed, Apr 12, 2006 at 12:47:14PM +1000, Robert Inglis wrote:
Larger turbines would have longer blades. Longer blades would probably
spin at lower revolutions than shorter blades. However, the tip speed
of longer blades would still be extremely high even at low revs.
I believe that the tip speed may be in excess of the speed of sound.
(Hence the noise problem.)
Based on the 600kW generators near Crookwell, NSW, the maximum tip speed
of the rotor (44m diameter, 28rpm) is only 232kph. What little noise
there is caused by turbulence as the air passes over the rotor blade
- think glider wings, not propellers. (The "whoosh" of a White-throated
Needletail is a good description of the noise produced.)
At such speeds the significant part of the blade would probably be
'invisible', at least to human eyes.
They aren't. At top speed, a rotor blade passes any given point once
every 1.4 seconds. (Again, based on the Crookwell specs.)
I would also think that the height of the tower has more to do with
the length of the blades than anything else and, no matter how high
the tower, the tips of the blades would always be at about the
same minimum height from the ground.
It's a compromise between performance and cost; the higher the better."
The blade tips don't travel as fast as I believed and the blades make a noise
like a swooping swift.
This demands the question:
"Why is there so much concern over noise from windfarms?"
But........I do think the information on the Crookwell website is rather simplistic and needs to be
read rather carefully. Some of it (eg, the info on revs and the control thereof) seems a little
ambiguous to me.
Cheers
Bob Inglis
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