Windfarms and Birds

Subject: Windfarms and Birds
Date: Wed, 12 Apr 2006 14:08:36 +1000
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.

   Paul Taylor                           Veni, vidi, tici -
                    I came, I saw, I ticked.

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