Wouter, possibly a stupid question: Does slowing, or increasing the rpm change the amount of vibration?
Not really, it will mostly change the frequency at which these disturbances occur.
Of course if you REALLY slowed it down then the aerodynamic forces will become alot smaller as well and so too the disturbance. However energy yield will drop sharply below some turning rate and then you win nothing. The turbines are already optimized as it is.
15rpm isn't very "fast", but I'm sure those tips are hauling butt.
Easy to calculate :
rotor blade length = about 50 mtr.
15rpm = 15 * 2*pi rad/min * 1/60 sec = 0.5*pi rad/sec
tip velocity = 50 mtr * 0.5*pi rad/sec = 25*pi mtr/sec = about 75 mtr/sec = about 300 kph or 200 Mph.
Wouter
