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'[TECH]:: Wind Turbine blade section and performanc'
2010\07\02@162708 by

Useful online wind-turbine blade design calculator that accepts design
parameters and outputs desired blade section at a user chosen number of
points along the blade. Feed the output to your NC machine (or your 3D
printer)  and ... :-).

Also provides a table of thrust, Watts, starting torque, power, RPM for a
range of windspeeds.

http://www.alton-moore.net/wind_calculations.html

I haven't checked to see if I can establish the correctness of the
underlying formulae that he's using but, if he's done as a good a job as it
seems this could be a useful "what if" calculator.

Interesting and not wholly intuitive relationships can be observed  by
playing with such a calculator.
eg what he terms "Prop tip/speed ratio" (commonly 'tip speed ratio' or TSR)
is the ratio of the velocity of  the propellor tips relative to the wind
speed. Higher ratios tend towards higher efficiency and more power per size.
Very high ratios (say 10:1)  result in brutal noisy machines which tend to
tear themselves apart and whose blades are subject to substantial erosion
from dust or even rain. These are the ones you can hear before you can see
them.
What may not be  obvious is the effect on startup  torque, which decreases
with the square of the tip speed ratio. A very low TSR design will produce
unspectacular RPM and probably lower efficiencies but MUCH more starting
torque. If you want a machine that will turn lazily in the slightest breeze
and produce at least a tiny amount of power in a;lmost any conditions then
low TSR is your friend.

The more widely know cubed power increase with wind speed is readily seen.
A prop which will produce 10 Watts in a 3 m/s breeze will produce 3 kiloWatt
in a 20 m/s (40 mph) storm.
The need for proficient braking / feathering / pitch control / stalling /
depowering mechanisms is clearly demonstrated.

Russell McMahon

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