Olin Lathrop <olin_piclist <at> embedinc.com> writes:

> 
> Peter wrote:
> > But the most efficient turbine is the two-blade 'propeller' type, by
> > far.
> 
> And why is 2 blades more efficient than some other number, like 3 or 4 or
> more?

I don't know the details. Any aerodynamics manual says so. 2 blades is most
efficient (1 blade may be even more efficient). All the others lag this. Going
from 2 to 3 blades etc. changes the power density not the efficiency.
2-blade top efficiency is given as >75%. Even two 2-bladed props one after the
other (tandem) are less efficient than one 2-bladed one. It is something to do
with the disturbed air (non-laminar flow) I think.

Google has a lot of material on this, usually applying to aircraft propellers,
not wind turbines. Here is a good start (the abstract is relevant):

http://naca.central.cranfield.ac.uk/report.php?NID=1544

the top page is also full of gems (from 1939!):

http://naca.central.cranfield.ac.uk/

I was looking for this page some days ago and could not find it ... hmm.

Peter


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