Re: Wind turbine shedding ice

On Wed, 10 Dec 2008 10:00:03 -0000, "Steve Pardoe"
<steveSP@xxxxxxxxxxxxx> wrote:

I agree it's counter-intuitive, but for the large scale turbines used for
wind generation a few slim blades (typically three) are more efficient than
a lot of smaller ones. I think it's to do with the interference between
blades, each blade having to operate in the slipstream of its neighbours, so
adding more blades offers diminishing returns from the extra material and
cost. It also explains why the turbines are widely spaced on the ground. I
have no idea whether the old-fashioned "prairie" wind pumps were efficient
for their scale, or whether they were just designed intuitively or perhaps
simply cheaper to make and install.

Modern wind turbines work by generating aerodynamic lift on one side
of the blade in a similar way to an aeroplane's wing. The most
aerodynamically efficient design would be a single blade but the
unbalanced stress would be an engineering nightmare. Most wind
turbines have 3 equally spaced blades as this design is balanced
around it's axis orf rotaton, and has a constant turning moment for
when the wind changes direction.

The old-fashioned "prairie" wind pumps and traditional wind mills work
on drag rather than lift. They are much less efficient and designed
mainly by trial and error, it's largely a case of more blades is
better.
.

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