On Sun, 14 Mar 1999 08:15:42 -0500 "robert" <robt@...> writes:
>bob, yes that’s exactly it. you want a controlled situation to
>evaluate and refine designs. automobiles have benefitted tremendously
from wind
>tunnels. look at the drag coefficients of today’s cars. Best to all,
robert

A controlled wind tunnel situation might be good for early testing, but
it is pure CRAP for trying to prove a turbine design. We have been over
this subject before on this list and I'm rather sorry to see it come up
again. (Robert, don't take this personally, I'm trying to promote
understanding and perhaps some education)

OK, so you can have wind-on-demand of whatever speed you could wish. In
theory you could shorten your testing by filling the necessary data bins
very quickly instead of waiting for wind. That's one point for a wind
tunnel. But there are more points against:

First, the wind is uni-directional and does not have the same turbulence.
So, you are not likely to see failures induced by dynamic yaw effects.
Under certain circumstances the turbine yaws very quickly and the blade
may be forced back further than might be expected. If improperly
designed, It may hit the tower, leading to a very quick end.

Second, wind has stuff in it: dirt, bugs, rain, & birds. Small turbines
turn very fast and I usually can't see the rotors very well -- I doubt if
birds could either. Will a bird-strike cause a rotor failure? The point
is that you won't see these type of failures in a wind tunnel. Well,
unless you plan to fire the occasional dust storm, bird, or swarm of
labybugs at it ...?

Third, a wind tunnel should have a large test section to accomodate a
wind turbine -- much larger that the rotor. There is a boundry layer of
wind attached to the wall of the wind tunnel, which, if it impinges on
the rotor, will mean non-uniform flow over that part of the rotor. In
addition, if a turbine is placed in the center of the usually square test
section, this boundry layer might just affect the tips when they are
closest to the sides of the wind tunnel.

Fourth, you measure the wind speed before it reaches the turbine in the
test section? How fast is it actually going when it hits the rotor? Well,
the wind sees the rotor as an obstruction (like a boulder in a narrow
creek) and tries to go around the sides. When it does, it hits the wall
(or the wall's boundry layer). And the wind is forced through a kind of
venturi formed by the rotor and the hard walls of the test section. This
is never the case in the real world -- unless you have a
diffuser/augmenter around the rotor.

But, perhaps the desire is to just "beat up" the turbine with a
unidirectional wind inside a venturi -- and the fact that nature isn't
represented is already accepted?

I'm afraid I'm going to have to go with Hugh, Bob, & Claus on this one.
If you want to prove wind turbines in the real world, you have to TEST
THEM IN THE REAL WORLD. I'd go with a harsh test site and a one year test
period as previously mentioned. This, at least, would give some data of
interest to the consumer.

Wind tunnels have a place ... elsewhere.

Cheers,

Eric

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