Apptech wrote:
> I'm trying to understand flat-plate lift well enough to
> model "bent flat plate" vertical axis wind turbines. While I
> started off thinking that these were a trivial or simplified
> version of a Savonius Rotor it appears that they are a
> combination lift and drag machine.

It's not clear what machine exactly you are referring to.  It is possible to
use flat plates in a pure drag design, like my idea explained at
http://www.embedinc.com/wind.

Most of the literature I looked at automatically assumes that lift is
somehow inherently better than drag, but I don't think that is true and I
haven't seen any justification for it.  I think lift was probably shown to
be better than drag for a particular application, and the conclusion has
stuck but the specific constraints forgotten.  Lift designs can intercept
more wind area than drag for the same airfoil area, but that is just one of
many tradeoffs in wind turbine design.

One advantage with drag designs is that the parts move slower than the wind
and therefore don't pose a hazard to birds.  The optimum power point for a
flat plate getting pushed straight downwind is 1/3 the wind speed.

A commercial group is trying to build a wind farm in Nantucket Sound off the
coast of Massachusetts, and the NIMBY crowd (even though it's miles from the
nearest back yard) are trying to squash it on the basis of birds getting
killed, so this is more a issue than it might appear at first.


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