Evan,
I am with you on this one...
I really do not think it is workable but tried to work out if you could use the shape of the shroud to form a low pressure area at the exit to enhance the venturi effect.
My thought with the sketch I put up was trying to enhance the venturi effect, by trying to set up the exit to add a bit of suction.
Keep in mind you are going to get a bit of pressure drop as the wind moves about the external shroud, granted not much but some...

Paul


Like I said this was something I was thinking about years ago (and dismissed as unworkable), I doubt that you could get much or any spin out of it.
Just for grins, I am going to hang a electric df unit out the car window and see if it will even spins as a test...
With a load I bet I have to do 50-60 mph just to get 1-2 rpm out of it, that is if it spins at all...


The only reason I had even thought about it was the old style wind mills used out on the plains to pump water, they were a fan as opposed to blades used in today's modern wind turbines.