The problem I foresee is that whatever you do you cannot increase the pressure of the air in the throat without stalling the flow, you are relying on the 'ram' effect to force air into a smaller and smaller volume, and this it will not do. The pressure might rise a tiny amount in the throat, but only until the ram pressure equals the static pressure, then flow stops. To turn your turbine you convert the kinetic energy of the air stream to rotational (torque) at the turbine shaft. If you were driving the turbine, then this venturi setup works, cause you are adding energy to a volume of air, and sucking it through the duct, but to get torque from the airstream, you need force times distance, and as the force you get from the air mass is dependent on the airspeed, the only other way to get more force is to increase the distance the force works over, the blade length. So, long thin blades, like glider wings, will extract energy from the airstream very efficiently, a small 'fan' in a duct will be lucky to overcome the drag of its bearings.
Evan, WB #12

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.

The storm issue would be a key factor, no doubt about it. With the big fans the blades are all controllable in pitch and in extreme cases they can be feathered to ride out the serious stuff. Not so with a giant ice cream scoop where there would be considerable resistance regardless of how the scoop is aimed.

You've also got the problems caused by the outside shape of your big old scoops. The load on your tower also includes the drag caused by what the tower supports. There will be the sudden loads that'd happen with a shifting wind direction during storms and such. None of those considerations exist with the present designs that are basically just blades on a relatively small generator.

Yea, pretty much what I was thinking...


Years ago I had given this idea some though and at that time the obstacles involve in the structure alone was an engineering nightmare.
When I sized the fan to work with winds of 5 mph up, I figured even for a 10-20 Kw unit, that they would have to be at least 6 meters in diameter.
Now enclose this within a scoop or shroud to boost the efficiency (not all that much of a gain) sticking that whole thing 120-200 feet up in the air was a nightmare.

Could it be made to work possibly in a commercial application, if you had real deep pocket for the R/D and construction, but still i think it is a case of very quickly diminishing return...
This is a case where you have to use Archimedes principals (he is still right after all these years) and not reinvent the wheel.

Oh, by the way...
At 30 mph and I got the DF to spin, if you had a hurricane you might be able to get 2-3 volts out of it...

For me, I am going to go with the blades attached to a generator, so much easier and cheaper, not to mention off the shelf technology.

I get the image of that Iron Eagle, arm out the window and all, did you back it up with a propellor on the same motor? Maybe 3x's the dia of the fan? For control purposes? My idea stems from an unusal stator design which might be best described as a turbine compressor wheel (model) stretched in depth or height to the same dia. The working turbine directly behind would would only occupy the area outlet of the conical stator in front of it. Low pressure behind the turbine would be created by a simple diffuser cone. Wow the more I type it out loud the more like a traditional jet turbine it sounds.