Vertical axis windmill question

[Merlino]

Hi all
Look at this VAWT:

http://img379.imageshack.us/img379/8044/alpha2lgjr7.th.jpg

I'm wondering what happen inside of that kind of turbine: i can't figure out if wind can enter in the middle and how it could affect turbine behaviour from inside...
I don't speak english perfectly so i've done a couple of designs to clarifying my question.

Here is the same turbine,
without shell:

http://img169.imageshack.us/img169/4426/turbinasenzaguscioxe0.th.jpg

and with shell:

http://img294.imageshack.us/img294/3644/turbinacongusciodj3.th.jpg

What kind of behavioral differences between the first one and the second one?
Thanks a lot

 

[Merlino]

Ops... sorry.. i've linked some really small images...
I try again with some bigger ones!

Real turbine:

http://img238.imageshack.us/my.php?image=alpha2lgqz4.jpg

Turbine with shell:

http://img525.imageshack.us/my.php?image=turbinacongusciopz4.jpg

Turbine without shell:

http://img103.imageshack.us/my.php?image=turbinasenzaguscioee4.jpg

Bye

 

[dalcazar]

It looks to me that surely the air flow can get inside the body of that wind turbine, it probably flows out the open top of the cylinder (or the bottom). Putting a cylinder inside the body would probably inhibit that flow and limit the amount of air passing thru it. In that case you would be generating power only based on drag, if you keep it open and let the air out you can get lift induced power as well.

There are some similar turbines with shrouds that duct in wind from one direction much like a snail shell and in those cases the air flows out the top and there is no drag from the wind against the vanes that are not in the perfect position to catch the incoming wind.

 

[Compositepro]

I'm guessing that turbine is used to measure wind speed. I don't see a generator and I don't think it would be efficient for energy extraction. Air would enter the center of the spinning squirrel cage and exit the downwind side. In design principles it is similar to an attic ventilator.

 

[crysta1c1ear]

Sound is carried by air molecules and the speed of sound is around 330 m/s. Since wind speed is significantly less, air molecules will have no problem getting in and out of the rotating cage. You can shout to somebody upwind of you. So wind speed is slow in comparison and the air will go whereever it wants.

If a bridge has a support in a river, then the flow rate has to increase to get the same mass of water through a smaller area.

So in my opinion the filled cage will provide more flow over the blades and increase performance.

 

[tmoritz]

This is a cross flow turbine. Usually it is shrouded. The basic principle is you get reaction forces as the air enters through the blades into the central void then again as it exits. Do a search on "crossflow" or "crossflow turbine" and see what you come up with. You'll probably find a lot of fans.

Tom Moritz
Mechanical Engineer
US Bureau of Reclamation

 

[tbuelna]

If it's blades are fixed pitch (as it appears) it a cross flow turbine. If the blade's pitch is actively varied throughout the rotation, I believe it's called a cycloidal.

http://www.rexresearch.com/kirsten/kirsten.htm

 

[Sparweb]

There's a fan like that in my microwave oven and my furnace.
The designer of this VAWT got his inspiration from sources like that. A shroud would help, like Tmoritz suggests, but implementing that would be complicated, since it would have to turn to follow the wind direction.
Do these guys offer any performance data?


Steven Fahey, CET