windgen.org vawt discussion

The dyson fan appears to use a comparatively low volume of air to induce a larger flow.  Their sweepers are simply amazing- well worth the turtlebucks we spent.  I would struggle spending that much for a fan.

With the pressure requirements on the VAWT blades, would the dyson principle be advantageous?

Turtle

A couple of thoughts:

1. The design they are using was used in the 1970s and 1980s as "Hush" kits to help reduce the sound produced by early turbojet engines. The need for which went away with the advent of the High Bypass Turbo Fan engine. The coupleing of a large diameter fan to the turbine section increase thrust and reduced sound.

2. Have you seen the new Dyson fan?

Some month ago i had done some experiments with diffursors.
I used a PC-Fan and glue it on the top of a bottle.
Than i put it in front of a ventilator, so that the PC-Fan works like a windmill.

You can do this experiment too. From thick paper you can build a difursor.
Its like a little funnel wich started at the repeller an ended with greater diameter behind the PC-Fan.

Using this difusor i could measure a higher rpm than without difusor.

Here a link to a stencil to build a simple difusor from thick paper :
http://www.daswindrad.de/forum/download/file.php?id=654








Bernd


-- Edited by Bernd on Thursday 11th of February 2010 07:50:26 PM

A vortex generator behind a horizontal windmill produces a stronger airflow through the turbine.
I know such kind of vortex generator as a "diffusor" around some turbines, also in germany.
The difusor generates a stronger airflow trough the windmill, but enlarge also the diameter of the turbine construction.
To calculate the effiecient you have to use the enlarge diameter in the calculation.
Mostly manufacters doesn't do so. They calculate with the pure windmill diameter.
So they get cp's above the betz limit.

Bernd

All they are doing is taking a design based on a jet engine and claiming that it would retain the same properties as a hawt. More PR and verbal "slight of hand" than science. This design shows up every so often then disappears into obscurity and then reappears as new technology.

I see a video with all kinds of fancy graphics and solid models, but I'm not sure I trust it to be accurate.  One clue is "Traditional turbines can only extract about 50% of the energy from the air...Our turbines can extract 4x as much energy as traditional turbines."   I think that means they can extract 200% of the energy that's in the air! :-)

No matter what fancy mixing of air paths you do, if you are extracting energy, then you are slowing the air down.   If you slow the air down, it becomes an obstruction for more air coming in.  This is the whole basis for the Betz limit.

To answer your original question...  We may be able to improve our VAWTs with turbulence using a method that was suggested in another thread, by making the surface properties different, maybe like a golf ball, or smooth in some parts and rough in others, etc.

Vortex augmented compact HAWT

http://www.youtube.com/watch?v=RagPPrHUMTY&feature=player_embedded#

Can we do this on a small scale?

Can it be incorporated into a VAWT?

Turtle, going deep