Anyone ever tried a "ducted fan"?
By nanotech, Section Wind Posted on Thu Dec 01, 2005 at 03:27:47 AM MST
I'm interested in feedback on an idea.......

After much interest in Dr. Moller's Skycar ( LINK ), I've often wondered about the feasability and added efficiency of adding a "ring" to the outside of a HAWT. I know it VASTLY increases the efficiency of a propeller, just wondering about in the reverse..... For those wondering just what I'm talking about, a picture paints a thousand words.... The only thing those pics don't point out is that the ring wouldn't be mounted to the end of the blades. It would make the blade assembly entirely too heavy and the gyroscopic forces of something like that would be INCREDIBLE!! I just didn't have the time (nor the energy this late at night) to complete the drawing like I would have wanted to. Any thoughts, ideas, rants, condemnations? :)

Anyone ever tried a "ducted fan"? | 13 comments (13 topical)

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#1) by Norm on Wed Nov 30, 2005 at 09:05:55 PM MST

It would make the blade assembly entirely too heavy and the gyroscopic forces of something like that would be INCREDIBLE!!     No problem.....   It'll see it as a complete ring...   At least that's the way they explained it in Popular Science about 40 or 50 years ago.                  (  :>) Norm ( :>) Norm

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#2) by richhagen on Wed Nov 30, 2005 at 09:59:27 PM MST

I think there was or is a company in England that sells a small "rooftop" wind turbine maybe 3 or 4 feet in diameter, with a ringed blade like that.  I beleive they claimed that it made the assembly stronger and less likely to fail.  Rich 'A Joule saved is a Joule made'

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#5) by CG on Thu Dec 01, 2005 at 03:19:15 AM MST

It's the Swift turbine and you can find that at www.renewabledevices.com. [ Parent ]

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#9) by elvin1949 on Thu Dec 01, 2005 at 08:34:24 AM MST

I think he is saying run the prop inside a short tunnel IE venturie. later elvin [ Parent ]

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#3) by Laylow on Wed Nov 30, 2005 at 10:48:13 PM MST

I think that's called a "ducted wind turbine" or dwt.  If you start going in that direction I would be thinking about a big funnel with a tiny turbine.  Then you have to think about keeping it pointed at the wind.  I personally like the idea for many reasons but I'm not very familiar with the obstacles involved.  Do a search for ducted wind turbine.

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#4) by hobot on Wed Nov 30, 2005 at 11:17:39 PM MST

Here's some ways to skin ducted turbines http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Urban%20wind.htm http://www.ibpsa.org/PDFs/BS03%20Papers/BS03_0407_414.pdf http://www.ifb.uni-stuttgart.de/~doerner/diffuser.html http://www.halfbakery.com/idea/Wind_20Sail_20Generator http://www.worldchanging.com/archives/001079.html http://www.cd-adapco.com/press_room/dynamics/21/wind_turbines.html http://www.imagineeringezine.com/e-zine/wind-4.html http://www.treehugger.com/files/2005/11/ultra-effective.php http://www.treehugger.com/files/2005/11/windside_vertic.php http://renewableenergylaw.blogspot.com/2004/12/wind-turbines-without-support-towers.html

great links :) (3.00 / 0) (#11) by willib on Thu Dec 01, 2005 at 04:51:51 PM MST

great links the first one said that 60.61 Watts is a practical number for power from a .6m (23.6 inches) dia , ducted wind turbine, with a 10m/sec (22MPH) wind . although that is a pretty stiff breeze ,it gives me hope that maybe one day i could fly my gen. to be, with small blades.. Carpe Ventum (seize the wind) One needs faith in the future [ Parent ]

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#6) by Kwazai on Thu Dec 01, 2005 at 06:13:15 AM MST

thinking outside the box-so to speak. it seems to me (and I'm no expert) that the 'ducting' serves to straighten the airflow, such that a pressure drop would occur behind the turbine that would be higher than unducted. this pressure drop would increase the volume flow(velocity?) thru the turbine blades. I would hesitate a guess that the frontal area of the ducting as it relates to the pressure drop at the back would be only a small percentage- something like a draft enhancer on a chimney. I would wonder if having a larger opening at the back of the turbine would work better than having it in the front(as compared to just having a larger turbine overall?) . anyway my .02$. L8r Mike

"ducted fan"...another offshoot (3.00 / 0) (#7) by spinner on Thu Dec 01, 2005 at 06:39:00 AM MST

http://saving.nu/wind/winddesignprimer.shtml proposes another way to utilize shrouding; seemed like an interesting concept too. spinner

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#8) by finnsawyer on Thu Dec 01, 2005 at 07:57:02 AM MST

Adding the ring, whether it is connected to the blades or not, serves to break up the power robbing vortices that form off of the blade tips.  If the ring is connected to the blades it will stiffen the blade assembly so it can not bend back.  In the case of free blades, as they bend back the distance in the circle around the blade tips becomes less.  The ring prevents that, so it stiffens the assembly.  As far as putting ducting around the blade assembly, that affects the velocity profile of the air through the blade assembly, which means you need to know what it is and need to design the blades accordingly.  Various ducted schemes have been proposed over the years, but apparently they were not too successful. GeoM

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#10) by DanG on Thu Dec 01, 2005 at 12:39:39 PM MST

Wingletts at the blade tips reduce vortice & increase efficiency - though on small scale turbines it may be possible to wrap them around 360°, susceptibility to turbulence stress increases several orders.. Since winglets are proprietary data, studying working turbines may give clues. Unknown if these pictures are accurate size wise. Enercon uses a low rpm design - three pictures lifted from Enercon's 'windblatt' newsletter showing wingletts follows: Looking like a whale flipper w/ tiny winglet just visible: Exagerated winglet perhaps? Top blade you can see the winglet shadow: Anyhow - thats my two-bits worth... [ Parent ]

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#12) by finnsawyer on Fri Dec 02, 2005 at 08:21:50 AM MST

I don't know what you mean by "turbulence stress".  The ring, because it is of uniform cross section, will not introduce any turbulence arising from its rotation.  Forces on the ring can be reduced by streamlining it.  I believe that the added stiffness more than compensates for these added axial forces.  Both the ring and the winglets will add their own peculiar effects to the air flow.  In the case of the streamlined ring it will be a speed up in the airflow near the blade tips as well as a reduction in the tip vortices.  In the case of the winglets, other than the effect on the vortices, ? GeoM [ Parent ]

Re: Anyone ever tried a "ducted fan"? (3.00 / 0) (#13) by ghurd on Fri Dec 02, 2005 at 09:28:43 AM MST

Everyone remembers Peppyy's "Sputnic" blade right? He did quite a bit of testing later. http://www.fieldlines.com/story/2004/11/24/17554/089 G- Ghurd.info

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