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This discussion relates to Technology Review's article A Design for Cheaper Wind Power .

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  amills61
  

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  12/01/2008 02:58 AM

  A good dose of history first

  Lots of attempts to make this type of technology work - it's worth a comparison to the previous trials to judge the new design:
  
  http://www.ifb.uni-stuttgart.de/~doerner/diffuser.html

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    phoenix
    

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    12/01/2008 10:01 AM

    Re: A good dose of history first

    If a good dose of history on the subject of windmills is just what the doctor ordered,  amills, just Google it. You will find that this technology can be traced back to the 1100's. Researching the historical background of any subject, which you might find interesting, is always a good place to start.

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      Kevin Bullis
      

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      12/02/2008 12:52 PM

      Re: A good dose of history first

      As the article says, the idea of a ducted design isn't new. But the use of something called a mixer-ejector, see comment below, is new.

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    arnetwork
    

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    12/01/2008 06:02 PM

    Re: A good dose of history first

    Try following the link on the animation referenced in the T.R. article. It is the most unfriendly and incompetent web site that I have ever seen. I tried to send them an email about their site but it is so poorly done I don't know if the message got sent or not.

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      Kevin Bullis
      

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      12/02/2008 12:52 PM

      Re: A good dose of history first

      Are you referring to the Flodesign website, or to this one? The link to the video with this article seems to be working.

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      Brittany Sauser
      

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      12/02/2008 01:14 PM

      Re: A good dose of history first

      arnetwork,
      
      I have checked the link and am not encountering any problems playing the video. I am looking into any technical issues that may have occurred when you tried to view the video. At the very bottom of the page is a "Feedback" link (http://www.technologyreview.com/cust/feedback.aspx) where you can send any issues or complaints. You can also email me directly as I would like to hear the details of the problem you encountered: brittany.sauser@technologyreview.com.
      
      Thanks,
      Brittany Sauser

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  NorthernPiker
  

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  12/01/2008 09:20 AM

  Synergy with Wind Prediction Techniques

  Given its sensitivity to wind direction, there should be further gains from this new design with an improved an ability to predict the wind direction and velocity a la your Nov. 6th article, "Laser Sensors for Wind Turbines"
  
  http://www.technologyreview.com/energy/21643/?a=f

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  Peter Williams
  

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  12/01/2008 10:15 AM

  Another benefit...?

  I'm guessing that this new design will have another benefit.  Unlike a conventional wind turbine it would appear more likely to be viewed as a solid object by birds, so they don't fly into the blades and get chopped up.  This is a big issue, for example, with the Altamont Pass windfarm in CA, which is on the Pacific Flyway - as a result, they regularly find diced eagle and such on the ground, which is to put it mildly an ecological drawback...

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    roberthe
    

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    12/02/2008 06:03 PM

    Re: Another benefit...?

    Have you ever seen a sliced up dead bird below a wind turbine? I have worked around wind turbine for 5 years and have never seen one. Wind turbines being responsible for slicing up birds in flight is an urban myth that sounds plausible, but in reality is not true.
    
    Wind turbines, depending on the wind speed, turn relatively slow (~20 rpm), much too slow to swat an unsuspecting bird. The blades are large (i.e. scary), move slow, and the system’s generator and gear box makes enough noise to warn or deter most birds or flying creatures from approaching the wind turbine when it active. Its possible that a bird could be struck by a moving wind turbine, but it is the rare exception not the rule.
    
    When you drive through northern Germany, and Holland you can see 100s of wind turbine systems actively working, large ones, small ones, some with one, two, and three blades, all installed in the last 15-20 years. Have you heard of Germany or Holland’s Environmentally active Green Party leaders complain of a demising bird population? My guess is that more birds die from flying into windows than by striking or being stuck by a wind turbine.

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  Silverthorn
  

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  12/02/2008 01:41 AM

  This is bilgewater!!!!

  I can't believe that the editors an a technology publication affiliated with MIT would let this piece of gargage get past them!  It reflects a total ignorance of basic physics -- say the conservation of energy, for starters.
  
  Any wind turbine device (regardless of design) produces power by extracting kinetic energy from the stream of passing air that it is able to act upon.  "Extracting kinetic energy" means "slowing it down". You absolutely cannot avoid slowing the air flow, as the video and article suggest, and still generate any power.
  
  When the speed of an air flow is reduced, the flow necessarily broadens and forces a portion of the upstream flow to divert around it.  The Betz limit is what you get when you optimize the tradeoff between the fraction of the kinetic energy extracted from each ton of air passing through the turbine's area of influence and the total flow through that area.  It's a fundamental limit, and can't be circumvented by clever design.
  
  There's some wiggle room in determining just what the turbine's "area of influence" actually is.  For a conventional wind turbine, it's the area swept out by the rotating blades.  For a shrouded device like this one it's .. something different, and very hard to calculate.  But the shroud can indeed act to enlarge the turbine's "area of influence", and accelerate the air flow through the turbine itself.
  
  As somebody noted above, it's been tried before.  Didn't work out too well, as the shroud was heavier and less effective at increasing output from the ducted fan than simply making the blades longer.
  
  This design does have a novel feature that I don't think anyone has tried before, and that's the scalloped trailing edge on the shroud.  It's just possible that the turbulent flow induced by those scallops does actually work to enlarge the turbine's "area of influence" more effectively than a smooth shroud. 
  
  If that is the case, you'd never know it from the article and video.  And it's inconsistent with the other big claim that is made, which is that these devices don't need to be spread out the way conventional conventional wind turbines must be.  Any wind device that can extract as much power from the wind as a conventional turbine will end up needing to be just as widely spaced from its neighbors as the conventional wind turbine.  That too is a fundamental consequence of fluid dynamics that can't be circumvented.

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  • 
    04heinm
    

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    12/02/2008 10:36 AM

    Re: This is bilgewater!!!!

    The bulk of your response is correct for free stream flow but this design is based on ducted airflow whereby the Betz Limit no longer applies.  Redirecting fluid flow is difficult but we do it all the time in jet engines.
    
    Have no fear...the space-time continuum will not lose its flux capacitance and the new Star Trek movie will still be in theaters May 2009.

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      jtencer
      

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      12/02/2008 10:53 AM

      Re: This is bilgewater!!!!

      It is not duct flow downstream.  The wake created by this should be significantly greater than that of a similarly sized conventional turbine.  You would have to space them farther apart if you have more than 1 row of them.  Meaning that even if you could space them closer together, you still wouldn't most likely be getting a better value for your acreage.

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        dmm
        

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        12/02/2008 12:21 PM

        Re: This is bilgewater!!!!

        Every wind farm picture I've ever seen only has a single row of windmills, usually along the top of a ridge.  Is this not the most common distribution?

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        Kevin Bullis
        

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        12/02/2008 12:49 PM

        Re: This is bilgewater!!!!

        What makes you so confident that the wake will be greater with the ducted design?

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    Kevin Bullis
    

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    12/02/2008 12:47 PM

    Re: This is bilgewater!!!!

    The "scalloped edge," as you call it, is part of something called a mixer-ejector. It mixes the faster air from outside the shroud with the air inside that was slowed down by the turbine blades. The way it mixes the two air streams creates vortices that make it possible to have a shorter duct (by increasing the interaction between the slow and fast air streams).
    
    The Betz limit was calculated specifically for open-bladed turbines.

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      Silverthorn
      

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      12/02/2008 04:08 PM

      Re: This is bilgewater!!!!

      It's not the design of the device itself that I'm saying is bilge, it's the claims for it made in the video and article.  They're totally bogus. 
      
      Whether the turbulent diffuser enables this device to work more effectively than earlier efforts in the same direction design remains to be seen.  It's at least plausible.
      
      If one defines the Betz limit only with respect to the diameter of the turbine or fan blades, then yes, it doesn't apply for a ducted fan.  That's why I used the more general term "area of influence".  The diffuser shroud can make the turbine "appear", to the wind, do be larger than the diameter of the fan blades. But the principles from which the Boetz limit was derived still apply: to extract power, you have to slow the air flow.  And the more you slow it, the more faster moving air in the upstream flow will divert around the obstruction.  Think of cars on a 6-lane LA freeway; if cars in the middle land are slowed to 35 mph at some point (by, say, a bad stretch of paving), you can't have all the cars in the lane behind them continuing at 70 mph without changing lanes. 
      
      What's true for an individual wind turbine applies as well to any wind farm as a whole; the amount of power it can produce depends on its area, and no tricks with shrouded fans or turbulent mixing can circumvent that limitation.

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    nielkmot
    

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    12/02/2008 02:43 PM

    Re: This is bilgewater!!!!

    all these arguments are very reminiscent of the "proofs" that airplanes cannot fly, and other such wonderful historical footnotes.
    
    there are many examples of inventions that "broke the rules", such as the jet engine or the laser or the transistor.  (and there were even more hoaxes along the way.)
    
    the best answer to both the promoters and the skeptics is to try the device and see what it can do.  as groucho might have said: "keep an open mind, but check your fly."

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  • 
    john@techreview
    

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    12/06/2008 02:17 PM

    Re: This is bilgewater!!!!

    I have a funny feeling about this one too. I don't see how you can extract energy from the flow and have the outlet velocity be greater than the inlet. 
    
    Maybe they are using their jet engine models and didn't get all the pluses changed to minuses ;)
    
    Perhaps someone with better fluids knowledge can explain.

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      judbarovski
      

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      12/07/2008 07:08 AM

      Re: This is bilgewater!!!!

      the jet like design with many blades offered has much  more material capacity, hence much heavier and expencive then conventional two/three blades wind turbines 8-(

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