Why arent there wind powered vertical axis boat generators ?

Discussion in 'OnBoard Electronics & Controls' started by rwatson, Nov 25, 2015.

  1. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    I think shrouds on a vawt have a bit more potential than shrouds on a hawt.

    It's possible they can close the efficiency gap.
    A shroud or a couple vanes might also provide a means of self-starting.
    I would think you can accomplish anything with a shroud or vanes and a fixed rotor that you could with adjustable rotor vanes.
    A shroud could provide all of the site-specific customization, allowing the tricky bit to be standardized, kept simple, and retaining the purported maintenance savings.
    A shroud would help reduce bird kills by being more visible.


    Leo, there has been some research on Pelton wheels where a pair of nozzles fed from a manifold would basically water hammer in sequence with the buckets. This cuts way down on wasted water and improves Cp. Instead of pivoting the vawt's rotor blades, why not flutter some vanes as the blades pass by. A bit more work mathematically, but easier to build and play with. You can test many different vanes using a single fixed-blade turbine.
     
  2. Leo Lazauskas
    Joined: Jan 2002
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    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member


    Vanes, or a small Savonius inside the trajectory of the main wings can
    help self-starting, but they reduce efficiency at higher tip-speed
    ratios because they are drag devices.

    The maths for reasonable "engineering" estimates of shrouds and ducts
    isn't all that tough. I'm not that interested in it myself, but Tuck
    did some work on it after I talked to him about several years ago.
    See attached pdf.
    I have more than enough other research to keep me busy until I'm 90
    when I might retire. :)

    My colleague Brian Kirke (co-author on the papers I cited earlier) looked at
    many devices including ones similar to the Pelton system.

    I'm not sure why he rejected that style. It was too long ago.
    Kirke also looked at trailing edge flaps, and a host of other airfoil "tricks" to
    assist self-starting and increasing efficiency, as well as ways to reduce
    vibrations and manufacturing costs. Maths is so much neater and cleaner
    than engineering ;)

    One nice feature of deploying VAWTs in tidal streams is that you don't have
    to design for 100 year maximum wind gusts. The flow is much more
    predictable and gentle than open air. Unfortunately, cavitation is something
    that you have to worry about.

    Thanks for the suggestions. At least they aren't crazy, like one suggestion I
    received from a bloke who claimed VAWT could be improved by reducing the
    drag on the blades and radial arms to zero. Unfortunately, his idea was to
    enclose the turbine and create a vacuum around it. I never found out the
    details because he wanted me to sign an NDA to protect his top secret
    system.
     

    Attached Files:

  3. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    About the starting: At low lambda values the Darrieus rotor is selfstarting (if unloaded) and will run at a lambda below 1, like a Savonius rotor. The thing is that in a gusty wind it will "lock" to the wind at a high lambda when the wind drops. With increasing wind speed, it will follow up to a high operating value, depending on load.

    We learned that the hard way in the late -70ies, when we made a 2-blade Darrieus rotor for a guy. We had then a legal limit for "household turbines" with a rotor dia of max 2,5 m. The creamwhipper was designed as a rule cheater with 2,5 m in dia with a height of 5 m, to create maximum cross sectional area.

    This rotor was coupled to a three-phase squirrel cage asyncronous motor with capacitor magnetizing to make it a generator. To allow the self-starting we used a centrifugal coupling from a "Ciao" moped, and all went smoothly; rotor lazily cirkling at "Savonius speed", and soon locking into "high gear" in a gust. Which was just the very moment the customer noted that he had not attached the capacitor Cables, so there was lo load on the generator.

    By then it was too late to regret that he had neglected the advice to put a brake to the turbine hub..... Fascinating, how far wooden debris with a foil shape can fly.... luckily no one was hurt, but the project was shelved, sadly enough; I still think it had potential - very low cost per swept area.
     

  4. Leo Lazauskas
    Joined: Jan 2002
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    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    You were lucky! There have been a few deaths because people thought they couldn't accelerate through TSR =1. As you said, it makes a huge difference if they are unloaded.
     
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