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Effectiveness of Dimpled Wind Turbine?

  1. Jun 21, 2011 #1
    http://www.sauerenergy.com/index.php?option=com_content&view=article&id=50

    The link above gives a picture and rough model of a Sauer Wind Turbine.

    I was wondering, since the dimples on the turbine were based on the idea that a golf ball reduced air resistances, how it would help the wind turbine?

    Since a wind turbine requires having a lot of drag from the air to help turn its blades.

    I do know that the dimples are on the side of the blade that shouldn't be catching the air, just wondering if it is effective.

    Also, the vertical wind turbine doesn't seem to spin very fast, how would that affect its energy output?

    It says elsewhere on the website that it is a 3.2 kwh unit, but what does that mean? I'm not sure if it can generate 3.2 kwh per hour.

    Any comments on the shape affecting things?

    (Was wondering since I saw this in a magazine, and it uses the golf dimpled blades as a marketing strategy, and wanted to know if it had a solid legitimate scientific basis to actually help the blades turn better)
     
  2. jcsd
  3. Jun 22, 2011 #2
    wouldnt this be better posted in the aero subforums?

    also, wouldnt "3.2 kwh per hour" be the same as 3.2 kilowatts ...

    off the top of my head, i think that the turbulence caused by the dimples will cause boundary layer seperation in the airflow which should reduce drag... but this is is mostly going in the opposite direction of the airflow, so im not sure how it applies here
    i've seen a paper where they modelled the airflow around a Savonius turbine and they showed the highest drag was around 3/4 of the way outside of each blade, perhaps their 'air disrupters' should be concentrated on that region?
     
  4. Jun 22, 2011 #3

    boneh3ad

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    Whoever wrote that page is pretty much a clown. Not very much of it makes sense. I can only hope it was some secretary that wrote it and not an engineer.

    Turbulent boundary layers are remarkably resistant to separation. In fact, the point of golf ball dimples is to prevent boundary-layer separation. Also, separation generally increases drag quite a big, not the other way around.

    In this case, the dimples seem to be doing the same thing in helping to keep the boundary layer attached as it flows along the back surface so that the air strikes the "torque converters" and helps turn the turbine. If the boundary layer instead separated, a large portion of the air would miss the converter and you would lose a ton of power.
     
  5. Jun 22, 2011 #4
    ah thanks for clearing that up, never realized i had it the other way round all this time
     
  6. Jul 7, 2011 #5
    It's designed to work like an anemometer where the wind resistance on one side is higher than on the other side. That's what the dimples are for, they reduce the wind resistance on the back of the blade while the vanes on the front of the blades increase the wind resistance. The whole thing is meant to rotate.
     
  7. Jul 8, 2011 #6

    boneh3ad

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    Dimples do not decrease drag the way you seem to think they do. They trip the boundary layer to go turbulent. Turbulent boundary layers are much more resistant to separation due to an adverse pressure gradient than a laminar boundary layer.

    For a golf ball, a smooth ball separates right around the top and bottom, leavin ga massive low pressure region. Behind it and causing a tone of form drag. With dimples, you trip the boundary layer so it stays attached farther back, making this separated region smaller and decreasing form drag. However, you increase viscous drag, just not as much as you decrease form drag.

    Here, it honestly doesn't appear to be drag related. Dimples on that side would not decrease drag.
     
  8. Jul 8, 2011 #7
    there is also a minor lift component as the blades are travelling sideways with respect to the wind direction, with a 2 bladed savonious design the blades are always exposed to the wind at all angles, but with 3 blades there is a certain angle where one blade will be obscured by the other 2 blades

    the point is, when the blades are at a sideways angle to the wind, the curvature acts like an aerofoil and creates a low pressure region which moves the blade forwards... it has the maximum effect with 2 blades, but with 3 blades the effect is less but still present... i wonder how will the dimples affect the lift factor...
     
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