Salient White Elephant

April 13, 2009

High Altitude Guyless Darrieus

High Altitude Guyless Darrieus
The key to this idea is that the torque tube encircles the top of a tubular tower (like you’d expect to find on a modern multi-megawatt horizontal axis wind turbine). Aerodynamic forces are approximately balanced with respect to the middle of the torque tube (that is, halfway down its longitudinal dimension). And the middle of the torque tube is the part that engages the bearing at the top of the tower. So aerodynamic forces inflict only a small overturning moment on the torque tube, and this overturning moment can easily be carried by some kind of wheel or bearing at the bottom of the torque tube that also engages the outside of the tower. The gearbox and generator are situated at the top of the tower just like they would be in a horizontal axis machine. Alternatively, the center part of the torque tube (barely visible in the above diagram) can extend all the way down to ground level where it connects to the gearbox and generator, all of which live in the comfortable surroundings of the inside the bottom of the tower.

I favor three bladed VAWTs, but I usually just draw two blades because it makes the diagram easier to understand.

The rule of thumb for siting horizontal axis wind turbines is that turbines should not be closer than two or three rotor diameters. I assume this means that by the time the streamtube has traveled two or three rotor diameters past the rotor disk, it has been re-energized by the surrounding wind. For this reason, I keep wondering what would happen if the diameter of a Darrieus rotor were three times larger than its height. Wouldn’t this mean that the maximum amount of energy that the machine could extract from the wind would be not 60%, but 120%? (60% for the upwind arc plus 60% for the downwind arc.) If so, wouldn’t this mean that the efficiency of a large diameter Darrieus might rival or even surpass the efficiency of a horizontal axis machine? In this case, we can build very robust arms that extend from the torque tube, two arms for each blade, and make the diameter very large. The parts of the arms near the axis of rotation can be large, very stiff, and very robust because the velocity is low near the hub, so we don’t need to worry about the arms generating too much drag.

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2 Comments »

  1. I have been doodling and researching for several weeks as I also am a little fixated on vawt turbines.

    I really like the design, I was on a similar concept and principle when I perused the diagram.

    I like your elaboration on extending blade diameter distance.

    The concept that is interesting is variable blade size and diameter in proportion to distance from centre.
    Possibly at the farthest point the blade would be at it’s widest and thickest?

    IDEAS
    In reaction to your design, I would consider joining the blades at the top. This could create better strength. Creating a more harmonious Darrieus shape/ possibly less stress. Joining the top, could be done with cabling?
    (This is in relation to the curve ie Quadratic Parabolic Curve/ Troposkein Curve~I am not so well versed in the technical names ;~/)

    Blue H shape
    I would like to see an A instead of a H design. I don’t know which would be better, but with an A, it may be more efficient with materials and lend to your concept of expanding the diameter.

    Lovely design, good job. ;~D

    Comment by Plus46 — September 7, 2009 @ 10:53 am

  2. I found a similar production model of a small turbine design.

    http://energysavingnow.com/plugin/windturbine.shtml

    An image link: http://energysavingnow.com/plugin/images/pluginwind.jpg

    These need to be blended with another type for self starting purposes. Savonius seems best.
    I would like to see a HAWT though!

    ;~D

    Comment by Plus46 — September 7, 2009 @ 11:22 am


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