Everything Old is new again - Flettner Rotor Ship is launched

Discussion in 'Boat Design' started by rwatson, Sep 1, 2008.

  1. hoytedow
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    hoytedow I'm not a cat.

    The stitches on a baseball help control the ball in flight. Would "stitches" on the column be of any help?
     
    Last edited: Dec 4, 2020
  2. rwatson
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    rwatson Senior Member

    Protrusions and Dimples and even spiral "fins" have all been tried.
    None of them seem to be in use any more, so it would seem the answer is no.

    [​IMG]
    MPPT of Magnus Wind System with DC Servo Drive for the Cylinders and Boost Converter https://www.hindawi.com/journals/jwe/2015/148680/

    But, there are some comments in this paper that seem to be positive about non-smooth surfaces

    "2.1.6. Effect of surface roughness In general, surface roughness affects the boundary layer flow. Advantages and disadvantages of applying a rough surface to a Magnus rotor are briefly summarized in this section. The surface of a golf ball is typically not smooth. The effect of the dimples of a golf ball is to delay separation of the boundary layer by inducing transition to turbulent flow. The result is a drop in drag from about CD¼0.4 to 0.1 [56]. Pressure drag is connected to flow separation, where earlier separation in general leads to higher pressure drag. With the help of a simple test setup, Thomson [1] explained the effect of surface roughness of balls. He demonstrated that the pressure difference measured on a rotating rough ball in a flow is more than twice that for the smooth ball. Luo et al. [57] studied the effect of surface roughness on the side force acting on an inclined ogive cylinder. The cylinder was coated with aluminum oxide particles with a relative roughness of dparticle/dcylinder¼0.0093. Their results showed that this surface roughness is capable of triggering the laminar to turbulent transition in the boundary layers of the ogive cylinder at a Reynolds number of 3.5 104 . At certain roll angles the boundary layer on both sides of the cylinder appeared to be turbulent, but at other roll angles, only one of the boundary layers was turbulent. Thom [17,18] also examined the effect of surface roughness on the lift and drag forces for the Reynolds number range 33ko Reo93k. He glued sand onto the cylinder surface but did not specify the relative roughness. The lift and drag coefficients are slightly increased for the sanded cylinder compared to the plain cylinder. In Fig. 16 the comparison of the lift coefficients of a smooth, a wooden, and a sanded cylinder is presented. Furthermore, Thom measured the torque of a rotating cylinder in still air and for Reynolds numbers between 33koReo93k [17]. He derived torque coefficients out of his results by introducing his own formulas. His formulas have to be applied carefully, as he utilized unusual units compared to today’s standard units (see Eq. (6)). One of his findings was that at low air speed rotation has the effect of reducing the air torque below that in still air, and that thereafter the torque increases with increasing air speed. Besides studies on the surface roughness of a lone rotating cylinder, extensive studies on airfoils with an integrated rotating cylinder were performed in the last decades. Modi et al. [58] made a comprehensive study involving wind-tunnel investigation, numerical simulation, and flow visualization which demonstrated that the momentum injection through Moving Surface Boundary Layer Control (MSBC) results in a significant delay in the stall angle (up to 501) and an increase in the lift coefficient. The airfoil performance can be improved further by endplate direction of rotation driving vane Fig. 15. Four-vaned cylindrical Magnus rotor, according to [51]. Fig. 16. Surface roughness effect on the lift coefficient. Data according to Thom [17]. J. Seifert / Progress in Aerospace Sciences 55 (2012) 17–45 25 proper selection of the cylinder surface condition. The cylinder with axial splines was found to be the most effective. Fig. 17 shows the effect of surface roughness and momentum injection on the lift coefficient of an airfoil, where a rotating cylinder is integrated in the leading edge"
    http://www.homepages.ed.ac.uk/shs/Climatechange/Flettner ship/Seifert Flettner apps.pdf
     
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  3. Burkhard
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    Burkhard Junior Member

    I had already thought about the rough surface. It would be very easy to test for me by turning the Coroplast sheets the other way around so that the cut side is on the outside. But first of all there are much more important things to test when testing on the water:
    - which wind directions are possible
    - speed in different winds
    - Tipping moment in the case of wind from the front / back
    The effectiveness of the Thom Fences should be tested as a constructive change. I could vary it quickly by making two additional discs with a D = 0.4 m ......
     
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  4. Burkhard
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    Burkhard Junior Member

    rwatson, thank you very much for this article. What amazes me is that their measurements have shown that P mech max is reached when the circumferential speed of the cylinders is seven times the wind speed. Maybe I misunderstood this graphic (8). Because both in the documents of Flettner and those of Prof. Lutz Fieser (Unikat in Flensburg), the maximum performance is reached at a rotor circumferential speed that is 3 - 4 times the wind speed.
     
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  5. TeddyDiver
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    TeddyDiver Gollywobbler

    Remember thou, considering the surface roughness and the separation as the end result it's most obvious reduction in induced drag, the outcome might have a very significant effect on the pointing ability.
     
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  6. rwatson
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    rwatson Senior Member

    I couldn't see a "graphic (8)". What page and Fig No is it?
     
  7. Burkhard
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    Burkhard Junior Member

  8. rwatson
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    rwatson Senior Member

    I am confused. "P mech max is reached when the circumferential speed of the cylinders is seven times the wind speed."
    is not "maximum (sailing) performance is reached at a rotor circumferential speed that is 3 - 4 times the wind speed."

    The Graph you quoted is the mechanical Input, not "maximum sail performance ... rotor circumferential speed that is 3 - 4 times the wind speed."

    We are talking about Power Input being compared to Power Output, which apparently do not correspond.

    That doesn't seem too strange.
     
  9. Burkhard
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    Burkhard Junior Member

    So, in your opinion, power is specified here, the cylinder rotation is required. Basically the power loss in the bearings etc .. I would have expected an electrical specification here.
     
  10. rwatson
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    rwatson Senior Member

    Actually, after re-reading it, I think the MPPT is the Output, not the input.

    2.3. The MPPT for a Magnus Wind Turbine
    The mechanical power produced by a Magnus wind turbine, as well as conventional wind turbines, is the product of the torque (N·m) and the rotation speed of the turbine (rads/s) according to (7). There is an optimal rotational speed producing the maximum mechanical shaft power.

    I think the difference in optimal ratio is that this experiment is using the Helical Cylinders
    upload_2020-12-8_12-12-12.png
     

    Attached Files:

  11. Burkhard
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    Burkhard Junior Member

    Thanks for your efforts.
    These are very high speeds with the small cylinder diameters ...
     
  12. Burkhard
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    Burkhard Junior Member

    Here is a very great Video

     
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  13. Squidly-Diddly
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    Squidly-Diddly Senior Member

    this is the same Flettner that created the world's first "series production" helicopter.Flettner Fl 282 - Wikipedia https://en.wikipedia.org/wiki/Flettner_Fl_282

    Latter developed into the (very popular with troops due to its unique rescue abilities) Husky.

    For some reason, I'm thinking that adding an adjustable stationary vertical blade, or two, somewhat off the surface of the cylinder would help, but I can't figure out how or where. Help the Rotor Ship, not the 'copters. lol.
     
    Last edited: Dec 8, 2020
  14. Yobarnacle
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    Yobarnacle Senior Member holding true course


  15. rwatson
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    rwatson Senior Member

    Like this ?
    "A rotatable cylinder integrated at the leading edge of a conventional wing is a favorable solution for a high lift device. In 1924, Reid and Flettner ..."
    upload_2020-12-10_14-16-33.png
    http://www.homepages.ed.ac.uk/shs/Climatechange/Flettner ship/Seifert Flettner apps.pdf

    upload_2020-12-10_14-22-51.png
     
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