Everything Old is new again - Flettner Rotor Ship is launched

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

  1. philSweet
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    philSweet Senior Member

    There aren't any scaling coefficients. Flettner rotors don't scale with Reynolds Numbers or anything else. At the top of the page was a report that when the wind changed from 8 to 12 knots, the drive force didn't change much. That makes perfect sense, and is an indication that there are no scaling laws for these machines whatsoever. This is true of most powered machinery by the way. When you quit thinking about it like a sail and instead think about it like a motor, you'll stop making these mistakes. You can't adapt data from one machine to one with different geometry. You can't relate rotor power to propulsion power across a range of sizes using coefficients. You can't relate rotor speed to performance across a range of sizes using coefficients. Nothing of interest scales nicely.
     
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  2. rwatson
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    rwatson Senior Member

    Yes, I remember that now. I just relooked at the spreadsheet, but to my untrained eye, it still didn't provide me with any insights.
    I find the Power to Rotate column , which doesn't state the units, ( I presume Watts), and the term "spin ratio", isn't meaningfull to me either.
    Are we talking surface speed to wind speed, surface speed to another dimension etc. ??


    It doesn't even correlate to my current project specifications, as the aspect ratios aren't within range.
    The other obvious mystery is what is "Power Cylinder", and "Power Plate" ?

    XLComparison.png

    In my ideal world, I would get someone to do a spreadsheet using Norwood's inputs.
    I can provide the preceding pages to anyone who would like more info.
     
  3. rwatson
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    rwatson Senior Member

    Meanwhile, an inspiring video example,

     
  4. Dolfiman
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    Dolfiman Senior Member

    Ok, so these clarifications about my file + a numerical application with your data :
    "Power to rotate / aero" means exactly the required power to rotate the rotor due to the aerodynamical friction on the cylinder and on an end plate if any :
    >> the column "Cp cyl" gives the adimensional coefficient used in the power formula for the cylinder (=rotor) part :
    "Power cyl" = Cp cyl * Cf * (1/2 * ρ * Sw cyl) * U^3
    Power cyl : in Watt
    ρ : is the air mass volumic of air (kg/m3)
    Cf : is the friction coefficient, that you can compute using Re = U*D/ν and Cf = 0,075 / (log10(Re) - 2)^2
    Sw cyl : wetted surface of the cylinder (m2)
    U : the upstream wind speed (m/s)
    >> the column "Cp plate" gives the adimensional coefficient used in the power formula for the end plate part :
    "Power plate" = Cp plate * Cf * (1/2 * ρ * Sw plate) * U^3
    Sw plate : being here the « wetted » surface of the end plate between diameters D (cylinder) and De (Diameter end plate) = π / 4 *(De^2 – D^2)

    Numerical application using your data (see also the revised file attached and with your input data) :
    Your input : Aspect Ratio 5,36 and Speed ratio 3,498 >>> Cp cyl = 59,76
    *** Estimation of the power to overcome the aerodynamical friction drag on the cylinder alone (without end plate) :
    U = 15 MPH = 6,71 m/s
    Length 3m ; Diameter D = 0,56 m >> Sw cyl = π D L = 5,278 m2
    v = air cinematic viscosity ~ 1,429 E-5 m2/s (estimated)
    Re = UD/v = 2,63 E5
    Cf = 0,075 / (log10(Re) - 2)^2 = 0,00641
    ρ ~ 1,23 kg/m3 (estimated)
    >>> Power cyl = 59,76 * 0,00641 * (0,5 * 1,23 * 5,278) * 6,71^3 = 375,6 W
    Is this power corresponds to the order of magnitude you have in mind ?

    *** To add an end plate of Diameter De = 1,5 * 0,56 m = 0,84 m :
    The file >>> Cp plate = 49,97
    Sw plate = = π / 4 *(De^2 – D^2) = 0,308 m2
    >>> Power plate = 49,97 * 0,00641 * (0,5 * 1,23 * 0,308) * 6,71^3 = 18,3 W , so an extra +4,9 % of required power

    *** CL and CD also given by the file (here, my approach was to use the numerical results of the De Marco and al. 2016 investigation attached, with ponderation factors to fit with available tests results : the Ackeret tests as reported by Pearson 2014 also attached and the Naca Reid tests) :
    CL = 9,28 / 8,87 in your file ; from the CL curve, with this speed ratio you are quasi at the maximum lift
    CD = 2,37 / 1,202 in your file ; from the CL/CD curve, the better lift/drag ratio is for speed ratio ~ 1,65, giving CL/CD ~ 5,3
     

    Attached Files:

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  5. rwatson
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    rwatson Senior Member

    Wow. Fantastic effort. I have just finished assimilating the formulae for the first time, and may have other questions soon , but this analysis provides one of the best answers my simple mind has gotten.
    The approach looks very similar to Norwood's methodology, as far as I can tell.

    Thank you for your efforts. Very much appreciated.

    ~ 400 Watts x 1.5 for mechanical losses (600 watts) = about 25 Amps on a 24 Volt system, is valuable information for my current project. Just by sheer luck, I bought 30 amp fuses.
    BUT - I guessed a suitable electric motor of 250 Watts, which now looks way too small. It looks like my anticipation of having to buy a bigger motor is now reality.
    The experimenter in me is inclined to initially fit the small motors, and see if they are overpowered in high winds. The power calcs estimate only 40 Watts required at 7mph (3.13 M/S) .
    The 2 x 12V batteries are 34 Amp hours each (600 watts) so theoretically they could spin the rig for 2 hours ?

    WireSizes.png

    Regarding the Lift Drag Ratios, on my calculations, I've always us Drag as a positive propulsion vector for any wind angle past 90 degrees.
    eg
    LowWindspeed.png

    This Low speed wind example, gives an analysis of the Lift Drag vectors for all wind angles, and even 45 degrees provides a 4:1 lift drag.

    Does this approach make sense to you ?
     
  6. rwatson
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    rwatson Senior Member

    After investigation, I would have to disagree, if I understand your points properly.
    Both Norwood and Dolfiman have to use the Aspect Ratio in calculate the energy used. This is definitely a Scalar.
    Also, the height versus diameter is a VERY critical part of the power derived, and that is also Scalar in nature.

    Have you had a chance to actually study the formulae?
     
  7. rwatson
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    rwatson Senior Member

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  8. rwatson
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    rwatson Senior Member

  9. rwatson
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    rwatson Senior Member

    New Ships planned for conversion
    "Berge Neblina, a 388k DWT Valemax Ore Carrier, and Berge Mulhacen, a 210k DWT Newcastlemax, will both be installed with 4 of Anemoi’s 3x35m folding Rotor Sails."

     
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  10. Paul Scott
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    Paul Scott Senior Member

    RWatson- I think you were wondering (many moons ago) if anyone had done a conical FR, so here, if you haven’t seen it already:

    https://www.marinepropulsors.com/proceedings/2019/MB3-4.pdf

    Would the tip of a conical rotor have enough of a smaller Re to warrant a smaller fence? Or would flow towards the tip overwhelm a smaller endplate?
     
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  11. Alan Cattelliot
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    Alan Cattelliot Senior Member

    Thanks for the link about Flettner's work. Amazing.

    I'm very impressed to see the effect of the heeling moment of the rotating "sails" of Enercon E-ship.... Not very used to see a boat of this size heeling that much on flat waters, ahead bearing.
    upload_2023-5-9_11-46-52.png

    In a research work, I've studied the use of the magnus effect, but without any tube rotations. In theory, the 50m air draft of a conventionnal rigged sailplane could be replaced by a single tube 10m high. So magnus effect sailplane are quite efficient. The use of electricty for ship propulsion, including the electricity needed to power the Flettner sails, is made possible by converters, transforming the power of ICE into electrical currents. In that case, ICE are most often used in their low consumption range, that contributes also to the fuel saving plan.
     
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  12. rwatson
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    rwatson Senior Member

    I'm not at all sure that the heel is from wind. It may just be wave action, or even a tight turn. The photo isn't clear enough to indicate sea state and wind direction.
    I couldn't find the photo online, to see what the circumstances were.

    But, I found this photo showing heeling.
    [​IMG]

    ... I would guess that its largely from the sea state, although as far as I can tell the wind direction is almost on the bow, which, if the rotors are spinning, will indeed induce a pronounced heeling motion, as the pressure vectors are almost athwartships in that configuration.
    This would be rare, because although there would be slight forward thrust, if the main motors were running, the apparent wind would negate any wind propulsion gain.

    Some few posts back, someone posted a historic study on the E-Ships actual performance, and the amount of propulsion gained with fine angles from the bow or stern, was nearly zero. I cannot find it again, after a fairly long search, maybe you can locate it. It will probably be before page 17.
    I would bet that the schedule of the ship didn't make it worthwhile to save the small amount of fuel savings from fine angles of wind, astern or forward.
     
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  13. rwatson
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    rwatson Senior Member

    Great questions
    I was particularly interested in this section

    upload_2023-5-10_14-41-23.png

    The very small improvement of the tapered rotor, as the spinning ratio (α) increases, is not surprising. The last dozen posts discussing cylinder ratios, show that the rotor performance is finely dependant on it.

    As regards the size of the end fence, this section is new to me, but very interesting
    upload_2023-5-10_14-52-58.png

    It appears that the fence size is significant.

    As far as fence sizes, I have two areas of research to follow.
    1. The effect of flat topped cylinder ends on practical performance. Would a semi- aerofoil upper surface top be a benefit ?

    2. The experiment with Slotted End fences
    upload_2023-5-10_15-2-0.png

    upload_2023-5-10_15-9-33.png



    and this



    that indicates possible better performance with slotted fences.

    Hopefully, I will be able to experiment on my rig, once running.
     
    Last edited: May 10, 2023
  14. rwatson
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    rwatson Senior Member


  15. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    By luck, I came across more information about this little Flettner Gem, worth including in this thread. It seems that metal ductwork is a good cylinder candidate.

    The author is not longer with us
    "Addendum of 08/25/2015: We mourn Reiner Höhndorf, born on 02/20/1927, died on 08/10/2015, as a result of a serious bicycle accident ."

    MagnusRobinNewtonefectHöhndorf11.JPG

    FlettnerRotor https://www.slimlife.eu/flettnerrotor.html

    More history here
    ReinerHistry.png

    zur Geschichte https://dl2swr.afu-wismar.de/flettner_mv.html

    Edit: First appeared in
    Everything Old is new again - Flettner Rotor Ship is launched https://www.boatdesign.net/threads/everything-old-is-new-again-flettner-rotor-ship-is-launched.24081/page-19#post-690472
     
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