Analyze of plano-convex hydrofoil

Discussion in 'Hydrodynamics and Aerodynamics' started by revintage, Oct 20, 2018.

  1. revintage
    Joined: Nov 2016
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    revintage Senior Member

    Got curious of how the plano-convex hydrofoil from the 50´s, in AYRS74 side 31 would work.

    Modified a Biconvex 16% to mimic the 8,3% foil.

    Anyone who would care to check cavitation in XFoil?

    Also added the 2512 to compare.

    AYRS74.png
    2512.png
     

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    Last edited: Oct 21, 2018
  2. Doug Halsey
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    Doug Halsey Senior Member

    I've had a hard time getting XFOIL to work for cases with sharp leading edges, but Hoerner has a few things to say about them:
    Hoerner_p6-13.jpg
     
  3. revintage
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    revintage Senior Member

    Guessed wasn´t good because of that.

    Tried without the up-nose at first but it was messy ;-) .

    Did the analyze because most hydrofoils in those days and later(even Icarus) used them.

    But maybe they rounded off the leading edge more?

    Also guess negative angles could be unstable and it probably works best with the bottom horizontal? This is CL ca 0.5.
     
    Last edited: Oct 21, 2018
  4. BlueBell
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    BlueBell Ahhhhh...

    Proahs often use a sharp leading edge, symmetrical foils.
    Research shows good results.
    Rob Denny (a member here) would have lots to say about them...
     
  5. revintage
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    revintage Senior Member

    Last edited: Oct 21, 2018
  6. Doug Halsey
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    Doug Halsey Senior Member

    Here's a page from Hoerner that I was trying to find earlier, showing how the plano-convex foil can be OK near its ideal angle & how much worse it is away from that angle.
    Hoerner_p11-28.jpg
     
  7. revintage
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    revintage Senior Member

    Just downloaded the book. This is 6-13 and 11-28 as pdf.
     

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  8. tspeer
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    tspeer Senior Member

    I've always suspected the ogive sections were why the early hydrofoil experimenters had so much trouble with ventilation. They wanted a sharp leading edge to "cut the water", but a sharp leading edge creates a laminar separation bubble for all but a narrow range of angles of attack. Two of the necessary conditions for ventilation are flow separation and a path for the air to get to the separated zone, and the leading edge bubble excels at both.
     

  9. revintage
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    revintage Senior Member

    The planoconvex I analyzed before is with a small upward tip. Ran a fully ogive 6% section in Javafoil but it looks weird to me. As Doug said above, XFOIL had problems with sharp leading edges, maybe JavaFoil has that to.

    If the polar and pressure are anywhere near correct, it is understandable that they must have had problems getting the boat flying and keep it at speed, back in the days.

    It is only a small window between 0 and 3 degrees where lift and Cp* is acceptable.

    ogive6.png

    fkacogpnbafakfok.png
     

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