Centerline channel for attached Turbulent Flow?

Discussion in 'Hydrodynamics and Aerodynamics' started by Redaidan345, Jan 22, 2024.

  1. Redaidan345
    Joined: Jan 2024
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    Redaidan345 New Member

    Hello,
    I am a big wave surfer and working on designing new foils and boards for larger waves. The current issue is drag shedding. As the wave increases in size, the magnitude of water rushing up the face thwarts the forces utilized by the surfer to surf down the wave. It seems like the overall fix will be to utilize foils to surf larger waves. In the meantime, I am working on optimizing board design to try and reduce drag.

    The goal is for an improved flow profile along the system (surfboard).
    To simply utilize a global optimization approach (VPP) to design a board from scratch, numerically we would get a tiny “torpedo” or spear like design with low buoyancy that would be fast and fairly stable but unrideable. Therefore, the design approach is to utilize the following set of variables to redesign tried and tested big wave boards.
    (As a note* I will not be focusing on rider posturing and aerodynamics because PORSCHE has already done so in a wind tunnel. They were able to find the biggest decrease in overall drag via changing the riders posture, something akin to 17% see link.)

    I am wondering what your thoughts are on creating a centerline channel so as to create a space for attached turbulent flow. My theory is that this will reduce the boards footprint and create less drag .
    I can expand on construction and answer any other questions as well.
    Please see the attached pictures. Also ignore the rail profiles, I plan on changing the profile to something with an aggressive tumblehome for stability and harder chines.

    Thank you so much for your time!
     

    Attached Files:

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  2. Alan Cattelliot
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    Alan Cattelliot Senior Member

    Hi,
    quite a lot of hull shapes have been tried...And I'm sure it is nothing new for you, since it seems you are, here, looking to develop a brand new shape. In essence, your shape could be seen as a "double convex", and geometrically speaking, there is nothing that says it won't work. Especially if you re-work chines. In the path you choose, the curvature will be your friend, but your enemy as well. Too little curvature or too much will increase the turbulence. To control the flow like you wish, I would also consider working the longitudinal curvature, in addition to the transversal curvature, in way of the inversion, trying to increase the channel effect in both directions of the flow. If only I had some free time, this is a very funny model I wish I can test on my cfd tools...
    Also many thanks for the link. It seems that Sebastian Steudtner has a big foot by Porsche...Vielleicht hat er ein wohnung in der nähe von Stuttgart :rolleyes:
     
    Last edited: Jan 23, 2024
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  3. gonzo
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    gonzo Senior Member

    Those boards used to be called elephant guns. They were a blast to ride. The shape was long and narrow with a pin tail, and the bottom flat.
     
  4. Paul Scott
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    Paul Scott Senior Member

    Have you looked at windsurfer board designs for inspiration?

    Your hull above looks kind of like a variation of the Hickman Sea Sled- might also take a look at the Laser Vortex for some inspiration. But how to keep your board (above) light and not split in 2?

    As one example, I shaped a windsurfer that had a step bottom, kind of like this (stick cartoon below) in body view (or cross section) in the middle- it was weirdly fast & smooth across motorboat wakes

    |_______—————————————_______|

    (inside walls vertically square to keep turbulence contained, flat bottomed for max lift- but some questions unexplored- how deep & wide to make the full length sponsons? Flat, concave,convex? For that matter, how wide or deep the mid tunnel?), and vertical rails felt kind of soft, and, at least have less wave drag, if the hulls are narrow enough. There were more than a few tri concave longboard windsurfers, quad concaves, and quads with a small center concave, for 5 concaves))

    which might give you less wetted surface at speed, ~ a slender possibly planing ‘catamaran’ with attached foam marbles rolling in the middle- vortex generators might help there? Or think of it as 2 slender torpedoes connected by a slender airboat …:D Experiment with different % of step depth, widths, side ‘hulls’ prismatic, depth (or no depth) towards the back, or maybe blended into a shallow vee at the stern? (How loose do you want the tail?). Asymmetric outer ‘hulls’? Symmetric? Stinger tails on the ‘catamaran’ hulls? Square tails?

    perhaps a low prismatic nose for accelerating to the wave, and then as the nose lifts with speed to a higher prismatic, which might call for a squash/squarish tail? Although with the channel down the middle that might get tricky, but if you like the stern to lift and keep the nose down….

    one thing that fascinates me about big wave boards is shaping them so they’re not so fast they out run a wave. If you try vortex generators, where to put them, and would you want a single fin in the middle with all the mush flow, or smaller duals on the outside in ‘cleaner’ flow?

    once you get into planing mode, what design software is going to help?

    anyway, random thoughts….

    have fun! EXP? EPS?
     
    Last edited: Jan 24, 2024
  5. Paul Scott
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    Paul Scott Senior Member

    Perhaps? :)
     
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  6. Paul Scott
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    Paul Scott Senior Member

    Vortex so you can see the hull, for a general idea. The nose pearled without a spinnaker.

    IMG_1595.jpeg
     
  7. Paul Scott
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    Paul Scott Senior Member

    Hickman SeaSled

    IMG_1596.jpeg
     
  8. Paul Scott
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    Paul Scott Senior Member

    You may be aware of this already, but (comes from Eric Mehelbergel’s windsurfing blog)

    Single concave means that there is a single concave section between the rails that runs a certain distance of the board length. If you can imagine this, the rails will be deeper in the water than the centerline of the board bottom. Double concave means that there are two parallel concave sections between the rails, one on each side of the board, that run a certain distance of the board length . If you can imagine this, the rails would be at the same water depth as the centerline of the board bottom while the middle of each concave section would be less deep in the water than the rails. A single concave section will provide more lift and speed than a double concave, but it will be bad in chop and will not turn great. Double concave will loosen up the board compared to single concave while still providing much better lift and speed than convex shaping. However, double concave can also be combined with vee so that the centerline of the board is deeper than the rails. This gives benefits of both vee and double concave. What are those benefits? The board will handle well in chop AND have good lift, speed, and turning.
     
  9. gonzo
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    gonzo Senior Member

    There is no chop when surfing. However, concave on the front, flat middle and shallow vee at the back has been done successfully. Joey Cabell won some championships with that type, which he shaped.
     
  10. Alan Cattelliot
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    Alan Cattelliot Senior Member

    Handling is something when riding several tones of water. And some waves are more specific than others. Big waves come only at location, durin a given season,under certain conditions. As a result, each big waves have a distinctive and sometimes unique slope, speed, surface tension. Surfers and surfboard shall adapt.
    What waves do you want to chase ? Winter season in West Coast ?
     
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  11. Paul Scott
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    Paul Scott Senior Member

    IMG_1597.jpeg
     
  12. Paul Scott
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    Paul Scott Senior Member


    Which, oh so inevitably, leads to George Greenough, etc. ^:)
     
    Last edited: Jan 24, 2024
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  13. kapnD
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    kapnD Senior Member

    That may be so in Wisconsin, but the big waves I know and love are often full of treacherous chops, especially on the initial drop.
    Don’t forget that rapid transition from rail to rail will be necessary, without any uncertainty between.
    Google “Bonzer Bottom”, concaves in the tail are not an untried concept.
     
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  14. gonzo
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    gonzo Senior Member

    Is your assumption that I never been out of Wisconsin?o_O
     

  15. gonzo
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    gonzo Senior Member

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