Swept Volume Theory

Discussion in 'Hydrodynamics and Aerodynamics' started by Sailor Al, Aug 2, 2022.

  1. Sailor Al
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    Sailor Al Senior Member

    To disprove a theory one has to either demonstrate a logical flaw in the theory or present contrary experimental evidence. Introducing the "Coanda Effect" does neither.
     
  2. Doug Halsey
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    Doug Halsey Senior Member

    You don't seem to realize that the surface of a foil becomes vertical at the leading edge, so different points can have the same X coordinates. To see the variations more clearly, you need to plot with respect to the arclength along the surface, rather than the X coordinate.

    Also that you can't tell the difference between a discontinuity and a steep gradient in data given only at discrete points.

    For a more modern textbook, I would encourage you to buy forum member Mark Drela's book Flight Vehicle Aerodynamics. The chapter on viscous effects has plots similar to the one I showed earlier.
     
    Last edited: Aug 30, 2022
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  3. Sailor Al
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    Sailor Al Senior Member

    I have already spent quite a lot on textbooks which has led me to this discussion, I'm not eager to spend more. Could I request you attach an image of the example to support your case?
     
  4. Sailor Al
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    Sailor Al Senior Member

    Of course you can!
    upload_2022-8-31_10-47-41.png
     
  5. Doug Halsey
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    Doug Halsey Senior Member

  6. Sailor Al
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    Sailor Al Senior Member

    Please, you're challenging my claim. It's up to you to present your evidence, not refer me to yet another technical paper.
     
  7. Doug Halsey
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    Doug Halsey Senior Member

    If you are presenting a new theory as an improvement, the onus of proof is on you.

    I'm not going to waste my time trying to understand every off-the-wall claim that you make.
     
  8. Sailor Al
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    Sailor Al Senior Member

    I challenged you to support this statement and now, two days later, you disengage with "the onus of proof is on you."
    I accept that as a withdrawal.
    The only claims I'd really like you to consider are contained the body of my paper in the sections "Swept Volume Theory" to "Conclusions".
    Please, take another look.
     
  9. gonzo
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    gonzo Senior Member

    If you choose the fluid as the frame of reference, then obviously there is no flow. You will have a body moving through the fluid. It only reverses the sign on some values (+ to -). It does not demonstrate there is no fluid flow. Flow is a relative value. As such, it is not an intrinsic property.
     
  10. latestarter
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    latestarter Senior Member

    I was looking at your theory and realised figures 6,7,9 and 11 need tweaking.

    The purpose of a yacht is to make progress approximately in the direction it is pointing.

    In the above figures the sail moves horizontally from right to left. If on a yacht it would also move from bottom to top.

    To match the figures as drawn the structure supporting the sails would need to be on rails.
     
  11. Remmlinger
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    Remmlinger engineer

    I looked at your paper.
    1.) sail forces exist also in incompressible flow. Prof. Milgram (Yacht and Racing Boat Development and Design: Jerome Milgram, Ph.D http://web.mit.edu/jmilgram/www/boat.html) conducted his famous experiments (https://ntrs.nasa.gov/api/citations/19710020417/downloads/19710020417.pdf) on sail sections in a water tank: MHL Information http://web.mit.edu/mhl/www/photos.html
    2.) you have drawn the resultant sail force at a right angle to the sail chord. Measurements show, that the force is rotated much more forward, almost at a right angle to the incoming flow. Search for leading edge "suction force".

    After more than 130 years of research in aerodynamics, that led to designs with breathtaking performances, I would recommend a humble approach and first to work hard to understand the explanations in the many available textbooks.
     
    Last edited: Aug 31, 2022
  12. Sailor Al
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    Sailor Al Senior Member

    At last an objection from someone who has thought about the paper. Thank you and welcome!
    And this is the mental challenge involved in the changed Frame of Reference.
    Fig's 6,7,9 and 11 use the same FoR as 5 and 4, so let's see how that is generated
    Fig 4 is the sail and the wind from Fig 3 rotated to align the apparent wind with the horizontal (X-) axis:
    upload_2022-9-1_7-24-44.png
    So in that FoR, you can see that the sail is only moving along the X-Axis, there is no movement from bottom to top.
    [add]
    The "rails" you speak of are provided by the lift from the keel keeping the boat moving along its course through the water (centreline + leeway).
     
    Last edited: Aug 31, 2022
  13. Sailor Al
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    Sailor Al Senior Member

    It's not my drawing, it's the standard drawing from all the textbooks. I took it from Fossati:
    upload_2022-9-1_7-31-49.png
    Whether it is much more forward or just a little more forward is the fascinating challenge! As trimmers, our challenge is to get that angle as far forward as we can, what I'm interested in doing is trying to understand now our manipulation of draft position and depth changes that angle. We know it does, but we don't know why!
     
    Last edited: Aug 31, 2022
  14. Sailor Al
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    Sailor Al Senior Member

    I do hope he's following this thread.
     

  15. Sailor Al
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    Sailor Al Senior Member

    No, it doesn't.
    It changes some values from non-zero to zero and others from zero to non-zero.
    In the FoR of the undisturbed air, the air speed changes from the apparent wind speed (AWS) to zero, and the sail's speed from zero to the AWS.
    That's the perspective change that makes sense of the idea that there's no fluid flow to consider.
     
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