Swept Volume Theory

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

  1. Doug Halsey
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    Doug Halsey Senior Member

    Your responses to my posts have only exposed your misunderstandings and unwillingness to learn.

    You continue to spout a lot of nonsense that doesn't belong on a reputable site like this.

    If you don't get responses to posts in the future, it would be a mistake to conclude that everyone agrees with you. More likely it would mean that we're all just sick of the subject.
     
    Ad Hoc, mc_rash and DCockey like this.
  2. Sailor Al
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    Sailor Al Senior Member

    If you are going to withdraw from this discussion, I would like to offer a final comment that the contradictions in the use of fluid mechanics that I offered in post #105 are even more troubling to me than they were three years ago when I set out to understand how sails work. Nothing in this or the other threads on this reputable forum has helped to reconcile these contradictions.
    In this and other arenas, when discussing the problem with sailors, "intelligent laymen", professionals or academics in fluid mechanics or aeronautics I am faced with the following dilemma.
    1. The "intelligent laymen" are not aware of the dilemma and feel inadequately equipped to engage on the subject.
    2. Racing sailors either are content to follow the established principles or claim lack of fluid mechanics knowledge to engage on the subject.
    3. Aeronautics professionals and academics are so immersed in the subject that, when faced with the contradictions such as offered in post #105 they resort to condescension, distractions, deception or bluster without providing any answers.
    I appreciate the time and consideration you have given to the discussion, and will use the ideas and challenges we have exchanged to further my exploration of what I still hope will become an alternative explanation of aerodynamic lift.
     
  3. Doug Halsey
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    Doug Halsey Senior Member

    If you told those groups of people that "fluid mechanics doesn't apply to air over sails" it's no wonder they didn't take you seriously.
     
  4. Sailor Al
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    Sailor Al Senior Member

    Your continued engagement with the subject is most appreciated.
    Yes, it is certainly a confronting statement, but I hoped that they might take the idea more seriously if they took the time to review the argument.
    Being the only in-step soldier in the platoon has destroyed my sleep for the past three months, but I am fortified when no-one in the platoon is able to explain why I'm out of step.
     
  5. Doug Halsey
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    Doug Halsey Senior Member

    When the conclusion of your argument is clearly absurd, you need to examine the premises.

    I'm pretty sure the earlier posts explained to you most of the things wrong with them.

    Were you paying attention?
     
  6. Sailor Al
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    Sailor Al Senior Member

    And that's my problem, I have been paying very close attention and I can't find where any the earlier posts have even responded to the challenges of post #105 let alone explained them.
     
  7. Sailor Al
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    Sailor Al Senior Member

    Can we park the contentious issue of the applicability of fluid mechanics for a moment and explore the simpler issue of why it's so important to confirm that the air does actually accelerate over the surface of the wing and ask that you review the attached 7-point argument. (Green boxes are facts, principles etc, pink boxes are conclusions).
    The Argument.png
    Obviously, the contentious principle upon which the argument rests is "Experimental evidence of an increase in air velocity over the surface is not available."
    I would like to present the following three points upon which I base that claim.
    1. As the attached graphic demonstrates, Babinsky's video not only fails to show any evidence of a velocity increase, it would appear that the air actually slows down slightly as it passes over the wing.
      Babinsky2.png
    2. I have done some experiments with a hand-held anemometer on the leeward side of the jib of a close-hauled racing yacht equipped with the sensors and instrumentation found on modern racing yachts. The wind speed on the leeward side was not measurably different from the apparent wind reported by the boat's instruments - in my tests it was around 12 kts. I accept my experimental methods were crude and the results could be affected by observer's bias, but I was surprised by the close correlation between the two values.

    3. Despite spending much of the past two years searching the available literature, I have been unable to find any published experimental data showing the existence of increased air velocity over an aerofoil.
    As I have said previously, in philosophical logic, there is no way of proving a negative, so in themselves these examples are not proof, and are not presented as such, but in my mind they do raise serious questions.
    Can I repeat my earlier request for experimental evidence of an increase in air velocity over the surface of a wing or sail?
     
  8. mc_rash
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    mc_rash Senior Member

    Ever heard of viscosity or boundary layer?
     
  9. Doug Halsey
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    Doug Halsey Senior Member

  10. Sailor Al
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    Sailor Al Senior Member

    My point is that the Babinsky video doesn't show the air velocity accelerating.
    I am appealing for experimental evidence that it does.
     
  11. Sailor Al
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    Sailor Al Senior Member

  12. Doug Halsey
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    Doug Halsey Senior Member

    From Theory Of Wing Sections by Abbott & Von Doenhoff, p 79.
    Are you satisfied with normalized velocity squared? Or the shape of the symbols? Or the fact it's from NACA?
    NACA66(215)-216.jpg
     
  13. mc_rash
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    mc_rash Senior Member

    A change in velocity, may it size or the direction, is always due to an acceleration.
     
  14. mc_rash
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    mc_rash Senior Member

    And basically that is what the foil does - accelerating the fluid in another direction, thus changing the velocity and resulting in change of pressures.
     

  15. Sailor Al
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    Sailor Al Senior Member

    The caption reports: "and experimental pressure distribution". (My emphasis)
    I'm appealing for experimental evidence of the velocity, not the pressure.
    We know the pressure differences have been experimentally measured.
     
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