Is circulation real?

Discussion in 'Hydrodynamics and Aerodynamics' started by Mikko Brummer, Jan 25, 2013.

  1. Pablo Sopelana
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    Pablo Sopelana Senior Member

    Hi,

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    https://navalapp.com/courses/introduction-to-aerodynamics/

    It is currently in "Early Access" mode.
     
  2. Paul Scott
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    Paul Scott Senior Member

    It could be that the truth of fluid flow is unknowable, along the lines of if you measure position you change speed, etc etc, but there are ways around that! (Kind of like nibbling around it- in a binary oppositional matrix, for example. Or sailing even.). But enough of that- this might aggravate, or amuse (sic) - I trust you’ll respondo_O, using that wascally bwain of yours honed by a universe or 10*60th of quantum adaptation. But we can hope we know parts of how sails work- frankly, applying an intuitive notion of circulation while I’m out sailing can be very convenient at times:

    http://philsci-archive.pitt.edu/11725/1/Modelling_scientific_confirmation.pdf
     
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  3. Sailor Al
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    Sailor Al Senior Member

    I think you are echoing my disquiet that the truth of fluid flow is not to be found in aerodynamics.
    Why else would you suggest that it is "unknowable"?
    You are correct, using the pseudo-science of aerodynamics, the truth of fluid flow is indeed unknowable.
     
  4. Sailor Al
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    Sailor Al Senior Member

    Fabulous video, striking demonstration, but what has it to do with the current discussion?
     
  5. Sailor Al
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    Sailor Al Senior Member

    The rotation in the vortex of the video has absolutely nothing whatsoever to do with the circulation in the name of this thread.
     
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  6. Howlandwoodworks
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    Howlandwoodworks Member

    .

    Al and TANSL,

    It has everything to do with the said thought experiment. You maybe looking at the circulation in three-dimensional and vorticity are four-dimensional objects as is the models thought experiment. The sailboat and airplane are in four-dimensional space time. Ergo we would thinking about a vortex to create the said effect in the model and not circulation. The airplane has lift moving the air down and back. I am not saying the example would create a vortex in the thought experiment or circulation. Just that it would have to be a vortex in three-dimensional space time. The airplane has lift moving the air down and back.

    I should have found a better example and not used the double vorticity and just used a video with single vortex in the title to make it easy to understand. She does explain a single vortex in the video.

    As for your criticism of my post. 48 pages 711 replies and you have singled out my post as you say has nothing to do with the original intent of this threads thought experiment.

    My intent is to stay within the original intent of the thread with my post, as we all should.

    Respectfully yours
    J. Howland

     
    Last edited: Feb 2, 2023
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  7. Howlandwoodworks
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    Howlandwoodworks Member

    Mikko Brummer,
    I liked your thread "Is circulation real?" very much and the fact that you were using Einstein "Principle of Equivalence" for your thought experiment was ingenious. The "Principle of Equivalence" is a great mind tool to formulate and generalize concepts to solve diverse problems and situations.
    Thanks for the great thread! It is over 10 years old last week.
    J. Howland
     
    Last edited: Feb 2, 2023
  8. TANSL
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    TANSL Senior Member

    @Howlandwoodworks, thanks for your explanations. The truth is that I am very bad at dealing with 4-dimensional objects and, perhaps for that reason, I have not been able to interpret your post. Some say that there are up to 11 dimensions, or better, that certain objects and phenomena can be explained if there are 11 directions, but I can only control 3 decently. Thanks again.
     
    Last edited: Feb 2, 2023
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  9. Howlandwoodworks
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    Howlandwoodworks Member

    Sailor Al & TANSL,
    I don't know if I am right about four-dimensional space time vortex or circulation.
    I am sorry for not posting an explanation early. Life get busy sometime.
    Well, got to go now. I hear some old tools calling my name.

    The best luck with all your endeavors.
    J. Howland
     
  10. TANSL
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    TANSL Senior Member

    Space has three dimensions, a 4-dimensional space is not possible. The fourth dimension is time (space-time universe) and the other dimensions, if they exist, do not belong to space, although everything is related.
    Since all this has nothing to do with the current thread, and I am not an expert in the universe that surrounds us (it seems that there could be several universes), I will not continue talking about "dimensions". Thank you again for your attempts to clarify the concepts of circulation theory.
     
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  11. Howlandwoodworks
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    Howlandwoodworks Member

    TANSL,
    If you are bad at dealing with 4-dimensional objects and don't seem to understand the how Einstein "Principle of Equivalence" works. Why are you replying to my post in the first place?
    Why are you talking about 11 dimension?
    These are both rhetorical question.

    TANSL,
    I am assuming you are talking about the "The Circulation Theory of Lift". A theory proposed first by: George Cayley discovered and identified the four forces which act on a heavier-than-air flying vehicle: lift, drag, weight, and thrust - originally proposed in about 1779.
    If you don't understand "dimensions" yes, it would be best practice that you don't post about them.
    How does your statement "I am not an expert in the universe that surrounds us it seems that there could be several universes" have to do with anything in this thread?
    In both of your post above you seem to be trying do inject concepts into my post that I have not put forth. Or is there some other reason you are talking about theories that I don't think have any thing with the original thread?
    These is not a rhetorical question.
    I think you are much smarter than your posts imply that I referenced above and if so, there is a 50/50 percent possibility you are trolling me.
    Have you read or understand Einstein's "General Theory of Relativity"? It would be required reading for comprehending and responding to my post about Einstein Thought Experiment "Principle of Equivalence". Mikko proposed a thought experiment in his tread as "Here's a mind experiment."
    "
    I am reposted the original thought experiment below:
    TANSL,
    If it makes you feel better you could take another jab at me and then I propose we agree to disagree, a truce, lets say a Modus Vivendi of sorts.

    Respectfully yours
    J. Howland
     
    Last edited: Feb 3, 2023
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  12. Sailor Al
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    Sailor Al Senior Member

    You highlight Lift in your response, but it does leave the false impression that you meant that George Cayley was the first to propose Circulation as the source of Lift.
     
  13. Sailor Al
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    Sailor Al Senior Member

    I think I have traced Circulation theory of aerodynamic lift via Tom Whidden, Arvel Gentry and C.A. Marchaj back to Ludwig Prandtl's application of Kelvin's circulation theorem.
    By all reports, Prandtl didn't publish much himself, but his lectures have been reproduced in L. Prandtl, & O.G. Tietjens, Applied Hydro- and Aeromechanics.
    The key paragraph is reproduced below is from p. 191;
    upload_2023-3-29_10-55-41.png

    I am disturbed by the phrase highlighted above: '... we form the line integral of the velocity along a closed "fluid line" '

    My reading of Kelvin's Circulation Theorem relates to the flow of a fluid acted upon by conservative forces. As soon as an object, such as a cylinder, a sail or a wing is introduced into the flow, an external force has to be applied to counter the non-conservative aerodynamic forces (lift/drag or thrust/lateral force) that are generated by the flow over the body.
    (This will only make sense to you if your maths/physics is up speed on forces, conservative forces, and Kelvin's theorem.)

    Does that mean it's incorrect to apply Kelvin's theorem of the conservation of circulation to a fluid being acted upon by a non-conservative force, such as a wing, sail, propeller, turbine, or windmill?
     
    Last edited: Mar 29, 2023
  14. Sailor Al
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    Sailor Al Senior Member

    In an attempt to elicit a response from the forum, let me clarify my post #718.
    After deriving Kelvin's theory of the conservation of circulation on earlier pages, on p. 193 Prandtl introduces the example of a region of stationary fluid surrounding, but not including a "strut" which I have highlighted in yellow in the attached extract.
    upload_2023-3-31_9-46-47.png
    Later, on the same page, he introduces motion around the strut (highlighted in blue) which causes the closed curve to deform (highlighted in green).
    Now, since the derivation of Kelvin's theory requires the fluid to have density and therefore mass, any deformation of the fluid which was previously "at rest" will require fluid to be moved from its original position at rest to the new position in motion.
    This motion will require acceleration and, in accordance with Newton's first law, any mass being accelerated requires a force.
    In other words, the deformation of a fluid previously at rest will require force, and so the fluid has to be subjected to a force in order to achieve this deformation.
    As noted in #718 above, Kelvin's Circulation Theorem relates to the flow of an inviscid, incompressible fluid acted upon by conservative forces.
    Whilst air might not exactly satisfy the requirement of being inviscid and incompressible, the issue of the forces being conservative is fundamental.
    As a reminder, a conservative force is one that offers the opportunity of two-way conversion between kinetic and potential energies, such as the force due to gravity, springs, magnetism and electric forces between charged bodies.
    There is no indication that the force causing strut's acceleration is conservative .
    Since Prandtl's example appears to violate the precondition of Kelvin's circulation theorem , I pose my question:
    Does that mean it's incorrect to apply Kelvin's theorem of the conservation of circulation to a fluid being acted upon by a non-conservative force, such as a wing, sail, propeller, turbine, or windmill?
     
    Last edited: Mar 31, 2023

  15. Sailor Al
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    Sailor Al Senior Member

    Interesting, no response. Maybe too complicated for this forum?
    Of course it's nonsense to invoke Kelvin's obscure theory of conservation of circulation to a foil moving through air, or moving air being disturbed by a foil. Both require the input of a non-conservative force to hold the foil against the air. Kelvin's theory does not apply.
    That mistake has set back any science of aerodynamics by a century.
     
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