Is circulation real?

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

  1. Remmlinger
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    Remmlinger engineer

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  2. Earl Boebert
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    Earl Boebert Senior Member

    No one is obligated to explain the circulation model in terms of "classical physics," the movement of particles of pixie dust, or any universe of discourse other than the model itself. To demand otherwise is to demonstrate a profound misunderstanding of the nature and application of models.
     
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  3. DCockey
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    DCockey Senior Member

    The arrows are the perturbation velocity because they do not include the "free stream" as seen by an observer traveling on the albatross. A streamline could be created using the arrows by by drawing a curve which is tangent to the arrows. This would be a perturbation velocity streamline or a streamline in the earth reference frame (assuming no ambient wind).

    "Streamline" is another word that aerodynamacists use which can cause confusion, A streamline is a curve which is tangent to the local velocity everywhere at a intant in time. Streamlines differ depending on the reference freame. A pathline is the curve a fluid partcle follows with time. Streamlines and pathlines coincide only if the flow is steady in the reference frame and if the streamline is based on the total velocity.

    Streaklines are a third type of curve used to illustrate fluid motion. A streakline is the curve of fluid particles which have all passed through a fixed point in the frame of reference. A streakline is different than a streamline and different than a pathline unless the flow is steady in the reference frame.

    These terms are confusing. An introduction to fluid mechanics book should cover them.
     
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  4. DCockey
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    DCockey Senior Member

    Unfortunately that appears to be true. But others appear to be receptive and I learn when I explain.
     
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  5. Remmlinger
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    Remmlinger engineer

    This is a very good point David! When I try to explain, I notice where my understanding is clear and where it is only fuzzy. So, even if the postings are sometimes annoying, it helps to clarify my thoughts. In the end, it is Mikkos thread and the pictures he has posted are fascinating. The linked video of the raptors was striking, I had never seen anything like that. Just for that, the visit to this forum is worth the time.
    Regards, Uli
     
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  6. DCockey
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    DCockey Senior Member

    Agree.
     

  7. Earl Boebert
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    Earl Boebert Senior Member

    Ditto.

    Cheers,

    Earl
     
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