Turbulence research

Discussion in 'Hydrodynamics and Aerodynamics' started by ImaginaryNumber, Feb 29, 2020.

  1. ImaginaryNumber
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    ImaginaryNumber Imaginary Member

    Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) may have identified a fundamental mechanism by which turbulence develops by smashing vortex rings head-on into each other, recording the results with ultra-high-resolution cameras, and reconstructing the collision dynamics using a 3-D visualization program. Coupled with the analysis of numerical simulations performed by collaborators at the University of Houston and ENS de Lyon, the researchers have gained unprecedented insight into how fluidic systems transform from order to disorder.....

    They used vortex cannons in a 75-gallon aquarium to produce the vortices. Each vortex was dyed a different color, so researchers could observe how they interact when they violently collide. It takes less than a second for the rings to disappear into a puff of dye after the collision, but within that time, a lot of physics happens.

    First, the rings stretch outward as they smash into each other and the edges form antisymmetric waves. The crests of these waves develop into finger-like filaments, which grow perpendicularly between the colliding cores.

    These filaments counter-rotate with their neighbors, creating a new array of miniature vortices that interact with each other for milliseconds. Those vortices also form filaments, which in turn form vortices. The research team observed three generations of this cascading cycle, each one the same as before, only smaller—a Russian nesting doll of disorder......
     
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  2. tspeer
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    tspeer Senior Member

    Big whorls have little whorls
    That feed on their velocity,
    And little whorls have lesser whorls
    And so on to viscosity.

    -- Lewis F. Richardson
     
  3. messabout
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    messabout Senior Member

    ^ Tom ,That's a clever new take on the troll bit. Infinite regression is everywhere it would seem, even in humor.
     
  4. tspeer
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    tspeer Senior Member

    Richardson studied atmospheric turbulence.

    This isn't related to the subject, but it's another of my favorite poems. (I don't know who wrote it)

    Crinkle, Crinkle, little spar,
    Strained beyond the yield point far.

    Up above the world so high,
    Bits and pieces in the sky.

    Getting back on the subject, here is a video of a researcher investigating vortex ring dynamics underwater:
     
  5. Manfred.pech
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    Manfred.pech Senior Member

    In german .. not quite correct... :
    Aus Wirbeln werden Wirbelkinder
    kleiner feiner und geschwinder,
    noch ein Weilchen, und nicht minder
    wirbeln Wirbelkindeskinder,
    und am End nach kurzem Lauf
    frißt die Reibung alle auf.

    Spektrum der Wissenschaften ,12, 1997, S.92ff, "Modellieren von Turbulenz", Parviz Moin u.
    John Kim."
     
    Last edited: Mar 13, 2020
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  6. Mikko Brummer
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    Mikko Brummer Senior Member

    Dolphins vortex rings explained in Scientific American.
     

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  7. patzefran
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    patzefran patzefran

    Wonderful !
     
  8. ImaginaryNumber
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    ImaginaryNumber Imaginary Member

  9. patzefran
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    patzefran patzefran

    IMHO the vortex are created by the collision on the circular boundary, this is not litterally a collision of vortex rings !
     

  10. Dolfiman
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    Dolfiman Senior Member

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