Turbulence level in the ocean

Discussion in 'Hydrodynamics and Aerodynamics' started by Remmlinger, May 20, 2013.

  1. Remmlinger
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    Remmlinger engineer

    1 person likes this.
  2. DCockey
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    DCockey Senior Member

    Thanks for posting your very interesting paper. The title does not convey the breadth of factors you discussed. Perhaps a more appropriate title would be something like "Factors affecting transition to turbulent flow on keels".
     
  3. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Thanks Uli!

    In the many papers you trawled through did you see any estimates
    of the turbulent (or eddy) viscosity close to the free-surface?

    I model viscous wave damping effects as a thin shear layer at the
    surface, so potential flow can be assumed throughout the rest of
    the flow domain. That model requires an estimate of the "turbulent
    viscosity" which can vary in the vertical direction from 10^-6 to
    1.0, i.e. a range of more than 6 orders of magnitude!
    I can narrow the range by fitting to towing tank data and some
    full-scale ship-wave wakes, but I'd like more references to wavy
    (but not violently wavy) conditions.

    I also agree with DCockey's comment regarding the title.
     
  4. Remmlinger
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    Remmlinger engineer

    David you are right. I thought with the current title the paper would attract more attention. I will think about an improvement.
     
  5. Remmlinger
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    Remmlinger engineer

    If you mean the 2-D "viscous sublayer" as shown in figure 2 of http://web.gfi.uib.no/publikasjoner/rmo/RMO-2010-1.pdf, then I have no information. The layer underneath, which is often called the "wave breaking layer" extends from the wave crest downwards for 1.1 * wave-height, so the lower limit would be slightly below the wave trough. The turbulence in this layer is under debate. Most oceanographers (e.g. Terray) reference their measurements to a coordinate system fixed to the still water level and assume epsilon to be constant in this layer. Gemmrich (http://journals.ametsoc.org/doi/pdf/10.1175/2009JPO4179.1) instead uses a coordinate system that is fixed to the instant water surface and he found out, that epsilon varies with 1/z, just like in the case of a wall layer. In his measurements wave breaking increased epsilon by a factor of 4 to 20 compared to a wall layer.
     
  6. Mikko Brummer
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    Mikko Brummer Senior Member

    Thank you Uli! This matter has intrigued me for years, if not decades, since the 80s' when I wrote my VPP. Not easy to find info about turbulence levels in sea water. I will read your paper with thought as soon as I find the time.
     
  7. Remmlinger
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    Remmlinger engineer

    Update

    I found an additional paper (via Google books) that describes turbulence measurements at full scale on the Alinghi keel. It supports the finding that the frequency spectrum is crucial and not only the turbulence level.
    I have updated http://www.remmlinger.com/TurbLevel.pdf with the additional reference
    Uli
     

  8. hoytedow
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    hoytedow Carbon Based Life Form

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