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My question is based around comparing the physics of a tornado against, what I imagine/assume to be the marine equivalent of a tornado, that is a whirlpool located either at sea, in a tidal region or in an estuary.

Whirlpool

My assumptions are:

  • They both have the same basic cause, opposing streams of fluid, (air versus water) meet and an "inward" velocity vector arises, creating the inital spinning motion, which then, temporarily, becomes self perpetuating, dragging in more fluid and increasing the angular momentum of the system.

  • I assume, from video footage of tornados that I have seen, that tornados generally seem to be created at the height of the cloudbase, which can, it seems to me, range from 100 to 500 metres in vertical height.

  • I would assume that, due to the much greater density of water relative to air, a whirlpool could not descend very far, as the forces required to maintain it are far greater that it's atmospheric equivalent. However, I don't know enough about fluid dynamics to estimate how far down it could actually descend before it dissipates. My (pretty obvious, I admit) guess would be on the order of metres, i.e. far less than tornado height.

In other words, how good is my analogy of picturing a whirlpool as the marine equivalent of a atmospheric tornado and where does it break down?

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    From what I learned in cartoons, if you pull the big plug out of the bottom of the ocean, the whirlpool will extend all the way down – Jim Aug 27 '15 at 17:36
  • I would guess the right answer contains (in)compressibility. – Bernhard Aug 27 '15 at 17:51
  • Interesting question. Can water spouts create deep whirlpools? – Alex Aug 27 '15 at 19:24
  • I suppose whether you could survive depends on what type of barrel and what is causing the whirlpool. Either way, you'd be fairly dizzy afterwards – Jim Aug 27 '15 at 20:25
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    People have survived going over Niagara Falls in a barrel. Given that, I won't say people couldn't survive a whirlpool in a barrel. Don't try this at home though – Jim Aug 27 '15 at 20:41
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    @Jim if I could fit a barrel in my bathtub I'd probably attempt it, just saying. – Asher Aug 27 '15 at 21:36
  • From what I have read about tornado's, they are driven by hot air, from the ground, rising through cold air. Once one is formed it is easier for the hot air to rise through it, so surrounding hot air gets pulled in, increasing in angular velocity. Due to the conservation of mass flow you could argue that a tornado forms over its entire length at the same time, but it only becomes visible when water condensates (when the hot and humid cools) or big enough material gets pulled in. – fibonatic Aug 28 '15 at 12:19
  • Your analogy does not seem apt to me. A tornado is a vortex tube contained entirely within the fluid. A whirlpool as you've shown is the surface of the fluid being pulled down into the vortex tube, but the vortex tube itself can extend down into the liquid much further. – pwf Sep 04 '15 at 17:58
  • @pwf Thanks very much, I had no idea of any valid comparison that could be made between the two systems. –  Sep 04 '15 at 18:17

1 Answers1

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According to Heimholz second theorem it goes all the way. It even can't end in the fluid. You of course mean just the air, but it's merely a matter of how the situation is developing. If the flow conditions goes over Froude number 1 you will allways have the connection. It's explained here; Air core Vortex; Physical explanation of the "air Entrainment Hook" at $F_{co}=0.7$ -on my answer.

And according to experience gathered at hydropowerplants it really goes "all the way." Here is a nice study about the issue see ie. picture in page one.

enter image description here

Note that the pressure in intake is not the same, and "all the way" is the connection between two pressures.

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Jokela
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  • Yes, it was only the honest structure of your question which motivated me to answer. There is a really nice video about the water analogy of the vortex, in youtube "13. Secondary Flow" in the channel of Barry Belmont, the point I mean is around 11 minutes from beginning, -if a I remember right. – Jokela Oct 14 '15 at 16:24