i have seen this video. https://www.youtube.com/watch?v=pnbJEg9r1o8&t=96s It is not completly clear how a difference of velocity can cause a vortex, can you explain me?

  • $\begingroup$ Reminded me about this comedy segment about toroidal vortexes (with reference to original paper): youtube.com/watch?v=Bcr9-93wXng $\endgroup$
    – user190081
    Oct 17, 2018 at 21:52
  • $\begingroup$ How much background in fluid mechanics and tensor algebra do you have? $\endgroup$
    – Deep
    Oct 18, 2018 at 5:11
  • $\begingroup$ Pretty good.... $\endgroup$ Oct 18, 2018 at 5:55
  • $\begingroup$ You must know that the motion at a point in a flow is the sum of translation, (rigid body) rotation, and straining (see this). Rotation part is vorticity. $\endgroup$
    – Deep
    Oct 21, 2018 at 7:04

1 Answer 1


There are a couple of effects causing that. As she explained, the water flows off & around the edge of the plate, to the back, causing the ring of water around the plate to spin. Also, if there is a moving fluid against a stationary (or slower moving) fluid, the bit in between gets rolled between the two, like rolling a stick between your hands.


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