Wednesday 25 July 2018

fluid dynamics - Why water in the sink follow a curved path?


When you fill the sink with water and then allow the water to be drained, the water forms a vortex.. And then it starts to follow a curved path downwards by effects of gravity.


Why this phenomena occurs while rain follows a straight line path (in perfect conditions) towards the ground.



I would guess that when the water molecules closest to the drain hole go through first, they create a temporary void causing other water molecules nearby (above and on the sides) to rush in and take their place each having an equal chance to fill that void (since pressure is equal in all directions at a certain point in liquids). So I was thinking more of cone like figure with water collapsing in, equally from each direction. Why the circular path??



Answer



In basic principle, both could do the same thing.


Pragmatically, water in a drain has the resistance of the sink/drain walls to influence the effect. (This is a hairpin vortex regime.) Basically, vortices differ per sink.


Surface tension of a rain drop exceeds wind friction. Coriolis forces still exist within the rain drop, and could produce a toroidal-like vortex flow therein.




The vortex is a cascade phenomenon influenced by



  1. molecular dynamics,

  2. boundary conditions, and


  3. environmental forces


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