They are round because it is the only shape that will not fall into the hole after removal.....
This suggests that Nature is economical, and efficient.
A ninety degree turn in a pipe is wicked drag, hence "elbow" or, camber.
I am trying to evolve an explanation for vortex, and I am not there yet.
Part of it has to do with the containment of energy in "shape", and least drag.
By the way, the vortex forms only within two limiting considerations. Pressure and Volume. I think. So that introduces "locality" (proximity). And 'locality' has to do with the point at which volume and Pressure are interchangeable as to effect, I think.
'Rate' is the bottom line for any Physics problem, imo.....
Last edited by Lyman; 17th Nov 2012 at 15:56.