David wrote.. My teacher in fluid mechanics Sten Herlitz taught us that a vortex was rotation free. He showed a movie showing that the small parts of the fluid did not rotate. This is what I was referring to.
Rotation is well defined as nabla cross velocity, ∇×v, sometimes called vorticity which is bad since the vortex is without rotation. Rotation is a differential aspect defined in the micro scale. A vortex motion is more like wagons in a Ferris wheel. They do not rotate either. They always have the same direction. It is good not to mix up the concepts because that will lead to confusion and wrong results. As far as I can see the funny special effects are due to rotation or vorticity, but not vortexes or vortecii. Howdy David, Would you mind repeating that and add more clarity to your explanation. Us'ns sitting 'cher staring down a vortex at the Dime Box saloon while the room is spinnin' around are confused. Richard
