On Nov 3, 2014, at 10:27 PM, Henry Baker <hbaker1@pipeline.com> wrote:
I've never done this computation (I wasn't in Course 16), but I seem to recall that fluid vortices can attract & repel one another analogous to the magnetic fields that surround two parallel current-carrying wires. The main effect is that the vortices advect one another: each vortex core moves such that it is stationary with respect to the flow field of the other. Two oppositely circulating vortices will therefore move with a uniform velocity parallel to each other and perpendicular to their separation, while like-circulating vortices will chase each other around a circle.
There is another effect, the Magnus force, when the vortex core has a significant mass difference relative to the equivalent volume of fluid (of either sign). In a nearly ideal fluid, such as superfluid helium, this Magnus force is very small. -Veit