What happens when two oppositely rotating whirlpools merge? Say both are upright and roughly equal in size and rotation speed. Or if this never happens in nature, what happens when it is simulated? Actually, this seems quite feasible in nature, and should result in something much less whirly than either of the whirlpools. Maybe at least as interesting would be what happens when two whirlpools merge that are rotating in the *same* sense. --Dan ----- On Mon, Nov 3, 2014 at 4:33 PM, Henry Baker <hbaker1@pipeline.com> wrote: What happens when 2 equal & oppositely-rotating black holes merge? . . . -----

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