my question relates to the axisymmetrical ring vortex. i know that vorticity must remain constant within a tube, (helmholtz vortex theorem 2) so does that mean that the vortex lines on the outside of the ring are longer (spinning faster) than the ones on the inside? also is that what makes vortex rings propagate? like, does the ring draw energy from its translational speed and put it into maintaining its vorticity, or is it the other way around? or am i completely off?