Dynamics of point vortices in a special rotating frame

A special rotating frame (SRF) is found in which the relative motion of point vortices is simpler, has minimum energy and reveals dynamical features not discernible in the usual fixed frame. The angular velocity of this frame is a solution of the equations of motion and generally is not constant. Examples of periodic, quasiperiodic and chaotic motions with respect to the SRF show that: (a) periodic orbits are closed lines (not space filling as in the fixed frame, (b) quasiperiodic orbits form steady patterns and (c) chaotic motions create asymptotic symmetries that reflect permutation symmetry of the Hamiltonian.