  We present event-by-event simulations for central asymmetric light+heavy and
Au+Au collisions to investigate the formation and evolution of vortex-ring
structures in the longitudinal flow velocity profile. The production-plane
polarization of $\Lambda$ hyperons, defined w.r.t. the $\Lambda$ momentum and
the beam, can track the "vortex-ring" feature in the event, a characteristic
vortical structure generated by longitudinal flow gradients. We make
comprehensive model predictions for the rapidity-dependent vortex-ring
observables for different collision system sizes at $\sqrt{s_\mathrm{NN}} =
200$ and 72 GeV. Our predictions at the latter energy can be explored in the
future LHCb fixed-target experiment at the Large Hadron Collider.
