GENERATION OF RING VORTICES IN AXISYMMETRICAL SPIN-DOWN - A NUMERICALINVESTIGATION

In this paper the sequence of finite-amplitude events that occurs prio r to the onset of Taylor-Gortler (TG) vortices in axisymmetric spin-do wn to rest is described. It is conjectured that the TG vortices are in duced by these events, which include internal waves that propagate alo ng the axis of rotation and transient vortex breakdown. The cascade of events is led by an internal ''solitary wave'' from each end wall. Th ese waves are induced by the end-wall (Bodewadt) boundary layers with concomitant Ekman ''blowing.'' The passage of the solitary wave causes a transient vortex breakdown followed by a train of internal waves. T he combined effect of these phenomena induces disturbances in the side wall boundary layer that grow and lead to the formation of TG vortices . The TG vortices that originate adjacent to the midplane of the cylin der in the sidewall (Rayleigh) boundary layer dominate the flow field at an intermediate time interval following the onset of spin-down. Fav orable comparisons with computationally determined onset times and sub sequent evolution of TG vortices reported in the literature support th e prediction that naturally occurring finite-amplitude phenomena induc e these vortices.