Convective vs. Absolute Instability in Couette-Taylor Flow with an Axial Flow

Couette-Taylor flow between cylinders with a superimposed axial flow is studied experimentally. The axial flow suppresses the basic stationary instability and leads to propagating Taylor vortices through a forward oscillatory bifurcation. While the throughflow velocity increases the propagating vortices are pushed downstream to the outlet so that at the velocity which corresponds to the absolute instability limit, the pattern is "blown" out of the system. The surprising coexistence of steady Ekman and propagating Taylor vortices close to the inlet and outlet boundaries was discovered. The wave number selection mechanism, similar to that existing in the front-propagating case, is also identified.