Interaction between the Ekman layer and the Couette-Taylor instability

The finite aspect ratio effect on Couette-Taylor how was studied by means o f three-segment electrodiffusion probes. The geometry of the Couette appara tus was characterized by the cylinders radii R-1 = 100 mm and R-2 = 110 mm and by the aspect ratio Gamma = L/(R-2-R-1)=9.85. The velocity gradient com ponents were measured by electrodiffusion probes placed at the steady outer wall and at a confining ring between cylinders. The distributions of the a zimuthal and axial components of velocity gradient at the outer wall indica ted the existence of Ekman vortices at rotation rates smaller than the crit ical rate of onset of Taylor vortices in an infinitely long gap. The amplit ude of the azimuthal component of velocity gradient of Ekman vortex grows l inearly with Taylor number. The results of measurements are in good agreeme nt with numerical simulations made by a finite element method which in turn gives a complete description of the flow. (C) 2000 Elsevier Science Ltd. A ll rights reserved.