Interaction between the Ekman layer and the Couette–Taylor instability

The finite aspect ratio effect on Couette–Taylor flow was studied by means of three-segment electrodiffusion probes. The geometry of the Couette apparatus was characterized by the cylinders radii R1=100 mm and R2=110 mm and by the aspect ratio Γ=L/R2−R1=9.85. The velocity gradient components were measured by electrodiffusion probes placed at the steady outer wall and at a confining ring between cylinders. The distributions of the azimuthal and axial components of velocity gradient at the outer wall indicated the existence of Ekman vortices at rotation rates smaller than the critical rate of onset of Taylor vortices in an infinitely long gap. The amplitude of the azimuthal component of velocity gradient of Ekman vortex grows linearly with Taylor number. The results of measurements are in good agreement with numerical simulations made by a finite element method which in turn gives a complete description of the flow.