On the creation of stagnation points near straight and sloped walls

We report the results of an experimental and numerical study of the creation of stagnation points in a rotating cylinder of fluid where one endwall is rotated. Good agreement is found with previous results where the stagnation points are formed on the free core of the primary columnar vortex. The effect of adding a small cylinder along the center of the flow is then investigated and the phenomena are found to be robust despite the qualitative change in the boundary conditions. Finally, we show that sloping the inner cylinder has a dramatic effect on the recirculation such that it can either be intensified or suppressed.