Boundary effects on confined swirling flows with vortex breakdown

Confined steady swirling flows, driven by the end disks of a cylindrical/truncated conical enclosure have been numerically studied. Particular attention is focused on combined kinematics and geometric conditions of generation and control of the vortex breakdown phenomenon. First, the basic steady flow topology in a truncated conical cavity is described, which is shown to depend strongly on the direction as well as the rate of rotation of the end disks. For a set of governing flow parameters, the computations revealed the occurrence of bubble-like reverse flows, characterised by onaxis stagnation points. The present work, explores means of controlling the evolution of this physical phenomenon, by modifying the boundary conditions upstream the vortex breakdown. These means are found to either suppress or enhance the occurrence and size of the bubble