Confined steady flows, which display on-axis or
off-axis vortex breakdown, have been numerically studied, with particular
attention focused on means of controlling the vortex breakdown bubbles.
Firstly, the model flow driven by one end disk of a cylindrical enclosure,
which exhibits two distinct on-axis vortex bubbles, has been considered. The
resulting computations revealed that, sloping slightly the stationary
sidewall, beyond a threshold angle, provided an effective means of removing
the secondary vortex structure, and the flow remains steady. Besides, this
technique is shown to significantly modify the flow topology which displays
off-axis bubbles, induced by the co-rotation of the end disks. Then, the
effectiveness of adding a near-axis swirl, as suggested in recent
experimental works, has been analysed numerically and found to substantially
alter on-axis reverse flows.