Vortex scenario and bubble generation in a cylindrical cavity with rotating top and bottom

The creation of recirculation bubbles in a steady, viscous flow in a cylindrical cavity with co-rotating top and bottom is investigated numerically. By varying the Reynolds number and the aspect ratio of the cylinder various axial-symmetric flow regimes are studied. It is observed that the topology of re-circulating vortex structures is associated with a change in helical symmetry of the vortex lines. The computations show that symmetry changes take place at increasing Reynolds numbers and that flow reversal on the center axis is associated with a growth of the twist parameter of the vortex lines. For all studied flow cases, independent of aspect ratio and Reynolds number, it was observed that the twist parameter of the central vortex attains a threshold value of K≅0.6 at the point where flow reversal takes place.