Three-dimensional steady vortex breakdown in laboratory models of confined swirling flows

Recent experiments (Spohn et al. 1998) have shown that the stationary vortex breakdown bubbles, which form along the axis of a closed cylindrical container with a rotating lid, are open, with inflow and outflow, and asymmetric at their downstream end. We study numerically the container flow, by solving the three-dimensional Navier-Stokes equations, in order to clarify the origin and elucidate the underlying physics of these complex, three-dimensional flow features. The stationary vortex breakdown bubbles we simulate exhibit all the asymmetries observed in the laboratory. By analyzing the Lagrangian characteristics of the calculated flowfields, we explain the origin of these asymmetries, clarify the experimentally documented filling and emptying mechanisms, and show that the flow in the interior of stationary vortex breakdown bubbles exhibits chaotic particle paths. In agreement with the observations of Spohn et al. (1998), we also find that the break of axial symmetry in this axisymmetric geometry is linked to the growth of three-dimensional modes inside the cylindrical wall boundary layer.