The structure of the confined swirling flow under different phase boundary conditions at the fixed end of the cylinder

The paper analyzes the complex topology of swirling flows generated in the cylinder by its rotating end face. Using the flow visualization for different parameters of swirl of the upper end of the cylinder, the general laws of the evolution of the region with a counter flow (bubble-like vortex decay) are shown regardless of the contact of the studied vortex flow with various liquids or gas at the free end. The research has found for the first time that the scenario for the appearance of the bubble-like breakdown region depends weakly on the properties of the medium that restricts the circulation of the working fluid, but differs significantly from the dynamics of vortex flows limited by the solid second wall - the fixed end of the cylinder. For example, during the axial vortex breakdown, the modes of stationary vortex motion with the appearance of the recirculation zone contact with the interface surface of two media have been revealed, which is not typical for closed flows. The results obtained are of interest for further development of vortex devices and reactors that provide complex vortex motion of ingredients for mass transfer intensification, both in terms of optimizing the operation of existing setups and for designing new devices.