L-transition from right- to left-handed helical vortices

摘要

This study is devoted to analysing changes in the helical symmetry of axial vortex structures. The aim is to provide an improved understanding of the appearance of recirculating bubbles in swirl flows. The bubble generation is usually referred to as vortex breakdown, see e.g. Leibovich 1978 or Escudier 1988. The study concerns a viscous, incompressible, axisymmetric flow in a closed cylinder with co-rotation of the end-covers in the regime where the appearance of the first bubble takes place, see Br0ns et al. 1999. For the investigated flow regime only one type of change in helical symmetry, denoted L-transition, was observed. The change of helical symmetry provides a possible explanation for the appearance of bubble structures in the vortex breakdown problem.