Experimental study of axial flow in a vortex ring

For a vortex ring at Re=1600, it was found that two types of azimuthal flow (axial flow) exist inside the vortex tube. The axial flow appears when the amplitude of a wavy deformation of the vortex ring becomes appreciable. The axial flow starts to grow before the wave-breaking and its speed increases gradually. In order to investigate the relation between the deformation of the vortex core and the axial flow, the flow field was examined experimentally using smoke visualization and the smoke wire technique simultaneously. Axial flow velocities are estimated from flow visualization images.