Abstract
The amplification rate of azimuthal waves of a vortex ring due to the Widnall instability is reduced by means of the axial flow along a vortex core called a "swirl", so that the vortex ring with swirl increases its movable distance. On the other hand, it leaves a part of circulation with its fluid particles in helical shape on the path just after the formation stage. A successive 3-D flow visualization images are reconstructed from a stack of parallel imaged planes obtained by using the laser scanning technique for the purpose to investigate the complicated 3-D structure of vortices. And we examine the early stage of a vortex ring with swirl and helical streak structures which are the main cause of the circulation decrease.
