A modeling of vortex rings in an axisymmetric pulsed jet.

The behavior of vortex rings in the initial region of an axisymmetric pulsed jet was simulated by replacing an annular shear layer with a particular vorticity distribution by an array of discrete vortex ring filaments. This modeling was restricted to an inviscid and axisymmetric condition. Consequently, the detailed structure in a real jet cannot be explained by this model. Nonetheless, it provided a good representation of the rolling-up of the shear layer, the vortex ring formation and the transport velocity of the vortex ring. The experimental result, that the pattern of vortex ring formation was roughly classified into three types by Strouhal number, was also explained by this model. The behavior of the vortex ring after formation (for example, vortex ring coalescence) was successfully simulated by replacing a vortex ring by a single vortex ring filament. It was found that vortex ring motion in the initial region of a jet was essentially inviscid.