Energetics of vortex ring formation

The mass and energy content of fully formed laminar vortex rings in air were compared with that of the original pulse that generated them for a variety of initial and boundary conditions. A preliminary comparison of multiple flash photographs of flow-visualized orifice- and chimney-generated vortices shows that: (1) the vortices produced with the chimney are appreciably larger, (2) the vortices produced by the orifices propagate considerably faster for a given pulse jet strength and jet diameter, (3) the slower-moving larger vortices tend to entrain more ambient fluid, and (4) the orifice-generated vortices tend to form more rapidly. A technique which enables calculation of kinetic energy of rotation from movie sequences is presented, and the ratio of characteristic translational speed to characteristic rotational speed is shown to be a useful parameter for correlation of vortex ring data. All data, regardless of initial and boundary conditions, fall on a single curve. A significant consideration for ejector technology is the observation that if the pulse duration is very short, vortices with high translational kinetic energy predominance may be formed.