Affiliations: Department of Mechanical Engineering, KAIST, 373-1
Guseong-dong, Yuseong-gu, Daejeon,305-701, Korea. E-mail:
[email protected]
Abstract: The effect of the exit geometry of a vortex ring generator was
studied experimentally. Two types of exit geometries were chosen: an orifice
and a nozzle. Vortex rings were generated by pushing a
solenoid-valve-controlled, pressurized-air jet through the circular opening of
the orifice or nozzle. Experiments were performed over a wide range of initial
Reynolds number (450 ⩽ Re ⩽ 4580) and
length-to-diameter ratio (0.7 ⩽ L / D ⩽ 7.0) of the air
jet. The exit geometry was found to significantly influence the entire course
of propagation of the vortex ring. The orifice-generated vortex ring had
superior characteristics to that produced by the nozzle under the same
conditions. The vorticity generated along the wall in the orifice exit plane
had a negligible effect on the circulation of the vortex ring within the
specified range of Reynolds number. Compared to the nozzle-generated vortex
ring, the orifice-generated ring showed reduced initial vorticity losses and
less diffusive entrainment of ambient fluid. The vortex rings produced by the
orifice attained more circulation, less entrainment of ambient fluid and hence
rapidly propagated through longer distances in comparison to the
nozzle-generated rings.
Keywords: vortex ring, evolution, propagation, pinch-off, mass entrainment