Effect of an Exit-Wedge Angle on Pinch-off and Mass Entrainment of Vortex Rings in Air
- 82 Downloads
The effects of exit-wedge angle on evolution, formation, pinch-off, propagation and diffusive mass entrainment of vortex rings in air were studied using digital particle image velocimetry. Vortex rings were generated by passing a solenoid-valve-controlled air jet through a cylindrical nozzle. Experiments were performed over a wide range of exit-wedge angles (10° ≤ α ≤ 90°) of the cylindrical nozzle, initial Reynolds numbers (450 ≤ Re ≤ 4,580) and length-to-diameter ratios (0.9 ≤ L/D ≤ 11) of the air jet. For sharp edges (α ≤ 10°), a secondary ring may emerge at high Reynolds numbers, which tended to distort the vortex ring if ingested into it. For blunt edges (α ≥ 45°), by contrast, stable vortex rings were produced. The formation phase of a vortex ring was found to be closely related to its evolution pattern. An exit-wedge angle of 45° was found to be optimal for rapid pinch-off and faster propagation and better stability of a vortex ring. Diffusive mass entrainment was found to be between 35% and 40% in the early stages of a vortex ring propagation and it gradually increased throughout the course of vortex ring propagation. Entrainment fraction was found to be sensitive to the L/D ratio of the initial jet and decreases when the L/D ratio is increased.
KeywordsVortex ring Evolution Pinch-off Mass entrainment
- 2.Lim, T.T., Nickels, T.B.: Vortex Rings. Fluid Vortices. Kluwer Academic, Norwell, pp. 95–153 (1995)Google Scholar
- 12.Muller, E.A., Didden, N.: Zur erzeugung der zirkulation bei der bildung eines ringwirbels an einer dusenmundung. Stroj. Casop. 31, 363–372 (1980)Google Scholar
- 20.Dziedic, M., Leutheusser, H.J.: An experimental study of viscous vortex rings. Exp. Fluids 21, 315–324 (1996)Google Scholar