Flow transition in swirled liquid sheets

Experiments are conducted to study the tulip-shaped and cone-shaped liquid sheets formed in swirl nozzles. It is shown that waves rapidly grow on the cone-shaped sheets and lead to its rupture unlike in the tulip-shaped sheets. The transition from the tulip-shaped to the cone-shaped sheet occurs when the liquid phase Weber number of the swirled annular sheet exceeds about 150. The turbulence level in the liquid sheet does not influence the Weber number at which the transition of the shape of the sheet takes place. The frequencies and rate of growth of the waves on the liquid sheets increase with Weber number. The transition takes place when the growth rate of waves is significant. The predicted variations of frequencies and growth rates, obtained by linear perturbation of the axial momentum equation, reproduce the increasing trends with Weber number observed in the experiments; however, the values are higher than those measured. A linear bifurcation analysis brings out the role of the different parameters influencing the stability of the swirled liquid sheet. The annular sheet is seen to be inherently unstable. The existence of a threshold value of Weber number, above which the transition of the shape of swirled liquid sheet takes place, is seen to be valid for all swirled liquid sheets.