Effect of confinement and prefilming on the stability of an annular liquid sheet

A linear temporal analysis describing the stability of an annular, swirling, inviscid liquid sheet is presented. The liquid sheet is considered to be exposed to swirling gas flows on either side. Realizing the importance of confining walls in practical atomizers, the effect of the walls on the growth rate of the instability has been elaborately reported in this work. Two different confining configurations have been shown: wall surrounding the outer gas; and confining walls around the annular liquid sheet. The latter geometry eliminates the interaction of the liquid with the outer air. The results are validated with the limiting case when the outer air stream thickness tends to infinity. The efficiency of confining the outer air in terms of increase in the growth rate has been shown. A prefilming atomizer is seen to produce a high critical wave number, which leads to the formation of smaller droplets. A parametric study is carried out with varying hydrodynamic parameters for both axisymmetric and higher helical modes for such atomizers with confinements. The role of swirl in the air streams in shifting the dominant mode from axisymmetric to higher helical modes is clearly shown. © 2013 by Begell House, Inc.