Aerodynamic primary breakup at the surface of nonturbulent round liquid jets in crossflow

Abstract

An experimental investigation of nonturbulent round liquid jets in air crossflows at normal temperature and pressure was carried out, using pulsed shadowgraphs to observe jet deformation and breakup. Test liquids included water, ethyl alcohol and glycerol mixtures; liquid jet diameters were in the range 0.8-13 mm; liquid velocities were in the range 0-50 m/s; and air velocities were in the range 0-24 m/s. The corresponding test range involved Weber numbers of 2-200, Ohnesorge numbers of 0.00006-0.3, liquid/gas momentum ratios of 100-8000 and liquid/gas density ratios of 580-1020. The observations suggest qualitative similarities between the surface breakup of nonturbulent round liquid jets in crossflow and the secondary breakup of drops; for example, for Ohnesorge numbers less than 0.1, the onset of breakup occurs as bag breakup beginning at a Weber number of 5, there is a second transition to a bag/shear breakup regime at a Weber number of 60 and a third transition to a shear breakup regime at a Weber number of 110. A long-ligament shear breakup regime appears at Ohnesorge numbers greater than 0.1. At the onset of breakup, the deformation of the liquid column yields a frontal diameter roughly twice the initial jet diameter, relatively independent of the breakup regime. The characteristics of waves associated with the breakup process were also studied, finding that bag and bag/shear breakup involved both liquid column and surface waves while shear breakup involved only surface waves. The results also showed that breakup characteristics were mainly influenced by the Weber number while effects of the liquid/gas momentum ratio are small. Nomenclature