Numerical analysis of ligament instability and breakup in shear flow

Abstract

In this study, we perform a numerical analysis of the instability of a ligament in a shear flow and investigate the effects of air–liquid shear on the growth rate of the ligament interface, breakup time, and droplet diameter formed by the breakup. The ligament is stretched in the flow direction by the shearing of airflow. Furthermore, as the influence of the shear flow increases, the ligament becomes deformed into a liquid sheet, and a perforation forms at the center of the liquid sheet. The liquid sheet breaks up due to the growth of the perforation and contracts under the influence of surface tension, forming two ligaments with diameters smaller than that of the original ligament. The shearing of the airflow causes the original ligament to elongate, and the cross section of the ligament becomes elliptical, which increases instability. As a result, the growth rate of the ligament exceeds the theoretical value and increases with increasing the wavenumber of the initial disturbance. Therefore, the diameter of the formed droplets in the shear flow decreases due to the increase in the wavenumber that governs the breakup of the ligament, and as the growth rate increases, the breakup time for the ligament decreases. As the velocity difference of the shear flow increases, constrictions of the ligament form earlier and the diameter of the satellite droplet increases. As the diameter of the satellite droplet increases and that of the main droplet decreases, the dispersion of the droplet diameter decreases, making the diameter uniform.