Abstract

The primary breakup of liquid sheets into ligaments has a great effect on the size, velocity, and penetration of the droplets produced further by the disintegration of ligaments. The generated ligaments can be categorized in two general types based on their orientation with respect to the flow field; span-wise and stream-wise ligaments. This work contains a two- and three-dimensional computational study of the primary breakup of a viscous liquid sheet. A Volume of Fluid (VOF) based code is used to solve the governing equations and capture the interface between the liquid sheet and the surrounding gas. Since the interaction between the liquid and gas is the major source of the breakup, the liquid-gas interface boundary is modified in this work and it is implemented using linear stability analysis. The variation in the breakup time and breakup length of liquid sheets with fluid properties is investigated by a two-dimensional study. Fluid properties are stated in three non-dimensional numbers: Weber number, Ohnesorge number and the gas to liquid density ratio. The liquid surface tension shows a stabilizing effect by increasing both the breakup time and breakup length of liquid sheets. The liquid viscosity has more complicated effects; it increases the breakup length while at a certain range of Weber numbers, increasing the viscosity decreases the breakup time. Increasing the surrounding gas density decreases both breakup length and time. The study is extended to three-dimension to capture the stream-wise ligaments as well as span-wise ligaments captured in two-dimension. The effect of fluid parameters on the formation of stream-wise ligaments is presented. A mesh refinement study is conducted which demonstrates that providing at least 7 computational cells per sheet thickness would lead to results which are not dependent on the mesh size.