Abstract
We present a front-tracking/finite difference method for tracking the unsteady motion and the breakup of a compound jet, which is governed by the incompressible Navier-Stokes equations for Newtonian fluids. Two different interfaces separating three fluids are represented by connected Lagrangian markers that move on a stationary Cartesian grid. The distribution of the density and viscosity jumps from the front to the nearby grid points is determined by using area weighting, and solving corresponding Poisson equations. The method is validated through comparisons with the linear and nonlinear analysis, and comparisons with experiments. Non-coflowing and coflowing systems formed by two and three different fluids have been investigated using the method. Here, we focus on the coflowing system in which various modes of the compound jet formation and breakup have been revealed: inner dripping-outer dripping mode, inner jetting-outer jetting mode and mixed drippingjetting mode; depending on the flow parameters such as the Reynolds number Re, the Weber number We, the interfacial tension ratio or the velocity ratios. Starting from the dripping mode, an increase in We or a decrease in Re results in the jetting mode. Decreasing the interfacial tension ratio forms the mixed dripping-jetting mode. In addition, the jetting mode can be produced by increasing the velocity ratios. These modes produce various types of drop such as simple drops and single-core and multi-core compound drops.
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