抄録
In this paper, we numerically study the formation and breakup of an axisymmetric immiscible, viscous and laminar compound jet flowing in a coflowing immiscible outer fluid. We use a front-tracking/finite difference method to track the evolution and breakup of the compound jet, which is governed by the incompressible Navier-Stoke equations for Newtonian fluids. The method is modified to account for three-fluid flows. The density and viscosity jumps at interfaces are distributed to the nearby grid points by using area weighting and solving Poisson equations. Thereby, we investigate the effects of interfacial tensions, in terms of the Weber number We and interfacial tension ratio σ_<21>, on the various modes of the compound jet breakup: inner dripping - outer dripping, inner dripping - outer jetting, and inner jetting - outer jetting. Numerical results show that the transition from dripping to jetting is affected not only by the Weber number but also by interfacial tension ratio since the compound jet possesses two different interfaces, i.e., either decreasing We or increasing σ_<21> promotes the dripping regime. In addition, the orifice ratio also affects the transitional values of We and σ_<21>, i.e., as it increases the transition We decreases and the transition σ_<21> increases. The transition from dripping to jetting is mapped in the We - σ_<21> parameter space. However, the variations of We and σ_<21> do not affect the aspect ratio of the compound drops.
