Numerical Investigation of Liquid-Liquid Coaxial Flows

This paper presents numerical results of the interfacial dynamics of axisymmetric liquid-liquid flows when the denser liquid is injected with a parabolic inlet velocity profile into a coflowing lighter fluid. The flow dynamics are studied as a function of the individual phase Reynolds numbers, viscosity ratio, velocity ratio, Bond number, and capillary number. Unsteady, axisymmetric flows of two immiscible fluids have been studied using commercial software, $FLUENT®$ with the combination of volume of fluid (VOF) and continuous surface force (CSF) methods. The flows have been categorized as “flow-accelerated regime (FAR) and “flow-decelerated regime” (FDR) based on acceleration/deceleration of the injected fluid. The injected jet diameter decreases when the average inlet velocity ratio is less than unity. The outer fluid velocity has a significant effect on the shape and evolution of the jet as it progresses downstream. As the outer liquid flow rate is increased, the intact jet length is stretched to longer lengths while the jet radius is reduced due to interfacial stresses. The jet radius appears to increase with increasing viscosity ratio and ratio of Bond and capillary numbers. The results of numerical simulations using $FLUENT$ agree well with experimental measurements and the far-field self-similar solution.