UNDERSTANDING INTERFACIAL EVOLUTION OF A TAYLOR DROP IN LIQUID FILLED PIPE JUNCTION USING LATTICE BOLTZMANN METHOD

Abstract

A lattice Boltzmann discretization based numerical study has been carried out to study the effect of sudden contraction in a rectangular channel during uprise of a lighter liquid droplet inside a heavier one. Diffused interface concept has been adopted for the prediction of liquid-liquid interface. Simulations are performed for passage of a kerosene droplet through restrictions like a sudden contraction, orifice, and remotely spaced contraction-expansion. A wide range of contraction ratio, droplet volume, and channel inclinations are considered to study the evolution of interface along the rectangular conduit. Symmetric change of interfacial shape has been observed while droplet tries to accommodate in the narrow confined zone after contraction. Using streamlines and velocity vectors, the reasons behind the interfacial evolution are established. With a decrease in contraction ratio, resistance against droplet passage increases which produces lengthier lamella like kerosene interface in the downstream of contraction. Droplet volume showed a significant effect in constructing the tail interfacial structure, which allows water to penetrate inside kerosene core for larger volumes. During the passage of a kerosene droplet in a channel with different inclination, stage of an asymmetric interface is observed. By providing offset contraction, local asymmetries are observed in the kerosene interface near the plane of area reduction. Efforts are continued to observe the kerosene droplet passage through an orifice which showed restricted and free interfacial evolution after contraction and expansion sections, respectively. The stabilizing zone between contraction and expansion showed influence on the generation of daughter droplets by fragmenting kerosene interface. Numerical investigation on interfacial evolution of kerosene Taylor drop in the water medium while bypassing through bends has been carried out using lattice Boltzmann method. To correctly capture the complex interface evolution, diffused interface concept has been implemented. During bypass through U bend, it has been observed that the drop reorients itself to adjust the effects caused by the restrictions along the bend. The phenomenon behind the interface evolution of drop has been explained with the help of phase contours, streamlines, averaged water film thickness at a particular cross sectional plane, drop tip Reynolds number and inscribed angle at bend centre. Simulations has been performed by considering the effect of inflow Reynolds number, gravity influence, sudden contraction at the bend, reduced connecting arm length in the return bends. In the return bends, with the increase of Reynolds number, the drop became more slender as it progresses along the bends. While considering gravity effect, during upflow in the connecting arm, drop has moved much faster than downflow. And observed an elongated tail near the first bend in downflow than upflow. Sudden reduction of cross sectional area at the bend has made the drop much more slender than situations having constant cross section. An effort has been also made to understand the significance of connecting arm length in the return bend which has shown lesser slenderness as compared to normal relaxed bend radius. Further study has been carried out to compare interfacial evolution steps between bypass of a drop through stepped forward bend and return U-bend at low Reynolds number.