CFD study of oil-in-water two-phase flow in horizontal and vertical pipes

Abstract

The effectiveness of the classical Lagrangian method implemented in 3D CFD solver to simulate highly turbulent vertical and horizontal liquid-liquid dispersed flows where intensive turbulent migration of droplets make the flow behaviour complex is in the focus of the study. Dispersed oil-in-water two-phase pipe flow is analysed numerically using CFD solver ANSYS Fluent where a three-dimensional mathematical model of two-phase flow in pipes is developed. The Euler-Lagrange scheme is employed to resolve the interaction between the fluid (water) and droplet (oil) phases. The flow field of the continuous fluid phase is calculated by solving the Reynolds-averaged Navier-Stokes (RANS) conservation equations that are coupled with a high Reynolds number k-ε turbulence model and standard wall function. The Lagrangian method is used to resolve the motion of oil droplets. The drag, gravity, buoyancy and shear-lift forces are considered. The shear-lift force is of primary focus and is modelled and incorporated into the governing equations of the solver through the User Define Function (UDF) option as the external program. The two-way coupling procedure is employed. Here, droplet breakup and coalescence are not modelled. Mean droplet size is calculated using analytical methods. The model is validated with high level of accuracy against published experiments where the frictional pressure drop in vertical and horizontal dispersed oil-water flows is measured. The effect of mixture flow velocity and fluid phase superficial velocity on the droplet dynamics in vertical and horizontal pipes is investigated numerically. The transition from dispersed two-phase flow to stratified flow regime is analysed for the case of horizontal pipe flow. It has been found that the shear-lift force has much higher importance for the adequate flow representation as compared to the break-up/coalescence phenomena in the case of highly turbulent liquid-liquid dispersed pipe flows.