Multiscale modeling and validation of the flow around Taylor bubbles surrounded with small dispersed bubbles using a coupled VOF-DBM approach

Abstract

This work presents a multiscale three-dimensional CFD model for the simulation of two-phase gas-liquid flows with different interface length scales, with focus on slug flow pattern. The model is based on the coupling of the Volume-of-Fluid (VOF) method, used to model the large-scale interface dynamics, and the Discrete Bubble Model (DBM) for modeling the small-scale bubbles, which allows to simulate two-phase flows with different interface length scales. A validation study is conducted independently for the VOF and DBM methods, by comparing the numerical results with experimental data from the literature, showing a very good agreement. A model for the collision between the VOF interface and Lagrangian bubbles is proposed and also independently validated. The coupled VOF-DBM model is used to study a liquid-gas two-phase flow with different interface length scales, where large Taylor bubbles and small dispersed bubbles are present. The results demonstrate that the presence of the small dispersed bubbles alters the flow structure around the Taylor bubble, increases the terminal velocity of the Taylor bubble and affects the flow structure in the wake region, which is directly related to heat and mass transfer rates in slug flow.