Comparison of Numerical Methods for Two-Fluid Model for Gas–Liquid Transient Flow Regime and Its Application in Slug Modeling Initiation

Abstract

The formation of slug in the horizontal pipes due to the hydrodynamic instabilities has always been of great interest to many researchers. In this research, the effect of various numerical methods on the simulation of slug flow initiation using pressure-free two-fluid model has been investigated. The two-fluid model has been solved by conservative shock-capturing method. When the slug is formed, a strong discontinuity will be developed in the flow stream. Therefore, a numerical method should have the capability to predict this discontinuity with high accuracy and should not have oscillation near the discontinuity. There are three different models to simulate two-phase flow systems: homogeneous equilibrium model, drift-flux model, and two-fluid model. This research used two-fluid model for predicting the slug flow initiation through a pipe. Four different numerical two-fluid methods, namely Lax-Friedrichs, Rusanov, Richtmyer and flux-corrected transport (FCT) have been used in this research. Results show that FCT is the most accurate method for the prediction of the slug flow initiation among other methods where Rusanov and Lax-Friedrichs numerical methods were in the next steps, respectively. Due to the oscillatory nature near the discontinuity caused by formation of slug regime, the Richtmyer numerical method is not an appropriate method for modeling slug flow regime. Results also show that as the numerical diffusion of these methods reduces in the flow field, the slug flow initiation will be predicted with higher accuracy.