Numerical modelling of transient gas-liquid flows (application to stratified & slug flow regimes)

A new methodology was developed for the numerical simulation of transient two-phase flow in pipes. The method combines high-resolution numerical solvers and adaptive mesh refinement (AMR) techniques, and can achieve an order of magnitude improvement in computational time compared to solvers using conventional uniform grids. After a thorough analysis of the mathematical models used to describe the complex behaviour of two-phase flows, the methodology was used with three specific models in order to evaluate the robustness and accuracy of the numerical schemes developed, and to assess the ability of these models to predict two physical flow regimes, namely stratified and slug flows. The first stage of the validation work was to examine the physical correlations required for an accurate modelling of the stratified smooth and wavy flow patterns, and a new combination of existing correlations for the wall and interfacial friction factors was suggested in order to properly predict the flow features of the experimental transient case investigated. The second and final phase of the work dealt with the complex and multi-dimensional nature of slug flow. This flow regime remains a major and expensive headache for oil producers, due to its unsteady nature and high-pressure drop. The irregular flow results in poor oil/water separation, limits production and can cause flaring. The modelling approached that was adopted here is based on the two-fluid model, which can theoretically follows each formed slug and predicts its evolution, growth and decay, as it moves along the pipe. However, the slug flow study, performed here through a test case above the Inviscid Kelvin-Helmholtz transition from stratified to slug flow, showed that the incompressible two-fluid model used is unable to accurately predict most of the features of this complex flow. Mechanisms such as the interfacial wave formation, the slug growth and propagation, although observed from the simulations, cannot be accurately determined by the model.