Abstract:
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.
