Abstract:
The present thesis describes the advances made in modelling two-phase flows in inclined
pipes using a transient one-dimensional approach. The research is a developement of an
existing numerical methodology, capable of simulating stratified and slugging two-phase
flows in horizontal or inclined single pipes. The aim of the present work is to extend the
capabilities of the approach in order (i) to account for the effect of the pipe topography
in the numerical solution of the two-fluid model, and (ii) to simulate vertical bubbly twophase
flows at various pressures in large diameter pipes, and (iii) to model stratified and
terrain-induced slugging in two-phase flow pipelines made of several uphill, downhill and
level sections.
A transient compressible two-fluid model based on the one-dimensional form of the mass
and momentum conservation equations for the gas and liquid phases, is developed to
predict those flow configurations. The wall to fluid and the interphase interactions are
accounted for by constitutive relations which are flow regime dependent. The conservation
equations are discretized using a finite volume method.
An algorithm is created to enable simulations on pipelines made of several sections, and
account for the effect of the topography in the simulations. The methodology is applied
to the compressible model in order to evaluate the robustness and accuracy of the numerical
schemes, especially for the high-resolution Advection Upwinding Splitting Method
(AUSM) associated to the compressible model. It also assesses the ability of the method
to predict three physical flow regimes, namely stratified, bubbly and terrain-induced slug
flows.
The terrain-induced slugging study is performed on a slightly inclined (±1.5°) V-section
system. The use of hydrodynamic slug correlations for hilly-terrain slugging is discussed.
It shows to be conclusive with a good agreement with experimental measurements obtained
for slug frequency and slug length predictions. Mechanisms such as the wave
formation at the interface, the slug growth and propagation as well as merging slugs, can
also be observed by the model. The bubbly model is extensively tested against available
data collected by Nottingham University from experimental systems of 70mm and 189mm
vertical pipes. In some cases, void fraction predictions are within 10% with experimental
data, and pressure predictions within 4%. The simulation results compare well in overall
with the measurements. In large diameter pipes, some variations are observed between the
numerical and the measured results: especially the model underpredicts the flow at the bottom of the pipe. Limitations of the model for this particular case are highlighted. It is
also observed that, in fully-developed flows, the model does give satisfactory predictions.