Numerical simulation of two-phase gas-liquid flows in inclined and vertical pipelines

摘要

The present thesis describes the advances made in modelling two-phase flows in inclinedpipes using a transient one-dimensional approach. The research is a developement of anexisting numerical methodology, capable of simulating stratified and slugging two-phaseflows in horizontal or inclined single pipes. The aim of the present work is to extend thecapabilities of the approach in order (i) to account for the effect of the pipe topographyin the numerical solution of the two-fluid model, and (ii) to simulate vertical bubbly twophaseflows at various pressures in large diameter pipes, and (iii) to model stratified andterrain-induced slugging in two-phase flow pipelines made of several uphill, downhill andlevel sections.A transient compressible two-fluid model based on the one-dimensional form of the massand momentum conservation equations for the gas and liquid phases, is developed topredict those flow configurations. The wall to fluid and the interphase interactions areaccounted for by constitutive relations which are flow regime dependent. The conservationequations are discretized using a finite volume method.An algorithm is created to enable simulations on pipelines made of several sections, andaccount for the effect of the topography in the simulations. The methodology is appliedto the compressible model in order to evaluate the robustness and accuracy of the numericalschemes, especially for the high-resolution Advection Upwinding Splitting Method(AUSM) associated to the compressible model. It also assesses the ability of the methodto predict three physical flow regimes, namely stratified, bubbly and terrain-induced slugflows.The terrain-induced slugging study is performed on a slightly inclined (±1.5°) V-sectionsystem. The use of hydrodynamic slug correlations for hilly-terrain slugging is discussed.It shows to be conclusive with a good agreement with experimental measurements obtainedfor slug frequency and slug length predictions. Mechanisms such as the waveformation at the interface, the slug growth and propagation as well as merging slugs, canalso be observed by the model. The bubbly model is extensively tested against availabledata collected by Nottingham University from experimental systems of 70mm and 189mmvertical pipes. In some cases, void fraction predictions are within 10% with experimentaldata, and pressure predictions within 4%. The simulation results compare well in overallwith the measurements. In large diameter pipes, some variations are observed between thenumerical 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 isalso observed that, in fully-developed flows, the model does give satisfactory predictions.