Abstracts Category : Other

CFD Prediction of Stratified and Intermittent Gas-LiquidTwo-Phase Turbulent Pipe Flow Using RANS

by Imad Taher Ali

The transport of multi-phase flow in pipelines canbe met in a wide range of industrial applications, including theoil and gas industry, showing great savings in developments. Inaddition, as the exploration of new fields in oil and gas expandsto harsh environments, such as ocean or polar, the multi-phase flowtransport sometimes becomes the only feasible option. The importantfeatures of such multi-phase flow applications include flowregimes, pressure drop and liquid holdup. The precise estimation ofthese parameters has significant technical and economical impactson the design and operation of an oil and gas pipelines. Manyprediction correlations and methods have been developed;computational fluid dynamics (CFD) being one of them. This type ofmodelling approach has many advantages over the conventionalapproaches such as its ability to solve 3D transient problems;offering access to a wealth of information which with conventionaltechniques is extremely difficult to obtain. Therefore, interest inapplying CFD for multi-phase flow transport in pipelines has beenon the rise.This thesis is aimed at presenting CFD simulationsbased on the use of the Volume of Fluid model (VOF) approach forvarious conditions of gas-liquid turbulent flow in a horizontalcircular pipe. In the current VOF formulation in addition to thesecondary phase transport equation, a geometric reconstructiontechnique based on a piecewise-linear interface constructionapproach is used for reconstructing the interface.A number ofmulti-phase studies using different turbulence models to thecurrent one have recently appeared in the open literature forsimple flow geometries such as rectangular channels. However, mostof them assume specific boundary conditions (such asfully-separated phases for stratified flows, the use of square waveat the inlet to represent slug flow or imposing an interfacialdisturbance to initiate slugging). These require case-by-caseempirical information such as, interfacial roughness forstratified- or slug frequency for intermittent-flow. However, mostof them have not presented any detailed validation of theirresults. The former two points are very crucial for the design oftransport pipelines as a pre-knowledge of the operative flow regimeand empirical information are not available at the design stage.Thepredictive accuracy of the present simulations is tested againstmost common mechanistic approaches and detailed measurements ofstratified two-phase flow in a horizontal pipe of Strand (1993) andhave been found to be in reasonable quantitative agreement. For theintermittent flow type cases, the numerical results arequalitatively compared against experiments in a horizontal pipe ofAl-alweet (2008). The computed flow data of intermittent flow typeare further tested against some empirical and mechanisticcorrelations; the numerical results are qualitatively in areasonable agreement. Gas compressibility effects on thesimulations of slug flow are also explored and are found to bringabout some positiveAdvisors/Committee Members: Craft, Timothy.