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原文传递 A Modified Cfd-Based Sand Erosion Prediction Procedure for Pipe Elbows and Similarity Analyses on Erosion Tests

论文题名：	A Modified Cfd-Based Sand Erosion Prediction Procedure for Pipe Elbows and Similarity Analyses on Erosion Tests
关键词：	Sand particle erosion;Elbow;Gas flow;Gas-mist flow
摘要：	The oil and gas mixture extracted from the wells and transported over long distancesis often in the form of multiphase flow, which is greatly complicated especially whenflowing through the fittings.The sand erosion in gas-predominant pipelines for drygas, gas-mist and annular flows is much more serious than that for other flow patterns. 　　Firstly, a mechanical model of film movements is developed based on thetreatments on the annular flow field.The initial conditions at the inlet are determinedby adopting a validated film thickness correlation for fully developed upward annularflow in vertical pipes.The overall pressure gradient is assumed to be uniform allalong the axial distance within the elbow and the static pressure is also uniform onevery cross section.The axial velocity normal to the cross-sectional plane is uniformrespectively for the liquid film and the core region.The droplets are assumed to travelin straight lines normal to the inlet plane until colliding on and absorbed by the liquidfilm surface.The liquid film motion is divided into the axial direction and the radialdirection.Energy conservation law and Newton's second law are respectively used inthe two directions.The film motion calculation is executed by using a discrete methodwith an explicit solution.The average film thickness and circumferential distributionon an arbitrary cross section can be obtained for given annular flow conditions.Themechanical model is verified by comparing the predicted average film thickness andcircumferential distribution with three sets of experimental data from the literature. 　　Secondly, a modified CFD-based erosion prediction procedure is proposed basedon mechanistic analyses of the three flow patterns.The procedure is developed to besuitable for the erosion calculation in elbows for gas, gas-mist and annular flows.Forfully developed flow field, the core region of the pipe is regarded as single-phase flowwith the property of gas or the mixture of gas and droplets.The difference is theparticle near-wall behavior determined by whether there is liquid film attached on thepipe wall.For gas and gas-mist flow conditions there is no velocity decay, while forannular flow the particle-wall impact velocity is calculated by using the predictedresults from the mechanical film thickness model.The turbulence models arevalidated through investigations on the velocity field and static pressure.Thenumerical settings of particle number and grid density are discussed on thecomputation stability.Over a hundred sets of experimental data are adopted for theverification of the CFD procedure by investigating on the maximum penetration rateand its position and the erosion profile on the elbow extrados.The comparison ofcalculation accuracy among the CFD procedure and four empirical or semi-empiricalmodels are also conducted.The present erosion prediction procedure proves to beefficient for gas, gas-mist and annular flow conditions. 　　Thirdly, the corresponding relationship between engineering conditions andmodel experiments is described by proposing a set of similarity criteria.The criteriacan help predicting the maximum penetration rate and its position in engineeringconditions through the corresponding experimental design.The similarity relationshipis made up respectively for gas and gas-mist flows by presenting the principaldimensionless numbers on the flow field and particle response behaviors.Typicalmodel tests from the literature are extrapolated to a series of similar engineering casesrespectively.Then two dimensionless similarity judgment numbers are calculated bythe present CFD procedure and four empirical or semi-empirical models.Thesimilarity criteria are verified by examining the equivalence trends of the twojudgment numbers of the model tests and engineering cases.The present similaritycriteria prove to be rational and applicable in building the corresponding relationshipbetween model experiments and engineering.
作者：	Mingyang Liu
专业：	Hydraulic Engineering;Port,Coastal and Offshore Engineering
导师：	Haixiao Liu
授予学位：	博士
授予学位单位：	天津大学
学位年度：	2016
正文语种：	中文