Numerical Simulation Of Flow Field And Local Resistance Of Oil-water Two-phase Flow Through Horizontal Pipe With Sudden Expansion

The sudden expansion structure has been widely used in energy,chemical industry,environmental protection and other fields.As most of the onshore oil fields have entered the middle or late stages of development,the method of water injection development makes the oil-water two-phase flow in the ground gathering system and the long-distance pipe network very typical.Therefore,the problems of mixing and conveying flow patterns and pressure drop characteristics of oil-water two-phase flow with different oil volume fraction and viscosity are investigated.For the rational selection of oil transportation mode and pumping efficiency,the flow pattern of two-phase flow through the expansion pipe is emphasized.Stability and local resistance studies are also critical for oil-water two phase flow.Based on the basic principles of fluid mechanics and the basic governing equations of fluid motion,combined with the relevant knowledge of oil-water two-phase flow,the flow pattern of white oil-water and lubricate oil-water two-phase flow through horizontal circular tube expansion is applied by CFD software FLUENT.The local resistance coefficient was numerically simulated with several factors such as different expansion ratio,viscosity,inlet mixing speed,Reynolds number and phase content.Intuitive means such as phase distribution cloud map,velocity vector diagram,streamline diagram,etc.,found that the sudden change of the boundary shape leads to the separation and reattachment of the flow after the sudden expansion of the cross section,which in turn causes the vortex behind the sudden expansion plane,right in the the two shoulders.The vortex flows counterclockwise direction in the upper shoudles,the lower shoulde is clockwise;under high Reynolds number,the symmetry and wall wettability of the two-phase flow field of white oil and lubricating oil are different;as the mixing flow rate increases,the length and flow rate of the recirculation zone are sufficient.The length of redevelopment area has become longer,and the vortex space has increased accordingly;While the ratio of sudden expansion has increased,the length and space of the vortex area after the expansion has also increased,and even multiple reverse vortices at the main vortex and boundary occer.The length of the influence of the flow rate core is also continuously extended.The change of the pressure through the sudden expansion is still positively correlated with the mixing density of the two phases.With the increase of the inlet mixing velocity,the larger the pressure variation of the flow through the sudden expansion,the more significant higher the pressure rise is.The two-phase sudden expansion coefficient shows no clear relationship between the viscosity of the oil,the oil content and the flow type,and there is no clear relationship with the Reynolds number,but the local resistance coefficient of the sudden expansion increases with the increase of the sudden expansion ratio.In addition,the traditional "Borda method" can cause large error,and the error value of the "trisection method" and in this paper is the smallest compared to the previous experimental data.The research results in this paper are very important for understanding the flow characteristics of sudden-expanding two-phase flow in heavy oil gathering pipeline network,reducing pipeline corrosion,optimizing pipeline structure,and reducing energy loss,so as to ensure safe production and optimize process,provide theoretical support for improving the efficiency of actual oil transportation.