Study On Flow Characteristics Of Slug Flow And Annular Flow In Horizontal Elbow

Mixed-fluid pipelines are universally applied in ground oil & gas gathering system and the flow characteristics are different with distinctive flow regimes.Thus far,the researches of multiphase flow in horizontal,inclined,and fluctuant pipelines have been done so much,however,for elbow pipeline,merely pertinent erosion studies based on simulation and experiments are cited.Therefore,it is imperative to investigate the two-phase flow characteristics in elbow pipeline.In this paper,air and water are used as the experimental medium to build the gas liquid two phase flow test loop,by adjusting the different gas and liquid flow,combined with high speed camera,the doppler velocimeter,pressure differential pressure data acquisition system and experiment means such as WMS measurement system of slug flow and annular flow horizontal elbow pipe gas liquid two phase flow of fluid distribution,void fraction,pressure,differential pressure and liquid film flow rate characteristics are studied,and analysis of gas and liquid flow rate change on the influence of elbow flow characteristics.Multi-Fluid VOF model in FLUENT software was chosen on the part of the experiment condition 3-d transient numerical simulation research,slug flow and annular flow in horizontal elbow pipe different corresponding to the flow field of gas and liquid flow,analysis of gas and liquid flow rate changes on the elbow gas liquid two phase flow distribution and pressure,the influence of liquid flow rate,the experimental research for this article content and supplement for the next elbow in the erosion research to provide theoretical foundation and reference basis.As to slug flow,the results indicate that the bubbles in the liquid plug move along the inside of the elbow.After the end of the liquid plug falls off,the liquid film swirls on the outside of the elbow first,and then the gas-liquid interface is stratified and stabilized.With the increase of gas-liquid flow rate,the bubbles inside the elbow become variable and large.The gas holdup of different sections of the horizontal elbow,the pressure at the inlet and outlet of the elbow,the pressure difference in the elbow section and the liquid film velocity at different positions of the elbow all show quasi-periodic fluctuations.The inlet section of the elbow has the largest gas holdup and the center section has the smallest gas holdup.The radial gas holdup at different sections of the horizontal elbow is smaller as it is closer to the pipe wall.The central section of the gas-holdup elbow near the pipe wall is the smallest,and the inlet section of the gas-holdup elbow near the pipe wall is the largest.The gas holdup decreases with the increase of liquid velocity and increases with the increase of gas velocity.The pressure of the whole pipe shows a downward trend,and the pressure inside the elbow is lower than that outside the elbow.The pressure at different positions of the elbow and the pressure difference in the elbow segment increase with the increase of the gas-liquid flow rate.The liquid velocity distribution in the elbow is uneven,and there is secondary flow in the elbow.The liquid plug velocity in the center of the elbow is the smallest,and the liquid plug velocity in the upstream of the elbow is the largest.The liquid velocity outside the elbow is greater than that inside the elbow.With the increase of gas-liquid velocity,the liquid velocity at different positions of the elbow increases,and the secondary flow phenomenon weakens.As to annular flow,the results show that the liquid film at the bottom and outside of the elbow is thicker than the top and inside of the elbow.The thickness of liquid film increases with the increase of liquid velocity and decreases with the increase of gas velocity.The outlet section of the elbow has the largest gas holdup,and the center section of the elbow has the smallest gas holdup.The radial gas holdup at different sections of the flat elbow is smaller as it is closer to the pipe wall.The inlet section of the elbow near the pipe wall is the largest,and the center section of the elbow near the pipe wall is the smallest.The gas holdup decreases with the increase of liquid velocity and increases with the increase of gas velocity.The pressure of the whole pipe shows a downward trend,and the pressure inside the elbow is lower than that outside the elbow.The pressure at different positions of the elbow and the pressure difference in the elbow segment increase with the increase of the gas-liquid flow rate.The liquid velocity distribution in the elbow is uneven.There is a secondary flow phenomenon in the elbow.The liquid film velocity at the bottom of the upstream pipe of the elbow is the smallest,the liquid film velocity at the bottom of the center pipe is the largest,and the liquid film velocity in the main area is the smallest.With the increase of gas-liquid velocity,the liquid velocity at different positions of the elbow increases,and the secondary flow phenomenon weakens.