Numerical Simulation Of Upward Gas-liquid Churn Flow In A Vertical Pipe

The churn flow is a complex flow pattern that occurs between the slug flow and the annular flow,as the gas velocity in the vertical upward increases.Is also named foam flow and quasi-annular flow.The facts that a lot of studies have been done by different scholars on the churn flow and there are different names to describe the flow phenomena also illustrate the complexity of this flow feature.The irregular up-and-down oscillating motion of liquid phase in churn flow can cause fluctuation of pressure or other physical parameters.The sudden change caused by its instability may cause damage to the power system,pipelines or other components in production and operation system.A large number of references show that the study of gas-liquid stirred flow has important practical significance and theoretical value.A three-dimensional model of gas-liquid churn flow in vertical upward pipe was created in this thesis.Based on the Eulerian and VOF multiphase model and RNG k-? turbulence model.A numerical simulation of gas-liquid churn flow in vertical upward pipe was carried out by Fluent software.In the simulation,it was observed that the curve of average gas content on the surface and average pressure on the surface at the specific monitoring surface both showed periodic fluctuations in the form of rapid rise and rapid fall,and the changes of the two had corresponding relations.The fundamental reason was the periodic passage of liquid structure in the pipe.The cross-area average void fraction increases with the increase of superficial gas velocity and decreases with the increase of superficial liquid velocity.The cross-area mean pressure decreases with the increase of superficial gas velocity and increases with the increase of superficial liquid velocity.The structure change of two phases and the circulation process of liquid structure during the occurrence of the characteristic flow pattern of churn flow at the monitoring area were also observed and analyzed through the pressure contours.In addition,the characteristics of single peak and broad tail of The Probability Density Function(PDF)of churn flow were observed.Finally,the flow field is analyzed through the velocity vector diagram,and the reverse velocity vector and its gradient at the wall are observed intuitively.The research results are helpful to better understand the gas-liquid two-phase distribution and flow state of churn flow in vertical upward pipe,and have certain guiding significance.