Numerical Simulation On Flow Characteristics Of Gas-water Two-phase Slug Flow In The Horizontal Variable Diameter Pipe

Slug flow,as a kind of flow pattern which is harmful to oil and gas pipelines and various instruments in gas-liquid two-phase flow,widely appears in various process links of oil industry.Variable diameter pipe widely used in energy,power,petrochemical and other fields.Therefore,the research on the slug flow characteristics of gas-water two-phase in horizontal variable diameter pipe is of great practical significance and theoretical value to understand its formation cause,control and elimination.In this paper,a three-dimensional transient model of gas-water two-phase slug flow in horizontal variable diameter pipe is established by using CFD commercial software FLUENT.The model is referring to the relevant experimental research and combining with CFD method,and it based on the VOF multiphase flow model and realisable k-? turbulence model.The numerical simulation of different conditions is carried out by controlling the taper angle of the variable diameter pipe,the liquid phase conversion speed and the gas phase conversion speed.Combined with the intuitional results such as the distribution nephogram,velocity vector graph and pressure nephogram,the power spectral density of flow fluctuation data of large and small diameter pipes is obtained by fast Fourier transform,and the slug flow characteristics in horizontal variable diameter pipe are analyzed.The main research contents and conclusions are as follows:Under the same working condition,the larger the taper angle,the lower the liquid film height in the small-diameter pipe,and the larger the gas-water two-phase slug flow from the large-diameter pipe to the small-diameter pipe,the greater the increase of gas-liquid mixing speed.The conversion velocity of liquid phase has an obvious effect on the flow pattern of gas-water two-phase flow in horizontal variable diameter pipeline.When the liquid phase conversion speed is low,there is no slug flow in the reducer,forming a wave flow with obvious characteristics;when the liquid phase speed is suitable,a stable slug flow can be formed in the reducer,the greater the liquid phase conversion speed is,the greater the pressure difference between the large-diameter pipe and the small-diameter pipe is,the greater the speed difference between the large-diameter pipe and the small-diameter pipe is;when the liquid phase conversion speed continues to increase,the two-phase flow in the pipe is The flow pattern is circular flow.The conversion velocity of gas phase has an effect on the gas-liquid phase distribution,pressure and velocity of gas-water two-phase slug flow in horizontal variable diameter pipeline.With the increase of gas conversion speed,the height of liquid film in the small-diameter tube decreases,and the pressure drop and velocity difference between the large-diameter tube and the small-diameter tube also increases;with the increase of gas conversion speed,the frequency of liquid plug also increases,which is more obvious in the small-diameter tube.