In order to reduce the hazards caused by the severe slug flow in the mixed pipeline, it is necessary to analyze and study its flow characteristics. Taking the experimental system of a horizontal downdip tube⁃catenary riser in some literature as the research object, the relevant mathematical and physical models are established. The CFD software is used to simulate the serious slug flow in this type of pipe, and the characteristics of the severe slug flow and the variation of pressure, velocity and gas content are analyzed.The flow pattern map is obtained by numerical simulation with different inclination angles, pressure curve and cycle variation analysis show that with the increase of the slope angle of the pipeline, the flow pattern map conversion boundary changes, the formation of severe slug flow to the superficial gas velocity increases, forming the intermittent flow to the superficial gas velocity decreases the maximum value; the maximum value of the severe slug flow pressure changes little with the tilt angle, and its period decreases with the increase of the tilt angle, and changes exponentially.

With the development of marine petroleum industry, marine risers appeared a variety of forms. Due to pipe shapes and the complex seabed terrain factors, severe slugging often happened. This special flow pattern damaged the equipment, production and so on. Therefore, the simulation and the research for the severe slug flow of the marine riser system had very important significance. The research was summarized by the domestic and foreign scholars on the severe slug flow of the multiphase flow riser system, including its research methods, mechanism and characteristic parameters and theoretical model, etc,which provided a reference for further study of severe slug flow in riser system.