Numerical Study on Severe Slug Flow in Declined Pipe-Riser System
Marine risers are often used to connect underwater wellheads with floating platforms.Oil and gas mixed transportation is prone to severe slug flow in the riser section,which will cause overload impact and damage to downstream equipment and pipelines.In this paper,a three-dimensional numerical model of the riser is established,and the computational fluid dynamics method is used to simulate the gas-liquid severe slug flow process.The results show that the evolution period,eruption time,pressure fluctuation amplitude and liquid slug length of severe slug flow decrease with the increase of gas velocity,and the flow pattern gradually changes from SSI severe slug to SSⅡ and SSⅢ.During the gas eruption stage,the gas plug in the riser moves in s shape,and the flow area of the gas plug coincides with the high-speed area.The high-speed area is located at the inner wall surface and the tube shaft of the elbow at the bottom and top of the riser,respectively.The high-speed area of severe slug flow in SSI is greater than that ofSSⅡ and SSⅢ.