The formation of a slug flow is simulated by the Xpsim dynamic feature.
The video shows the slug formation and its progression in a pipeline 1 km long with internal diameter of 30 cm.
The fluid is oil plus natural gas flowing at a pressure of about 68 bar. This case is taken from the fundamental and historically important article:
Taitel Y., Dukler A.E., 1976, A Model for Predicting Flow Regime Transitions in Horizontal and Near Horizontal Gas-Liquid Flow, AIChE Journal, 22,1, 47-55.
A time interval of 5 minutes is shown by 3 different views: "bar", "trend" and finally the "pipeline" view.