The article importance lies in the interest among scientists in describing such complex streams as multiphase flows, which physical models have now been developed and corrected. This research aims at studying the behaviour of flows of multiphase mixtures in pipes, when there is a difference in elevations. The study method is based on computer modelling using a simulator of multiphase flows created by the authors. The simulator is appropriate for describing the flow of multiphase mixtures in complex systems, with implementation of two-velocity motion model of various phases. In liquid-gas mixture, it results in different velocities of phases motion. The analysis results demonstrate that velocities differ substantially. The presence of gravitational component greatly affects the nature of flow, and, in some cases, leads to a change in flow regimes. The work shows that regimes can also be implemented without reaching steady-state conditions. The article materials are of practical value to design long-distance pipelines, placed across the terrains of certain topography.

hydrodynamics of multiphase media, modelling of technical systems, flow regimes, software codes, phase equilibria