The extension of the one-dimensional two-fluid slug capturing method to simulate slug flow in vertical pipes

While many studies have been conducted on the application of the one-dimensional (1D) two-fluid model in horizontal and nearly horizontal pipes under slug flow condition, very few works have been carried out on the mechanistic simulation of the slug flow regime in vertical pipe configurations. This article presents the extension of a novel numerical scheme for slug capturing in pipes in vertical slug flows. The original numerical scheme includes an 1D transient, hyperbolic five-equation two-fluid model, and it has been embodied in a computer code called 5ESCARGOTS (5 Equations for Slug Capturing Analysis by a Roe solver in Gas and Oil Transient Simulation). This article demonstrates that the model is able to properly automatically capture and simulate the slug generation even in vertical flow. It shows that when appropriate closure relations are used for interfacial shear forces, the model is able to properly characterize the vertical slug flow. Numerous simulations have been carried out for different pipe configurations and flow conditions leading to slug flow. First, a qualitative discussion of the numerical results is proposed underlining that the model is able to properly simulate the evolution of the slug flow in vertical pipes. Experimental flow pattern maps have also been numerically computed and it has been demonstrated that the model correctly simulates slug conditions. Moreover, slug frequency, velocity, and average liquid holdup, computed numerically, have been compared with experimental data in order to quantitatively validate the model. It is shown that the numerical results agree fairly well with the experimental data. A sensitivity analysis on the mesh size and on the inlet boundary conditions has also been carried out.