A collocated coupled solver for multi-dimensional two-phase flows

A staggered-grid scheme is efficient and stable for a structured grid and used in many two-phase system analysis codes such as RELAP5-3D and MARS. However, in a multi-dimensional component analysis, the geometry is complex and a structured grid is hard to use. An unstructured grid is useful in this case. And the collocated scheme, where all the system variables are defined at cell center, is easy to apply to the unstructured grid. The purpose of this work is to extend the semi-implicit coupled scheme to the collocated grid system for the analysis of transient two-phase fluids in a complex geometry. A 3D pilot code is developed to verify the numerical scheme