A semi-implicit numerical scheme for transient two-phase flows on unstructured grids

A component-scale two-phase analysis code, CUPID, has been developed for a realistic simulation of transient two-phase flows in light water nuclear reactor components. In the CUPID code, a two-fluid three-field model is adopted and the governing equations are solved on an unstructured grid to make CUPID very useful for flow analysis in complicated geometries. For the numerical solution scheme, the semi-implicit method of the RELAP5 code, which has been proved to be very stable and accurate for most practical applications, was used with some modifications for an application to an unstructured non-staggered grid. This paper presents the modified semi-implicit numerical method for an unstructured grid and the preliminary results of the calculations.