Abstract
To evaluate directly gas entrainment (GE) phenomena in fast breeder reactors, we have been studied a numerical simulation method based on a highprecision volume-of-fluid (VOF) methodology. In addition, we have been employed unstructured meshes to subdivide simulation domains because exact modeling of complicated geometries in each simulation domain is a key to simulate gas entrainment phenomena accurately. Therefore, as important parts of our study, formulations of each calculation procedure in the high-precision VOF methodology on unstructured meshes are conducted in this paper. In concrete terms, calculation procedures for 1) interfacial gradient vectors, 2) interface reconstructions, 3) fluxes of volume fraction on each mesh cell face are formulated on unstructured meshes. Calculation procedures of Surface tension forces are also formulated in this paper. Then, unphysical behaviors of velocity distributions near gas-liquid interface induced by inappropriate formulation of pressure gradient are discussed and an appropriate formulation is derived considering proper balance conditions between pressure and surface tension forces. It is confirmed that this new formulation reduces the unphysical behaviors in a numerical simulation of a rising gas bubble in liquid. Finally, the basic GE experiment is simulated using our numerical simulation method. The simulation results shows that the GE phenomena occurs in the same mechanism with the experimental results.
