Development and validation of unstructured adaptive mesh technique for gas-liquid two-phase flows

For the purpose of direct numerical simulations of gas entrainment (GE) phenomenon in sodium-cooled fast reactors, a high-precision numerical simulation method for gas-liquid two-phase flows have been developed. To reproduce the GE phenomenon by numerical simulations, there are three key issues, i.e. geometry dependency, interfacial dynamics and locality. Former two issues are already addressed by employing an unstructured mesh and a high-precision simulation method for gas-liquid two-phase flow, respectively. In addition, the locality of the GE phenomenon has been addressed by developing an unstructured adaptive mesh technique by which high mesh resolutions can automatically applied transiently to the occurrence regions of the GE phenomenon. As for single-phase flows, it has been confirmed that the unstructured adaptive mesh technique is efficient to simulate vortices with less computational costs than that on non-adaptive meshes. In this paper, the unstructured adaptive mesh technique is extended to two-phase flows. For that purpose, the redistribution algorithms for two-phase flow variables are developed based on the conservation laws of the variables. Finally, the unstructured adaptive mesh technique is validated by solving the well-known slotted-disk revolution and dam-break problems. As a result, the adaptive mesh technique succeeds in maintaining the slotted-disk shape after one revolution by using relatively small number of cells. The interfacial dynamics in the dam-break problem is also resolved well on the unstructured adaptive mesh. (author)