Application Study of Adaptive Mesh Refinement Method on Unsteady Wake Vortex Analysis

Abstract

There is a possibility of Ar cover gas filled in the upper part of the reactor vessel (RV) to get into the sodium coolant by vortices causing output disturbance. Hence, it is necessary to evaluate this gas entrainment phenomenon. To predict the flow pattern in the upper part of the RV by Compurational Fluid Dynamics (CFD) analysis, there is a need to establish an appropriate mesh arrangement. In this study, the applicability of the Adaptive Mesh Refinement (AMR) method to predict gas entrainment vortices accurately was examined. An initial coarse mesh (20mm) that simulate the test section of the experimental apparatus in the circulating water loop was created. The initial mesh was refined with two indexes: the first index (Index- 1) is when the second invariant Q of the velocity gradient tensor is negative and the second one (Index-2) is the pressure gradient index added to the Index-1. Then, transient calculation was performed on the refined meshes under each condition, and the results were compared with a Reference mesh with cubic cells of 5 mm width. As a result, comparing the pressure distribution of the Reference mesh with other meshes refined with the two indexes, Index-2 was found to be more similar to that of the Reference mesh. In conclusion, the applicability of the AMR method with the condition of the Index-2 was confirmed for this experimental system in which unsteady wake vortices are generated. In addition, to confirm the applicability of the AMR method on actual reactors, a simulation of the upper plenum of SFR was conducted. Results indicate that AMR method is also applicable, and the analysis load can be reduced up to 600%.