Development of gas entrainment evaluation model based on distribution of pressure along vortex center line – Application to a gas entrainment experiment with traveling vortices in an open water channel flow –

Abstract

Establishing an evaluation method for the gas entrainment (GE) of argon cover gas due to surface vortices is required from the perspective of safety design of sodium-cooled fast reactors (SFRs). An in-house evaluation tool for GE evaluation named StreamViewer has been developed. In previous studies, an evaluation model (original model) assuming the Burgers stretch vortex was implemented in the StreamViewer to evaluate the vortex dimple depth (gas core length). It was based on the calculation results of the pressure decrease at the vortex center point at the free surface. Since the conservativeness of the StreamViewer evaluation result with the original model has been proposed in a specific condition for a pool-type SFR, a modified evaluation model on the pressure distribution along the vortex center line (PVL model) was proposed to identify the vortex center lines as evaluation targets by connecting continuous vortex center points from the suction port to the surface using all vortex center points in an evaluation area. In the PVL model, each gas core length was evaluated based on the balance between the hydrostatic pressure and the pressure decrease distribution along the vortex center line using the three-dimensional results of computational fluid dynamics analysis. The applicability of the PVL model was confirmed by performing three-dimensional numerical analyses for the experiments where a rectangular thin plate induced unsteady traveling vortices in the open channel flow. Consequently, the GE evaluation using StreamViewer with the PVL model for the numerical analysis results could reproduce the relation between the inlet flow velocity and the gas core length, in other words, the elongation behavior of the gas core length with increased inlet velocity, in the unsteady vortex flow experiments.