Numerical study on onset of gas entrainment from free surface

Kunugi, Tomoaki*; Ezure, Toshiki ; Sakai, Takaaki; Ito, Kei

In order to design a compact fast reactor, it is necessary to clarify a criterion of a gas entrainment (GE) from the coolant free surface of the vessel. The surface velocity is considered as a key parameter of the GE. However, there is no quantitative criterion regarding the onset condition of the GE. In this study, two-dimensional waterfall simulation and a three-dimensional dimple simulation for the GE have been performed by means of the MARS method. The final goal of this study is to establish the evaluation procedure and clarify a criterion of these phenomena. Resulting two-dimensional waterfall simulations, the time-averaged wave shape is very similar to the experimental one. The surface wave velocity, the maximum surface head and the maximum surface slope are well correlated with inflow energy, i.e., Froude number. Moreover, the three-dimensional unsteady vortex-dimple motion can be captured by the MARS method and three flow modes in the vortex-dimple evolution can be observed.