420 バスタブ渦の気液界面構造に関する数値解析(S35-1 乱流渦構造(1),S35 乱流渦構造)  [in Japanese] 420 Numerical Simulation for Interfacial Structure of Bathtub Vortex  [in Japanese]

Bathtub vortices, which have free surface dents (gas cores), are of concern in design studies on fast breeder reactors (FBRs) because of their potential causes of gas entrainments. Authors have conducted numerical simulations for the bathtub vortices to establish a prediction method for the onset of the gas entrainment and showed that the numerical simulations can roughly reproduce the structures of the bathtub vortices in the steady state. As an extension of the previous simulations, two unsteady behaviors were simulated to validate the applicability of the numerical simulations for the unsteady behaviors of the bathtub vortices in this research. As a result, the numerical simulations could reproduce the same oscillation of the gas core surface with experimental result when the perturbation was applied to the vortex flow. The oscillation was considered theoretically to deduce that the cause of the oscillation was the Kelvin-Helmholtz instability. In addition, the bubble entrainment from the tip of the gas core also could be calculated. These results showed that the numerical simulations are applicable to the unsteady behaviors of die bathtub vortices.