LAUSR

Abstract Free surface vortex, especially in a pattern of full air core vortex, causes serious security problems in the residual heat removal system. Vortex in a T-junction pipe system was numerically investigated under the premise that the simulation results are in agreement with the experimental results. First, four typical states were obtained in the formation and evolution process of vortex, namely, surface dimple, critical submergence state, air entrainment vortex state, and large air entrainment state. With increasing Froude (Fr) number, the time from an initiate flow field to the critical submergence state decreased, and the time interval between critical submergence state and large air entrainment state increased. Finally, the variation law of vortex intensity was analyzed during the evolution process. The vortex intensity initially increased with time and reached its maximum value and then decreased until it reached a minimum value before the large air entrainment state. With the increase of Fr, the maximum values of vortex intensity gradually increased.