Numerical Simulation of Cavitation by Sub-Surface Vortex (1st Report, High-Precision Numerical Simulation Scheme for Vortical Flow)

Abstract

For the safety operation of a large-scale sodium-cooled fast reactor in Japan (JSFR), structural integrity has to be maintained. Therefore, several thermal-hydraulics phenomena, which may reduce the integrity, have been studied. One of them is the cavitation due to sub-surface vortex which can damage structural surfaces. Such a sub-surface vortex is induced by high-speed suction flow into an outlet pipe in the reactor vessel. However, the onset condition of the cavitation can not be clarified easily because the cavitation shows highly complicated behaviors associated with phase change. Therefore, the authors are developing a CFD code to simulate the cavitation accurately and to investigate the onset condition of the cavitation. In this paper, as the first part of the development, a high-precision simulation scheme for vortical flows is presented. In this scheme, a vortical flow is identified in each cell and a vortical velocity distribution is determined locally to be consistent with the local velocity distribution. Then, the calculations of momentum transport through cell faces are performed in consideration with the vortical velocity distribution. In addition, a pressure distribution near the vortex center is also considered to simulate accurately the mechanical balance between pressure gradient and centrifugal force. As a fundamental verification of the developed scheme, the reproducibility of the burgers vortex is checked. Furthermore, inviscid vortex attenuation in two-dimensional domain is simulated. As a result, it is confirmed that the developed scheme can simulate vortical flows more accurately than conventional schemes.