Numerical study on free surface flow of liquid metal lithium for IFMIF

The IFMIF presents an intense neutron source to develop fusion reactor materials. The free surface flow of a liquid metal Li is planned as a target irradiated by two deuteron beams to generate intense neutrons and it is thus important to obtain information on the surface wave characteristic for the safety and the efficiency of system in the IFMIF. We have been studying on surface wave characteristics numerically using computational fluid dynamics code in order to establish the mechanism of the formation and the development of the free surface wave of the Li jet. This paper reports results of the Li free surface flow simulation using large eddy simulation and volume of fluid as the turbulence model and the interface tracking method, respectively, including the inside of a two-staged contraction nozzle. In our simulation, two cases of velocities of 9 and 15 m/s at the nozzle exit were conducted as the flow condition from the nozzle exit to 20 mm downstream. It is found that the surface wave transits to the three-dimensional wave mode induced by both longitudinal and transverse vortices at the position of 15 mm downstream in the case of the velocity of 15 m/s.