The international fusion materials irradiation facility (IFMIF) presents an intense neutron source to develop fusion reactor materials. The liquid metal Lithium (Li) jet with a free surface is planned as a target irradiated by two deuteron beam 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 experimentally using the liquid metal Li circulation facility at Osaka University (Li loop) and numerically using computational fluid dynamics (CFD) code, FLUENT.

The CFD simulation has been used in order to establish the mechanism of the formation and development of the surface wave of the liquid Li jet. The introduction of a two-staged contraction nozzle is planned in the IFMIF and the 1/2.5 size of the IFMIF’s nozzle has been also used and tested in our Li loop. These nozzles have a concave wall at each contraction part, and it was then predicted that Görtler vortices in the boundary layer inside the nozzle was generated and flowed out from the nozzle exit at the high velocity condition in our previous simulation. The Li free surface flow simulation including the flow inside the nozzle set in our Li loop was conducted to compare simulation results with experimental results and to evaluate the influence of Görtler vortices on the surface wave formation and development. In our simulation, large eddy simulation and volume of fluid models are used as turbulence model and interface tracking method, respectively. Our simulation result indicates that both transverse vortices due to gas-liquid shear stress and longitudinal vortices induced by Görtler vortices downstream the nozzle exit contribute to the formation of three-dimensional wave of the Li free surface flow at the velocity of 15 m/s. It was found that the vortex structure and the flow pattern under the free surface due to the flow inside the nozzle strongly contributed the development of the surface wave of the liquid Li jet.

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