Investigation on development of free-surface structures in turbulent liquid lithium flow

The liquid lithium film thickness facing the Deuterium beam of the International Fusion Material Irradiation Facility (IFMIF) determines the neutron flux to be generated. Hence, apart from its thickness also its spatio-temporal behaviour plays a decisive role in the performance of the target. Two aspects contributing to the free surface shape are the evolution of the viscous wall boundary layer in the nozzle and the development of turbulence downstream the nozzle exit, which are analysed here numerically by means of a fluid dynamic Large Eddy Simulation (LES). The numerical method is validated by experiments conducted at Osaka University with respect to mean and turbulent flow quantities in a broad spectrum of mean flow velocities. Thereby, both a qualitative and a quantitative agreement have been attained identifying different flow regimes and, moreover, allowing for a more refined, realistic IFMIF target prediction performance.