Surface wave on high speed liquid lithium flow for IFMIF

Experimental study on free surface liquid metal flow is one of the most important issues for the design of intense neutron source like International Fusion Materials Irradiation Facility (IFMIF). The lithium loop facility in Osaka University was modified to conduct such high speed flow experiment. In this study, the jet flow free surface was recorded as a photo for a velocity of more than 15 m/s. Two-dimensional surface waves were observed, and these appeared in the velocity range of from 5 to 8 m/s. The wavelength was approximately 1–1.5 mm and it decreased with increasing the velocity. Comparison with water experimental results shows that wavelength in lithium is approximately 30% longer than that in the case of water. The measured wavelength was also compared with free shear layer linear instability theory in the form of non-dimensional wavenumber, and these were found to agree, with respect to most unstable wavenumber and neutral stable Weber number. In the velocity region of more than 9 m/s, free surface waves are found to show no periodic structure, probably because of transition into turbulent flow in the nozzle.