Nonlinear interactions in superfluid dynamics: Supercritical counterflow and shockwaves

It was the purpose of the program to investigate some aspects of the fluid mechanics of LHeII, in particular nonlinear phenomena such as turbulence and shock waves and their effect on the critical conditions in HeII. The major accomplishments which resulted from the GALCIT research program are: The development of the first cryogenic shock tube for the production of strong shock waves. In this small (1 inch diameter) tube, shock Mach numbers of M _42 in Helium gas have been reached; the extension of the cryogenic tube techniques to work with liquid Helium II led to the first careful mapping of the nonlinear wave diagrams in He II, involving both first sound and second sound shock waves; ultra-second sound waves with frequencies up to 1 MHz have been used as a velocimeter for He II counterflow; a similarity rule was developed on the two-fluid equation with the additional Gorter-Mellink terms. This rule permits the reduction of all known critical heat flow experiments in capillaries and tubes to a single number reminiscent of a critical Reynolds number for laminar-turbulent transition in classical fluid mechanics.