Fluid Dynamics of Liquid Helium

Liquid helium at low temperatures owes its existence to$\hslash$through the zero point energy; classically it should be solid. He the common isotope, owes its peculiar behavior as a fluid to its spin and hence again to$\hslash$; classically the difference between He and He should be trivial. In liquid helium flow we deal with a system which still shows all the usual behavior of a liquid plus some additional strange properties which reflect directly macroscopic quantum effects. The governing equations of motion due largely to Landau and London are, except in their linearized form, not as well founded and most certainly less well confirmed than one would like. Consequently, the experimental fluid dynamicist working with helium should have a field day exploring flow problems in an atmosphere more adventureous than with any ordinary fluid. This indeed is often the case. One does, however, ruefully discover that some of the more interesting and significant flow configurations which one likes to study in this strange field are by no means sufficiently well explored in the corresponding classical cases. One therefore likes to design simple fluid flow experiments which bring out the essentially new properties of He II and permit an experimental contribution to, or decision among, the theories of He II flow. In this spirit, experiments associated with the propagation of shock waves in liquid helium have been initiated at GALCIT. The design and construction of a cryogenic shock tube and its application to liquid helium are discussed in this paper.