Schlieren photography of second-sound shock waves in superfluid helium

Abstract

A conventional schlieren system has been used to study second-sound shock waves produced in a shock tube with optical windows. Initially planar shocks are observed to remain so, even after several reflections from the end walls. No interaction of the shocks with the side wall boundary layers is seen, attesting to the thinness of these layers. Second-sound shocks are reflected from the liquid–vapor interface, producing transmitted gasdynamic shocks and reflected second-sound shocks. Several strong shocks are fired with short separation times, generating observable fluctuations in the fluid.