Abstract
The velocity and shock Mach number of shock waves in superfluid helium (He II) were studied experimentally by using superconductive temperature sensors, piezo pressure transducers, and Schlieren visualization method with an ultra-high-speed video camera. The shock waves are induced by a gas dynamic shock wave impingement upon a He II free surface. The wave trajectories induced in He II are shown through dimensionless velocity X-τ diagram. It is found that the propagation speed of a thermal shock wave coincides well with the second sound velocity under each compressed He II state condition. It is also found from visualization results that a dark zone in the immediate vicinity of the vapor-He II interface region is formed because of the high compressibility of He II and is developed toward bulk He II with the flowing-down speed of the vapor-He II interface. The mass velocity behind a transmitted compression shock wave that is equal to the contraction speed of He II amounts to 10m/s, the Reynolds number of which reaches 107. This fact suggests that the superfluid shock tube facility can be applied to an experimental facility for high Reynolds number flow as an alternative to the superfluid wind tunnel.
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