ELECTRON BEAM MEASUREMENTS OF DENSITY IN SHOCK WAVES REFLECTING FROM A COLD WALL

Abstract

The normal shock wave is a rarefied-gas flow in which large departures from thermodynamic equilibrium and strong non-linearities occur and it is the simplest such flow due to its one-dimensionality and the absence of solid boundaries. Because of this, both theoretical and experimental studies of the structure of normal shock waves have been used successfully in recent years to get a better understanding of such phenomena. The present work is an extension of the earlier studies to the more complicated problem of shock-wave reflection. The density distribution of a normal shock wave in argon is measured during its reflection from a heat-conducting wall using an electron beam densitometer in the GALCIT 17-in diameter shock tube at incident Mach numbers 6.00, 4.00 and 2.96. During each run a density history is obtained at a certain distance from the wall by measuring electron-beam current as a function of time. By defining a consistent zero of time for all runs at the same conditions, these histories are converted by a cross-plot to families of density profiles at different times. x-t diagrams are obtained from the density history plots, and a wall-density history is obtained from the density profiles. Measured in terms of the ideal conditions behind the incident shock wave, the distances extend from 0.25 to 56 mean free paths from the wall and the times to 160 mean collision times after the beginning of the reflection. The results presented here give both quantitative and qualitative information about the interaction of the incident shock wave with the wall, the effects of the wall heat transfer and accommodation on the density near the wall, the formation of the reflected shock wave, its strength and trajectory on the x-t diagram, and the nature of the flow field lying between the thermal layer and the reflected shock wave at large times.