Shock Tubes in Rarefied Gas Flow Research

In any real fluid motion there exists regions in space-time in which the fluid is far from thermodynamic equilibrium. The relative extent of these non-equilibrium regions is determined by the ratio of the molecular relaxation times and the corresponding length scales to the macroscopic time and space scales appropriate to the flow. Gas flow within such non-equilibrium regions is properly called "rarefied". In recent years the shock tube has become a rather efficient tool in the investigations of rarefied gas flows and I intend to illustrate progress in this use through a discussion of some very recent and typical investigations of the GALCIT group carried out under NASA sponsorship.