Shock Tubes in Rarefied Gas Flow Research

The flow within a shock wave is governed by the relaxation times of the molecular degrees of freedom. Advances in shock-tube design and instrumentation in recent years have made it possible to resolve all the relaxation times including the shortest, corresponding to the translational degrees of freedom. The shock tube thus becomes an important tool for critical experiments in the study of the range of applicability of the Navier-Stokes equations and similar approximations and of the character of solutions of the Boltzmann equation. Significant progress has recently been made in the understanding of the most obvious such problem, the flow within a shock in a monatomic gas. Theory and experiment are now in substantial agreement and the over-all process of energy exchange is understood. Progress has been made in problems connected with shock wave reflection from real walls, but a host of others remain to be studied including surface interaction effects. The extension of this type of shock-tube research to more complicated systems, reacting gases, gas mixtures, and the like has begun and some progress can be reported. Recent experimental progress is illustrated by a number of measurements made in the 6- and 17-in. shock tubes at the California Institute of Technology