Diagnostics of Shock Tube Flows by Laser Interferometry

Abstract

In this paper, the diagnostics of shock tube flows by a laser differential interferometer using Wollaston prisms is described. This method has some advantages. It can apply to a case in which the optical path change is only a small fraction of the wave length, and the influence of vibration and laser ripple can be suppressed whereby excellent resolutions in space and time are obtained. In the present work, this method was applied to the measurements of the density change across a shock generated in a shock tube and a shock Mach number. From the investigations of the incident shock, reflected shock and contact surface, it was concluded that the influence of the boundary layer on the side and end wall becomes large when the initial pressure in the test chamber is less than 1.0 kPa. It was also concluded that a strong interaction of the reflected shock with the side-wall boundary layer is caused for air. Through these experiments, a technique of the density measurement by means of this interferometer has been established. It was confirmed that this method is an excellent way for density measurements in a case where the density change is very small.