Interaction between the reflected shock wave and the unsteady jet in a shock tube experiment. Theoretical base and proof for the behavior of a reflected shock wave.

Abstract

Nitrogen gas is set to discharge from a small circular hole located at the end wall of a shock tube at about 3-5 ms before the shock wave arrives and undergoes reflection. Interacting with the jet, the reflected shock wave changes its shape from a normal shock wave to a hemispherical one. We observed the phenomenon by the use of a schlieren system, time counters and pressure gauges. We calculated the pressure and the temperature behind the apex of the hemisperical reflected shock wave by using its distance-time relations, differentiation of cubic natural smoothing spline functions, and Rankine-Hugoniot equations. In this paper, we want to prove that the method that we proposed in a previous work is a reasonable and available one. The results are as follows. (1) From pressure profiles, we cold show that the proposed method, in fact, was a reasonable and available one. (2) When an unstable hemispherical reflected shock wave reconverts to a stable, normal shock wave, it generates some expansion waves, which cause a temporary pressure-drop (about 120μs) in the Kistler transducer on the side wall after the passing of the reflected shock wave. (3) The calculated results using the proposed method are supported by the experimental facts of (2), and the facts show that a strong inverse flow is poaduced by the interaction between the reflected shock wave and the jet behind the reflected shock wave.