Chapter 4.1 - Shock Tubes and Tunnels: Facilities, Instrumentation, and Techniques

Abstract

Shock tube is a facility for investigating the structure of a shock wave, shock wave propagation, and reflection. This chapter discusses shock jump relation followed by one dimensional propagation of a small disturbance. The jump relations across a normal shock wave is given for easier understanding of a shock tube flow and the wave propagation in it. Further, the operation principle of the simplest shock tube with a constant cross section is explained. This type of a shock tube is composed of high-pressure and low-pressure sections, which are initially separated by a diaphragm. The rupture of the diaphragm generates a shock wave, which travels into the low-pressure section. The shock wave is reflected from the end wall of the shock tube and encounters an opposing contact surface that is the interface initially separating the high-pressure and low-pressure gases. The reflected shock wave partly penetrates the contact surface and partly is reflected from it as a shock wave or an expansion fan. Thereafter, multiple wave reflections occur between the end wall and contact surface. The high-pressure gas is expanded into the low-pressure section of the shock tube immediately after the diaphragm rupture. This generates an expansion wave traveling at the speed of sound from the initial position of the diaphragm to left, into the high-pressure section and carrying the information of the expansion to the undisturbed portion of the high-pressure gas. This is an expansion wavefront.