Studies on Shock Wave Attenuation in Small Tubes

Abstract

Shock waves are formed when there is a sudden release of energy in limited space resulting in a supersonic displacement of the gas. Shock tubes are one of the easiest ways to generate good repeatable shock waves in ground-based test facilities with a good control over its parameters. A classical shock tube consists of a driver section(filled with high pressure gas) and a driven section(filled with low pressure gas) separated by a metal diaphragm. The rupture of the metal diaphragm generates a shock wave in the driven section of the shock tube. This mechanism of shock generation has been used for many decades and has been well investigated[1]. For classical aerodynamics studies, shock tubes of circular, rectangular or square crosssection and length scales of the order 50-100 mm are usually used. But the applications of shock wave assisted techniques in new areas like industry and medicine has led to reduction in the diameter of shock tubes and requires the understanding of shock tube flow at different length scales. The Ideal shock tube theory is based on assumptions like inviscid adiabatic flow, instantaneous diaphragm rupture and ignores aspects like diameter of the tube, surface roughness, boundary layer effects, heat and mass transfer effects, non-uniformity in driver section (Eg: combustion driven shock tube), possibilities of combustion at the contact surface and chemical kinetic effects. These effects which are ignored at macro-scales play a very important role when the diameter of the shock tubes are reduced and give rise to very interesting gasdynamic phenomena.