Micro-blast waves using detonation transmission tubing

Abstract

Micro-blast waves emerging from the open end of a detonation transmission tube were experimentally visualized in this study. A commercially available detonation transmission tube was used (Nonel tube, M/s Dyno Nobel, Sweden), which is a small diameter tube coated with a thin layer of explosive mixture (HMX \(+\) traces of Al) on its inner side. The typical explosive loading for this tube is of the order of 18 mg/m of tube length. The blast wave was visualized using a high speed digital camera (frame rate 1 MHz) to acquire time-resolved schlieren images of the resulting flow field. The visualization studies were complemented by computational fluid dynamic simulations. An analysis of the schlieren images showed that although the blast wave appears to be spherical, it propagates faster along the tube axis than along a direction perpendicular to the tube axis. Additionally, CFD analysis revealed the presence of a barrel shock and Mach disc, showing structures that are typical of an underexpanded jet. A theory in use for centered large–scale explosions of intermediate strength \((10\, < \Delta {p}/{p}_0 \lesssim \, 0.02)\) gave good agreement with the blast trajectory along the tube axis. The energy of these micro-blast waves was found to be \(1.25 \pm 0.94\) J and the average TNT equivalent was found to be \(0.3\). The repeatability in generating these micro-blast waves using the Nonel tube was very good \((\pm 2~\%)\) and this opens up the possibility of using this device for studying some of the phenomena associated with muzzle blasts in the near future.