An experimental investigation of variable energy blast waves
Abstract
The results of an experimental investigation of spherical blast waves are reported. Shock trajectories and flow field densities are compared with approximate and/or numerical predictions. The numerical predictions are based upon a finite difference formulation of the conservation equations in Lagrangian coordinates. Experimentally, blast waves in air and chloroform have been induced by focusing the output of a high energy pulsed ruby laser onto a flat target to form a hemispherical field. Both Qswitched and open lase output were used. The open lase mode results in an approximation of linear energy input. Flow field data were obtained during and subsequent to the energy input interval using a MachZehnder interferometer in conjunction with a high speed rotating mirror framing camera. Shock trajectories in the form of radiustime ( R t) plots were obtained from the camera records. These shock trajectories were found at early times to follow similarity predictions of R ∼ t^{2/5} for instantaneous energy input and R ∼ t^{3/5} for linear energy input, while at later times they tended to follow the approximate/numerical predictions. Radial density profiles, obtained from interferometric records through Abel integral inversion techniques, agreed with the following predictions. Starting at the shock front and progressing radially inward, it is predicted that for instantaneous energy input, the density decreases rapidly at first and gradually thereafter, asymptotically approaching zero at the blast wave center. Conversely, for the linear energy input mode, the density initially decreases gradually, but then the gradient steepens and the density rapidly approaches zero close to the shock front, thus forming a shelllike region near the shock front.
 Publication:

Acta Astronautica
 Pub Date:
 April 1977
 DOI:
 10.1016/00945765(77)900583
 Bibcode:
 1977AcAau...4..391D
 Keywords:

 Detonation Waves;
 Energy Dissipation;
 Flow Distribution;
 Laser Heating;
 Shock Wave Propagation;
 Spherical Waves;
 Chloroform;
 Energy Transfer;
 MachZehnder Interferometers;
 Q Switched Lasers;
 Ruby Lasers;
 Shock Fronts;
 Fluid Mechanics and Heat Transfer