The properties of a blast wave obtained from an analysis of the particle trajectories

Abstract

It is shown that all of the flow properties within an unsteady shock wave of intermediate strength can be determined by an analysis of the experimentally observed particle trajec­tories. The analysis has been applied to the blast waves from two large trinitrotoluene (t. n. t.) explosions. The particle trajectories were observed by high-speed photography of smoke tracers formed close to the charges immediately before detonation. The density throughout the flow was determined by application of the Lagrangian conservation of mass equation. This was then used to calculate the pressure, assuming adiabatic flow for each air element between shock fronts. The temperature and sound speed throughout the flow were found from the pressure and density, assuming a perfect gas equation of state. The particle velocity within the flow was obtained from the time derivative of the observed particle trajectories. The results have been compared with other blast measurements and with theoretical calcula­tions. It is estimated that the technique gives the flow properties to an accuracy comparable with that for other forms of measurement, namely, 5 to 10%. This is the first time that it has been possible to describe all the properties of a blast wave based on experimental measurements, only.