High-Speed Photogrammetry Of Real And Ideal Reflections Of Spherical Blast Waves

Abstract

Two types of high speed photogrammetry have been used to study the reflection of spherical blast waves from real and ideal surfaces. The spherical blast waves were produced by 500 kg charges. In each experiment two identical charges were simultaneously detonated, suspended one above the other so that the distance between them was twice the height of the lower charge above the ground. Observations were made of the blast wave from the lower charge as it reflected from the ground surface, and of the waves from the two charges as they interacted along the plane of symmetry between the charges. Since there was no energy loss in the interaction of the two waves, this could be considered as an ideal reflection. The refraction (shadow-graph) images of the shock fronts were photographed at 4000 pps against a 15 m high backdrop of black and white stripes. The positions of the shocks at regular time intervals were calculated and used to determine the shock velocities and thus the pressure, density and entropy behind each shock. On the other side of the charges an array of approximately 250 smoke puffs was generated. The puffs acted as tracers of the air flow within the blast waves and the 5000 pps photographic records of their positions were used to determine the particle velocities and densities throughout the waves.