Particle jet formation during explosive dispersal of solid particles

Abstract

Previous experimental studies have shown that when a layer of solid particles is explosively dispersed, the particles often develop a non-uniform spatial distribution. The instabilities within the particle bed and at the particle layer interface likely form on the timescale of the shock propagation through the particles. The mesoscale perturbations are manifested at later times in experiments by the formation of coherent clusters of particles or jet-like particle structures, which are aerodynamically stable. A number of different mechanisms likely contribute to the jet formation including shock fracturing of the particle bed and particle-particle interactions in the early stages of the dense gas-particle flow. Aerodynamic wake effects at later times contribute to maintaining the stability of the jets. The experiments shown in this fluid dynamics video were carried out in either spherical or cylindrical geometry and illustrate the formation of particle jets during the explosive dispersal process. The number of jet-like structures that are generated during the dispersal of a dry powder bed is compared with the number formed during the dispersal of the same volume of water. The liquid dispersal generates a larger number of jets, but they fragment and dissipate sooner. When the particle bed is saturated with 1 arXiv:1110.3090v2 [physics.flu-dyn]

Development of instabilities in explosively dispersed particles

“…These results also correlate well with the previous work of Frost et al [10], who introduced a compaction Reynolds number for the particle layer. The compaction Reynolds number is described by the following expression: Re = (ρUL)/(γ s c s d s ) where ρ, U, and L are the density, velocity, and characteristic length (e.g., layer thickness), of the layer, respectively.…”

“…In the denominator, γ s , c s , and d s are the particle mass density, solid-phase sound speed, and mean particle diameter, respectively. It has been observed, that the number of jets tends to increase with increasing compaction Reynolds number [10].…”

The ALMA View of the OMC1 Explosion in Orion

“…The CO morphology resembles the jet-like features seen in high-speed videos of powerful terrestrial explosions occurring inside a damping medium. Experiments with explosives embedded in the center of a sphere of solid beads, wet-beads, or liquids produce hundreds of jet-like streamers with ejection speeds increasing with distance and a morphology similar to those seen in Orion (Frost et al 2012;Milne et al 2016; for videos, see https://www. youtube.com/watch?v=78l4cU5F2YE).…”

Metalized heterogeneous detonation and dense reactive particle flow

“…Fracturing of a particle bed to form jet structures should be correlated to both the detonation (that determines particle expansion velocity) and the stochastic nature of the particle system (morphology, bed configuration and material properties). In an attempt to set a criterion for jet formation, a particle flow Reynolds number is introduced equalling the ratio of inertial force to friction force of a particle system [21]:…”