On turbulent chemical explosions into dilute aluminum particle clouds

Abstract

We use a hybrid two-phase numerical methodology to investigate the flow-field subsequent to the detonation of a spherical charge of TNT with an ambient distribution of a dilute cloud of aluminum particles. Rayleigh–Taylor instability ensues on the contact surface that separates the inner detonation products and the outer shock-compressed air due to interphase interaction, which grows in time and results in a mixing layer where the detonation products afterburn with the air. At early times, the ambient particles are completely engulfed into the detonation products, where they pick up heat and ignite, pick up momentum and disperse. Subsequently, as they disperse radially outwards, they interact with the temporally growing Rayleigh–Taylor structures, and the vortex rings around the hydrodynamic structures results in the clustering of the particles by also introducing local transverse dispersion. Then the particles leave the mixing layer and quench, yet preserve their hydrodynamic ‘footprint’ even until much later; due to this clustering, preferential heating and combustion of particles is observed. With a higher initial mass loading in the ambient cloud, larger clusters are observed due to stronger/larger hydrodynamic structures in the mixing layer – a direct consequence of more particles available to perturb the contact surface initially. With a larger particle size in the initial cloud, clustering is not observed, but when the initial cloud is wider, fewer and degenerate clusters are observed. We identify five different phases in the dispersion of the particles: (1) engulfment phase; (2) hydrodynamic instability-interaction phase; (3) first vortex-free dispersion phase; (4) reshock phase; and (5) second vortex-free dispersion phase. Finally, a theoretical Buoyancy-Drag model is used to predict the growth pattern of the ‘bubbles’ and is in agreement with the simulation results. Overall, this study has provided some useful insights on the post-detonation explosive dispersal of dilute aluminum particle clouds.

Keywords:

• explosive
• mixing layer
• aluminum combustion
• clustering
• dispersion
• Rayleigh–Taylor instability

Acknowledgements

This research is supported by the Office of Naval Research (Dr. Cliff Bedford, Program Manager), the Air Force Research Laboratory, Eglin Air Force Base (Dr. Douglas V. Nance, Program Manager), and the Air Force Office of Scientific Research (Dr. Fariba Fahroo, Program Manager). Simulations were carried out at the DoD HPC Centers at the US Army Research Laboratory Major Shared Resource Center and the Maui High Performance Computing Center. Dr. Douglas V. Nance supplied the initial detonation profiles. The first author acknowledges the brief private communications with Dr. Aaron Miles of the Lawrence Livermore National Laboratory.