On the Role of Ambient Reactive Particles in the Mixing and Afterburn behind Explosive Blast Waves

A hybrid two-phase numerical methodology is used to study the propagation of explosive blast waves from spherical charges of TNT and their interaction with an ambient dilute distribution of aluminum particles. The presence of these particles is found to cause perturbations at the contact surface between the inner detonation products and the outer shock-compressed air, which results in Rayleigh-Taylor instabilities at the contact surface. These instabilities grow in time, thereby creating a mixing layer characterized by enhanced mixing between the detonation products and air, resulting in afterburn. The afterburn energy release is observed to affect the pressure decay rate behind the blast wave and the speed and the strength of the secondary shock. The passage of the secondary shock through the mixing layer results in a Richtmyer-Meshkov instability, which is characterized by the creation of vorticity in the mixing layer through baroclinic torque effects. This phenomenon is observed to sustain the mixing process subsequently. The amount of mixing and afterburn are investigated for a range of aluminum particle sizes, mass loading, and initial distribution, and the role played by these particles in the growth of hydrodynamic instabilities is studied. It is shown that for the range of sizes investigated, particle size does not play a significant role in the mixing, but the initial distribution and mass loading do have appreciable impact. Furthermore, the late stages of the afterburn are observed to be self-similar, and independent of the initial triggering of the hydrodynamic instabilities. This study has provided some useful insights on the instabilities induced by ambient reactive particles in detonation flowfields and establishes a simulation capability to study turbulent two-phase processes in an explosive environment.