Characterization of the Mixing Layer Resulting from the Detonation of Heterogeneous Explosive Charges

A dense, two-phase numerical methodology is used to study the mixing layer developing behind the detonation of a heterogeneous explosive charge, i.e., a charge comprising of a high explosive with metal particles. The filtered Navier–Stokes equations are solved in addition to a sub-grid kinetic energy equation, along with a recently developed Eulerian–Lagrangian formulation to handle dense flow-fields. The mixing layer resulting from the post-detonation phase of the explosion of a nitromethane charge consisting of inert steel particles is of interest in this study. Significant mixing and turbulence effects are observed in the mixing layer, and the rms of the radial velocity component is found to be about 25% higher than that of the azimuthal and zenith velocity components due to the flow being primarily radial. The mean concentration profiles are self-similar in shape at different times, based on a scaling procedure used in the past for a homogeneous explosive charge. The peak rms of concentration profiles are 23–30% in intensity and decrease in magnitude with time. The behavior of concentration gradients in the mixing layer is investigated, and stretching along the radial direction is observed to decrease the concentration gradients along the azimuth and zenith directions faster than the radial direction. The mixing and turbulence effects in the mixing layer subsequent to the detonation of the heterogeneous explosive charge are superior to that of a homogeneous explosive charge containing the same amount of the high explosive, exemplifying the role played by the particles in perturbing the flow-field. The non-linear growth of the mixing layer width starts early for the heterogeneous explosive charge, and the rate is reduced during the implosion phase in comparison with the homogeneous charge. The turbulence intensities in the mixing layer for the heterogeneous explosive charge are found to be nearly independent of the particle size for two different sizes considered in the initial charge. Overall, this study has provided some useful insights on the mixing layer characteristics subsequent to the detonation of heterogeneous explosives, and has also demonstrated the efficacy of the dense, multiphase formulation for such applications.