Even though the interaction of blast waves with dense particle distributions is ubiquitous in nature and in industry, the underlying physics of the multiphase system evolution is not clearly understood. A canonical multiphase system composed of an embedded monodisperse distribution of spherical particles in a spherical, high-energy gaseous charge is studied numerically using an Eulerian–Lagrangian approach to elucidate the role of non-dilute particle effects on the dynamics of the two-phase flow system. The direct simulation Monte Carlo method is modified to model inelastic particle–particle collisions and to model the gaseous flow inter-leaving through complex structures of monodisperse dense distributions of spherical particles to obtain parameters that are fit to semi-empirical particle cloud drag laws that account for aerodynamic interactions. The study reveals that inter-particle collisions decrease the total particle kinetic energy at early stages of the particle-laden blast wave system evolution, but near-particle interaction increases the particle kinetic energy at this stage. In contrast, at later stages of evolution, collisions tend to retain more kinetic energy, while the aerodynamic interactions tend to dissipate particle kinetic energy.

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Although the mobility or transport parameters, such as lift drag and pitching moments for regular-shaped particulates, are widely studied, the mobility of irregular fractal-like aggregates generated by the aggregation of monomers is not well understood. These particulates which are ubiquitous in nature, and industries have very different transport mechanisms as compared to their spherical counterpart. A high-fidelity direct simulation Monte Carlo (DSMC) study of two fractal aggregates of different shapes or dimensions is undertaken in the slip and transitional gas regime to understand the underlying mechanism of gas-particle momentum transfer that manifests as the orientation-averaged mobility parameters of the particulates. The study specifically focuses on the viscous contribution of these parameters and develops a non-linear correlation for drag and lift parameters p and q obtained from DSMC by normalizing the axial and lateral forces. The drag parameter p predicted a monotonic increase in fractal particulate drag with respect to a spherical monomer while the lift parameter q shows an initial increasing trend but a decreasing tendency toward the high Mach number or high compressibility regime. The approximate model that captures the compressibility and rarefaction effects of the fractal mobility is used to study the evolution of these particulates in a canonical Rankine vortex to illustrate the wide disparity in the trajectories of the fractal aggregate vs a spherical geometry approximation generally found in the literature.

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