Multiscale understanding of explosion-induced particle jetting

The explosive dispersal of granular media, exemplified by the rapid radial expansion of a dense particle ring driven by internal pressurised gases, serves as a paradigmatic system for investigating multiphase blast dynamics. Despite the ubiquity of jetting and clustering phenomena in explosive dispersal scenarios, their governing mechanisms remain poorly resolved. In this work, we combine compressible computational fluid dynamics-discrete parcel method simulations, and theoretical modelling to elucidate the multiscale physics underlying explosion-induced particle jetting. We reveal a hierarchy of jetting structures, comprising non-jetting, suppressed jetting and prominent jetting, which are governed by the interplay between microscale particle force-chain evolution, mesoscale gas-particle coupling and macroscale ring dynamics. Jetting initiation emerges from the transient competition between shock-induced particle compaction and gas filtration during the early expansion phase, whereas sustained jet development requires subsequent ring implosion driven by adverse pressure gradients. By unifying this multiscale dynamics, we reduce the system's complexity into two dimensionless parameters: one characterising mesoscale gas-particle interactions and another quantifying macroscale implosion intensity. A phase diagram for jetting morphology under weak-shock conditions is established in this dimensionless parameter space, delineating two necessary criteria for jet formation. Systems failing either criterion exhibit no jetting, resolving long-standing ambiguities in the prediction of explosive dispersal structures.