The deformation evolution and the formation pattern of hot regions of particle cloud with cavity under shock impact

The formation of hotspots and ignition phenomena in cavitated explosive particle clouds under shock wave impacts have garnered widespread attention. However, at the mesoscale, under shock wave impact, there is a notable scarcity of research on the deformation, temperature rise patterns, and heat transfer mechanisms of particle clouds. Most studies focus on loading methods such as drop hammer and falling tests. In our study, we introduce a particle motion elastoplastic contact model based on the discrete element method, enabling precise analysis of particle motion and collision behavior. Furthermore, we consider bidirectional coupling between the particle and gas phases, optimizing momentum and energy equations for the particle phase. This approach allows for a detailed analysis of the dynamics and thermodynamics between particles, systematically considering the elastoplastic collision and shear history between particles. Friction, rolling resistance, plastic dissipation, inter-particle heat transfer, and heat transfer between particles and the fluid are regarded as source terms in the energy equation. In this investigation, the deformation behavior and temperature rise process of particle clouds under shock wave impacts are thoroughly discussed. The temporal evolution of particle cloud temperature under shock wave impacts represents a spatiotemporal correlation phenomenon, delineated into two stages: accelerated temperature rise and steady temperature rise, resulting in the formation of symmetric critical high-temperature regions near the cavity perpendicular to the incoming shock wave direction. Notably, during the accelerated temperature rise stage, plastic dissipation, and two-phase heat transfer jointly contribute, whereas during the steady temperature increase stage, heat is primarily provided by two-phase heat transfer. Sustained heat transfer from the high-temperature shock-impacted gas phase to the particle phase acts as the primary mechanism triggering the formation of wide-range high-temperature regions. The role of plastic dissipation is mainly evident in the plastic collisions of particles near the cavity in the early stages. Additionally, we analyze the influence of incoming shock wave Mach numbers on temperature evolution and hot region formation patterns: stronger shock waves lead to quicker completion of the impact process and higher stable average temperatures. Under shock wave impact, the spatiotemporal characteristics of particle clouds differ from the results of the falling process. Prolonged two-phase heat transfer and intense plastic contact among particles near the cavity in the initial stages are factors triggering critical high-temperature regions.