Study on multiphase flow and thermal response of melt-cast explosive filled projectiles during cook-off

To investigate the ignition mechanisms of melt-cast explosives under thermal stimuli, a chemical reaction ignition model incorporating multiphase flow and pore gas release was developed. By predicting the cook-off behavior of Comp-B charges under heating rates of 16, 1, and 0.055 K/min, the study reveals that the heating rate dictates the transition between conduction-dominated and convection-driven ignition regimes. High heating rates create steep vertical thermal gradients and localized molten pools at the top, triggering rapid hotspot formation and ignition in the upper region. Low heating rates promote thermal diffusion and internal convection, which progressively homogenize the temperature field until late-stage self-heating occurs. Across all cases, the buoyancy-driven migration of released pore gases and decomposition products creates a high-diffusivity gas film at the top, consistently shifting the eventual ignition site to the upper region. This indicates that porosity-controlled gas transport is a decisive mechanism in the thermal safety assessment of confined melt-cast munitions. • Multiphase model for Comp-B couples Bingham viscosity with UCM kinetics. • Pore gas release is modeled to capture pressure rise and flow characteristics. • Gas volume evolution exhibits unique cycles depending on the heating rate. • Buoyancy-driven gas migration determines the ignition location near the top.