Oblique droplet impact: Pressure evolution, fluid–solid coupling, and stress-wave localization

Oblique droplet impact induces complex pressure-field evolution and fluid–solid interactions, yet the physical mechanisms governing pressure redistribution and the subsequent stress response remain insufficiently understood. A coupled smoothed particle hydrodynamics–finite element method was employed to investigate the effects of droplet size, impact velocity, and normal-tangential momentum partition on droplet pressure, liquid–solid interface pressure, and the resulting stress-wave response. The results show that the initial pressure response is governed primarily by rapid normal compression, whereas the subsequent evolution is controlled by momentum redistribution between the normal and tangential directions. When normalized by the acoustic pressure scale ρcVn, the internal-pressure coefficient remains of order unity but varies with the momentum-partition state, while the interface-pressure coefficient remains within ∼0.78–1.16 across the investigated conditions, demonstrating that ρcVn provides a consistent characteristic scale for the initial interface loading. Droplet size mainly regulates the spatial extent and persistence of stress-wave propagation, while impact velocity governs its intensity and penetration. The normal-tangential momentum partition primarily determines the directionality and spatial localization of the transmitted loading. Among the investigated states, the normal-dominant oblique condition Wen/We = 0.75, Wet/We = 0.25 combines substantial stress-wave penetration with finite directional redistribution, producing persistent localized loading within the substrate. These findings establish a mechanistic relationship between acoustic pressure generation, momentum redistribution, and stress-wave localization during oblique droplet impact.