The development of efficient energy storage technologies is critical as global energy demand rises and environmental issues become increasingly serious. Large eddy simulation is employed to model the phase change heat storage process in a packed bed system consisting of a double-layer cascade capsule-stacked structure based on the pore scale. The temperature

streamlines

and vortex distributions of phase change materials(PCMs) with various melting points and physical properties are investigated within the structure. The thermal characteristics of the capsule-type stacked structure are analyzed at different entrance velocities

and the simulation results are validated by experimental data. The simulation results demonstrate that

the interstitial flow and vorticity fields of the stacked structure exhibit significant dynamic characteristics during heat storage. At the pore scale

the phase transition induces streamline bending

vortex formation

and the increase of local velocity. After the phase transition

the flow field and vorticity tends to stabilize

with low-vorticity regions occupying most of the area.Eventually

the vortex structure is analyzed by the Q-criterion

revealing that the high-intensity vortices are primarily concentrated near the tank wall.