Transient dynamics of gas–solid flows from packed beds to spouting regimes: A particle based computational fluid dynamics-discrete element method study

Gas–solid granular systems exhibit complex transient dynamics that are of fundamental interest in fluid physics and various industrial applications, ranging from chemical reactors to geophysical phenomena. In this study, a graphics processing unit accelerated smooth particle hydrodynamics–discrete element method (DEM) framework is developed to resolve coupled hydrodynamic and thermal behaviors from dense packed beds to dynamic spouting regimes. The fluid phase is governed by the volume-averaged Navier–Stokes equations, where a key feature is the direct evaluation of local porosity and its temporal derivative (dε/dt) from instantaneous particle configurations. By applying the chain rule to interpolated quantities, the porosity change rate is expressed as an inner product between kernel gradients and DEM particle velocities. This approach enables the explicit integration of transient porosity effects into the momentum balance without introducing additional empirical closures, ensuring consistent pressure–velocity coupling under highly transient conditions. The framework is validated against benchmark experiments, demonstrating accurate predictions of pressure drop and thermal responses in granular beds. Notably, the model reveals that accounting for transient porosity evolution systematically amplifies the velocity and elevation overshoot during spouting onset, a phenomenon found to be negligible in the subsequent quasi-steady state. These findings emphasize the critical necessity of considering temporal porosity variations to capture the full physics of early stage gas–solid interactions and provide a robust computational basis for extending toward more complex multiphase systems.