A resolved CFD–DEM investigation on granular sand sedimentation considering realistic particle shapes

In this study, a resolved framework coupling computational fluid dynamics (CFD) with the discrete-element method (DEM) is proposed to simulate the sedimentation of granular sand. Realistic sand particles were reconstructed by spherical harmonic representation combined with the multi-sphere clump method, and a fictitious domain method for irregular clumps was further developed to solve the fluid–particle interaction. This resolved CFD–DEM offers a direct and robust approach for computing real fluid forces on irregular-shaped granular sands, without relying on any empirical drag force models. Initially, the effectiveness and accuracy of the proposed CFD–DEM were validated through a series of single-particle free settling simulations for various ideal-shaped particles. Critical fluid–particle interacting behaviours in terms of drag force and wake structure were mainly investigated and corroborated with experimental data. The study subsequently progressed to simulate the sedimentation processes of various granular sand assemblies composed of realistic-shaped sand particles, utilising the proposed CFD–DEM. Detailed numerical analyses concentrated on particle-scale mechanics during sedimentation, including settling trajectories and velocities of particles, as well as the coordination and anisotropy of inter-particle contacts. The results and findings gained from this study provide a novel insight into the micro-mechanisms underlying the sedimentation and accumulation process of granular soils in geological environments.