Transportation of the coarse materials is one of the major challenges in slurry transport for dredging. Unfavorable situations may occur, e.g., the strong hydraulic resistance and the blocking in the pipe. In this study, An Eulerian-Lagrangian coupled algorithm is implemented to model the pipeline transport process of coarse particles. Codes of computational fluid dynamics (CFD) and discrete element modeling (DEM) are utilized for simulating the fluid and the solid behavior respectively. The numerical modeling of particles with a diameter of 10mm transported in a pipeline with a diameter of 15.24cm is carried out under three different conveying line speeds. Qualitative study is made on the transitions between different flow regimes, and quantitative analysis is made on the volumetric concentration and the hydraulic gradient in the pipe.

The behavior of fully-suspended slurry flow in horizontal pipeline can be simulated through two very distinct models, the Computational Fluid Dynamics (CFD) model and the Delft Head Loss & Limit Deposit Velocity (DHLLDV) model. The predicted results from simulations are compared with a series of experiment data from the literature, involving the effects of different particles volume concentration (9–42%), particle size (90–440 μm), mixture velocity (1–9 m/s), and pipe diameter (51.5–263 mm) on hydraulic gradient and particles concentration distribution, and revealing excellent agreements between two model predictions and the experimental data. Both CFD and DHLLDV, however, still have some deviations in the near-wall concentration distribution as for larger particles. Though it is observed that the accuracy for CFD will decline when particle size increases and further research is needed for improving the accuracy of the models for the near-wall flow of larger particles, it can be concluded that both CFD model and DHLLDV model apply to calculations for fully-suspended flow.

Slurry transport is a very important means of transporting solids through a pipeline. To improve the efficiency of slurry transport, especially in coarse particle transport, which is subject to problems such as strong resistance and easy blockage, more of the internal structure of the flow must be known. Empirical and analytical models are inadequate for this purpose. Therefore, in this study, a coupling mechanism is established between the computational fluid dynamics (CFD) and discrete element method (DEM). The CFD-DEM coupling was applied and research was conducted on the internal flow structure characteristics of microscopic motion and flow transition for coarse particles in a pipeline. The flow-regime transition processes of coarse 10-mm particles were analyzed qualitatively at velocities of 2 m·s ⁻¹ , 5 m·s ⁻¹ , 8 m·s ⁻¹ and 10 m·s ⁻¹ in a 0.1524-m diameter pipe, and quantitative analyses were performed on both the concentration distribution and the pressure gradient of particles in regimes of fixed bed flow, sliding bed flow and heterogeneous flow. Moreover, from the perspective of force analysis of particles, the law of sedimentation movement of particles is discussed, and the reason for the change in concentration distribution is explained. The research presented here provides insight into the internal structure of the flow and gives quantitative indications of pressure gradient and concentration distributions.