Validation of a Eulerian–Lagrangian numerical algorithm for simulating ultra-coarse particles transported in horizontal and vertical hydraulic pipes

Abstract

Investigation on the characteristics of coarse and ultra-coarse particles transported in hydraulic conveying pipe is essential to design hydraulic conveying system with high efficiency and reliability. However, the modeling of the particles with a finite size larger than the mesh for fluid discretization is intractable, because the unresolved point-particle methods are difficult to converge in the calculation and the particle-resolved methods cannot afford the computational cost for engineering problem. A numerical algorithm based on the Eulerian–Lagrangian framework is developed to simulate such two-phase flows. The solvers of the computational fluid dynamics (CFD) and the discrete element method (DEM) are coupled through an in-house developed interface code. In the code, a diffusion-based averaging method is employed to smooth the contributions of large particle in the particle volume fraction, the interphase forces and the interactions between turbulence and particles. The interpolation of fluid velocity is also improved so that the calculations of the interphase forces are more accurate. The authenticity of the numerical algorithm is validated against available experimental results. The validating scenarios are the millimeter- and centimeter-sized particles conveyed in both horizontal and vertical pipes under various conveying speeds and particle concentrations. The results show the numerical algorithm can simulate large particles in the fine CFD meshes. More importantly, some distinct features in the particle distribution and the characteristics of turbulence in the experiments are well reproduced by the simulations.