Development and validation of a hybrid unresolved CFD-DEM coupling framework for drilling slurry penetration

Abstract:

Conventional unresolved CFD-DEM methods are limited by the constraint between grid size and particle diameter， making it difficult to efficiently simulate large-scale geomaterials with a wide particle size distribution. To address this issue， this paper presents the secondary development of a mixed unresolved CFD-DEM coupling framework. In this method， the ratio of fluid grid size to particle diameter serves as an automatic criterion. For fine particles with a ratio greater than 3， a sampling-point method is employed for volume fraction mapping and particle-fluid momentum exchange； whereas for coarse particles with a ratio less than 3， a Gaussian kernel function is introduced for smoothed volume fraction mapping， and the particle-induced fluid momentum source term is distributed over an extended region. Furthermore， to correct the mapping error caused by truncation of the kernel function''s extended domain at fluid boundaries when particles approach walls， a normalization correction based on grid-volume weighting is adopted to ensure conservation near boundaries. Based on the developed program， three verification tests， namely， volume fraction conservation， single-particle settling velocity， and Ergun pressure drop in a spherical particle column are designed to evaluate the reliability of the mixed unresolved CFD-DEM coupling framework in applications involving wide particle size distributions. The results demonstrate that the proposed method can balance computational efficiency and coupling stability in simulations of polydisperse particle systems， providing a feasible numerical approach for problems such as grouting permeation in soil-rock mixtures， fine particle migration， and seepage through particle columns.