A semi-resolved CFD-DEM coupling model using a two-way domain expansion method

Abstract

The unresolved model is widely applied in the CFD-DEM coupling simulation for particulate flows due to its lower computational cost compared with the resolved model. However, it requires that the size ratio of a particle to the located CFD cell is small enough, usually less than 1/3, otherwise the precision and stability of the simulation cannot be guaranteed. In this work, a semi-resolved model was developed using a two-way domain expansion method, in which both the dependent domain and influential domain of a considering particle were expanded from the particle-located CFD cell. A weighting factor using the Gauss kernel function was applied to interpolate the ambient fluid variables of a considering particle from all the CFD cells in the dependent domain. The interphase forces and the volume of particles were allocated to the CFD cells in the influential domain. A hierarchical searching algorithm was established to efficiently index the CFD cells located in the expanded domain. The developed model was first employed to simulate the settling of a single spherical particle in liquid driven by gravity. The results were compared with the experiments to validate the two-way domain expansion method and verify the model performance on eliminating the limitation of the unresolved model. The model performance was further investigated and validated in the test cases of the granular group settling. The analysis of the vortex structures for cases with different fluid volume fractions focused on validating the capability of the updated model to simulate the complex fluid flow induced by the granular group settling.