An extended CFD-DEM model based on micropolar fluid for debris flow

CFD (computational fluid dynamics)-DEM (discrete element method) model has been widely applied in the simulation of the multiphase flow involving granular materials, but it’s time-consuming for the calculation of a large number of particles with different sizes in DEM. In this study, a model based on the computational micropolar fluid dynamics and discrete element method, viz. a CMFD-DEM model, is proposed to describe the coupling system that consists of gas-liquid two phases and discrete particles with different sizes. In this model, micropolar fluid model is employed to describe the mixture of the pure fluid with fine particles, while discrete element method is used to calculate the motion of the larger particles. In addition, VOF (volume of fluid) method is adopted to track the free surface of the liquid. The implementation of the CMFD-DEM model is based on the open source software, OpenFOAM and LIGGGHTS, and is validated in single particle sedimentation and particles pouring into quiescent water cases. Then, the simulation of debris flow is carried out. The results show that specific dynamic behaviors of debris flow can be reproduced by CMFD-DEM model. The average velocity and runout of debris flow are decreased with the increase of micropolar parameter N/L. Through the comparisons to the exiting results, it suggests that CMFD-DEM model is capable to describe the multi-size effect of the granular materials in debris flow.