This work presents a new structure-based drag model for downer reactors combining with the computational fluid dynamics (CFD) method to systematically study the hydrodynamics of downer reactors. Previous studies are limited to simulate the radial performance in downers because of using the conventional drag model. Based on the new drag model, the hydrodynamics of downers in the radial and the axial direction are simulated. Meanwhile, the effect of clusters, which is the typical meso-scale structure, are investigated. It was found that, compared to risers, the drag force would not be influenced by the cluster diameter and voidage in downers heavily. The simulation results by the new structure-based drag model showed reasonable agreements with the experimental data in the radial and axial direction. The unique trends of downers were also obtained, e.g. the dense ring flow structure, axial velocity flow structure and pressure distribution. These results demonstrated that the new structure-based drag model could reflect the hydrodynamics of downer reactors and provide a good understanding on the physical mechanism of the gas-solid flow in downers. (C) 2016 Published by Elsevier B.V.