In the present work, a k(1)-epsilon(1)-k(2)-k(12) two-fluid model based on the kinetic theory of granular flow (KTGF) was employed to predict the flow behavior of gas and solids in downers, where the particles of small size as 70 mu m in diameter apparently interact with the gas turbulence. The turbulence energy interaction between gas and solids was described by different k(12) transport equations, while the particle dissipation by the large-scale gas turbulent motion was taken into account through a drift velocity. Johnson-Jackson boundary condition was adopted to describe the influence of the wall on the hydrodynamics. The simulation results by current CFD model were compared with the experimental data and simulation results reported by Cheng et al. (1999. Chem. Eng. Sci. 54, 2019) and Zhang and Zhu (1999. Chem. Eng. Sci. 54, 5461). Good agreement was obtained based on the PDE-type k(12) transport equation. The results demonstrated that the proposed model could provide good physical understanding on the hydrodynamics of gas-solid multiphase flow in downers. Using the current model, the mechanism for formation and disappearance of the dense-ring flow structure and the scale-up characteristics of downers were discussed. (C) 2011 Elsevier Ltd. All rights reserved.