This manuscript reports the fluid dynamics in the developed flow region of a cocurrent gas-solid down flow fluidized bed unit. Gas-solid flows are simulated using a Computational Particle Fluid Dynamics (CPFD) numerical scheme and experimental data from the CREC-GS-Optiprobes. This model represents clusters in a downer unit. It is hypothesized that in downers, clusters are formed via a Random Particle Selection Method (RPSM) ensuring cluster dynamic stability. To accomplish this, a statistical particle selection of clusters (SPSC) method is developed. This hybrid model is validated with experimental data obtained in a 2 m height and 2.57 cm diameter column. Observed time-averaged axial and radial velocities and solid concentration profiles are successfully simulated by the Hybrid CPFD/CREC-GS-Optiprobes Data Model. These findings support: (a) a narrow distribution of particle cluster residences, (b) the relatively flat radial solid concentrations and solid cluster velocities, and (c) a valuable approach for establishing slip velocities in downer units. (C) 2016 Elsevier Ltd. All rights reserved.