<p>This work investigates the hydrodynamics of a circulating fluidized-bed riser by combining CFD simulations with noninvasive gamma-radiation transmission measurements. Two drag models, Gidaspow and EMMS, were evaluated. The computational setup underwent mesh-independence verification using the Grid Convergence Index, and model performance was quantified against experiments with RMSE and NRMSE. The analysis shows that EMMS generally provides closer agreement with measured solids volume-fraction profiles, particularly in the dilute core and in regions prone to particle clustering, while both models reproduce the principal axial and radial trends. In some sections with lower local solids concentration, Gidaspow tends to underestimate the solids holdup. Predictions of axial pressure variation are consistent with experimental tendencies for both closures. The integrated use of gamma-radiation diagnostics and CFD is shown to be effective for validating model predictions and for guiding model selection in riser simulations, balancing accuracy and computational cost. These results provide a documented, reproducible basis for simulations of gas–solid flows in circulating fluidized-bed systems and inform design and optimization decisions where reliable estimates of cross-sectional solids distribution are required.</p>