This study aims to investigate the impact of particles on flow characteristics within the framework of downward turbulent gas-solid flow through a sudden expansion backward-facing step. Employing the Eulerian-Lagrangian approach, the simulation encompasses both gas and solid phases. A custom FORTRAN code, based on the finite volume technique with a hybrid scheme in a staggered grid, is developed to simulate the scenario. This research introduces and compares the standard k-ε and Chen-Kim turbulence models with experimental outcomes. The investigation utilizes experimental measurements and numerical simulations to comprehend flow dynamics. Upon juxtaposing the results with published experimental data, the current code displays favorable outcomes, motivating further theoretical exploration and parameter investigation. The sudden expansion backward-facing 's performance is evaluated across mass loading ratios. Computational findings emphasize the considerable influence of mass loading ratio on flow behavior. An increase in mass loading ratio leads to heightened solid phase concentration and distinct flow patterns.