A robust three-dimensional discrete particle model (3D DPM) for unstructured meshes is presented to model the gasâsolid flows in fluidized beds. The finite volume method is used to discretize the governing equations of the gas phase. Inter-particle interactions are taken into account through the hard-sphere approach. The numerical models for the solid phase were implemented as a separate module in FLUENT by overcoming some limitations of the user-defined function approach. A multifaceted numerical strategy was developed to enhance the computational efficiency. Simulation results demonstrate the ability of the model to capture many important characteristics such as bubbling, spouting, particle clustering and coreâannulus flow structures in gasâsolid systems at specified operating conditions.