Abstract: To describe the impact of clusters as the meso-scale structure, a cluster-structure-dependent (CSD) drag model is proposed based on stability criterion of the minimum energy dissipation consumed by drag, where the heterogeneous flow structure is characterized by the gas-rich dilute phase and the particle-rich dense phase. Under the framework of the two-fluid model, the CSD drag model is employed for the investigation of the hydrodynamics in risers with Geldart B particles. By comparisons with experimental results, the CSD drag model shows reasonable predictions. Local structural parameters including dense phase fraction, local velocities in dense and dilute phases are obtained. Meanwhile, the profiles of energy consumption by drag with local gas volume fraction are analyzed, which reveals that the direction of particles will significantly alter the distribution of energy consumption by the heterogeneous drag.