Clusters and anisotropic turbulence of gas-particle flow in fluidized risers studied using the four-way coupled second-order moment method

The gas-particle flow in a fluidized bed is characterized as a “core-annulus” pattern with transient clusters moving along the riser. These clusters exist as regions with a higher concentration of particles and are surrounded by dispersed particles at lower concentrations. In this study, clusters and their fluid dynamics were investigated using the four-way coupled second-order moment method of the fluid–particle Eulerian–Eulerian two-fluid model. This model was evidenced in modeling the fluid-particle two phase flow in the previous research, especially when the particles were in medium concentration while the particle turbulence was far from equilibrium to satisfy the Boussinesq approximation. In the simulation, the gas-particle flow in the fluidized risers was predicted. The fluid dynamics of the Geldard B particle clusters in the risers were characterized. In addition, the anisotropic turbulence of either phase in the clusters was studied. According to the turbulence intensity of both the phases, the gas-particle flow in the fluidized riser was classified into six zones. As the volume fraction of the particles increased, the anisotropic ratios of the turbulence intensities in both phases increased in the dispersed zone and decreased in the cluster zone, respectively.