Comparative analysis of sub-grid drag modifications for dense gas - particle flows in bubbling fluidized beds

Many subgrid drag modifications have been put forth to account for the effect of small unresolved scales on the resolved mesoscales in dense gas-particle flows. These subgrid drag modifications significantly differ in terms of their dependen- cies on the void fraction and the particle slip velocity. We, therefore, compare the hydrodynamics of a three- dimensional bubbling fluidized bed computed on a coarse grid using the drag correlations of the groups of (i) EMMS, (ii) Kuipers, (iii) Sundaresan, (iv) Simonin, and the homogenous drag law of (v) Wen and Yu with fine grid simulations for two different superficial gas velocities. Furthermore, we present an (vi) alternative approach, which distinguishes between resolved and unresolved particle clusters revealing a grid and slip velocity dependent heterogeneity index. Numerical results are analyzed with respect to the time-averaged solids volume fraction and its standard deviation, gas and solid flow patterns, bubble size, number density, and rise velocities.