Drag force model corrections based on nonuniform particle distributions in multi-particle systems

The drag force is one major particle-fluid interaction force in multiphase flows. Conventional drag force models do not accurately consider the effect of nonuniform particle distributions which limits their applicability with considerable nonuniform particle distributions. A meshless method (Element-Free Gelerkin method) was used for direct numerical simulations to simulate real particle collisions and investigate the drag coefficient variations in various nonuniform particle distributions. The classical drag force model is corrected using nonuniformity coefficients based on various nonuniform particle distributions in various multiphase flow types. The results show that the nonuniform particle distribution greatly affects the drag coefficient with different compacting directions having different results. In most situations, only the effect of compacting in the direction perpendicular to the main flow direction needs to be considered and the effect of compacting in the main flow direction can be neglected. The particle nonuniformity in the direction perpendicular to the main flow direction reflects the overall dynamic effect of the drag coefficient while the nonuniformity in the main flow direction reflects local fluctuations. Thus, the modified drag force model considering the nonuniform distribution more accurately reflects the dynamic effect of the drag coefficient. It can be more widely used than conventional drag force models. (C) 2011 Elsevier B.V. All rights reserved.