EFFECT OF FLOW CONFINEMENT ON THE DRAG FORCE COEFFICIENT IN HOMOGENEOUS BUBBLY FLOW AT MODERATE VOLUME FRACTION

摘要

This paper presents an investigation of the drag force coefficient modification in homogenous turbulent two-phase bubbly flows at moderate volume fractions (less than 10%). We focus on the analysis of the aptitude of the assumption of the confinement of the bubble surrounding flow at moderate volume fraction to explain the evolution of the drag force coefficient at this volume fraction range. A numerical study using computational fluid dynamics (CFD) was conducted to investigate the effect of the flow confinement on the drag force exerted on a fixed ellipsoidal bubble. An analytical model of the drag force correction function is equally proposed. The results obtained by both numerical and analytical approaches have been validated by comparing them with the experimental data from a previously published work that studied a uniform monodisperse swarm of bubbles, in which there was no significant effect of recirculating motion in the liquid phase. All of the results showed that the confinement of the surrounding bubble flow hypothesis can explain the drag force coefficient evolution at moderate void fractions. The results also suggest that the influence of the bubble's shape on the drag force coefficient is not important at this void fraction range. On the other hand, the analytical model seems to be in concordance with both the experimental and numerical results obtained by the CFD approach.