Influence of drag forces of a swarm of bubbles in isothermal bubbly flows conditions

Driven by the extensive demands of simulating highly concentrated gas bubbly flows in many engineering fields, numerical studies have been performed to investigate the neighbouring effect of a swarm of bubbles on the interfacial drag forces. In this study, a novel drag coefficient correlation (Simonnet et al., 2007) in terms of local void fraction coupled with the population balance model based on average bubble number density (ABND) has been implemented and compared with Ishii-Zuber densely distributed fluid particles drag model. The predicted local radial distributions of three primitive variables: gas void fraction, Sauter mean bubble diameter, and gas velocity, are validated against the experimental data of Hibiki et al. (2001). In general, satisfactory agreements between predicted and measured results are achieved by both drag force models. With additional consideration for closely packed bubbles, the latest coefficient model by Simonnet et al. (2007) shows considerably better performance in capturing the reduction of drag forces incurred by neighbouring bubbles.