Density ratio effects on turbulent bubbly upflow in a vertical channel: similarities and differences

In this study, we investigate the effects of density ratio on turbulent bubbly upflow in a vertical channel. High-resolution numerical simulations were conducted using a coupled level-set and volume-of-fluid method to accurately capture the liquid-gas interface. Various cases were analyzed to examine flow morphology and turbulence statistics. Results indicate that increasing the density ratio from 10 to 30 leads to increased drag and a reduction in mean momentum. However, further increases in the density ratio to 1000 do not significantly alter bubble morphology, turbulence statistics, or drag. An analysis of the Reynolds stress transport equation reveals that the insignificant differences in drag at high density ratios (> 30 ) are caused by the reduced wall-normal gradient of the streamwise velocity above large bubbles, resulting in less production. Additionally, we introduce new inner layer transformation and outer layer scaling to re-establish the law of the wall (LoW) and the defect law for the mean velocity profiles in bubbly flows. The results show that the transformed velocity profiles collapse to the LoW much better than the original velocity profiles and that the Zagarola-Smits scaling successfully recovers the defect law for the outer layer of the mean velocity profiles.