Numerical investigation on turbulence drag reduction by small bubbles in horizontal channel with mixture model combined with population balance model

The drag reduction by small bubbles is investigated with mixture multiphase flow model combined with population balance model for the horizontal channel turbulence. The influence of liquid-phase Reynolds number and global void fraction on the drag reduction is fully analyzed. The present results show that the addition of small bubbles cause the drag reduction, and the liquid-phase Reynolds number and the global void fraction have the great influence on the drag reduction rate. For the same global void fraction, the larger the liquid-phase Reynolds number is, the sharper the bubble breakup phenomenon is, which leads to that the bubble diameter is smaller and the drag reduction rate is higher. The influence of the global void fraction on the drag reduction rate is related to the liquid-phase Reynolds number. For the low liquid-phase Reynolds number, the case with the lower global void fraction has the higher drag-reducing rate. However, for the high liquid-phase Reynolds number, the higher void fraction corresponds to the larger drag reduction rate. It is very important for investigating the drag reduction by bubbles to consider the bubble coalescence and breakup phenomena. And the present results show that the drag reduction rate strongly depends on the bubble size.