On the Influences of Air Bubbles on Water Flow in a Two-Dimensional Channel

As an inevitable trend for the sustainable development of the global economy, saving energy and reducing emissions are key goals for the entire world. The use of air bubbles to reduce viscous friction is one of the most effective approaches to achieve this goal, as it may significantly reduce the frictional drag of ships. However, the injection of air bubbles will change flow characteristics near the wall due to the significant differences in density and viscosity between air and water. In addition, parameters such as bubble size, bubble surface tension, bubble number and bubble position also affect the flow near the wall, resulting in significant diversity and instability in two-phase flow. To clarify the mechanism of these effects, a two-dimensional channel flow with air bubbles is studied using Computational Fluid Dynamics (CFD). The interactions between bubbles and water and between bubbles and wall are studied, and the detailed characteristics of bubbles moving in fully developed flow are considered. This study shows that the velocity gradient is the main factor influencing wall shear stress, and the presence of bubbles has a marked impact on the local velocity gradient distribution of the nearby flow. It is also found that shorter distance between a bubble and the wall enhances the flow interaction and leads to more significant perturbations of wall shear stress.