Numerical analysis of the formation of bubble clusters rising near an inclined wall*

The formation of bubble clusters near a wall can significantly alter the entire structure of bubbly flows by eliminating large-scale vortical structures in turbulent boundary layers. It is known that the occurrence of bubble clustering plays a crucial role for the macroscopic bubbly flow structures. In this study, we conduct direct numerical simulations using the Volume of Fluid (VOF) method to investigate the formation of bubble clusters rising near an inclined wall. Under certain conditions, accumulated bubbles near the wall form a stable bubble cluster. The present numerical results are compared with the experimental results by Ogasawara & Takahira (2018). And simplified model equations for bubble motion is discussed to predict the trajectories of bubbles and the formation of bubble clusters through the comparison with the present numerical results.