Peak structure in downward gas–liquid bubbly flow and its transition to slug flow – A numerical investigation

► Downward gas–liquid bubbly flow and its transition studied numerically.
► Combined two fluid-population balance model used for simulation.
► Both core peaking and wall peaking obtained for different superficial velocities.
► Bubbly-slug transition criteria for upflow also holds for downflow.
► Comparative study between up and downflow has been made.