The inner structure of a two-phase plume, driven by air bubble buoyancy and formed in a stratification ambient fluid in a rectangular tank, is numerically simulated by means of two-phase flow theory and Large-eddy simulation technology. Focusing on the discrete nature of the buoyant dispersed phase and on the role of momentum exchange between two phases during plume formation, we investigated the phenomena of mass "entraining-in" and "peeling-out" that occurs inside the stratified ambient plume. These phenomena are thought to result from an intricate interplay among phase interaction, static stability of the stratification ambient fluid itself, and dynamic stability due to turbulence. Numerical simulations show that there exists an inner-out structure of the stratified ambient plume, while at the same time predicting that the re-entraining-in mass flux is on the same order of magnitude as that of the inner peeling-out mass flux within the annular region centered around the plume. This further explains the mechanism underlying the formation of multi-scale eddies at the edge of the air bubble plume, which also constitutes the boundary between the inner and outer zones of this inner-out stratified fluid plume. Within the inner part of the plume, the mass entraining-in and peeling-out appeared as a spatial discontinuity. The numerically visualized three-dimensional density fields are consistent with the two-phase plume characteristics.
