Affiliations: Research Institute of Innovative Technology for the
Earth, 9-2 Kizugawadai, Soraku-gun, Kyoto 619-0292, Japan. e-mail:
b.chen@aist.go.jp | National Institute of Advanced Industrial Science and
Technology, 1-2 Namiki, Tsukuba-shi, Ibaraki 305-8564, Japan
Abstract: 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.
Keywords: Two-phase plume, Numerical simulation, LES, Stratification, Mass flux
