  An iterface structure between turbulence and laminar flow is investigated in
two-dimensional channel flow. This spatially localized structure not only
sustains itself, but also converts laminar state into turbulence actively. In
other words, this coherent structure has a functionality to generate
inhomogeneity by its inner dynamics. The dynamics of this functional coherent
structure is isolated using the filtered simulation, and a physical perspective
of its dynamics is summarized in a phenomenological model called an
"ejection-jet" cycle, which includes multiscale interaction process.
