Recent progress in dynamics of boundary layer transition*

The dynamics in transitional boundary layers involve interactions among various flow structures. It is not easy to identify unambiguously the dominant structures which give the major turbulent production. In this paper, we study the flat plate boundary layer was studied by means of using two-dimensional hot film velocity measurements and flow visualization. Our results present direct evidences of the existence of soliton-like coherent structures that are dominant flow structures in turbulent production processes for both the early and late stages of boundary layer transition. Furthermore, we observe it is concluded that in boundary layer flows these soliton-like coherent structures are the building blocks to produce other coherent structures.