Dominant structure for turbulent production in a transitional boundary layer

The nonlinear evolution of the three-dimensional soliton-like coherent structure (SCS) in a transitional boundary layer is described in this paper. Hydrogen bubble visualizations and two-dimensional hot film measurements were used to analyze the dynamic relationships between the SCS and the Lambda-vortex, the secondary closed vortices and the low-speed streak. The results show that the three-dimensional SCS is the dominant flow structure in almost all dynamic processes in both the early and later stages of boundary-layer transitions as well as in a turbulent boundary layer. Further, the SCS is shown to be the building block that produces other coherent structures in wall-bounded flows.