Dominant structure for turbulent production in a transitional boundary layer

Abstract

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 Λ -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.

Keywords:

• Soliton-like coherent structure
• Turbulent production

PACS:

• PACS numbers: 47.27.cn

Acknowledgements

This work is supported by the National Outstanding Young Scientists Foundation of China (Grant No. 10525208). The encouragement from Professor S. Chen (Johns Hopkins University and Peking University) and Professor M. D. Zhou (University of Arizona) has been very helpful.