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Session: Lagrangian aspects of turbulence 3
Session starts: Thursday 27 August, 15:00
Presentation starts: 15:00
Room: Room F

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Guosheng He (Fluid Mechanics Key Laboratory of Ministry of Education, Beijing University of Aeronautics and Astronautics, Beijing, China)
Chong Pan (Fluid Mechanics Key Laboratory of Ministry of Education, Beijing University of Aeronautics and Astronautics, Beijing, China)
Qi Gao (Fluid Mechanics Key Laboratory of Ministry of Education, Beijing University of Aeronautics and Astronautics, Beijing, China)
Lihao Feng (Fluid Mechanics Key Laboratory of Ministry of Education, Beijing University of Aeronautics and Astronautics, Beijing, China)
Jinjun Wang (Fluid Mechanics Key Laboratory of Ministry of Education, Beijing University of Aeronautics and Astronautics, Beijing, China)

Abstract:
The evolution of coherent structures in a flat plate boundary layer transition induced by the cylinder wake is investigated using the particle image velocimetry (PIV) technique. The finite-time Lyapunov exponent (FTLE), which characterizes the amount of stretching about the flow trajectory, is used to extract the Lagrangian coherent structures. It is revealed that secondary vortex is induced by the cylinder wake vortices in the near wall region,which would evolve into hairpin vortex as it convects downstream. The subsequent evolvement of the hairpin vortex, characterized by the regeneration of offspring hairpin vortex upstream of it, leads to the appearance of the hairpin packet and the boundary layer finally reaches a turbulent state.