Abstract
Experiments with a moving single-frame and long-exposure (MSFLE) imaging method, which is a Lagrangian-type measurement, is carried out to study the vortex structures in a fully developed turbulent boundary layer at low Reynolds number on a flat plate. In order to give the process of the vortex generation and evolution, on the one hand, the measurement system moves at the substantially same velocity as the vortex structure; on the other hand, a long exposure time is selected for recording the paths of the particles. In the experiment, the vortex structure characteristics as well as the temporal-spatial development can be shown by the streamwise-normal (x-y)-plane and streamwise-spanwise (x-z)-plane images which are extracted from a fully developed turbulent boundary layer. The result shows that the interaction between high- and low-speed streaks induces the generation, deformation and ‘breakdown’ of the vortex structures, and badly influences the vortex evolution.
Keywords: Boundary layer, High- and low-speed streaks, Low Reynolds number, Moving single-frame and long-exposure time, Vortex structures, Vortex generation, Vortex evolution, Vortex breakdown, Turbulent.
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