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.