Internal structures of turbulent spots

The evolution of turbulent spots over a flat plate is investigated using time-resolved tomographic particle image velocimetry. Timelines and material surfaces are used to visualize flow structures within the turbulent spots. The results reveal soliton-like coherent structures within the spots that act as three-dimensional (3D) waves, inducing wave-like peaks on material surfaces. The lift-up of these 3D waves and the downward movement of the surrounding fluid form high-shear layers, which serve as precursors to vortices at the edges of the turbulent spots. These findings suggest that 3D waves may serve as the fundamental structures of turbulent spots and play a dominant role in their development.