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Internal Flows
Published in Wen-Jei Yang, Handbook of Flow Visualization, 2018
The concept of coherent structure started with rather simple flow visualization experiments. Hama, in [21], revealed the streaklines (see Fig. 4) near the flat plate by using the dye-injection method. Since turbulent flow was considered to be irregular then, his experimental technique was questioned. However, the flow visualization photographs [18] (see Figs. 5 and 6) obtained by Kline and his co-workers using the hydrogen bubble technique conclusively proved the existence of a coherent turbulent structure. The low-speed streaks formed in the region very near the wall interact with the outer portions of the flow through a process of gradual “lift-up”; then there is sudden oscillation, bursting, and ejection. Flow visualization clarifies the flow structure near the wall and paves the way for the current active research on coherent structures in turbulent flow.
Energy dissipation for supercritical flows by using screens with triangular shape openings
Published in ISH Journal of Hydraulic Engineering, 2023
Ujjawal Kumar Singh, Parthajit Roy
The flow in the transition zone is a highly turbulent flow associated with air entrainment, surface waves and spray. The system of equations required for linking the flow properties upstream and downstream of the jump can be developed by the application of continuity and momentum principles in an integral form. The turbulent flow in the transition zone leads to the development of large-scale vortices and intense interactions between entrained air and coherent turbulent structures (Zhang et al. 2013). The entrapped air bubbles and pockets are advected within the turbulent flow in the transition zone. The air pockets are entrained either locally or continuously along with the air–water interface, usually parallel to the flow direction (H. Chanson 2009). Further, the air-water shear region and the upper free-surface layer are two distinct air-water regions associated with hydraulic jump rollers. The air-water shear region receives the transfer of momentum in its recirculation region from the high-velocity jet and entrained air bubbles through the convictive transport process. While an uncontrolled exchange of air and water between the recirculation region and the atmosphere takes place in the upper free-surface region.