Three Dimensional Bursting Phenomena in Open Channel Bends

The turbulent coherent structure of flow in open channel bends is a stochastic process in nature. The coherence structure of the flow or bursting process is very important for the entrainment of sediment particles from the bed. In this study, first-order Markov process combined with three-dimensional quadrant analysis is applied to the measured turbulent data in open channel bends. The turbulent data was measured in an experimental flume using three-dimensional acoustic Doppler velocity meter (ADV). It was found that the stable movements of velocity fluctuations have higher transition probabilities than other movements, and the cross movements have the least transition probability. In addition, the internal group of events occurs more frequently than external group, particularly the internal ejection and internal sweep events and the probabilities decrease from the concave bank to the convex bank periodically, and reach the maximum at the top of the curved concave bank.

Characteristics of Heat Transfer and Flow on a Surface With Small-Scale Concave Spherical Pits

Small-scale concave spherical pits, which have a special effect on heat transfer enhancement and turbulent drag reduction, are investigated by numerical simulation in detail. Two kinds of small-scale concave pits structures are designed on surface of a plate, which are located in the bottom of a rectangle channel. The characteristics of heat transfer and flow in channel are investigated and compared with a same channel with plate bottom by means of LES. Flow structure and temperature distribution near the pits are analyzed. The numerical simulation results indicate that the concave spherical pits disturb the flow field and vortex is induced by the pits. The turbulent coherent structure is affected by the induced vortex. The numerical simulation indicates that small scale pit can generate the vortex in couple. The range of vortex is accord with the array of small scale pit. The small scale pit can enhance the intensity of vortex. As a result, the temperature field near the pit is changed with generation of the vortex. The heat transfer mechanism on plate with small scale concave spherical pit is summarized.