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Analysis of turbulent flow characteristics in the vicinity of the bar in a braided river model
M.A. Khan,
Published in Taylor and Francis Ltd.
Volume: 23
Issue: 3
Pages: 267 - 275
Turbulent phenomenon in braided rivers is much more complex as compared to the straight and meandering rivers. Turbulent flow characteristics around the braid bar are not thoroughly studied till now. The results of measurements of three-dimensional velocities carried out in a laboratory model of braided river are presented in this paper. Velocity is measured with the help of acoustic Doppler velocimeter. The main purpose of the study is the recognition of structure of Reynolds stresses in turbulent flow near the bar. Sweep quadrant event is considered to be the most important for entrainment of sediment particles as it exerts forces in the flow direction resulting in rolling and sliding of sediment particle. Similarly, the ejection event has been considered important for sediment transport since these events maintain the sediment particles in suspension. Special attention has been given to sweep and ejection bursting events due to their relation with the sediment entrainment and transport. The fractional Reynolds stresses are examined by a quadrant technique with an arbitrarily chosen hole size. It has been observed near the bed, the largest fractional Reynolds stress contribution comes from the second quadrant and the fourth quadrant. Angle of sweep and ejection events was plotted against the flow depth, in order to relate the sweep and ejection events with the scouring/depositional pattern around the bar. The maximum residence time of each event is also computed. From computation, it was found that the maximum residence time of the even events is much greater than for the odd events near the bed. In order to examine the depth-wise distribution of turbulent flow, Reynolds stress and higher moment Fku are plotted against the flow depth. These parameters assess the sediment characteristics in the vicinity of the bar. Results show that the Fku parameter better assesses the sediment characteristics of flow around the bar. © 2017 Indian Society for Hydraulics.
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Published in Taylor and Francis Ltd.
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