Assessment of Momentum Balance Method in the Determination of Shear Stress in Compound Meandering Channels

Document Type : Article

Authors

1 Associate Professor . Water Science and Engineering Dept. Ferdowsi university of mashhad

2 Ferdowsi University of Mashahd

Abstract

Shear stress is one of the most important effective factors in the flow dynamics of open channels. The hydraulics of sediment transport in channels is affected by how and the amount of this factor. Considering the three-dimensional and complex nature of the flow in meandering compound channels, based on the effective role of secondary flows and momentum transfer, especially in curves, calculating this parameter by the methods provided for straight channels is challenging. The Momentum balance method, which is introduced as one of the shear stress determination methods in straight channels, can be used to determine the shear stress in meander channels. In this research, using the 3-D flow velocity components data, measured by ADV, the distribution of shear stress in the flow path in a meandering compound channel was investigated. In a physical model, including a rectangular concrete channel, a meander main channel, and two flood plains, the transverse distribution of streamwise velocity is investigated. Then, the transverse distribution of the shear stress in five sections along the flow is calculated using the momentum balance method, and the results have been compared using the logarithmic distribution method of velocity and Reynolds shear stress in these sections. Also, the amount of shear stress in the four depths of the main channel is illustrated. Since the determination of maximum shear stress areas can be effective in flow and sediment studies and issues related to river maintenance, such as bed erosion, especially in arches, the maximum values of relative shear stress in MBM, RSM, and LLM methods were determined as 5.43 and 7.24 in the fourth section and 6.05 in the first section, respectively. The minimum amounts of shear stress observed in section 5 in both RSM and MBM methods. According to the reviewed results, the MBM method can be introduced as a practical method for evaluating shear stress values in meandering Rivers.

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Sharif Journal of Civil Engineering

Articles in Press, Accepted Manuscript
Available Online from 20 December 2024

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