Predictions of bulk velocity for open channel flow through submerged vegetation
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Predictions of bulk velocity for open channel flow through submerged vegetation * Wei-jie Wang1, 2, Xiao-yu Cui1, 2, Fei Dong1, 2, Wen-qi Peng1, 2, Zhen Han1, 2, Ai-ping Huang1, 2, Xue-kai Chen1, 2, Yuan Si1, 2 1. State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China 2. Department of Water Ecology and Environment, China Institute of Water Resources and Hydropower Research, Beijing 100038, China (Received June 1, 2020, Revised July 2, 2020, Accepted July 3, 2020, Published online August 6, 2020) ©China Ship Scientific Research Center 2020 Abstract: Vegetation is of great significance in river ecosystems in terms of hydrodynamics, water environment and ecology. The question of how to predict the bulk velocity in channel flow through submerged vegetation is currently a hot topic in hydraulics research. The present study addresses this question. The various formulae used for bulk velocity estimation in previous work were reviewed and compared. The main novelty of this paper is that a new expression of friction factor is proposed as a function of two dimensionless factors, and the number of tuning parameters is less than that in previous work. A comparison of measured and calculated data was conducted for flow through submerged rigid and flexible vegetation. The comparison showed that the proposed new model can make more accurate predictions than previous models. It is envisaged that the proposed formulation can be usefully employed in eco-hydraulics predictions. Key words: Vegetation, resistance, drag coefficient, bulk velocity, open channel flow
Investigating the flow characteristics of vegetated channels is an important research direction in environmental hydraulics[1-7]. The flow region can be divided into a single layer, two layers, three layers, or four layers along the vertical direction according to different flow turbulence characteristics, which include the viscous bottom zone, wake correction zone, mixing layer, and boundary layer zone[8-13]. In practical applications, most attention is paid to the bulk velocity of flow through vegetation, i.e., the depth-averaged velocity for the whole flow depth. In the present paper, predictions from different research groups are illustrated and compared, and, from the analysis, a new empirical expression is proposed. Stone and Shen[14] conducted laboratory experiments using circular cylindrical roughness to * Project supported by the National Key Research and Development Program of China (Grant No. 2019YFD1100205), the National Natural Science Foundation of China (Grant Nos. 51809286, 51809288). Biography: Wei-jie Wang (1988-), Male, Ph. D., Senior Engineer, E-mail: [email protected] Corresponding author: Fei Dong, E-mail: [email protected]
investigate the hydraulics of vegetated flow, and showed that the depth-averaged velocity for the whole flow depth was 1 U b,stone = 1.385
1 gDS f 4
(1)
where U b is bulk velocity for whole flow depth hw
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