Manning's roughness coefficient in a truncated triangular open-channel flow section

IF 1.6 Q3 WATER RESOURCES Water Practice and Technology Pub Date : 2023-03-28 DOI:10.2166/wpt.2023.044
Sehtal Sabah, Achour Bachir
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Abstract

In uniform flows, Manning's roughness coefficient n plays an important role in the calculation of the normal depth in the open channels. When calculating uniform flows in open conduits and channels, Manning's coefficient is arbitrarily chosen. This arbitrary choice is not physically justified because the coefficient n must be determined according to the parameters that influence the flow, particularly the normal depth sought. In this paper, a new method is presented to compute Manning's coefficient in a truncated triangular channel section. In the first step, the study proposes to establish the general relationship that allows computing Manning's coefficient in this type of channel. The relationship is presented in dimensionless terms, giving it a character of general validity, including the dimensionless Manning's resistance coefficient, denoted as N. The latter is shown to depend on the aspect ratio of the wetted area, the side slope of the channel, the relative roughness and the modified Reynolds number, which is physically justified since flow resistance is closely related to flow depth. In the second step, the rough model method is proposed to express Manning's coefficient when the horizontal dimension of the channel is not a given data of the problem.
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截断三角形明渠断面的曼宁粗糙度系数
在均匀流动中,曼宁粗糙度系数n在明渠法向深度的计算中起着重要作用。在计算明渠均匀流量时,曼宁系数是任意选择的。这种任意选择在物理上是不合理的,因为系数n必须根据影响流动的参数确定,特别是所寻求的正常深度。本文提出了一种计算截断三角形通道截面曼宁系数的新方法。在第一步,研究建议建立一般关系,允许在这种类型的通道中计算曼宁系数。该关系以无量纲形式呈现,使其具有普遍有效性,包括无量纲曼宁阻力系数,表示为n,后者取决于湿区长径比,通道的边坡,相对粗糙度和修正雷诺数,这在物理上是合理的,因为流动阻力与流动深度密切相关。第二步,提出了当通道的水平尺寸不是问题的给定数据时,用粗糙模型方法表示曼宁系数。
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来源期刊
CiteScore
2.30
自引率
6.20%
发文量
136
审稿时长
14 weeks
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