Numerical Simulation of the Effect of Channel bed Slope on the Hydraulic Performance of Sharp-Crested Rectangular Side Weir with Subcritical and Supercritical Regimes

Document Type : Research Paper

Authors

1 Department of civil engineering; Faculty of civil engineering; University of Tabriz,; Tabriz; Iran.

2 Ph.D student; Department of civil engineering; Faculty of civil engineering; University of Tabriz; Tabriz; Iran.

Abstract

Side weirs are types of hydraulic structures, which are used for different purposes in water transmission systems. In most of the construction operations of irrigation channels and water transfer, based on the topographic conditions of the land, the bottom of the channels is sloped. The purpose of this research is to numerically investigate the changes in the slope of the bottom bed and evaluate the performance of the side weirs in flood conditions and supercritical and subcritical flow regimes. To simulate the flow, CFD method and FLOW-3D® software and RNG turbulence model were used. By examining the surface profile of the flow passing through the weirs at different bed slopes, it was observed that in a fixed slope, in the subcritical flow regime, the surface profile trend is increasing from the beginning to the end of the weir, and decreasing in the supercritical flow regime. As the slope of the main channel bed increases, the level of flow passing over the weir decreases. On average, by changing the regime from subcritical to supercritical, the weir efficiency decreased by 11.21%. Increasing the bed slope decreased the weir efficiency and discharge coefficient in the subcritical flow regime up to 14.54% and in the supercritical flow regime up to 9.26%. The increase in discharge coefficient with the increase of the weir height varied between 4.6 and 7.8 percent. With the increase of the slope of the channel bed, the velocity along the weir in the subcritical and supercritical flow regimes increased by 10.88 and 6.17%, respectively, and the transverse velocity decreased by 22.23 and 4.8 percent, respectively for the subcritical and supercritical flow regimes.

Keywords

Main Subjects

EXTENDED ABSTRACT

Introduction

Side weirs are types of hydraulic structures, which are used for different purposes in water transmission systems. In most of the irrigation and water transfer channel construction operations, based on the topography of the land, the bottom of the channels is sloped, and depending on the hydrological conditions of the region, both subcritical and supercritical flow regimes may be created. The aim of this research is to numerically investigate the effect of bed slope on the hydraulic performance of side weirs in supercritical and subcritical flow.

 

Methodology

The computational fluid dynamics method and FLOW-3D® software and RNG turbulent method were used to simulate the flow. The present research was carried out in 2022 and the literature review is presented in the period from 1934 to 2022. By examining the surface profile of the flow passing through the weirs at different bed slopes, it was observed that in a fixed slope, in the subcritical flow regime, the trend of the surface profile is increases from the beginning to the end of the weir, and decreasing in the supercritical flow regime. As the slope of the main channel bed increases, the level of flow passing over the weir decreases. On average, by changing the regime from subcritical to supercritical, the weir efficiency decreased by 11.21 percent.

 

Finding

Validation of numerical data with laboratory results was done by comparing the level of water passing through the side weir, and the coefficient of flow. The MAE, and APE error values of the flow surface profile for the Froude number (Fr=0.63) were 0.0053, and 2.24%, respectively, and the relative error value for the discharge coefficient was 4.93%, which indicates the low error and acceptable agreement between the values It is numerical and experimental. Increasing the bed slope decreased the weir efficiency and flow rate coefficient in the subcritical flow regime up to 14.54 percent and in the supercritical flow regime up to 9.26 percent. The increase in flow rate coefficient with the increase of the weir height varied between 4.6 and 7.8 percent. With the increase of the slope of the channel bed, the velocity along the length of the weir increases by 10.88 and 6.17 percent, respectively, in the subcritical and supercritical flow regimes, and the transverse velocity along the transverse direction for the subcritical and supercritical flow regimes decreased by 22.23 and 4.8 percent, respectively. By examining the longitudinal distribution of the velocity, it was observed that in the subcritical flow regime, the maximum longitudinal velocity occurs at the beginning of the upstream of the side weir, and by moving towards the downstream of the weir, the flow velocity decreases and increases again after leaving the length of the weir. In the supercritical flow regime, it has an increasing trend when the flow enters from the upstream of the side weir, and it decreases when it reaches the end of the weir, and goes out of the length of the weir.

 

Keywords: Bed slope, Flow rate coefficient, Flow regime, Side weir, Velocity distribution.

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Iranian Journal of Soil and Water Research
Volume 54, Issue 1
April 2023
Pages 67-84

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