Document Type : Original Article

Authors

• Amirreza Shahriari ¹
• Mehdi Daryaee ²
• SeyedMahmood Kashefipour ³
• Mohammadreza Zayeri ⁴

¹ Department of Water Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.

² Associate Professor,, Department of hydraulic structures,Faculty of water and environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.

³ Professor, Department of Water Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.

⁴ Assistant Professor, Department of Water Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.

Abstract

Introduction
Side weirs are widely used hydraulic structures in irrigation, drainage, and flood control systems. These structures allow excess water to be diverted from the main channel, helping to manage flow capacity effectively. In converging channels, the presence of guiding structures, such as flow deflectors, can influence the hydraulic performance of side weirs. Recent studies have highlighted the potential of guiding structures to enhance discharge capacity. However, uncertainties persist regarding the impact of convergence and added structures on specific energy variations in the main channel. The classical assumption of spatially varied flow with lateral outflow suggests that specific energy remains constant along the weir. This study aims to evaluate the validity of this assumption in converging channels with guiding structures by investigating specific energy variations using numerical simulations.
 Methodology
A three-dimensional numerical model was developed using FLOW-3D to simulate flow over a converging side weir. The experimental setup by Maranzoni et al., (2017) was used as a reference for model validation. The numerical domain consisted of a converging channel with a side weir, and guiding structures were placed on the weir crest at three different longitudinal positions (upstream, middle, and downstream) with installation angles of 60°, 90°, and 120° relative to the horizontal.
The Reynolds-averaged Navier-Stokes (RANS) equations were solved using the RNG k-ε turbulence model. Boundary conditions included a specified flow rate at the inlet, a pressure outlet at the downstream boundary, and wall conditions for the channel boundaries. Grid independence was ensured by testing different mesh resolutions, with the final model consisting of approximately 1.5 million cells. The numerical model was validated against experimental data, with a maximum simulation error of less than 4%.
 Results and Discussion
The numerical results showed that guiding structures influenced specific energy variations along the weir. The middle position of the weir exhibited the least change in specific energy (0.8%) , making it the optimal location for installing guiding structures. In contrast, upstream and downstream placements resulted in greater energy variations, with mean differences of 1.17% and 1.37%, respectively.
The effect of installation angle on specific energy variations was negligible. Across different angles, the mean variation ranged from 1.03% to 1.22%, indicating that the angle of installation had little impact on energy conservation. The influence of the inflow Froude number was also examined. For Froude numbers below 0.3, specific energy variations remained under 0.5%. As the Froude number increased to 0.45, energy variations reached 1.6%, which is still within an acceptable range. These findings suggest that specific energy variations are more sensitive to the location of guiding structures than their installation angle.
The results confirm that the classical assumption of constant specific energy in spatially varied flow with lateral outflow holds even in converging channels with guiding structures. Although minor deviations were observed, they were within acceptable limits for practical applications.
 Conclusions
In this study, by comparing the simulation results with experimental data, it was found that the model used for simulating flow over side weirs possesses high accuracy and reliably predicts the actual performance of these structures. One of the key aspects of this research is the accurate simulation of side weirs in converging channels. Despite numerous studies in this area, especially in recent years, certain aspects of the design and hydraulic behavior of these types of weirs still require more detailed investigation and numerical modeling.
The findings of this study demonstrated that the classical concept of specific energy stability in gradually varied flow with decreasing discharge remains valid even under converging conditions and in the presence of guiding structures. The average difference in specific energy between the upstream and downstream of the weir in all simulations was 1.24%. Additionally, the influence of the Froude number on the increase in specific energy variations was clearly observed. However, within the range of Froude numbers less than 0.5, which is typically dominant in irrigation and drainage channels, specific energy variations did not exceed 3%.
Finally, for future research, it is recommended to investigate the effects of factors such as the crest height of the side weir, the presence of orifices within the weir structure, and the influence of supercritical flow regimes on specific energy variations along side weirs, in order to develop a more comprehensive understanding of their hydraulic behavior.
 Acknowledgement
We are grateful to the Research Council of Shahid Chamran University of Ahvaz for financial support (GN: SCU.WH1402.31370).

Keywords

• CFD
• De Marchi
• Spatially varied flow
• Water structures

Main Subjects

• Hydraulic