Three-dimensional numerical simulation of flow in converging non-prismatic compound channels with emphasis on geometry and hydraulic parameters effects

Subject Areas : Analysis, design and construction of water structures

Soran Ezati ¹ , Ziaedin Aydi ² , Seyed Hossein Mohajeri ³

1 - Environmental Engineering Division, Civil & Environmental Engineering Faculty, Tarbiat Modares University, Tehran, Iran.
2 - River Engineering Department, Regional Water Company of Alborz, , Karaj, Iran.
3 - Department of Civil Engineering, Faculty of Engineering, Kharazmi University, Tehran, Iran.

Received: 2025-06-16 Accepted : 2025-09-14 Published : 2025-11-27

Keywords: Numerical model, Compound channel, Experimental data, Flow3D, Fluent ,

Abstract :

Remarkable advances in numerical computing technology have enabled more detailed numerical analysis of open-channel flows in three dimensions, and today, many problems related to these channels can be effectively solved using two- and three-dimensional simulation models. Composite hydraulic sections, formed by the combination of a main channel and floodplains, require the use of three-dimensional numerical models for a comprehensive analysis of flow behavior due to the complexities arising from the flow characteristics in such channels and the dynamic hydraulic interactions between these two parts. This study primarily focuses on the three-dimensional numerical model Flow3D with Cartesian grid, which was employed to simulate flow in non-prismatic compound channels with converging floodplains; a comparison was also made with the Fluent model using a curvilinear grid. To evaluate the accuracy of the models, the coefficient of determination (R²) between the numerical results and experimental data was calculated, which was above 0.96 in all cases for both models; the results of these models were validated against reliable experimental data from research at the Catholic University of Leuven, Belgium. The method of gridding the sloped sidewalls of the channel in Flow3D with Cartesian meshing demonstrated high accuracy in reconstructing the water surface profile, depth-averaged velocity distribution, and velocity field. Although the influence of the mesh type on the water surface profile and depth-averaged velocity distribution was limited, it showed a significant advantage over the curvilinear method in simulating the velocity field, especially in near-boundary regions. Sensitivity analysis results indicated that the convergence angle had the greatest effect on reducing the water level, while relative depth and discharge played key roles in momentum transfer and flow velocity, respectively.

 

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