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Bed sill effectiveness in reducing flow separation at open channel confluences: an openfoam-VOF 3D CFD study
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  • Published: 21 April 2026

Bed sill effectiveness in reducing flow separation at open channel confluences: an openfoam-VOF 3D CFD study

  • Shashank Shekhar Sandilya1,
  • Bhabani Shankar Das1 &
  • Abhishek Kumar Pandey2 

Scientific Reports (2026) Cite this article

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We are providing an unedited version of this manuscript to give early access to its findings. Before final publication, the manuscript will undergo further editing. Please note there may be errors present which affect the content, and all legal disclaimers apply.

Subjects

  • Energy science and technology
  • Engineering
  • Mathematics and computing

Abstract

The Flow Separation Zone (FSZ) is a key hydrodynamic feature of open channel confluences, and its reduction contributes to improved channel efficiency. This study employs the open-source computational fluid dynamics (CFD) software OpenFOAM to examine the influence of a bed sill on reducing the FSZ at a right-angled open channel confluence. The flow is simulated by solving the three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) equations with the SST k–ω turbulence model, while the interFoam multiphase solver is used to capture the water–air interface via the Volume of Fluid (VOF) method. The numerical model is validated against experimental data from the literature by comparing velocity fields and water surface elevations. Different sill sizes, locations, and configurations are tested to evaluate their effectiveness in reducing the FSZ. The results indicate that strategically placed sills can shorten the FSZ length by up to 55%, while modifying velocity profiles and reducing flow recirculation. Using multiple sills, particularly a three-sill configuration, further enhances this effect, reducing the FSZ length by as much as 74%. Analysis of secondary currents shows that sills intensify these currents, thereby enhancing momentum exchange and reducing the flow separation. Furthermore, energy loss analyses conducted for various sill configurations demonstrate that strategically positioned sills can reduce the energy loss significantly.

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Data availability

All data, numerical models, and related code (including OpenFOAM files and post-processing scripts) that support the findings of this research are available from the corresponding author upon reasonable request.

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Acknowledgments

The authors extend their sincere gratitude to NIT Patna for their financial support.

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Authors and Affiliations

  1. Civil Engineering Department, NIT Patna, Patna, India

    Shashank Shekhar Sandilya & Bhabani Shankar Das

  2. Civil Engineering Department, IIT (ISM) Dhanbad, Dhanbad, India

    Abhishek Kumar Pandey

Authors
  1. Shashank Shekhar Sandilya
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  2. Bhabani Shankar Das
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Contributions

Shashank S. Sandilya: Writing – original draft, Visualization, Numerical simulation setup, Methodology, Results interpretation. Bhabani S. Das: Writing – review & editing, Supervision, Conceptualization. Abhishek K. Pandey: Conceptualization, Methodology, Results interpretations, Writing – review & editing.

Corresponding author

Correspondence to Bhabani Shankar Das.

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Cite this article

Sandilya, S.S., Das, B.S. & Pandey, A.K. Bed sill effectiveness in reducing flow separation at open channel confluences: an openfoam-VOF 3D CFD study. Sci Rep (2026). https://doi.org/10.1038/s41598-026-47318-8

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  • Received: 23 November 2025

  • Accepted: 31 March 2026

  • Published: 21 April 2026

  • DOI: https://doi.org/10.1038/s41598-026-47318-8

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Keywords

  • CFD
  • Channel confluence
  • Channel hydraulics
  • Energy dissipation
  • Flow separation zone
  • OpenFOAM
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