Journal of New Approaches in Water Engineering and Environment
Scientific Journal

Numerical Investigation of Step Edge Geometry Effects on Hydrodynamic Flow Behavior in Stepped Spillways Using FLOW-3D

Document Type : Original Article

Authors

Elham Karimzadeh 1
Mahdi Mollazadeh 2

1 Department of Civil Engineering, Faculty of Engineering, Birjand University, Birjand, Iran.

2 Department of civil engineering, Faculty of Engineering, University of Birjand, Birjand, Iran.

10.22034/nawee.2026.579642.1211
Abstract
Objective: This study aims to numerically examine the effect of three different step edge shapes: plain, grated, and circular types, on the complex hydrodynamic characteristics of flow over a ten-step spillway. It also seeks to assess energy dissipation, velocity distribution, and pressure variations for each configuration to determine the most suitable geometry for stable flow conditions.
Methods: Three-dimensional numerical simulations were carried out using FLOW-3D. The Volume of Fluid method along with the RNG turbulence model was applied. Simulations were performed at a constant discharge of 0.09 m³/s. The numerical outcomes were compared with reliable experimental data for validation. The comparison showed good agreement, with an average relative error ranging from 5% to 8%.
Results: The meshed-edge spillway creates the highest energy dissipation by reducing the flow velocity by 15 to 20 percent compared to the simple edge. Although the positive pressure on the horizontal face of the meshed-edge steps increased by 16.4% compared to the simple-edge spillway, spillways with simple and circular edges exhibit more stable behavior against negative pressures on the vertical faces of the steps. Therefore, they are safer options for conditions where flow stability and the prevention of structural fatigue or cavitation risk are priorities.
Conclusions: Despite its higher energy dissipation capacity, the grated edge is not recommended because it generates strong fluctuations that increase the likelihood of cavitation and structural damage. The plain edge is suggested as the best practical option due to its acceptable hydraulic performance, flow stability, simpler construction, and lower cost.

Keywords

Stepped spillway
FLOW-3D
RNG model
Energy dissipation
Step edge geometry
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Journal of New Approaches in Water Engineering and Environment
Volume 5, Issue 3
Summer 2026
Pages 187-209

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