University of Tehran Press Iranian Journal of Soil and Water Research 2008-479X 56 3 2025 05 22 Numerical Modeling of the Effect of Orifices in Stepped Spillways on Flow Energy Dissipation Using the FLOW-3D Model Numerical Modeling of the Effect of Orifices in Stepped Spillways on Flow Energy Dissipation Using the FLOW-3D Model 589 606 102195 10.22059/ijswr.2025.383840.669816 FA Mehdi Daryaee Department of Water Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran. Seyedeh Massomeh Sharifi Department of Water Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran. Amirreza Shahriari Department of Water Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran. SeyedMahmood Kashefipour Department of Water Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran. Mohammadreza Zayeri Department of Water Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran. Journal Article 2024 10 21 Stepped spillways, as one of the most efficient hydraulic structures for energy dissipation, play a crucial role in reducing the destructive energy of water discharged from dam reservoirs. These structures, utilizing their geometric features, contribute to the dissipation of turbulent and supercritical flows. In this research, with the aim of increasing the efficiency of stepped spillways in energy dissipation, the effect of creating orifices on the spillway steps has been investigated. The FLOW-3D software was used for numerical simulation, and the model's accuracy was evaluated using statistical indicators. The simulation results indicate that the RNG turbulence model is capable of simulating turbulent flows over stepped spillways with high accuracy (R²=0.96). Creating orifices on the floor of the steps, compared to the walls, generates greater energy dissipation. The outflow from the floor openings of the stepped spillway causes the water jet to collide with the overflow, resulting in greater energy dissipation. In contrast, wall openings, due to their alignment with the overflow direction, lead to less energy loss. Additionally, increasing the number of orifices led to improved spillway performance. Specifically, creating three orifices in the spillway floor was able to increase energy dissipation by 16% compared to the case without orifices (control). Furthermore, creating three orifices in the floor allows a higher discharge to pass through the spillway and increased the initial depth of the hydraulic jump downstream of the spillway by 40%. These results demonstrate the effectiveness of using orifices as an efficient method for improving the performance of stepped spillways in managing outflows from dams. Stepped spillways, as one of the most efficient hydraulic structures for energy dissipation, play a crucial role in reducing the destructive energy of water discharged from dam reservoirs. These structures, utilizing their geometric features, contribute to the dissipation of turbulent and supercritical flows. In this research, with the aim of increasing the efficiency of stepped spillways in energy dissipation, the effect of creating orifices on the spillway steps has been investigated. The FLOW-3D software was used for numerical simulation, and the model's accuracy was evaluated using statistical indicators. The simulation results indicate that the RNG turbulence model is capable of simulating turbulent flows over stepped spillways with high accuracy (R²=0.96). Creating orifices on the floor of the steps, compared to the walls, generates greater energy dissipation. The outflow from the floor openings of the stepped spillway causes the water jet to collide with the overflow, resulting in greater energy dissipation. In contrast, wall openings, due to their alignment with the overflow direction, lead to less energy loss. Additionally, increasing the number of orifices led to improved spillway performance. Specifically, creating three orifices in the spillway floor was able to increase energy dissipation by 16% compared to the case without orifices (control). Furthermore, creating three orifices in the floor allows a higher discharge to pass through the spillway and increased the initial depth of the hydraulic jump downstream of the spillway by 40%. These results demonstrate the effectiveness of using orifices as an efficient method for improving the performance of stepped spillways in managing outflows from dams. https://ijswr.ut.ac.ir/article_102195_1e28f8ba30032e89883e3509c11cedd8.pdf