نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه سازه های آبی- دانشکده مهندسی آب و محیط زیست -دانشگاه شهید چمران اهواز-اهواز-ایران.
2 گروه سازه‌های آبی، دانشکده مهندسی آب و محیط زیست، دانشگاه شهید چمران اهواز، اهواز، ایران.
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
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.
کلیدواژه‌ها [English]
In water engineering, controlling and guiding water flow is of paramount importance. One of the primary challenges in this field is managing the high kinetic energy of water during discharge from structures such as dams. This energy can cause severe damage to downstream structures and the environment. Stepped spillways have emerged as one of the most effective hydraulic structures for energy dissipation, which is crucial in reducing the destructive force of water exiting dams.
Stepped spillways, with their unique design, cause water to flow in a step-by-step manner, losing a significant portion of its kinetic energy at each stage. This energy dissipation process results in the formation of a smaller hydraulic jump downstream, consequently allowing for the construction of smaller stilling basins (Chanson, 2002).
While modifying the geometric structure of steps to increase energy dissipation is an effective approach, it faces practical challenges in large-scale implementations due to time and cost constraints. Additionally, the use of elements and structures installed on spillway steps can increase the likelihood of cavitation, potentially causing serious damage to the structure.
This research investigates the impact of creating orifices in spillway steps as a novel and cost-effective approach to enhance energy dissipation in stepped spillways. These orifices can contribute to increased energy dissipation by creating localized flows and enhancing turbulence between steps, while also potentially leading to better and more uniform flow distribution.
FLOW-3D is recognized as a powerful tool in hydraulic engineering due to its diverse capabilities, including accurate simulation of multiphase flows and fluid-structure interactions. The FLOW-3D model was calibrated using experimental data from a stepped spillway study conducted at the Hydraulic Laboratory of Shahid Chamran University of Ahvaz by Eslami (2017). The calibration process was based on data obtained from experiments on a simple stepped spillway (without gaps) at various flow rates (25, 30, 35, 40, 45, 50, 55, and 60 liters per second), with a total of 8 experiments used for model validation.
Following calibration, six additional simulations were performed to investigate the effect of orifices on energy dissipation and flow rate improvement. In these simulations, three 3x3 cm orifices were placed on two spillway steps. The orifice configurations were designed to align with Eslami's (2017) experimental setups: one orifice in the center, two orifices at one-third and two-thirds of the step width, and three orifices at one-quarter, half, and three-quarters of the step width. All experiments with orifices were conducted at an inlet flow rate of 60 liters per second.
The results demonstrate that increasing the number of orifices leads to enhanced interaction between the exiting jets and the main spillway flow, resulting in increased energy dissipation. Placing orifices at lower elevations was found to be more effective due to the higher velocity of exiting jets.
The study revealed that orifices on the step floor have a more significant impact on energy dissipation compared to those on the walls. Energy dissipation increased by 5%, 7%, and 9% for one, two, and three orifices, respectively. This enhanced dissipation is attributed to the upward movement of water jets from floor orifices, which collide with the main spillway flow, causing significant energy reduction and additional energy dissipation. Altogether, the creation of three floor orifices increased energy dissipation by approximately 16% compared to the control case.
This research validates the effectiveness of FLOW-3D in simulating stepped spillway flows with interacting jets from orifices. Using the RNG turbulence model, these flows were modeled with high accuracy (R² = 0.96 and KGE = 0.94).
The findings strongly support the efficacy of incorporating orifices in stepped spillway structures, especially when placed on step floors. The presence of orifices significantly increases energy dissipation, with the effect amplifying as the number of orifices increases. The configuration with three floor orifices showed the highest energy dissipation at 73% and increased the initial jump depth by 40%.
Future research should delve deeper into the phenomenon of intersecting flow interference as an innovative approach to controlling the destructive energy of dam outflows.
1st Author: assisted in the data analysis, and guided the modeling process. 2nd Author: helping to complete numerical modeling, collecting and analyzing data. 3rd Author: collecting and analyzing data, writing the Persian version of this manuscript. 4th Author: provided expertise in data validation and analysis, 5th Author: helping to complete numerical modeling.
The data presented in this manuscript was collected during the MS thesis program of the 2nd author and are available any time in request.
We are grateful to the Research Council of Shahid Chamran University of Ahvaz for financial support (GN: SCU.WH1402.31370).
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The authors declare there is no conficts of interest.
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