نوع مقاله : مقاله پژوهشی
نویسندگان
گروه مهندسی آب، دانشکده مهندسی عمران، دانشگاه تبریز، تبریز، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
This study investigates the hydraulic characteristics of flow, including flow velocity, pressure, and cavitation index, at various inflow rates using FLOW-3D. The results indicate that as flow passes over the ogee spillway, the flow velocity increases, and this upward trend continues gradually along the chute section. Due to the steep slope of the chute section, the maximum flow velocity occurs here and is eventually dissipated upon entering the stilling basin, where dynamic energy is absorbed. Longitudinal pressure distribution along the spillway reveals a reduction in pressure from upstream to downstream, with the most significant decrease occurring at the downstream end of the chute. The maximum flow velocities at inflow rates of 300 (minimum design discharge), 830 (10,000-year flood discharge), and 2270 m³/s (maximum probable flood, P.M.F.) were recorded as 34.25, 41.80, and 44.90 m/s, respectively, at the downstream end of the chute. Additionally, the minimum flow pressures for these discharge rates were 1.23, 1.52, and -5.9 kPa, respectively. Examination of the cavitation index along the channel bed indicated that cavitation occurs in the chute section under all inflow conditions. However, the cavitation index assessment on the sidewalls showed that the ogee, chute, and initial sections of the chute sidewalls remain unaffected by cavitation. Conversely, the cavitation index in the downstream chute sections decreases below the critical threshold, indicating potential cavitation risk in these regions. Therefore, to prevent the occurrence of the destructive cavitation phenomenon, the implement of flow aeration method from the floor and sidewalls of the channel is recommended.
کلیدواژهها [English]
EXTENDED ABSTRACT
The present study investigates the hydraulic performance of the Nazlu Dam spillway in West Azerbaijan, Iran, with a focus on key parameters such as flow velocity, pressure distribution, and cavitation index. Due to the high velocities involved and the steep slope of the spillway chute, the structure faces a potential risk of cavitation— a phenomenon that can damage the spillway by causing erosion or pitting on concrete surfaces. Cavitation occurs when water pressures fall below the vapor pressure, leading to vapor bubble formation and subsequent collapse, which can cause severe structural damage over time. Using FLOW-3D, a computational fluid dynamics (CFD) tool, this research aims to simulate the spillway’s hydraulic behavior under various flow conditions, assessing potential risk areas for cavitation and proposing solutions for damage mitigation. This research is particularly relevant given the dam’s importance in regional water resource management, serving irrigation, potable water, and industrial needs.
The Nazlu Dam spillway includes an ogee crest, a convergent channel, a steeply sloped chute, and a stilling basin designed for energy dissipation. The study uses FLOW-3D software to simulate the behavior of water flow over this structure. The Volume of Fluid (VOF) method is applied to capture the free surface dynamics of water flow, while the RNG k-ε turbulence model is employed to simulate turbulent flow behavior accurately. Simulations are conducted for a range of discharge rates, from the minimum design flow to the maximum probable flood, to evaluate hydraulic performance under different conditions. Boundary conditions are defined based on these flow rates, with inlet and outlet conditions specified for accurate modeling. The spillway geometry is meshed carefully to capture detailed hydraulic characteristics, allowing for precise simulation of flow velocity, pressure, and cavitation indices across the structure.
Simulation results show a notable increase in flow velocity as water progresses from the ogee crest to the chute section, reaching its peak in the steepest portion of the spillway. This peak velocity corresponds to a marked decrease in pressure, particularly toward the downstream end of the chute, as predicted by Bernoulli's principle. The cavitation index—calculated based on velocity and pressure distributions—reveals that the downstream chute and the entrance of the stilling basin are particularly prone to cavitation under high-flow scenarios, especially during maximum flood conditions. The lowest cavitation indices fall below the critical threshold, indicating a high probability of cavitation in these regions.
To address the risk of cavitation damage, aeration is suggested as a preventive measure. Aeration involves introducing air into the flow, which can help maintain higher pressures along the chute, reducing the likelihood of cavitation. This practice is widely recognized in hydraulic engineering as an effective method to mitigate cavitation damage. Introducing air bubbles into the flow acts as a buffer by absorbing energy and keeping pressures above the vaporization threshold, thus protecting the spillway surface.
The FLOW-3D simulations conducted in this study provide a detailed evaluation of hydraulic parameters along the Nazlu Dam spillway, identifying regions vulnerable to cavitation. The analysis indicates that high velocities and low pressures in certain sections of the chute heighten the risk of cavitation, with potential for structural damage in high-flow conditions. The study recommends aeration techniques, such as air injection, to mitigate cavitation risks, particularly at high discharge rates. Implementing these measures will help preserve the structural integrity of the spillway over the long term, safeguarding the dam’s role in critical water resource management for the region.
The insights derived from this study serve as valuable guidelines for spillway design and maintenance, particularly for structures exposed to extreme hydraulic loads. These findings underscore the need for regular monitoring and proactive maintenance to manage cavitation risks effectively and ensure the safety and durability of dam spillways.
Conceptualization, Mahdi Tabrizchi, Yousef Hassanzadeh and Mohammad Taghi Aalami; methodology, Mahdi Tabrizchi, Yousef Hassanzadeh and Mohammad Taghi Aalami; software, Mahdi Tabrizchi; validation, Mahdi Tabrizchi, Yousef Hassanzadeh and Mohammad Taghi Aalami; formal analysis, Mahdi Tabrizchi, Yousef Hassanzadeh, Mohammad Taghi Aalami and Hamidreza Abbaszadeh; investigation, Mahdi Tabrizchi, Yousef Hassanzadeh, Mohammad Taghi Aalami and Hamidreza Abbaszadeh; resources, Mahdi Tabrizchi, Yousef Hassanzadeh, Mohammad Taghi Aalami and Hamidreza Abbaszadeh; data curation, Mahdi Tabrizchi; writing—original draft preparation, Mahdi Tabrizchi, Yousef Hassanzadeh and Hamidreza Abbaszadeh; writing—review and editing, Mahdi Tabrizchi, Yousef Hassanzadeh and Hamidreza Abbaszadeh; supervision, Yousef Hassanzadeh; project administration, Yousef Hassanzadeh and Mohammad Taghi Aalami; All authors have read and agreed to the published version of the manuscript. All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.
Data available on request from the authors.
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The author declares no conflict of interest.
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