CALCULATION OF THE DIAPHRAGM THAT REDUCES FLOW ENERGY IN HIGH-PRESSURE HYDRAULIC STRUCTURES

ABSTRACT

Effective operation of high-pressure hydraulic structures involves addressing various challenges, including the evaluation of hydraulic processes within water conveyance tunnels. The flow in these tunnels often carries substantial kinetic energy, which can create complexities, particularly in the downstream area. To mitigate these issues, researchers have proposed several structural solutions, one of which involves installing diaphragms along the tunnel path. These diaphragms act as local resistances, reducing the flow pressure and dissipating energy. This study focuses on the hydraulic processes involved in pressure reduction using diaphragms and provides a detailed analysis of their design and installation requirements.

Furthermore, the study explored the effects of varying diaphragm diameters and numbers on pressure loss, concluding that using a single diaphragm with a smaller diameter could result in significant pressure drops, posing structural challenges. The arrangement of the diaphragms in five sections, each spaced 8-10 tunnel diameters apart, ensures effective energy dissipation while maintaining tunnel stability. Reinforcements at diaphragm locations include four rows of steel anchors and reinforced concrete rings for structural integrity.

АННОТАЦИЯ

Эффективная эксплуатация высоконапорных гидротехнических сооружений требует решения различных задач, включая оценку гидравлических процессов в туннелях для транспортировки воды. Поток в этих туннелях часто содержит значительную кинетическую энергию, что может создавать сложности, особенно в нижней части. Для смягчения этих проблем исследователи предложили несколько конструктивных решений, одно из которых включает установку диафрагм вдоль пути туннеля. Эти диафрагмы действуют как местные сопротивления, уменьшая давление потока и рассеивая энергию. Данное исследование сосредоточено на гидравлических процессах, связанных с уменьшением давления с использованием диафрагм, и предоставляет детальный анализ их проектирования и требований к установке.

Кроме того, в исследовании были изучены эффекты изменения диаметра и количества диафрагм на потерю давления, и сделан вывод о том, что использование одной диафрагмы с меньшим диаметром может привести к значительным падениям давления, создавая структурные проблемы. Расположение диафрагм в пяти секциях, каждая из которых расположена на расстоянии 8-10 диаметров туннеля, обеспечивает эффективное рассеивание энергии при сохранении стабильности туннеля. Укрепления в местах установки диафрагм включают четыре ряда стальных анкерных болтов и кольца из армированного бетона для обеспечения структурной целостности.

Keywords: Diaphragms, Energy dissipation, Hydraulic efficiency, Flow reduction, Sustainable management.

Ключевые слова: Диафрагмы, Рассеивание энергии, Гидравлическая эффективность, Снижение потока, Устойчивое управление.

1. Introduction. In hydraulic engineering, drainage structures play a pivotal role in managing water flow in diverse applications such as irrigation, flood control, and urban drainage. One significant issue faced in these systems is the dissipation of excessive flow energy, which, if unmanaged, can lead to erosion, turbulence, structural damage, and sediment transport issues[1-3]. To address these challenges, engineers often employ diaphragms within drainage structures to reduce the kinetic energy of water flow, ensuring smoother and safer operations. This introduction aims to summarize the key considerations and approaches for calculating diaphragms that reduce flow energy, drawing on findings from several published studies[4-5].

Diaphragms are energy-dissipating elements integrated into flow channels to interrupt and slow down high-velocity water, facilitating a reduction in turbulent energy downstream. Studies have demonstrated that the design of diaphragms—considering factors such as size, shape, material, and placement—can significantly impact their effectiveness in managing hydraulic conditions. Research [6,7] shows that optimized diaphragm configurations can achieve flow velocity reductions of 50-70%, depending on the initial flow conditions and structure characteristics. These results indicate the potential of diaphragms to improve the hydraulic efficiency of water management systems by distributing flow energy more evenly and minimizing adverse effects.

The design and calculation of diaphragms necessitate a comprehensive analysis of several parameters, including flow rate, velocity, sediment load, and structural constraints. The use of Computational Fluid Dynamics (CFD) simulations has become increasingly popular for modeling the flow patterns around diaphragms and assessing their impact on energy dissipation. CFD tools allow for the analysis of various design scenarios, such as changes in diaphragm thickness or installation angles, as shown by[8-10] Additionally, empirical equations based on dimensional analysis and laboratory experiments have been formulated to predict the head loss and velocity reduction attributable to diaphragm installation.

Recent advancements in diaphragm research emphasize the importance of considering sediment transport when designing energy dissipation systems. Sediment accumulation can affect flow dynamics and diaphragm performance, as discussed by researchers like [11-13]. These studies recommend incorporating sediment characteristics into the diaphragm calculation process to optimize designs that reduce clogging risks and ensure long-term system stability.

Moreover, the environmental benefits associated with effective diaphragm usage include reduced erosion and protection of aquatic habitats. The findings of [14,15] highlight the ability of diaphragms to decrease the intensity of scouring downstream of spillways, promoting sediment balance in river systems. By mitigating the adverse effects of high-velocity flows, diaphragms contribute to sustainable water management practices.

In conclusion, designing diaphragms for flow energy reduction in drainage structures involves integrating hydraulic, structural, and environmental considerations. The calculation process requires careful analysis supported by CFD modeling and empirical data to optimize diaphragm placement and dimensions. The extensive body of literature on diaphragm applications underscores their importance in improving the efficiency and sustainability of drainage systems.

2. Methodology. To analyze hydraulic processes in high-pressure structures with diaphragm installations, it is essential to evaluate the dynamic conveyance of the tunnel first. Based on differential calculations and formulas, the resistance coefficients, head losses, and conveyance indicators of the diaphragms are determined. The flow dynamics related to the number, diameter, and placement of the diaphragms are analyzed through diagrams and graphs. Subsequently, the constructive parameters of the diaphragms, including anchored rings and reinforcement elements, are specified. Based on the research findings, optimal solutions are developed to ensure the efficiency and effectiveness of the diaphragms.

One of the challenges in the effective operation of high-pressure hydraulic structures is evaluating the hydraulic processes within water conveyance tunnels. The flow in these tunnel pipes possesses substantial kinetic energy, which can create several complexities, particularly in the downstream area. To address this issue, researchers have proposed various structural solutions, including the installation of diaphragms along the tunnel path, which create local resistance and reduce flow pressure.

Figure 1. Diaphragm installed in the Pskom drainage tunnel

Diaphragm installation is necessary to reduce tunnel permeability during operational period, which according to previous studies [16-18] is about 1300 m³/s, which is almost twice the maximum water consumption (673m³/s).

It is intended to determine by calculation the required number and size of the internal opening of the diaphragm, which is widely used in hydraulics. The resistance coefficient of the well-known diaphragm is determined as follows [16].

                                                =                                                            (1)    

Where; w and ω0 are the cross-sectional areas of the pipe and diaphragm, respectively; e - compression ratio

                                                         (2)

Then the pressure loss in the diaphragm is calculated using the Darcy-Weisbach formula [8,10]:

 ,                                                                  (3.)

Here; - average speed.

  The consumption of water passing through the tunnel is determined as follows.

                                                                  (4) 

Where; H_D-high pressure symbol. YuBSS symbol.          

Therefore, it is desirable to have 5 diaphragms with a diameter D₀= 5.08 m, then the pressure drop across this diaphragm does not exceed 30 m. The coefficient of consumption to determine the permeability of construction and operational water discharge is calculated according to the following formula.

                                                             (5)

The results of the calculation books (Figures 1) showed that in order to ensure the required permeability of the construction and operational water discharge, 5 diaphragms with a diameter of = 5,08 m, 2 diaphragms with a diameter of = 4,95  m or 4,45  m it is necessary to use one diaphragm. However, the pressure drop across the aperture = 4,45  m reaches 130 m. which leads to great difficulties in ensuring the strength of this diaphragm (Fig. 1).

3. Analysis of results and examples. This study emphasizes the critical role of diaphragms in enhancing the hydraulic efficiency of drainage structures. The analysis demonstrates that strategically placed diaphragms effectively reduce flow energy and manage pressure losses. The installation of five diaphragms, each with a diameter of 5.08 m, optimizes energy dissipation while preserving structural integrity. Notably, smaller single diaphragms can result in substantial pressure drops, leading to stability challenges.

The spacing of diaphragms, maintained at 8-10 diameters apart, facilitates effective energy dissipation, minimizing the risks of downstream erosion and turbulence. The calculated resistance coefficients and pressure losses highlight the importance of meticulous design and placement, underscoring the utility of computational fluid dynamics (CFD) simulations for validating design choices.

Additionally, the study incorporates structural reinforcements, including steel anchors and reinforced concrete rings, to ensure the longevity and functionality of the drainage systems. Overall, the findings contribute to sustainable water management practices by effectively addressing the challenges posed by high-velocity flows and their ecological impacts. The integration of these design elements marks a significant advancement in hydraulic engineering, enhancing operational efficiency and environmental protection.

Figure 2. Dependence of construction and operational water consumption on the number and diameter of diaphragms

As a result of calculations, it was determined that the coefficients of pressure loss along the length of the construction and operation water discharge, taking into account local losses, are z = 1,38 and for 5 diaphragms = 5,08 m = 5,49. Consumption coefficients for non-diaphragm construction and operational water discharge are equal to μ = 0,65 and decrease to 0.36 when diaphragms are installed.

Figure 3. Dependence of the resistance coefficient on the number of apertures

Figure 4. Transfer of water consumption during operation

Diaphragm placement is provided in 5 blocks, the distance between them corresponds to 8-10 diameters, that is, about 50 m. Each diaphragm has a cross-sectional area of ​​5.08 m. The accepted form of the diaphragm is a volumetric metal ring welded to a 30 mm thick coating. In the places where the diaphragms are located, the tunnel lining is reinforced and made in the form of a 4.0 m deep reinforced concrete ring with four rows of anchors with a thickness of 80 cm.

Figure 5. Capacity of construction and operation water discharge

During the construction period, the water consumption Q=417 m3/s (1st year) provides a flow rate of 10% of the supply and Q=449 m3/s (from the 2nd year of operation) at 3% of the supply. With the increase of the water flow (upper bef) to 1166.0 m (NDS), the maximum consumption of water passing through the water during the period of use is 673.0 m3/s.

The construction and operational discharge capacity is shown in Figure 3.5. When 5 diaphragms are installed in its path, the construction and operation show a decrease in the water discharge capacity. In this case, the water consumption calculated with YuBSS = NDS = 1166 m decreases from 1290 to 673 m³ / s.

4. Conclusion

The study highlights the importance of diaphragms in enhancing the hydraulic efficiency of drainage structures by reducing flow energy and managing pressure losses effectively. The installation of five diaphragms, each with a diameter of 5.08 m, is recommended to ensure optimal energy dissipation while maintaining structural integrity. The research emphasizes that single smaller diaphragms can lead to significant pressure drops, posing challenges in structural stability.

The design and placement of the diaphragms are crucial; spacing them 8-10 diameters apart allows for effective energy dissipation and minimizes the risk of erosion and turbulence downstream. The findings indicate that the resistance coefficients and pressure losses can be effectively managed through careful calculations and simulations, resulting in improved operational efficiency.

Moreover, the study incorporates the use of advanced computational fluid dynamics (CFD) for modeling flow dynamics around diaphragms, validating the proposed design choices. Overall, the integration of structural reinforcements, such as steel anchors and reinforced concrete rings, ensures the longevity and functionality of the drainage systems, contributing to sustainable water management practices and reducing potential ecological impacts.

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