Hydraulic research of the operational water supply tunnel of pskom hydrousel

. This article analyzes the hydraulic processes in the spillway tunnels of high-pressure hydraulic units. The conducted studies involve the examination of the spatial model of the Pskom HPP production spillway tunnel section and address one of the issues that arise during the efficient operation of high-pressure facilities: hydraulic processes in the spillway tunnel. Based on the observed studies, it can be stated that calculated values of hydraulic resistances in the diaphragms are presented. These diaphragms are designed to reduce the energy of the flow while ensuring the permeability and hydraulic efficiency of the operational discharge of water. As a result of the calculations, resistances along the length of the operational spillway and the head loss on local resistances in the diaphragm were computed, and resistance coefficients were also estimated.


Introduction
Issues such as the effective utilization of water resources, the development of technologies ensuring the safe operation of hydrotechnical structures, and the enhancement of hydraulic efficiency in hydrotechnical structures are significant concerns in today's context [1,2,10].
It's worth noting that our country is currently undergoing a series of consistent reforms aimed at harnessing the potential of natural and artificial water flows for clean energy production.This includes the construction of 35 hydroelectric power stations with a total capacity of 1,537 MW.Furthermore, there are plans to increase the total capacity of hydroelectric power stations in the republic to 3,416 MW by 2030 through the gradual modernization of 27 existing hydroelectric power stations, resulting in a capacity increase of 186 MW

Study area
Construction is currently underway for the Pskom Hydroelectric Plant in the Bostonliq district of the Tashkent region.This hydroelectric plant will have an annual capacity of 400 MW and is being erected at an elevation of 1,045 meters above sea level.The reservoir associated with this plant will cover a total area of 900 hectares and have a storage capacity of 500 million cubic meters.
In accordance with the project specifications, the lower section of the dam for this reservoir will be 1,350 meters wide, 195 meters high, and 10 meters wide at the top.The Pskom Hydroelectric Plant is designed to accommodate four large turbines, each capable of generating 100 MW of power.
This article focuses on presenting the findings of hydraulic research conducted within the operational spillway tunnel of the Pskom Hydro Line, as depicted in Figure 1.These studies were initiated to identify strategies for reducing the energy of the water flow within the spillway tunnel.It's worth noting that the tunnel responsible for diverting water has a cylindrical shape, and the section under investigation has a length of 400 meters (Figure 2).An important concern in ensuring the efficient operation of high-pressure structures is evaluating the hydraulic processes within the spillway tunnel.The flow within the tunnel pipes possesses significant kinetic energy, which can lead to various challenges downstream.To address this issue, several constructive solutions have been put forward by researchers.Essentially, these recommendations revolve around the concept of introducing local resistance to mitigate flow pressure, as outlined in references [9,12].To control and reduce the flow within the water thrower tunnel, the project proposes the installation of diaphragms in the pipes.Hydrological studies [6,10] have indicated a flow rate of around 1,300 m^3/s, which is nearly twice the maximum water consumption of 673 m^3/s.Research has shown that using partial gates (sluices) to restrict the flow of operational water discharge can lead to a significant increase in water consumption downstream of the gate.
However, when diaphragms are installed during the construction of the operational sprinkler, they reduce its permeability, preventing it from accommodating the consumption.Therefore, the plan is to address this issue by installing diaphragms.The objective is to assess how pressure changes occur when regulating water consumption using these diaphragms.The calculations will determine the dimensions and the necessary number of diaphragm diameters required.The hydraulic calculation of pressure loss in the diaphragm is computed using the formula provided in references [8]: here: ϑ -average speed,  ∂ -diaphragm drag coefficient. here:  and ω 0 -cross-sectional areas of the pipe and diaphragm, respectively; εcompression ratio.
The consumption of water passing through the tunnel is determined as follows [14].
here: H ∂ − high pressure sign, HBWL symbol.The coefficient of consumption to determine the permeability of operational water discharge is calculated according to the following formula.
The total value of the resistance coefficient  s along the length of the pipe and taking into account local losses is determined as follows: When using steel cladding with transverse welded joints according to recommendations (absolute roughness к э = 0.1 mm).We determine the coefficient of hydraulic friction as follows [15].
here: D = 6,5 m (diameter of the operational water discharge pipe); Then, according to the formula (1.7), the coefficient of hydraulic friction is =0.007.The coefficient of resistance along the length of the operational sprinkler pipe is determined as follows: Here: ℓ -tunnel length ( ℓ=400 m)

Results and discussions
In the studies, in the range of diameters of the diaphragm (D=4.45 m; D=4.95 mm; D=5.5 m; D=5.75 m) calculations were carried out and the following connections were obtained (Fig. 3).The calculation results show that to ensure the required permeability of the operational water discharge, it is necessary to install 5 diaphragms with a diameter of d_0= 5.5 m, 2 diaphragms with a diameter of d_0= 4.95 m or one diaphragm with a diameter of d_0= 4.45 m.
However, the pressure drop reaches 130 m in the diaphragm with a diameter d_0= 4.45 m, which can cause great difficulties in ensuring the strength of the diaphragm.
Therefore, the following arrangement of 5 diaphragms with diameter d_0= 5.5 m is recommended according to the project.The pressure drop across each diaphragm does not exceed 30 m.In the turning part of the tract, the distance between the diaphragms is increased.Two diaphragms are placed before the turn, and three after (Fig. 4).Based on the experimental findings, the project data indicates a consumption coefficient for both the construction and operational sprinkler, denoted as "m," to be approximately 0.35.This value closely aligns with the calculated results.With this coefficient in mind, it's established that at the 0.1% exceedance probability level, the water flow capacity (Q0.1%) is 673 m^3/s, provided that the water level remains at the normal damped level (NDS) without the need for partial opening of the segmental gates.

Conclusion
Based on the research conducted above, it can be concluded that calculations have been performed to assess hydraulic losses, ensuring the effectiveness of diaphragms installed to maintain the necessary water discharge permeability while reducing flow energy.The structural elements of the diaphragms must be designed to withstand the specified pressure levels.
Through these calculations, it was determined that the overall resistance and local resistance along the length of the construction and operational sprinkler, while accounting for losses, are ζ = 1.38 and d_0 = 5.5 meters, respectively, for a system involving five diaphragms.
These calculations demonstrate a reduction in the water permeability of the construction and operational drainage when diaphragms are in place.In this scenario, the water consumption, initially calculated at HBWL (High Water Level) = NDL (Normal Damped Level) = 1,166 m^3/s, decreases from 1,290 m^3/s to 673 m^3/s.

Fig. 3 .
Fig. 3. Dependence of pressure loss in construction and operational water discharge diaphragm on water consumption

Fig. 4 .
Fig. 4. Scheme of placement of diaphragms at the outlet of the construction and operation water discharge.