Studies of rational methods of water selection in water intake areas of hydroelectric power plants

Up to 2021, 42 new hydropower stations will be created in Uzbekistan and 32 existing hydropower stations will be repaired. Hydraulic engineering designers face a number of problems with the open flow division nodes in the field, which are part of the hydraulic structures of such hydropower plants. Considering the above, the main objectives of the research were determined: a) development of a refined method for the hydraulic calculation of flow division nodes with a quiet flow regime; b) the development of methods for predicting deformation of the channel in the area of the division node. The studies were carried out using theoretical and experimental studies using the equation for changing the amount of movement, laboratory studies on a hydraulic model, field surveys of existing water intake nodes, as well as analysis of experimental data available in the literature on this issue. Based on the theoretical and experimental studies, recommendations were made for the open flow division nodes. These recommendations are valid for division nodes at a division angle not exceeding 90 °, for prismatic channels of rectangular cross section with relatively small bottom slopes. These recommendations are intended for flows with values of B / H = 3 ÷7.


Introduction
Solving the problems of hydropower development is one of the main tasks for the Republic of Uzbekistan. The Government of the state approved the Program for the further development of hydropower industry until 2021. The main objectives of this program are scheduled: • Increasing the share of renewable energy sources in the country's energy sector; • Creation of new environmentally friendly generating capacity; • Providing technical and technological re-equipment of existing hydropower plants; • Effective water management; • Improving the balance of energy resources; • Ensuring the most complete satisfaction of the needs of enterprises and the public in electric power.
Up to 2021, 42 new hydropower stations will be built in Uzbekistan and 32 existing hydropower stations will be repaired. Currently, Uzbekistan has 32 hydropower plants with a total capacity of less than 2 gigawatts, which produce only about 15% of all electricity in the country. In the next five years, it is planned to substantially change this proportion through the construction of small and medium hydropower plants and the modernization of existing systems.Along with the construction and reconstruction of large hydropower plants, much attention is paid today to the construction of medium and small hydropower plants, including hydroelectric power stations located on small rivers and irrigation canals of the republic. Hydraulic engineering designers face a number of problems with the open flow division nodes in the field, which are part of the hydraulic structures of such hydropower plants.As is known, significant reserves of hydropower resources are concentrated in the mountainous areas of small rivers, in the foothill areas of irrigation canals. In characteristic areas of natural and artificial watercourses, the use of a derivational method of creating pressure in the construction of small hydropower plants is considered most appropriate.These parts of the watercourses are characterized by high velocities of water flow and significant channel deformations. In the water flow of the watercourses in the period of the flood flow, there is a significant increase in the content of suspended and bottom sediments. The passage of water containing a significant amount of sediment leads to a strong hydro abrasive wear of the main hydraulic units and the water-supplying path of the hydroelectric station.With a strong hydro abrasive wear of hydraulic units, there is a sharp decrease in the energy performance of hydraulic units. In addition, hydro abrasive wear of the main hydraulic units and the water-supplying path of a hydroelectric station can contribute to the formation of emergency situations at hydroelectric power stations and can even lead to human victims. To prevent such situations and develop measures to prevent them at the site of water intake from the water source, you must have an idea about the movement of the bottom layer of sediment and the surface layer of suspended sediment. Given the particular importance of this issue, in conducting research, special attention was paid to the study of methods and methods for rational selection of water in the open flow division nodes, which are often found in water intake areas from small rivers and irrigation canals to various hydropower stations.

Goals and objectives of research
Considering the above, the main objectives of the research were defined, which were as follows: a) development of a refined method for the hydraulic calculation of flow division nodes with a smooth flow regime; b) the development of methods for predicting the deformation of the channel in the area of the division node. This goal is achieved by solving the following tasks: -the study of the nature of the occurring channel deformations in the area of the division node, as well as the study of the nature of the development and changes in the whirlpool zone in the diversion channel; -the study of the nature of changes in the bands of the bottom and surface water intakes; -drawing up recommendations for the reduction of channel deformations.

Methods
Theoretical and experimental studies using the equation for changing the amount of movement, laboratory studies on the hydraulic model, field surveys of existing water intake nodes, as well as analysis of experimental data available in the literature on this issue were used.

Results
Experimental studies of the separation of flows in rectangular channels carried out on a special hydraulic model installation showed that the overall picture of the division is similar to that noted in the works of many authors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Namely, at the beginning of the left bank of the diverting channel, at the entrance edge, a whirlpool zone is formed, the transverse dimensions of which substantially depend on the size of the intake flow. In the alignment, where the whirlpool has the greatest width, the average depth of the flow is the smallest, thereby determining the location of the so-called compressed section.
where: Вв.з.width of the whirlpool. As for the length of the whirlpool, as shown by experimental studies, the length of the whirlpool that occurs in the diverting channel depends on the width of the outlet and the angle of division. According to the results of experimental studies, a relationship was obtained to determine the length of the whirlpool: where the coefficient N is determined by A comparison of this dependence with the data of our experiments shows that there is good convergence between them and it can be used for practical calculations. Study of the nature of changes in the bottom and surface water intake bands One of the most important characteristics of separated flows is the relative width of the surface and bottom water intake bands. On the basis of the obtained results of the conducted research, the nature of the change in the width of the water intake bands of surface and bottom jets of the water flow was analyzed depending on the change in head flow. As shown by the results of experimental studies, a change in the angle of allotment has practically no effect on the width of the water collection with an increase in the cost ratio Qв / Q1. Studies show that the relative width of the water intake band for surface Bп / B and bottom Вд / B jets increases with increasing Qв / Q1. On this basis, we carried out detailed studies of the width of the water intake system from measurements of boundary current lines for an angle of φ = 30 °, depending on the total flow rate of the main flow. An analysis of the studies conducted to determine the width of the water intake band for surface and bottom jets of a water flow showed that their values can be determined by the following empirical dependencies or graphic dependencies: .  In the mainstream, the following characteristic zones are noted: -zone of lowering the water surface. The depths here vary from the household value h1b for the head flow Q1 to the value h1 near the alignment located at the upper edge of the outlet.

Conclusions
-the zone of direct dividing the flow, where there is an increase in depth and decrease in velocity. This zone is located between the upper and lower edges of the outlet.
-flow stabilization zone, where the depth of the main flow goes into the domestic depth h2 for the remaining flow rate Q2. In the diversion channel, the following zones occur: -education area of the whirlpool area. In this zone, the depth of the diverting channel first decreases from the initial section to the section of the compressed section, and then increases. As for speeds, on the contrary, speeds first increase to a compressed section, and then decrease further.
-flow stabilization zone. It is located below the station of the disappearance of the whirlpool area, where the depths are set to the values of household hв for the discharge of the diverting channel Qв. Analysis of the studies on the division of quiet open flows showed that significant channel deformations occur at the beginning of the section of the diverting channel, in the zone of formation of the whirlpool area and in the initial section of the main channel. To reduce the size of the whirlpool in the diverting channel and the volume of channel deformations, it is necessary to make the division node at a small angle and to adjoin the upper and lower edges of the diverting channel with the main one to produce smoothly by rounding them. To reduce the channel deformations for the fission sites located on the eroded soils, it is necessary to mount the main channel, starting with the alignment located at a distance of 2B above the upper edge of the outlet to the distance B below the lower edge of the outlet. For the diversion channel, to fix the channel, starting from the initial section of the outlet at a distance of 5B in the downstream.