The article discusses the results of numerical studies of the flow movement with a sharp change in the parameters of the channel. Basically, the results of the study using the system of two-dimensional equations of hydrodynamics-Saint-Venant are analyzed. The divergent form of two-dimensional equations describing the movement of a water stream at a site of regulation of a channel by protective and regulatory dams is given. The influence of the length step on the results of numerical experiments is investigated numerically. Graphs of the time variation of the longitudinal velocity component behind the sudden double expansion of the channel are compiled. The flow was unsteady all the time and had the character of stationary pulsations, and the finer the grid, the richer the spectrum of these pulsations. It was noted that in numerical calculations, the time step in the calculations was always much less than the minimum pulsation period, therefore, these pulsations were not associated with difference oscillations that can arise when approximating by central differences. It is concluded that, according to the authors from the following and the present work, they collectively show that the pulsations on different grids differ significantly, the average values of the velocities are close, and thereby the solution for the average values is well converged, this shows that the pulsations are a property source equations of Saint-Venant. The applicability of the numerical model, consisting of two-dimensional shallow water equations, the vector equation of momentum conservation and the scalar equation of mass conservation, in description the flow with the presence of circulation zones, which is typical when water flows are constrained by protective-regulatory structures. In this case, the solution pulsates around a certain average value, and the average length of the circulation zone behind the sudden expansion of the open flow is in good agreement with the laboratory experiments of G.L. Mazhbits.
This topic is the design characteristics of the liquid and solid runoff of the Amudarya river in the area of the hydroelectric complex, according to which the average long-term flow of the river at the site of the hydroelectric complex is 46.5 km3, the discharge is 1470 m3/s, the maximum is 5760 m3/s (July) and the minimum is 186 m3/s (March). The amount of suspended sediment reaches 5 – 6 kg/m3, and bottom 5 – 8% of suspended sediment. The annual volume of suspended sediment is 120 million tons, and taking into account bottom sediments – 130 million tons. It is noted that due to low water conditions, the Takhiatash dam operated with completely closed gates in all spans for a significant part of the year. The authors of the article provide data comparing the actual flow rates of turbidity and backwater at the Takhiatash hydroelectric complex with the calculated ones. It is proved that sharp fluctuations in the water level in front of the dam and water intake into the canals lead to a change in the hydraulic and alluvial operation of the canals. As shown by the analysis of the river channel cross-sections in the upper reach of the Takhiatash hydroelectric complex, in the initial period of operation, there is a decrease in the level of the river bed bottom. The subsequent years of operation of the hydroelectric complex (after 1982) were characterized by the stability of the ongoing channel processes in the downstream, which is characterized by its own level and discharge regime for each characteristic year. It is noted that the operating mode for dry years, which are characterized by the fact that during periods of chronic low water the gates of the shield dam are almost completely closed and its role in regulating the level regime is almost lost. In this case, the level and flow rates are regulated mainly by end regulators in the right-bank and left-bank systems of main canals, which in turn depend on the demands of limited water consumers. Under these conditions, it is extremely difficult to regulate the water level in the headwater, since it is required to keep at a certain level of the water level. It is noted that there were no difficulties with water intakes in high-water years, and the main difficulties are associated with the passage of flood flows through the shield dam. In recent years, there has been a rapid rise in the water level in the upstream, despite all the open gates of the dam, the navigable lock and water intake structures, which are explained by the influence of the introduced ponds on the throughput of the shield dam. It has been substantiated that without any damage to the water intake during the growing season, it is possible to effectively flush the headwater with a constant decrease in the water intake coefficient below the critical value of the water intake coefficient Kv < 0.55. In practice, for the Takhiatash hydroelectric complex, this means that the flushing flow rate should be at least Q ≥ 250 – 300 m3/s. Recommended: for the normal functioning of the Takhiatash hydroelectric complex, taking into account the requirements of all water consumers and sanitary passes to the downstream, it is necessary to clearly link with the operating regime of the Tuyamuyun reservoir.
A mathematical model is presented, a hydraulic jump that appears during the transition of the flow from a turbulent state (Fr>1.0) to critical (Fr<1.0). The main assumptions made to obtain the divergent form of the Saint-Venant hydrodynamic equations are given: - planned (two-dimensional) effects do not affect the flow (but still local energy losses due to sharp turns and changes in the channel shape in the plan can be taken into account; to take into account such losses in local sections of the channel increased local hydraulic resistance is introduced). The results of numerical studies of the downstream of the culvert structure of the medium-pressure reservoir are presented. The developed numerical model using explicit difference schemes is presented. Based on the results of numerical studies of the hydraulic jump, the possibility of establishing the degree of quenching of the excess flow energy having the destructive ability of the construction of the downstream of medium-pressure reservoirs is substantiated. The calculation results showed that an increase in the hydraulic resistance value promotes the displacement of the hydraulic jump against the current and an increase in its associated depths. At the concatenation site of the upstream, there was a sharp decrease in the Froude number from 2.76 to 0.69, with a change in average speed from 8.81 m/s to 3.26 m/s. It is substantiated that from the calculated values of the vertical dimensions of the hydraulic jump with various values of hydraulic resistance and the throughput of the structure, it is possible to determine the horizontal dimensions of the jump, which makes it possible to select the optimal sizes of the downstream attachment zone in and after the hydraulic jump.
The article describes the nature of the ongoing channel processes occurring in large damless water intakes from the Amudarya-Karakum, Karshi, and Amu – Bukhara channels located in its middle course. The characteristic features of the ongoing channel processes in the area of water intake are given. Based on the analysis of the current state of damless water intake, a method for improving its operation is recommended. To solve the problems of ensuring high-quality water intake and water supply, experimental studies were carried out to determine the angle of the bottom threshold in the inlet section of the head structure in the ABMCh. The analysis of the studies showed that for the threshold angles to the shore β = 30°, 45° 60°, an increase in the angle β from 30° to 60° increases the intensity of the artificial transverse circulation formed in the flow. It is proved that this circumstance is also true for a constant angle of threshold β with an increase in the relative threshold height H rth . The bottom threshold ensures the entry of bottom sediments into the head structure of the damless water intake. The threshold height is set to 1.44 m, which is determined in comparison with the height of the beds of sediments. To prevent the entry of a large amount of bottom sediment into the head structure of a damless intake, it is recommended that the device be used especially in the inlet section of the channel. It is shown that a Karakum channel is intensively exposed to deigish. Moreover, in this process a certain sequence is traced. First, one deigish is formed, the erosion products of which create favorable conditions for the occurrence of the next deigish. So the chain of deigish “walks” along the shore. The distance between deigish, also a “step,” varies widely: from 3-7 to 15-40 m or more. Then, the remaining protrusions between the deigish are washed out, which leads to a general expansion of the channel. It has been established that deigish appears and develops in both straight and curved sections of the channel. In the latter case, they are formed mainly on the concave bank, although there are cases of their location on the convex. This means that there are corresponding conditions for its formation in both straight and curved sections of the channel. It is substantiated that the formation and intensive development of deigish are associated with the intense channel-forming activity of the flow, which manifests itself both in the process of developing channel forms and in active sediment transport. It is recommended that in order to prevent the deigish process, it is necessary to carry out water management measures aimed at strengthening the channel of the channel. The implementation of concrete cladding using modern materials to reduce losses on filtering the channel in addition to preventing deigish channel and also helps to increase the efficiency of the irrigation channel.
The paper presents the results of field research in the area of the damless water intake of the KMC on the Amudarya River. The article developed the optimal route and boundaries of the pioneer digging location, depending on the area of the main stream of the river relative to the point of the damless intake. It also provides hydraulic calculations for improving the condition of a damless water intake and recommendations for the rational use and placement of a dredgers fleet when laying a route of a ditch and cleaning it.
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