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Mamajonov Makhmud, Shakirov Bakhtiyar Makhmudovich, Shermatov Rakhmatilla Yuldashevich, Andijan branch of Tashkent State Agrarian University E-mail: [email protected]
HYDRAULIC OPERATING MODE OF THE WATER RECEIVING STRUCTURE OF THE POLYGONAL CROSS SECTION
Abstract: The article presents the results of laboratory studies of the irrigation pumping station carried out on the model of the vestibule to study the hydraulic operating conditions.
Keywords: pumping station, sediment, water supply, flow, pressure.
The receipt of guaranteed agricultural products by farms is largely dependent on water management facilities, which is associated with a reliable and uninterrupted workflow in these facilities.
Experience in the operation of pumping stations has shown that many of them work with the supply much lower than the design ones. The main reasons for this are the unsatisfactory hydraulic regime of the water intake structures and the wear of the elements of the flowing part of the pumps.
Research by a number of scientists has shown that inadequate cleaning of irrigation water leads to a decrease in water supply of pumping stations located on main canals - up to 73%, and to dead-end ones - up to 63%. In addition, the clogging of the gratings and the level difference of 0.1 m causes an increase in electricity consumption of up to 1.22 kWt/h per each cubic meter ofwater supplied, whereas in normal operation the consumption is 0.6 ... 0.7 kWt/h. In the process of operating the systems, the difference in the co-retaining gratings can reach 0.3 ... 0.5 m, which causes cavitation processes in the pump-power units, rapid wear of the impellers and the output of the pumping equipment [1, 9-10].
Design, operation and reconstruction of water intake structures of pumping stations require scientifically based hydraulic calculation and based on it the forecast of hydraulic flow parameters. Disruptions in the hydraulic mode of the vestibule cause its gradual silting up. This leads to a reduction in the supply of pumping stations, an increase in electricity consumption, and cavitation wear of impellers of pumping units [2, 12-18].
In some cases, the construction of new water intake facilities is not possible, which entails the need to select other alternative technical solutions to level the problems that arise in their operation, namely: the entry of bottom sediments into the receiving facilities and the unsatisfactory hydraulic operation of the outermost water intake chambers and, as a consequence, pumps below the design [3, 192-196]. The design of a number of water receiving structures built decades
ago was carried out using computational methods that do not meet modern requirements. Therefore, in order to rationally operate old systems, it is necessary to update data on the operating modes that have taken shape on them and take them into account in the practice of water supply, environmental protection, and the use of deposits as meliorants [4, 62-72].
In this regard, when solving tasks to improve the operation of water intake facilities, it is necessary to carry out studies that make it possible to compare the projected mode of operation of pumping station facilities with those actually existing during operation, and also to obtain data on the regime that ensures its most efficient operation [5, 75-82].
To establish a favorable hydraulic mode of operation of the vestibule and water intake chambers, experimental studies were carried out on a laboratory installation in three variants. In these versions, the models of the pre-chamber are structurally executed in the same way: the central angle of the taper, the slope of the bottom, the depth of the inlet of the suction pipeline under the water horizon h2 are the same and are set horizontally with respect to the rear wall of the chamber.
The air-chambers differ only in the width of the water intake chamber, for the 1-variant, the chamber width bch = 2D in, and for the variant 2 it is equal to bch = 1.2Den in, where Den in the diameter of the inlet part of the suction pipe. Therefore, the length of the pre-chamber is respectively L = 81 sm and L = 33 sm.
an an
Experiments have shown that the spreading of the flow does not occur along the axis of the chamber, as a result of the flow around the bulls at an angle leads to the formation of swirl zones. The vortex zones are formed in the outer chambers in the joint mode of operation 5, 4(1 + 2 + 3 + 4), 3(1 + 2 + 5), 2(1 + 2), 2(1 + 3), 2(1+ 5) and 1(1) pumps. To prevent the funnel formation, it is recommended to install flow control devices at the entrance to the chamber, but they worsen the operating conditions of the camera. In addition, the oblique flow to the chamber leads to an increase in hydraulic resistance [3, 192-196].
According to a number of researchers, the sudden expansion of the flow leads to the formation of two corresponding characteristic sites: 1-the distance from the beginning of the expansion of the flow to the center of the vortex zones or its length is approximately 2/3 of the length of the vortex zones, in this section the flow gradually expands [2, 12-18].
The boundary of the transit flow is usually straight in plan, the line ofbending relative to the axis ofthe channel is very small.
A. G. Solovyova at the laboratory installation carried out studies with various roughness's, changing the ratio of the channel width to the depth of the channel h in the ratio from 4 to 10 [6, 241-253]. According to her data, the angle f between the channel axis and the transit flow in the first section varies from 20 to 80, with increasing roughness 9 increases, and with decreasing ratio v/h the angle ty decreases. Accord-
2
ing to A. Averkiev, the length of the first segment is —l2 [7, 84-88]. In our experiments, the 2nd site is located from the center of the vortex zone to the end of the expansion zone, its length is 1/3 of the length of the vortex zone. According to A. G. Solovyova, in this area there is a sharp expansion of the flow, the boundary of the transit flow is a curve line in the form of an ensemble.
In our studies, the expanded spreading of the flow occurs forcibly, we achieve in the experiments an extended flow motion, the boundary of the separation of the transit flow and the eddy zone does not have the form of a vertical section, so it is impossible to show in the plan what kind of line. Surface and bottom flow do not participate in the water supply of the receiving chambers, but in depth the layer of flow in the center is closest to the simple case to the expanding flow.
1 4
To activate the flow in the bottom of the vestibule and uniform spreading of the flow into the intake chambers, and also in order to reduce the entrance angle, a new design of the water intake structure of the polygonal cross section was developed (Figure 1 and 2).
The longitudinal slope towards the middle chamber along the bottom of the precautionary chamber is i = 0.1, adjacent to it from two sides 2 and 4 of the chamber with the bottom of the channel are connected along the longitudinal slope equal to 0.15, at the outer chambers 1 and 5 the longitudinal slope of the connection with the bottom of the channel is 0.2.
In addition, each longitudinal section has a transverse slope or in 3 chambers the longitudinal slope ih = 0, the right-hand ones 1 and 2 of the chamber have a lateral slope to the right equal to ih = 0.1, and the transverse slope on the left 4 and 5 of the chamber have the equal ih = 0.1. The slope of the bottom of the pre-chamber in this structure, together with the activation of the bottom stream, reduces the deposition of sediment in it. The slope of the cone in the plan is equal to a = 35° (Figure 1). The width of the water intake chamber is equal to bch = l.2Den or is assumed to be the same as in the second variant, here the length of the pre-chamber is equal to L =32sm.
an
The side walls of the outer 1 and 5 chambers with a supply channel are connected by means of a vertical wall. Therefore, the side walls of the vestibule in the initial part under the slope, then along the length gradually move into a vertical position. The cross-section of the vestibule is polygonal or represents the shape of a polygon (Figure 2).
Figure 1. The plan of the water receiving structure of the polygonal cross section (option - 3): 1 - the inlet channel; 2 - the pre-chamber; 3 - service bridge; 4 - water intake chamber; 5 - bulls; 6 - suction pipe
1-1
5
Figure 2. Cross-section of water intake chambers (option - 3)
Experiments have shown that the volume of the transit flow and swirls varies significantly in the 3rd version of the vestibule. The direction of the bottom stream located in the gap in the center of the vestibule coincides with the axis of the middle and outer chambers. This phenomenon is observed in all modes of operation of pumps. The angle of entry of the flow into the outer chambers is approximately 6 ... 8o, determined by experimental means.
A slight flow around the camera affects the camera's operating mode. In all modes of operation of the pumping station in the central and outer chambers, the formation of swirl zones did not occur. This indicates the unstressed inlet of the flow into the receiving chambers. Determination of hydraulic resistance in the third option in the fore-chamber and water-intake chambers was carried out in the same way as in versions 1 and 2 [8, 58-59].
Table 1. - Hydraulic coefficient of resistance for the pre-chamber and water intake chambers with a polygonal cross-section
Coefficient resistances Working Pumps
5 pumps 2(1 + 2) pumps 1(1) pumps 1(2) pumps
.b 0.567 0.542 0.69 -
Yz / j^t.m 0.16 0.386 - 0.61
0.363 0.464 0.69 0.61
The measured cross-sections are taken at the beginning of the 1-wing vestibule and the 2-yard is taken 10 cm deep from the inlet of the water intake chamber. In the 3-variant, under any operating conditions of the pumps, the flow spreads uniformly into the chambers, formation of swirl zones was not observed.
The results of the measurement showed that the coefficient of kinetic energy in the 1 and 2-dimensional sections relative to the 2-variant remained unchanged.
The 1st table shows the hydraulic coefficients of resistance of the receiving chambers and the pre-cameras in the joint and separate operation of pumps 5, 2 (1 + 2), 1 (1) and 1 (2).
The results of the conducted studies show that when 5 pumps work together, in the 3rd version the total coefficient of resistance is .b = 0.567, and in the second variant b = 0.7, or a decrease in the coefficient The resistance was = 0.133. In the middle chamber, in the 3-variant
^^t.m = 0.16, and in the second variant = 0.158 or the
decrease in the resistance coefficient is insignificant. The sum of the coefficients of resistance = 0.363 (in version 3) and = 0.429 (in the 2-variant), the reduction is
A^t = 0.066.
Operating pumps according to scheme 2 (1 + 2) and 1 (1) also showed a decrease in the resistance coefficient in the outer chambers. When the average pump 1 (3) was operating, the coefficient of resistance changed insignificantly.
At the site of the vestibule, water intake chambers, a reduction in the head loss is due to an improvement in the inlet conditions of the flow into the outermost chambers. Since the length of the vestibule is constant, the head loss in it relative to the 2 options is almost unchanged.
When carrying out the experiments in the third variant, the amount of sediment in the vortex zone relative to the two variants is 1.5 times, and in relation to the 1st variant it is 2.2
... 2.4 times smaller. Hence, the expansion of the flow in plan and vertically activates the bottom stream of the vestibule, reduces the degree of expansion of the transit flow and the degree of reduction in speed, and the deposition in it of sediments decreases. In the course of the experiments, the pump feed and head were measured. With simultaneous operation of 5 pumps, supply of an average of 3 pumps 5.6 l/s, 2 and 4 pumps, respectively, 5.48 ... 5.61 l/s, in 1 and 5 pumps, respectively, 5.28 and 5.31 l/s.
This means that spreading the flow in the fore cabin creates a uniform distribution of the bottom stream into the water intake chambers and, by decreasing the angle of rotation at the inlet, the circulation near the suction pipeline disappears, the flow velocity of the flow is equalized, and the hydraulic resistances decrease. Therefore, the supply of the 3 pumps does not change, but for 1 and 5 pumps, relative to 3 pumps, 5.2 ... 5.7%, and for 2 and 4 pumps, 1.6 ... 2% less water supply. In the third variant, the supply of the extreme pumps 1 and 5 with respect to the 2 options is 5 ... 5.5%, and in relation to 1 variant increases by 11 . 12%.
In the third variant, the areas of the swirl zones decrease, the activity of the bottom flow of the vestibule increases, and the flow spreads into the receiving chambers.
Proceeding from the foregoing, according to the design of the water receiving structure of the polygonal cross-section, the following conclusions can be drawn:
1) an unstressed inlet of the flow to all the chambers is ensured and the formation of the swirl zones is prevented due to the oblique entry of the flow into the outermost chambers;
2) when carrying out experiments according to the 3-vari-ant, the amount of sediment in the swirl zone relative to the
2-variant is 1.5 times less, and relative to the 1-variant in 2.2 ... 2.4 times;
3) the angle of the inlet of the flow into the outermost chambers is determined, which is within the range of 6 ... 80, due to the improvement of flow spreading to the outermost chambers and the reduction of the vortex zone in the fore cabin, sedimentation is reduced;
4) when 5 pumps operate in the variant 3, the total resistance coefficient ^^tb = 0.567, and in the second variant
= 0.7 or the reduction in the coefficient ofresistance is A^t = 0.133;
5) with simultaneous operation of 5 pumps, the average
3-pump supply was 5.6 l/s, 2 and 4 pumps, respectively, 5.61 and 5.48 l/s, and 1 and 5 pumps, respectively, 5.28 and 5.31 l/s;
6) in the third variant, the supply of the extreme pumps 1 and 5 of the relative second variant increases in 5 ... 5.5%, and in relation to the first variant in 11 ... 12%.
References:
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3. Mamajonov M. Improving the efficiency of operation of centrifugal and axial pumps of pumping stations of irrigation systems. Author's abstract. dis ... Doct. tech. of Sciences.- Tashkent.: TIME. 2006.- P. 192-196.
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