Model studies of a curved suction pipe of pumping units

. The purpose of the research was to study the hydraulic conditions of the flow supply in the new design of the curved suction pipe and to study the effect of these conditions on the pump operation. Improving the suction pipes provides a predetermined schedule of water supply, reducing unproductive losses and the cost of electricity for water lifting. Therefore, such studies are relevant. The article uses methods of physical modeling with the introduction of the obtained data on full-scale structures. The values of the dimensionless coefficients and the corresponding hydraulic gradients for various times are studied on a suction pipe model at Q max and Q min, over the entire range of operating parameters. The chosen method of improving the suction pipes provides an optimal water supply schedule, reducing unproductive losses and electricity costs for water lifting. During the reconstruction of pumping stations, projects for the modernization of water supply facilities were introduced with annual energy efficiency amounting to 1312 million sum for the pumping stations Kuyumazor, Kiziltepa-1 - 105 million sum.


Introduction
In modern conditions, the recommendations of Uzbek engineers on the reconstruction of existing pumping stations (PS) in order to improve their performance are becoming important.When developing measures to facilitate the operating conditions and increase the stability of the operation of large PSs on the unique Amubukhara (ABMC), Karshi (KMC) cascades, it is necessary to study measures that increase the reliability and efficiency of water supply of such PSs [1,2].
When solving operational issues related to the calculation of large pumps, accurate information about the kinematic characteristics of the flow formed by the suction pipes is necessary.In particular, knowledge of the flow parameters in the outlet section of the suction pipes is important when installing new impellers during the ongoing rehabilitation of the Karshi Main Canal PS.The flow parameters at the impeller grate inlet have a significant impact on the flow structure behind the impeller, which determines the losses in the pump.In this regard, the authors were faced with the task of studying the flow structure and determining the hydraulic and energy characteristics of the curved suction pipe of vane pumps.

Methods
The article uses methods of physical modeling of water supply structures, developed the theoretical foundations for modeling suction pipes.The methodological foundations of the ongoing research are based on the fundamentals of hydraulics, hydraulic structures, pumping stations, since the research topic is a complex physical phenomenon that occurs under the conditions of a complex of factors during pump operation.Research methods include generalization and scientific analysis of available published materials, conducting model studies using modern technical instruments.Analytical methods were used to test laboratory experiments in nature [3,4].

Results and Discussion
At present, no single theory reveals the full picture of the complex phenomenon of hydraulic conditions for supplying flow to the pump impeller.A significant number of works have been published in which researchers are trying to estimate the quantitative ratio of hydraulic losses along the entire length of the flow [5,6].
In the latest designs, ribs and protrusions are installed on the inner surface of the water intake chambers with the formation of annular cavities.In the body of the suction pipes there are channels for connecting the cavities to the pressure source, which leads to a decrease in the liquid supply to the pump.This design is very difficult to manufacture and operate the pump, since the housing has a cylindrical chamber and a channel for connecting the cavities to the pressure source.
The aim of the authors in this work is to increase the efficiency of the device with equalization of the flow rates in front of the pump.The set goal is solved by installing new flow-forming elements.
On fig. 1 shows the design of the investigated pipe.

Fig. 1. Suction pipe of vertical vane pump
The suction pipe of a vertical centrifugal pump contains a flat horizontal and vertical confusers 1 and 2, connected by an elbow 3. Flow-forming elements 4 are installed on the confuser 1 at the beginning of the upper section and 5 at its end, in front of the convex side 6.Elements 4 and 5 are made in the form of a truncated pyramid with a large base directed towards the flow.On the concave side 7 of the knee 3 arrows show the direction of flow velocities.The vertical and horizontal confusers are connected by an elbow to a chamber enclosing it.Channels on the convex and concave sides are connected to the cavity of the knee.The direction of the channels on the concave side towards the flow, and on the convex side along the flow increases the leakage due to the use of dynamic pressure by the channels on the concave side and the ejection effect on the convex side.Preferably, the flow-forming elements are elastic.In this case, they respond more flexibly to changes in the flow structure in the suction pipe when the pump flow changes and do not allow hydraulic resistance due to better streamlining when the flow increases.
When the pump is running, the pumped water enters the horizontal confuser 1, and then through the elbow 3 and the vertical confuser 2 to the pump.Due to the action of centrifugal force on the concave side 7 of the elbow 3, the pressure increases, and on the convex side it decreases.Flow-forming elements 4 and 5, due to vertical compression of the flow, stabilize the diagram of average cross-sectional velocities in the suction pipe, preventing separation of the flow from the upper plane of the confuser 1 in the suction pipe.
As a result, the velocities in the vertical confuser 2 in front of the pump are equalized, which leads to an increase in the efficiency of the pump.The centrifugal pump does not have the ability to control the flow and therefore the proposed utility model is the only way to stabilize speeds and increase efficiency in all modes.
With any change in pump parameters, flexible flow-forming elements produce an additional stabilizing effect on the flow structure in front of the pump impeller.This design of the authors is protected by patents [7,8].
The study of the flow structure and determination of the hydraulic and energy characteristics of a new design of a curved suction pipe was carried out in model tests of pipe options [9.10].The purpose of the research was to study the kinematics of the flow in a curved suction pipe; identification of the influence of the impeller and the operating mode of the pump on the flow structure in the suction pipe and in front of the impeller grate; study of the influence of the impeller and the operating mode of the pump on the energy qualities of the suction pipe.
The model of the PS block was assembled at the Research Institute of Irrigation and Water Problems, it has the geometry of the flow path with a curved suction pipe, in accordance with the current guidelines [11,12].
To comply with the conditions of self-similarity of the work of the model and nature, hydraulic studies were carried out at numbers R е = 4 10 5 ...5,75 10 5 , determined in the outlet section of the suction pipe.
The velocity field in the outlet section of the pipe was measured using an M-6X micro-rotator with an electronic revolution counter in front of the impeller in six sections located in a circle with a diameter of 250 mm.The measured section is taken at a distance of 0.4 D I from the axis of rotation of the impeller blades.The studies were carried out at 10 pump operating modes: 1) at a speed of rotation n-11.10;12.77; 14.43; 16.1s -1 constant angle of rotation of the blades  = 0° and feed rate K Q = 0.5; 2) at  = + 3°; 0 o ; -3 o ; -6°, frequency, rotation n = 12.77 s -1 and feed rate K Q = 0.5; 3) at K Q = 0.4; 0.45; 0.5; 0.55, constant  = 0° and n = 12.77 s -1 .
Flow studies in the suction pipe at Q=80 l/s correspond to a supply factor K Q =0.4.
At each investigated point of the flow, the following were measured: the magnitude of the absolute velocity V, its axial component V z , the circumferential component V u , the radial component V r , and the static head  /  .The relative error in measuring the velocity V did not exceed 1%.
For each mode, the flow parameters averaged over the cross section were calculated by the method of equal rings using the following formulas: (1) where is the kinetic energy of the flow; V z -axial velocity component; F -measuring area; The coefficient characterizing the non-uniformity of the velocity field in front of the impeller was calculated by the formula [13,14]: where V -absolute speed in section; z V -average speed in section.
The flow swirl was evaluated by the angle between the axial and circumferential velocity components according to the formula: The distortion of the velocity profile in the cross section in front of the impeller is characterized by the coefficients of radial unevenness [15,16].The coefficient of radial non-uniformity v  is usually called the ratio of the maximum increment of the local axial velocity in any radial section to the average value of the velocity z V in the same section: .max The hydraulic resistance coefficient of the suction pipe is determined by the following formula: where E sp = E I -E II is the loss of specific energy between sections I-I and II-II.
The quality assessment of the suction pipe was defined as: where  -Pipe hydraulic resistance coefficient: The efficiency of the suction pipe was determined for an axial pump with a speed factor n s = 500.
From the analysis of isototes in the section in front of the impeller, one can note a significant change in velocities (Fig. 2).The impeller presses the flow against the walls of the pump chamber and leads to a decrease in velocities in the center of the section.The field of velocities remained the same when the distribution of velocities in the confuser mating with the water inlet changed.
Experimental studies, in order to test the new elements from which the parts of the chamber and the flow part of the pump are made, were carried out on the D2000-21 pump.The impeller, mounted on the shaft, is located in a spiral chamber with separating spiral baffles inside the casing.The power consumption rates of PS Malikobod ABMC, taking into account the resource of pumps, were 8.1, and the calculation of specific power consumption (kW per thousand m 3 /Hg) showed a decrease to 7.36.A comparative analysis of the characteristics is presented in Fig. 3.

Fig.3. Study of the characteristics of the model pump
For subsequent research and modernization, a hydraulic calculation of the operation of ANDRITS pumps of the PR1045 type with modified characteristics was performed [17,18].Energy efficiency was achieved by increasing the efficiency of pumps and a significant reduction in repair costs during the reconstruction of suction pipelines (Fig. 4).Reconstruction of the initial section of the suction pipe prevents air from being sucked through the whirlpool funnels.The elements located at the end of the confuser in front of the suction pipe bend form an improved picture of the distribution of velocities in front of the pump impeller due to vertical compression of the flow [19,20].

Conclusions
1.The disadvantages of the well-known models of suction pipes of vane pumps are the complicated designs of elements that increase losses and do not prevent air from being sucked through whirlpool funnels in water intakes.An increase in the efficiency of the suction pipe is achieved due to the combined effect on the flow of a number of interacting flow-forming elements.
2. The new suction pipe of the vertical vane pump contains flat horizontal and vertical confusers, and in order to increase the efficiency in operating modes by improving the alignment of flow rates, the flow-forming elements in front of the pump in the confusers are made elastic.
3. The chosen method of improving the suction pipes provides a given water supply schedule, reducing unproductive losses and electricity costs for water lifting.The replacement of pumps with new more efficient models of suction pipes made it possible to reduce repair costs in 2021 compared to 2020 at the PS "Kiziltepa" from 1521737 to 298821 thousand sum, improve reliability, ensure trouble-free operation, reduce electricity consumption by 4-6%.

Fig. 2 .
Fig.2.Study of velocities in section II-II of the suction pipe model.a) at Q max b) at Q min