Blade top water spraying device and method for improving stability of axial flow pump

Abstract

The blade tip water spraying device for improving the stability of the axial flow pump comprises a booster pump, the booster pump is connected with a flow dividing box through a pipeline, the side wall of the flow dividing box is connected with a plurality of hoses, and the hoses are evenly distributed on the side wall of the flow dividing box in the circumferential direction; and one end of each hose extends into the shunting box, and the other end is provided with a nozzle device. The invention further discloses a blade top water spraying method for improving the stability of the axial flow pump, and the method specifically comprises the steps that the flow dividing box is connected with the booster pump through a pipeline, the nozzle device is tightly connected with the rim end wall of the axial flow pump, and then a water source is stably sprayed into an impeller channel through the nozzle. According to the blade top water spraying device, the nozzles are evenly installed in the end wall of the wheel rim of the axial flow pump in the circumferential direction, leakage vortexes of the blade top of the axial flow pump are driven by high-speed jet flow to smoothly flow out of an impeller channel, and blockage of the blade top of the axial flow pump is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluid mechanical equipment, and in particular relates to a blade top water spraying device for improving the stability of an axial flow pump, and also relates to a blade top water spraying method for improving the stability of an axial flow pump. Background Art

[0002] Axial flow pumps have the characteristics of low head, large flow, and high efficiency, and are widely used in agricultural irrigation, ship propulsion and other fields. However, in actual operation, due to the hump area in the flow-head curve of the axial flow pump, especially when the head drops sharply under low flow conditions, rotational stall is prone to occur, thus entering a hydraulically unstable condition. When the axial flow pump stalls, it will cause increased vibration and noise, and the efficiency will drop sharply. Frequent entry or long-term operation in the unstable zone will cause blade breakage, seriously affecting the safe and stable operation of the unit. Therefore, it is urgent to establish a flow control method that can improve the stable operating range of the axial flow pump to ensure the safe operation of the axial flow pump.

[0003] In response to the problem of unstable operation of fluid machinery, scholars have studied various stabilization measures, including adjustable guide vanes, adjusting blade placement angles and gaps, and end wall treatment. End wall treatment uses grooves and slits to inhibit the development of tip leakage vortices, which has a good stabilization effect on the performance of axial flow pumps, but it affects the design point efficiency and incidental cavitation, and is currently difficult to apply in engineering.

[0004] As an effective flow control method, tip water injection is widely used in the field of compressors. Many results show that tip water injection can effectively improve the stable operating range of the compressor without reducing the peak efficiency. However, in the field of axial flow pumps, there is still a lack of relevant flow control methods, especially the design of experimental devices for realizing tip water injection. The current research is still relatively scarce. Summary of the invention

[0005] The purpose of the present invention is to provide a blade top water spraying device for improving the stability of an axial flow pump, thereby solving the problem that the existing axial flow pump is prone to sudden drop in head when operating under low flow conditions.

[0006] Another object of the present invention is to provide a blade tip water injection method for improving the stability of an axial flow pump.

[0007] The technical solution adopted by the present invention is a blade top water spray device for improving the stability of an axial flow pump, comprising a booster pump, the booster pump is connected to a diversion box through a pipeline, the side wall of the diversion box is connected to a plurality of hoses, and the plurality of hoses are evenly arranged on the side wall of the diversion box along the circumferential direction; one end of each hose extends into the interior of the diversion box, and a nozzle device is provided at the other end.

[0008] The present invention is also characterized in that: The nozzle device includes a sealing cover, a threaded hole is opened at the center of the sealing cover, the sealing cover is threadedly connected to the hose through the threaded hole, and the end of the hose is connected to the bottom of the threaded hole; the bottom of the sealing cover is connected to a water filling chamber, and a square through hole is arranged at the center of the water filling chamber; the bottom of the water filling chamber is connected to a nozzle seat, and a crescent-shaped nozzle is arranged at the center of the nozzle seat, the inlet of the crescent-shaped nozzle is located at the bottom of the square through hole, and the outlet of the crescent-shaped nozzle is located at the bottom of the nozzle seat, and the shape of the crescent-shaped nozzle from the inlet to the outlet is gradually reduced.

[0009] The three-dimensional structure of the crescent-shaped nozzle is obtained by rotating the two-dimensional geometric line. The two-dimensional geometric body is composed of two lines, including the first arc and the second arc. The radius of the first arc and the second arc are both R. The second arc is obtained by translating the first arc. The first arc and the second arc are tangent to each other at the end wall of the wheel rim. The position of the second arc directly determines the throat height of the nozzle. h , h The size is controlled at 2 to 6 times the tip clearance. The throat height is expressed as the minimum distance between the second arc and the first arc at the tangent point. Therefore, before determining the position of the second arc, the throat height needs to be determined first. Then, the first arc is translated to the right to the tangent point of the second arc to determine the position of the second arc. The two-dimensional geometric line is centered on the central axis of the axial flow pump impeller. By sweeping left and right, a nozzle with a jet direction of 90° to the front line of the impeller leading edge can be obtained. Then, a crescent-shaped nozzle can be obtained by rotating through the center of the nozzle.

[0010] The upper surface of the sealing cover is provided with a plurality of through holes.

[0011] A pressure sensor is installed on the top of the diverter box.

[0012] A solenoid valve, a flow meter and a pulse valve are arranged on the pipeline connecting the booster pump and the diversion box.

[0013] Each hose is provided with a valve.

[0014] Another technical solution adopted by the present invention is a blade top water spraying method for improving the stability of an axial flow pump, specifically: The diverter box is connected to the booster pump through a pipeline, and the booster pump outlet is connected to the solenoid valve inlet to control the real-time flow of the pipeline; the solenoid valve outlet is connected to the flow meter inlet to measure the real-time flow of the pipeline; the flow meter outlet is connected to the pulse valve inlet, and the pulse valve outlet is connected to the diverter box, and the nozzle device is tightly connected to the rim end wall of the axial flow pump, and then the water source is stably sprayed into the impeller channel through the nozzle.

[0015] The beneficial effects of the present invention are as follows: the blade top water spraying device for improving the stability of the axial flow pump of the present invention installs the nozzle evenly in the circumference of the axial flow pump wheel rim end wall, and uses the high-speed jet to drive the axial flow pump blade top leakage vortex to smoothly flow out of the impeller channel, thereby reducing the clogging of the axial flow pump blade top. On the other hand, the blade top water spraying device of the present invention can be used to study the influence of different water spraying flow rates, water spraying frequencies, water spraying speeds and quantities on the stability margin and efficiency of the axial flow pump. After adopting the blade top water spraying device of the present invention, the optimal water spraying parameters can be obtained, and the problem of the sudden drop in head when the axial flow pump is running under low flow conditions can be effectively solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of a blade top water spraying device for improving the stability of an axial flow pump according to the present invention; Figure 2 It is a structural schematic diagram of a nozzle device in a blade top water spraying device for improving the stability of an axial flow pump according to the present invention; Figure 3 It is a cross-sectional view of the internal structure of the nozzle device in the blade top water spraying device for improving the stability of the axial flow pump according to the present invention along the axial direction; Figure 4 It is a two-dimensional geometric line diagram of a nozzle in a blade top water spraying device for improving the stability of an axial flow pump according to the present invention; Figure 5 It is a schematic diagram of the assembly structure of the nozzle device of the blade top water spraying device for improving the stability of the axial flow pump according to the present invention; Figure 6 It is a schematic diagram of the connection between the nozzle device in the blade top water spraying device for improving the stability of the axial flow pump and the rim end wall of the axial flow pump of the present invention; Figure 7 It is a head characteristic curve diagram of the steady-state jet flow of the blade top water spraying device used for improving the stability of the axial flow pump of the present invention; Figure 8 The present invention is a pulse jet head characteristic curve diagram of the blade top water spraying device used for improving the stability of the axial flow pump.

[0017] In the figure, 1. diversion box, 2. hose, 3. nozzle device, 4. sealing cover, 5. threaded hole, 6. water filling chamber, 7. through hole, 8. square through hole, 9. nozzle seat, 10. nozzle. DETAILED DESCRIPTION

[0018] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Example 1 The present invention is used for improving the stability of the axial flow pump blade top water spray device, such as Figure 1As shown, it includes a booster pump, which is connected to a diversion box 1 through a pipeline. The pipeline is provided with a solenoid valve, a flow meter and a pulse valve. The diversion box 1 is cylindrical and can withstand a maximum pressure of 1 MPa. A pressure sensor is installed on the top of the diversion box 1 to monitor the water spraying pressure, thereby maintaining the operating stability of the water spraying device; The booster pump outlet is connected to the solenoid valve inlet to control the real-time flow of the pipeline; the solenoid valve outlet is connected to the flow meter inlet to measure the real-time flow of the pipeline, and its measurement range is 4-60m 3 / h; the flow meter outlet is connected to the pulse valve inlet, and the pipeline is opened and closed by changing the duty cycle of the pulse valve, thereby realizing the steady-state jet and pulse jet of the blade top spray.

[0020] The side wall of the diverter box 1 is connected to a plurality of hoses 2, which are evenly arranged circumferentially on the side wall of the diverter box 1; each hose 2 is provided with a valve; preferably, there are 6 hoses 2, with a length of 2m and a diameter of 0.02m; one end of each hose 2 extends into the interior of the diverter box 1, and the other end is provided with a nozzle device 3; after the water flow enters the diverter box 1 and is fully mixed, it is ejected at high speed through the nozzle device 3.

[0021] like Figure 2 and Figure 3 As shown, the nozzle device 3 includes a sealing cover 4, a threaded hole 5 is provided at the center of the sealing cover 4, and its specification refers to the national standard NPT1 / 2 standard model. The sealing cover 4 is threadedly connected to the hose 2 through the threaded hole 5, and the end of the hose 2 is connected to the bottom of the threaded hole 5; it is tightly connected to the hose 2 outlet on the side wall of the diverter box 1 through the threaded hole, and the junction between the two is wrapped with raw tape to ensure sealing; a plurality of through holes 7 are provided on the upper surface of the sealing cover 4 for fixing the nozzle device to the end wall of the rim; a water filling chamber 6 is connected to the bottom of the sealing cover 4, and the water filling chamber 6 A square through hole 8 is provided at the center; a nozzle seat 9 is connected to the bottom of the water filling chamber 6, a crescent-shaped nozzle 10 is provided at the center of the nozzle seat 9, the inlet of the crescent-shaped nozzle 10 is located at the bottom of the square through hole 8, the outlet of the crescent-shaped nozzle 10 is located at the bottom of the nozzle seat 9, and the shape of the crescent-shaped nozzle 10 from the inlet to the outlet is gradually contracted; the Coanda effect is used at the outlet of the crescent-shaped nozzle 10 to make the outlet water flow and the rim end wall flow against the wall, and after the water flow enters the water filling chamber 6 for sufficient mixing, it is ejected at high speed through the crescent-shaped nozzle 10.

[0022] The sealing cover 4, the water filling chamber 6, and the nozzle seat 9 are all rectangular; the sealing cover 4 is equal in size to the water filling chamber 6; the length of the nozzle seat 9 is less than the length of the water filling chamber 6; Example 2 The three-dimensional structure of the crescent-shaped nozzle 10 is obtained by rotating a two-dimensional geometric line. The two-dimensional geometric body is composed of two lines, including a first arc and a second arc. Figure 4As shown, the radii of the first arc and the second arc are both R, the second arc is obtained by translating the first arc, and the first arc and the second arc are both tangent to each other at the rim end wall, in order to ensure that the water flow at the nozzle outlet can flow along the rim end wall.

[0023] The specific process of determining the line type of the first arc and the second arc is as follows: First, determine the position of the first arc; for the first arc: take the origin (0,0) as the center and R as the radius, and you can get a full circle. Take the fourth quadrant arc, which is the contour of the first arc.

[0024] Then, determine the position of the second arc; the position of the second arc directly determines the throat height of the nozzle h , h The size of the throat should be controlled at 2 to 6 times the tip clearance. Too large a throat height will result in a decrease in the nozzle outlet velocity. The throat height is expressed as the minimum distance from the second arc to the first arc at the tangent point, such as Figure 4 As shown, before determining the position of the second arc, it is necessary to first determine the throat height, and then translate the first arc to the right to the tangent point of the second arc to determine the position of the second arc.

[0025] The distance between the two ends of the inlet of the crescent-shaped nozzle 10 is determined by the second arc. The throat height is determined, and the second arc is determined, that is, the distance between the two ends of the nozzle inlet can be determined.

[0026] The outlet position of the crescent-shaped nozzle 10 should be located before the leading edge of the impeller, so as to ensure that the nozzle can fully act on the impeller head position.

[0027] The two-dimensional geometric line is centered on the central axis of the axial flow pump impeller. By sweeping left and right, a nozzle with a jet direction of 90° to the frontal line of the impeller leading edge can be obtained. Then, by rotating the center of the nozzle, a crescent-shaped nozzle of the present invention can be obtained, that is, the jet at the crescent-shaped nozzle outlet forms a certain angle with the frontal line of the impeller leading edge, which can ensure that the jet acts on the impeller channel.

[0028] The schematic diagram of the structure assembly of the crescent-shaped nozzle is as follows: Figure 5 As shown, the axial chord length of the axial flow pump blade tip is Ca=40.2mm, the nozzle outlet jet position is 18%Ca away from the blade leading edge, the left side of the nozzle device is 9mm away from the center of the bolt, and the distance from the center of the nozzle device is 39.5mm. The center of the sealing cover is national standard NPT1 / 2, with a thickness of 20mm, and the size of the square through hole is 28mm*24mm.

[0029] Example 3 The blade top water spraying method for improving the stability of an axial flow pump according to the present invention is specifically as follows: like Figure 6As shown, the diverter box 1 is connected to the booster pump through a pipeline, the booster pump outlet is connected to the solenoid valve inlet to control the real-time flow of the pipeline; the solenoid valve outlet is connected to the flow meter inlet to measure the real-time flow of the pipeline; the flow meter outlet is connected to the pulse valve inlet, and the pulse valve outlet is connected to the diverter box 1, the nozzle device 3 is tightly connected to the rim end wall of the axial flow pump, and then the water source is stably sprayed into the impeller channel through the nozzle.

[0030] Example 4 Relying on the axial flow pump closed cycle test bench, the blade top water spraying device for improving the stability of the axial flow pump of the present invention is specifically described. The main design parameters of the axial flow pump are shown in Table 1:

[0031] The main parameters of the hydraulic external characteristic test of the axial flow pump include: speed, flow, inlet and outlet pressure, torque and power. The inlet and outlet pressure tests are realized by pressure transmitters installed at the inlet and outlet of the axial flow pump. The flow is measured by an electromagnetic flowmeter installed in the outlet pipeline. The torque and power are tested by a torque tachometer installed between the pump and the motor. All test equipment is connected to the control system, which can continuously record the measured system data. During the experiment, the system flow is changed by controlling the outlet regulating valve to obtain the characteristic curve of the axial flow pump; The blade top water spraying device for improving the stability of the axial flow pump of the present invention is used to synchronously test the external characteristics of the axial flow pump. While testing the external characteristics of the axial flow pump, the blade top water spraying device is turned on, and by setting the pressure of the jet system, adjusting and changing the opening of the electromagnetic valve of the jet system or the duty cycle of the pulse valve, the blade top water spraying test of the axial flow pump under different water spraying flow rates and water spraying frequencies can be carried out; on the other hand, by opening or closing the valve on the side wall hose of the diverter box, the blade top water spraying test of the axial flow pump under different numbers of nozzles can be carried out; During the experiment, the following parameters are recorded synchronously: the pressure of the inlet and outlet of the axial flow pump and the jet system, the flow rate of the outlet of the axial flow pump and the jet system, and the speed and torque of the motor. The data is transmitted to the display through the data transmission line, and the following formula is processed to obtain the external characteristic curves of the axial flow pump under the blade top water spraying device for improving the stability of the axial flow pump with and without the present invention.

[0032] Axial flow pump head H and efficiency η The calculation formula is as follows:

[0033] In the formula, and Respectively represent the test section readings of the inlet and outlet elbows of the inlet pipe, in Pa; Z is the vertical height difference between the inlet and outlet sections of the pump; ρ is the density of the fluid, in kg / m 3 ;g is the acceleration due to gravity, in m / s 2 ; Q is the flow rate through the pump, in m 3 / h; M is the main shaft torque, in N·m; ω is the spindle speed in rad / s.

[0034] The blade top water spraying device for improving the stability of the axial flow pump of the present invention can be used for experimental research on different water spraying flow rates, water spraying frequencies, water spraying speeds and quantities. The water spraying flow rate research range is 0~18m 3 / h; the research range of water spray number is 0~6, and different arrangements with the same number can also be studied. The research range of water spray frequency is 0~∞Hz.

[0035] Example 5 Figure 7 The jet flow rate is given as 18m 3 / h, the number of nozzles is 6, the jet frequency is ∞Hz, that is, the head comparison diagram of the axial flow pump under steady-state jet and when the blade top water spraying device of the present invention is not used, it can be found that the use of the blade top water spraying device of the present invention eliminates the hump phenomenon of the axial flow pump and greatly improves the stable operation range of the axial flow pump; Example 6 Figure 8 The jet flow rate is given as 14m 3 / h, the number of nozzles is 6, the jet frequency is 0.5Hz, that is, the head comparison diagram of the axial flow pump under pulse jet and the case where the blade top water spraying device of the present invention is not used. It can be found that when the blade top water spraying device of the present invention is used, the hump phenomenon of the axial flow pump is eliminated, and the stable operation range of the axial flow pump is greatly improved.

Claims

1. A blade top water spraying device for improving the stability of an axial flow pump, characterized in that: The invention comprises a booster pump, the booster pump is connected to a diversion box (1) via a pipeline, the side wall of the diversion box (1) is connected to a plurality of hoses (2), and the plurality of hoses (2) are evenly arranged on the side wall of the diversion box (1) along the circumferential direction; one end of each of the hoses (2) extends into the interior of the diversion box (1), and the other end is provided with a nozzle device (3).

2. The blade top water spraying device for improving the stability of an axial flow pump according to claim 1, characterized in that: The nozzle device (3) comprises a sealing cover (4), a threaded hole (5) is provided at the center of the sealing cover (4), the sealing cover (4) is threadedly connected to the hose (2) through the threaded hole (5), and the end of the hose (2) is connected to the bottom of the threaded hole (5); the bottom of the sealing cover (4) is connected to a water filling chamber (6), and a square through hole (8) is provided at the center of the water filling chamber (6); the bottom of the water filling chamber (6) is connected to a nozzle seat (9), and a crescent-shaped nozzle (10) is provided at the center of the nozzle seat (9), the inlet of the crescent-shaped nozzle (10) is located at the bottom of the square through hole (8), and the outlet of the crescent-shaped nozzle (10) is located at the bottom of the nozzle seat (9), and the shape of the crescent-shaped nozzle (10) from the inlet to the outlet is a tapered shape.

3. The blade top water spraying device for improving the stability of an axial flow pump according to claim 2, characterized in that: The three-dimensional structure of the crescent-shaped nozzle (10) is obtained by rotating a two-dimensional geometric line. The two-dimensional geometric body is composed of two lines, including a first arc and a second arc. The radii of the first arc and the second arc are both R. The second arc is obtained by translating the first arc. The first arc and the second arc are both tangent to each other at the end wall of the wheel rim. The position of the second arc directly determines the throat height of the nozzle. h , h The size is controlled at 2 to 6 times the tip clearance. The throat height is expressed as the minimum distance between the second arc and the first arc at the tangent point. Therefore, before determining the position of the second arc, the throat height needs to be determined first. Then, the first arc is translated to the right to the tangent point of the second arc to determine the position of the second arc. The two-dimensional geometric line is centered on the central axis of the axial flow pump impeller. By sweeping left and right, a nozzle with a jet direction of 90° to the front line of the impeller leading edge can be obtained. Then, a crescent-shaped nozzle can be obtained by rotating through the center of the nozzle.

4. The blade top water spraying device for improving the stability of an axial flow pump according to claim 2, characterized in that: The upper surface of the sealing cover (4) is provided with a plurality of through holes (7).

5. The blade top water spraying device for improving the stability of an axial flow pump according to claim 1, characterized in that: A pressure sensor is installed on the top of the diversion box (1).

6. The blade top water spraying device for improving the stability of an axial flow pump according to claim 1, characterized in that: A solenoid valve, a flow meter and a pulse valve are arranged on the pipeline connecting the booster pump and the diversion box (1).

7. The blade top water spraying device for improving the stability of an axial flow pump according to claim 1, characterized in that: Each of the hoses (2) is provided with a valve.

8. A blade top water spraying method for improving the stability of an axial flow pump, using a blade top water spraying device for improving the stability of an axial flow pump as claimed in any one of claims 1 to 7, characterized in that: Specifically: The diverter box (1) is connected to the booster pump through a pipeline, the booster pump outlet is connected to the solenoid valve inlet, so as to control the real-time flow of the pipeline; the solenoid valve outlet is connected to the flow meter inlet, so as to measure the real-time flow of the pipeline; the flow meter outlet is connected to the pulse valve inlet, and the pulse valve outlet is connected to the diverter box (1), the nozzle device (3) is tightly connected to the wheel rim end wall of the axial flow pump, and then the water source is stably sprayed into the impeller channel through the nozzle.

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