阅读说明：本技术 一种应用于诱导轮空化实验的压力控制系统及方法 (Pressure control system and method applied to inducer cavitation experiment ) 是由 陈晖� 项乐 刘军年 许开富 李随波 刘成胜 张留欢 于 2021-06-25 设计创作，主要内容包括：本发明公开一种应用于诱导轮空化实验的压力控制系统及方法,通过系统可实现增压、减压和除气三种功能,通过除气降低实验系统回路中水的含气量,减小含气量对空化发生的影响,同时在含气量水平较低的条件下实现增压或减压,提升了空化实验的可信度。本系统包括气囊、储水箱、除气罐、增压单元、减压单元和除气单元；所述增压单元通过向对气囊充入高压气,气囊体积膨胀,实现对储水箱的增压；所述减压单元通过逐步将气囊中气体排出,降低气囊的压力使气囊体积缩减,实现对储水箱的减压；所述除气单元、储水箱和除气罐实现连通循环,储水箱中的水经除气罐过滤析出气体,除气单元在除气罐内制造低压环境,将析出气体排出,实现对储水箱中水的除气。(The invention discloses a pressure control system and a pressure control method applied to an inducer cavitation experiment, which can realize three functions of pressurization, decompression and degassing through the system, reduce the air content of water in an experiment system loop through degassing, reduce the influence of the air content on cavitation, realize pressurization or decompression under the condition of lower air content level, and improve the reliability of the cavitation experiment. The system comprises an air bag, a water storage tank, a degassing tank, a pressurizing unit, a pressure reducing unit and a degassing unit; the pressurizing unit inflates high-pressure air into the air bag, so that the volume of the air bag is expanded, and the water storage tank is pressurized; the pressure reducing unit gradually discharges gas in the air bag, reduces the pressure of the air bag to reduce the volume of the air bag, and realizes the pressure reduction of the water storage tank; the degassing unit, the water storage tank and the degassing tank are communicated and circulated, water in the water storage tank is filtered by the degassing tank to separate out gas, the degassing unit is used for manufacturing a low-pressure environment in the degassing tank, the separated gas is discharged, and degassing of water in the water storage tank is realized.)

1. The utility model provides a be applied to pressure control system of inducer cavitation experiment which characterized in that: comprises an air bag (1), a water storage tank (2), a degassing tank (3), a pressurization unit, a decompression unit and a degassing unit;

the air bag (1) is arranged in the water storage tank (2) and positioned at the top, and the air bag (1) is communicated with the high-pressure air passage (7);

the degassing tank (3) is communicated with the water storage tank (2), and the degassing tank (3) is used for separating out gas in water in the tank;

the pressurizing unit is connected with the air bag (1), and the air bag (1) is inflated by high-pressure air so that the volume of the air bag (1) is expanded and water in the water storage tank (2) is extruded to complete pressurizing of the water storage tank (2);

the pressure reducing unit is connected with the air bag (1), and the pressure of the air bag (1) is reduced by gradually discharging the gas in the air bag (1) so as to reduce the volume of the air bag (1) and complete the pressure reduction of the water storage tank (2);

the degassing unit, the water storage tank (2) and the degassing tank (3) are communicated and circulated, water in the water storage tank (2) filters separated gas through the degassing tank (3), the degassing unit is used for manufacturing a low-pressure environment in the degassing tank (3) and discharging the separated gas, and degassing of the water storage tank (2) is completed.

2. The pressure control system applied to the inducer cavitation experiment as recited in claim 1, wherein:

the degassing tank (3) comprises a tank body (30), a nozzle (31), a baffle (32), a cylinder (37), a partition plate (36) and an oxygen dissolving instrument (38);

the tank body (30) is provided with a water inlet (33) and a water outlet (34);

the partition plate (36) is arranged in the tank body (30) and divides the tank body (30) into a lower cavity (301) and an upper cavity (302);

the water inlet (33) is communicated with the lower cavity (301), and the water outlet (34) is communicated with the lower part of the upper cavity (302);

the lower end surface of the cylinder (37) is connected with the partition plate (36);

the nozzle (31) is communicated with the lower cavity (301) and the cylinder (37) and the nozzle faces the cylinder (37);

the baffle (32) is arranged on the upper end surface of the cylinder (37), and a plurality of filtering holes are formed in the baffle (32);

the dissolved oxygen meter (38) is arranged in the upper cavity (302) and extends out of the tank body (30).

3. The pressure control system applied to the inducer cavitation experiment as recited in claim 2, wherein:

the inner hole of the nozzle (31) is divided into three sections, and the lengths of the three sections are respectively 4mm, 21mm and 1 mm;

the radiuses of three sections of inner holes of the nozzle (31) are gradually reduced from bottom to top, and the inner diameters of the three sections of inner holes are 6mm, 3mm and 1mm respectively.

4. The pressure control system applied to the inducer cavitation experiment as recited in claim 3, wherein:

the baffle (32) is provided with small holes at equal intervals along the radial direction and is used for effectively filtering bubbles and impurities in water;

the outer diameter of the baffle (32) is 180mm, and the diameter of the small hole is 0.5 mm.

5. The pressure control system applied to the inducer cavitation experiment as recited in claim 4, wherein:

the baffle (32) is provided with 9 rows of small holes along the radial direction at equal intervals.

6. The pressure control system applied to the inducer cavitation test as set forth in any one of claims 1 to 5, wherein:

a safety valve (10) and an exhaust valve (11) are arranged on the water storage tank (2);

the opening pressure of the safety valve (10) is set to be 1.05-1.1 times of the working use pressure, and the safety valve is used for preventing potential safety hazards caused by overhigh pressure in the water storage tank;

the pressurization unit comprises a high-pressure air passage (7) arranged between the water storage tank (2) and the high-pressure air source, and a first regulating valve (15) and a first flow meter (6) which are arranged on the high-pressure air passage (7);

the degassing unit comprises a second flowmeter (14), a circulating pump (4) and a second regulating valve (16) which are connected in sequence;

the inlet of the second flowmeter (14) is connected with the lower part of the water storage tank (2), the outlet of the circulating pump (4) is connected with the water inlet of the degassing tank (3), the water outlet of the degassing tank (3) is connected with the inlet of the second regulating valve (16), and the outlet of the second regulating valve (16) is connected with the top of the water storage tank (2);

the pressure reducing unit comprises an exhaust passage (8), an air suction passage (9) and a fourth regulating valve (18) communicated with the exhaust passage (8) and the air suction passage (9);

a fifth regulating valve (19) is arranged on the exhaust passage (8), the inlet of the fifth regulating valve (19) is communicated with the air bag (1), and the outlet of the fifth regulating valve (19) is communicated with the external atmosphere;

the air pumping passage (9) is sequentially provided with a third regulating valve (17) and a vacuum pump (5); the inlet of the third regulating valve (17) is communicated with the top of the degassing tank (3);

the inlet of the fourth regulating valve (18) is communicated with the air bag (1), and the outlet of the fourth regulating valve (18) is communicated with the inlet of the vacuum pump (5); and the outlet of the vacuum pump (5) is connected with a water source.

7. The pressure control system applied to the inducer cavitation experiment as recited in claim 6, wherein:

the first regulating valve (15), the second regulating valve (16), the third regulating valve (17), the fourth regulating valve (18) and the fifth regulating valve (19) are respectively a coarse regulating valve, a fine regulating valve and a fine regulating valve which are connected in parallel;

the coarse adjusting valve and the fine adjusting valve balance cage type single-seat adjusting valve;

the fine adjustment valve is a low-noise cage type adjusting valve.

8. The pressure control system applied to the inducer cavitation experiment as recited in claim 7, wherein:

the coarse regulating valve (151), the fine regulating valve (152) and the fine regulating valve (153) are all linear regulating valves, the regulating precision is +/-1%, and the calibers are respectively 80mm, 50mm and 25 mm;

the coarse regulating valve (151) and the fine regulating valve (152) are preliminarily regulated to 0-150L/s according to the flow, the pressure drop is calculated according to 0.2MPa, and the valve C_vValues of 148.9 and 75, respectively;

the fine adjustment valve (153) C_vThe value was 4.0.

9. The pressure control system applied to the inducer cavitation experiment as recited in claim 8, wherein:

the tank body of the water storage tank (2) is made of stainless steel materials, and the design temperature of the water storage tank (2) is not lower than 100 ℃;

under the standard atmospheric pressure, the volume of the air bag (1) is 4% of the volume of the water storage tank (2);

the degassing tank (3) is made of stainless steel materials, and the effective volume of the degassing tank (3) accounts for 6 percent of the volume of the water storage tank (2).

10. A pressure control method for inducer cavitation test, which adopts the pressure control system applied to inducer cavitation test as claimed in any one of claims 1-9, and is characterized in that: the method comprises a pressurization working condition, a decompression working condition and a degassing working condition;

in the three working conditions, firstly, the air bag (1) needs to be properly inflated, the internal pressure is kept at a standard atmospheric pressure, all regulating valves are closed, the water storage tank (2) is filled with water, and the water storage tank is attached to the air bag (1);

the supercharging condition comprises the following steps:

s101: the high-pressure air passage (7) is communicated, high-pressure air is filled into the air bag (1), so that the volume of the air bag (1) is expanded, and water in the water storage tank (2) is extruded;

s102: the pressure of the water storage tank (2) is accurately adjusted to reach the pressure required by the experiment by adjusting a coarse adjusting valve, a fine adjusting valve and a fine adjusting valve in the first adjusting valve (15);

s103: closing the first regulating valve (15) and stopping inflation;

the decompression condition comprises the following steps:

s201: the exhaust passage (8) is communicated, and the fifth regulating valve (19) is regulated to ensure that the gas in the air bag (1) is exhausted to the atmosphere, the volume of the air bag (1) is reduced, and the water in the water storage tank (2) is reduced for extrusion;

s202: the air pumping passage (9) is communicated, the vacuum pump (5) is started, and the fifth regulating valve (19) and the fourth regulating valve (18) are adjusted and regulated in a matching manner, so that the gas in the air bag (1) is further discharged, and the pressure of the water storage tank (2) is reduced until the pressure reaches the pressure required by the experiment;

s203: the vacuum pump (5), the fifth regulating valve (19) and the fourth regulating valve (18) are closed, and exhaust is stopped;

s204: after the experiment is finished, opening a fifth regulating valve (19), enabling the atmosphere to enter the air bag (1), recovering the pressure to the atmospheric pressure state, and enabling the air bag (1) to be in a free state;

the degassing condition comprises the following steps:

s301: opening the exhaust valve (11), adjusting the second adjusting valve (16) to enable the water level in the water level degassing tank (3) of the water storage tank (2) to be level, and closing the exhaust valve (11);

s302: starting a circulating pump (4) to enable the water storage tank (2) and the degassing tank (3) to be communicated, circulating water between the water storage tank (2) and the degassing tank (3), increasing the flow velocity of a water flow nozzle (31), and filtering bubbles and impurities in water by water flow through a baffle plate (32);

s303: the air pumping passage (9) is communicated, the vacuum pump (5) is started, the third regulating valve (17) is regulated and regulated, and the discharged air is continuously discharged;

s304: monitoring the oxygen content in the water storage tank (2) in real time through an oxygen dissolving instrument (38), and judging the air content of the water in the water storage tank (2) until the air content in the water storage tank (2) is reduced to the experimental requirement;

s305: and (3) closing the second regulating valve (16) and the third regulating valve (17), and closing the circulating pump (4) and the vacuum pump (5) to finish external circulation degassing.

Technical Field

The invention relates to a pressure control system applied to an inducer cavitation experiment, which can provide pressure and gas content meeting experiment requirements for a circulation loop of a pump cavitation experiment system.

Background

Cavitation refers to the phenomenon of phase change of a liquid when the ambient pressure is lower than the saturated vapor pressure, and the primary process of the cavitation depends on the ambient pressure, and is also related to the content of gas which is dissolved in the liquid and is not dissolved in the liquid, surface tension, viscosity and other factors. The content of gas which is dissolved in and insoluble in liquid has great influence on the development of cavitation and the cavitation performance of the inducer, the gas can be separated out in a low-pressure area, the volume of the gas can be increased to become cavitation nuclei for inducing cavitation initiation, and the occurrence of cavitation is promoted, so that when a cavitation experiment taking water as a medium is carried out, the content of the gas in the liquid needs to be reasonably controlled to reduce the influence of the gas on the experiment effect. The traditional pump hydraulic experiment system directly pressurizes a water storage tank through a high-pressure air source, so that the content of gas dissolved in water and gas not dissolved in water is obviously increased when the pressure is increased. Meanwhile, because a degassing device is not provided, the incoming flow of the experimental section usually contains a certain amount of dissolved gas which can also become cavitation nuclei for inducing cavitation initiation to promote cavitation initiation, so that the experimental system cannot accurately obtain the cavitation performance of the tested product.

Disclosure of Invention

In order to reduce the influence of the air content increase caused by the pressurization system of the experiment system on the cavitation performance of the tested product in the cavitation experiment process, the invention provides the pressure control system applied to the inducer cavitation experiment, and the three functions of pressurization, pressure reduction and degassing in the inducer cavitation experiment can be realized through the pressure control system. The air content of water in the experimental system loop is reduced through degassing, the influence of the air content on cavitation is reduced, pressurization or decompression is realized under the condition of low air content level, and the reliability of a cavitation experiment is improved.

A plastic air bag is arranged in a water storage tank of the experimental system and is connected with a high-pressure air source, and the water storage tank is pressurized and depressurized through the change of the pressure (volume) in the air bag; meanwhile, the water storage tank is connected with a degassing circulation loop, water in the water storage tank can be degassed before the formal experiment is started, the pressurization, decompression and degassing functions are integrated through the optimized design of the loop, and different adjusting functions are realized through the matching of different valves and pump sets.

The technical solution of the invention is as follows:

a pressure control system applied to inducer cavitation experiments is characterized in that: comprises an air bag 1, a water storage tank 2, a degassing tank 3, a pressurization unit, a decompression unit and a degassing unit;

the air bag 1 is arranged in the water storage tank 2 and positioned at the top, and the air bag 1 is communicated with the high-pressure air passage 7;

the degassing tank 3 is communicated with the water storage tank 2, and the degassing tank 3 is used for separating out gas in water in the tank;

the pressurizing unit is connected with the air bag 1, and the air bag 1 is inflated by high-pressure air, so that the volume of the air bag 1 is expanded, water in the water storage tank 2 is extruded, and the pressurizing of the water storage tank 2 is completed;

the pressure reducing unit is connected with the air bag 1, and the pressure of the air bag 1 is reduced by gradually discharging the gas in the air bag 1, so that the volume of the air bag 1 is reduced, and the pressure reduction of the water storage tank 2 is completed;

degassing unit, storage water tank 2 and degassing tank 3 realize the intercommunication circulation, and the water in the storage water tank 2 filters through degassing tank 3 and separates out gas, and the degassing unit makes the low pressure environment in degassing tank 3, will separate out gas and discharge, accomplishes the degasification to storage water tank 2.

Further, the degassing tank 3 comprises a tank body 30, a nozzle 31, a baffle 32, a cylinder 37, a partition plate 36 and an oxygen dissolving instrument 38;

the tank 30 is provided with a water inlet 33 and a water outlet 34;

the partition plate 36 is arranged in the tank 30 and divides the tank 30 into a lower cavity 301 and an upper cavity 302;

the water inlet 33 is communicated with the lower cavity 301, and the water outlet 34 is communicated with the lower part of the upper cavity 302;

the lower end surface of the cylinder 37 is connected with a partition plate 36;

the nozzle 31 communicates the lower cavity 301 and the cylinder 37 and the nozzle is directed towards the cylinder 37;

the baffle 32 is arranged on the upper end surface of the cylinder 37, and a plurality of filtering holes are formed in the baffle 32;

the dissolved oxygen meter 38 is disposed in the upper cavity 302 and extends out of the tank 30.

Further, the inner hole of the nozzle 31 is divided into three sections, and the lengths of the three sections are respectively 4mm, 21mm and 1 mm;

the radiuses of three sections of inner holes of the nozzle 31 are gradually reduced from bottom to top, and the inner diameters of the three sections of inner holes are 6mm, 3mm and 1mm respectively.

When water passes through the small holes with the gradually reduced flow area, the local pressure of the flow field is gradually reduced, and the separation of non-soluble gas in water is facilitated.

Furthermore, the baffle 32 is provided with small holes along the radial direction at equal intervals for effectively filtering bubbles and impurities in the water;

the outer diameter of the baffle 32 is 180mm, and the diameter of the small hole is 0.5 mm.

Further, the baffle 32 is provided with 9 rows of small holes distributed at equal intervals along the radial direction.

Further, a safety valve 10 and an exhaust valve 11 are installed on the water storage tank 2;

the opening pressure of the safety valve 10 is set to be 1.05-1.1 times of the working use pressure, and the safety valve is used for preventing potential safety hazards caused by overhigh pressure in the water storage tank;

the pressurizing unit comprises a high-pressure air passage 7 arranged between the water storage tank 2 and the high-pressure air source, and a first regulating valve 15 and a first flow meter 6 which are arranged on the high-pressure air passage 7;

the degassing unit comprises a second flowmeter 14, a circulating pump 4 and a second regulating valve 16 which are connected in sequence;

the inlet of the second flowmeter 14 is connected with the lower part of the water storage tank 2, the outlet of the circulating pump 4 is connected with the water inlet of the degassing tank 3, the water outlet of the degassing tank 3 is connected with the inlet of the second regulating valve 16, and the outlet of the second regulating valve 16 is connected with the top of the water storage tank 2;

the decompression unit includes an exhaust passage 8, an air extraction passage 9, and a fourth regulating valve 18 communicating the exhaust passage 8 and the air extraction passage 9;

a fifth regulating valve 19 is arranged on the exhaust passage 8, the inlet of the fifth regulating valve 19 is communicated with the air bag 1, and the outlet of the fifth regulating valve 19 is communicated with the external atmosphere;

the air pumping passage 9 is sequentially provided with a third regulating valve 17 and a vacuum pump 5; the inlet of the third regulating valve 17 is communicated with the top of the degassing tank 3;

the inlet of the fourth regulating valve 18 is communicated with the air bag 1, and the outlet of the fourth regulating valve 18 is communicated with the inlet of the vacuum pump 5; and the outlet of the vacuum pump 5 is connected with a water source.

Further, the first regulating valve 15, the second regulating valve 16, the third regulating valve 17, the fourth regulating valve 18 and the fifth regulating valve 19 are all connected in parallel by a coarse regulating valve, a fine regulating valve and a fine regulating valve;

the coarse adjusting valve and the fine adjusting valve balance cage type single-seat adjusting valve;

the fine adjustment valve is a low-noise cage type adjusting valve.

Further, the coarse regulating valve 151, the fine regulating valve 152 and the fine regulating valve 153 are all linear regulating valves, the regulating precision is +/-1%, and the calibers are respectively 80mm, 50mm and 25 mm;

the primary flow regulating range of the coarse regulating valve 151 and the primary flow regulating range of the fine regulating valve 152 are 0-150L/s, the pressure drop is calculated according to 0.2MPa, and the valve C is_vValues of 148.9 and 75, respectively;

the fine adjustment valve 153C_vThe value was 4.0.

Further, the tank body of the water storage tank 2 is made of stainless steel materials, and the design temperature of the water storage tank 2 is not lower than 100 ℃;

under the standard atmospheric pressure, the ratio of the volume of the air bag 1 to the volume of the water storage tank 2 is 4 percent;

the degassing tank 3 is made of stainless steel materials, and the effective volume of the degassing tank 3 accounts for 6 percent of the volume of the water storage tank 2.

The invention also provides a pressure control method for the inducer cavitation experiment by adopting the pressure control system applied to the inducer cavitation experiment, which is characterized in that: the method comprises a pressurization working condition, a decompression working condition and a degassing working condition;

in the three working conditions, firstly, the air bag 1 needs to be properly inflated, the internal pressure is kept at a standard atmospheric pressure, and all regulating valves are closed; the water storage tank 2 is filled with water and is attached to the air bag 1;

the supercharging condition comprises the following steps:

s101: the high-pressure air passage 7 is communicated, high-pressure air is filled into the air bag 1, so that the volume of the air bag 1 is expanded, and water in the water storage tank 2 is extruded;

s102: the pressure of the water storage tank 2 is accurately adjusted to reach the pressure required by the experiment by adjusting a coarse adjusting valve, a fine adjusting valve and a fine adjusting valve in the first adjusting valve 15;

s103: the first regulating valve 15 is closed, and the inflation is stopped;

the decompression condition comprises the following steps:

s201: the exhaust passage 8 is communicated, and the fifth regulating valve 19 is regulated, so that the gas in the air bag 1 is exhausted to the atmosphere, the volume of the air bag 1 is reduced, and the water in the water storage tank 2 is reduced for extrusion;

s202: the air pumping passage 9 is communicated, the vacuum pump 5 is started, and the fifth regulating valve 19 and the fourth regulating valve 18 are adjusted and regulated in a matching way, so that the gas in the air bag 1 is further discharged, and the pressure of the water storage tank 2 is reduced to reach the pressure required by the experiment;

s203: the vacuum pump 5, the fifth regulating valve 19 and the fourth regulating valve 18 are closed, and the exhaust is stopped;

s204: after the experiment is finished, the fifth regulating valve 19 is opened, the atmosphere enters the air bag 1, the pressure is recovered to the atmospheric pressure state, and the air bag 1 is in a free state;

the degassing condition comprises the following steps:

s301: opening the exhaust valve 11, adjusting the second adjusting valve 16 to enable the water level in the water level degassing tank 3 of the water storage tank 2 to be level, and closing the exhaust valve 11;

s302: the circulating pump 4 is started to enable the water storage tank 2 and the degassing tank 3 to be communicated, water between the water storage tank 2 and the degassing tank 3 circulates, the flow velocity of the water flow nozzle 31 is increased, and water flow filters bubbles and impurities in water through the baffle plate 32;

s303: the pumping passage 9 is communicated, the vacuum pump 5 is started, the third regulating valve 17 is regulated and regulated, and the discharged gas is continuously discharged;

s304: monitoring the oxygen content in the water storage tank 2 in real time through an oxygen dissolving instrument 38, and judging the air content of the water in the water storage tank 2 until the air content in the water storage tank 2 is reduced to the experimental requirement;

s305: and closing the second regulating valve 16 and the third regulating valve 17, and closing the circulating pump 4 and the vacuum pump 5 to complete the external circulation degassing.

Compared with the prior art, the invention has the advantages that:

1. the air bag is arranged in the water storage tank, so that the direct contact between the gas from the high-pressure gas source and the water in the water storage tank is avoided, and the excessive gas content cannot be introduced into the water in the pressurization process.

2. Possess the degasification ability, can carry out the degasification to the water in the experimental system before carrying out the cavitation experiment, reduce aquatic tolerance, promote the credibility of cavitation experiment.

3. Pressurization or decompression is realized under the condition of low gas content level, and the reliability of the cavitation experiment is improved.

4. The influence of the increase of the air content of the pressurization system of the experiment system on the cavitation performance of the tested product is reduced.

Drawings

FIG. 1 is a schematic diagram of a pressure control system applied to an inducer cavitation test according to the present invention;

FIG. 2 is a schematic structural diagram of a gas removal tank in a pressure control system applied to an inducer cavitation test according to the present invention;

FIG. 3 is a schematic diagram of a nozzle structure in a degassing tank in a pressure control system for an inducer cavitation test according to the present invention;

FIG. 4 is a schematic diagram of a baffle structure in a degassing tank in a pressure control system applied to an inducer cavitation experiment.

Reference numerals: 1-an air bag, 2-a water storage tank, 3-a degassing tank, 4-a circulating pump, 5-a vacuum pump, 6-a first flowmeter, 7-a high-pressure air source, 8-atmosphere, 9-a water source, 10-a safety valve, 11-an exhaust valve, 12-a water filling port, 13-a water draining port, 14-a second flowmeter, 15-a first regulating valve, 151-a coarse regulating valve, 152-a fine regulating valve, 153-a fine regulating valve, 16-a second regulating valve, 17-a third regulating valve, 18-a fourth regulating valve and 19-a fifth regulating valve;

30-tank body, 31-nozzle, 32-baffle, 33-water inlet, 34-water outlet, 36-baffle, 37-cylinder and 38-dissolved oxygen meter.

Detailed Description

The invention is further described with reference to the following figures and specific embodiments.

As shown in figure 1, the pressure control system applied to the inducer cavitation experiment comprises a water storage tank 2 and a pressurizing unit, wherein the tank body of the water storage tank 2 is made of stainless steel materials to prevent the experiment medium water from being corroded, and the design temperature is not lower than 100 ℃. The air bag volume under the standard atmospheric pressure accounts for 4% relative to the water storage tank volume, is connected with the tank body through reliable sealing, and a safety valve 10 and an exhaust valve 11 are installed on the water storage tank 2, and the opening pressure of the safety valve 10 is set to be 1.05-1.1 times of the working service pressure, so that potential safety hazards caused by overhigh pressure in the water storage tank are prevented.

The pressurizing unit comprises a high-pressure air source, a high-pressure air passage 7 arranged between the water storage tank 2 and the high-pressure air source, and a first regulating valve 15 and a first flow meter 6 which are arranged on the high-pressure air passage 7, and compared with the prior art, the air bag 1, the degassing unit and the depressurizing unit are added. The air bag 1 is made of high-temperature-resistant rubber materials, is arranged in the water storage tank 2 and is positioned at the top, and the high-pressure air passage 7 is communicated with the air bag 1.

The degassing unit comprises a second flowmeter 14, a circulating pump 4, a degassing tank 3 and a second regulating valve 16 which are connected in sequence; the inlet of the second flowmeter 14 is connected with the lower part of the water storage tank 2, and the outlet of the second regulating valve 16 is connected with the top of the water storage tank 2; the degassing tank 3 is used for separating out dissolved or undissolved gas in the water in the tank;

the decompression unit includes an exhaust passage 8, an air extraction passage 9, and a fourth regulating valve 18 communicating the exhaust passage 8 and the air extraction passage 9; a fifth regulating valve 19 is arranged on the exhaust passage 8, the inlet of the fifth regulating valve 19 is communicated with the air bag 1, and the outlet of the fifth regulating valve 19 is communicated with the external atmosphere;

the air pumping passage 9 is sequentially provided with a third regulating valve 17 and a vacuum pump 5, and the inlet of the third regulating valve 17 is communicated with the top of the degassing tank 3; the inlet of the fourth regulating valve 18 is communicated with the air bag 1, the outlet of the fourth regulating valve 18 is communicated with the inlet of the vacuum pump 5, and the outlet of the vacuum pump 5 is connected with a water source.

The degassing tank 3 shown in fig. 2 is of a nonstandard design, the degassing tank 3 is made of stainless steel, and the ratio of the effective volume to the volume of the water storage tank is 6%. The working principle is that a depressurization method is adopted for degassing, so that the water storage tank 2 is communicated with the degassing tank 3, the separated gas is filtered by a gas separation barrel in the degassing tank 3, a low-pressure environment is manufactured by using a vacuum pump 5, and the separated gas is discharged to meet the experimental requirements.

The degassing tank 3 includes a tank 30, a partition 36, a dissolved oxygen meter 38, and a gas evolution portion. The tank 30 is provided with a water inlet 33 and a water outlet 34, and the water inlet 33, the water outlet 34 and the air outlet are connected by flanges.

The tank 30 is provided with a partition 36 therein, and the tank 30 is divided into a lower chamber 301 and an upper chamber 302, the water inlet 33 is communicated with the lower chamber 301, and the water outlet 34 is communicated with the lower portion of the upper chamber 302. The gas separation part comprises a nozzle 31, a baffle 32 and a cylinder 37, the lower end surface of the cylinder 37 is connected with the baffle 36, the nozzle 31 is communicated with the lower cavity 301 and the cylinder 37, and the nozzle is towards the cylinder 37. The nozzle 31 is used to increase the velocity of the water flowing into the degassing tank 3, so that the water flows into the cylinder 37, passes through the baffle 32 having a porous filtering function provided on the upper end surface of the cylinder 37, and filters bubbles and impurities in the water. And a dissolved oxygen meter 38 is arranged in the tank body 30, the vacuum pump 5 is started to pump air above the degassing tank 3, a negative pressure environment is manufactured, and gas separated out from water is pumped out under the negative pressure environment until the oxygen content monitored by the dissolved oxygen meter 38 arranged in the tank body 30 reaches the experimental requirement, so that the degassing process is completed.

The nozzle 31 is used to increase the velocity of the water entering the degassing tank 3, so that the water enters the cylinder 37 and gas is separated out through the baffle 32. The inner hole of the nozzle 31 is divided into three sections, the lengths of the three sections are respectively 4mm, 21mm and 1mm, the radiuses of the inner holes of the three sections are gradually reduced from bottom to top, and the inner diameters of the three sections are respectively 6mm, 3mm and 1 mm. When water passes through the small holes with the gradually reduced flow area, the local pressure of the flow field is gradually reduced, and the separation of non-soluble gas in water is facilitated.

The outer diameter of the baffle 32 is 180mm, 9 rows of small holes which are uniformly distributed are arranged on the baffle 32 at equal intervals along the radial direction, the diameter of each small hole is 0.5mm, and effective filtration of bubbles and impurities in water can be realized.

A first regulating valve 15, a second regulating valve 16, a third regulating valve 17, a fourth regulating valve 18 and a fifth regulating valve 19 in the system are respectively a coarse regulating valve, a fine regulating valve and a fine regulating valve which have the calibers of 80mm, 50mm and 25mm and are connected in parallel, the coarse regulating valve, the fine regulating valve and the fine regulating valve are all linear regulating valves, the regulating precision is +/-1%, wherein the coarse regulating valve and the fine regulating valve are balance cage type single-seat regulating valves, the calculation is carried out preliminarily according to the flow regulating range of 0-150L/s and the pressure drop of 0.2MPa, and a valve C_v Values of 148.9 and 75, respectively, the trim valve being a low noise cage valve, C_vThe value was 4.0.

Three working conditions of pressurization, decompression and degassing can be realized through the matching of different parts. In order to ensure that the system has enough adjusting capacity, the air bag is properly inflated, the internal pressure is kept at a standard atmospheric pressure, then other valves in the drawing are kept closed, the water storage tank is filled with water, the water tank is completely filled with water so as to ensure that the air bag is completely attached to the water, and then the air bag is adjusted according to the required working condition of the experiment.

And (3) pressurization working condition:

in the pressurizing process, high-pressure air is filled into the air bag 1, the air bag 1 expands in volume, and water in the water storage tank 2 is extruded, so that the pressurizing of the water storage tank 2 is realized.

Firstly, properly inflating the air bag 1, keeping the internal pressure at a standard atmospheric pressure, closing all regulating valves, filling water into the water storage tank 2 until the water tank is completely full of water so as to ensure that the air bag 1 is completely attached to the water, and then performing pressure control according to the working condition required by the experiment. The method comprises the steps of opening a coarse regulating valve in a first regulating valve 15 on a high-pressure gas path, closing all other regulating valves, filling high-pressure gas into an air bag 1, increasing the pressure in a water storage tank 2, closing the coarse regulating valve when the pressure of the water storage tank 2 is close to a target pressure value, selecting a fine regulating valve or a fine regulating valve according to the pressure value to continue to inflate, accurately regulating the pressure of the water storage tank 2, closing the fine regulating valve or the fine regulating valve when the pressure in the water storage tank 2 meets requirements, stopping filling the high-pressure gas, and completing the pressure increase working condition required by experiments.

And (3) decompression working condition:

the decompression process adopts 1 exhaust gas to gasbag, recycles vacuum pump 5 and bleeds, further reduces gasbag pressure, and 1 volume reduction of gasbag realizes the decompression of storage water tank 2.

Before decompression begins, the water storage tank 2 is filled with water until the water tank is completely filled, the air bag 1 is completely attached to the water, the air bag 1 is properly inflated and is in a free state, the coarse regulating valve in the fifth regulating valve 19 is opened, all other regulating valves are closed, high-pressure air in the air bag 1 is discharged into the atmosphere, when the pressure in the air bag 1 is close to the atmospheric pressure, the coarse regulating valve in the fifth regulating valve 19 is closed, the fine regulating valve or the fine regulating valve is opened according to requirements for regulating the exhaust rate, then any regulating valve in the fourth regulating valve 18 is opened, and the vacuum pump 5 is started to pump air, so that the pressure of the air bag 1 is continuously reduced, and the pressure value required by an experiment is ensured. After the experiment is finished, the vacuum pump 5 and the fourth regulating valve 18 are closed, the coarse regulating valve in the fifth regulating valve 19 is opened, the atmospheric air enters the air bag 1, and when the pressure is restored to the atmospheric pressure state, the fifth regulating valve 19 is closed, and the air bag 1 is in a free state.

Degassing conditions:

the degassing process adopts depressurization method degassing, makes storage water tank 2 and degassing tank 3 realize the intercommunication, and the gaseous separation section of thick bamboo in the degassing tank 3 filters out the gas, utilizes vacuum pump 5 to make the low pressure environment, will separate out gaseous discharge, reaches the experimental requirement.

Firstly, an exhaust valve 11 at the top of a water storage tank 2 is opened, any regulating valve in a second regulating valve 16 is closed, all other regulating valves are closed, the water level in a water level degassing tank 3 of the water storage tank 2 is regulated to be level, then the exhaust valve 11 is closed, then a circulating pump 4 is opened to realize communication between the water storage tank 2 and the degassing tank 3, meanwhile, any regulating valve in a third regulating valve 17 is opened, water circulation between the water storage tank 2 and the degassing tank 3 is realized, the flow velocity of a water flow nozzle 31 is increased, bubbles and impurities in water are filtered out by water flow through a baffle 32, then a vacuum pump 5 is started, a low-pressure environment is manufactured at the upper part of the degassing tank 3, the separated gas is continuously discharged, the pressure is reduced, the oxygen content in the water is reduced, dissolved or undissolved gas in the water is separated out, the gas content in the water is continuously reduced, the oxygen content in the water is monitored in real time through an oxygen dissolving instrument 38 until the gas content is reduced to meet experimental requirements, and closing the second regulating valve 16 and the third regulating valve 17, and closing the circulating pump 4 and the vacuum pump 5 to complete the external circulation degassing.

The experimental system of the invention has been subjected to verification experiments, has good effect, reduces the air content of water in a loop of the experimental system, accurately obtains the cavitation characteristic of the inducer, and can be popularized and applied in similar pump cavitation experimental systems.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.