CN111306076A - Device and method for testing backflow vortex cavitation of vane pump - Google Patents

Abstract

The invention provides a test device and method for realizing the backflow vortex cavitation of the vane pump, which is used for testing the performance and dynamic characteristics of the backflow vortex cavitation of the vane pump under the working condition of small flow. In the device, the vane pump is fixed on the workbench, and a pressure pulsation sensor is installed on the plexiglass inlet pipe 1*D _s away from the impeller inlet, and multiple sensors are installed at intervals of 45° along the circumferential direction of the volute flow channel. A pressure pulsation sensor is installed, and a pressure pulsation sensor is installed at a distance of 2*D _s from the pump outlet pipe, and the sensor and the acquisition card are connected in series to a computer system equipped with signal acquisition and data processing software. The test method is based on the fact that backflow will occur at the inlet of the pump impeller, and the mainstream flow of the pump inlet and its hydraulic performance will be affected. The pressure pulsation information inside the pump is collected in real time through the pressure pulsation sensor, combined with the flow condition inside the pump when the backflow vortex cavitation occurs, Accurately realize the identification and judgment of the backflow vortex cavitation of the vane pump.

Description

A kind of test device and method for realizing vortex cavitation in backflow of vane pump

technical field

The invention belongs to the technical field of fluid mechanics, and relates to an experimental testing method for cavitation of a centrifugal pump, in particular to a device and method for testing the vortex cavitation in the return flow of a vane pump.

Background technique

Centrifugal pumps can be widely used in electric power, metallurgy, coal, building materials and other industries to transport slurry containing solid particles, widely used in aerospace, petroleum, chemical, water conservancy and other important national economic fields, with simple structure, reliable performance and easy maintenance. Etc. When the pump runs under the deviating design conditions, especially when the small flow conditions are used, the inlet of the centrifugal pump is prone to backflow, the pressure at the center of the backflow vortex is extremely low, and the phenomenon of steam bubbles and sudden bursts is generated in the liquid water flow, and it is easy to be in the water. There is a low-pressure area in the suction pipeline, and the low-pressure area will lead to cavitation. In severe cases, it will induce low-frequency pressure pulsation in the centrifugal pump and its pipeline system, resulting in strong mechanical vibration, energy consumption, and reduced operating reliability and work of the pump. performance.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a device and method for testing the backflow vortex cavitation, by observing the dynamic characteristics of the cavitation changes in the cavitation inside the pump, combined with the cavitation development status of the cavitation phenomenon, the pulsation signal and its axial or radial characteristics , it is easier to judge whether the backflow vortex cavitation occurs when the vane pump is running.

The present invention achieves the above technical purpose through the following technical means.

A vortex cavitation test device for realizing the return flow of a vane pump, which is characterized in that it comprises a water tank, a vane pump, a visual test system for realizing the reproduction of the pump inlet flow field, a pressure pulsation signal acquisition system and a signal processing device;

The visual test system consists of a transparent plexiglass inlet pipe, a high-speed camera and a digital camera. The transparent plexiglass inlet pipe is used to connect the vane pump and the water tank. The high-speed camera and the digital camera are respectively installed on the front of the inlet section of the transparent plexiglass inlet pipe. The outlet of the vane pump is connected with the water tank through a pipeline to form a loop, and the outlet of the vane pump and the pipeline of the water tank are provided with flow meters and valves; the water tank is also connected with the vacuum pump, and the pipeline between the vacuum pump and the water tank is also provided with Vent;

The pressure pulsation signal acquisition system includes a plurality of pressure pulsation sensors installed at the pump inlet and pump outlet of the vane pump and along the circumferential direction of the volute flow channel of the vane pump; the pressure pulsation sensor at the pump inlet, the pump The outlet pressure pulsation sensor is installed directly above the transparent plexiglass inlet pipe 1*D _s away from the impeller inlet and 2*D _s away from the outlet pipe;

The signal processing device is composed of a first acquisition card, a second acquisition card, a voltage divider, a power supply box and a computer equipped with signal acquisition and data processing software. The first acquisition card is connected to the pump inlet pressure sensor and the outlet pressure sensor. The second acquisition card is connected with a plurality of pressure pulsation sensors, and the first acquisition card and the second acquisition card are connected to a computer equipped with signal acquisition and data processing software. The first acquisition card and the second acquisition card The card is connected to the power box through a voltage divider.

Further, a plurality of pressure pulsation sensors are evenly distributed in the circumferential direction inside the vane pump.

Further, the number of the pressure pulsation sensors is 8.

The test method for realizing the backflow vortex cavitation test device of the vane pump is characterized in that, comprising the following steps:

1). Complete the installation of the reflux vortex cavitation test device;

2). Turn on the power, start the vane pump, and make the speed of the vane pump reach the required test speed; start the computer, and collect the sensor offset before starting the machine;

3). By adjusting the valve in the outlet pipeline of the pump, set the flow value for the pump cavitation performance test to a small flow condition; in each flow condition test, continuously adjust the valve in the outlet pipeline so that the Keep the flow value constant in the whole reflux vortex cavitation experiment;

4) Adjust the inlet pressure of the water tank by starting the vacuum pump to change the inlet pressure of the vane pump, so that cavitation does not occur inside the vacuum pump; collect the corresponding cavitation flow field distribution and pressure pulsation information when cavitation occurs inside the vane pump at this time, At this time, it is used to detect the state that cavitation does not occur inside the vane pump;

5). The pump inlet pressure of the vane pump is gradually depressurized by the vacuum pump, and the inlet pressure of the vane pump is set, so that the backflow vortex cavitation gradually occurs inside it;

6). Under the condition of constant inlet pressure or constant cavitation coefficient, obtain the cavitation test information of the vane pump synchronously collected by the pressure pulsation sensor, high-speed camera and digital camera when the vane pump occurs cavitation, and perform the following data processing:

a). Calculate the cavitation performance data of the vane pump:

By gradually reducing the inlet pressure p ₁ of the centrifugal pump, the effective NPSHA _NPSHA is decreased until cavitation occurs; The cavitation margin of the pump is indirectly calculated from the characteristic equation of the pump, and the primary cavitation performance point of the pump is determined to evaluate the cavitation performance of the pump; different NPSHA values correspond to different head H values, and finally a series of head H are obtained for calculating cavitation. The cavitation performance curve of the pump can be obtained, and the cavitation performance of the pump under each working condition can be compared to judge the initial point of cavitation;

b) Visualization data of the cavitation flow field of the vane pump:

Obtain the process of occurrence, development and disappearance of vortex cavitation in the return flow inside the pump;

c). Pressure pulsation test data of vane pump:

Simultaneously collect the pressure pulsation signal flowing inside the vane pump, extract the pressure pulsation information of the pressure pulsation sensor at the monitoring points of the vane pump inlet pipe, impeller and outlet pipe, and import it into the data processing software for pressure pulsation frequency domain analysis. Fast Fourier transform is performed on the pressure pulsation signal of each monitoring point to obtain the pressure pulsation frequency domain map of each monitoring point to obtain the frequency spectrum analysis map of the cavitation flow inside the pump, and the pressure pulsation frequency domain of the pump inlet and outlet pipes and the volute is extracted, namely Extract the peak signal in the pressure pulsation spectrum diagram of the pump inlet, outlet pipe and volute; at the same time, perform cross-correlation analysis on the pressure pulsation signals collected by each two pressure pulsation sensors with the same axial position but different installation angles, and obtain the cross-correlation analysis. The relative phase is used to determine the axial and radial characteristics of various cavitation phenomena of the pump, that is, the number of rotating units and their rotation directions, and to determine whether the cavitation phenomenon is axial instability or rotational instability, so as to obtain the blade The phenomenon of flow instability inside the pump and its characteristics;

7). Adjust the working conditions and repeat steps 3)-6) until all working conditions are completed.

Further, the concrete method of the c) of described step 7) is:

First, divide the pressure pulsation signal flowing inside the vane pump according to different time periods: each series of data, the total length of which is _Tr , is divided into N intervals nd with time interval T, where _d =1,2 ,…,n _d ; the pressure pulsation signal in each interval is windowed by using the Hanning window function;

Fourier transform is performed on the data n _d in each time interval using formula (2),

In the formula, i=1, 2,..., n _d ; k=0, 1,..., (N-1); Δt is the sampling time, the unit is s; x _in is any data point collected; n _d is The number of data in equal intervals is n _d ; X _i (f _k ) is the frequency domain signal, Hz.

Considering the influence of the Hanning window function, the Fourier transform data is scaled; the frequency domain diagram of each monitoring point is obtained, the pressure pulsation frequency domain analysis is performed, and the frequency spectrum analysis diagram of the cavitation phenomenon inside the pump is obtained, thereby obtaining the pump. Spectral analysis diagram of internal cavitation flow, extracting the pressure pulsation frequency domain of pump inlet, outlet pipe and volute;

The spectrum analysis diagram of the cavitation phenomenon inside the pump obtained by Fourier transform of the signals collected by two pressure sensors at the same axial position but different installation angles is based on formula (3) for cross-correlation analysis,

In the formula, S _xy (f _k ) is the signal correlation analysis function; X _i (f _k ), Y _i (f _k ) are the pressure pulsation frequency domain signals at two different positions, Hz.

值为0°，则叶片泵内部出现了轴向流动的不稳定空化现象；If its cross-correlation phase

If the value is 0°, the unstable cavitation phenomenon of axial flow occurs inside the vane pump;

时，则叶片泵内部出现了旋转不稳定空化现象，旋转单元体数目

其中Δθ为该2个相邻的压力传感器实际安装的角度间隔。If its cross-correlation phase

When , the phenomenon of rotationally unstable cavitation occurs inside the vane pump, and the number of rotating units

where Δθ is the angular interval between the two adjacent pressure sensors actually installed.

Further, to obtain the initial and developing flow field information of cavitation in the vane pump under low flow rate, a high-speed photographic camera and a digital camera are used to photograph the front and side of the transparent plexiglass inlet section of the vane pump respectively.

Further, in c) of the step 7), the data processing software is Origin or Matlab software.

The present invention has beneficial effects

The invention gradually reduces the inlet pressure of the vane pump to cause the backflow vortex cavitation inside the pump, and at the same time describes the dynamic process of the backflow vortex cavitation inside the vane pump by means of the visualization method of the internal flow of the pump, and intuitively shows the development process of the cavitation. Better observe and master the dynamic characteristics of cavitation changes when cavitation occurs at the leading edge of the impeller blade, including the convenience of observing the inception and development of the vane pump and internal cavitation, so as to achieve the best visualization effect.

The invention evaluates the cavitation performance of the pump by synchronously collecting the performance data of the pump when cavitation occurs, calculating the cavitation margin of the pump based on the pump cavitation characteristic equation, and comparing the performance of the pump under various working conditions. Cavitation performance, judging the initial point of cavitation, and obtaining the cavitation occurrence under different cavitation coefficients.

Based on the signal acquisition program software, the present invention can collect real-time pressure pulsation signals flowing inside the pump under the condition of no cavitation and cavitation. By extracting the pressure pulsation information of the pressure pulsation sensor at the monitoring points of the inlet pipe, impeller and outlet pipe of the vane pump , so as to obtain the spectrogram of the instability phenomenon inside the pump to analyze the occurrence and characteristics of various flow instability phenomena.

By comprehensively analyzing the occurrence, development and pressure pulsation characteristics of cavitation in the backflow vortex, the relationship between the initiation and development of cavitation in the pump, the data of pump cavitation performance and the change of the pressure pulsation signal inside the pump is established, and finally based on From the experimental results, the initiation and development of cavitation in the pump, the correlation between the data of pump cavitation performance and the change of the pressure pulsation signal inside the pump are established and displayed by graphical method. This provides a simple test method for detecting whether the backflow cavitation occurs in the vane pump in the future, and provides a reference for the study of the backflow, cavitation and other flow instability caused by the vane pump under non-design conditions. It provides a basis for guiding the actual operation of the pump in engineering, so as to conduct an in-depth analysis of the performance and fault diagnosis of the vane pump, and to a large extent detect whether the pump is running stably, which not only improves the efficiency of the pump, but also plays an important role in the pump. good protection.

Description of drawings

Figure 1 is a schematic diagram of the backflow of fluid at the impeller.

FIG. 2 is a schematic structural diagram of a test device for realizing reflux vortex cavitation according to the present invention.

FIG. 3 is a schematic diagram of the connection of electronic equipment.

Figure 4 is a schematic diagram of the circuit connection between the sensor and the acquisition card.

FIG. 5 is an installation schematic diagram and a cross-sectional view of the inlet pressure pulsation sensor. Wherein, the length of the transparent plexiglass pipe is L=10D _s .

Figure 6 is a structural diagram of a visual testing system for inlet flow field testing.

FIG. 7 is a schematic diagram and a cross-sectional view of the installation of eight pressure pulsation sensors on the periphery of the volute.

Figure 8. The cavitation performance curve of the pump under small flow conditions.

Figure 9 shows the volume change of the internal cavitation of the small flow pump when cavitation occurs, where (a1) and (a2) are the cavitation coefficients of σ=2.8; (b1) and (b2) are the cavitation coefficients of σ=1.7 ; (c1), (c2) are cavitation coefficients of σ=1.1; (d1), (d2) are cavitation coefficients of σ=0.9.

Figure 10. Pressure pulsation diagram of monitoring points in the cavitation pump under low flow conditions.

In the picture:

1-water tank, 2-vane pump, 3-visualization test system, 4-pressure pulsation signal acquisition system, 5-signal processing device, 6-base, 7-transparent plexiglass inlet pipe, 8-digital camera, 9-high-speed camera , 10-first pressure pulsation sensor, 11-second pressure pulsation sensor, 12-third pressure pulsation sensor, 13-torque meter, 14-motor, 15-flange, 16-flowmeter, 17-valve, 18- Exhaust valve, 19-vacuum pump, 20-first capture card, 21-second capture card, 22-pressure divider, 23-power box, 24-computer, 25-writing desk.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

FIG. 1 is a schematic diagram of the backflow of fluid at the impeller; the device for realizing the vortex cavitation test of the backflow of the vane pump according to the present invention is shown in FIG. 2 . The vortex cavitation test device for realizing the backflow of the vane pump includes a water tank 1 , a vane pump 2 , a visual test system 3 for realizing the reproduction of the pump inlet flow field, a pressure pulsation signal acquisition system 4 and a signal processing device 5 .

The water tank 1 is fixedly installed on the ground, and the vane pump 2 is fixedly installed on the base 6 and connected to the motor 14 . The vane pump 2 and the water tank 1 are connected by a transparent plexiglass inlet pipe 7 to form a visual test system of the inlet flow field, and then other pipes connect the outlet of the vane pump 2 and the water tank 1 to form a fluid flow loop from the pump inlet to the outlet.

The visual test system 3 is composed of a transparent plexiglass inlet pipe 7, a high-speed camera 8 and a digital camera 9. The transparent plexiglass inlet pipe 7 is used to connect the vane pump 2 and the water tank 1, and the high-speed camera 8 and the digital camera 9 are respectively installed. On the front and side of the inlet section of the transparent plexiglass inlet pipe 7, as shown in Figure 6. The outlet of the vane pump 2 is connected with the water tank 1 through a pipeline to form a circuit, and a flange 15 is connected between the outlet pipelines. The outlet of the vane pump 2 and the pipeline of the water tank 1 are provided with a flow meter 16 and a valve 17;

As shown in FIG. 4 , the pressure pulsation signal acquisition system 4 includes a first pressure pulsation sensor 10 installed at the pump inlet, a second pressure pulsation sensor 11 installed at the outlet, and a second pressure pulsation sensor 11 installed along the circumferential direction of the volute flow channel of the vane pump 2 The 8 pressure pulsation sensors 12; the circumferential uniform distribution of the 8 third pressure pulsation sensors 12 inside the vane pump is shown in FIG. 7 . The first pressure pulsation sensor 10 at the inlet and the second pressure pulsation sensor 11 at the outlet are respectively installed directly above the transparent plexiglass inlet pipe 7 at a distance of 1*D _s from the impeller inlet and at a distance of 2*D _s from the outlet pipe, As shown in Figure 5.

As shown in Figure 3, the signal processing device 5 is composed of a first acquisition card 20, a second acquisition card 21, a voltage divider 22, a power supply box 23 and a computer 24 equipped with signal acquisition and data processing software. The first acquisition card 20. The second capture card 21 is connected to the power supply box 23 through wires and a voltage divider to obtain power. The first acquisition card 20 is connected to the first pressure pulsation sensor 10 at the pump inlet and the second pressure pulsation sensor 11 at the pump outlet. The third pressure pulsation sensor 12 is connected, and the first acquisition card 20 and the second acquisition card 21 are both connected to the computer 24 equipped with signal acquisition and data processing software; input the collected pressure pulsation information into a computer equipped with signal acquisition and data processing software The computer of the software can obtain the pressure pulsation data flowing inside the pump by using the signal acquisition program, and import it into data processing software such as Origin or Matlab software, and perform fast Fourier transform on the pressure pulsation signal of each monitoring point to obtain each The frequency domain diagram of the monitoring point is used to analyze the pressure pulsation frequency domain. Combined with the occurrence, development and changes of the pump inlet pipe and its internal cavitation in the visualization, combined with the analysis results of the internal pressure pulsation of the pump, the dynamic characteristics of the backflow and the backflow vortex cavitation of the vane pump can be obtained, and the corresponding backflow vortex cavitation can be obtained by calculation. The cavitation margin NPSHA value or the cavitation coefficient σ, and at the same time, the phase intersection and correlation analysis are carried out for the pressure pulsation signals of the monitoring points at different positions, and the above analysis results are combined to determine the critical work for the occurrence of reflux and reflux vortex cavitation. The axial and radial characteristics of backflow and backflow vortex cavitation and the number of unstable flow elements are obtained. Therefore, it provides a basis for judging whether the backflow vortex cavitation occurs inside the pump in the future and for preventing the backflow vortex cavitation from occurring in the pump under low flow conditions.

The principle of the test method of the present invention is as follows: taking clean water as an example here, when the vane pump operates under the design condition of small flow rate, the water is drawn out from the water tank, flows through the transparent plexiglass tube and enters the suction chamber, and an inlet pressure is generated at the inlet at this time. , enter the impeller; at the same time, part of the clean water will flow back from the impeller outlet to the pump inlet pipe, resulting in a backflow, and the fluid backflow condition in the pipe can be observed initially; the pressure in the inlet pipe will deviate and hinder the flow of the main flow of the inlet, and the pressure in the backflow center is reduced to the level of the fluid. When the saturated vaporization pressure of the medium at this temperature reaches the cavitation occurrence condition, that is, the cavitation coefficient σ reaches σ≈σ _head-drop , at this time, reflux vortex cavitation occurs in the impeller.

p ₁ is the static pressure at the impeller inlet, p _v is the saturated vapor pressure of clean water; U is the peripheral speed at the impeller inlet.

The experimental test process to realize the reflux vortex cavitation:

The backflow vortex cavitation performance test of the vane pump is realized by the unsteady test method of continuously reducing the inlet pressure of the vane pump, and the experimental results obtained during the test time are divided equally. During each backflow vortex cavitation experiment of the vane pump, the flow rate in the circuit of the whole experimental device was kept constant. When the inlet pressure gradually decreases and falls to a certain value, cavitation is born and develops continuously. The front and side surfaces of the transparent plexiglass inlet section of the vane pump are photographed by a combination of high-speed photographic camera and digital camera. Based on the signal acquisition program, the cavitation performance data of the vane pump without and when the backflow vortex cavitation occurs can be obtained, and the data when the backflow vortex of the vane pump occurs can be obtained when a series of head drops occur. The specific experimental steps are as follows:

1) Complete the installation of the reflux vortex cavitation test device;

2) Turn on the power of the pump cavitation experiment test system, start the motor, and make the vane pump impeller gradually reach the required speed of the experiment; start the computer equipped with the signal acquisition and data processing software; perform sensor offset acquisition before starting.

3) By adjusting the valve 17 in the pump outlet pipeline, set the flow value for the pump cavitation performance test to a small flow condition; in each flow condition test, by continuously adjusting the valve 17 in the outlet pipeline, In order to keep the flow value constant throughout the reflux vortex cavitation experiment.

4) Adjust the inlet pressure information of the water tank by starting the vacuum pump to change the inlet pressure of the vane pump, so that cavitation does not occur inside the vacuum pump; collect the corresponding cavitation flow field distribution and pressure pulsation information when cavitation occurs inside the pump at this time , at this time, it is used as the state that cavitation does not occur inside the detection pump.

5) The vacuum pump is used to gradually depressurize the pump inlet, and the inlet pressure of the vane pump is set, so that the backflow vortex cavitation gradually occurs inside it.

6) Under the condition of constant inlet pressure or constant cavitation coefficient, obtain the cavitation test information of the vane pump synchronously collected by the pressure pulsation sensor, high-speed camera and digital camera when the vane pump occurs cavitation. The pressure pulsation signal data when the pump is pumped, and the inlet and outlet pressure values when the pump is cavitated are collected synchronously to obtain the pump cavitation performance data through formula calculation, such as the corresponding cavitation allowance NPSHA or cavitation coefficient σ value when a series of pump head drops. ; and the frequency characteristics of various cavitation phenomena in the vane pump and the axial and radial characteristics of various cavitation phenomena.

specific:

a). Calculate the cavitation performance data of the vane pump:

By gradually reducing the inlet pressure p ₁ of the centrifugal pump, the effective NPSHA _NPSHA is decreased until cavitation occurs; The cavitation margin of the pump is indirectly calculated from the characteristic equation of the pump, and the primary cavitation performance point of the pump is determined to evaluate the cavitation performance of the pump; different NPSHA values correspond to different head H values, and finally a series of head H are obtained for calculating cavitation. The cavitation performance curve of the pump can be obtained, and the cavitation performance of the pump under each working condition can be compared to judge the initial point of cavitation.

b) Visualization data of the cavitation flow field of the vane pump:

A high-speed photographic camera and a digital camera were used to photograph the front and side of the transparent plexiglass inlet section of the vane pump, respectively, to obtain the process of the occurrence, development and disappearance of the vortex cavitation in the internal inlet of the pump.

c). Pressure pulsation test data of vane pump:

Simultaneously collect the pressure pulsation signal flowing inside the vane pump, extract the pressure pulsation information of the pressure pulsation sensor at the monitoring points of the vane pump inlet pipe, impeller and outlet pipe, and import it into the data processing software for pressure pulsation frequency domain analysis. Fast Fourier transform is performed on the pressure pulsation signal of each monitoring point to obtain the pressure pulsation frequency domain map of each monitoring point to obtain the frequency spectrum analysis map of the cavitation flow inside the pump, and the pressure pulsation frequency domain of the pump inlet and outlet pipes and the volute is extracted, namely Extract the peak signal in the pressure pulsation spectrum diagram of the pump inlet, outlet pipe and volute; at the same time, perform cross-correlation analysis on the pressure pulsation signals collected by each two pressure pulsation sensors with the same axial position but different installation angles, and obtain the cross-correlation analysis. The relative phase is used to determine the axial and radial characteristics of various cavitation phenomena of the pump, that is, the number of rotating units and their rotation directions, and to determine whether the cavitation phenomenon is axial instability or rotational instability, so as to obtain the blade Flow instabilities inside the pump and their characteristics.

First, divide the pressure pulsation signal flowing inside the vane pump according to different time periods: each series of data, the total length of which is _Tr , is divided into N intervals nd with time interval T, where _d =1,2 ,…,n _d ; the pressure pulsation signal in each interval is windowed by using the Hanning window function;

Fourier transform is performed on the data n _d in each time interval using formula (2),

In the formula, i=1, 2,..., n _d ; k=0, 1,..., (N-1); Δt is the sampling time, the unit is s; x _in is any data point collected; n _d is The number of data in equal intervals is n _d ; X _i (f _k ) is the frequency domain signal, Hz.

Considering the influence of the Hanning window function, the Fourier transform data is scaled; the frequency domain diagram of each monitoring point is obtained, the pressure pulsation frequency domain analysis is performed, and the frequency spectrum analysis diagram of the cavitation phenomenon inside the pump is obtained, thereby obtaining the pump. Spectral analysis diagram of internal cavitation flow, extracting the pressure pulsation frequency domain of pump inlet, outlet pipe and volute;

The spectrum analysis diagram of the cavitation phenomenon inside the pump obtained by Fourier transform of the signals collected by two adjacent pressure pulsation sensors is based on formula (3) for cross-correlation analysis,

In the formula, S _xy (f _k ) is the signal correlation analysis function; X _i (f _k ), Y _i (f _k ) are the pressure pulsation frequency domain signals at two different positions, Hz.

值为0°，则叶片泵内部出现了轴向流动的不稳定空化现象；If its cross-correlation phase

If the value is 0°, the unstable cavitation phenomenon of axial flow occurs inside the vane pump;

时，则叶片泵内部出现了旋转不稳定空化现象，旋转单元体数目

其中Δθ为该2个相邻的压力传感器实际安装的角度间隔。If its cross-correlation phase

When , the phenomenon of rotationally unstable cavitation occurs inside the vane pump, and the number of rotating units

where Δθ is the angular interval between the two adjacent pressure sensors actually installed.

Adjust the working conditions and repeat steps 2) to 6) until the experiments of all working conditions are completed.

During the unsteady test process of the entire return vortex cavitation performance of the vane pump, the pressure reduction at the inlet should be kept constant. The acquired experimental data were equally divided into quasi-steady-state time periods to keep the inlet pressure nearly constant. The time period of the average interval must be long enough to ensure that the amount of collected data is not scattered, and the superposition of the experimental data in this time interval can make the whole continuous reflux vortex cavitation test result better.

In the cavitation experiment, the effective NPSHA NPSHA is reduced by gradually reducing the inlet pressure p ₁ of the centrifugal pump until cavitation occurs; ) ₃ , indirectly calculate the cavitation margin of the pump (NPSHR) ₃ measure the primary cavitation performance point of the pump. Different NPSHA values correspond to different head H values, and finally a series of head H can be obtained, which can be used to calculate the head drop value caused by the development of cavitation, and then draw the curve of the change of head with the cavitation allowance, and then the cavitation of the pump can be obtained. The performance curve is shown in Figure 9. Table 1 shows the volume change of the internal cavitation and its corresponding cavitation coefficient when cavitation occurs in the small flow pump.

Table 1 Reference table of internal flow field of cavitation pump and its cavitation coefficient at small flow rate

The internal flow field of the cavitation pump corresponding to the cavitation coefficient shown in Table 1 is shown in Figure 10, which shows the change of the internal cavitation volume of the small flow pump when cavitation occurs, where (a1) and (a2) are the cavitation coefficients σ. = 2.8; (b1), (b2) are cavitation coefficients of σ=1.7; (c1), (c2) are cavitation coefficients of σ=1.1; (d1), (d2) are cavitation coefficients of σ=0.9 .

It can be seen from Table 1 that as the cavitation inside the pump develops to become more and more serious, the cavitation of the inlet reflux vortex will appear, develop and disappear. That is, with the gradual decrease of the cavitation coefficient, the cavitation inside the impeller has been fully developed, and the cavitation volume almost occupies a single blade flow channel. At this time, the fluid returning from the impeller to the inlet pipe decreases, the inlet return gradually weakens, and the inlet returns. The phenomenon is not obvious or even disappears. At the same time, the cavitation phenomenon of the inlet reflux vortex disappears, and there is no more cavitation in the inlet pipe. By combining the numerical calculation or test results of the visualization of the internal flow field of the pump, the cavitation margin or cavitation coefficient of the pump is calculated based on the pump cavitation characteristic equation to evaluate the cavitation performance of the pump, and compare the cavitation performance, Determine the initial point of cavitation, establish the relationship between the initial and developing cavitation volume distribution in the pump and the pump performance data, and provide the basis for the next cavitation pressure pulsation test.

In order to obtain the dynamic characteristics of the cavitation change caused by the return vortex cavitation of the vane pump, combined with the occurrence and development process of the inlet return vortex cavitation phenomenon, an inlet pressure sensor is installed at the pipeline 1*D _s away from the inlet, and the pipeline is transparent organic. The glass pipe is shown in Figure 5; at the same time, the front and side surfaces of the plexiglass inlet section of the vane pump are photographed by a combination of high-speed camera and digital camera, so as to better observe the inlet return state as shown in Figure 6; Eight pressure pulsation sensors are installed on the circumference of the volute surface, and a pressure pulsation sensor is installed every 45°, as shown in Figure 7. Simultaneously collect the pressure pulsation signal flowing inside the pump, and obtain the spectrum analysis diagram of the cavitation flow inside the pump by extracting the pressure pulsation information of the pressure pulsation sensor at the monitoring points of the inlet pipe, impeller and outlet pipe of the vane pump. At the same time, the signals of the pressure pulsation sensors at two adjacent positions, that is, the main frequency, are analyzed for phase crossover, so as to analyze the flow instability phenomenon and its characteristics inside the pump under the small flow condition.

值均为0°，可认为泵内部出现与该频率对应的轴向流动现象；频率f₂交叉相位

值几乎均呈现线性关系，可认为泵内部出现了与该范围频率相对应的旋转不稳定流动现象。根据两个传感器之间的安装相位差Δθ＝45°及该两个传感器采集的压力脉动信号的频谱作交叉相关性分析后所得到的交叉相位

泵中出现与频率f₂＝125Hz相对应的旋转不稳定流动现象中，存在3个旋转单元体，且其真实频率为该压力脉动监测点频率的1/3，而与频率f₁＝1.465Hz相对应的轴流不稳定流动现象具有低频特征，这也说明，小流量下泵内部轴向不稳定流动现象具有低频特征。为泵内部发生回流漩涡空化时的频率特性。Figures 10(a1) and (a2) are the pressure pulsation frequency domain diagrams of the internal monitoring points of the pump under small flow conditions. The main frequencies of the pressure pulsation at the monitoring points inside the pump are both f ₁ =1.465Hz and f ₂ =125Hz. Similarly, for the signals of every two pressure pulsation monitoring points, the phase cross-correlation analysis of the main frequencies is carried out, and the results are shown in Figure 10 (b1 ), (b2), it is obvious from this figure that the cross-phase of frequency f ₁

The value is 0°, it can be considered that the axial flow phenomenon corresponding to this frequency occurs inside the pump; the frequency f ₂ crosses the phase

The values are almost linear, and it can be considered that there is a rotationally unstable flow phenomenon inside the pump corresponding to the frequency in this range. According to the installation phase difference Δθ=45° between the two sensors and the frequency spectrum of the pressure pulsation signal collected by the two sensors, the cross-phase obtained by cross-correlation analysis

In the rotationally unstable flow phenomenon corresponding to the frequency f ₂ =125Hz in the pump, there are 3 rotating units, and the real frequency is 1/3 of the frequency of the pressure pulsation monitoring point, and the frequency f ₁ =1.465Hz The corresponding unstable flow phenomenon of axial flow has low frequency characteristics, which also shows that the phenomenon of axial unstable flow inside the pump at small flow rate has low frequency characteristics. It is the frequency characteristic when backflow vortex cavitation occurs inside the pump.

The embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or All modifications belong to the protection scope of the present invention.

Claims (7)

1. A device for realizing vortex cavitation of backflow of a vane pump is characterized by comprising a water tank (1), the vane pump (2), a visual test system (3) for realizing the reappearance of a pump inlet flow field, a pressure pulsation signal acquisition system (4) and a signal processing device (5);

the visual testing system (3) consists of a transparent organic glass inlet pipe (7), a high-speed camera (8) and a digital camera (9), the transparent organic glass inlet pipe (7) is used for connecting the vane pump (2) and the water tank (1), and the high-speed camera (8) and the digital camera (9) are respectively arranged on the front side and the side surface of an inlet section of the transparent organic glass inlet pipe (7); the outlet of the vane pump (2) is connected with the water tank (1) through a pipeline to form a loop, and a flowmeter (16) and a valve (17) are arranged on the outlet of the vane pump (2) and the pipeline of the water tank (1); the water tank (1) is also connected with a vacuum pump (19), and an exhaust valve (18) is also arranged on a pipeline between the vacuum pump (19) and the water tank (1);

the pressure pulsation signal acquisition system (4) comprises a pump inlet and a pump outlet which are arranged on the vane pump (2), and a plurality of pressure pulsation sensors (10, 11, 12) which are arranged along the circumferential direction of a volute flow channel of the vane pump (2); the pressure pulsation sensor (10) at the pump inlet and the pressure pulsation sensor (11) at the pump outlet are respectively arrangedMounted at a distance 1 x D from the impeller inlet_sRight above and at a distance 2 x D from the transparent plexiglass inlet tube (7) of the device_sAt least one of (1) and (b);

the signal processing device (5) is composed of a first acquisition card (20), a second acquisition card (21), a partial pressure plate (22), a power box (23) and a computer (24) filled with signal acquisition and data processing software, wherein the first acquisition card (20) is connected with a pump inlet pressure sensor (10) and an outlet pressure sensor (11), the second acquisition card (21) is connected with a plurality of pressure pulsation sensors (12), the first acquisition card (20) and the second acquisition card (21) are connected to the computer (24) filled with the signal acquisition and data processing software, and the first acquisition card (20) and the second acquisition card (21) are connected with the power box (23) through the partial pressure plate (22).

2. The device for testing vortex cavitation for realizing backflow of the vane pump according to claim 1, is characterized in that: the plurality of pressure pulsation sensors (12) are uniformly distributed in the circumferential direction inside the vane pump.

3. The device for testing vortex cavitation for realizing backflow of the vane pump according to claim 1, is characterized in that: the number of the pressure pulsation sensors (12) is 8.

4. The testing method for realizing the return flow vortex cavitation testing device of the vane pump as claimed in claim 1, is characterized by comprising the following steps:

1) completing the installation of the backflow vortex cavitation test device;

2) starting a power supply, starting the vane pump and enabling the rotating speed of the vane pump to reach the required testing rotating speed; starting a computer, and carrying out sensor offset acquisition before starting the computer;

3) setting the flow value for carrying out pump cavitation performance test as a low-flow working condition by adjusting a valve (17) in a pump outlet pipeline; in each flow working condition test, a valve (17) in the outlet pipeline is continuously adjusted so as to keep the flow value constant in the whole backflow vortex cavitation experiment;

4) regulating the pressure at the inlet of the water tank by starting the vacuum pump to change the pressure at the inlet of the vane pump, so that the inside of the vacuum pump is not cavitated; collecting corresponding cavity flow field distribution and pressure pulsation information thereof when the cavity in the vane pump occurs at the moment, and detecting the state that the cavity in the vane pump does not occur at the moment;

5) gradually reducing the pump inlet pressure of the vane pump through the vacuum pump, and setting the inlet pressure of the vane pump so as to gradually generate backflow vortex cavitation in the vane pump;

6) under the condition of constant inlet pressure or constant cavitation coefficient, acquiring cavitation test information of the vane pump synchronously acquired by a pressure pulsation sensor, a high-speed photography camera and a digital camera when the vane pump is cavitated in real time, and processing the following data:

a) calculating cavitation performance data of the vane pump:

by stepwise reduction of the inlet pressure p of the centrifugal pump₁Thereby reducing the effective cavitation margin NPSHA until cavitation occurs; the cavitation starts from the initial state, and the initial stage of cavitation is referred to as NPSHA (NPSHR)₃Indirectly calculating the cavitation allowance of the pump based on a pump cavitation characteristic equation to determine the initial cavitation performance point of the pump, and evaluating the pump cavitation performance; different NPSHA values correspond to different lift H values, a series of lift H are finally obtained and used for calculating a lift drop value caused by cavitation development, a curve of the lift changing along with cavitation allowance is further drawn, a cavitation performance curve of the pump can be obtained, the cavitation performance of the pump under various working conditions is compared, and a cavitation initial point is judged;

b) visual data of the cavitation flow field of the vane pump:

acquiring the process that the backflow vortex cavitation at the inlet of the pump occurs, develops and disappears;

c) vane pump pressure pulsation test data:

synchronously collecting pressure pulsation signals flowing inside the vane pump, introducing the pressure pulsation signals of pressure pulsation sensors at monitoring points of an inlet pipe, an impeller and an outlet pipe of the vane pump into data processing software for pressure pulsation frequency domain analysis by extracting the pressure pulsation information of the pressure pulsation sensors at the monitoring points, obtaining a pressure pulsation frequency domain diagram of each monitoring point by performing fast Fourier transform on the pressure pulsation signals of each monitoring point so as to obtain a frequency spectrum analysis diagram of cavitation flow inside the pump, and extracting pressure pulsation frequency domains of the inlet pipe, the outlet pipe and the volute, namely extracting peak signals in the pressure pulsation frequency domain diagrams of the inlet pipe, the outlet pipe and the volute; meanwhile, performing cross correlation analysis on pressure pulsation signals acquired by 2 pressure pulsation sensors which are the same in axial position but different in installation angle to acquire cross correlation phases of the pressure pulsation signals, determining the axial and radial characteristics of various cavitation phenomena of the pump, namely the number and the rotation direction of the rotating unit bodies, and judging whether the cavitation phenomena are axial instability phenomena or rotation instability phenomena so as to acquire the flow instability phenomena and the characteristics of the interior of the vane pump;

7) adjusting the working conditions, and repeating the steps 3) -6) until all the working conditions are finished.

5. The test method as claimed in claim 4, wherein the specific method of c) of step 7) is:

firstly, dividing pressure pulsation signals flowing inside the vane pump according to different time periods: each series of data having a total length of T_rDivided into N time intervals of T_dWhere d is 1,2, …, n_d(ii) a Windowing the pressure pulsation signal of each interval by adopting a Hanning window function;

for data n in each time interval_dThe fourier transform is performed using equation (2),

wherein i is 1,2, …, n_d(ii) a k is 0, 1, …, (N-1); Δ t is the sampling time in units of s; x is the number of_inAny collected data point; n is_dThe number of data in equal interval is n_d；X_i(f_k) Is a frequency domain signal, Hz.

Taking the influence of a Hanning window function into consideration, and carrying out scale conversion on the data subjected to Fourier transform; obtaining a frequency domain diagram of each monitoring point, carrying out pressure pulsation frequency domain analysis, thus obtaining a frequency spectrum analysis diagram of the cavitation flow in the pump, and extracting pressure pulsation frequency domains of the inlet pipe, the outlet pipe and the volute of the pump;

the cross correlation analysis is carried out on a frequency spectrum analysis chart of the pump internal cavitation phenomenon obtained by carrying out Fourier transform on signals collected by 2 pressure sensors at the same axial position but different installation angles based on a formula (3),

in the formula, S_xy(f_k) Analyzing a function for signal correlation; x_i(f_k)，Y_i(f_k) Is the pressure pulsation frequency domain signal at 2 different locations, Hz.

If it is cross-correlated in phase

The value is 0 degrees, and the unstable cavitation phenomenon of axial flow occurs in the vane pump;

if it is cross-correlated in phase

When the pump is in operation, the phenomenon of unstable cavitation appears in the vane pump, and the number of the rotating unit bodies

Where Δ θ is the angular interval at which the 2 adjacent pressure sensors are actually mounted.

6. The testing method of claim 4, wherein the obtaining of the initial and developed flow field information of cavitation in the vane pump at low flow rate is performed by photographing the front and side surfaces of the transparent organic glass inlet section of the vane pump with a high-speed camera and a digital camera, respectively.

7. The test method of claim 4, wherein in step 7) c), the data processing software is Origin or Matlab software.

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