GB2590289A

GB2590289A - Vane pump cavitation determination and state evaluation methos and system

Info

Publication number: GB2590289A
Application number: GB2101247.1A
Authority: GB
Inventors: Dong Liang; Zhao Yuqi; Liu Houlin; Pan Qi; Dai Cui; Tan Minggao; Wang Yong; Wang Kai; Wu Xianfang
Original assignee: Jiangsu University
Current assignee: Jiangsu University
Priority date: 2018-07-31
Filing date: 2018-08-10
Publication date: 2021-06-23
Anticipated expiration: 2038-08-10
Also published as: CN109190166A; GB202101247D0; WO2020024325A1; GB2590289B; CN109190166B

Abstract

A vane pump cavitation determination and state evaluation method and system, the method comprising the following steps: collecting water pump inlet and outlet pressure, liquid-borne noise, solid-borne vibration, and flow data, and selecting a cavitation determination mode on the basis of the flow condition; in a constant flow condition, determining a solid-borne vibration and liquid-borne noise cavitation signal total value threshold by means of an experiment method, thereby proposing a cavitation determination method using a total value method, having higher reliability and precision than a traditional cavitation determination method; in a variable flow condition, acquiring a frequency range with high sensitivity to cavitation, determining a cavitation frequency band value threshold, and using a frequency band broadband value method to implement cavitation determination. The evaluation method and system have the advantages of strong anti-interference, high reliability, accurate evaluation criteria, high cavitation sensitivity, strong applicability, and convenient operation, and can effectively improve the reliability of pump operation, reduce the damage caused to the pump by cavitation, and increase the working life of the pump.

Description

METHOD FOR DETERMINATION OF CAVITATION AND EVALUATION

OF CAVITATION STATUS IN VANE PUMP AND SYSTEM THEREFOR

Technical Field

The present invention relates to the field of pump cavitation research, and in particular to a method for determination of cavitation and evaluation of cavitation status in a vane pump and a system therefor.

Background

Pumps are a general-purpose machine, mainly used to convert mechanical energy from a prime mover into energy of a liquid, and have a wide range of types, and are widely used in various fields of the national economy, such as drainage and irrigation, petrochemical industry, aerospace, fire safety, and hydraulic engineering. It can be said that wherever there is liquid flowing, there is a pump working. However, although pumps are a well-established and general-purpose machine, they suffer from the problem of cavitation, which has become one of the main factors limiting their development. The occurrence of cavitation not only causes the hydraulic performance of the pump to decline, but also causes cavitation erosion to flow-through components, which will affect the stability and reliability of the pump operation. Conventional maintenance is either post-accident maintenance or scheduled maintenance. In some special occasions, operation continued after occurrence of cavitation will severely impair the safety of the equipment, and regular maintenance wastes a lot of manpower and material resources, and also increases costs for assembly and disassembly. Therefore, it is very necessary to determine the pump cavitation status.

Cavitation fault has always been one of the difficult problems in pumps. During operation of a pump, when the pressure in a local region of a flow-through component drops below the current saturated vapor pressure of the medium at the corresponding temperature, cavitation will occur. At present, no practical and effective detection and diagnosis techniques have been proposed that can realize online diagnosis of inception of a pump cavitation fault, which is typically only determined by operators based on their own experience or through parameters displayed on supplementary instruments, leading to inaccurate results, low sensitivity, and cumbersome operations. The searched patents related to the present invention include Chinese Patent Publication No. CN 202402268 U entitled DEVICE FOR DIAGNOSING CAVITATION FAULT OF WATER PUMP BASED ON ACOUSTIC EMISSION DETECTION, in which cavitation status of a water pump is monitored using acoustic emission technology and cavitation degree is determined by constructing a 5-dimensional vector of 5 different frequency bands; and Chinese Patent Publication No, CN 105240187 A entitled METHOD FOR REALIZING STATUS MONITORING AND FAULT DIAGNOSIS IN HYDRAULIC TURBINE BASED ON CHAOS THEORY, in which wavelet transform is used for noise reduction of pressure pulsation signals and cavitation degree in operation of a hydraulic turbine is detennined using chaotic dynamics Current methods for determining pump cavitation have the following problems and drawbacks: determination of cavitation and evaluation of cavitation status are not performed in different modes according to the occurrence of cavitation under different working conditions, therefore cavitation statuses are not distinguished clearly, the evaluation criteria are single, and the reliability is low, leading to poor accuracy and sensitivity in the determination of cavitation.

Summary

In view of the problems mentioned above, it is an object of the present invention to provide a method for determination of cavitation and evaluation of cavitation status in a vane pump and a system therefor. In this method, flow rate, inlet pressure and outlet pressure, liquid-borne noise signal and solid-borne vibration signal during operation of the pump are acquired in real time by a high-performance data acquisition system, to determine cavitation and evaluate cavitation status in different modes according to the occurrence of cavitation under different working conditions. The present invention has the advantages such as high anti-interference, high reliability, accurate evaluation criteria, high sensitivity to cavitation, good applicability, and convenient operation, and can effectively improve the reliability of pump operation, reduce the damage to the pump by cavitation, and prolong the service life of the pump.

The technical solution of the present invention includes a method for determination of cavitation and evaluation of cavitation status in a vane pump, characterized by including the following steps: Step S I. data acquisition: acquiring inlet pressure and outlet pressure, liquid-borne noise, solid-borne vibration, and flow rate data in a water pump; Step S2. selection of a mode for determination of cavitation based on a flow condition: under a constant flow condition where a change rate of flow rate, AO, is less than x, performing the determination of cavitation using a change rate of overall sound pressure level and proceeding with Step S3; and under a variable flow condition where the change rate of flow rate, AO, is greater than or equal to x, performing the determination of cavitation using a frequency range broadband level value and proceeding with Step S4; Step S3. determination of cavitation under the constant flow condition: when a change rate of overall sound pressure level of liquid-borne noise, AL, is greater than y, starting cavitation alarm and proceeding with evaluation of cavitation status under the constant flow condition, and proceeding with Step S5, wherein the change rate of overall sound pressure level, AL, is calculated by the following calculation formula: AL= (L0-40) /Lo in the formula, L", is an overall sound pressure level of liquid-borne noise in the i-th sampling time and is calculated by the following calculation formula: LP = 101og if- (Pa / V1)2 -10 log * ( p I VI) ' Af in the formula, Afi is a spectral resolution, fmin and juax are a lower limit and an upper limit of an acquisition frequency, respectively, p, and pa are effective sound pressures measured in pa, and po is a reference sound pressure in water which takes a value of p0=10-6 pa. In the formula, the reference benchmark sound pressure level Lo is calculated by the following calculation formula: Lpo = (Lpt+Lp2+Lp3),3 in the formula, f,pt, [p2 and [p3 are overall sound pressure levels of the first three sets of liquid-borne noise during non-cavitation. Through multiple sets of experiments and CFD numerical calculations, it is concluded that the experimental data obtained in the first three sets of sampling time is relatively stable. Therefore, it is more accurate to select an average value of the overall sound pressure levels of the first three sets of liquid-borne noise as the reference benchmark sound pressure level; Step S4. determination of cavitation under the variable flow condition: when a change rate of broadband sound pressure level of liquid-borne noise in a predetermined frequency band, AFL, and a change rate of broadband vibration level of solid-borne vibration in a predetermined frequency band, AFv, are both greater than s, starting cavitation alarm and proceeding with evaluation of cavitation status under the variable flow condition, and proceeding with Step SG, wherein a broadband level value I,' is calculated by the following calculation formula: f (x)P, .f (x)P 0 - n [* ]/-v2)2 =101g 2 Af yo in the formula,fix) is a filter function, FL0 and Pro are calculated by the following calculation formulas: FLO-(FL1+FL2+FL3) /3 Fvo= (Fvi+fiv2+Fv3) /3 FL1, FL2 and FL3 are average broadband sound pressure levels of the first three sets of liquid-borne noise acquired before head change in a predetermined frequency range, and Fvi, PV, and FV3 are average broadband vibration levels of the first three sets of solid-borne vibration acquired before head change in a predetermined frequency range, AFL and AFT-are calculated by the following calculation formulas:

SEFL-FLU

-x100%

FLU

-Fl o - x100% F;-o in the formula, PIA is an average broadband sound pressure level of liquid-borne noise in a predetermined frequency range in the i-th sampling time, Evi is an average broadband vibration level of solid-borne vibration in a predetermined frequency range in the i-th sampling time, AFL is the change rate of broadband sound pressure level of liquid-borne noise in a predetermined frequency band, and AFv is the change rate of broadband vibration level of solid-borne vibration in a predetermined frequency band; Step S5. evaluation of cavitation status under the constant flow condition: when the change rate of overall sound pressure level of liquid-borne noise, AL, is less than y, evaluating the cavitation status as a non-cavitation status; when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than y, and a change rate of head, AFT, is less than z, evaluating the cavitation status as a cavitation inception status when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than y, the change rate of head, ALL is greater than z, and a continuous change rate of overall vibration level of solid-borne vibration, AP, is positive, evaluating the cavitation status as a severe cavitation status; and when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than y, the change rate of head, AH, is greater than z, and the continuous change rate of overall vibration level of solid-borne vibration, A is negative, evaluating the cavitation status as an excessively severe cavitation status; and Step S6. evaluation of cavitation status under the variable flow condition: when the change rate of broadband sound pressure level of liquid-borne noise in a predetermined frequency band, A FL, and the change rate of broadband vibration level of solid-borne vibration in a predetermined frequency band, Ah'v. are both less than s, evaluating the cavitation status as a non-cavitation status; when the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, Ativ, are both greater than s and the change rate of head, AH, is less than z, evaluating the cavitation status as a cavitation inception status when the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, APV, are both greater than s, the change rate of head, AR, is greater than z, and a continuous change rate of broadband vibration level of solid-borne vibration, AFV, is positive, evaluating the cavitation status as a severe cavitation status; and when the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, AE, are both greater than s, the change rate of head, An, is greater than z, and the continuous change rate of broadband vibration level of solid-borne vibration, APV, is negative, evaluating the cavitation status as an excessively severe cavitation status.

In the solution described above, the x is 10% in the Step S2.

Under the constant flow condition where the change rate of flow rate, AQ, is less than 10%, the determination of cavitation is performed using the change rate of overall sound pressure level, and under the variable flow condition where the change rate of flow rate, AO, is greater than or equal to 10%, the determination of cavitation is performed using the frequency range broadband level value.

In the solution described above, they is 0.5% in the Step S3. When the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, the cavitation alarm is started and the evaluation of cavitation status under the constant flow condition proceeds.

In the solution described above, the broadband sound pressure level of liquid-borne noise is 2000 to 3000 Hz, and the broadband vibration level of solid-borne vibration is 10 to 50 Hz in the Step 54.

In the solution described above, the s is 1% in the Step S4.

When the change rate of broadband sound pressure level of liquid-borne noise in a frequency band of 2000 to 3000 Hz, AEL, and the change rate of broadband vibration level of solid-borne vibration in a frequency band of 10 to 50 Hz, AFv, are both greater than 1%, the cavitation alarm is started and the evaluation of cavitation status under the variable flow condition proceeds.

In the solution described above, in the Step S5, when the change rate of overall sound pressure level of liquid-borne noise, AL, is less than 0.5%, the cavitation status is evaluated as the non-cavitation status; when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, and the change rate of head, Aft, is less than 3%, the cavitation status is evaluated as the cavitation inception status; when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, the change rate of head, AK, is greater than 3%, and the continuous change rate of overall vibration level of solid-borne vibration, AV', is positive, the cavitation status is evaluated as the severe cavitation status; and when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, the change rate of head, AK, is greater than 3%, and the continuous change rate of overall vibration level of solid-borne vibration, AV', is negative, the cavitation status is evaluated as the excessively severe cavitation status.

In the solution described above, in the Step S6, when the change rate of broadband sound pressure level of liquid-borne noise in the frequency band of 2000 to 3000 Hz, AFL, and the change rate of broadband vibration level of solid-borne vibration in the frequency band of 10 to 50 Hz, AFv, are both less than 1%, the cavitation status is evaluated as the non-cavitation status; when the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, Afiv, are both greater than 1%, and the change rate of head, AK, is less than 3%, the cavitation status is evaluated as the cavitation inception status; when the change rate of broadband sound pressure level of liquid-borne noise, A FL, and the change rate of broadband vibration level of solid-borne vibration, AFv,are both greater than 1%, the change rate of head, AK, is greater than 3%, and the continuous change rate of broadband vibration level of solid-borne vibration, AFv', is positive, the cavitation status is evaluated as the severe cavitation status; and when the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, AFv, are both greater than 1%, the change rate of head, AK, is greater than 3%, and the continuous change rate of broadband vibration level of solid-borne vibration, AFv', is negative, the cavitation status is evaluated as the excessively severe cavitation status.

A system for implementing the method for determination of cavitation and evaluation of cavitation status in a vane pump, including a data acquisition unit, a data processing unit, a cavitation alarm unit, and a display unit.

The data acquisition unit includes a flowmeter, a pressure transducer, a hydrophone, a vibration acceleration sensor and a camera device. The flowmeter is configured to acquire a flow signal. The pressure transducer is configured to acquire pump inlet pressure and outlet pressure signals. The hydrophone is configured to acquire a liquid-borne noise signal. The vibration acceleration sensor is configured to acquire a solid-borne vibration signal. The camera device is configured to acquire a cavitation bubble pattern signal at an impeller inlet The data acquisition unit is connected to the data processing unit and transfers the acquired signal to the data processing unit. The data processing unit, based on the signal from the data acquisition unit, determines a flow condition and selects different modes for determination of cavitation based on the flow condition. When cavitation occurs, the cavitation alarm unit initiates an alarm and feeds the signal back to the data processing unit to proceed with evaluation of cavitation status.

The display unit is connected to the data acquisition unit, the data processing unit and the cavitation alarm unit and is configured to display data.

Compared with the prior art, the present invention has the following beneficial effects.

1. According to the present invention, the pump head, flow rate, solid-borne vibration and liquid-borne noise signals resulting from the test for the point corresponding to each cavitation number are compared with the high-speed photography results to obtain reasonable indicators and criteria for the determination of cavitation and provide a suitable threshold for determination, thereby achieving determination of the cavitation status in the vane pump.

2. The present invention provides a method for determination of cavitation that distinguishes between different working conditions, i.e., a variable flow condition and a constant flow condition, and adopts different detection modes for cavitation under the constant flow condition and abruptly variable flow condition to improve accuracy and sensitivity to determination of cavitation. For cavitation under the constant flow condition, determination of cavitation and evaluation of cavitation status are performed using combined overall level values. For the variable flow condition, the frequency range in which cavitation is most sensitive to liquid-borne noise and solid-borne vibration among different frequency ranges is found, i.e., the broadband sound pressure level of liquid-borne noise in 2000 to 3000 Hz and the broadband vibration level of solid-borne vibration in I 0 to 50 Hz. The present invention also proposes that determination of cavitation under the variable flow condition is performed based on a broadband level value after frequency band broadband filtering, thereby presenting higher sensitivity and reliability than a conventional method for determination of cavitation.

3. The present invention has the advantage that the whole process of cavitation is divided into four statuses by means of acquisition and analysis of the hydraulic performance and the quantity of liquid-borne noise and solid-borne vibration signals in the pump, which exhibits higher accuracy than conventional cavitation status division. Evaluation of cavitation status is performed on the basis of real-time solid-borne vibration and liquid-borne noise signals, which presents higher reliability than a single criterion.

Brief Description of the Drawings

FIG. I is a flow diagram of a method according to the present invention; FIG. 2 is a schematic view of a test bench according to an embodiment of the present invention; FIG. 3 shows an analysis of determination basis with 10% as a change rate of flow rate according to the present invention; FIG. 4 is a graph of change of overall sound pressure level of liquid-borne noise at a cavitation coefficient according to an embodiment of the present invention; and FIG. 5 shows the results of high-speed photography at different cavitation numbers according to an embodiment of the present invention.

Reference signs: I. flowmeter; 2. pressure transducer; 3. hydrophone; 4, vibration acceleration sensor; 5, first gate valve; 6. second gate valve; 7. third gate valve; 8. fourth gate valve; 9. model pump; 10. motor pressure stabilizer; 11. first ball valve; 12. second ball valve; 13. third ball valve; 14. vacuum pump; 15. cavitation tank.

Detailed Description of the Embodiments

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

FIG. I shows a flow diagram of the method for determination of cavitation and evaluation of cavitation status in a vane pump according to the present invention. A suitable measurement location and sampling frequency are selected for a sensor. Liquid-borne noise, vibration, inlet pressure and outlet pressure, flow rate, and cavitation bubble distribution at an impeller inlet, etc. are acquired synchronously by a signal acquisition system, and liquid-borne noise and solid-borne vibration signals are subjected to time-frequency conversion and broadband filtering. A mode for determination of cavitation and evaluation of cavitation status are selected according to the flow condition, and in turn, the whole process of cavitation is divided into four statuses. Compared with high-speed photography test results, in the case of a constant flow rate, a threshold of the overall level value of solid-borne vibration and liquid-borne noise cavitation signals is determined through a testing method. A method for determination of cavitation using an overall level value approach is provided, which has a higher reliability and precision than a conventional method for determination of cavitation. In the case of a variable flow rate, a frequency range with higher sensitivity to cavitation is obtained through spectrum analysis of test results, and the broadband of frequency domain signals is filtered to determine a threshold of cavitation frequency range level value. Then, determination of cavitation is performed by a frequency range broadband level value approach. Finally, cavitation alarm is realized by a signal feedback system. The present invention has the advantages such as high anti-interference, high reliability, accurate evaluation criteria, high sensitivity to cavitation, good applicability, and convenient operation, and can effectively improve the reliability of pump operation, reduce the damage to the pump by cavitation, and prolong the service life of the pump.

A system for implementing the method for determination of cavitation and evaluation of cavitation status in a vane pump includes a data acquisition unit, a data processing unit, a cavitation alarm unit, and a display unit. The data acquisition unit includes a flowmeter I, a pressure transducer 2, a hydrophone 3, a vibration acceleration sensor 4 and a camera device. The flowmeter I is configured to acquire a flow signal. The pressure transducer 2 is configured to acquire pump inlet pressure and outlet pressure signals. The hydrophone 3 is configured to acquire a liquid-borne noise signal. The vibration acceleration sensor 4 is configured to acquire a solid-borne vibration signal. The camera device is configured to acquire a cavitation bubble pattern signal at an impeller inlet. The data acquisition unit is connected to the data processing unit and transfers the acquired signal to the data processing unit. The data processing unit, based on the signal from the data acquisition unit, determines a flow condition and selects different modes for determination of cavitation based on the flow condition. When cavitation occurs, the cavitation alarm unit initiates an alarm and feeds the signal back to the data processing unit to proceed with evaluation of cavitation status. The display unit is connected to the data acquisition unit, the data processing unit and the cavitation alarm unit and is configured to display data.

In this embodiment, a single-stage single-suction centrifugal pump with a specific speed ns=117.3 is studied, and the pump body and impeller are casted from a transparent organic glass material. The design parameters of the pump include flow rate Qd=40m311, head H=8 m, and speed n=1450 ninin. In the pump, the diameter of the impeller inlet is 90 mm, the diameter of the impeller outlet is 170 mm, the number of blades is 6, the blade wrap angle is 1200, the width of the impeller outlet is 13.1 mm, the base circle diameter of the volute is 180 mm, the width of the volute inlet is 32 mm, and the diameter of the volute outlet is 80 mm.

The test bench used in this embodiment is shown in FIG. 2. The test apparatus includes a flowmeter 1, a pressure transducer 2, a hydrophone 3, a vibration acceleration sensor 4, gate valves 5, 6, 7 and 8, a model pump 9, a motor 10, a pressure stabilizer 11, ball valves 12 and 13, a vacuum pump 14 and a cavitation tank 15. The fluid enters the model pump 9 from an inlet pipe. The model pump 9 is connected to the motor 10. The motor 10 is rotated to drive the impeller of the model pump 9 to rotate and do work. The fluid passes through the model pump 9 and then flows out via an outlet pipe into the pressure stabilizer 11. The fluid then flows out of the pressure stabilizer 11 and flows into a pipe connecting the pressure stabilizer 11 to the cavitation tank 15, then flows out of the pipe and then into the cavitation tank 15, and finally, the fluid flows out of the cavitation tank 15 into the inlet pipe of the model pump 9, thereby forming a closed loop.

Components such as sensors are installed depending on the specific size and working condition of the pump under test.

The inlet pipe diameter and outlet pipe diameter of the pump are measured. Holes are formed on the inlet pipeline at a distance of four times the pipe diameter from the pump inlet flange and on the outlet pipeline at a distance of four times the pipe diameter from the pump outlet flange to install the inlet and outlet pressure transducer 2 as a water pump head acquisition unit with an output connected to a data processing unit. A hole is formed on the pump outlet pipeline at a distance of eight times the pipe diameter from the pump outlet flange to install the hydrophone 3 as a liquid-borne noise signal acquisition unit. The hydrophone is equipped with a signal amplifier at the front end to pick up liquid-borne noise data in 0 to 12.8 kHz, and has an output connected to the data processing unit. The vibration acceleration sensor 4 is installed on the pump outlet flange along the pump axis direction as a solid-borne vibration data processing unit to pick up vibration data in 0 to 12.8 kHz, and has an output connected to the data processing unit. The flowmeter 1 is installed at the pump outlet at a distance of ten times the pipe diameter from the outlet flange or outlet elbow as a flow rate acquisition unit with an output connected to the data processing unit. A corresponding sampling time interval of 30 s is set to synchronously acquire the inlet pressure and outlet pressure, flow rate, liquid-borne noise and solid-borne vibration.

In this embodiment, holes are formed on the inlet pipeline at a distance of 360 mm from the pump inlet flange and on the outlet pipeline at a distance of 320 mm from the pump outlet flange to install the pressure transducer 2. The pressure transducer 2 is Model HIV190 pressure transducer that serves as the water pump head acquisition unit with an output connected to the data processing unit. A hole is formed on the pump outlet pipeline at a distance of 640 mm from the pump outlet flange to install the hydrophone 3. The hydrophone 3 is Model RHSA-10 hydrophone that serves as the liquid-borne noise signal acquisition unit. The hydrophone 3 is equipped with a signal amplifier at the front end to pick up liquid-borne noise data in 0 to 12.8 kHz, and has an output connected to the data processing unit. The data processing unit is DASP data acquisition card. The vibration acceleration sensor 4 is installed axially on the pump outlet flange as the solid-borne vibration data acquisition unit to pick up vibration data in 0 to 12.8 kHz, and has an output connected to the data processing unit. The flowmeter 1 is installed at a distance of 800 mm from the pressure stabilizer outlet as the flow rate acquisition unit and has an output connected to the data processing unit. The corresponding sampling time interval is set to synchronously acquire the inlet pressure and outlet pressure, flow rate, liquid-borne noise and solid-borne vibration. The camera device is placed at the impeller inlet and is preferably a high-speed camera to synchronously acquire the cavitation bubble pattern at the impeller inlet.

In this embodiment, the method for determination of cavitation and evaluation of cavitation status in a vane pump specifically includes the following steps.

Step S I. data acquisition: the inlet pressure and outlet pressure, liquid-borne noise, solid-borne vibration and flow rate data in a water pump are acquired.

In a unit sampling time, the data acquisition unit acquires the flow rate, water pump inlet pressure and outlet pressure, liquid-borne noise and solid-borne vibration time-frequency signals, and transfers them to the data processing unit.

Step S2: a mode for determination of cavitation is selected on the basis of the flow condition.

The change rate of flow rate, AQ, is calculated by the data processing unit to determine whether it is greater than 10%. FIG. 3 shows an analysis of determination basis with 10% as the change rate of flow rate, wherein FIG. 3a shows the pattern of change of the liquid-borne noise and air-borne noise as a function of the flow rate, and FIG. 3b shows the pattern of change of the solid-borne vibration as a function of the flow rate. It can be seen from FIG. 3 that as the flow rate increases, the overall level values of liquid-borne noise, solid-borne vibration and air-borne noise all exhibit a change trend of first decreasing and then increasing. The maximums of the overall level values of different measurements all occur under a low flow condition, and the level value of each measurement is at a relatively low level at a rated condition point. In terms of the liquid-borne noise and solid-borne vibration, the magnitudes of test error at different flow coefficients are very small, whereas in terms of the air-borne noise, the change in the magnitude of error of sound pressure level has an even greater impact on the sound pressure level than the change in flow rate. Therefore, determination of cavitation on the basis of the air-borne noise does not provide sufficient reliability.

Also, as the change in flow rate or reduced cavitation number will lead to generation of cavitation and cause changes in the measurement level value, relying merely on the overall sound pressure level of liquid-borne noise for determination of cavitation, although has some improvement in terms of sensitivity over the conventional method, still has some limitations. Given that the frequency ranges of the change in noise or vibration spectrum caused by the change in flow rate and the generation of cavitation may be different, analysis and study may be performed on the signal spectrum to find the frequency range that is more sensitive to cavitation and less sensitive to the change in flow rate. Similar to the method for determination of cavitation based on overall level value, a predetermined threshold for determination of cavitation is set for influences from cavitation on different frequency ranges of different measurements, and cavitation is determined using the spectrum analysis approach.

Under a constant flow condition where the change rate of flow rate, AQ, is less than 10%, the overall sound pressure level in a unit sampling time is calculated by the data processing unit, and determination of cavitation is performed on the basis of the change rate of overall sound pressure level in a step-by-step determination mode. Under a variable flow condition where the change rate of flow rate, AQ, is greater than or equal to 10%, frequency-domain statistics is performed on the liquid-borne noise and solid-borne vibration signals in each unit sampling time by the data processing unit, and determination of cavitation status is performed on the basis of the frequency range broadband level value.

The change rate of flow rate, AD, is calculated by the following calculation formula: AD =12 Q1/0, /100% (i=2, n) where 01 is the flow rate in the first sampling time and 0; is the flow rate in the i-th sampling time, measured in m3/h.

In this embodiment, the unit sampling time T is set to 30 s and the working flow is set to 40 m3/h, The time-frequency signals of liquid-borne noise and solid-borne vibration are acquired by the data acquisition system, and the change in flow rate is calculated by the data processing unit to determine whether it is greater than 4 m3/h. When the change in flow rate is less than 4 m3/h, the overall sound pressure level in a unit sampling time is calculated by the data processing unit, and determination of cavitation is performed on the basis of the change rate of overall sound pressure level in a step-by-step determination mode. When the change in flow rate is greater than or equal to 4 ms/h, frequency-domain statistics is performed on the liquid-borne noise and solid-borne vibration signals in each unit sampling time by the data processing unit, and determination of cavitation and evaluation of cavitation status are performed on the basis of the frequency range broadband level value.

Step S3. determination of cavitation under the constant flow condition When the change in flow rate is less than 4 m3/h, the overall sound pressure level in a unit sampling time is calculated by the data processing unit, and the change rate of overall sound pressure level is calculated in a step-by-step determination mode. Cavitation inception is determined on the basis of change rate of 0.5% for overall sound pressure level of liquid-borne noise relative to the reference benchmark sound pressure level. When the change rate of overall sound pressure level of liquid-borne noise, AL is less than 0.5%, it is deemed that no cavitation occurs in the pump. When the change rate of overall sound pressure level of liquid-borne noise, A L, is greater than 0.5%, it is deemed that cavitation starts to occur in the pump, whereupon a signal is sent to the cavitation alarm unit. Upon receiving the alarm signal, the cavitation alarm unit feeds the signal back to the data processing unit for evaluation of cavitation status under the constant flow condition.

The change rate of overall sound pressure level, AL, is calculated by the following calculation formula: AL= (Lpi-Lpo) /40 in the formula, Lin is the overall sound pressure level of liquid-borne noise in the i-th sampling time and is calculated by the following calculation formula-(p I Ar2)2 I = [Wog if- (pi df 10 log I Af, AI P-0 P 0 in the formula, All is the spectral resolution, Ann andfi. are the lower limit and upper limit of the acquisition frequency, respectively, A and pa are effective sound pressures measured in pa, and po is the reference sound pressure in water which takes a value of p0=10-6 pa. In the formula, the reference benchmark sound pressure level /Apo is calculated by the following calculation formula: Lpo = (Lp1+4,2+Lp 3)/3 in the formula, Lpi, Lp2 and Lp3 are overall sound pressure levels of the first three sets of liquid-borne noise during non-cavitation.

In this embodiment, the reference benchmark sound pressure level Lp0=158.6 dB is obtained through data acquisition, processing and analysis. When the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, i.e., the overall sound pressure level of liquid-borne noise, lip, is greater than 159.5 dB, it is deemed that cavitation starts to occur in the pump at this time. Then a signal is sent to the cavitation alarm unit and the evaluation of cavitation status proceeds. FIG. 4 shows a graph of changes of overall sound pressure level of liquid-borne noise at different cavitation coefficients. As shown in FIG. 4, the corresponding cavitation inception points at different flow coefficients are different. At a flow coefficient T=0.032, the inception point of liquid-borne noise, CA0, is 0.282; at a flow coefficient (p0065, the inception point of liquid-borne noise, Q., is 0.318; and at a flow coefficient T=0.098, the inception point of liquid-borne noise, a,", is 0.357. It can be seen that at a large flow rate, cavitation is more likely to occur in the model pump. FIG. 5 shows the high-speed photography results at different cavitation numbers. It can be seen that when the overall sound pressure level of liquid-borne noise is increased by 0.5%, it can be observed from the high-speed photography results that at this cavitation number of 0.321, cavitation bubbles just start to occur. Therefore, the use of 0.5% increase in overall sound pressure level of liquid-borne noise as the basis for determination of the cavitation inception point provides a higher accuracy.

Step S4. determination of cavitation under the variable flow condition.

When the change in flow rate is greater than or equal to 4 m3/h, the frequency-domain signals of liquid-borne noise and solid-borne vibration are processed to calculate the broadband level value F with a bandwidth of I Hz for liquid-borne noise in a frequency range of 2000 to 3000 Hz and for solid-borne vibration in a frequency range of 10 to 50 Hz. The average broadband sound pressure level ELO and average broadband vibration level ''vu, respectively, of the first three sets of liquid-borne noise and solid-borne vibration in this frequency range acquired before head change are used as the reference benchmark and the change rates of broadband level values in the corresponding frequency range acquired in each unit time that change over time relative to the benchmark level, AFL and AFT-, are determined one by one. Cavitation inception is determined on the basis of the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, Ally, both being 1%. When the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, AFv, are both greater than 1%, it is deemed that the cavitation inception status is reached at this time, and a signal is sent to the cavitation alarm unit. Upon receiving the alarm signal, the cavitation alarm unit feeds a signal back to the data processing unit for evaluation of cavitation status at a variable flow rate.

The broadband level value F is calculated by the following calculation formula: f(x)p, + f(x)p( -1) [ ]/v2) 2 F =1101gY 2 2 Af e=in., p 0 in the formulad(x) is a filter function, and FLU and FV6i are calculated by the following calculation formulas: FLU= (FL1+FL2+FL3) /3 vo-(/"vi+Ev2+Ev3) ELI, EL2 and are average broadband sound pressure levels of the first three sets of liquid-borne noise acquired before head change in the frequency range of 2000 to 3000 Hz, and Fvi, FV2 and FV3 are average broadband vibration levels of the first three sets of solid-borne vibration acquired before head change in the frequency range of 10 to 50 Hz. The data in the first three sampling times is selected as the reference benchmark of the average broadband sound pressure level Fp) and the average broadband vibration level Fp-o. Through multiple sets of experiments and numerical simulations, it has been found that the first three sets of liquid-borne noise have substantially the same broadband sound pressure level curves in the frequency range of 2000 to 3000 Hz, and the solid-borne vibrations in the first three sampling times have substantially the same broadband vibration level curves in the frequency range of 10 to 50 Hz, whereas these spectrum curves are different after the three sampling times. Therefore, to obtain the accurate benchmark value, the average broadband sound pressure level PLO and average broadband vibration level Ey°, respectively, of the first three sets of liquid-borne noise and of the first three sets of solid-borne vibration acquired before head change in this frequency range are used as the reference benchmarks.

APL and AFT-are calculated by the following calculation formulas: Fr -P1(1 A/ b- x100% Pro - o AF% = Fro in the formula, Fu is the average broadband sound pressure level of liquid-borne noise in the i-th sampling time in the frequency range of 2000 to 3000 Hz, and FAR is the average broadband vibration level of solid-borne vibration in the i-th sampling time in the frequency range of 10 to 50 Hz. AFL is the change rate of broadband sound pressure level of liquid-borne noise in the frequency band of 2000 to 3000 Hz. ALTV is the change rate of broadband vibration level of solid-borne vibration in the frequency band of 10 to 50 Hz.

In this embodiment, the reference broadband benchmark sound pressure level FL0=120.1 dB and solid-borne vibration benchmark broadband vibration level Fv0=122.4 dB are obtained through data acquisition, processing and analysis. When the broadband level value FL of liquid-borne noise in the frequency range of 2000 to 3000 Hz is greater than 121.3 dB and the broadband vibration level FL of solid-borne vibration in the frequency range of 10 to 50 Hz is greater than 123.6 dB, it is deemed that cavitation starts to occur in the pump at this time, and a signal is sent to the cavitation alarm unit, and the evaluation of cavitation status proceeds.

Step S5. evaluation of cavitation status under the constant flow condition.

During evaluation of cavitation status under the constant flow condition, the change rate of overall sound pressure level of liquid-borne noise, AL, the change rate of head, Au, and the continuous change rate of overall vibration level of solid-borne vibration, AV', are calculated synchronously. When the change rate of overall sound pressure level of liquid-borne noise, AL, is less than 0.5%, the cavitation status at this time is a non-cavitation status; when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, and the change rate of head, Aft, is less than 3%, the cavitation status at this time is a cavitation inception status when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, the change rate of head, ALL is greater than 3%, and the continuous change rate of overall vibration level of solid-borne v bra on, AV', is greater than 0, the cavitation status at this time is a severe cavitation status; and when the change rate of overall sound pressure level of liquid-borne noise, A L, is greater than 0.5% and the change rate of head, All, is greater than 3%, and the continuous change rate of overall vibration level of solid-borne vibration, AV', is less than 0, the cavitation status at this time is an excessively severe cavitation status.

The head H is calculated by the following calculation formula: H =Pow -P LR P8 in the formula, Pout and Pin are outlet pressure and inlet pressure measured in pa acquired by the pressure transducer, respectively, pis the delivered liquid density measured in kg/m', and g is the acceleration of gravity.

The change rate of head, AH, is calculated by the following calculation formula: AH =1H --x100% (i=2, 3,...,n) where Hi and H.j are the head values in the i-th and i-l-th sampling times measured in m.

The overall vibration level of solid-borne vibration, Va., is calculated by the following calculation formula: = 101g L.: fo=.17,1 112 (t)dt in the formula, fit) is an effective value of vibration acceleration at a unit sampling frequency measured in m/s2, T is a unit sampling time measured in s, and fe is an overall effective vibration acceleration measured in mis2.

The continuous change rate of overall vibration level of solid-borne vibration, A is calculated by the following calculation formula: AV '= x100% IoU -where V," and V, (i,1) are the overall vibration acceleration levels at the i-th and i-1 -th sampling times measured in dB.

In this embodiment, when the overall sound pressure level of liquid-borne noise, Lp, is less than 159.5 dB, it is deemed that the cavitation status at this time is a non-cavitation status; when the overall sound pressure level of liquid-borne noise, 4, is greater than 159.5 dB, and the head Hi is greater than 7.86 m, the cavitation status at this time is a cavitation inception status; when the overall sound pressure level of liquid-borne noise, lip, is greater than 159.5 dB, the head H; is less than 7.86 m, the overall vibration level of solid-borne vibration, Va, is greater than 125.5 dB, and the continuous change rate of overall vibration level of solid-borne vibration is greater than 0, the cavitation status at this time is a severe cavitation status; and when the overall sound pressure level of liquid-borne noise, Lp, is greater than or equal to 159.5 dB and the head H is less than 7.86 m, and the continuous change rate of overall vibration level of solid-borne vibration is less than 0, the cavitation status at this time is an excessively severe cavitation status.

Step 56. evaluation of cavitation status under the variable flow condition.

During evaluation of cavitation status under the variable flow condition, the change rate of broadband sound pressure level of liquid-borne noise in the frequency band of 2000 to 3000 Hz, A FL, the change rate of head, LH, the change rate of broadband vibration level of solid-borne vibration in the frequency range of 10 to 50 Hz, AFv, and the continuous change rate of broadband vibration level of solid-borne vibration in the frequency range of 10 to 50 Hz, AFV, are synchronously calculated and determined 11Fv1 is calculated by the following calculation formula: F-Fvt x100% 1/v(, 1) in the formula, 11vi and /:V(i_,) are the broadband level values of solid-borne vibration in the i-th and i-1-th sampling times.

When the change rate of broadband sound pressure level of liquid-borne noise in the frequency band of 2000 to 3000 Hz, AFL, is less than 1%, and the change rate of broadband vibration level of solid-borne vibration in the frequency range of 10 to 50 Hz, AFv, is less than I °A, it is deemed that the cavitation status at this time is a non-cavitation status. When the change rate of broadband sound pressure level of liquid-borne noise in the frequency band of 2000 to 3000 Hz, AFL, is greater than 1%, and the change rate of broadband vibration level of solid-borne vibration in the frequency range of 10 to 50 Hz, AFv, is greater than or equal to 1%,and the change rate of head, AH, is less than 3%, it is deemed that the cavitation status at this time is a cavitation inception status; when the change rate of broadband sound pressure level of liquid-borne noise in the frequency band of 2000 to 3000 Hz, AFL, is greater than 1%, the change rate of broadband vibration level of solid-borne vibration in the frequency range of 10 to 50 Hz, AF is greater than 1%, the change rate of head, AH, is greater than 3%, and the continuous change rate of broadband vibration level of solid-borne vibration in the frequency range of 10 to 50 Hz, AFV, is greater than 0, it is deemed that the cavitation status at this time is a severe cavitation status; when the change rate of broadband sound pressure level of liquid-borne noise in the frequency band of 2000 to 3000 Hz, AFL, is greater than 1%, the change rate of broadband vibration level of solid-borne vibration in the frequency range of 10 to 50 Hz, AE, is greater than 1%, the change rate of head, API, is greater than 3%, and the continuous change rate of broadband vibration level of solid-borne vibration in the frequency range of 10 to 50 Hz, AFv', is less than 0, it is deemed that the cavitation status at this time is an excessively severe cavitation status.

In this embodiment, the reference broadband benchmark sound pressure level FL0=120.1 dB, the benchmark broadband vibration level of solid-borne vibration Fv0=121.3 dB and the initial head Ho=8.1 m are obtained through data acquisition, processing and analysis. When the broadband sound pressure level FL of liquid-borne noise in 2000 to 3000 Hz is less than 121.3 dB and the broadband vibration level Fv of solid-borne vibration in the frequency band of 0 to 50 Hz is less than 122.4 dB, it is deemed that the cavitation status at this time is a non-cavitation status; when the broadband sound pressure level IL of liquid-borne noise in 2000 to 3000 Hz is greater than 121.3 dB, the broadband vibration level Ev of solid-borne vibration in the frequency band of 0 to 50 Hz is greater than 122.4 dB and the head H, is greater than 7.86 in, the cavitation status at this time is a cavitation inception status; when the broadband sound pressure level FL of liquid-borne noise in 2000 to 3000 Hz is greater than 121.3 dB, and the broadband vibration level Ev of solid-borne vibration in the frequency band of 0 to 50 Hz is greater than 121.3 dB, and the head is less than 7.86 m, and the continuous change rate of broadband vibration level of solid-borne vibration in the frequency range of 10 to 50 Hz, EV', is positive, the cavitation status at this time is a severe cavitation status; and when the broadband sound pressure level EL of liquid-borne noise in 2000 to 3000 Hz is greater than 121.3 dB, the head Hi is less than 7.86 m, and the continuous change rate of broadband vibration level of solid-borne vibration in the frequency range of I 0 to 50 Hz, AF\i', is negative, the cavitation status at this time is an excessively severe cavitation status.

The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention shall fall within the scope of protection of the present invention.

Claims

Claims What is claimed is: 1. A method for determination of cavitation and evaluation of cavitation status in a vane pump, characterized by comprising the following steps: Step S I. data acquisition: acquiring inlet pressure and outlet pressure, liquid-borne noise, solid-borne vibration, and flow rate data in a water pump; Step 52. selection of a mode for determination of cavitation based on a flow condition: under a constant flow condition where a change rate of flow rate, AO, is less than x, performing the determination of cavitation using a change rate of overall sound pressure level and proceeding with Step S3; and under a variable flow condition where the change rate of flow rate, AO, is greater than or equal to x, performing the determination of cavitation using a frequency range broadband level value and proceeding with Step S4; Step S3. determination of cavitation under the constant flow condition: when a change rate of overall sound pressure level of liquid-borne noise, AL, is greater than y, starting cavitation alarm and proceeding with evaluation of cavitation status under the constant flow condition, and proceeding with Step S5, wherein the change rate of overall sound pressure level, AL, is calculated by the following calculation formula: AT= (41-4o) /To in the formula, Li); is an overall sound pressure level of liquid-borne noise in the -th sampling time and is calculated by the following calculation formula.(p, 115)2 fp =10logi f (Pa 1,5)2 2 -10 log P u P u in the formula, A ji is a spectral resolution, Lilt1 is an upper limit of an acquisition frequency and filax is a lower limit of an acquisition frequency, pi and pa are effective sound pressures measured in pa, and po is a reference sound pressure in water which takes a value of po= le pa, wherein the reference benchmark sound pressure level Lpo is calculated by the following calculation formula: = (41+42+43)/3 in the formula, Lpi, 42 and Lp3 are overall sound pressure levels of the first three sets of liquid-borne noise during non-cavitation; Step S4. determination of cavitation under the variable flow condition: when a change rate of broadband sound pressure level of liquid-borne noise in a predetermined frequency band, La, and a change rate of broadband vibration level of solid-borne vibration in a predetermined frequency band, AFv, are both greater than s, starting cavitation alarm and proceeding with evaluation of cavitation status under the variable flow condition, and proceeding with Step SG, wherein a broadband level value F is calculated by the following calculation formula: [t(x)P! +f(x)p1 1)1/,5)2 =101g 22 Afi p 0 twin in the formula, fix) is a filter function, FLO and livo are calculated by the following calculation formulas: FLO= (FL 1+FL2+FL3) /3 Evo-(Evi+Fv2+Fv3) FL2 and FL3 are average broadband sound pressure levels of the first three sets of liquid-borne noise acquired before head change in a predetermined frequency range, and FV1, EV2 and EV3 are average broadband vibration levels of the first three sets of solid-borne vibration acquired before head change in a predetermined frequency range, Li-11 and APr are calculated by the following calculation formulas:FT -FTAFL - x100%FLU -FroArv - x100% in the formula, Ph is an average broadband sound pressure level of liquid-borne noise in a predetermined frequency range in the i-th sampling time, /iv, is an average broadband vibration level of solid-borne vibration in a predetermined frequency range in the i-th sampling time, LEL is the change rate of broadband sound pressure level of liquid-borne noise in a predetermined frequency band, and AFv is the change rate of broadband vibration level of solid-borne vibration in a predetermined frequency band; Step S5, evaluation of cavitation status under the constant flow condition when the change rate of overall sound pressure level of liquid-borne noise, AL, is less than y, evaluating the cavitation status as a non-cavitation status; when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than y, and a change rate of head, AK, is less than z, evaluating the cavitation status as a cavitation inception status; when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than y, the change rate of head, ALL is greater than z, and a continuous change rate of overall vibration level of solid-borne vibration, AV, is positive, evaluating the cavitation status as a severe cavitation status; and when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than y, the change rate of head, Aft, is greater than z, and the continuous change rate of overall vibration level of solid-borne vibration, A Tn, is negative, evaluating the cavitation status as an excessively severe cavitation status; and Step SG, evaluation of cavitation status under the variable flow condition: when the change rate of broadband sound pressure level of liquid-borne noise in a predetermined frequency band, AFL, and the change rate of broadband vibration level of solid-borne vibration in a predetermined frequency band, Ativ, are both less than s, evaluating the cavitation status as a non-cavitation status; when the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, AFv, are both greater than s and the change rate of head, AK, is less than z, evaluating the cavitation status as a ca itation inception status; when the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, AFv, are both greater than s, the change rate of head, AR, is greater than z, and a continuous change rate of broadband vibration level of solid-borne vibration, APVI, is positive, evaluating the cavitation status as a severe cavitation status; and when the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, Ltiv, are both greater than s, the change rate of head, Alf, is greater than z, and the continuous change rate of broadband vibration level of solid-borne vibration, ARV, is negative, evaluating the cavitation status as an excessively severe cavitation status.
2. The method for determination of cavitation and evaluation of cavitation status in the vane pump according to claim I, characterized in that in the Step S2, the x is 10%; and under the constant flow condition where the change rate of flow rate, AO, is less than 10%, the determination of cavitation is performed using the change rate of overall sound pressure level, and under the variable flow condition where the change rate of flow rate, AQ, is greater than or equal to 10%, the determination of cavitation is performed using the frequency range broadband level value.
3. The method for determination of cavitation and evaluation of cavitation status in the vane pump according to claim 2, characterized in that in the Step S3, the y is 0.5%; and when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, the cavitation alarm is started and the evaluation of cavitation status under the constant flow condition proceeds.
4. The method for determination of cavitation and evaluation of cavitation status in the vane pump according to claim 2, characterized in that the broadband sound pressure level of liquid-borne noise is 2000 to 3000 Hz, and the broadband vibration level of solid-borne vibration is 10 to 50 Hz in the Step S4.
5. The method for determination of cavitation and evaluation of cavitation status in the vane pump according to claim 4, characterized in that in the Step S4, the s is 1%; and when the change rate of broadband sound pressure level of liquid-borne noise in a frequency band of 2000 to 3000 Hz, AFL, and the change rate of broadband vibration level of solid-borne vibration in a frequency band of 10 to 50 Hz, AFv, are both greater than 1%, the cavitation alarm is started and the evaluation of cavitation status under the variable flow condition proceeds.
6. The method for determination of cavitation and evaluation of cavitation status in the vane pump according to claim 3, characterized in that in the Step S5, when the change rate of overall sound pressure level of liquid-borne noise, AL, is less than 0.5%, the cavitation status is evaluated as the non-cavitation status; when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, and the change rate of head, An, is less than 3%, the cavitation status is evaluated as the cavitation inception status; when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, the change rate of head, AH, is greater than 3%, and the continuous change rate of overall vibration level of solid-borne vibration, AV, is positive, the cavitation status is evaluated as the severe cavitation status; and when the change rate of overall sound pressure level of liquid-borne noise, AL, is greater than 0.5%, the change rate of head, API, is greater than 3%, and the continuous change rate of overall vibration level of solid-borne vibration, AV', is negative, the cavitation status is evaluated as the excessively severe cavitation status.
7. The method for determination of cavitation and evaluation of cavitation status in the vane pump according to claim 5, characterized in that in the Step S6, when the change rate of broadband sound pressure level of liquid-borne noise in the frequency band of 2000 to 3000 Hz, AFL, and the change rate of broadband vibration level of solid-borne vibration in the frequency band of 10 to 50 Hz, A/7v, are both less than 1%, the cavitation status is evaluated as the non-cavitation status; when the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, AFv, are both greater than 1%, and the change rate of head, An, is less than 3%, the cavitation status is evaluated as the cavitation inception status; when the change rate of broadband sound pressure level of liquid-borne noise, A FL, and the change rate of broadband vibration level of solid-borne vibration, Arv, are both greater than 1%, the change rate of head, LB, is greater than 3%, and the continuous change rate of broadband vibration level of solid-borne vibration, Ativ', is positive, the cavitation status is evaluated as the severe cavitation status; and when the change rate of broadband sound pressure level of liquid-borne noise, AFL, and the change rate of broadband vibration level of solid-borne vibration, AFv, are both greater than 1%, the change rate of head, AH, is greater than 3%, and the continuous change rate of broadband vibration level of solid-borne vibration, AFv', is negative, the cavitation status is evaluated as the excessively severe cavitation status.
8. A system for implementing the method for determination of cavitation and evaluation of cavitation status in the vane pump according to claim I, characterized by comprising a data acquisition unit, a data processing unit, a cavitation alarm unit, and a display unit; the data acquisition unit comprises a flowmeter (1), a pressure transducer (2), a hydrophone (3), a vibration acceleration sensor (4) and a camera device; the flowmeter (1) is configured to acquire a flow signal; the pressure transducer (2) is configured to acquire pump inlet pressure and outlet pressure signals; the hydrophone (3) is configured to acquire a liquid-borne noise signal; the vibration acceleration sensor (4) is configured to acquire a solid-borne vibration signal; the camera device is configured to acquire a cavitation bubble pattern signal at an impeller inlet; the data acquisition unit is connected to the data processing unit and transfers the acquired signal to the data processing unit; the data processing unit, based on the signal from the data acquisition unit, determines a flow condition and selects different modes for determination of cavitation based on the flow condition; when cavitation occurs, the cavitation alarm unit initiates an alarm and feeds the signal back to the data processing unit to proceed with evaluation of cavitation status; and the display unit is connected to the data acquisition unit, the data processing unit and the cavitation alarm unit and is configured to display data.