CN116593126B - Cavitation performance evaluation method of cavitation nozzle - Google Patents
Cavitation performance evaluation method of cavitation nozzle Download PDFInfo
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Abstract
The invention belongs to the technical field of fluid mechanics, and relates to a cavitation performance evaluation method of a cavitation nozzle, which is used for identifying pressure pulsation and obtaining discrete accumulated pulsation quantity according to a cavitation jet pressure signal diagram of the cavitation nozzle; obtaining a dimensionless pressure-dimensionless accumulated pulsation quantity function after fitting of the cavitation nozzle, a nozzle pressure drop-characteristic pressure function after fitting and a nozzle pressure drop-characteristic accumulated pulsation quantity function after fitting; selecting one cavitation nozzle as a standard nozzle A, and judging whether other cavitation nozzles B and the standard nozzle A have cavitation similarity; and forming a cavitation similar nozzle cavitation performance comparison plate or a nozzle cavitation performance plate. The cavitation performance comparison plate of the cavitation similar nozzles can intuitively compare the cavitation performance of the cavitation nozzles with cavitation similarity, and provide guidance for the optimal design of the cavitation nozzles; the cavitation performance plate of the nozzle can uniformly compare and evaluate the cavitation performance of different cavitation nozzles, and provides a basis for selecting the nozzles according to the working condition requirements.
Description
Technical Field
The invention belongs to the technical field of fluid mechanics, and relates to a cavitation performance evaluation method of a cavitation nozzle.
Background
Cavitation is a phase change process and phenomenon of liquid and its vapor that occurs inside a liquid or at the liquid-solid interface due to hydrodynamic factors. Cavitation is generated through a cavitation nozzle, is a way of hydrodynamic cavitation, and the specially designed cavitation nozzle is commonly used in the fields of petroleum drilling acceleration, polluted water body treatment, biological medicine preparation and the like, and has wide application. When the cavitation nozzle is designed and selected, the intensity of the cavitation field needs to be quantitatively described so as to evaluate the performance of the cavitation nozzle. However, cavitation is a complex process, is a comprehensive phenomenon of a plurality of physical and chemical processes, and needs to consider the requirements of working conditions on specific cavitation effects when evaluating the cavitation performance of the nozzle, so that a unified physical quantity for evaluating the cavitation performance of the nozzle does not exist. At present, cavitation nozzle performance evaluation is mainly performed indirectly by using cavitation effect, and the commonly used cavitation nozzle evaluation methods include the following steps:
(1) Cavitation method for aluminium foil
And (3) placing the aluminum foil with the thickness of the sub-millimeter level into a certain position to be detected of a cavitation field generated by the nozzle, taking out after a plurality of seconds to a plurality of minutes, observing cavitation erosion patterns of the aluminum foil, or measuring cavitation erosion mass loss of the aluminum foil. The advantage of this approach is intuitive; the disadvantage is that the quantitative description error is large, and cavitation quality is seriously dependent on the surface property of the aluminum foil;
(2) Cavitation noise method
The acoustic waves generated by the pulsation or rupture of cavitation bubbles are measured by hydrophone measurements. The method has the advantages that the equipment required by measurement does not need to be specially designed, the sound spectrum can be obtained by recording dozens of sound periods, and the time and space resolution is high; the defect is that the signals recorded by the hydrophone are not only caused by cavitation, but also the unsteady characteristics of the flow field are recorded, and the unsteady influence of the flow field can be eliminated by clearly knowing the flow structure of the flow field;
(3) Calorimetric method
Measuring the rise in liquid temperature caused by cavitation;
(4) Acousto-optic effect method
The optical radiation generated by the violent pulsation and rupture of cavitation bubbles is measured by an optoelectronic device. The method has the advantages of high precision, high speed and non-release; the disadvantage is that only cavitation to a certain extent can produce optical radiation, a weaker cavitation field cannot be measured;
(5) Ultrasonic decomposition method
Measuring free radicals generated during cavitation ruptureOH - The intensity of cavitation can be effectively characterized, but since the measured compound concentration is the integral of cavitation effect versus time, not transient effect, only the cavitation time-space average intensity can be characterized.
In summary, the currently-used cavitation performance evaluation methods have advantages and disadvantages, and cannot be replaced by each other, but can be combined with a measurement subsequent data processing method to seek a simple, efficient and applicable cavitation performance evaluation method aiming at the technical field of the specific application of the cavitation nozzle.
Disclosure of Invention
The invention provides a cavitation performance evaluation method of a cavitation nozzle, which comprises the steps of performing pretreatment such as pressure pulsation identification, discrete accumulated pulsation quantity calculation and the like on a cavitation jet pressure signal diagram acquired through experiments or calculated through numerical simulation, judging the cavitation similarity of the nozzle, forming a cavitation performance comparison plate of the cavitation similar nozzle or a cavitation performance plate of the nozzle, and qualitatively and quantitatively evaluating the cavitation performance of various cavitation nozzles. The method provided by the invention can judge whether the cavitation and pulsation principles generated by a plurality of cavitation nozzles are the same; the method can be used as an objective function of cavitation nozzle structure optimization, and can be used for qualitatively and quantitatively evaluating the improvement effect of cavitation performance of cavitation nozzle structure optimization; the cavitation nozzle type selection method can be used as a cavitation nozzle type selection basis, and the type and structure of the cavitation nozzle are selected according to the requirements of working conditions on the pulsation pressure and the pulsation width and the limitation of pressure drop of the cavitation nozzle.
The invention relates to a cavitation performance evaluation method of a cavitation nozzle, which comprises the following steps:
(1) Identifying pressure pulsation according to a cavitation jet pressure signal diagram of the cavitation nozzle;
(2) Obtaining discrete accumulated pulsation quantity according to a cavitation jet flow pressure signal diagram of a cavitation nozzle;
(3) Obtaining a dimensionless pressure-dimensionless accumulated pulsation quantity function after fitting of the cavitation nozzle, a nozzle pressure drop-characteristic pressure function after fitting and a nozzle pressure drop-characteristic accumulated pulsation quantity function after fitting;
(4) Selecting one cavitation nozzle as a standard nozzle A, and judging whether the fitted nozzle pressure drop-characteristic pressure function and the fitted nozzle pressure drop-characteristic accumulated pulsation quantity function of the rest cavitation nozzles B and the standard nozzle A are linearly related, namely whether cavitation similarity exists;
(5) And drawing a cavitation similar nozzle cavitation performance comparison plate or a nozzle cavitation performance plate.
The discrete accumulated pulsation number obtaining process in the step (2) is as follows:
(2-1) numbering the pressure pulsations in time;
(2-2) calculating the pulsating pressure of each pressure pulsationPPulse width deltaTNumbering of pressure pulsations and pulsations pressure and pulsation width deltaTThe array is formed:；
(2-3) establishing a two-dimensional Cartesian coordinate System with the horizontal axis of the coordinate being the pulsating pressurePThe vertical axis is the pulse width deltaTDividing the transverse axis and the longitudinal axis into scales;
the scale of the horizontal axis is divided into:；
wherein:
P t -pressure threshold, MPa;
ndividing the parameters of the pulse pressure horizontal axis scale, and having no dimension;
∆Presolution of the pulsating pressure horizontal axis scale division, MPa;
P max -maximum pulsating pressure of each pressure pulsation in the pressure signal map, MPa;
the vertical axis scale is divided into:；
wherein:
m-dividing the parameters of the pulse width vertical axis scale, and having no dimension;
δ（ΔT) -resolution of the pulse width vertical axis scale division, s;
∆T max -maximum pulse width of each pressure pulse in the pressure signal map, s;
(2-4) grouping all of the arraysAccording to the codeMSequentially judging the pulsation pressurePWhether or not it satisfies:
(1)；
in the method, in the process of the invention,iis an iteration parameter, and is dimensionless;
if the above condition is satisfied, continuously judging the pulse width deltaTWhether or not it satisfies:
(2)；
in the method, in the process of the invention,jis an iteration parameter, and is dimensionless;
the number of pulses satisfying the formulas (1) and (2) is defined asΝ；
(2-5) nodeThe pulse number density at this point is:
；
(2-6) in the formula (2)jReset toj=j+1, repeating processes (2-4), (2-5), (2-6) to；
(2-7) in the formula (1)iReset toi=i+1，Repeating the processes (2-4), (2-5), (2-6), (2-7) to；
(2-8) calculating the discrete cumulative pulse quantity of the pressure at the pulse pressure horizontal axis scale point；
;
The pressure at the scale point of the horizontal axis of the pulsating pressure and the discrete accumulated pulsation quantity calculated by the methodThe cavitation jet nozzle pressure-discrete accumulated pulsation quantity data of the corresponding nozzle pressure drop are formed.
The pressure threshold value of the inventionThe pressure value is designated according to the requirement, and can be taken between the minimum pressure and the maximum pressure of the pressure signal, and is usually taken as zero; the pressure threshold line is a straight line parallel to the time horizontal axis in the pressure signal graph with the time horizontal axis and the pressure vertical axis, and the intersection point of the pressure threshold line and the pressure vertical axis is the pressure threshold +.>And has a plurality of intersections with the pressure signal; in the pressure signal above the pressure threshold line in the pressure signal diagram, the pressure signal part between every two left and right adjacent intersection points is defined as pressure pulsation; pulsating pressure according to the invention +.>Maximum pressure value for pressure pulsation; the pulse width ∈>Is the time difference between the intersection of the pressure pulsation and the pressure threshold line (see fig. 1).
In the case of pressure pulsation identification, a pressure threshold line is defined in a pressure signal diagram, and the pressure signal above the pressure threshold line in the pressure signal diagram has a peak value between each two adjacent left and right intersections (i.e., a pulsating pressureP) Is identified as a pressure pulsation; each pressure pulsation has a pulsating pressureAnd pulse width->Two parameters.
The specific process of the step (3) is as follows:
(3-1) for a certain cavitation nozzle, changing the pressure drop of the nozzle for a plurality of times to obtain a plurality of groups of pressure-discrete accumulated pulsation quantity data corresponding to different nozzle pressure drops; a series of pressures in each set of pressure-discrete cumulative pulse number dataData are divided by the characteristic pressure of the corresponding nozzle pressure drop +.>A series of discrete accumulated pulse numbersData are divided by characteristic cumulative pulse number of corresponding nozzle pressure drop +.>And obtaining corresponding dimensionless pressure-dimensionless accumulated pulsation quantity data, and performing curve fitting to obtain a dimensionless pressure-dimensionless accumulated pulsation quantity function after fitting.
More specifically, according to pressure drop at a certain nozzle for a certain cavitation nozzleCavitation radiation obtained by experimental or numerical simulation calculationThe flow pressure signal diagram is used for calculating the pressure drop of the cavitation nozzle in the nozzle by the method for calculating the discrete accumulated pulsation quantity>The next series of pressure->Discrete cumulative number of pulsations at；
;
The pressure drop of the nozzle is changed for a plurality of times, so that a plurality of groups of pressure-discrete accumulated pulsation quantity data corresponding to different nozzle pressure drops can be obtained. Since the same cavitation nozzle is used, the various sets of data are plotted in a plot of pressure versus discrete cumulative pulse number to form multiple curves that are similar, i.e., have the same shape (see FIG. 4).
Will correspond to nozzle pressure dropPressure of->-cumulative pulsation count->A series of pressures in the data>Data are divided by a value +.>Series->Data are divided by another value->A set of corresponding nozzle pressure drops is obtained>Dimensionless pressure-dimensionless cumulative pulsation number data;
;
numerical valueN * Referred to as the characteristic cumulative pulse number,P * referred to as the characteristic pressure. The value of the characteristic pressure should be selected within a range greater than the vicinity of the maximum pressure value in the series of pressures of the set of data, and the characteristic cumulative pulse number should be selected within a range greater than the vicinity of the maximum cumulative pulse number value in the series of cumulative pulse numbers of the set of data.
The characteristic pressure and the characteristic accumulated pulsation amount of the other groups of pressure-discrete accumulated pulsation amount data can be arbitrarily selected, but the groups of data can be overlapped into a curve after being drawn on a dimensionless pressure-dimensionless accumulated pulsation amount chart (refer to fig. 5);
combining all the dimensionless pressure-dimensionless accumulated pulsation quantity data into one group of data, performing curve fitting, wherein the dimensionless pressure-dimensionless accumulated pulsation quantity functional relation after fitting is as follows:
；
wherein:
-accumulating the pulsation number after fitting, dimensionless;
-feature accumulated pulsation number, dimensionless;
dimensionless cumulative pulsation after fittingNumber, dimensionless;
-post-fitting pressure, MPa;
-characteristic pressure, MPa;
-dimensionless pressure after fitting, dimensionless;
(3-2) performing curve fitting by taking nozzle pressure drop as an independent variable and characteristic pressure as a dependent variable, wherein the nozzle pressure drop-characteristic pressure function relationship after fitting is as follows (see fig. 5):
；
wherein:
-characteristic pressure, MPa;
nozzle pressure drop, MPa.
(3-3) performing curve fitting by taking nozzle pressure drop as an independent variable and characteristic accumulated pulsation quantity as a dependent variable, wherein the function relation of nozzle pressure drop and characteristic accumulated pulsation quantity after fitting is as follows (see fig. 5):
；
-feature accumulated pulsation number, dimensionless;
nozzle pressure drop, MPa.
The fitting mode can be arbitrarily selected on the premise of ensuring the fitting precision, but exponential fitting is selected as much as possible on the premise of ensuring certain fitting precision for the convenience of subsequent calculation.
The specific process of the step (4) is as follows:
(4-1) selecting one cavitation nozzle as a standard nozzle A and the rest cavitation nozzles B, wherein the cavitation nozzles comprise:
dimensionless pressure-dimensionless cumulative pulsation magnitude function after standard nozzle a fitting: (1-1)；
standard nozzle a fitted to the post nozzle pressure drop-characteristic pressure function: (1-2)；
nozzle pressure drop-characteristic cumulative pulsation magnitude function after standard nozzle a fitting: (1-3)；
the cavitation nozzle B is fitted with a dimensionless pressure-dimensionless cumulative pulsation quantity function: (2-1)；
cavitation nozzle B fits post nozzle pressure drop-characteristic pressure function: (2-2)；
after cavitation nozzle B fitting, nozzle pressure drop-characteristic cumulative pulsation magnitude function: (2-3)；
(4-2) the fitted nozzle pressure drop-characteristic pressure function of the cavitation nozzle B divided by the fitted nozzle pressure drop-characteristic pressure function of the standard nozzle a is a constant, and the fitted nozzle pressure drop-characteristic accumulated pulsation amount function of the cavitation nozzle B divided by the fitted nozzle pressure drop-characteristic accumulated pulsation amount function of the standard nozzle a is a constant, so that the cavitation nozzle B and the standard nozzle a have cavitation similarity and are cavitation similar nozzles; in contrast, there is no cavitation similarity, not cavitation-like nozzles.
The specific process for drawing cavitation performance comparison plate of cavitation similar nozzle comprises:
(1) Cavitation nozzle B has cavitation similarity to standard nozzle a, then:
；
in the method, in the process of the invention,being a constant, dimensionless, then for cavitation nozzle B:
(3)；
and is also provided with；
In the method, in the process of the invention,being a constant, dimensionless, then for cavitation nozzle B:
(4)；
when formula (3) and formula (4) are substituted into formula (2-1), there is a cavitation nozzle B:
(5)；
characteristic pressure of standard nozzle ADenoted as->Accumulating the characteristic pulse number of the standard nozzle +.>Denoted as->Then formula (5) can be expressed as:
(6)；
equation (6) gives another form of the cavitation nozzle B dimensionless pressure-dimensionless cumulative pulsation magnitude function.
(2) Drawing the dimensionless pressure-dimensionless cumulative pulsation quantity function of the cavitation nozzle B in another form with the dimensionless pressure-dimensionless cumulative pulsation quantity function of the standard nozzle A after fitting to form a dimensionless pressure-dimensionless cumulative pulsation quantity plate, drawing the nozzle pressure drop-characteristic pressure function of the standard nozzle A after fitting to form a nozzle pressure drop-characteristic pressure plate, drawing the nozzle pressure drop-characteristic cumulative pulsation quantity function of the standard nozzle A after fitting to form a nozzle pressure drop-characteristic cumulative pulsation quantity plate, and jointly forming a cavitation performance comparison plate of the cavitation similar nozzles A and B by the three plates.
The drawing method of cavitation performance plate of cavitation nozzle comprises:
(1) Cavitation nozzle B and standard nozzle A do not have cavitation similarity, and the following relationship exists between nozzle pressure drop-characteristic pressure function after the fit of the standard nozzle A and the cavitation nozzle B:；
in the method, in the process of the invention,is an adjusting function taking nozzle pressure drop as an independent variable, and has no dimension;
the nozzle pressure drop-characteristic accumulated pulsation quantity function after the fitting of the standard nozzle A and the cavitation nozzle B has the following relation:
；
in the method, in the process of the invention,is an adjusting function taking nozzle pressure drop as an independent variable, and has no dimension;
then for cavitation nozzle B, its characteristic pressure may be expressed as:
(7)；
the characteristic cumulative pulse number may be expressed as:
(8)；
bringing formula (7) and formula (8) into formula (2-1), then:
；
namely:
(9)；
in the method, in the process of the invention,accumulating the pulsation quantity for the characteristic of the standard nozzle A in the corresponding nozzle pressure drop, having no dimension,；/>for the characteristic pressure of standard nozzle A at the corresponding nozzle pressure drop, +.>；
The cumulative number of pulsations of the standard nozzle a is expressed asThen formula (2-1) can be expressed as:
(10)；
dividing formula (9) by formula (10), then:
；
the above indicates that cavitation nozzle B and standard nozzle A have the same nozzle pressure dropAnd pressure->The ratio of the number of accumulated pulses down is the nozzle pressure drop +.>And pressure->Is a function of (1), namely:
；
specifying the pressureAfter the value, the ratio of the cumulative pulse number generated by the cavitation nozzle B to the standard nozzle ATo be nozzle pressure drop->Is a single-valued function of (2);
(2) At different pressuresAt the value, the ratio of the accumulated pulse quantity of the cavitation nozzle B to the standard nozzle APressure drop with nozzle->Is plotted in a nozzle pressure drop-cumulative pulse number ratio plot to form a nozzle B cavitation performance plot.
The beneficial effects of the invention are as follows:
(1) According to the nozzle cavitation similarity judging method provided by the invention, after the pressure signal diagrams of different nozzle pressure drops of a certain cavitation nozzle X obtained by experiment or numerical simulation calculation are subjected to data processing, whether the cavitation nozzle X has cavitation similarity with the existing cavitation nozzle or not can be judged, and whether the cavitation nozzle X has the same cavitation principle or not can be judged;
(2) The cavitation performance comparison plate of the cavitation similar nozzle provided by the invention can intuitively compare the cavitation performance of the cavitation similar nozzle; the influence of cavitation performance on the structure and the size optimization of the cavitation nozzle can be intuitively and comprehensively reflected by comparing the cavitation performance of the cavitation similar nozzle with the dimensionless pressure-dimensionless accumulated pulsation number curve of the cavitation nozzle before and after optimization in a template, so that the effect of guiding the structure and the size optimization of the cavitation nozzle can be achieved;
(3) The cavitation performance of various cavitation nozzles can be quantitatively evaluated and compared through the cavitation performance plate of the nozzle provided by the invention, so that the cavitation nozzle can be optimized according to the requirement of pulsating pressure generated by the cavitation nozzle and the limitation of pressure drop of the nozzle.
Drawings
FIG. 1 is a cavitation jet pressure signal diagram and definition schematic;
FIG. 2 is a schematic diagram of a discrete cumulative pulse number calculation;
FIG. 3 is a graph showing pressure signals for a standard nozzle a at various nozzle pressure drops;
FIG. 4 is a graph showing the discrete cumulative pulse number for different nozzle pressure drops for a standard nozzle a;
FIG. 5 is a graph of the dimensionless pressure-dimensionless cumulative pulse number function curve, the fitted nozzle pressure drop-characteristic pressure function curve, and the fitted nozzle pressure drop-characteristic cumulative pulse number curve for a standard nozzle a;
FIG. 6 is a graph of pressure signals of cavitation nozzle b at various nozzle pressure drops;
FIG. 7 is a graph of the dimensionless pressure-dimensionless cumulative pulse number function of the cavitation nozzle b after fitting, the nozzle pressure drop-characteristic pressure function after fitting, and the nozzle pressure drop-characteristic cumulative pulse number function after fitting;
FIG. 8 is a comparative plate of cavitation performance of a cavitation similar nozzle;
FIG. 9 is a graph of pressure signals of cavitation nozzle c at various nozzle pressure drops;
FIG. 10 is a graph of the dimensionless pressure-dimensionless cumulative pulse number function curve, the fitted nozzle pressure drop-characteristic pressure function curve, and the fitted nozzle pressure drop-characteristic cumulative pulse number function curve for cavitation nozzle c;
FIG. 11 is a graph of nozzle cavitation performance;
fig. 12 is a flow chart of the present invention.
Detailed Description
The preferred embodiments of the present invention will be described below with reference to the accompanying drawings, it being understood that the preferred embodiments described herein are for illustration and explanation of the present invention only, and are not intended to limit the present invention.
Examples
According to the pressure signal diagram (refer to fig. 3) of the cavitation nozzle a under different nozzle pressure drops, carrying out data preprocessing such as pulse identification, discrete accumulated pulse quantity calculation and the like, and obtaining a dimensionless pressure-dimensionless accumulated pulse quantity function curve, a nozzle pressure drop-characteristic pressure function curve and a nozzle pressure drop-characteristic accumulated pulse quantity function curve (refer to fig. 5) of the cavitation nozzle a through data fitting. The fitted dimensionless pressure-dimensionless accumulated pulsation quantity function of the cavitation nozzle a, the fitted nozzle pressure drop-characteristic pressure function and the fitted nozzle pressure drop-characteristic accumulated pulsation quantity function are respectively as follows:
(11)；
(12)；
(13)；
according to the pressure signal graph of the cavitation nozzle b under different nozzle pressure drops (see fig. 6), carrying out data preprocessing such as pulsation identification, discrete accumulated pulsation quantity calculation and the like, and obtaining a dimensionless pressure-dimensionless accumulated pulsation quantity function curve, a nozzle pressure drop-characteristic pressure function curve and a nozzle pressure drop-characteristic accumulated pulsation quantity function curve of the cavitation nozzle b (see fig. 7) through data fitting. The fitted dimensionless pressure-dimensionless cumulative pulsation quantity function of the cavitation nozzle b, the fitted nozzle pressure drop-characteristic pressure function and the fitted nozzle pressure drop-characteristic cumulative pulsation quantity function are respectively as follows:
(14)；
；
；
the cavitation nozzle a is taken as a standard nozzle, and the ratio of nozzle pressure drop to characteristic pressure function after the cavitation nozzle b is fitted with the standard nozzle a is as follows:；
the ratio of nozzle pressure drop-characteristic cumulative pulse number function after fitting cavitation nozzle b to standard nozzle a is:；
cavitation nozzle b has cavitation similarity to standard nozzle a, so that the fitted dimensionless pressure-dimensionless cumulative pulsation magnitude function (14) of cavitation nozzle b can be converted into another form:
(15)；
drawing a dimensionless pressure-dimensionless cumulative pulsation quantity chart by another form (15) of the dimensionless pressure-dimensionless cumulative pulsation quantity function after fitting of the cavitation nozzle b and the dimensionless pressure-dimensionless cumulative pulsation quantity function (11) after fitting of the standard nozzle a; and simultaneously, drawing a nozzle pressure drop-characteristic pressure function (12) after fitting of the standard nozzle a into a nozzle pressure drop-characteristic pressure chart, and drawing a nozzle pressure drop-characteristic accumulated pulsation quantity function (13) after fitting of the standard nozzle a into a nozzle pressure drop-characteristic accumulated pulsation quantity chart. The three plates together form a comparative plate of cavitation performance for cavitation similar nozzles a and b (see fig. 8).
According to the pressure signal graph of the cavitation nozzle c under different nozzle pressure drops (see fig. 9), carrying out data preprocessing such as pulse identification, discrete accumulated pulse quantity calculation and the like, and obtaining a dimensionless pressure-dimensionless accumulated pulse quantity function curve, a nozzle pressure drop-characteristic pressure function curve and a nozzle pressure drop-characteristic accumulated pulse quantity function curve of the cavitation nozzle c (see fig. 10) through data fitting. The fitted dimensionless pressure-dimensionless cumulative pulsation quantity function of the cavitation nozzle c, the fitted nozzle pressure drop-characteristic pressure function and the fitted nozzle pressure drop-characteristic cumulative pulsation quantity function are respectively as follows:
；
；
；
the ratio of nozzle pressure drop to characteristic pressure function after fitting cavitation nozzle c to standard nozzle a is:
；
the ratio of nozzle pressure drop-characteristic cumulative pulse number function after fitting cavitation nozzle c to standard nozzle a is:
；
cavitation nozzle c does not have cavitation similarity to standard nozzles.
Cavitation nozzle c pressure drop at the same nozzle as standard nozzle aAnd pressure->The ratio of the number of accumulated pulses is:
；
specifying the pressure=100, 150, 200, 250MPa will nozzle c +.>The relationship is plotted in a plate to obtain a plate of nozzle cavitation performance (see fig. 11).
By way of specific example, the beneficial effects are seen as follows:
(1) According to the nozzle cavitation similarity judging method provided by the invention, the standard nozzle a and the cavitation nozzle b are judged to have cavitation similarity; standard nozzle a does not have cavitation similarity to cavitation nozzle c;
(2) According to the cavitation performance comparison drawing method of the cavitation similar nozzle provided by the invention, the cavitation performance comparison drawing of the cavitation similar nozzle of the standard nozzle a and the cavitation nozzle b is obtained. In the comparison plate, the fitted dimensionless pressure-dimensionless cumulative pulsation quantity function curve of the other form of the cavitation nozzle b is positioned above the fitted dimensionless pressure-dimensionless function curve of the standard nozzle a, so that the cavitation performance of the cavitation nozzle b is intuitively reflected to be better than that of the standard nozzle a, and the pressure pulsation quantity which can be generated by the cavitation nozzle b and is higher than a certain pressure is always higher than that of the standard nozzle a under the condition of the same nozzle pressure drop. If cavitation nozzle b is an optimized nozzle based on standard nozzle a configuration, the plate shows: the cavitation performance of the cavitation nozzle is improved through optimization;
(3) The nozzle cavitation performance plate of the cavitation nozzle c is obtained by the nozzle cavitation performance plate provided by the invention, and the cavitation performance of the cavitation nozzle c without cavitation similarity and the cavitation performance of the standard nozzle a can be quantitatively evaluated and compared. In the cavitation performance plate, the ratio of the pulse pressure generated by the cavitation nozzle c to the accumulated pulse quantity generated by the standard nozzle a under different pressure drops is always smaller than 1, which indicates that the capacity of the cavitation nozzle c for generating the pressure pulse with the pulse pressure larger than the designated pressure is worse than that of the standard nozzle a, and the cavitation performance of the cavitation nozzle c is weaker than that of the standard nozzle a.
Claims (4)
1. The cavitation performance evaluation method of the cavitation nozzle is characterized by comprising the following steps of:
(1) Identifying pressure pulsation according to a cavitation jet pressure signal diagram of the cavitation nozzle;
(2) Obtaining discrete accumulated pulsation quantity according to a cavitation jet flow pressure signal diagram of a cavitation nozzle;
(3) Obtaining a dimensionless pressure-dimensionless accumulated pulsation quantity function after fitting of the cavitation nozzle, a nozzle pressure drop-characteristic pressure function after fitting and a nozzle pressure drop-characteristic accumulated pulsation quantity function after fitting;
(4) Selecting one cavitation nozzle as a standard nozzle A, and judging whether the fitted nozzle pressure drop-characteristic pressure function and the fitted nozzle pressure drop-characteristic accumulated pulsation quantity function of the rest cavitation nozzles B and the standard nozzle A are linearly related, namely whether cavitation similarity exists;
(5) Drawing a cavitation similar nozzle cavitation performance comparison plate or a nozzle cavitation performance plate;
the discrete accumulated pulsation number is obtained by the following steps:
(2-1) numbering the pressure pulsations in time;
(2-2) calculating the pulsating pressure of each pressure pulsationPPulse width deltaTNumbering of pressure pulsations and pulsations pressure and pulsation width deltaTThe array is formed:；
(2-3) establishing a two-dimensional Cartesian coordinate System with the horizontal axis of the coordinate being the pulsating pressurePThe vertical axis is the pulse width deltaTDividing the transverse axis and the longitudinal axis into scales;
the scale of the horizontal axis is divided into:；
wherein:
P t -pressure threshold, MPa;
ndividing the parameters of the pulse pressure horizontal axis scale, and having no dimension;
∆Presolution of the pulsating pressure horizontal axis scale division, MPa;
P max -maximum pulsating pressure of each pressure pulsation in the pressure signal map, MPa;
the vertical axis scale is divided into:；
wherein:
m-dividing the parameters of the pulse width vertical axis scale, and having no dimension;
δ（ΔT) -resolution of the pulse width vertical axis scale division, s;
∆T max -maximum pulse width of each pressure pulse in the pressure signal map, s;
(2-4) grouping all of the arraysAccording to the codeMSequentially judging the pulsation pressurePWhether or not it satisfies:
(1)；
in the method, in the process of the invention,iis an iteration parameter, and is dimensionless;
if the above condition is satisfied, continuously judging the pulse width deltaTWhether or not it satisfies:
(2)；
in the method, in the process of the invention,jis an iteration parameter, and is dimensionless;
the number of pulses satisfying the formulas (1) and (2) is defined asΝ；
(2-5) nodeThe pulse number density at this point is:
；
(2-6) in the formula (2)jReset toj=j+1, repeating processes (2-4), (2-5), (2-6) to；
(2-7) in the formula (1)iReset toi=i+1，Repeating the processes (2-4), (2-5), (2-6), (2-7) to；
(2-8) calculating the discrete cumulative pulse quantity of the pressure at the pulse pressure horizontal axis scale point；
。
2. The cavitation performance evaluation method of cavitation nozzle according to claim 1, wherein the specific process of step (4) is:
(4-1) selecting one cavitation nozzle as a standard nozzle A and the rest cavitation nozzles B, wherein the cavitation nozzles comprise:
dimensionless pressure-dimensionless cumulative pulsation magnitude function after standard nozzle a fitting: (1-1)；
standard nozzle a fitted to the post nozzle pressure drop-characteristic pressure function: (1-2)；
nozzle pressure drop-characteristic cumulative pulsation magnitude function after standard nozzle a fitting: (1-3)；
the cavitation nozzle B is fitted with a dimensionless pressure-dimensionless cumulative pulsation quantity function: (2-1)；
cavitation nozzle B fits post nozzle pressure drop-characteristic pressure function: (2-2)；
after cavitation nozzle B fitting, nozzle pressure drop-characteristic cumulative pulsation magnitude function: (2-3)；
(4-2) the fitted nozzle pressure drop-characteristic pressure function of the cavitation nozzle B divided by the fitted nozzle pressure drop-characteristic pressure function of the standard nozzle a is a constant, and the fitted nozzle pressure drop-characteristic accumulated pulsation amount function of the cavitation nozzle B divided by the fitted nozzle pressure drop-characteristic accumulated pulsation amount function of the standard nozzle a is a constant, so that the cavitation nozzle B and the standard nozzle a have cavitation similarity and are cavitation similar nozzles; in contrast, there is no cavitation similarity, not cavitation-like nozzles.
3. The cavitation nozzle cavitation performance evaluation method according to claim 2, wherein the specific process of drawing cavitation similar nozzle cavitation performance comparison plate is:
(1) Cavitation nozzle B has cavitation similarity to standard nozzle a, then:
；
in the method, in the process of the invention,being a constant, dimensionless, then for cavitation nozzle B:
(3)；
and is also provided with；
In the method, in the process of the invention,being a constant, dimensionless, then for cavitation nozzle B:
(4)；
when formula (3) and formula (4) are substituted into formula (2-1), there is a cavitation nozzle B:
(5)；
characteristic pressure of standard nozzle ADenoted as->Integrating the characteristic pulse quantity of standard nozzleDenoted as->Then formula (5) can be expressed as:
；
(2) Drawing the dimensionless pressure-dimensionless cumulative pulsation quantity function of the cavitation nozzle B in another form with the dimensionless pressure-dimensionless cumulative pulsation quantity function of the standard nozzle A after fitting to form a dimensionless pressure-dimensionless cumulative pulsation quantity plate, drawing the nozzle pressure drop-characteristic pressure function of the standard nozzle A after fitting to form a nozzle pressure drop-characteristic pressure plate, drawing the nozzle pressure drop-characteristic cumulative pulsation quantity function of the standard nozzle A after fitting to form a nozzle pressure drop-characteristic cumulative pulsation quantity plate, and jointly forming a cavitation performance comparison plate of the cavitation similar nozzles A and B by the three plates.
4. The cavitation performance evaluation method of the cavitation nozzle according to claim 2, wherein the drawing method of the cavitation performance plate of the cavitation nozzle comprises the following steps:
(1) Cavitation nozzle B and standard nozzle A do not have cavitation similarity, and the following relationship exists between nozzle pressure drop-characteristic pressure function after the fit of the standard nozzle A and the cavitation nozzle B:；
in the method, in the process of the invention,is an adjusting function taking nozzle pressure drop as an independent variable, and has no dimension;
the nozzle pressure drop-characteristic accumulated pulsation quantity function after the fitting of the standard nozzle A and the cavitation nozzle B has the following relation:
；
in the method, in the process of the invention,is an adjusting function taking nozzle pressure drop as an independent variable, and has no dimension;
then for cavitation nozzle B, its characteristic pressure may be expressed as:
(7)；
the characteristic cumulative pulse number may be expressed as:
(8)；
bringing formula (7) and formula (8) into formula (2-1), then:
；
namely:
(9)；
in the method, in the process of the invention,accumulating the pulsation quantity for the characteristic of the standard nozzle A in the corresponding nozzle pressure drop, having no dimension,；/>for the characteristic pressure of standard nozzle A at the corresponding nozzle pressure drop, +.>；
The cumulative number of pulsations of the standard nozzle a is expressed asThen formula (2-1) can be expressed as:
(10)；
dividing formula (9) by formula (10), then:
；
the above indicates that cavitation nozzle B and standard nozzle A have the same nozzle pressure dropAnd pressure->The ratio of the number of accumulated pulses down is the nozzle pressure drop +.>And pressure->Is a function of (1), namely:
；
specifying the pressureAfter the value, the ratio of the number of accumulated pulsations generated by cavitation nozzle B to standard nozzle A +.>To be nozzle pressure drop->Is a single-valued function of (2);
(2) At different pressuresAt the value, the ratio of the cumulative pulse number of cavitation nozzle B to standard nozzle A +.>Pressure drop with nozzle->Is plotted in a nozzle pressure drop-cumulative pulse number ratio plot to form a nozzle B cavitation performance plot.
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