CN114487476A - System and method for measuring particle image flow field velocity related to space-time state - Google Patents
System and method for measuring particle image flow field velocity related to space-time state Download PDFInfo
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Abstract
The invention discloses a system and a method for measuring the flow field velocity of a particle image related to a space-time state, and relates to the technical field of hydrodynamics and fluid measurement. Measuring the flow velocity of fluid in a fluid conveying pipeline through a measuring system, wherein two vertical planes of axes in the fluid conveying pipeline are data acquisition positions; the measuring system comprises a semiconductor laser, two linear array CCDs, an acquisition card and a processor; laser emitted by the semiconductor laser is led into the first position and the second position through two laser emitting optical fibers to form two laser beams which pass through the axis of the pipeline and are coplanar and parallel so as to illuminate fluid particles in the pipeline; respectively leading out the fluid particle images illuminated by the laser beams at the first position and the second position to two linear array CCDs for imaging storage; one-dimensional image sequences acquired by the two linear array CCDs are transmitted to a processor through an acquisition card, and are stored and operated through the processor. Provides a new primary standard of the flow quantity value and has wide application prospect.
Description
Technical Field
The invention relates to the technical field of hydrodynamics and fluid metering, in particular to a system and a method for measuring flow field velocity by utilizing the correlation of the space-time state of particle image information.
Background
The flow measurement is one of the components of the measurement science and technology, and has close relation with national economy, national defense construction and scientific research. At present, several gas flow meters commonly used in industrial metering include differential pressure type flow meters, volumetric flow meters and velocity type flow meters, wherein the velocity type flow meters take basic physical quantities, namely displacement and time, as measuring objects, belong to an original-level measuring method, avoid error transmission and theoretically have higher measuring precision.
The non-contact measurement method is the most ideal method for measuring the speed of the fluid and the flow field. With the rapid development of computer software and hardware technologies, Particle Image Velocimetry (PIV) technology appears in the field of flow field display and measurement, and has been widely applied to the measurement of two-dimensional and three-dimensional flow fields. The PIV technology has the greatest characteristic of breaking through the limitation of flow field single-point measurement technologies such as Laser Doppler Velocimetry (LDV) and the like, can record the flow information of the whole flow field at the same time, obtains the overall structure and transient images of a planar two-dimensional or spatial three-dimensional flow field, and simultaneously ensures the precision and resolution of single-point measurement.
In the flow velocity and flow measurement of fluid conveying pipelines such as natural gas and petroleum, the PIV technology has specific application cases, as shown in chinese patent application with application number "200810240036.1" and named as "particle imaging device in natural gas pipeline", but the flow field velocity is measured by using the PIV technology, two-dimensional image information of the flow field needs to be obtained, so that the fluid conveying pipelines need to be subjected to transparentization treatment, the difficulty is high, and the pipeline strength can be reduced; in addition, the flow in the straight line section of the pipeline, whether laminar flow or turbulent flow, can be regarded as unidirectional steady flow in statistics, and the PIV technology is not needed to measure the characteristic length of a two-dimensional unsteady flow field, so that the waste of equipment investment is caused.
Disclosure of Invention
Aiming at the problems, the invention provides a measuring system and a measuring method for measuring the unidirectional flow velocity such as linear pipeline flow and the like by utilizing one-dimensional particle image information without two-dimensional particle image information.
The technical scheme of the invention is as follows: measuring the flow velocity of fluid in a fluid conveying pipeline through a measuring system, wherein two axis vertical planes in the fluid conveying pipeline are data acquisition positions, the positions are sequentially marked as a first position and a second position along the flow direction of the fluid, two laser emission holes and two data acquisition holes are formed in the fluid conveying pipeline and are respectively positioned on the first position and the second position, the two laser emission holes are positioned on the same axis parallel line of the pipe wall, and the two data acquisition holes are also positioned on the same axis parallel line of the pipe wall;
the measuring system comprises a semiconductor laser, two linear array CCDs, an acquisition card and a processor;
the semiconductor laser is connected with the fluid conveying pipeline through two laser emission optical fibers, and the two laser emission optical fibers are respectively connected with the two laser emission holes, so that laser emitted by the semiconductor laser is led into the first position and the second position through the two laser emission optical fibers to form two laser beams which pass through the axis of the pipeline and are coplanar and parallel, and fluid particles in the pipeline are illuminated;
the two linear array CCDs are respectively connected with the fluid conveying pipeline through two data acquisition optical fibers, and the two data acquisition optical fibers are respectively connected with two data acquisition holes, so that fluid particle images illuminated by laser beams at the first position and the second position are respectively led out to the two linear array CCDs for imaging storage;
the processor is simultaneously connected with the two linear array CCDs through the acquisition card, one-dimensional image sequences acquired by the two linear array CCDs are transmitted to the processor through the acquisition card, and are stored and operated through the processor.
And the time sequences of the two linear array CCDs are synchronous.
The speed measurement is carried out according to the following steps:
s1, data acquisition;
opening the semiconductor laser, and forming two laser beams which pass through the pipeline axis and are coplanar and parallel on the first position and the second position; opening two linear array CCDs to continuously acquire and store one-dimensional image sequences at the first position and the second position at a constant millisecond time interval delta t;
s2, constructing a two-dimensional space-time particle image matrix;
get time T1To TmM lines of array particle images of the position of the inner position I are recorded as an image matrix I;
get time TiTo TnThe n-i +1 column array particle image at the position of the inner position II is recorded as an image matrix II;
wherein i, n and m are positive integers, n is greater than m, i is not less than 1, and n-i = m-1;
s3, calculating a correlation coefficient;
i, taking a positive integer, and performing two-dimensional correlation operation on the n-i +1 row array particle image at the second position and the m row array particle image at the first position to obtain a correlation coefficient r; gradually increasing the value of i from 1 until the correlation coefficient r is greater than 0.8 and then decreasing to 0.5, or decreasing five times after r is greater than 0.8;
then, i is used as an abscissa and r is used as an ordinate, a change curve of the correlation coefficient r along with i is obtained, and a maximum value r of the curve is obtainedmaxAt a time imax；
S4, outputting a speed result;
the velocity of the fluid flow can be found as: v = D/(i)maxX Δ t), where D is the distance between position one and position two.
The technical scheme of the invention has the following beneficial effects:
the flow of the flow field is measured by utilizing a space-time state correlation method, the principle and the method of non-contact flow field measurement are expanded, a new primary standard of flow quantity values is provided, and the method has wide application prospect.
And secondly, the flowing speed is obtained by utilizing the one-dimensional flow field information, a two-dimensional imaging system is not needed, the method is simple and convenient, and the investment of equipment can be saved during implementation and application.
And thirdly, when the one-dimensional flow field information is acquired, the arrangement space of the required measuring device is small, and the problem that the measuring device is not easy to install in a limited space can be solved.
On the whole, a two-dimensional matrix based on which a flow field (such as a PIV) is measured by the existing correlation method is formed by two-dimensional space information, and a two-dimensional matrix based on the method is formed by one-dimensional space information and one-dimensional time information, so that fundamentally different acquisition modes are simpler and the calculated amount is smaller in the measurement principle, and the method is a new flow field measurement method. The space-time two-dimensional matrix not only comprises the spatial characteristics of the flow, but also comprises the time characteristics of the flow, and is particularly suitable for flow fields with stable statistical characteristics, such as turbulence. The device is adaptive to the measurement principle, the equipment investment, the application scene and the like are different from those of the existing system, and the device has the advantages of wide application range and good use effect.
Drawings
FIG. 1 is a schematic view of the principle of the present invention,
FIG. 2 is a schematic diagram of a two-dimensional spatiotemporal particle image matrix,
figure 3 is a schematic view of a correlation curve,
fig. 4 is a diagram of an embodiment of the present disclosure.
Detailed Description
In order to clearly explain the technical features of the present patent, the following detailed description of the present patent is provided in conjunction with the accompanying drawings.
As shown in fig. 4, the flow velocity of the fluid in the fluid conveying pipeline is measured by the measuring system, two vertical planes of the axis in the fluid conveying pipeline are data acquisition positions, and are sequentially recorded as a first position and a second position along the flow direction of the fluid, two laser emitting holes and two data acquisition holes are formed in the fluid conveying pipeline and are respectively located at the first position and the second position, the two laser emitting holes are located on the same parallel line of the axis of the pipe wall and are respectively a hole a1 and a hole a2, and the two data acquisition holes are also located on the same parallel line of the axis of the pipe wall and are respectively a hole B1 and a hole B2; the inner diameters of the through holes A1, B1, A2 and B2 are small enough, so that the leading-out optical fibers can be installed and perfect sealing can be realized, and fluid leakage of the pipeline can not be caused.
The measuring system comprises a semiconductor laser, two linear array CCDs (respectively a linear array CCD1 and a linear array CCD 2), an acquisition card and a processor;
the semiconductor laser is connected with the fluid conveying pipeline through two laser emission optical fibers, and the two laser emission optical fibers are respectively connected with the two laser emission holes, so that laser emitted by the semiconductor laser is led into the first position and the second position through the two laser emission optical fibers to form two laser beams which pass through the axis of the pipeline and are coplanar and parallel, and fluid particles in the pipeline are illuminated; the fluid particles may be impurities contained in the fluid itself or may be tracer particles applied upstream of the pipe.
The two linear array CCDs are respectively connected with the fluid conveying pipeline through two data acquisition optical fibers, and the two data acquisition optical fibers are respectively connected with two data acquisition holes, so that fluid particle images illuminated by laser beams at the first position and the second position are respectively led out to the two linear array CCDs for imaging storage;
the processor is simultaneously connected with the two linear array CCDs through the acquisition card, the two linear array CCDs and the one-dimensional image sequence acquired by the linear array CCDs are transmitted to the processor through the acquisition card, and storage and operation are carried out through the processor. The construction and correlation operation of a two-dimensional space-time particle image matrix are carried out by the following space-time state correlation algorithm, namely steps S2 and S3, and the flow field flow velocity in the fluid conveying pipeline is displayed in real time. In addition, the flow rate of fluid delivery can be obtained in real time on the premise of a given inner diameter of the pipeline.
The time sequences of the two linear array CCDs can be synchronized.
The speed measurement is carried out according to the following steps:
s1, data acquisition;
opening the semiconductor laser, and forming two laser beams which pass through the pipeline axis and are coplanar and parallel on the first position and the second position; opening two linear array CCDs to continuously acquire and store one-dimensional image sequences at the first position and the second position at a constant millisecond time interval delta t; Δ t is the time resolution of the one-dimensional flow field information acquisition device;
specifically, at two different positions downstream in the fluid flow direction, spatial one-dimensional flow field information perpendicular to the flow direction is acquired (as shown in fig. 1). Due to the unidirectional flow, fluid passing through position one will, at some point in the future, necessarily flow through position two in a statistical sense. The length of time that the fluid passes through the two locations depends on the average flow rate of the fluid and the distance D between the two locations. At the first and second positions, the means for acquiring one-dimensional flow field information can be precisely synchronized and each acquired and stored continuously at constant millisecond time intervals Δ t.
S2, constructing a two-dimensional space-time particle image matrix;
get time T1To TmObtaining m-line array particle images of a position I; forming a two-dimensional spatiotemporal particle image 1;
get time TiTo TnAcquiring an n-i +1 array particle image of the position II; forming a two-dimensional spatiotemporal particle image 2;
wherein i, n and m are positive integers, n is greater than m, i is not less than 1, and n-i = m-1;
at the first position and the second position, the one-dimensional flow field information continuously acquired in a period of time can be respectively constructed into two-dimensional spatio-temporal particle image matrixes (as shown in fig. 2), wherein the longitudinal dimension is determined by the spatial resolution of the equipment for acquiring the one-dimensional flow field information, and the transverse dimension is determined by the temporal resolution of the equipment for acquiring the one-dimensional flow field information.
E.g. in position one, when T = T1Then, acquiring a line array particle image; when T = T2=T1When + delta t, acquiring a linear array particle image of an adjacent column; when T = Tm=T1And when the image is positive (m-1) multiplied by delta t, the last row of linear array particle images is obtained.
Similarly, at position one, when T = T1Then, acquiring a line array particle image; when T = T2=T1When + delta t, acquiring a linear array particle image of an adjacent column; when T = Tn=T1And when the image is positive (n-1) multiplied by delta t, the last line array particle image is obtained.
At position two, take T = TiThe linear array particle image of the moment is used as the first column of the two-dimensional space-time particle image matrix, and T = TnAnd taking the linear array particle image at the moment as the last column of the two-dimensional space-time particle image matrix, wherein i is more than or equal to 1, and n-i = m-1, so as to ensure that the two-dimensional space-time particle image matrices at the position two and the position one respectively have the same longitudinal dimension and transverse dimension.
S3, calculating a correlation coefficient;
it can be seen that the variable i x Δ t represents the time interval between the acquisition of the two-dimensional spatiotemporal particle image 2 and the two-dimensional spatiotemporal particle image 1. i, taking a positive integer, and performing two-dimensional correlation operation on the n-i +1 row array particle image at the second position and the m row array particle image at the first position to obtain a correlation coefficient r; gradually increasing the value of i from 1 until the correlation coefficient r is greater than 0.8 and then decreasing to 0.5, or decreasing five times after r is greater than 0.8;
then, using i as abscissa and r as ordinate, obtaining the variation curve of the correlation coefficient r with i (as shown in fig. 3), and obtaining the maximum value r of the curvemaxAt a time imax(ii) a If 10 Δ t is required from position one to position two, then the value range of i isFinally, 10 is covered, and 10 is also covered in the range of the abscissa of the correlation coefficient curve, such as 1-20; theoretically, the correlation coefficient is maximum when i =10, and gradually decreases when i = 9-1 or i = 11-20.
In the calculation process of the correlation coefficient, specifically, the linear array CCDs adopted at the first position and the second position both contain 30 pixels. At position one, if let M =20, the two-dimensional spatio-temporal particle image obtained is a matrix M0 of 30 × 20 (longitudinal dimension × transverse dimension). At position two, i takes a positive integer, and n-i = m-1. When i =1, n =20, resulting in a two-dimensional spatiotemporal particle image matrix M1 with a first dimension of 30 × 20; when i =2, n =21, resulting in a two-dimensional spatiotemporal particle image matrix M2 with a second dimension of 30 × 20; by analogy, at any i, n = m-1+ i, the two-dimensional spatio-temporal particle image matrix Mi with the i-th dimension of 30 × 20 can be obtained. The matrixes M1 and M2 … Mi … are respectively used for carrying out correlation operation with the matrix M0 to obtain correlation coefficients r1 and r2 … ri …. In practice, the value of the positive integer i should be large enough so that the correlation coefficient r increases and then decreases with increasing i, i.e. there is a maximum value rmax. So that r takes the corresponding value i of rmax, i.e. imax.
S4, outputting a speed result;
according to the principle of functional correlation, the maximum value r of the correlation coefficientmaxThe two-dimensional space-time particle image matrixes at position two have the maximum similarity, namely the fluid distribution at position two and imaxThe fluid distribution at one position before time at is most similar, i.e. the fluid at one position passes through imaxTime duration x Δ t, flow to position two. Thus, the velocity of the fluid flow can be obtained as: v = D/(i)maxX Δ t), where D is the distance between position one and position two. As internal parameters of the measuring system, the distance D between the first position and the second position and the time resolution delta t of the one-dimensional flow field information acquisition equipment can be adjusted according to actual requirements.
While the invention has been described in terms of its preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
Claims (3)
1. A measurement system for particle image flow field velocity related to a space-time state is characterized in that the flow velocity of fluid in a fluid conveying pipeline is measured through the measurement system, two axis vertical surfaces in the fluid conveying pipeline are data acquisition positions, the flow direction of the fluid is sequentially marked as a first position and a second position, two laser emission holes and two data acquisition holes which are respectively positioned on the first position and the second position are arranged in the fluid conveying pipeline, the two laser emission holes are positioned on the same axis parallel line of a pipe wall, and the two data acquisition holes are also positioned on the same axis parallel line of the pipe wall;
the measuring system comprises a semiconductor laser, two linear array CCDs, an acquisition card and a processor;
the semiconductor laser is connected with the fluid conveying pipeline through two laser emission optical fibers, and the two laser emission optical fibers are respectively connected with the two laser emission holes, so that laser emitted by the semiconductor laser is led into the first position and the second position through the two laser emission optical fibers to form two laser beams which pass through the axis of the pipeline and are coplanar and parallel, and fluid particles in the pipeline are illuminated;
the two linear array CCDs are respectively connected with the fluid conveying pipeline through two data acquisition optical fibers, and the two data acquisition optical fibers are respectively connected with two data acquisition holes, so that fluid particle images illuminated by laser beams at the first position and the second position are respectively led out to the two linear array CCDs for imaging storage;
the processor is simultaneously connected with the two linear array CCDs through the acquisition card, one-dimensional image sequences acquired by the two linear array CCDs are transmitted to the processor through the acquisition card, and are stored and operated through the processor.
2. A system for measuring spatio-temporal state-dependent particle image flow field velocities as recited in claim 1, wherein the timing of the two line CCDs is synchronized.
3. A method for measuring the velocity of a particle image flow field related to the spatio-temporal state of a measurement system according to claim 1, which is characterized by comprising the following steps:
s1, data acquisition;
opening the semiconductor laser, and forming two laser beams which pass through the pipeline axis and are coplanar and parallel on the first position and the second position; opening two linear array CCDs to continuously acquire and store one-dimensional image sequences at the first position and the second position at a constant millisecond time interval delta t;
s2, constructing a two-dimensional space-time particle image matrix;
get time T1To TmM lines of array particle images of the position of the inner position I are recorded as an image matrix I;
get time TiTo TnThe n-i +1 row array particle image of the position of the inner position II is recorded as an image matrix II;
wherein i, n and m are positive integers, n is greater than m, i is not less than 1, and n-i = m-1;
s3, calculating a correlation coefficient;
i, taking a positive integer, and performing two-dimensional correlation operation on the n-i +1 row array particle image at the second position and the m row array particle image at the first position to obtain a correlation coefficient r; gradually increasing the value of i from 1 until the correlation coefficient r is greater than 0.8 and then decreasing to 0.5, or decreasing five times after r is greater than 0.8;
then, i is used as an abscissa and r is used as an ordinate, a change curve of the correlation coefficient r along with i is obtained, and a maximum value r of the curve is obtainedmaxAt a time imax；
S4, outputting a speed result;
the velocity of the fluid flow can be found as: v = D/(i)maxX Δ t), where D is the distance between position one and position two.
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