CN110807796B - Method and device for measuring turbulent three-dimensional velocity field - Google Patents
Method and device for measuring turbulent three-dimensional velocity field Download PDFInfo
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Abstract
The invention discloses a method and a device for measuring a turbulent three-dimensional velocity field, wherein the method comprises the following steps: placing tracer particles into the scanning area; controlling an OCT (optical coherence tomography) scanning system to scan a scanning area to obtain a three-dimensional transient image of the tracer particles corresponding to a first moment, and recording the three-dimensional transient image as a first transient image; obtaining a three-dimensional transient image of the tracer particles corresponding to the second moment, and recording the three-dimensional transient image as a second transient image; performing correlation calculation on the first transient image and the second transient image to obtain a correlation coefficient; when the correlation coefficient is larger than or equal to 0.9, the position coordinates of each tracer particle of the first transient image are calculated, and all the position coordinates are averaged to obtain a first average position coordinate; calculating the position coordinate of each trace particle of the second transient image, and averaging all the position coordinates to obtain a second average position coordinate; and obtaining a turbulent three-dimensional velocity field by using a velocity mathematical model. The device comprises: a control unit and a calculation unit. The invention is mainly used in the field of measurement.
Description
Technical Field
The invention relates to the technical field of measurement, in particular to a method and a device for measuring a turbulent three-dimensional velocity field.
Background
The central problem of the turbulence theory is to solve the statistical solution of the Navier-Stokes equation of the turbulence basic equation. Because the numerical solution calculation workload for solving the irregular turbulence by directly using the Navier-Stokes equation is very large, the engineering usually uses the Reynolds equation, which is a basic equation of the turbulence average flow field derived from the Navier-Stokes equation, to solve the turbulence parameter. To obtain the solution of the reynolds equation, a plurality of velocity fields measured under the same condition need to be obtained as arithmetic mean values, so how to measure the turbulent three-dimensional velocity field more accurately in real time is an important problem for fluid motion research.
There are two main methods for turbulent instantaneous velocity field measurement. One is particle image velocimetry, a certain amount of tracer particles are put into a flow field in advance, a test section of the flow field is illuminated by pulse laser sheet light, the test section is exposed for multiple times by a CCD (charge coupled device), a plurality of particle images are obtained, and finally the acquired images are processed by adopting a velocity extraction algorithm to realize the full-field transient measurement of the flow field velocity field. The other method is laser Doppler velocity measurement, trace particles with certain concentration are generated in advance, the Doppler frequency shift quantity of scattered light to original incident light is measured by using scattering signals of the trace particles in a flow field, and then the velocity is obtained according to the relation between the velocity and the Doppler signals, so that the non-contact measurement of the flow field is realized. The laser Doppler velocity measurement is not directly connected with physical parameters such as the temperature, the pressure and the like of a flow field to be measured, so that the technology has extremely high measurement precision.
The particle image velocimetry can display the physical form of flow field flow, obtain instantaneous full-field flow field information, and has higher measurement precision and resolution. However, in practical applications, when the concentration of trace particles is high, particle images are overlapped, and since laser is interference light, a laser speckle effect appears on a collected image, the stability of a speckle field is poor, and the accuracy and precision of a measurement result are reduced.
Disclosure of Invention
The present invention is directed to a method and apparatus for measuring a turbulent three-dimensional velocity field, which solves one or more of the problems set forth in the prior art, and provides at least one useful alternative or creation.
The solution of the invention for solving the technical problem is as follows: a method for measuring turbulent three-dimensional velocity field, which is based on OCT scanning system, includes:
step 1, putting tracer particles into a scanning area;
step 2, controlling an OCT scanning system to scan a scanning area to obtain a three-dimensional transient image of the tracer particles corresponding to a first moment, and recording the three-dimensional transient image as a first transient image; obtaining a three-dimensional transient image of the tracer particles corresponding to the second moment, and recording the three-dimensional transient image as a second transient image; the first time and the second time have a difference of unit time;
step 3, performing correlation calculation on the first transient image and the second transient image to obtain a correlation coefficient;
step 4, when the correlation coefficient is larger than or equal to 0.9, the position coordinates of each tracer particle of the first transient image are calculated, and all the position coordinates are averaged to obtain a first average position coordinate; calculating the position coordinate of each trace particle of the second transient image, and averaging all the position coordinates to obtain a second average position coordinate;
step 5, obtaining a turbulent flow three-dimensional velocity field by using a velocity mathematical model, wherein the velocity mathematical model is as follows:
wherein (a, b, c) is expressed as a first average coordinate, (x, y, z) is expressed as a second average coordinate, t is expressed as a unit time, and v is expressed as a turbulent three-dimensional velocity field.
Further, before performing step 3, noise reduction processing needs to be performed on the first transient image and the second transient image. The noise of the first transient image and the second transient image can be reduced through the noise reduction processing, and the processing of the first transient image and the second transient image is facilitated.
Further, the method of noise reduction processing includes but is not limited to: mean filtering, median filtering, gaussian filtering.
Further, the correlation calculation in step 3 is specifically:
wherein A is x,y,z Expressed as the grey value of the first transient image in point (x, y, z), B x,y,z Expressed as a gray value of the second transient image in a point (x, y, z), m is expressed as a maximum coordinate value of the first transient image and the second transient image in the x-axis, k is expressed as a maximum coordinate value of the first transient image and the second transient image in the y-axis, and n is expressed as a maximum coordinate value of the first transient image and the second transient image in the z-axis.
Further, the diameter of the tracer particle is 20 μm.
Further, the tracer particles are polyethylene pellets.
A turbulent three-dimensional velocity field measuring device comprising:
the control unit is connected with the calculation unit and is used for controlling the OCT scanning system to scan the scanning area to obtain a three-dimensional transient image of the trace particles corresponding to the first moment and recording the three-dimensional transient image as a first transient image; obtaining a three-dimensional transient image of the tracer particles corresponding to the second moment, and recording the three-dimensional transient image as a second transient image; the first time and the second time have a difference of unit time;
the calculation unit is used for carrying out correlation calculation on the first transient image and the second transient image to obtain a correlation coefficient; when the correlation coefficient is larger than or equal to 0.9, the position coordinates of each tracer particle of the first transient image are calculated, and all the position coordinates are averaged to obtain a first average position coordinate; calculating the position coordinate of each trace particle of the second transient image, and averaging all the position coordinates to obtain a second average position coordinate; obtaining a turbulent flow three-dimensional velocity field by using a velocity mathematical model, wherein the velocity mathematical model is as follows:
wherein (a, b, c) is expressed as a first average coordinate, (x, y, z) is expressed as a second average coordinate, t is expressed as a unit time, and v is expressed as a turbulent three-dimensional velocity field; and outputting the calculated turbulent three-dimensional velocity field in a signal form.
The invention has the beneficial effects that: the method for measuring the turbulent three-dimensional velocity field utilizes an OCT (optical coherence tomography) scanning system to scan trace particles to obtain a first transient image and a second transient image, and judges whether the first transient image and the second transient image have strong correlation or not through correlation calculation, so that the turbulent three-dimensional velocity field is obtained by using a velocity digital model. The measuring device of the turbulent three-dimensional velocity field has the beneficial effects of the method because the method is carried out.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly described below. It is clear that the described figures are only some embodiments of the invention, not all embodiments, and that a person skilled in the art can also derive other designs and figures from them without inventive effort.
FIG. 1 is a flow chart of a method of measuring a turbulent three-dimensional velocity field;
fig. 2 is a schematic block diagram of a turbulent three-dimensional velocity field measurement device.
Detailed Description
The conception, the specific structure, and the technical effects produced by the present invention will be clearly and completely described below in conjunction with the embodiments and the accompanying drawings to fully understand the objects, the features, and the effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention. In addition, all the connection relations mentioned herein do not mean that the components are directly connected, but mean that a better connection structure can be formed by adding or reducing connection auxiliaries according to specific implementation conditions. All technical characteristics in the invention can be interactively combined on the premise of not conflicting with each other.
Referring to fig. 1, a method for measuring a turbulent three-dimensional velocity field, the method being based on an OCT scanning system, comprising:
step 1, putting tracer particles into a scanning area;
step 2, controlling an OCT scanning system to scan a scanning area to obtain a three-dimensional transient image of the tracer particles corresponding to a first moment, and recording the three-dimensional transient image as a first transient image; obtaining a three-dimensional transient image of the tracer particles corresponding to the second moment, and recording the three-dimensional transient image as a second transient image; the first time and the second time have a difference of unit time;
step 3, performing correlation calculation on the first transient image and the second transient image to obtain a correlation coefficient;
step 4, when the correlation coefficient is larger than or equal to 0.9, the position coordinates of each tracer particle of the first transient image are calculated, and all the position coordinates are averaged to obtain a first average position coordinate; calculating the position coordinate of each trace particle of the second transient image, and averaging all the position coordinates to obtain a second average position coordinate;
step 5, obtaining a turbulent flow three-dimensional velocity field by using a velocity mathematical model;
wherein the speed mathematical model is:
(a, b, c) is expressed as a first average coordinate, (x, y, z) is expressed as a second average coordinate, t is expressed as a unit time, and v is expressed as a turbulent three-dimensional velocity field.
In step 3, the correlation calculation specifically includes:
wherein A is x,y,z Expressed as the grey value of the first transient image in point (x, y, z), B x,y,z Expressed as a gray value of the second transient image in a point (x, y, z), m is expressed as a maximum coordinate value of the first transient image and the second transient image in the x-axis, and k is expressed as the first transient image and the second transient imageThe maximum coordinate values of the two transient images in the y-axis, and n is represented as the maximum coordinate values of the first transient image and the second transient image in the z-axis.
The scanning area is predetermined and generally a rectangular body. The measuring method can measure the turbulent three-dimensional velocity field in the rectangular body. In order to measure the turbulent three-dimensional velocity field, trace particles are put into a scanning area, and the turbulent three-dimensional velocity field is traced and reflected through the trace particles. And scanning the scanning area through the depth scanning capability of the OCT scanning system so as to obtain a three-dimensional transient image of the trace particles, wherein the three-dimensional transient image of the trace particles reflects a turbulent three-dimensional velocity field. By setting at least two scans, the first scan obtains a first transient image, and the second scan obtains a second transient image. Both the first transient image and the second transient image record transient position information of the trace particle. In order to improve the accuracy of the calculation, in some preferred embodiments, the first transient image and the second transient image are subjected to noise reduction processing. The method of noise reduction processing includes but is not limited to: mean filtering, median filtering, gaussian filtering. Since the first transient image and the second transient image both record the transient position information of the trace particles, the velocity information of the trace particles can be obtained from the position information. It is of course the prerequisite that the transient position information of the trace particles recorded in the first and second transient images have a certain correlation. Based on the above principle, the technical scheme obtains the correlation coefficient by performing correlation calculation on the first transient image and the second transient image. When the correlation coefficient is greater than or equal to 0.9, it indicates that the transient position information of the trace particles recorded by the first transient image and the second transient image have a strong correlation. Thus, the turbulent three-dimensional velocity field can be calculated by a velocity mathematical model. In the calculation process, because the first transient image and the second transient image have strong correlation, the first average position coordinate is obtained by averaging the position coordinates of all the trace particles of the first transient image, and the second average position coordinate is obtained by averaging the position coordinates of all the trace particles of the second transient image. And dividing the plurality of trace particles into a whole in an average mode, and reflecting the motion displacement of the trace particles in a mode of making a difference between the first average position coordinate and the second average position coordinate. Thereby finally measuring the turbulent three-dimensional velocity field.
In some embodiments, the tracer particles are 20 μm in diameter. The tracer particles are polyethylene pellets.
Referring to fig. 2, the present embodiment further provides a measuring apparatus for a turbulent three-dimensional velocity field, which is applied to an OCT scanning system, and includes: the device comprises a control unit and a calculation unit, wherein the control unit is connected with the calculation unit.
The control unit is used for comprising: controlling an OCT (optical coherence tomography) scanning system to scan a scanning area to obtain a three-dimensional transient image of the trace particles corresponding to a first moment, and recording the three-dimensional transient image as a first transient image; obtaining a three-dimensional transient image of the tracer particles corresponding to the second moment, and recording the three-dimensional transient image as a second transient image; wherein the first time and the second time have a difference of unit time;
a computing unit to include: performing correlation calculation on the first transient image and the second transient image to obtain a correlation coefficient; when the correlation coefficient is larger than or equal to 0.9, the position coordinates of each tracer particle of the first transient image are calculated, and all the position coordinates are averaged to obtain a first average position coordinate; solving the position coordinates of each tracer particle of the second transient image, and averaging all the position coordinates to obtain a second average position coordinate; obtaining a turbulent flow three-dimensional velocity field by using a velocity mathematical model, wherein the velocity mathematical model is as follows:
wherein (a, b, c) is expressed as a first average coordinate, (x, y, z) is expressed as a second average coordinate, t is expressed as a unit time, and v is expressed as a turbulent three-dimensional velocity field; and outputting the calculated turbulent three-dimensional velocity field in a signal form.
Since the measuring device of the turbulent three-dimensional velocity field is used for executing the measuring method of the turbulent three-dimensional velocity field, the measuring device of the turbulent three-dimensional velocity field has the beneficial effect of the measuring method of the turbulent three-dimensional velocity field.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that the present invention is not limited to the details of the embodiments shown and described, but is capable of numerous equivalents and substitutions without departing from the spirit of the invention and its scope is defined by the claims appended hereto.
Claims (6)
1. A measurement method of turbulent three-dimensional velocity field is based on OCT scanning system, which is characterized in that: the method comprises the following steps:
step 1, putting tracer particles into a scanning area;
step 2, controlling an OCT scanning system to scan the scanning area to obtain a three-dimensional transient image of the trace particles corresponding to the first moment, and recording the three-dimensional transient image as a first transient image; obtaining a three-dimensional transient image of the tracer particles corresponding to the second moment, and recording the three-dimensional transient image as a second transient image; wherein the first time and the second time have a difference of unit time;
step 3, performing correlation calculation on the first transient image and the second transient image to obtain a correlation coefficient;
step 4, when the correlation coefficient is larger than or equal to 0.9, the position coordinates of each tracer particle of the first transient image are calculated, and all the position coordinates are averaged to obtain a first average position coordinate; calculating the position coordinate of each trace particle of the second transient image, and averaging all the position coordinates to obtain a second average position coordinate;
step 5, obtaining a turbulent flow three-dimensional velocity field by using a velocity mathematical model, wherein the velocity mathematical model is as follows:
wherein (a, b, c) is expressed as a first average coordinate, (x, y, z) is expressed as a second average coordinate, t is expressed as a unit time, and v is expressed as a turbulent three-dimensional velocity field;
the correlation calculation in step 3 is specifically as follows:
wherein the content of the first and second substances,
expressed as the gray value in a point (x, y, z) of the first transient image, is/are>
Expressed as a gray value of the second transient image in a point (x, y, z), m is expressed as a maximum coordinate value of the first transient image and the second transient image in the x-axis, k is expressed as a maximum coordinate value of the first transient image and the second transient image in the y-axis, and n is expressed as a maximum coordinate value of the first transient image and the second transient image in the z-axis.
2. A method of measuring a turbulent three-dimensional velocity field according to claim 1, wherein: before step 3, noise reduction processing needs to be performed on the first transient image and the second transient image.
3. A method of measuring a turbulent three-dimensional velocity field according to claim 2, wherein: the method of noise reduction processing includes but is not limited to: mean filtering, median filtering, gaussian filtering.
4. A method of measuring a turbulent three-dimensional velocity field according to claim 1, wherein: the diameter of the tracer particles is 20 μm.
5. A method of measuring a turbulent three-dimensional velocity field according to claim 4, wherein: the tracer particles are polyethylene pellets.
6. A measuring device for turbulent three-dimensional velocity field is characterized in that: the method comprises the following steps:
the control unit is connected with the calculation unit and is used for controlling the OCT scanning system to scan the scanning area to obtain a three-dimensional transient image of the trace particles corresponding to the first moment and recording the three-dimensional transient image as a first transient image; obtaining a three-dimensional transient image of the tracer particles corresponding to the second moment, and recording the three-dimensional transient image as a second transient image; the first time and the second time have a difference of unit time;
the computing unit is used for carrying out correlation computation on the first transient image and the second transient image to obtain a correlation coefficient; when the correlation coefficient is larger than or equal to 0.9, the position coordinates of each tracer particle of the first transient image are calculated, and all the position coordinates are averaged to obtain a first average position coordinate; calculating the position coordinate of each trace particle of the second transient image, and averaging all the position coordinates to obtain a second average position coordinate; obtaining a turbulent flow three-dimensional velocity field by using a velocity mathematical model, wherein the velocity mathematical model is as follows:
wherein (a, b, c) is expressed as a first average coordinate, (x, y, z) is expressed as a second average coordinate, t is expressed as a unit time, and v is expressed as a turbulent three-dimensional velocity field; outputting the turbulence three-dimensional velocity field obtained by calculation in a signal form;
in the calculation unit, the correlation calculation specifically includes:
wherein the content of the first and second substances,
expressed as the gray value in a point (x, y, z) of the first transient image, is/are>
Expressed as grey values of the second transient image in points (x, y, z), and m is expressed as grey values of the first transient image and the second transient image in the x-axisK is expressed as the maximum coordinate value of the first transient image and the second transient image in the y-axis, and n is expressed as the maximum coordinate value of the first transient image and the second transient image in the z-axis. />
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| CN107525945A (en) * | 2017-08-23 | 2017-12-29 | 南京理工大学 | 3D 3C particle image speed-measuring systems and method based on integration imaging technology |
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| CN107525945A (en) * | 2017-08-23 | 2017-12-29 | 南京理工大学 | 3D 3C particle image speed-measuring systems and method based on integration imaging technology |
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