CN101231299A - Method for measuring particle velocity - Google Patents
Method for measuring particle velocity Download PDFInfo
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- CN101231299A CN101231299A CNA2007100367275A CN200710036727A CN101231299A CN 101231299 A CN101231299 A CN 101231299A CN A2007100367275 A CNA2007100367275 A CN A2007100367275A CN 200710036727 A CN200710036727 A CN 200710036727A CN 101231299 A CN101231299 A CN 101231299A
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Abstract
The invention relates to a method for measuring particle velocity using grey scale autocorrelation of particle image, belonging to the technical field of optical measurement of velocity. The method comprises obtaining particle image with grey scale difference formed by double exposure of flow field using an imaging system of a particle image velocity field meter, pre-treating with digital image processing technique, pairing particle image points corresponding to double exposure of the same particle in a divided sub-region according to the total grey scale of the obtained particle image points and the internal correlation with different widths of laser optical pulse, and obtaining the velocity vector of the particle according to the position information of two particle image points and the difference of the total grey scale, so as to obtain the velocity information of the total flow field. The invention reduces the performance and control requirements to camera, reduces the influence of Gaussian distribution of laser optical intensity on the results, so as to improve the timeliness of velocity measurement, and solve the direction ambiguity problem. The invention is characterized in substantive distinguishing features and marked improvement by overcoming the shortcomings in the prior art.
Description
Technical field
The invention belongs to the speed field of optical measuring technologies, what relate to is the method for measuring the flow field particle rapidity, and particularly a kind of use particle picture velocity field instrument (PIV) is taken the flow field particle picture and utilized the method for particle picture gray scale autocorrelation measurement particle rapidity.
Background technology
Particle picture velocity field instrument PIV (Particle Image Velocimetry) is a kind of brand-new fluid-velocity survey instrument that closely grows up during the last ten years, disturb characteristics little and realization whole flow field speed instantaneous measurement with its stream field, become the main tool that flow field velocity is measured rapidly.
The PIV system mainly is divided into auto-correlation and two kinds of technology of simple crosscorrelation by the querying method difference.Autocorrelation technique is the image of record double exposure on same frame picture, after the division query region, same frame picture is adopted auto-correlation computation, obtains velocity information according to the auto-correlation peak value.Because the auto-correlation peak value is symmetrical, thereby the directions of the velocity information that obtains existence 180 degree are fuzzy, just the direction ambiguity problem of so-called autocorrelation technique.Cross-correlation technique is characteristics of utilizing the CCD camera, and the double exposure image recording on the different picture of two frames, is divided identical big or small query region respectively to two frame pictures, does computing cross-correlation, according to cross-correlation peak value acquisition speed information.Cross-correlation technique has solved the direction ambiguity problem, but camera properties and control thereof have been proposed new requirement.
In the prior art, Wu Zhijun is at " the greyness discriminance querying method of laser particle image velocimetry " (" application laser ", Vol.21NO.2 April 2001) the speed measurement method of introducing in the literary composition based on associating gray-scale statistical frequency, it is the image of record double exposure on same frame picture, the laser illuminator light intensity difference that double exposure is used, thereby the gray-scale value of corresponding particle picture point is also different, then single image is divided query region, by query region the particle picture point is calculated associating gray-scale statistical frequency, the displacement of the corresponding query region particle image of statistics frequency maximal value obtains velocity information with this.This method be with the double exposure image recording on same frame picture, thereby inherited autocorrelation technique advantage low for equipment requirements, Liang Cibaoguang laser illuminator light intensity difference by distinguishing the corresponding different particle picture points of double exposure, solves the ambiguous problem of auto-correlation direction simultaneously; But because the illuminating laser sheet optical intensity of this method is problems such as Gaussian distribution shape and flow field to be measured particle size span, make the corresponding particle picture gray-scale value of double exposure occur crossover phenomenon easily, be unfavorable for the double exposing differentiation of particle picture point is the main problem of this method.
Summary of the invention
The object of the present invention is to provide a kind of method of new measurement particle rapidity, the particle picture velocity field instrument imaging system that this method utilization is used for the gray-scale statistics classification inquiry obtains the particle picture with gray difference that the flow field double exposure forms, after the digital image processing techniques pre-service, in the zonule of dividing, realize the double expose pairing of corresponding particle picture point of same particle in correlativity by the interior of the particle picture point gray scale summation under the laser sheet optical pulse irradiation of different in width, difference according to two particle image point position information and gray scale summation obtains the particle's velocity vector, thereby obtains the velocity information in whole flow field.
Further, the present invention can be achieved through the following technical solutions, and specifically comprises:
(1) choose reasonable be used to double expose laser sheet optical pulse light intensity, the laser sheet optical pulse width of illumination is that camera exposure time, camera shutter are opened duration and laser sheet optical interpulse period: according to particle size and the used double exposure laser illuminator of concrete condition setting measurement sheet light impulse lengths such as dense degree and Measurement Resolution in the flow velocity speed in flow field to be measured, the flow field is camera double exposure time t
1And t
2, camera shutter opens the laser output power P of duration T, laser sheet optical Δ interpulse period t and decision laser sheet optical pulse light intensity I.
(2) the particle picture velocity field instrument imaging system that is used for the gray-scale statistics classification inquiry is taken the particle picture with gray difference of the flow field double exposure under the width of cloth laser pulse illumination: the particle picture velocity field instrument imaging system that is used for the gray-scale statistics classification inquiry is successively launched the laser sheet optical pulsing light flow field that two bundles have identical light intensity distinct pulse widths, camera follows laser pulse to double expose, obtain the particle picture that a width of cloth has gray difference, the input computing machine.
(3) adopt digital image processing techniques that particle picture is done pre-service: to adopt suitable digital image processing techniques such as level and smooth and denoising that particle picture is done pre-service at the various flows field characteristic, remove background and other noise effect in the image, improve picture quality.
(4) obtain the position of each particle picture point on the image, big or small and gray scale summation information.Be meant: particle picture is made rim detection, distinguish each particle picture point on the image, obtain positional information x and the y and the area size S of each particle picture point; Obtain the original gray scale summation information G of each particle picture point correspondence again in conjunction with particle picture after the pre-service.
(5) to the reasonable division of cells of particle picture territory: according to the requirement adjustment of flow field particle dense degree and Measurement Resolution and set the size that the zonule is divided.
(6) the particle picture point of exposing at twice at the zonule inner region, match the particle picture point of the corresponding different gray scale summations of each particle double exposure: the particle picture point that particle picture point in the zonule is replaced to identical size, same grayscale, the fast two-dimensional fourier transformation computing is done in the zonule, obtain the relative displacement of regional flow field by the auto-correlation peak value that draws, in conjunction with the double exposure particle picture point gray scale summation ratio (G of each particle
1/ G
2) (wherein, G
1Be the same particle particle picture point gray scale summation of exposing for the first time, G
2Be the same particle particle picture point gray scale summation of exposing for the second time) with laser sheet optical pulse width ratio (t
1/ t
2) internal relation, particle elementary area size ratio (S
1/ S
2) (wherein, S
1Be the same particle particle elementary area size of exposing for the first time, S
2Be the same particle particle elementary area size of exposing for the second time) with laser sheet optical pulse width ratio (t
1/ t
2) condition of particle rapidity similarity in internal relation and the zonule, in the zonule, realize the pairing of same particle double exposure particle picture point.
(7) velocity information that obtains whole flow field according to the diverse location and the half-tone information of the paired two particle picture point of each particle centering: the positional information according to pairing particle picture point obtains particle displacement, in conjunction with double exposure laser sheet optical interpulse period, according to the two-dimension speed computing formula
(wherein, v is particle rapidity to be asked to obtain the particle rapidity size; x
1, y
1Center position for the particle picture point of exposing for the first time; x
2, y
2Center position for the particle picture point of exposing for the second time; Δ t is the interval time of twice laser sheet optical pulse); The different gray scale summations of paired two particle picture point according to each particle obtain the particle rapidity direction; Add up each particle rapidity vector in all zonules and obtain the velocity information in whole flow field.
Further, also can comprise: (8) output speed frame: the whole flow field velocity information that will obtain is presented on the computer screen with image format, or is exported by printer prints.
Beneficial effect of the present invention: the present invention utilizes the corresponding exposure with camera in laser pulse illumination flow field recorded stream field particle double exposure image on same frame picture of twice identical light intensity different in width of priority, to the performance and the control requirement reduction of camera; Inherent correlativity according to same particle double exposure particle picture point gray scale summation realizes same particle double exposure particle picture point pairing in the zonule, has avoided the influence of factors such as laser sheet optical Intensity of Gaussian distribution to the result; The pairing algorithm of the double exposure particle picture point of same particle is simple, the ageing raising of velocity survey; Difference according to the double exposure particle picture point gray scale summation of same particle obtains velocity reversal information, has solved the direction ambiguity problem.Overcome deficiency of the prior art and defective, had substantive distinguishing features and marked improvement.
Embodiment
Below in conjunction with the embodiment that in the tank flow field, adds trace particle measurement tank water velocity information technical scheme of the present invention is described in further detail:
1. because the flow velocity in tank flow field is slow, particle is big and more sparse in the flow field, and Measurement Resolution is less demanding, thereby the used double exposure laser illuminator of setting measurement sheet light impulse length is the camera time t that double exposes
1=5ms and t
2=10ms, camera shutter open duration T=130ms, and laser sheet optical interpulse period is Δ t=100ms, and laser sheet optical pulse light intensity I sets P=100mw by laser output power P decision
2. the particle picture velocity field instrument imaging system that is used for gray-scale statistics classification inquiry is successively launched two beam pulse width and is respectively t
1=5ms and t
2The laser sheet optical pulsing light tank flow field of=10ms, camera follows laser pulse to double expose, and obtains the flow field particle picture that a width of cloth has gray difference, and the input computing machine is as pending particle picture.
3. the particle picture of input computing machine is set the background gray threshold with removal flow field background influence according to the experiment situation, and eliminate the isolated bright spot in the particle picture, reach and remove the picture noise composition, improve the purpose of picture quality.
4. adopt improved differentiating operator that particle picture is made rim detection according to the experiment concrete condition, distinguish each particle picture point on the image, obtain positional information x and the y and the area size S of particle picture point; Utilize the predecessor image to obtain the original gray value information G of each particle picture point correspondence again.
5. because tank flow field particle is more sparse, Measurement Resolution requires lower, is 64 pixels * 64 pixels so set zonule division size.
6. particle picture point in the zonule being replaced to size is that 3 pixels * 3 pixels and each pixel grey scale are 255 particle picture point, the fast two-dimensional fourier transformation computing is done in the zonule, obtain the relative displacement of regional flow field by the auto-correlation peak value that draws, in conjunction with double exposure particle picture point gray scale summation ratio (G
1/ G
2) (wherein, G
1Be the same particle particle picture point gray scale summation of exposing for the first time, G
2Be the same particle particle picture point gray scale summation of exposing for the second time) with laser sheet optical pulse width ratio (t
1/ t
2) linear within the specific limits condition, particle elementary area size ratio (S
1/ S
2) (wherein, S
1Be the same particle particle elementary area size of exposing for the first time, S
2Be the same particle particle elementary area size of exposing for the second time) with laser sheet optical pulse width ratio (t
1/ t
2) each these subsidiary conditions of particle rapidity similarity in internal relation and the zonule, in the zonule, realize the pairing of same particle double exposure particle picture point.
7. obtain the particle displacement of double exposure according to the positional information of the paired particle picture point of each particle, in conjunction with laser sheet optical Δ interpulse period t=100ms, according to the two-dimension speed computing formula
(wherein, v is particle rapidity to be asked to obtain each particle's velocity size; x
1, y
1Central point location of pixels for the particle picture point of exposing for the first time; x
2, y
2Central point location of pixels for the particle picture point of exposing for the second time; Δ t is the interval time of twice laser sheet optical pulse); Obtain each particle rapidity direction according to the different gray scale summations of each particle double exposure particle picture point; Add up that each particle's velocity vector obtains whole flow field velocity information in all zonules.
8. the whole flow field velocity information that will obtain is presented on the computer screen with image format, or is exported by printer prints.
The above-mentioned description to embodiment is can understand and apply the invention for ease of those skilled in the art.The person skilled in the art obviously can easily make various modifications to these embodiment, and needn't pass through performing creative labour being applied in the General Principle of this explanation among other embodiment.Therefore, the invention is not restricted to the embodiment here, those skilled in the art should be within protection scope of the present invention for improvement and modification that the present invention makes according to announcement of the present invention.
Claims (6)
1. a method of measuring particle rapidity is characterized in that: be used for the particle picture velocity field instrument imaging system shooting flow field particle picture of gray-scale statistics classification inquiry, and utilize particle picture gray scale auto-correlation to measure particle rapidity.
2. the method for measurement particle rapidity according to claim 1, it is characterized in that: the particle picture velocity field instrument imaging system that is used for the gray-scale statistics classification inquiry obtains the particle picture with gray difference that the flow field double exposure forms, after the digital image processing techniques pre-service, in the zonule of dividing, realize the double expose pairing of corresponding particle picture point of same particle in correlativity by the interior of the particle picture point gray scale summation under the laser sheet optical pulse irradiation of different in width, difference according to two particle image point position information and gray scale summation obtains the particle's velocity vector, thereby obtains the velocity information in whole flow field.
3. the method for measurement particle rapidity according to claim 1 is characterized in that: comprising:
(1) be the laser output power P that camera double exposure time t1 and t2, camera shutter are opened duration T, laser sheet optical Δ interpulse period t and decision laser sheet optical pulse light intensity I according to particle size and the used double exposure laser illuminator of concrete condition setting measurement sheet light impulse lengths such as dense degree and Measurement Resolution in the flow velocity speed in flow field to be measured, the flow field;
(2) the particle picture velocity field instrument imaging system that is used for the gray-scale statistics classification inquiry is successively launched the laser sheet optical pulsing light flow field that two bundles have identical light intensity distinct pulse widths, camera follows laser pulse to double expose, obtain the particle picture that a width of cloth has gray difference, the input computing machine;
(3) adopt suitable digital image processing techniques such as level and smooth and denoising that particle picture is done pre-service at the various flows field characteristic, remove background and other noise effect in the image, improve picture quality;
(4) particle picture is made rim detection, distinguish each particle picture point on the image, obtain positional information x and the y and the area size S of each particle picture point, obtain the original gray scale summation information G of each particle picture point correspondence again in conjunction with particle picture after the pre-service;
(5) size of dividing according to the requirement adjustment and the setting zonule of flow field particle dense degree and Measurement Resolution;
(6) particle picture point in the zonule is replaced to the particle picture point of identical size, same grayscale, the fast two-dimensional fourier transformation computing is done in the zonule, obtain the relative displacement of regional flow field by the auto-correlation peak value that draws, in conjunction with the double exposure particle picture point gray scale summation ratio (G of each particle
1/ G
2) and laser sheet optical pulse width ratio (t
1/ t
2) internal relation, particle elementary area size ratio (S
1/ S
2) and laser sheet optical pulse width ratio (t
1/ t
2) condition of particle rapidity similarity in internal relation and the zonule, in the zonule, realize the pairing of same particle double exposure particle picture point;
(7) positional information according to pairing particle picture point obtains particle displacement, in conjunction with double exposing laser sheet optical interpulse period, according to the two-dimension speed computing formula
Obtain the particle rapidity size, obtain the particle rapidity direction, add up the velocity information that each particle rapidity vector in all zonules obtains whole flow field according to the different gray scale summations of paired two particle picture point of each particle
4. the method for measurement particle rapidity according to claim 3 is characterized in that: also comprise: the whole flow field velocity information that will obtain is presented on the computer screen with image format, or is exported by printer prints.
5. the method for measurement particle rapidity according to claim 3 is characterized in that: the double exposure laser illuminator sheet light impulse length described in the step (1) is camera double exposure time t
1=5ms and t
2=10ms, camera shutter open duration T=130ms, and laser sheet optical interpulse period is Δ t=100ms, laser output power P=100mw.
6. the method for utilizing particle picture gray scale autocorrelation measurement particle rapidity according to claim 3 is characterized in that: the zonule size that the particle picture described in the step (5) is divided is 64 pixels * 64 pixels.
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|---|---|---|---|
| CN2007100367275A CN101231299B (en) | 2007-01-23 | 2007-01-23 | Method for measuring particle velocity |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2007100367275A CN101231299B (en) | 2007-01-23 | 2007-01-23 | Method for measuring particle velocity |
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| CN101231299A true CN101231299A (en) | 2008-07-30 |
| CN101231299B CN101231299B (en) | 2010-12-01 |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106706956A (en) * | 2015-11-17 | 2017-05-24 | 清华大学 | Device for recording air velocity field information and method thereof |
| CN108120850A (en) * | 2017-12-15 | 2018-06-05 | 南昌工程学院 | A kind of subsurface runoff field measurement device system and measuring method |
| CN113139989A (en) * | 2021-06-22 | 2021-07-20 | 浙江大学 | Particle image velocity measurement method and device based on deep learning |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6879708B2 (en) * | 2001-05-24 | 2005-04-12 | Case Western Reserve University | Planar particle/droplet size measurement technique using digital particle image velocimetry image data |
| CN2606895Y (en) * | 2003-03-19 | 2004-03-17 | 申功炘 | Digital particle image velocity measurement system |
| CN1763546A (en) * | 2005-11-03 | 2006-04-26 | 上海交通大学 | Imaging system of particle image velocimetry for gray scale statistics, discrimination and query |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106706956A (en) * | 2015-11-17 | 2017-05-24 | 清华大学 | Device for recording air velocity field information and method thereof |
| CN106706956B (en) * | 2015-11-17 | 2023-08-25 | 清华大学 | Device and method for recording air speed field information |
| CN108120850A (en) * | 2017-12-15 | 2018-06-05 | 南昌工程学院 | A kind of subsurface runoff field measurement device system and measuring method |
| CN108120850B (en) * | 2017-12-15 | 2019-11-05 | 南昌工程学院 | A kind of subsurface runoff field measurement device system and measurement method |
| CN113139989A (en) * | 2021-06-22 | 2021-07-20 | 浙江大学 | Particle image velocity measurement method and device based on deep learning |
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