CN106290256B - Quantitative background schlieren method based on video measuring - Google Patents
Quantitative background schlieren method based on video measuring Download PDFInfo
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- CN106290256B CN106290256B CN201610626659.7A CN201610626659A CN106290256B CN 106290256 B CN106290256 B CN 106290256B CN 201610626659 A CN201610626659 A CN 201610626659A CN 106290256 B CN106290256 B CN 106290256B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
- G01N21/455—Schlieren methods, e.g. for gradient index determination; Shadowgraph
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C11/00—Photogrammetry or videogrammetry, e.g. stereogrammetry; Photographic surveying
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C11/00—Photogrammetry or videogrammetry, e.g. stereogrammetry; Photographic surveying
- G01C11/36—Videogrammetry, i.e. electronic processing of video signals from a single source or from different sources to give parallax or range information
Abstract
The invention discloses a kind of quantitative background schlieren (BOS) methods for being based on video measuring (VM), VM technology is combined with BOS optical path, background dot using uniformly distributed dot as BOS, on the one hand the circular markers image processing techniques of VM maturation is utilized, it is ensured that the spot placement accuracy of dot imaging reaches 0.02 pixel；On the other hand, it is accurately calculated by collinearity equation from background dot to the light beam at camera shooting center and passes through the deviation displacement that flow field generates on background board, and provide accurate deflection angle calculation formula, it is intended to accurately obtain the deflection angle and optical path difference of each background dot position, to eliminate the error that existing BOS uses directional light deflection angle calculation formula to generate, image cross-correlation technique is overcome to the existing BOS limitation measured and its to the adverse effect of measurement accuracy.
Description
Technical field
The present invention relates to FLOW VISUALIZATIONs and Pneumatic optical the field of test technology, in particular to a kind of to be determined based on video measuring
Measure background schlieren method.
Background technique
Stration technique as the existing last 100 years of FLOW VISUALIZATION means, however in practical applications, usually only determine by schlieren
Property observation and analysis, few means of testing as quantification.This is main, and there are two reasons:
1) there are many factor for influencing schlieren image grayscale, such as the intensity of light source, glass transmission, test section thickness, cause
The quantitative relationship being difficult to set up between image and measured physical quantity；
2) the first derivative field of schlieren image reflection refractive index, extracts difficulty data.
For this purpose, existing background schlieren (BOS) technology on the basis of traditional schlieren principle, incorporates Particle Image Velocimetry
The Particle-beam Tracing and particle picture processing technique of (Particle Image Velocimetry, PIV) carry out flow field survey, excellent
Point is as follows:
1) as shown in Figure 1, different from traditional stration technique, BOS quantifies deflection of light amount not by light intensity, but logical
It crosses PIV technology and seeks offset of the background spot on camera CCD, the quantitative deflection of light position for obtaining given light and passing through flow field
It moves, can avoid environment light or measures influence of the flow field self-luminous to measurement result.
2) BOS is without using a large amount of optical instruments in traditional schlieren, such as diaphragm and lens equipment, not only cost
It is low, and eliminate the limitation of lens or reflecting mirror to measurement field range.
But existing BOS technology still has following problems:
1) the deflection angle calculation formula of existing directional light is not suitable for the BOS optical path of Fig. 1.Reason is: such as Fig. 2 institute
Show, for the background spot A of given position, from point A to the light of camera shooting center OImaging point is a on CCD,
ObviouslyIt is not parallel with z-axis, it is obtained when using the small deflection angle calculation formula of directional lightError is obvious, and especially when background spot A is remoter apart from z-axis, error is got over
Greatly.
2) the light deflection displacement of some set point position cannot be accurately obtained: due to seeking background spot using PIV technology
It is displaced in the deflection of light of imaging plane, i.e., obtains the displacement of entire window by seeking the cross correlation of iterative query window
Variable quantity, therefore, what is obtained is the average displacement amount of entire iterative window.
3) size of iterative query window influences the precision of existing BOS big: will if image cross-correlation window selection is too small
It cannot get correct offset, and window selection is excessive, and can reduce the precision of offset, especially when flowing variation is violent,
When passing through supersonic speed shock wave such as light beam, the background spot deviation Displacement Saltation amplitude at shock wave is big, PIV image cross-correlation window technique
Seeking offset can then fail because image change is violent, poor robustness.
4) existing BOS uses random image as background, if occurring that there is the structure of space periodicity in background image,
PIV algorithm will be unable to correct interpretation background displacement vector.
Summary of the invention
In order to overcome the disadvantages mentioned above of the prior art, the quantitative background schlieren based on video measuring that the invention proposes a kind of
Method combines (Videogrammetric measurement, VM) technology with BOS optical path, is made using uniformly distributed dot
For the background dot of BOS, the circular markers image processing techniques of VM maturation is on the one hand utilized, it is ensured that the point location of dot imaging
Precision reaches 0.02 pixel；On the other hand, it is accurately calculated by collinearity equation from background dot to camera shooting center
The light beam at (i.e. entrance pupil center) passes through the deviation displacement that flow field generates on background board, and provides accurate deflection angle and calculate public affairs
Formula, it is intended to the deflection angle and optical path difference of each background dot position are accurately obtained, to eliminate existing BOS using directional light deflection angle
Calculation formula generate error, overcome image cross-correlation technique to existing BOS measure limit and its to measurement accuracy not
Benefit influences.
The technical solution adopted by the present invention to solve the technical problems is: a kind of quantitative background schlieren based on video measuring
Method includes the following steps:
Step 1: building BOS system: background board is vertical with the Z axis of coordinate system O-XYZ, arranges between ranks on background board
Every equal dot；
Step 2: the dot coordinate uniformly distributed using ranks on background board, using video measuring scaling method, calibration for cameras exists
Location parameter (the X of coordinate system O-XYZs,Ys,Zs) and attitude parameter (φ, ω, κ) and camera intrinsic parameter；
Step 3: when having flowing, with camera shooting background plate timing image；
Step 4: calculating the deviation displacement of set point A, deflection angle, light path on the background board image of given t moment shooting
Difference:
If deviation imaging point of the A on the camera CCD of t moment is a',Intersection point with background board is A',
1) (X, the Z) coordinate value of A' at coordinate system O-XYZ is calculated using collinearity equation, recycles collinearity equation further
Calculate X and Y-coordinate value of the A' under wind tunnel axis system；
2) the deviation displacement of A point is calculated:
If A is the dot of the i-th row jth column on background board, its X and the displacement of the deviation of Y direction are denoted as Δ X respectively(i,j)
With Δ Y(i,j), then:
ΔX(i,j)The X-coordinate value of the X-coordinate value-A of=A'；
ΔY(i,j)The Y-coordinate value of the Y-coordinate value-A of=A'；
3) deflection angle of A point is calculated:
The deflection angle of A point X and Y direction are denoted as respectivelyWithThen:
In formula, b be flow field center between background board at a distance from,
In formula, x(i,j)And y(i,j)For X and Y-coordinate value of the imaging dot a at coordinate system O-XYZ of A point；
4) optical path difference of A point is calculated:
Compared with prior art, the positive effect of the present invention is: different from existing BOS method, the present invention surveys video
Amount (VM) technology is combined with BOS optical path, and the background dot using uniformly distributed dot as BOS obtains following innovative point:
1) deflection angle of non-parallel light and the precise calculation of optical path difference are given；
2) background dot diameter and spacing parameter calculation formula based on BOS optical path parameter are established, to ensure dot
The spot placement accuracy of imaging reaches 0.02 pixel；
3) deviation displacement quantitative scaling formula is established, will pass through the distance for changing background board to flow field center, scaling
Light deflection displacement on background board at dot, adjusts the sensitivity of the quantitative background schlieren based on video measuring.
Therefore, it can accurately calculate and be worn from each background dot to the light beam at camera shooting center (i.e. entrance pupil center)
Deviation displacement, deflection angle and optical path difference that flow field generates on background board are crossed, realizes the quantitative measurment of background schlieren.
The present invention proposes the BOS based on VM, and the deflection angle and optical path difference for giving non-parallel light first accurately calculate public affairs
Formula eliminates the error that existing BOS uses directional light deflection angle calculation formula to generate, and can accurately calculate small from each background
The light beam that dot sets out to camera shooting center (i.e. entrance pupil center) passes through deviation displacement, the deviation that flow field generates on background board
Angle and optical path difference realize the accurate measurement of background schlieren.
Secondly, deviation displacement quantitative based on foundation scales formula, by change flow field center between background board at a distance from,
The sensitivity of the quantitative background schlieren based on video measuring is adjusted, to ensure to measure the deviation displacement field and deviation of ideal signal-to-noise ratio
Angle field data.
Finally, the present invention is based on the background dot diameter of BOS optical path parameter and spacing parameter calculation method, in conjunction with maturation
Video measuring technology, the background dot using uniformly distributed dot as BOS accurately calculate each background dot with collinearity equation
Deviation displacement, scale formula in conjunction with deviation displacement quantitative of the invention, promote the robustness of BOS, overcome image cross-correlation
Technology to the existing BOS limitation measured and its to the adverse effect of measurement accuracy, even if when flowing variation is violent, as light beam is worn
When crossing supersonic speed shock wave, remain to effectively obtain high-precision measurement result.
Detailed description of the invention
Examples of the present invention will be described by way of reference to the accompanying drawings, in which:
Fig. 1 is BOS schematic diagram；
Fig. 2 is deflection angle schematic diagram calculation；
Fig. 3 is that background board dot parameter determines schematic diagram.
Specific embodiment
A kind of quantitative background schlieren method based on video measuring, includes the following steps:
1, principle builds BOS system as shown in Figure 1, it is desirable that background board is vertical with Z axis shown in Fig. 2, arranges on background board
Having ranks interval is the dot of S, and roundlet spot diameter is ΦD.The design method that dot A is given on background board is as follows:
1) as shown in figure 3, the diameter of point A
ΦD=u Φd/f (1)
Φ in formuladThe diameter of dot a is imaged on camera for the dot on background board, it is desirable that ΦdMore than or equal to 6 pixels,
To ensure that the spot placement accuracy of dot imaging is up to 0.02 pixel.U is distance of the background board to camera shooting center O, and f is coke
Away from.
2) the ranks interval of dot
S=us/f (2)
S is that the spacing distance between dot is imaged in the dot on background board on camera in formula, and s is generally taken to be equal to 1.5 to 2 times
Φd。
3) the dot sharp on background board is required, such as: white with black dot or white background bullet.
2, Fig. 2 is geometrical relationship of the three-dimensional eulerian coordinate system O-XYZ of standard on the perspective plane YOZ, using on background board
The uniformly distributed circular dot coordinate of ranks, using mature video measuring scaling method, (camera calibration such as based on plane template is calculated
Method), location parameter (X of the calibration for cameras in coordinate system O-XYZ as shown in Figure 2s,Ys,Zs) and attitude parameter (φ, ω, κ), and
Camera intrinsic parameter.
3, when having flowing, with camera shooting background plate timing image.Wherein on the background board image of given t moment shooting
The deviation displacement of set point A, deflection angle, optical path difference (OPD) calculation method are as follows:
As shown in Fig. 2, since flowing causes lightDeviation occurs, if deviation imaging of the A on the camera CCD of t moment
Point is a',Intersection point with background board is A'(, that is, A because generating deviation position of the light deflection phenomenon on background board)
1) (X, Z) coordinate value under A' coordinate system shown in Fig. 2 is calculated using collinearity equation.Collinearity equation describes VM phase
The mathematical model of dot and its picture point three on machine, examination background board, expression formula are
(x in formula0,y0) be respectively camera as planar central, (x, y) is the picture plane coordinates of tested point, (X, Y, Z) be to
Three-dimensional coordinate under measuring point coordinate system shown in Fig. 2, (a1,a2,a3,b1,b2,b3,c1,c2,c3) be camera attitude angle (φ, ω,
9 direction cosines in spin matrix R composed by κ).
Due to the pose parameter (X of cameras,Ys,Zs) and (φ, ω, κ), point a' as the Z of plane coordinates and point A' sit
Scale value (as vertical installation position of the background board on Z axis) is it is known that can find out X of the A' under wind tunnel axis system by formula (3)
With Y-coordinate value.
2) the deviation displacement of A point is calculated.If A is the circular dot of the i-th row jth column on background board, by its X and Y direction
Deviation displacement is denoted as Δ X respectively(i,j)With Δ Y(i,j), then calculating formula is as follows
ΔX(i,j)The X-coordinate value (4) of the X-coordinate value-A of=A'
ΔY(i,j)The Y-coordinate value (5) of the Y-coordinate value-A of=A'
3) deflection angle of A point is calculated.The deflection angle calculation formula of X and Y direction is as follows:
In formula b be flow field center between background board at a distance from (shown in Fig. 2), and
X in formula(i,j)And y(i,j)For the X and Y-coordinate value under the imaging dot a coordinate system O-XYZ shown in Fig. 2 of A point.
4) optical path difference of A point is calculated.Calculating formula is as follows:
4, by adjusting flow field center between background board distance b, scale background board on dot deviation displacement, to adjust
The sensitivity of quantitative background schlieren based on video measuring.Wherein set point A on the background board image of given t moment shooting
The calculating formula with b scaling of deviation displacement is as follows:
Claims (7)
1. a kind of quantitative background schlieren method based on video measuring, characterized by the following steps:
Step 1: building BOS system: background board is vertical with the Z axis of coordinate system O-XYZ, and ranks interval phase is arranged on background board
Deng dot；
Step 2: the dot coordinate uniformly distributed using ranks on background board, using video measuring scaling method, calibration for cameras is in coordinate
It is the location parameter (X of O-XYZs, Ys, Zs) and attitude parameter (φ, ω, K) and camera intrinsic parameter；
Step 3: when having flowing, with camera shooting background plate timing image；
Step 4: calculating the deviation displacement of set point A, deflection angle, optical path difference on the background board image of given t moment shooting:
If deviation imaging point of the A on the camera CCD of t moment is a ',Intersection point with background board is A ',
1) (X, the Z) coordinate value of A ' at coordinate system O-XYZ is calculated using collinearity equation, collinearity equation is recycled to further calculate
X and Y-coordinate value of the A ' under wind tunnel axis system out；
2) the deviation displacement of A point is calculated:
If A is the dot of the i-th row jth column on background board, its X and the displacement of the deviation of Y direction are denoted as Δ X respectively(i, j)With Δ Y(i, j), then:
ΔX(i, j)The X-coordinate value of one A of X-coordinate value of=A '；
ΔY(i, j)The Y-coordinate value of the Y-coordinate value-A of=A '；
3) deflection angle of A point is calculated:
The deflection angle of A point X and Y direction are denoted as respectivelyWithThen:
In formula, b be flow field center between background board at a distance from,
In formula, x(i, j)And y(i, j)For X and Y-coordinate value of the imaging dot a at coordinate system O-XYZ of A point, f is focal length；
4) optical path difference of A point is calculated:
2. the quantitative background schlieren method according to claim 1 based on video measuring, it is characterised in that: the dot
Diameter is ΦDIt determines as follows:
ΦD=u Φd/f
In formula, ΦdThe diameter of dot a is imaged on camera for the dot on background board, u is background board to camera shooting center O's
Distance.
3. the quantitative background schlieren method according to claim 2 based on video measuring, it is characterised in that: the ΦdIt is greater than
Equal to 6 pixels.
4. the quantitative background schlieren method according to claim 2 based on video measuring, it is characterised in that: the dot
Ranks interval S is determined as follows:
S=us/f
In formula, s is that the spacing distance between dot is imaged in the dot on background board on camera.
5. the quantitative background schlieren method according to claim 4 based on video measuring, it is characterised in that: s is equal to 1.5 and arrives
2 times of Φd。
6. the quantitative background schlieren method according to claim 1 based on video measuring, it is characterised in that: as follows
Flow field center distance b between background board is adjusted, dot deviation displacement on background board is zoomed in and out:
7. the quantitative background schlieren method according to claim 1 based on video measuring, it is characterised in that: the dot is
White with black dot or white background bullet.
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| CN109709071A (en) * | 2018-12-17 | 2019-05-03 | 南京理工大学 | Circulating display device and method based on synthesis RGB phase shift color fringe background schlieren |
| CN112629679B (en) * | 2020-12-02 | 2021-11-30 | 中国人民解放军国防科技大学 | High-precision measurement method suitable for background schlieren, electronic equipment and medium |
| CN113516689B (en) * | 2021-09-10 | 2022-03-22 | 北京理工大学 | Schlieren characteristic visualization enhancement method based on associated frame constraint |
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| CN114757993B (en) * | 2022-06-13 | 2022-09-09 | 中国科学院力学研究所 | Motion and parameter identification method and system for schlieren image |
| CN116580076B (en) * | 2023-07-10 | 2023-09-12 | 中国空气动力研究与发展中心计算空气动力研究所 | Device, method, apparatus and medium for acquiring particle graph containing model boundary |
| CN116929701B (en) * | 2023-09-15 | 2023-12-01 | 中国空气动力研究与发展中心低速空气动力研究所 | Method and system for measuring flow trace of airfoil surface |
| CN117421517B (en) * | 2023-12-18 | 2024-03-01 | 中国空气动力研究与发展中心高速空气动力研究所 | Poisson equation source term rapid calculation method for background schlieren measurement density field |
| CN117455919B (en) * | 2023-12-25 | 2024-03-15 | 中国空气动力研究与发展中心高速空气动力研究所 | Background schlieren method, device, equipment and medium based on virtual knife edge |
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| CN103257029B (en) * | 2013-05-14 | 2016-01-20 | 张征宇 | Without blade organization visible ray schlieren system and measuring method thereof |
| US9710917B2 (en) * | 2013-05-15 | 2017-07-18 | Massachusetts Institute Of Technology | Methods and apparatus for refractive flow measurement |
| CN104155071A (en) * | 2014-08-12 | 2014-11-19 | 中国科学院合肥物质科学研究院 | Gas leakage monitoring device based on background schlieren technology, and gas leakage monitoring method based on background schlieren technology |
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