阅读说明：本技术 一种流动粒子速度测量方法及系统 (Method and system for measuring velocity of flowing particles ) 是由 胡文成 张宝华 李孝堂 范玮 于 2019-10-11 设计创作，主要内容包括：本申请涉及一种流动速度测量方法,所述方法包括：生成至少两个平行的平面光束,并使所述平面光束汇聚形成用于示踪粒子通过的有效测量区域,所述有效测量区域划分成若干的子区域,每个平面光束至少包括两个按预定时间间隔发送的光源汇聚而成；分别获取光源发出且通过所述子区域的入射光强和出射光强,并根据所述入射光强和出射光强的衰减形成所述示踪粒子的第一分布图像和第二分布图像；互相关所述第一分布图像和第二分布图像形成所述示踪粒子的流动分布。本申请的流动速度测量方法及系统可以解决粒子的互相遮蔽现象,且光强分布、被测区域的背景噪声等均不会影响速度的测量结果,还可通过选择适合的波长避免碳烟的影响。(The application relates to a flow velocity measurement method, comprising: generating at least two parallel plane light beams, converging the plane light beams to form an effective measuring area for trace particles to pass through, wherein the effective measuring area is divided into a plurality of sub-areas, and each plane light beam at least comprises two light sources which are sent at preset time intervals and converged; respectively obtaining incident light intensity and emergent light intensity which are emitted by a light source and pass through the sub-regions, and forming a first distribution image and a second distribution image of the tracer particles according to the attenuation of the incident light intensity and the emergent light intensity; cross-correlating the first distribution image and the second distribution image forms a flow distribution of the tracer particles. The flow velocity measuring method and the flow velocity measuring system can solve the problem of mutual shielding of particles, the measuring result of the velocity cannot be influenced by light intensity distribution, background noise of a measured area and the like, and the influence of soot can be avoided by selecting proper wavelength.)

1. A method of measuring flow velocity, the method comprising

Generating at least two parallel plane light beams, converging the plane light beams to form an effective measuring area for trace particles to pass through, wherein the effective measuring area is divided into a plurality of sub-areas, and each plane light beam at least comprises two light sources which are sent at preset time intervals and converged;

acquiring incident light intensity and emergent light intensity which are emitted by at least one light source and pass through the sub-region, and forming a first distribution image of the trace particles according to attenuation of the incident light intensity and the emergent light intensity; and

acquiring incident light intensity and emergent light intensity which are emitted by at least one other light source and pass through the sub-region, and forming a second distribution image of the tracer particles according to the attenuation of the incident light intensity and the emergent light intensity;

cross-correlating the first distribution image and the second distribution image forms a flow distribution of the tracer particles.

2. The method of claim 1, wherein each planar beam comprises at least two light sources, at least one of which is refracted and converged with another light source before being scattered to form the planar beam.

3. The flow rate measurement method according to claim 1, wherein the at least two light sources are emitted at predetermined time intervals by coordinated control.

4. A method of measuring flow velocity according to any of claims 1 to 3, wherein the light source is a pulsed laser.

5. The flow rate measurement method according to claim 1, wherein the attenuation of the incident light intensity and the emergent light intensity follows the following relationship:

I_λe＝I_λ0exp(-β_λ△)

in the formula I_λeTo output a set light intensity, I_λ0β for incident light intensity_λTo determine the attenuation coefficient, and relative to the surface area of the liquid, △ is the path taken by the light.

6. A flow velocity measurement system, characterized in that the system comprises

The device comprises at least two plane light beam forming devices, a tracking particle detection device and a tracking particle detection device, wherein the plane light beam forming devices are used for generating at least two parallel plane light beams and converging the plane light beams to form an effective measuring area for the tracking particles to pass through, the effective measuring area comprises a plurality of sub-areas, and each plane light beam at least comprises two light sources which are sent at preset time intervals and converged;

the first distribution image generating device is used for acquiring incident light intensity and emergent light intensity which are emitted by at least one light source and pass through the sub-area, and forming a first distribution image according to the attenuation of the incident light intensity and the emergent light intensity;

the second distribution image generating device is used for acquiring incident light intensity and emergent light intensity which are emitted by at least one other light source and pass through the sub-area, and forming a second distribution image according to the attenuation of the incident light intensity and the emergent light intensity;

flow distribution generating means for cross-correlating the first and second distribution images to form a flow distribution of the tracer particles.

7. The flow rate measurement system of claim 6, wherein the planar beam forming means comprises

At least two light source emitting modules for generating and emitting light sources;

the light source refraction module is used for reflecting or refracting the at least one light source at a preset angle so that the light sources emitted by the at least two light source emission modules are converged; and

the sheet light adjusting module is used for scattering the converged light source to form a plane light beam.

8. The flow rate measurement system of claim 6, wherein the planar beam forming means further comprises

And the control module is used for coordinating and controlling at least two light source emitting modules to emit light sources according to a preset time interval.

9. The flow rate measurement system according to any one of claims 6 to 8, wherein the light source generated by the light source emitting module is a pulsed laser.

10. The flow rate measurement system according to claim 6, wherein the first and/or second distribution image generating means determines from the attenuation of the incident and emergent light intensities that the distribution image of the tracer particles follows the relationship:

I_λe＝I_λ0exp(-β_λ△)

in the formula I_λeTo output a set light intensity, I_λ0β for incident light intensity_λTo determine the attenuation coefficient, and relative to the surface area of the liquid, △ is the path taken by the light.

Technical Field

The application belongs to the technical field of imaging, and particularly relates to a method and a system for measuring the velocity of flowing particles.

Background

Particle Image Velocimetry (PIV), which is traditionally performed using chromatography, uses a high-energy short-wavelength pulsed YAG laser (Yttrium Aluminum Garnet) (wavelength of about 532 nm).

However, the conventional chromatographic PIV method has the following disadvantages:

1) the energy of the single pulse laser is generally more than 30mJ, and the short wavelength laser with high energy has great harm to human eyes;

2) the traditional chromatography PIV method adopts a dispersion technology, if a plurality of tracer particles are overlapped on a certain chromatography calculation plane at the same detection angle, different particles can not be distinguished due to mutual shielding with a certain probability;

3) the three-dimensional space size of a traditional chromatography PIV measuring region is limited by the depth of field of a camera, the light intensity distribution of the traditional chromatography PIV measuring region influences an image processing result, and the background light noise of the measured region also influences speed measurement;

4) according to the traditional PIV technology, 532nm laser is used as a light source, and the speed field under the environment with soot is measured and influenced by incandescent light.

Disclosure of Invention

It is an object of the present application to provide a flow velocity measurement method and system to solve or mitigate at least one of the problems of the background art.

In one aspect, the technical solution provided by the present application is: a method of flow velocity measurement, the method comprising:

generating at least two parallel plane light beams, converging the plane light beams to form an effective measuring area for trace particles to pass through, wherein the effective measuring area is divided into a plurality of sub-areas, and each plane light beam at least comprises two light sources which are sent at preset time intervals and converged;

acquiring incident light intensity and emergent light intensity which are emitted by at least one light source and pass through the sub-region, and forming a first distribution image of the trace particles according to attenuation of the incident light intensity and the emergent light intensity; and

acquiring incident light intensity and emergent light intensity which are emitted by at least one other light source and pass through the sub-region, and forming a second distribution image of the tracer particles according to the attenuation of the incident light intensity and the emergent light intensity;

cross-correlating the first distribution image and the second distribution image forms a flow distribution of the tracer particles.

In an embodiment of the method of the present application, each planar light beam includes at least two light sources, and at least one light source is converged with another light source by refraction and then scattered to form the planar light beam.

In an embodiment of the method of the present application, the at least two light sources are emitted at predetermined time intervals by coordinated control.

In one embodiment of the method of the present application, the light source is a pulsed laser.

In one embodiment of the method of the present application, the attenuation of the incident light intensity and the emergent light intensity follows the following relationship:

I_λe＝I_λ0exp(-β_λ△)

in the formula I_λeTo output a set light intensity, I_λ0β for incident light intensity_λTo determine the attenuation coefficient, and relative to the surface area of the liquid, △ is the path taken by the light.

On the other hand, the technical scheme provided by the application is as follows: a system for simultaneously measuring a two-dimensional distribution of liquid concentration and liquid motion, the system comprising:

the device comprises at least two plane light beam forming devices, a tracking particle detection device and a tracking particle detection device, wherein the plane light beam forming devices are used for generating at least two parallel plane light beams and converging the plane light beams to form an effective measuring area for the tracking particles to pass through, the effective measuring area comprises a plurality of sub-areas, and each plane light beam at least comprises two light sources which are sent at preset time intervals and converged;

the first distribution image generating device is used for acquiring incident light intensity and emergent light intensity which are emitted by at least one light source and pass through the sub-area, and forming a first distribution image according to the attenuation of the incident light intensity and the emergent light intensity;

the second distribution image generating device is used for acquiring incident light intensity and emergent light intensity which are emitted by at least one other light source and pass through the sub-area, and forming a second distribution image according to the attenuation of the incident light intensity and the emergent light intensity;

flow distribution generating means for cross-correlating the first and second distribution images to form a flow distribution of the tracer particles.

In an embodiment of the system of the present application, the planar beam forming apparatus includes:

at least two light source emitting modules for generating and emitting light sources;

the light source refraction module is used for reflecting or refracting the at least one light source at a preset angle so that the light sources emitted by the at least two light source emission modules are converged; and

the sheet light adjusting module is used for scattering the converged light source to form a plane light beam.

In an embodiment of the system of the present application, the planar beam forming apparatus further includes:

and the control module is used for coordinating and controlling at least two light source emitting modules to emit light sources according to a preset time interval.

In an embodiment of the system of the present application, the light source generated by the light source emitting module is a pulsed laser.

In an embodiment of the system of the present application, the first distribution image generating device and/or the second distribution image generating device determine that the distribution image of the trace particles follows the following relationship according to the attenuation of the incident light intensity and the emergent light intensity:

I_λe＝I_λ0exp(-β_λ△)

in the formula I_λeTo output a set light intensity, I_λ0β for incident light intensity_λTo determine the attenuation coefficient, and relative to the surface area of the liquid, △ is the path taken by the light.

The flow velocity measuring method and the flow velocity measuring system can solve the problem of mutual shielding of particles, the measuring result of the velocity cannot be influenced by light intensity distribution, background noise of a measured area and the like, and the influence of soot can be avoided by selecting proper wavelength.

Drawings

In order to more clearly illustrate the technical solutions provided by the present application, the following briefly introduces the accompanying drawings. It is to be expressly understood that the drawings described below are only illustrative of some embodiments of the invention.

FIG. 1 is a flow chart of a method for simultaneously measuring two-dimensional distributions of liquid concentration and liquid motion according to the present application.

FIG. 2 is a diagram of the system components for simultaneous measurement of two-dimensional distribution of liquid concentration and liquid motion according to the present application.

Fig. 3 is a sub-region diagram of an effective measurement region partition according to the present application.

Fig. 4 is a schematic diagram of effective measurement area division and imaging effect according to an embodiment of the present application.

Fig. 5 is a schematic diagram of an exposure timing sequence of a laser emitting and imaging device according to an embodiment of the present application.

Fig. 6 is a schematic view illustrating a particle image reconstruction process according to an embodiment of the present application.

Fig. 7 is a schematic diagram of trace particles after a graph is reconstructed according to an embodiment of the present disclosure.

Detailed Description

In order to make the implementation objects, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described in more detail below with reference to the drawings in the embodiments of the present application.

In order to make the technical solution of the present application easier to understand, the method provided by the present application and the system provided by the present application will be described together in the following description.

As shown in fig. 1, the flow velocity measurement method 100 provided by the present application includes the following steps:

step 110: at least two parallel plane light beams are generated and converged to form an effective measuring region 230 for trace particles to pass through, the effective measuring region 230 is divided into a plurality of sub-regions, and each plane light beam at least comprises two light sources which are sent at preset time intervals and converged.

In order to generate at least two planar light beams according to the above method, at least two planar light beam forming devices 210 are provided in the system of the present application, the planar light beam forming devices 210 are used to generate the planar light beams, and the planar light beams generated by each of the planar light beam forming devices 210 are parallel to each other and converge to form an effective measuring region 230.

In the embodiment shown in fig. 2, three sets of planar light beam forming devices 210 are given as an example, and in practical applications, only two planar light beam forming devices 210 are required to operate, so that when the number of planar light beam forming devices 210 is increased, the spatial resolution of the two-dimensional distribution measurement of the liquid concentration can be increased.

In the system of the present application, the planar light beam forming device 210 includes at least two light source emitting modules 211, at least one light source refracting module 212, and a sheet light adjusting module 213. Each light source emitting module 211 is for generating and emitting a light source. The light source refraction module 212 is configured to reflect or refract the light source generated by the at least one light source emission module 211 at a predetermined angle, so that the tube bundle generated by the light source emission module 211 is converged into one beam, and finally the light adjustment module 213 scatters the refracted light source to form a planar light beam.

In the embodiment shown in fig. 2, two light source emitting modules 211 and one light source refracting module 212 are provided. It is understood that in the system of the present application, the number of the light source emitting modules 211 may be three, four or more, and accordingly, the light source refraction module 212 may be added to make all the light emitted by the light source emitting modules 211 realize a common beam output.

In addition, since the light sources emitted by the light source emitting modules 211 in the present application need to be emitted at predetermined time intervals, the system in the present application further has a control module 214, and the control module 214 is connected to the light source emitting modules 211 to control each light source emitting module 211 to emit at predetermined time.

Further, the sheet light adjusting module 213 includes a first adjusting module 2131 and a second adjusting module 2132, the first adjusting module 2131 expands and expands the thinner common beam output light source to form a light source with a larger area, and the second adjusting module 2132 performs parallel constraint and outputs the expanded light source to form a planar light beam.

In some embodiments, the light source refraction module 212 is generally made of a material with a reflection or refraction function, such as reflective glass or a triangular prism. In some embodiments, the sheet light adjusting module 213 is an optical element made of a transparent material, such as a lens made of glass or crystal.

In order to make the light source easy to control and have better imaging effect, the light source in this application adopts a laser (pulse) light source, i.e. the light source emitting module 211 is a laser emitting device, such as a pulse laser diode. In order to ensure the stability of the emitted light intensity, microsecond-magnitude pulse laser is adopted as a light source in the application. In order to ensure that the output wavelength has a narrow linewidth, the light source refraction module 212 employs a reflection grating to implement a wavelength adjustment function.

In this application, the effective measurement area needs to be substantially perpendicular to the flow direction of the trace particles.

When the planar light beams generated by the plurality of planar light beam forming devices 210 are shaped into parallel light by the lens group and then converged in the effective measurement region 230, the effective measurement region 230 can measure the position of the trace particles.

As shown in fig. 4, the sub-region 231 divides the effective measurement region 230 into several sub-regions 231, and each sub-region 231 (hereinafter referred to as voxel) has a certain thickness. When the effective measurement region 230 is divided, the division may be performed using a cartesian coordinate system or a polar coordinate system.

Step 120: and acquiring incident light intensity and emergent light intensity which are emitted by at least one light source and pass through the sub-area, and forming a first distribution image according to the attenuation of the incident light intensity and the emergent light intensity.

Step 130: similarly, the incident light intensity and the emergent light intensity which are emitted by at least one other light source and pass through the sub-area are obtained, and a second distribution image is formed according to the incident light intensity and the emergent light intensity.

In order to realize the position distribution measurement of the trace particles, the system of the present application is provided with a first distribution image generation device and a second distribution image generation device, wherein the first distribution image generation device and the second distribution image generation device are the same, and in actual use, the first distribution image generation device and the second distribution image generation device are all imaging devices 220 (such as a CCD camera, a COMS camera, or an SCOMS camera, etc.), which generate a two-dimensional distribution image of the trace particles by acquiring and recording the incident light intensity and the emergent light intensity of a planar light beam, and determining an attenuation coefficient according to the incident light intensity and the emergent light intensity.

The attenuation of light by the tracer particles in each voxel at the time of measurement satisfies Beer's-Lambert law (equation 1). I.e. the intensity of the light I emitted through the voxel_λeAnd the incident light intensity I_λ0Satisfying exponential decay (β)_λRelated to the liquid surface area). The attenuated laser light passes through the lens and is incident into the imaging device 220 for imaging. The imaging device 220(CCD camera, COMS camera, SCMOS camera, etc.) and the light source emitting module 211 are operated at a certain timing.

Wherein, the incident light intensity, the emergent light intensity and the attenuation coefficient β_λThe travel of the light in the voxel satisfies the following relation:

I_λe＝I_λ0exp(-β_λ△) (1)

in the formula I_λeTo output a set light intensity, I_λ0β for incident light intensity_λ△ is the path taken by the light, which is the carbon dioxide absorption coefficient.

When the reconstruction of the particle space distribution is calculated, the region to be measured is divided into a plurality of voxels, parameters β in the voxels according to the number of pixels of the selected imaging device 220_λ△ is the unknown number, it can be obtained from formula 1 that the relation between the incident light intensity and the emergent light intensity of a certain voxel satisfies formula 2 and formula 3, the ratio of the emergent light intensity and the incident light intensity of a certain row/column voxel satisfies formula 4, n in the formula represents the nth voxel (n is related to the number of voxels divided by the region to be detected, I belongs to n), I belongs to n_λeThe attenuated light intensity of the trace particles sensed by the imaging device 220, i.e. the emergent light intensity, I_λ0The light intensity is the light intensity without attenuation, namely the incident light intensity.

For each imaging device 22The images made by 0 all satisfy an equation similar to that shown in equation 4. The results obtained for each imaging device 220

β corresponding to the voxel is obtained by iterative calculation_λi△_iThe value is obtained. The iterative algorithm is similar to the ct (computed tomogry) algorithm. In the application, a MART (generalized adaptive reconstruction techniques) algorithm is adopted, and the method can be suitable for two-dimensional reconstruction calculation with large gradient change. For symmetric sprays, a group theory approach can be introduced to apply to the iterative computation in order to arrive at a precise solution.

For the above processes, details are not repeated herein, and related documents may be specifically referred to.

β_λi△_iDependent on the refractive index or relative refractive index of the transparent tracer particle and the path traveled by the light, β from the space being measured_λi△_iThe value distribution finds the trace particles (formula 4), and the particle image three-dimensional reconstruction can be realized by performing reconstruction calculation on the particle image. The speed measurement function is realized through a three-dimensional cross-correlation algorithm. By adopting the method and the device for measuring the tracer particle speed, calibration work needs to be carried out so as to confirm the functional relation between the voxel and the measured space.

The trace particle may occupy a plurality of voxels, in which case it may be according to β_λi△_iValue judges if it is the same trace particle β_λi△_iThe values are close to each other and can be considered to be the same particle (it can be judged from the Gaussian distribution of the light intensity if they are adjacent β_λi△_iThe value distribution satisfying the gaussian distribution is considered to be the same particle).

Fig. 5 shows an example of a graph of the numerical simulation calculation result obtained in the case of the effective measurement region division using the left graph in the right graph.

Finally, step S140, cross-correlating the first distribution image and the second distribution image to form a flow distribution of the tracer particles.

As shown in fig. 6, the light source emitting module 211 numbered 1 in each of the planar light beam forming devices 210 in the present application simultaneously triggers the measured "planar liquid surface concentration distribution" result to form an image 1. after a time interval of △ T, the light source emitting module 211 numbered 2 in each of the planar light beam forming devices 210 simultaneously triggers the measured "planar liquid surface concentration distribution" result to be an image 2. the velocity measurement distribution is calculated based on the cross-correlation between the images 1 and 2.

It should be noted that the exposure time of image 1 is substantially equal to the laser pulse width of number 1, and the exposure time of image 2 is greater than the laser pulse width of number 2, and is covered before and after the time.

Particle image reconstruction is realized through reconstruction calculation of images recorded by the cross-frame image recording device (figure 7). Tracer particle displacement calculation is realized through a three-dimensional cross-correlation algorithm (△ s), and the movement speed of the tracer particles is obtained through the known cross-frame time △ T (formula 11).

Transient three-dimensional speed calculation based on a tomography technology adopts a three-dimensional cross-correlation algorithm. The method is only explained by a two-dimensional PIV algorithm, and an actual three-dimensional cross-correlation algorithm can be obtained by looking up the existing relevant documents. The cross-correlation algorithm includes direct cross-correlation calculation and fourier transform. Both methods have now proven to be equivalent under conditions of less displacement. The fourier transform methods now use FFT methods (fast fourier transforms) which are faster in computation.

Taking two-dimensional velocity measurement as an example, the FFT method is briefly described as follows:

for image 1 g₁(x, y) and image 2 g₂(x, y) are respectively FFT transformed to obtain

In the formula

And

are respectively an image g₁(x, y) and g₂And (x, y) FFT transformation. x, y are image coordinates. And omega is a frequency-domain value corresponding to Fourier transform.

By using the translation characteristic of Fourier transform, the method can obtain

Wherein △ x, △ y are particle displacements.

Function(s)

By inverse Fourier transform

Substituting equation 7 into equation 8 results in

G(x,y)＝g(x+△x,y+△y)(9)

Wherein g (x + △ x, y + y) is

G (x, y) has a maximum gray peak at (x, △ x, y + y), which is composed of 3 components due to the existence of background noise and other related quantities (equation 10). the position of the maximum gray value (coherence peak) contains displacement information, so that the image displacement can be obtained by extracting the displacement of the peak center,the peak fitting method (such as gaussian peak fitting) is generally adopted, and the accuracy can reach 0.1 pixel.

R(S)＝R_C(S)+R_D(S)+R_F(S) (10)

In the formula, R_DAnd (S) represents the maximum gray value and represents the displacement information. R_C(S)+R_FAnd (S) is random correlation and background noise correlation quantity.

By the above processing, the relative displacement of the density distributions of the image 1 and the image 2 can be obtained. From this, the moving speed of the concentration distribution, i.e., the liquid moving speed, can be calculated. The calculation formula is shown in formula (11):

wherein △ s is the displacement (vector) of the liquid, △ t is the time interval for recording the images of the "planar liquid surface concentration distribution" at different times, and the instantaneous velocity vector v of the liquid is obtained when △ t → 0.

The reconstruction calculation is performed based on the extinction technology (light attenuation), so compared with the traditional PIV technology, the influence of background light is not required to be considered. Recording I with the imaging device only before the start of the acquisition_λ0Optical imaging, the light intensity I of the particles during reconstruction and measurement can be known from formula 2_λeAnd I_λ0Is related to the ratio of (A) to (B). Therefore, the background noise can be considered to be included in I_λ0And I_λeThe final particle position calculation result is not affected.

The light intensity attenuation also obeys Beer's Lambert law, but the soot and the measured transparent tracer particle are not the same kind of substances, and the attenuation coefficients of the soot and the measured transparent tracer particle are β_λDifferent. The soot concentration spatial distribution can also be calculated according to equation 4. The following methods can be adopted when filtering out the soot influence:

1) before addition of the tracer particles, the average I is recorded under constant conditions_λ0Value of I after addition of tracer particles_λeParticle image reconstruction calculation is performed based on equation 4. The soot influence is here treated as background noise, enabling measurements under soot conditions. The method of the present application considers the overall average soot concentration of the measured area to be constant (I)_λ0Unchanged) from which the effect of soot can be filtered out.

2) Due to the fact that attenuation coefficients of soot and transparent tracer particles to light are different, numerical mutation points exist in reconstructed soot concentration and tracer particle images. As shown in fig. 7, the thick line dots in the graph indicate the positions of particles having a larger attenuation coefficient than soot, and the thin line dots indicate the positions of particles having a smaller attenuation coefficient than soot. Since the attenuation coefficient of soot for the laser wavelength that has been used can be obtained experimentally, it can be considered as a known quantity. From this, the position information of the transparent tracer particles can be obtained by processing of the reconstructed image.

The flow velocity measuring method and the flow velocity measuring system can solve the problem of mutual shielding of particles, the measuring result of the velocity cannot be influenced by light intensity distribution, background noise of a measured area and the like, and the influence of soot can be avoided by selecting proper wavelength.

The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.