CN103472256A - Flow two-dimensional velocity profile measuring method and device based on planar array CCD spatial filter - Google Patents

Abstract

The invention discloses a two-dimensional velocity field measuring device and a measuring method based on an area array CCD space filter, wherein the measuring device includes a laser, a lens group, an area array CCD and an image processor. Compared with the prior art, the present invention has the following advantages: without the need for high-power lasers, high-resolution CCDs and complex synchronization devices, the full-field velocity measurement of the measured object can be realized; the area array CCD sensor is fully utilized as a The spatial filter and detector are combined with the image processor, the system equipment is simple, and the data processing is convenient, which avoids the problems of the correlation method image processing calculation workload, slow search speed and the traditional spatial filter method cannot realize the flow velocity field measurement, etc. It has lower requirements on the installation, commissioning and use environment of the instrument, and is suitable for fluid flow field measurement in different occasions.

Description

Flow two-dimensional velocity field measurement method and device based on area array CCD spatial filter

technical field

The invention belongs to the technical field of velocity measurement, and in particular relates to a flow two-dimensional velocity field measurement method and device based on an area array CCD spatial filter.

Background technique

For the measurement of two-dimensional plane velocity, there are mainly Particle Tracer Velocimetry (PTV for short), Particle Image Velocimetry (PIV for short) and Laser Speckle Velocimetry (LSV for short). PTV/PIV is a very important instrument developed in the 1980s to study fluid mechanics, but the current commercialized PIV instruments are complex and expensive, which greatly limits the application and development of PIV measuring instruments.

In 1977, speckle measurement technology was introduced into the field of fluid mechanics to measure the velocity of the flow field, called laser speckle velocimetry, and gradually developed into a particle image velocimetry method, which is especially widely used in the measurement of flow field velocity . The basic process is to irradiate the flow object to be measured with laser light to form speckle, receive the speckle with photoelectric receiver, and finally process and analyze the speckle image to obtain the required velocity information. In this technology, speckle image processing is the focus and difficulty. At present, the digital image correlation method is mostly used for processing, and its basic principle is to analyze the speckle image through the method of image matching, and on this basis to obtain the measured velocity. When the digital image correlation method is used to measure the speed of the object to be measured, the quality of the image is high. When the speed of the object to be measured is too fast, the image will become blurred. Therefore, this method is used to measure the speed of the object to be measured The scope is small; in terms of algorithms, some algorithms are simple but computationally intensive, such as the early coarse and fine search method, which is simple to program and easy to implement, but the search speed is slow.

Existing spatial filters, such as parallel slit gratings, linear optical fiber bundles, and linear photodetector arrays, can also measure the flow velocity, but the structural interval g of these filters cannot guarantee high accuracy, and at the same time requires follow-up The amplifying circuit is relatively complex, and it is not convenient for system integration. More importantly, the existing spatial filtering method can only realize the measurement of the fluid single point velocity, but cannot realize the measurement of the flow velocity field.

Contents of the invention

Technical problem: Aiming at the shortcomings of the particle image method and the existing spatial filter method in the flow field measurement, the present invention proposes a method and device for measuring the fluid velocity field based on a CCD spatial filter, and performs selective interlacing and Sampling every other column is used to simulate the spatial filtering characteristics of the grating, and then the measurement of the two-dimensional velocity field of the fluid can be realized through the method of spectrum analysis. The method and device of the present invention only need to use a low-power, small-scale continuous light-emitting gas laser as a light source, use a high-speed CCD camera to obtain the image of the flow object to be measured, and then analyze the velocity field of the flow object, which has the advantages of easy implementation, simple data processing, and measurement Wide range, low cost and other advantages.

Technical solution: Based on the principle of spatial filter velocity measurement, the present invention proposes a method and device for measuring two-dimensional velocity field using an area array CCD spatial filter. To measure the flow object, the area array CCD sensor is used as the image detector to shoot the fluid, and the flow image containing velocity information is obtained, and the flow image captured by the CCD is selectively interlaced and alternately sampled, and through the method of spectrum analysis, it can further The flow two-dimensional velocity field is obtained, thereby realizing the optical non-contact measurement of the velocity of the flow object to be measured.

A two-dimensional velocity field measuring device based on an area array CCD spatial filter, characterized in that it comprises:

a laser for emitting light;

A lens group for imaging the tracer particles irradiated by the outgoing light;

A side-array CCD for collecting images imaged by the lens group;

An image processor divides the area array CCD into different sub-regions, each sub-region is used as a spatial filter, and then converts each frame of image acquired into a gray value matrix; on this basis, the gray value The matrix is also divided into different sensitive sub-areas, and each sensitive sub-area is used as a space velocity measurement area, and the pixel gray values of all sensitive sub-areas are selectively accumulated in alternate rows and columns to simulate the traditional grating filter. Shading and light transmission, and finally perform Fourier transform on the gray-level original signal sequence accumulated in the same sensitive area of all collected images to obtain the peak frequency of the signal; calculate the vector of each sensitive sub-area according to the peak frequency of the obtained signal Velocity: Perform the above-mentioned processing on all sensitive sub-areas to realize the measurement of the two-dimensional velocity distribution of the fluid within the field of view of the area array CCD.

The laser is a continuous emitting He-Ne laser or a diode laser.

The lens group includes two ordinary optical lenses, the magnification ratio of the lens group is 0.8, the focal length is 69 mm, and the f number is 1.4.

A method for measuring a two-dimensional velocity field based on an area array CCD spatial filter, characterized in that it comprises the steps:

Step 1. Add tracer particles with a volume concentration of 0.0005% to 0.005% in the flow object to be measured. The light emitted by the laser line source is irradiated on the flow object containing tracer particles. Due to the scattering of light, the area array CCD is used to The sensor can acquire a series of particle motion images, which are collected by the image acquisition unit of the image processor and stored in the storage unit of the image processor;

In the second step, the area array CCD sensor array is divided into different sub-regions, and each sub-region is used as a spatial filter, and then the acquired image is converted into a gray value matrix, and on this basis, the gray value matrix is also Divided into different sensitive sub-areas, each sensitive sub-area serves as a space velocity measurement area;

In the third step, the pixel gray values of all sensitive sub-regions are selectively accumulated in alternate rows and columns to simulate the light-shielding and light-transmitting effects of traditional grating filters, and finally accumulate in the same sensitive region of all collected images The original signal sequence of the gray level is Fourier transformed to obtain the peak frequency of the signal; the horizontal velocity V _x is obtained by accumulating the gray value of every row of pixels in the sensitive sub-region and the peak frequency f _x of the time-domain spectrum of the sequence, and the vertical velocity V _y is obtained by accumulating the gray values of interlaced pixels in the sensitive sub-region and the peak frequency f _y of the time-domain spectrum of the sequence. The specific speed measurement relationship is:

V _x =g f _x /M (1)

V _y = g·f _y /M (2)

In the formula, g is the interval between columns or rows in the sensitive sub-area, and M is the proportional magnification factor of the image, which is determined by the optical lens parameters of the lens group;

The fourth step is to calculate the vector sum of the horizontal velocity V _x and the vertical velocity V _y obtained in the sensitive sub-area, and then the vector velocity V of the sensitive sub-area can be obtained:

$\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; =</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; +</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The fifth step is to repeat the above steps three and four for each sensitive sub-region divided by the area array CCD sensor array, and the vector V in each sensitive sub-area can be obtained, so the two-dimensional velocity of the fluid within the field of view of the area array CCD sensor can be realized Distribution measurement.

The present invention is based on the measurement device of the flow two-dimensional velocity field measurement method of the above-mentioned area array CCD sensor, comprising a laser, a lens group, an area array CCD and an image processor with an image acquisition unit (image acquisition card) and a storage unit, wherein the image processing The commonly used computer can be selected as the laser. The laser is a line light source with a cylindrical mirror inside to realize the expansion from the point light source to the line light source; the lens group is connected to the area array CCD through the bayonet, and the area array CCD is connected to the image of the computer through the signal cable. Capture card connection.

Beneficial effects: Compared with the prior art, the present invention has the following advantages: without the need of high-power lasers, high-resolution CCDs and complex synchronization devices, the full-field velocity measurement of the measured object can be realized; full use of the area array The CCD sensor is used as a spatial filter and detector, combined with an image processor, the system equipment is simple, and data processing is convenient, avoiding the heavy workload of image processing calculations by the correlation method, the slow search speed and the inability to realize the flow velocity field measurement by the traditional spatial filtering method And other issues, there are lower requirements for the installation, commissioning and use environment of the instrument, and it can be suitable for fluid flow field measurement in different occasions.

Description of drawings

FIG. 1 is a schematic structural diagram of a flow two-dimensional velocity field measurement device based on a CCD spatial filter according to the present invention; wherein, a laser line light source 1 , a lens group 2 , an area array CCD 3 , and an image processor 4 .

Fig. 2 is a schematic diagram of division of sensitive areas for two-dimensional velocity distribution measurement based on the area array CCD spatial filter.

Figure 3 shows the measurement results of the flow velocity field of the nanofluid in the horizontal pipeline.

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. After reading the present invention, those skilled in the art all fall into the appended claims of the present application to the amendments of various equivalent forms of the present invention limited range.

The working principle of the present invention: plant tracer particles in the fluid to be tested, and the tracer particles are irradiated by the laser line light source. Under the control of the calculation software, the high-speed area array CCD3 collects and obtains the flow field image by the image processor 4 and stores it in the In the image processor; in the image processor 4, the image processing software first selects a plurality of sensitive sub-regions for the acquired multi-frame images, and then in each sub-region, the rows and columns are selectively interlaced and column-accumulated To simulate the light-shielding and light-transmitting effects of traditional grating filters, and finally perform Fourier transformation on the accumulated interlaced and every other original gray signal sequence to obtain the peak frequencies f _x and f _y of the signal, and calculate the sensitive sub-region Velocity, the two-dimensional velocity field distribution of the fluid to be measured can be obtained.

As shown in FIG. 1 , the CCD spatial filter-based flow two-dimensional velocity field measurement device of the present invention mainly includes a light source 1 , a lens group 2 , an interlaced scanning CCD 3 , and an image processor 4 . The light source can be a continuous laser line light source 1 (such as a He-Ne laser 1). The lens group 2 includes two ordinary optical lenses (the magnification of the lens group 2 is 0.8, the focal length is 69mm, and the f number is 1.4, and the specific parameters can be selected according to the experimental requirements), which are connected to the high-speed area array CCD3 through the C bayonet. The high-speed area array CCD3 is connected with the image processor through a signal cable. Under the control of the image data processing software in the image processor 4, the overall coordination of image acquisition, storage and processing can be completed.

In conjunction with Fig. 1 and Fig. 2, the working process and data processing flow of the present invention are specifically described below in conjunction with the measurement of the flow velocity field of the nanofluid in the horizontal pipeline:

1. Since the nanofluid contains nanoparticles and can follow the flow of the base fluid, there is no need to add tracer particles to the fluid to be tested. The output light of the laser line light source 1 is a fan-shaped sheet light. Under the irradiation of the sheet-shaped light source, the nanoparticles in the nanofluid each form a small scattering spot. The high-speed area array CCD sensor 3 is used to obtain a series of fluid motion images. 4 is collected and stored in the processor.

2. Divide the CCD sensor array into 25x25 different sub-areas, each sub-area contains 10x10 pixels, as a spatial filter, correspondingly divides the acquired sequence image gray value matrix into different sensitive sub-areas, Each sub-area serves as a space velocity measurement area.

3. Do the following processing for each sensitive sub-region respectively:

1) In a certain sub-area, the processing steps of the horizontal velocity V _x are as follows: For the m-th frame image, starting from the first column of the sensitive sub-area, add the image gray values of the first column to obtain C _m1 (wherein the lower corner The mark m indicates which frame of image), after one column, add the gray value of the next column of pixels to get C _m2 , and so on, after 5 times of cumulative processing, C _m1 , C _m2 , and C _m3 can be obtained , C _m4 , C _m5 . The area array CCD can simulate the light-shielding and light-transmitting functions of the traditional grating filter by using this method of accumulating every other column, and then add C _m1 , C _m2 , C _m3 , C _m4 , and C _m5 to get C _m , that is, :

C _m ＝C _m1 +C _m2 +C _m3 +C _m4 +C _m5 (4)

For n images in the same sampling period, a sequence C=(C ₁ ,C ₂ ,...,C _m ,...C _n ) can be obtained, where n is the frame number of the image, and then the sequence C The power spectrum distribution diagram is obtained by performing Fourier transform, and the peak frequency f _x can be obtained from the power spectrum distribution diagram, and the horizontal velocity of the fluid in this sub-region can be determined.

V _x =g f _x /M (1)

2) For the vertical velocity V _y in the sub-area, the gray value of interlaced pixels with similar processing is used to accumulate the time sequence D=(D ₁ , D ₂ ,...D _n ), and the sequence D is The power spectrum distribution diagram is obtained by Fourier transform, and the peak frequency f _y can be obtained from the power spectrum distribution diagram, and the vertical velocity of the fluid in this sub-region can be determined.

V _y = g·f _y /M (2)

3) Vector summation of the horizontal velocity V _x and the vertical velocity V _y in the sub-areas can obtain the velocity V of each sensitive sub-area.

$\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; =</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; +</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

4) Repeat the above steps 3 and 4 for the 25x25 sensitive sub-areas divided by the area array CCD sensor array, and then the vector V in each sensitive sub-area can be obtained, so the two-dimensional velocity distribution measurement of the fluid within the field of view of the CCD can be realized. Figure 3 shows the measurement results of the flow velocity field of the nanofluid in the horizontal pipeline.

Claims (4)

1. A two-dimensional velocity field measuring device based on an area array CCD spatial filter, characterized in that it comprises: a laser for emitting light; A lens group for imaging the tracer particles irradiated by the outgoing light; A side-array CCD for collecting images imaged by the lens group; An image processor divides the area array CCD into different sub-regions, each sub-region is used as a spatial filter, and then converts each frame of image acquired into a gray value matrix; on this basis, the gray value The matrix is also divided into different sensitive sub-areas, and each sensitive sub-area is used as a space velocity measurement area, and the pixel gray values of all sensitive sub-areas are selectively accumulated in alternate rows and columns to simulate the traditional grating filter. Shading and light transmission, and finally perform Fourier transform on the gray-level original signal sequence accumulated in the same sensitive area of all collected images to obtain the peak frequency of the signal; calculate the vector of each sensitive sub-area according to the peak frequency of the obtained signal Velocity: The above-mentioned processing is performed on all sensitive sub-areas to realize the measurement of the two-dimensional velocity distribution of the fluid within the field of view of the CCD array. 2. The two-dimensional velocity field measurement device based on the area array CCD spatial filter according to claim 1, characterized in that: the laser is a continuously emitting He-Ne laser or a diode laser. 3. The two-dimensional velocity field measuring device based on the area array CCD spatial filter according to claim 1, characterized in that: the lens group comprises two ordinary optical lenses, the magnification of the lens group is 0.8, and the focal length is 69mm , f number 1.4. 4. a kind of measurement method that adopts the two-dimensional velocity field measuring device based on the area array CCD spatial filter described in claim 1, is characterized in that, comprises the steps: Step 1. Add tracer particles with a volume concentration of 0.0005% to 0.005% in the flow object to be measured. The light emitted by the laser line source is irradiated on the flow object containing tracer particles. Due to the scattering of light, the area array CCD is used to The sensor can acquire a series of particle motion images, which are collected by the image acquisition unit of the image processor and stored in the storage unit of the image processor; In the second step, the area array CCD sensor array is divided into different sub-regions, and each sub-region is used as a spatial filter, and then the acquired image is converted into a gray value matrix, and on this basis, the gray value matrix is also Divided into different sensitive sub-areas, each sensitive sub-area serves as a space velocity measurement area; In the third step, the pixel gray values of all sensitive sub-regions are selectively accumulated in alternate rows and columns to simulate the light-shielding and light-transmitting effects of traditional grating filters, and finally accumulate in the same sensitive region of all collected images The original signal sequence of the gray level is Fourier transformed to obtain the peak frequency of the signal; the horizontal velocity V _x is obtained by accumulating the gray value of every row and column of pixels in the sensitive sub-region and the peak frequency f _x of the time-domain spectrum of the sequence, and the vertical velocity V _y is obtained by accumulating the gray values of interlaced pixels in the sensitive sub-region and the peak frequency f _y of the time-domain spectrum of the sequence. The specific speed measurement relationship is: V _x =g f _x /M (1) V _y = g·f _y /M (2) In the formula, g is the interval between columns or rows in the sensitive sub-area, and M is the proportional magnification factor of the image, which is determined by the optical lens parameters of the lens group; The fourth step is to calculate the vector sum of the horizontal velocity V _x and the vertical velocity V _y obtained in the sensitive sub-area to obtain the vector velocity V of the sensitive sub-area: $\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; =</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; +</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ Step 5: Repeat the above steps 3 and 4 for each sensitive sub-area divided by the area array CCD sensor array, and then the vector V in each sensitive sub-area can be obtained, so the two-dimensional velocity distribution measurement of the fluid within the field of view of the CCD can be realized .

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