CN114740222B - Device and method for measuring uniformity of three-dimensional velocity field between moving blade and static blade grids - Google Patents

Abstract

The invention discloses a measuring device and a measuring method for the uniformity of a three-dimensional velocity field between dynamic and static blade cascades, belonging to the field of multiphase flow testing. The invention proposes a three-dimensional velocity field uniformity measurement device and measurement method between dynamic and static cascades. The optical path system is designed by using light interference, and an interlaced laser grid is formed in the flow field to be measured to realize the marking and excitation of tracer molecules. . The synchronous controller is used to realize the timing control of the enhanced high-speed camera and the pulse laser, and the synchronous measurement of the three-dimensional velocity field and its uniformity between the moving and static cascades can be realized. At the same time, the invention reconstructs the phosphorescence grid image according to the characteristics of laser light intensity, which can improve the precision of the velocity field to sub-pixel precision.

Description

A device and method for measuring the uniformity of three-dimensional velocity field between dynamic and static cascades

technical field

The invention belongs to the field of multiphase flow testing, in particular to a measuring device and a measuring method for the uniformity of a three-dimensional velocity field between dynamic and static blade cascades.

Background technique

In the field of modern aerospace, the high-precision measurement of the flow velocity between the dynamic and static cascades in the engine and the measurement of the stability of the flow field are of great significance. However, the space between the dynamic and static cascades is small and the speed is high, which has become a difficulty in measurement (the distance between the dynamic and static cascades is 8-10mm, and the speed can reach several thousand to tens of thousands of revolutions). Due to manufacturing tolerances in the processing process, the flow field will be unstable, and high-precision measurement of the uniformity of the flow field within a cycle is required. Traditional measurement methods, such as Pitot tubes and hot air linear velocity meters, have great interference to the flow field and slow response, making it difficult to adapt to the measurement of high-speed flow fields in small spaces. In recent years, with the development of optical equipment and high-speed photography technology, some optical non-contact velocimetry technologies have also been developed rapidly, such as: molecular marker velocimetry technology, laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). )wait. Among them, laser Doppler velocimetry and particle image velocimetry need to add tracer particles in the flow field, because the addition of tracer particles will affect the normal operation of the impeller, and due to the large inertia of the particles, the hysteresis of the particles is very large. It is difficult to measure the uniformity of the flow field at the same time.

Contents of the invention

The object of the present invention is to overcome the above-mentioned shortcomings of the prior art, and provide a three-dimensional velocity field uniformity measurement device and measurement method between dynamic and static blade cascades.

In order to achieve the above object, the present invention adopts the following technical solutions to achieve:

A device for measuring the uniformity of a three-dimensional velocity field between moving and static cascades, including a pulse laser and an optical path system. The pulse laser is used to emit laser light. The laser light enters the optical path system to change the optical path, and then passes through the exit of the optical path system to become two beams of thin sheets. Laser, the laser sheet enters the flow field to be measured between the moving blade and the stationary blade to form a staggered laser grid;

In the flow field to be measured, biacetyl or acetone is used as a tracer molecule, and the flow field to be measured is an oxygen-free environment;

A first enhanced high-speed camera and a second enhanced high-speed camera are respectively arranged on both sides of the flow field to be measured, and the first enhanced high-speed camera and the second enhanced high-speed camera are respectively connected to a synchronous controller through a connection line, and the synchronous controller Connected with an image processing system;

The first enhanced high-speed camera and the second enhanced high-speed camera are used for synchronously shooting phosphorescence images generated after the tracer molecules are excited.

Further, the optical path system includes mirrors, beam splitters and air wedges;

When a laser beam passes through the air wedge, it is divided into multiple sheet-shaped lasers, and then the laser beam is divided into two laser beams by a beam splitter and a mirror. The two laser beams enter the flow field to be measured to form an interlaced laser grid.

Further, the air wedge includes first quartz glass and second quartz glass, one end of the first quartz glass and the second quartz glass are in contact, and a metal wire is arranged between the other ends;

An air film is formed between the two quartz glasses, and the air film uses light interference to divide a beam of laser light into multiple thin slices;

The laser can fully penetrate the upper surface of the first quartz glass, emit on a part of the lower surface, refract the other part, and fully emit on the upper surface of the second quartz glass.

A method for measuring the uniformity of the three-dimensional velocity field between static and dynamic cascades, based on the implementation of the device for measuring the uniformity of the three-dimensional velocity field between the static and dynamic cascades of the present invention, comprising the following steps:

Step 1. Carry out a calibration experiment, and calculate the relationship between the first enhanced high-speed camera, the second enhanced high-speed camera and the actual space position, so as to obtain the image pixel coordinate a

32` and the conversion relationship between the actual space coordinates:

In the formula: (u, v) represents the pixel coordinates; (X _w , Y _w , Z _w ) represents the actual space coordinates; k _ij represents the solution parameters, i=1,2,3, j=1,2,3,4 ;

Step 2. Within the phosphorescence lifetime of the tracer molecule, use the first enhanced high-speed camera and the second enhanced high-speed camera to obtain two consecutive phosphorescence images at time t ₁ and t ₂ , which are expressed as:

和/>

根据磷光最大强度点进行网格交点一一匹配，得到实际空间中同一个网格交点在两个不同相机拍摄图片中像素点的坐标，随后将两个像素点坐标带入式，计算出实际网格空间点的坐标(X_w,Y_w,Z_w)_t1；Step 3: Phosphorescence images obtained by the first enhanced high-speed camera and the second enhanced high-speed camera at time _t1

and />

Match the grid intersection points one by one according to the phosphorescence maximum intensity point, and obtain the pixel coordinates of the same grid intersection point in the actual space in the pictures taken by two different cameras, and then bring the coordinates of the two pixel points into the formula to calculate the actual grid The coordinates of the grid space point (X _w , Y _w , Z _w ) _t1 ;

和/>

和/>

进行互相关计算，得到同一个相机捕捉到两个不同时刻磷光网格图片中网格交点的对应关系；利用互相关算法计算得到t₂时刻两个相机磷光图像/>

和/>

中网格交点的像素点的坐标，带入式，计算出t₂时刻网格交点在实际空间中的坐标(X_w,Y_w,Z_w)_t2；Step 4. Obtain phosphorescence images at two moments for the first enhanced high-speed camera and the second enhanced high-speed camera respectively

and />

and />

Carry out cross-correlation calculations to obtain the corresponding relationship between grid intersection points in two phosphorescent grid pictures captured by the same camera at different times; use cross-correlation algorithm to calculate phosphorescence images of two cameras at time _t2 >

and />

The coordinates of the pixel points of the grid intersection in the middle are brought into the formula to calculate the coordinates (X _w , Y _w , Z _w ) _t2 of the grid intersection in the actual space at time _t2 ;

Step _5. According to the relationship between the position (X _w , Y _w , Z _w ) _t1 and (X _w , Y _w , Z _w ) t2 of the grid intersection point in the actual space at time t ₁ and _{time t 2} and the time, calculate The three-dimensional velocity field of the flow field is

Further, step 2 also includes:

performing denoising processing on the phosphorescence image while enhancing image contrast;

For a single phosphorescent grid image, a Gaussian function is used to fit the phosphorescent beam in the direction perpendicular to the grid lines.

Further, through the timing control of the pulsed laser, the first enhanced high-speed camera and the second enhanced high-speed camera, the velocity field of each moving blade passing the same stationary blade can be measured, and by comparing the The difference of the velocity field, so as to realize the measurement of the uniformity of the flow field in the cycle.

Further, the specific operation of measuring the uniformity of the velocity field is as follows:

此时同一个静叶片经历2个相邻的叶片所需要的时间为/>

此时脉冲激光器的频率为f＝nk，高速相机拍摄时间/>

When the rotating speed of the moving blade is n and the number of moving blades is k, the time for the moving blade to rotate one circle is

At this time, the time required for the same stationary blade to experience two adjacent blades is />

At this time, the frequency of the pulsed laser is f=nk, and the shooting time of the high-speed camera />

The excitation time of two adjacent pulse lasers satisfies:

时，脉冲激光器的频率为/>

高速摄像机拍摄时间

when

, the frequency of the pulsed laser is />

High-speed camera shooting time

Further, at time t ₁ , the initial distribution of the phosphorescent grid images is arranged in the middle of the two rotor blades.

Compared with the prior art, the present invention has the following beneficial effects:

The invention proposes a three-dimensional velocity field uniformity measurement device and measurement method between dynamic and static cascades. The optical path system is designed by using light interference, and an interlaced laser grid is formed in the flow field to be measured to realize the marking and excitation of tracer molecules. . The synchronous controller is used to realize the timing control of the enhanced high-speed camera and the pulse laser, and the synchronous measurement of the three-dimensional velocity field and its uniformity between the moving and static cascades can be realized. At the same time, the invention reconstructs the phosphorescence grid image according to the characteristics of laser light intensity, which can improve the precision of the velocity field to sub-pixel precision.

Furthermore, the air wedge is designed according to the wavelength of the laser, which can further improve the quality of the marking laser, improve the spatial resolution of the grid, and form a high-quality grid phosphorescence image in the flow field.

Further, according to the rotating speed, radius, and blade number of the static and dynamic cascades, the present invention designs the phosphorescence shooting sequence, determines the camera frequency, pulse laser frequency, and camera exposure time, etc., so that the measurement of the uniformity of the flow field can be realized, and the measurement accuracy can be improved. the accuracy.

Further, the present invention uses the molecular marker velocity measurement technology to measure the three-dimensional velocity field between the dynamic and static blade cascades, without interference to the flow field, and has high measurement accuracy.

Description of drawings

Figure 1 is a structural diagram of the three-dimensional velocity field measurement device between the moving and static cascades;

Fig. 2 is the structural diagram of optical path system;

Fig. 3 is the structural diagram of air wedge;

Figure 4 is an image of the phosphorescent grid.

Among them: 01-pulse laser; 02-laser; 03-first data transmission line; 04-first enhanced high-speed camera; 05-optical system; 06-moving blade; 07-second enhanced high-speed camera; 08-second Data transmission line; 09-stator blade; 10-synchronous controller; 11-third data transmission line; 12-image processing system; 01-pulse laser; 13-mirror; 14-beam splitter; 15-air splitter; 16- First quartz glass; 17 - wire; 18 - second quartz glass.

Detailed ways

In order to enable those skilled in the art to better understand the solutions of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only It is an embodiment of a part of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terms "first" and "second" in the description and claims of the present invention and the above drawings are used to distinguish similar objects, but not necessarily used to describe a specific sequence or sequence. It is to be understood that the data so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein can be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having", as well as any variations thereof, are intended to cover a non-exclusive inclusion, for example, a process, method, system, product or device comprising a sequence of steps or elements is not necessarily limited to the expressly listed instead, may include other steps or elements not explicitly listed or inherent to the process, method, product or apparatus.

The invention adopts the molecular marker velocity measurement technology to realize the synchronous measurement of the three-dimensional velocity field and the uniformity of the flow field between the dynamic and static blade cascades. Among them, the molecular marker velocimetry technology is a non-invasive, non-contact laser diagnostic technology. The principle is to use a laser with a specific wavelength to excite tracer molecules in the flow field to emit phosphorescence. After a certain time interval, the phosphorescence signal is directly captured to determine the position of the tracer molecules, and then the velocity is calculated according to the displacement-time relationship of the tracer molecules. Molecular marker velocimetry technology can effectively overcome the shortcomings of laser Doppler velocimetry and particle image velocimetry, and can be well applied to high-precision measurement of the velocity field between dynamic and static cascades. Uniformity measurement. The present invention proposes a three-dimensional velocity field uniformity measurement device and measurement method between dynamic and static cascades based on molecular marker velocity measurement technology, which can overcome the shortcomings of previous testing methods and realize simultaneous measurement of the three-dimensional velocity field and velocity field uniformity between dynamic and static cascades .

The present invention is described in further detail below in conjunction with accompanying drawing:

Refer to Fig. 1, Fig. 1 is a structural diagram of the three-dimensional velocity field measuring device between the dynamic and static cascades, a high-precision measurement device for the three-dimensional velocity field between the dynamic and static cascades. It consists of four parts. The moving and static cascade structure is composed of moving blades 06 and stationary blades 09, and this structure may exist in engines and gas turbines. The optical path system is mainly composed of a pulsed laser 01, a mirror 13, an air wedge 15, and a beam splitter 14, which are used to construct a staggered laser grid in the area to be measured in the flow field to realize the excitation and marking of tracer molecules in the flow field to be measured. The image capture system is mainly composed of a synchronous controller 10, a first enhanced high-speed camera 04 and a second enhanced high-speed camera 07, which can obtain two consecutive phosphorescence grid images of traced molecules at different times. The image processing system 12 mainly reconstructs the three-dimensional model of the phosphorescence grid based on the phosphorescence grid image of the tracer molecules, and develops a cross-correlation algorithm to obtain the relationship between the spatial positions of the grid at different times according to the distribution characteristics of the phosphorescence intensity, thereby obtaining the three-dimensional velocity field.

The dynamic and static blade cascade structure can exist in the engine gas turbine, and the area to be measured is visualized by using quartz glass. At the same time, in order to avoid the influence of other fluorescence on the phosphorescence of the tracer molecules during the shooting process, the blades should be oxidized and blackened. If the tracer molecule is biacetyl or acetone, the gas in the flow field should be free of oxygen. Oxygen quenches tracer molecule phosphorescence.

Referring to Fig. 2, Fig. 2 is a structural diagram of the optical path system. In the optical path system, a beam of laser light is divided into a plurality of laser slices by an air wedge 15, and then a beam of laser light is divided into two beams of laser light by a beam splitter 14 and a reflector 13, and then the beam of laser light is divided into two laser beams in the waiting state. A staggered laser grid is formed in the flow field. Using the interference of light to build a high-quality laser grid, in which the phosphorescence of the tracer molecules is proportional to the laser intensity. According to the characteristics of the laser intensity, the phosphorescence image reconstruction algorithm can be developed to improve the accuracy of the velocity field to sub-pixel accuracy.

Referring to Fig. 3, Fig. 3 is the structural diagram of the air splitter, the air splitter 15 is mainly composed of two pieces of quartz glass and a metal wire, an air film is formed between the two quartz glasses, and a beam of laser light is divided into multiple parts by interference of light. slices. Wherein, the upper surface of the first quartz glass 16 can fully penetrate the laser light, a part of the lower surface is emitted, and a part is refracted; the upper surface of the second quartz glass 18 is fully emitted.

形成明暗条纹的条件为：The laser light interferes on the upper and lower surfaces of the air film, forming light and dark laser flakes. Since the diameter D of the metal wire is very small, the path difference when two coherent lights meet is about

The conditions for forming light and dark stripes are:

可知相邻两条明纹之间的距离为l＝Δdsinθ，由于空气薄膜的角度从θ很小，近似为/>

金属丝直径D和相邻两条明纹间距l之间的关系为/>

Thickness difference of air film between two adjacent bright grains

It can be seen that the distance between two adjacent bright lines is l=Δdsinθ, since the angle of the air film is very small from θ, it is approximated as />

The relationship between the wire diameter D and the distance l between two adjacent open grains is />

When the distance between the dynamic and static cascades is 10mm, the space of the flow field to be measured is small, and the quality of the laser grid is required to be high. Diacetyl was selected as the tracer molecule, the laser wavelength was 355nm, L was 20mm, the distance between two bright lines was 1mm, and the diameter of the metal wire was 3.55×10 ^-6 m. A 6×6 laser marking grid is formed in the flow field to be measured by using 6 bright stripe lasers, so as to realize the marking and excitation of the flow field to be measured.

为了避免求解速度场时产生错误的信息，相邻图像中网格节点的最大位移应保持在网格间距的一半以下/>

此时，相机的频率为/>

且由于拍摄流场为高速流场，相机每一帧图像的曝光时间不宜太长，否则将会造成较大的拖影，对速度场的求解精度有较大的影响。为了保证测量精度，曝光时间Δt应满足/>

The enhanced high-speed camera in the image capture system consists of a high-speed camera, an image intensifier, a lens, and a filter, which can accurately capture phosphorescence signals. During the test, filters of different sizes need to be selected according to the phosphorescence characteristics of the tracer molecules. The synchronous controller 10 is connected with the image processing system 12 through the third data transmission line 11, the synchronous controller 10 is connected with the first enhanced high-speed camera 04 through the first data transmission line 03, and the synchronous controller 10 is connected with the second enhanced high-speed camera 04 through the second data transmission line 08. Type High Speed Camera 07. Simultaneously, use synchronous controller 10 to trigger and control the first enhanced high-speed camera 04, the second enhanced high-speed camera 07 and the pulsed laser 01 to ensure that each frame of images captured by the two cameras is synchronized, thereby realizing the pulsed laser and enhanced High-speed camera timing control. In the image capture system, within the phosphorescence lifetime of the tracer molecule, the phosphorescence grid patterns in the flow field at two different times t ₁ and t ₂ can be obtained continuously. Among them, the continuous shooting time is determined by the camera frequency

To avoid erroneous information when solving the velocity field, the maximum displacement of grid nodes in adjacent images should be kept below half the grid spacing />

At this point, the frequency of the camera is />

And because the shooting flow field is a high-speed flow field, the exposure time of each frame of the camera image should not be too long, otherwise it will cause a large smear, which will have a great impact on the solution accuracy of the velocity field. In order to ensure the measurement accuracy, the exposure time Δt should satisfy />

获得包含以下步骤：The image processing part mainly uses the tracer molecular phosphorescence image obtained by the image capture system, and combines theoretical analysis and image processing technology to obtain the three-dimensional velocity field between the cascades. Within the biacetyl phosphorescence lifetime, use the first enhanced high-speed camera 04 and the second enhanced high-speed camera 07 to obtain phosphorescence images at two consecutive moments, and the obtained phosphorescence grid images are shown in Figure 4 as follows:

Obtaining involves the following steps:

Step 1. Carry out a calibration experiment, and calculate the relationship between the two cameras and the actual space position, so as to obtain the conversion relationship between the image pixel coordinates and the actual space coordinates:

In the formula: (u, v) represents the pixel coordinates; (X _w , Y _w , Z _w ) represents the actual space coordinates; k _ij represents the solution parameters, i=1,2,3, j=1,2,3,4 );

Step 2, preprocessing the obtained phosphorescence image, using Gaussian filter and mean value filter to denoise the image to remove background noise, using image processing software to uniformly process the image, enhancing the image contrast, and improving the brightness of the phosphorescence image ;

Step 3. For a single phosphorescent grid image, a Gaussian function is used to fit the phosphorescent beam in the direction perpendicular to the grid lines, thereby improving the spatial resolution of the image and improving the image accuracy to sub-pixels;

根据磷光最大强度点进行网格交点一一匹配，得到实际空间中同一个网格交点在两个不同相机拍摄图片中像素点的位置，随后将两个像素点坐标带入式2，计算出实际网格空间点的坐标(X_w,Y_w,Z_w)_t1；Step 4. Phosphorescence images obtained by two cameras at time t ₁

Match the grid intersection points one by one according to the phosphorescence maximum intensity point, and obtain the pixel position of the same grid intersection point in the actual space in the pictures taken by two different cameras, and then bring the coordinates of the two pixel points into Equation 2 to calculate the actual Coordinates (X _w , Y _w , Z _w ) _t1 of grid space points;

和/>

和/>

进行互相关计算，得到同一个相机捕捉到两个不同时刻磷光网格图片中网格交点的一一对应关系。利用互相关算法计算得到t₂时刻两个相机磷光图像(/>

和/>

)中网格交点的像素点的坐标，带入式2，计算出t₂时刻网格交点在实际空间中的坐标(X_w,Y_w,Z_w)_t2；Step 5: Obtain phosphorescence images at two moments for camera 1 and camera 2 respectively

and />

and />

Perform cross-correlation calculations to obtain the one-to-one correspondence between grid intersections in two phosphorescent grid pictures captured by the same camera at different times. Using the cross-correlation algorithm to calculate the phosphorescence images of the two cameras at time t ₂ (/>

and />

), bring the coordinates of the pixel points of the grid intersection point into formula 2, and calculate the coordinates (X _w , Y _w , Z _w ) _t2 of the grid intersection point in the actual space at time _t2 ;

Step _6. According to the relationship between the position (X _w , Y _w , Z _w ) _t1 and (X _w , Y _w , Z _w ) t2 of the grid intersection in the actual space at time t ₁ and time _{t 2} and the relationship between time and calculation The three-dimensional velocity field of the flow field is obtained as

Furthermore, due to the difference in the actual manufacturing process, the flow field between the static and dynamic cascades will be uneven due to the difference in the process. In order to measure the size of the three-dimensional velocity field and the unevenness of the flow field between the dynamic and static cascades, the , The timing control of the enhanced high-speed camera measures the velocity field of each moving blade when it passes the same stationary blade, and by comparing the difference in the velocity field between different moving blades, the measurement of the uniformity of the flow field within a period is realized. Velocity field inhomogeneity measurement can be described as:

此时同一个静叶片需经历2个相邻的叶片所需要的时间为/>

此时脉冲激光器的频率为f＝nk，高速相机拍摄时间/>

由于示踪分子的磷光寿命可达1ms，为了保证同一时间待测流场中不会出现两组磷光网格图像，相邻两次脉冲激光激发时间应满足：/>

当

时，为了保证待测流场中不会出现两组磷光网格图像，脉冲激光器的频率为

高速摄像机拍摄时间/>

虽然脉冲激光器频率减小，但高速相机拍摄也随之变周期增大，将导致相机的内存增大。同时，为了保证测量的准确性，初始时刻，磷光网格图像初始分布应布置在两个动叶片中间位置。When the rotating speed of the moving blade is n, the number of moving blades is k, and the time for the blade to rotate one circle is

At this time, the time required for the same stationary blade to experience two adjacent blades is />

At this time, the frequency of the pulsed laser is f=nk, and the shooting time of the high-speed camera />

Since the phosphorescence lifetime of tracer molecules can reach 1 ms, in order to ensure that two sets of phosphorescence grid images do not appear in the flow field to be measured at the same time, the excitation time of two adjacent pulse lasers should meet: />

when

, in order to ensure that two groups of phosphorescent grid images do not appear in the flow field to be measured, the frequency of the pulsed laser is

High-speed camera shooting time/>

Although the frequency of the pulsed laser decreases, the shooting cycle of the high-speed camera also increases, which will lead to an increase in the memory of the camera. At the same time, in order to ensure the accuracy of the measurement, the initial distribution of the phosphorescent grid image should be arranged in the middle of the two moving blades at the initial moment.

A measurement process of velocity field uniformity between static and dynamic cascades is as follows:

1) According to the characteristics of the flow field to be measured, select the type of tracer molecules, determine the wavelength of the excitation laser, the structure of the air wedge, and the size of the filter;

2) Determine the pulse laser frequency and shooting period according to the rotating speed and number of blades;

3) Determine the estimated flow field velocity V _est,max according to the blade speed and blade diameter, and calculate the camera frequency and exposure time;

4) Set the parameters of each equipment, carry out the camera calibration experiment, conduct the velocity field measurement experiment between the dynamic and static cascades, and calculate the flow field velocity V _act at the same time;

5) Compare V _est,max and V _act,max , if V _est,max >V _act,max , the test is over; if V _est,max <V _act,max , you need to recalculate the camera according to V _act,max Frequency and exposure time, repeat the experiment until the end.

The above content is only to illustrate the technical ideas of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solutions according to the technical ideas proposed in the present invention shall fall within the scope of the claims of the present invention. within the scope of protection.

Claims (6)

1. A method for measuring the uniformity of the three-dimensional velocity field between the static and dynamic cascades, characterized in that, based on a measuring device for the uniformity of the three-dimensional velocity field between the static and dynamic cascades, the measuring device for the uniformity of the three-dimensional velocity field between the static and dynamic cascades includes a pulse The laser (01) and the optical path system (05), the pulse laser (01) is used to emit laser light (02), and the laser light (02) enters the optical path system (05) to change the optical path, and then changes the optical path through the exit of the optical path system (05). into two beams of sheet-shaped lasers, and the laser sheets enter the flow field to be measured between the moving blade (06) and the stationary blade (09) to form a staggered laser grid; In the flow field to be measured, biacetyl or acetone is used as a tracer molecule, and the flow field to be measured is an oxygen-free environment; A first enhanced high-speed camera (04) and a second enhanced high-speed camera (07) are respectively arranged on both sides of the flow field to be measured, and the first enhanced high-speed camera (04) and the second enhanced high-speed camera (07) are respectively A synchronous controller (10) is connected through a connection line, and the synchronous controller (10) is connected with an image processing system (12); The first enhanced high-speed camera (04) and the second enhanced high-speed camera (07) are used for synchronous shooting of phosphorescent images produced after the tracer molecules are excited, including the following steps: Step 1. Carry out a calibration experiment, and calculate the relationship between the first enhanced high-speed camera (04), the second enhanced high-speed camera (07) and the actual space position, thereby obtaining the conversion relation between the image pixel coordinates and the actual space coordinates:

In the formula: (u, v) represents the pixel coordinates; (X _w , Y _w , Z _w ) represents the actual space coordinates; k _ij represents the solution parameters, i=1,2,3, j=1,2,3,4 ; Step 2. Within the phosphorescence lifetime of the tracer molecule, use the first enhanced high-speed camera (04) and the second enhanced high-speed camera (07) to obtain two consecutive phosphorescence images at time t ₁ and t ₂ , respectively expressed as:

Step 3, for the phosphorescence images obtained by the first enhanced high-speed camera (04) and the second enhanced high-speed camera (07) at time _t1

and />

According to the maximum intensity point of phosphorescence, the grid intersection points are matched one by one, and the pixel coordinates of the same grid intersection point in the actual space in the pictures taken by two different cameras are obtained, and then the coordinates of the two pixel points are brought into formula (2) to calculate coordinates (X _w , Y _w , Z _w ) _t1 of the actual grid space point; Step 4. Obtain phosphorescence images at two moments for the first enhanced high-speed camera (04) and the second enhanced high-speed camera (07) respectively

and />

and />

Carry out cross-correlation calculations to obtain the corresponding relationship between grid intersection points in two phosphorescent grid pictures captured by the same camera at different times; use cross-correlation algorithm to calculate phosphorescence images of two cameras at time _t2 >

and />

The coordinates of the pixel points of the grid intersection in the middle grid are brought into formula (2), and the coordinates (X _w , Y _w , Z _w ) _t2 of the grid intersection in the actual space at time _t2 are calculated; Step _5. According to the relationship between the position (X _w , Y _w , Z _w ) _t1 and (X _w , Y _w , Z _w ) t2 of the grid intersection point in the actual space at time t ₁ and _{time t 2} and the time, calculate The three-dimensional velocity field of the flow field is

Through the timing control of the pulse laser (01), the first enhanced high-speed camera (04) and the second enhanced high-speed camera (07), the time when each moving blade (06) passes the same stationary blade (09) The velocity field is measured, and the measurement of the uniformity of the flow field within a cycle is realized by comparing the difference of the velocity field between different moving blades (06). 2. The method for measuring the uniformity of the three-dimensional velocity field between moving and static cascades according to claim 1, wherein the optical path system (05) includes a mirror (13), a beam splitter (14) and an air wedge (15); When a beam of laser light passes through the air wedge (15), it is divided into multiple lamellar laser beams, and then the laser beam is divided into two laser beams by the beam splitter (14) and mirror (13), and the two laser beams enter the flow field to be measured A staggered laser grid is formed in the 3. The method for measuring the uniformity of the three-dimensional velocity field between moving and static cascades according to claim 1, wherein the air wedge (15) comprises a first quartz glass (16) and a second quartz glass (18), the first One end of the quartz glass (16) is in contact with the second quartz glass (18), and a metal wire (17) is arranged between the other ends; An air film is formed between the two quartz glasses, and the air film uses light interference to divide a beam of laser light into multiple thin slices; When the laser is incident, the laser can fully penetrate the upper surface of the first quartz glass (16), partly emit on the lower surface, refract the other part, and fully emit on the upper surface of the second quartz glass (18). 4. The method for measuring the uniformity of the three-dimensional velocity field between the static and dynamic cascades according to claim 1, wherein step 2 further comprises: performing denoising processing on the phosphorescence image while enhancing image contrast; For a single phosphorescent grid image, a Gaussian function is used to fit the phosphorescent beam in the direction perpendicular to the grid lines. 5. The method for measuring the uniformity of the three-dimensional velocity field between the dynamic and static cascades according to claim 4, wherein the specific operation of measuring the uniformity of the velocity field is as follows: When the rotating speed of the moving blade (06) is n and the number of moving blades (06) is k, the time for the moving blade (06) to rotate one circle is

At this time, the time required for the same stationary blade (09) to experience two adjacent blades is />

At this time, the frequency of the pulsed laser is f=nk, and the shooting time of the high-speed camera />

The excitation time of two adjacent pulse lasers satisfies:

when

, the frequency of the pulsed laser is />

High-speed camera shooting time/>

6. The method for measuring the uniformity of the three-dimensional velocity field between the moving and static cascades according to claim 4, characterized in that, at time _t1 , the initial distribution of the phosphorescence grid image is arranged in the middle of the two moving blades.

Images