Three-dimensional flow field optical measurement system and method adopting multiple flexible probes
By using a flexible multi-probe optical measurement system and image processing technology, the problem of measuring the flow field in the confined space of an aero-engine was solved, achieving high-resolution and high-precision three-dimensional flow field reconstruction, and reducing system complexity and cost.
Patent Information
- Application Number
- CN202511027339.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-24
- Publication Date
- 2025-11-07
AI Technical Summary
Existing technologies for measuring three-dimensional flow fields in the confined space of aero-engines suffer from problems such as large vibration of rigid rod endoscopes, small aperture, low resolution, severe lens distortion, stray light intensity, and difficulty in system calibration, which make PIV calculation difficult and hinder the achievement of high-precision measurements.
A flexible multi-probe three-dimensional flow field optical measurement system is adopted, which combines a flexible fiber bundle with a CCD camera and an endoscopic imaging lens, and image processing technology to achieve multi-angle capture and three-dimensional reconstruction of flow field images.
Achieving high-resolution flow field measurement in confined spaces and under strong vibration environments reduces system complexity and maintenance costs, eliminates lens distortion and stray light, and provides a high-precision means of studying flow characteristics.
Smart Images
Figure CN120907839A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of three-dimensional flow field endoscopic optical testing in a narrow space, in particular to a three-dimensional flow field optical measurement system and method using a flexible multi-probe coupled optical fiber bundle. BACKGROUND
[0002] Aero-engines, known as the "crown jewel of industry", provide power for the flight of aviation equipment, and need to work for a long time with high reliability in a high-temperature, high-pressure, high-speed and complex and variable environment, which poses a severe challenge to the accurate testing of key thermal parameters during engine operation. Among them, the accurate acquisition of the three-dimensional velocity field in the narrow space of the fan / compressor of an aero-engine is a difficult problem that has plagued the industry for many years. At present, the difficulties and key points of related work are that the commonly used ultra-wide-angle hard rod endoscope has serious image distortion and poor anti-vibration ability, and under the condition of severe vibration of the rotor blades, it is difficult to accurately obtain the flow field tracer particle image, which leads to extremely difficult subsequent cross-correlation particle image velocimetry (PIV) operation.
[0003] In view of such problems, the existing technology mostly adopts endoscopic PIV for flow field testing in a restricted space. Although endoscopic PIV can break through the limitation of the traditional measurement light path and reduce the light path requirement during flow field measurement, the combination of the existing endoscopic technology and PIV technology has problems such as large vibration of the hard rod endoscope caused by engine vibration, poor matching, small aperture, low resolution, serious lens distortion, strong stray light, difficult system calibration, strong reflection, background noise and the like, so that endoscopic PIV has not been widely used in internal flow field measurement in a restricted space. Therefore, the three-dimensional flow field endoscopic optical testing technology based on a flexible multi-probe coupled optical fiber bundle has important technical value and broad application prospects in the research on flow characteristics in a restricted space. SUMMARY
[0004] The present application aims to avoid the shortcomings of the prior art and provides a three-dimensional flow field optical measurement system and method using a flexible multi-probe, which captures flow field images by combining a fiber bundle with a camera, and finally obtains three-dimensional flow field information in a narrow space by using image processing technology.
[0005] In order to achieve the above object, the technical scheme adopted by the present application is as follows: a three-dimensional flow field optical measurement system using flexible multi-probe, comprising a three-dimensional holder and a laser arranged corresponding to a flow field region to be measured, an endoscopic imaging lens and a particle generator are arranged on the three-dimensional holder, a CCD camera is arranged on one side of the three-dimensional holder, the CCD camera is connected with the endoscopic imaging lens through a flexible optical fiber bundle, the laser and the CCD camera are respectively installed on a first lifting platform and a second lifting platform, the particle generator scatters tracer particles to the flow field region to be measured, and the laser generates bulk laser to irradiate the tracer particles in the flow field region to be measured.
[0006] Further, the three-dimensional holder is in a square structure, the endoscopic imaging lens is arranged as four, including a first endoscopic imaging lens, a second endoscopic imaging lens, a third endoscopic imaging lens and a fourth endoscopic imaging lens, a coordinate system is established with the geometric center of the square structure three-dimensional holder as the origin, the four endoscopic imaging lenses are arranged at the four corners of the square structure three-dimensional holder respectively, the side length of the square structure three-dimensional holder is a, the position of the first endoscopic imaging lens in the coordinate system is (0, -a, a), the position of the second endoscopic imaging lens in the coordinate system is (0, a, a), the position of the third endoscopic imaging lens in the coordinate system is (0, a, -a), and the position of the fourth endoscopic imaging lens in the coordinate system is (0, -a, -a), the geometric center of the flow field region to be measured is located at a position with a distance of b from the geometric center of the square structure three-dimensional holder in the x-axis direction, and the position of the geometric center of the flow field region to be measured is (b, 0, 0); the laser is arranged on one side of the flow field region to be measured, the position of the laser is (b, d, 0), and the particle generator is located below the flow field region to be measured, and the position of the particle generator is (b, 0, e).
[0007] Further, the flexible optical fiber bundle is a 1 / 4 structure optical fiber bundle, the bundle end of the flexible optical fiber bundle is connected with the CCD camera through a fixing device, the CCD camera is fixedly installed on the second lifting platform, the fixing device is a fixing sleeve with the same diameter as the armored shell of the flexible optical fiber bundle, and the four receiving ends of the flexible optical fiber bundle are connected with the first endoscopic imaging lens, the second endoscopic imaging lens, the third endoscopic imaging lens and the fourth endoscopic imaging lens respectively.
[0008] Further, the three-dimensional gimbal geometric center in a square structure as the origin of the coordinate system refers to the X-axis positive direction along the engine nozzle outlet direction, the Y-axis positive direction perpendicular to the X-axis and horizontally to the right, and the Z-axis positive direction vertically upward; in the coordinate system of the system, the initial attitude of the endoscopic imaging lens is defined as: when the main shaft of the endoscopic imaging lens is aligned with the X-axis positive direction and the Y / Z-axis has no deflection, it is the reference state (0°, 0°, 0°), the endoscopic imaging lens is rotated around the Z-axis by an angle of roll angle α, the range is ±90°; the endoscopic imaging lens is rotated around the Y-axis by an angle of yaw angle β, the range is ±90°, and the endoscopic imaging lens is rotated around the X-axis by an angle of pitch angle γ, the range is ±90°. The position b of the to-be-measured flow field region needs to meet the constraints of the depth of field range and the working distance of the endoscope imaging lens, and the working distance d of the laser needs to meet the requirement that the laser energy is the strongest under the premise that the laser thickness is consistent with the width of the to-be-measured flow field region, in order to ensure that the concentration of the scattered tracer particles is within the measurement requirement of 0.05 ppp~0.1 ppp, the particle generator is required to be located at a position with a distance e below the to-be-measured flow field region.
[0009] Further, the particle generator scatters tracer particles, which are diisooctyl sebacate (DEHS) or titanium dioxide particles, and the particle concentration of the tracer particles is 0.05 ppp~0.1 ppp.
[0010] The application also provides a measurement method measured by the three-dimensional flow field optical measurement device with a flexible multi-probe as described above, which comprises the following steps: Step one, the three-dimensional flow field optical measurement system with a flexible multi-probe, the aperture of the endoscopic imaging lens is adjusted to the minimum, the CCD camera is set to a double-frame mode and the first frame exposure time t 0μs, the time interval of the double-pulse signal of the laser is adjusted by using a time sequence synchronization controller t 1μs, so that the two laser pulses fall on the double-exposure time of the camera, so that the camera shoots two consecutive frames of flow field images; the first frame exposure time t 0μs is set in the range of 20~50μs, and the time interval of the double-pulse signal t 1μs is used in the range of 50~100μs, which ensures that the laser energy is sufficient to illuminate the tracer particles in the to-be-measured region while triggering the CCD camera to collect the particle image at the moment of laser illumination; Step two, according to the width of the flow field to be measured, the body laser with the same width as the flow field to be measured in the flow field region is incident into the flow field, and the tracer particles scattered in the flow field to be measured make the tracer particles produce scattered light, and two frames of images with the angles (α, β, 0), (α, -β, 0), (-α, -β, 0), (-α, β, 0) between the flow field to be measured and the endoscopic imaging lens provided by the flexible optical fiber bundle are shot by the CCD camera at one time; Step three, the computer is used to process the images shot to obtain the 3D-3C velocity field through tomographic reconstruction and three-dimensional cross-correlation calculation in turn.
[0011] Further, the image processing process is specifically: first, the collected images are subjected to brightness homogenization processing to make the brightness of the images shot at different angles the same; Secondly, the image is subjected to phase enhancement processing, including adjusting the gamma value curve of the image, using histogram equalization and CLAHE to enhance contrast, and using Gaussian filtering and median filtering to denoise; Then, the image is subjected to cutting processing, and the geometric center position of the flow field to be measured is selected as the center position of each picture, and the picture of m×n pixel size is cut; Finally, the image subjected to the cutting processing is input into the tomographic reconstruction program to obtain the three-dimensional spatial distribution of the flow field to be measured.
[0012] Further, the tomographic reconstruction process is specifically: the algebraic reconstruction algorithm is used to convert the flow field data at different angles into three-dimensional body data; the particle distribution reconstruction of the flow field to be measured is converted into the solving process of a linear equation set by the algebraic reconstruction algorithm, and the three-dimensional spatial distribution position relationship of the particles of the flow field to be measured is substituted into the three-dimensional cross-correlation calculation program to solve the velocity field.
[0013] Further, the three-dimensional cross-correlation calculation process is specifically: the multi-grid iteration adaptive query window algorithm is used to set three-dimensional query windows of different sizes for the three-dimensional spatial distribution image of the flow field to be measured, and the three-dimensional cross-correlation calculation is performed on each three-dimensional query window, and the corresponding cross-correlation peak value is obtained through the calculation of the query window; The window corresponding to the position of the cross-correlation peak value is the corresponding position of the particle group in the first image, and the velocities of all particles in the same window are the same, and then the local displacement vector of the particle can be obtained, and the displacement is the motion direction of the particle, and the velocity vector result of each query window is obtained; The invalid, error velocity vector identification and correction are carried out on the velocity field result at the edge of the flow field, including but not limited to using a global threshold, median filtering, average filtering to detect error vectors in the velocity field vector, and using linear interpolation or cubic spline interpolation to correct the error vectors; and finally obtaining a three-dimensional velocity vector diagram of the flow field to be measured.
[0014] The beneficial effects of the present application are: the present application provides a three-dimensional flow field optical measurement system and method using flexible multi-probe, which reduces the number of cameras through multiple fiber bundle coupling, effectively partitions the image sensor and simultaneously observes multiple angles from one image sensor, thereby reducing the cost, spatial complexity and overall size of the tomographic imaging system, simplifying the synchronous control mode, and using the equipment which is more simple and convenient, has lower maintenance cost and is more simple and convenient. In a narrow space, strong vibration, strong reflection, and large background noise environment, high-resolution, limited space internal flow field measurement eliminating lens distortion and stray light are realized, and a new technical means is provided for the study of flow characteristics in a limited space. BRIEF DESCRIPTION OF DRAWINGS
[0015] Figure 1 is a schematic diagram of the principle of the present application; Figure 2 is a schematic diagram of the camera position layout main view structure in the present application; Figure 1 Figure 3 is a schematic diagram of the left view structure of the present application; Figure 2
[0016] In the figure, 1, CCD camera, 2, flexible fiber bundle, 3, endoscopic imaging lens, 3-1, first endoscopic imaging lens, 3-2, second endoscopic imaging lens, 3-3, third endoscopic imaging lens, 3-4, fourth endoscopic imaging lens, 4, three-dimensional gimbal, 5, laser, 6, particle generator, 7-1, first lifting platform, 7-2, second lifting platform, 8, flow field area to be measured, 9, engine exhaust nozzle. DETAILED DESCRIPTION
[0017] The principles and characteristics of the present application are described below in conjunction with the drawings, and the examples are only used to explain the present application and are not used to limit the scope of the present application.
[0018] In order to achieve the above-mentioned purpose, the present application provides the following specific embodiments: Figure 1 , Figure 2 , Figure 3 As shown, the three-dimensional flow field optical measurement system with flexible multi-probe is characterized in that a three-dimensional holder 4 and a laser 5 are arranged corresponding to a flow field area 8 to be measured, the three-dimensional holder 4 is provided with endoscopic imaging lenses 3 and a particle generator 6, a CCD camera 1 is arranged on one side of the three-dimensional holder 4, the CCD camera 1 is connected with the endoscopic imaging lenses 3 through a flexible optical fiber bundle 2, the laser 5 and the CCD camera 1 are respectively installed on a first lifting platform 7-1 and a second lifting platform 7-2, the particle generator 6 scatters tracer particles to the flow field area 8 to be measured, and the laser 5 generates bulk laser to irradiate the tracer particles in the flow field area 8 to be measured.
[0019] The three-dimensional holder 4 is in a square structure, the endoscopic imaging lenses 3 are arranged as four, including a first endoscopic imaging lens 3-1, a second endoscopic imaging lens 3-2, a third endoscopic imaging lens 3-3 and a fourth endoscopic imaging lens 3-4, a coordinate system is established with the geometric center of the square structure three-dimensional holder as the origin, the four endoscopic imaging lenses are arranged at the four corners of the square structure three-dimensional holder respectively, the side length of the square structure three-dimensional holder is a, the position of the first endoscopic imaging lens 3-1 in the coordinate system is (0, -a, a), the position of the second endoscopic imaging lens 3-2 in the coordinate system is (0, a, a), the position of the third endoscopic imaging lens 3-3 in the coordinate system is (0, a, -a), and the position of the fourth endoscopic imaging lens 3-4 in the coordinate system is (0, -a, -a), the geometric center of the flow field area 8 to be measured is located at a position with a distance of b from the geometric center of the square structure three-dimensional holder in the x-axis direction, and the geometric center of the flow field area 8 to be measured is located at (b, 0, 0), the laser 5 is arranged on one side of the flow field area 8 to be measured, the position of the laser is (b, d, 0), and the particle generator 6 is located below the flow field area 8 to be measured, and the position of the particle generator 6 is (b, 0, e).
[0020] The flexible optical fiber bundle 2 is a 1 / 4 structure optical fiber bundle, the bundle end of the flexible optical fiber bundle 2 is connected with the CCD camera through a fixing device, the CCD camera is fixedly installed on the second lifting platform, according to the length of the flexible optical fiber bundle used, the CCD camera can be placed at any position on one side of the holder, and the placement position is (0, c, 0) in the system, the fixing device is a fixing sleeve with the same diameter as the armored shell of the flexible optical fiber bundle 2, and the four receiving ends of the flexible optical fiber bundle 2 are connected with the first endoscopic imaging lens 3-1, the second endoscopic imaging lens 3-2, the third endoscopic imaging lens 3-3 and the fourth endoscopic imaging lens 3-4 respectively.
[0021] The three-dimensional gimbal geometric center in a square structure is taken as the origin of the coordinate system, which means that the positive direction of the X axis is along the outlet direction of the engine nozzle 9, the positive direction of the Y axis is perpendicular to the X axis and horizontally to the right, and the positive direction of the Z axis is vertically upward. In the coordinate system of the present system, the initial attitude of the endoscopic imaging lens 3 is defined as follows: when the main shaft of the endoscopic imaging lens 3 is aligned with the positive direction of the X axis and there is no deflection of the Y / Z axis, it is the reference state (0°, 0°, 0°); the endoscopic imaging lens 3 is rotated around the Z axis by an angle of roll angle α, which ranges from -90° to 90°; the endoscopic imaging lens 3 is rotated around the Y axis by an angle of yaw angle β, which ranges from -90° to 90°; and the endoscopic imaging lens 3 is rotated around the X axis by an angle of pitch angle γ, which ranges from -90° to 90°.
[0022] The position b of the to-be-measured flow field region 8 needs to satisfy the constraints of the depth of field range and the working distance of the endoscope imaging lens 3. The working distance d of the laser 5 needs to satisfy the requirement that the laser energy is the strongest under the premise that the laser thickness is consistent with the width of the to-be-measured flow field region. In order to ensure that the concentration of the scattered tracer particles is within the measurement requirement of 0.05 ppp ~ 0.1 ppp, the particle generator needs to be located at a position with a distance e below the to-be-measured flow field region.
[0023] The tracer particles scattered by the particle generator 6 are diisooctyl sebacate (DEHS) or titanium dioxide particles, and the particle concentration of the tracer particles is 0.05 ppp ~ 0.1 ppp.
[0024] All components are assembled and placed according to the structure shown in the accompanying drawings. Figure 1 The CCD camera 1 is a pco.pixelfly usb type CCD (Charge Coupled Device, CCD) camera with a double-frame mode from the German PCO company, which has a cross-frame function. The optical axis of the combined beam of the CCD camera 1 and the flexible optical fiber bundle 2 is adjusted to ensure clear imaging in the camera. The four endoscopic imaging lenses connected to the input end of the flexible multi-probe optical fiber bundle are arranged in a matrix with a spacing of 1 m at the four corners of the square gimbal. The first endoscopic imaging lens 3-1 has an angle of (45°, 60°, 0°) with the to-be-measured flow field, the second endoscopic imaging lens 3-2 has an angle of (45°, -60°, 0°) with the to-be-measured flow field, the third endoscopic imaging lens 3-3 has an angle of (-45°, -60°, 0°) with the to-be-measured flow field, and the fourth endoscopic imaging lens 3-4 has an angle of (-45°, 60°, 0°) with the to-be-measured flow field. Diisooctyl sebacate (DEHS) is selected as the tracer particle during testing. In order to control the particle concentration, the particle generator is placed at a position with a distance of 0.5 mm from the flow field, and the particle concentration is between 0.05 ppp and 0.1 ppp.
[0025] The interval of the double pulse laser signals of the laser is adjusted to 50 μs, i.e. the interval of two frames of images is 50 μs, the laser intensity is adjusted to the maximum power, the aperture of the CCD camera is adjusted to the minimum, the exposure time of the CCD camera is set to 20 μs, the CCD camera is triggered externally to work, and four angles of two frames of images of the tracer particles are captured in an instant to process the velocity. A bulk laser with a width of 30 mm is incident to the flow field, and a Beamtech Vlite-200 series Nd:YAG low-frequency double pulse laser of Beijing Laibao Company is used as a light source system. The laser has an output wavelength of 532 nm and a single pulse energy of 200 mJ, and the light beam position and direction are flexibly adjusted through a light guide arm. A lens group is used to convert the point laser into a bulk laser with a thickness of about 30 mm to ensure that the measured flow field area is uniformly illuminated. The tracer particles with good flow following and optical visibility are scattered in the measured flow field, so that the tracer particles generate scattered light, and two frames of images at four angles set by the flexible optical fiber bundle can be captured by the camera at one time; The three-dimensional flow field optical measurement method with a flexible multi-probe has the following steps. Step one, the three-dimensional flow field optical measurement system with a flexible multi-probe, the aperture of the endoscopic imaging lens is adjusted to the minimum, the CCD camera is set to a double frame mode and a first frame exposure time t 0 μs, the time interval of the double pulse signals of the laser is adjusted by using a time sequence synchronization controller t 1 μs, so that the two laser pulses fall on the double exposure time of the camera, so that the camera captures two consecutive frames of flow field images; the first frame exposure time t 0 μs is set in the range of 20-50 μs, and the time interval of the double pulse signals t 1 μs is in the range of 50-100 μs, which ensures that the laser energy is sufficient to illuminate the tracer particles in the measured area and triggers the CCD camera to collect the particle images at the moment of laser illumination; Step two, according to the width of the measured flow field, a bulk laser with the same width as the measured flow field in the measured flow field region is incident to the flow field, and the tracer particles scattered in the measured flow field make the tracer particles generate scattered light, and two frames of images at four angles set by the endoscopic imaging lens set by the flexible optical fiber bundle are captured by the CCD camera at one time. The angles are (α, β, 0), (α, -β, 0), (-α, -β, 0), and (-α, β, 0). Step three, the computer is used to process the captured images, tomographic reconstruction, and three-dimensional cross-correlation calculation to obtain a 3D-3C velocity field. The image processing process comprises: firstly, performing brightness homogenization processing on the collected images, so that the brightness of images taken at different angles is the same; secondly, performing image enhancement processing, including adjusting a gamma value curve of the images, using histogram equalization and CLAHE to enhance contrast, and using Gaussian filtering and median filtering to remove noise; then, performing cutting processing on the images, selecting a geometric center position of the flow field to be measured as a center position of each picture, and cutting a picture with a size of 150*150n pixels; finally, inputting the cut images into a tomographic reconstruction program to obtain a three-dimensional spatial distribution of the flow field to be measured. The tomographic reconstruction process comprises: using an algebraic reconstruction technique (ART) to convert flow field pictures at different angles, i.e., flow field data, into three-dimensional body data; the ART algorithm converts the particle distribution reconstruction of the flow field to be measured into a solving process of a linear equation group, and the obtained three-dimensional spatial distribution position relationship of the flow field to be measured is substituted into a three-dimensional cross-correlation calculation program to solve a velocity field. The three-dimensional cross-correlation calculation process comprises: using a multi-grid iterative adaptive query window algorithm to set three-dimensional query windows of different sizes for the reconstructed three-dimensional spatial distribution image of the flow field to be measured, perform three-dimensional cross-correlation calculation on each three-dimensional query window, and obtain a corresponding cross-correlation peak value through the calculation of the query window; the window corresponding to the position of the cross-correlation peak value is the corresponding position of the particle group in the first image, and all particles in the same window have the same velocity, so that a local displacement vector of the particle can be obtained, which is the motion direction of the particle, and a velocity vector result of each query window is obtained; the velocity field result at the edge of the flow field is identified and corrected for invalid and error velocity vectors, including but not limited to using a global threshold, median filtering, and average filtering to detect error vectors in the velocity field vector, and using linear interpolation or cubic spline interpolation to correct the error vectors; finally, a three-dimensional velocity vector diagram of the flow field to be measured is obtained.
[0026] The above only describes preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims
1. A three-dimensional flow field optical measurement system employing a flexible multi-probe, characterized by, The system comprises a three-dimensional holder corresponding to the flow field region to be measured, an endoscopic imaging lens and a particle generator arranged on the three-dimensional holder, a CCD camera arranged on one side of the three-dimensional holder, the CCD camera being connected to the endoscopic imaging lens through a flexible optical fiber bundle, and a laser and the CCD camera being respectively installed on a first lifting platform and a second lifting platform.
2. A three-dimensional flow field optical measurement system employing flexible multi-probes as claimed in claim 1, wherein: The three-dimensional holder is in a square structure, the endoscopic imaging lens is arranged in four, including a first endoscopic imaging lens, a second endoscopic imaging lens, a third endoscopic imaging lens and a fourth endoscopic imaging lens, a coordinate system is established with the geometric center of the three-dimensional holder in the square structure as the origin, the four endoscopic imaging lenses are arranged at the four corners of the three-dimensional holder in the square structure, the side length of the three-dimensional holder in the square structure is a, the position of the first endoscopic imaging lens in the coordinate system is (0, -a, a), the position of the second endoscopic imaging lens in the coordinate system is (0, a, a), the position of the third endoscopic imaging lens in the coordinate system is (0, a, -a), and the position of the fourth endoscopic imaging lens in the coordinate system is (0, -a, -a), the geometric center of the flow field region to be measured is located at a position with a distance of b from the geometric center of the three-dimensional holder in the square structure in the x-axis direction, and the position of the geometric center of the flow field region to be measured is (b, 0, 0); the laser is arranged on one side of the flow field region to be measured, the position of the laser is (b, d, 0), and the particle generator is located below the flow field region to be measured, the position of the particle generator is (b, 0, e).
3. A three-dimensional flow field optical measurement system using flexible multi-probes according to claim 1, wherein: The flexible optical fiber bundle is a 1 / 4 structure optical fiber bundle, the bundle end of the flexible optical fiber bundle is connected to the CCD camera through a fixing device, the CCD camera is fixedly installed on the second lifting platform, the fixing device is a fixing sleeve with the same diameter as the armored shell of the flexible optical fiber bundle, and the four receiving ends of the flexible optical fiber bundle are connected to the first endoscopic imaging lens, the second endoscopic imaging lens, the third endoscopic imaging lens and the fourth endoscopic imaging lens respectively.
4. A three-dimensional flow field optical measurement system using flexible multi-probes according to claim 2, wherein: The coordinate system is established with the geometric center of the three-dimensional holder in the square structure as the origin, the positive direction of the X-axis is along the direction of the engine nozzle outlet, the positive direction of the Y-axis is perpendicular to the X-axis and horizontally to the right, and the positive direction of the Z-axis is vertically upward; in the coordinate system of the system, the initial attitude of the endoscopic imaging lens is defined as: when the main shaft of the endoscopic imaging lens is aligned with the positive direction of the X-axis and the Y / Z-axis is not deflected, it is the reference state (0°, 0°, 0°), the endoscopic imaging lens is rotated around the Z-axis by an angle of roll angle α, the range is ±90°, the endoscopic imaging lens is rotated around the Y-axis by an angle of yaw angle β, the range is ±90°, and the endoscopic imaging lens is rotated around the X-axis by an angle of pitch angle γ, the range is ±90°. The position b of the to-be-measured flow field region needs to satisfy the constraints of the depth of field range and the working distance of the endoscope imaging lens, and the working distance d of the laser needs to satisfy the requirements of the strongest laser energy under the premise that the laser thickness is consistent with the width of the to-be-measured flow field region, so as to ensure that the concentration of the scattered tracer particles is within the measurement requirement of 0.05 ppp to 0.1 ppp, and the particle generator is required to be located at a position below the to-be-measured flow field region with a distance of e.
5. A three-dimensional flow field optical measurement system using flexible multi-probe according to any one of claims 1-4, characterized in that: The tracer particles scattered by the particle generator are diisooctyl sebacate (DEHS) or titanium dioxide particles, and the particle concentration of the tracer particles is 0.05 ppp to 0.1 ppp.
6. A measurement method of measuring by a three-dimensional flow field optical measurement apparatus using a flexible multi-probe, characterized by, The method comprises the following steps: Step one, using flexible multi-probe three-dimensional flow field optical measurement system, the diaphragm of endoscopic imaging lens is adjusted to the minimum, the CCD camera is set to double frame mode and the first frame exposure time t 0 μs, the time interval of the double pulse signal of the laser is adjusted by the timing synchronization controller t 1 μs, the two laser pulses are respectively on the double exposure time of the camera, so that the camera shoots two consecutive frames of flow field images; the first frame exposure time t 0 μs is set in the range of 20~50μs, the time interval of the double pulse signal t 1 μs is used in the range of 50~100μs, which ensures that the laser energy is sufficient to illuminate the tracer particles in the measured area while triggering the CCD camera to collect the particle image at the moment of laser illumination; Step 2: According to the width of the to-be-measured flow field, a bulk laser with the same width as the to-be-measured flow field in the to-be-measured flow field region is incident into the flow field, the tracer particles scattered in the to-be-measured flow field make the tracer particles generate scattered light, and two frames of images with angles (α, β, 0), (α, -β, 0), (-α, -β, 0) and (-α, β, 0) between the to-be-measured flow field are set by the endoscope imaging lens provided by the flexible optical fiber bundle are shot at one time by a CCD camera; Step 3: The computer is used to process the shot images in sequence, so as to obtain the 3D-3C velocity field through tomographic reconstruction and three-dimensional cross-correlation calculation in sequence.
7. The measurement method of the three-dimensional flow field optical measurement device with a flexible multi-probe according to claim 6, wherein The image processing process is specifically as follows: first, the collected images are subjected to brightness homogenization processing, so that the brightness of the images shot at different angles is the same; secondly, the images are subjected to phase enhancement processing, including adjusting the gamma value curve of the images, enhancing the contrast by histogram equalization and CLAHE, and denoising by Gaussian filtering and median filtering; then, the images are subjected to cutting processing, the geometric center position of the to-be-measured flow field is selected as the center position of each picture, and the m×n pixel size picture is cut; finally, the cut processed images are input into the tomographic reconstruction program to obtain the three-dimensional spatial distribution of the to-be-measured flow field.
8. The measurement method of the three-dimensional flow field optical measurement device with a flexible multi-probe according to claim 6, wherein The tomographic reconstruction process is specifically as follows: the algebraic reconstruction algorithm is used to convert the to-be-measured flow field pictures at different angles, i.e. the flow field data, into three-dimensional volume data; the algebraic reconstruction algorithm converts the particle distribution reconstruction of the to-be-measured flow field into a solving process of a linear equation group, and the obtained three-dimensional spatial distribution position relationship of the to-be-measured flow field particles is substituted into the three-dimensional cross-correlation calculation program for velocity field solving.
9. The measurement method of the three-dimensional flow field optical measurement device with a flexible multi-probe according to claim 6, wherein The three-dimensional cross-correlation calculation process is specifically as follows: the multi-grid iteration adaptive query window algorithm is used to set different sizes of three-dimensional query windows for the reconstructed three-dimensional spatial distribution image of the to-be-measured flow field particles, the three-dimensional cross-correlation calculation is performed on each three-dimensional query window, and the corresponding cross-correlation peak value is obtained through the calculation of the query window. The window corresponding to the position of the cross-correlation peak is the corresponding position of the particle group in the first image, and all particles in the same window have the same velocity, and then the local displacement vector of the particle can be obtained, the displacement is the motion direction of the particle, and the velocity vector result of each query window is obtained; The velocity field result at the edge of the flow field is invalid, and the error velocity vector is identified and corrected, including but not limited to using a global threshold, a median filter, an average filter to detect error vectors in the velocity field vector, and using linear interpolation or cubic spline interpolation to correct the error vector; finally, a three-dimensional velocity vector diagram of the flow field to be measured is obtained.