Three-dimensional temperature field measurement system and method based on Scanning LIF technology

Abstract

The invention belongs to the related technical field of fluid temperature field measurement, and discloses a Scanning LIF technology-based three-dimensional temperature field measurement system and method, which comprises a sheet light scanning module and a double-color image synchronous acquisition module, and is characterized in that a parallel sheet light source is generated through double-camera double-color synchronous imaging and galvanometer scanning; according to the system, space calibration images, temperature calibration images and experiment images at different positions can be obtained through testing, the experiment images collected by the two cameras are subjected to ratio processing after space calibration, and a fluorescence intensity ratio-temperature relation curve is generated through temperature calibration at different positions. And a temperature field image corresponding to each position can be calculated. The system can generate parallel sheet light sources, and can change the number of scanning sheet light, the deflection angle of the galvanometer, the motion mode of the galvanometer, the residence time and the moving time of the galvanometer in a period, the exposure time of a camera and the like according to measurement requirements so as to meet actual use requirements.

Description

Technical Field

[0001] This invention belongs to the technical field of fluid temperature field measurement, and more specifically, relates to a three-dimensional temperature field measurement system and method based on ScanningLIF technology. Background Technology

[0002] Laser-induced fluorescence (LIF) is an optical flow field observation method widely used in fluid mechanics for flow field visualization, concentration field, and temperature field measurement. Its core principle involves illuminating the flow field with a sheet laser to excite a fluorescent tracer to generate characteristic fluorescence signals. A high-speed camera then captures the temporal and spatial evolution of the fluorescence intensity, enabling non-invasive dynamic observation of fluid motion characteristics. Thanks to its high sensitivity and high spatiotemporal resolution, LIF technology has become an important tool for two-dimensional flow field measurement.

[0003] However, turbulent flows possess complex three-dimensional flow field structures, and traditional LIF technology, limited by a single-plane detection mode, can only acquire two-dimensional cross-sectional information. To overcome this limitation, some scholars have proposed ScanningLIF (Scanning Three-Dimensional Laser-Induced Fluorescence). This technology, similar in principle to a CT scanner, rapidly scans the laser plane, simultaneously acquiring fluorescence data from multiple cross-sections, and then uses algorithms to perform three-dimensional reconstruction, ultimately obtaining the three-dimensional transient distribution of the flow field. Currently, the internationally used Scanning LIF sheet light scanning light source systems mainly employ three schemes: rotating scanners, rotating drums, and galvanometers, but all have certain problems and shortcomings. The rotating drum and rotating scanner schemes have relatively complex structures and stringent requirements for the concentricity, installation angle, and position calibration of the device. The galvanometer is the most commonly used scheme, with a simple overall structure, but the fan-shaped sheet light source generated by the laser through the Powell prism often exhibits a fan-shaped Gaussian distribution. Furthermore, the non-parallel sheet light sources generated during scanning have a certain impact on measurement accuracy and calibration. The practical application of ScanningLIF technology still requires solving problems such as sheet light shaping, laser collimation, and image calibration.

[0004] Meanwhile, temperature field measurements often employ Two-Color Laser Induced Fluorescence (2CLIF) technology. This involves using two different fluorescent dyes, excited by an incident laser of a specific wavelength, to obtain fluorescence intensity images of different fluorescent dyes at different wavelengths in the same spatial region at the same time. The two fluorescence intensity images are then compared to eliminate the influence of laser intensity and dye concentration on the accuracy of subsequent temperature field fitting calculations. Therefore, a special image acquisition system needs to be designed to ensure that the fluorescence images of the two fluorescent dyes at different wavelengths, captured simultaneously, are as spatially consistent as possible. Two mature methods on the market are single-camera imaging with dual-imagers and dual-camera imaging. However, single-camera imaging with dual-imagers has lower spatial resolution and requires solving optical problems such as aberrations, making it technically challenging. The dual-camera, two-color synchronous imaging acquisition scheme is the key to 2CLIF temperature field measurement.

[0005] Therefore, it is necessary to design a three-dimensional temperature field measurement system and method based on Scanning LIF technology, which includes a galvanometer scanning system that can generate parallel sheet light sources and a dual-color image synchronous acquisition system to realize the three-dimensional measurement of transient temperature fields. Summary of the Invention

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a three-dimensional temperature field measurement system and method using Scanning LIF technology. Its purpose is to achieve non-invasive dynamic observation of the three-dimensional temperature field of fluids, thereby solving the technical problems of dual-camera dual-color synchronous imaging and generating parallel plate light sources through galvanometer scanning.

[0007] To achieve the above objectives, according to one aspect of the present invention, a three-dimensional temperature field measurement system based on Scanning LIF technology is first provided. The system includes a sheet light scanning module and a dual-color image synchronous acquisition module. The sheet light scanning module is used to excite a fluorescent dye in the test container 700 from below the test container 700. The dual-color image synchronous acquisition module is used to acquire fluorescence images inside the test container 700. The sheet light scanning module includes a laser 100, a scanning galvanometer 200, a biconvex lens 300, an aperture 400, and a reflector 500 arranged in sequence at intervals. The end of the scanning galvanometer 200 away from the laser 100 and the scanning galvanometer 200 is connected to a galvanometer control box 600. The dual-color image synchronous acquisition module includes a dual imager 800, a short-pass filter 900, a band-stop filter 1000, a long-pass filter 1100, a first camera 1200, a second camera 1300, a camera synchronizer 1400, and a computer 1500. The first camera 1200 and the second camera 1300 are distributed symmetrically in parallel with the axis of the dual imager 800. The short-pass filter 900 and the band-stop filter 1000 are connected sequentially between the dual imager 800 and the first camera 1200. The long-pass filter 1100 is connected between the dual imager 800 and the second camera 1300. The other end of the first camera 1200 and the second camera 1300 is connected in parallel with the computer 1500 through the camera synchronizer 1400. The other end of the galvanometer control box 600 is connected in parallel with the camera synchronizer 1400 through the computer 1500. The galvanometer control box 600 is used to control the deflection angle and motion mode of the scanning galvanometer 200.

[0008] Preferably, the biconvex lens 300 is fixed inside the frame 310, and the optical axes of the reflector 500, aperture 400, biconvex lens 300 and scanning galvanometer 200 coincide with the central axis, and the laser 100 is positioned perpendicular to the central axis.

[0009] Preferably, the dual-imager 800 includes a black cavity cover plate 810, The structure includes a through hole 811, a black cavity body 820, an open viewing window 821, a beam splitter slot 822, a fixing through hole 823, a second reflector slot 824, a third reflector slot 825, a fourth reflector slot 826, an observation window 1 827, an observation window 2 828, a connecting threaded hole 829, a beam splitter 1600, a second reflector 1700, a third reflector 1800, and a fourth reflector 1900. The open viewing window 821 is located on the front side of the black cavity body 820. The first and second observation windows 827 and 828 are located on the rear side of the black cavity body 820 and are symmetrically distributed. The beam splitter slot 822, the second reflector slot 824, the third reflector slot 825, the fourth reflector slot 826, the first observation window 827, the second observation window 828, and the connecting threaded hole 829 are located at... Located inside the black cavity body 820, the fixing through hole 823 is located outside the black cavity body 820 to facilitate the fixation of the dual imager; the black cavity cover plate 810 is connected and fixed to the black cavity body 820; the position of the opening window 821 is consistent with the height of the area to be measured; the beam splitter 1600 is fixed inside the beam splitter slot 822; the second reflector 1700 is fixed inside the second reflector slot 824; the third reflector 1800 is fixed inside the third reflector slot 825; and the fourth reflector 1900 is fixed inside the fourth reflector slot 826. The beam splitter 1600, the second reflector 1700, the third reflector 1800, and the fourth reflector 1900 are all arranged at 45° with the horizontal axis, and their central axes coincide with the observation window 1 827 and the observation window 2 828.

[0010] Preferably, the system further includes a tilting stage, multiple rotary stages, multiple displacement stages, and an optical platform. A portion of the multiple rotary stages is used to support the dual-color image synchronous acquisition module, while another portion, along with the tilting stage 3300, is used to support the sheet light scanning module. The multiple displacement stages are used to connect the multiple rotary stages and the optical platform and drive the multiple rotary stages to move. The tilting stage 3300 is used to tilt and adjust the laser direction provided by the sheet light scanning module.

[0011] Preferably, the plurality of rotary stages include rotary stage one 2500, rotary stage two 2600, and rotary stage three 2700; the plurality of displacement stages include Z-axis displacement stage one 2100, Z-axis displacement stage two 2200, XY dual-axis displacement stage one 2300, XY dual-axis displacement stage two 2400, XYZ three-axis displacement stage one 2800, XYZ three-axis displacement stage two 2900, XYZ three-axis displacement stage three 3000, XYZ three-axis displacement stage four 3100, XYZ three-axis displacement stage five 3200, and XYZ three-axis displacement stage six 3400.

[0012] Preferably, the laser 100 is fixed at the center of the rotating stage 2500, which is fixed on the surface of the XYZ three-axis displacement stage 2800. The scanning galvanometer 200 is fixed at the center of the rotating stage 2600, which is fixed on the surface of the XYZ three-axis displacement stage 2900, ensuring that the laser 100 and the scanning galvanometer 200 are at the same height, guaranteeing that the laser beam passes through the center of the galvanometer window. The mirror holder 310 is fixed at the center of the rotating stage 2700, which is fixed on the surface of the XYZ three-axis displacement stage 2900. The XYZ three-axis displacement stage 3000 is mounted on the platform; the aperture 400 is fixed on the aperture adapter plate 410, which is fixed on the XYZ three-axis displacement stage 4100; the reflector 500 is fixed inside the reflector adapter plate 510, which is fixed at the center of the inclined worktable 3300, which is fixed on the XYZ three-axis displacement stage 5200, maintaining the same vertical position as the area to be measured in the container 700; the dual imager 800 is fixed at the center of the XYZ three-axis displacement stage 6400.

[0013] Preferably, camera 1200 is fixed at the center of the Z-axis displacement stage 2100, the Z-axis displacement stage 2100 is fixed on the XY dual-axis displacement stage 2300, the XY dual-axis displacement stage 2300 is fixed on the optical platform 2000, the lens height of camera 1200 is the same as the height of observation window 827, the lens height of camera 1300 is the same as the height of observation window 828, camera 1300 is fixed at the center of the Z-axis displacement stage 2200, the Z-axis displacement stage 2200 is fixed on the XY dual-axis displacement stage 2400, and the XY dual-axis displacement stage 2400 is fixed on the optical platform 2000.

[0014] Preferably, the camera synchronizer 1400 is connected to camera 1200, camera 2 1300, galvanometer control box 600 and computer 1500 via cables, and is used to receive synchronization signals output by the galvanometer to control the synchronous shooting of camera 1200 and camera 2 1300; the computer 1500 is connected to camera 1200, camera 2 1300, camera synchronizer 1400 and galvanometer control box 600 via cables, and is used to control the galvanometer deflection and the shooting of camera 1200 and camera 2 1300, and to display fluorescence images for storing and processing experimental data.

[0015] According to another aspect of the present invention, a method for measuring a three-dimensional temperature field using the above-described measuring device is also provided, the method comprising: (1) Determine the power and wavelength of the laser, the types and concentrations of the two fluorescent dyes in the container to be tested, the size of the three-dimensional measurement area, the frame rate of the camera, the number of temperature field images captured by the camera in one cycle, and the motion mode and deflection angle of the scanning galvanometer. (2) Start the laser and adjust the spatial position of the laser, scanning galvanometer, biconvex lens, aperture and reflector in the sheet light scanning module to ensure that the laser passes through the center position of the scanning galvanometer, biconvex lens and reflector, and ensure that the laser area scanned by the laser under the deflection of the scanning galvanometer meets the size of the area to be measured, while the scanning sheet light remains parallel. (3) Adjust the spatial position of the camera and dual imager in the dual-color image synchronous acquisition module to ensure that the area captured by the two cameras includes the area to be measured, and that the spatial position of the two cameras is the same. (4) Perform spatial calibration by placing the calibration plate at different positions in the area to be tested and taking images of the calibration plate at different positions using two cameras. Perform spatial calibration based on the shooting results. (5) Adjust the laser to the maximum power, wait for the light source to stabilize, and then excite the two fluorescent dyes in the container to be tested; (6) Perform temperature calibration, change the temperature of the fluorescent dye in the container to be tested, and take pictures of the fluorescence intensity at different temperatures and spatial positions. By the ratio of the fluorescence intensity of the two dyes, obtain the fluorescence intensity ratio-temperature relationship curve at different positions. (7) Take experimental images, change the experimental conditions inside the container to be tested, input the required frame rate of the experimental images into the computer to control the deflection of the scanning galvanometer, and the camera one and camera two record the fluorescence intensity at different positions within one cycle according to the deflection position of the galvanometer. (8) Turn off all light sources and take a picture of the light intensity of the experimental background without changing the camera shooting frequency; (9) Calculation of temperature field experimental results at different locations: After subtracting the light intensity of the experimental background image from the light intensity of the experimental image, spatial calibration is performed using the spatial calibration image, and the temperature field images at different spatial locations are calculated using the fluorescence intensity ratio-temperature relationship curve. (10) Three-dimensional temperature field interpolation reconstruction: interpolate and reconstruct the temperature field images at different locations within a period to form a three-dimensional temperature field.

[0016] Preferably, in the test container, the fluorescence intensity of one of the two fluorescent dyes is positively correlated with temperature, while the fluorescence intensity of the other fluorescent dye is negatively correlated with temperature; or the fluorescence intensity of the two fluorescent dyes is not simultaneously correlated with temperature.

[0017] In summary, compared with the prior art, the three-dimensional temperature field measurement system based on Scanning LIF technology provided by this invention has the following advantages: This invention can generate parallel sheet light sources and can adjust the number of scanning sheet lights, galvanometer deflection angle, galvanometer motion mode, galvanometer dwell time and movement time within one cycle, and camera exposure time according to measurement requirements to meet practical application requirements. 2. The preferred dual-imager structure of this invention avoids in-depth research on optical imaging and does not need to consider difficulties such as aberration elimination. The designed dual-imager black cavity avoids the influence of stray light to a certain extent, which can improve the measurement accuracy of the temperature field.

[0018] 3. In this invention, the spatial positions of each component in the sheet light scanning module and the dual-color image synchronous acquisition module are flexibly adjustable through the cooperation of multiple rotational displacement platforms. The rotational position and tilt angle of some components are also adjustable, which facilitates the adjustment of the optical path and the camera, ensuring that the two cameras capture the same spatial position.

[0019] 4. The size of the three-dimensional temperature field region that can be measured by this invention is adjustable to adapt to different scales of application, and it has advantages in large-scale measurement. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a three-dimensional temperature field measurement system based on Scanning LIF technology according to this application; Figure 2 This is a top view of a dual-imager; Figure 3 This is a schematic diagram of the black cavity structure of a dual-imager; Figure 4 This is a front view of the camera position deviation in the dual-color image synchronous acquisition module; Figure 5 This is a schematic diagram of the layout of the dual-color image synchronous acquisition module; Figure 6 These are images of the calibration board captured by the dual-color image synchronous acquisition module; Figure 7 This is a schematic diagram of the layout of the optical scanning module; Figure 8 These are schematic diagrams and three-view drawings of the aperture diaphragm. Figure 9 This is a schematic diagram showing the movement sequence of the scanning galvanometer at five set deflection positions; Figure 10 This is a schematic diagram of the spatial and temporal sequences of a three-dimensional temperature field; In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 100-Laser, 200-Scanning Galvanometer, 300-Biconvex Lens, 310-Lens Mount, 400-Aperture, 410-Aperture Adapter Plate, 500-Reflector 1, 510-Reflector 1 Adapter Plate, 600-Galvanometer Control Box, 700-Container Under Test, 800-Dual Imager, 810-Black Cavity Cover Plate, 811-Through Hole, 820-Black Cavity Body, 821-Open Viewing Window, 822-Beam Splitter Slot, 823-Fixing Through Hole, 824-Reflector 2 Slot, 825-Reflector 3 Slot, 826-Reflector 4 Slot, 827-Observation Window 1, 828-Observation Window 2, 829-Cover Plate Connecting Threaded Hole, 900-Short Pass Filter, 1000-Band Stop Filter, 1100-Long Pass Filter, 1200-Camera 1, 1300-Camera 2, 1400-Camera Synchronizer, 1500-Computer, 1600-Beam Splitter, 1700-Reflector 2, 1800-Reflector 3, 1900-Reflector 4, 2000-Optical Platform, 2100- Z-axis displacement stage 1, 2200- Z-axis displacement stage 2, 2300- XY dual-axis displacement stage 1, 2400- XY dual-axis displacement stage 2, 2500- Rotary stage 1, 2600- Rotary stage 2, 2700- Rotary stage 3, 2800- XYZ three-axis displacement stage 1, 2900- XYZ three-axis displacement stage 2, 3000- XYZ three-axis displacement stage 3, 3100- XYZ three-axis displacement stage 4, 3200- XYZ three-axis displacement stage 5, 3300- Tilting stage, 3400- XYZ three-axis displacement stage 6. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0022] In one aspect of the invention, a three-dimensional temperature field measurement system based on Scanning LIF technology is proposed. The main components of the system are shown in the attached figure. Figure 1 The system consists of a container under test 700, a sheet light scanning module, and a dual-color image synchronous acquisition module.

[0023] The test container 700 is made of a custom-made acrylic sheet with a thickness of 10mm to facilitate laser transmission, and its dimensions are 1100×220×300mm (length×width×height). The fluorescent dyes added to the test container 700 are FL27 and KR, both at a concentration of 300μg / L.

[0024] The laser 100, scanning galvanometer 200, biconvex lens 300, aperture 400, reflector 500, and galvanometer control box 600 are the main components of the sheet light scanning module. The laser 100 excites the fluorescent dye inside the test container 700 to produce fluorescence intensities in two wavelengths. The scanning galvanometer 200 deflects the sheet laser to a designated position. The biconvex lens 300 corrects the fan-shaped laser surface into a rectangular laser surface, ensuring that the laser surfaces at different positions remain parallel. The aperture 400 ensures that the laser deflection position is at the designated location. The reflector 500 reflects the scanning sheet light into the test container 700.

[0025] The main components of the dual-color image synchronous acquisition module are: dual imager 800, short-pass filter 900, band-stop filter 1000, long-pass filter 1100, camera one 1200, camera two 1300, camera synchronizer 1400, and computer 1500. The dual imager 800 ensures that the two cameras capture the same area. The short-pass filter 900, band-stop filter 1000, and long-pass filter 1100 ensure that the cameras collect fluorescence intensity at a fixed wavelength. Camera one 1200 and camera two 1300 capture fluorescence intensity images. The camera synchronizer 1400 synchronizes the two cameras' images. The computer 1500 controls the experimental equipment and displays, stores, and processes the captured images.

[0026] The galvanometer control box 600 is connected to the scanning galvanometer 200, camera synchronizer 1400, and computer 1500 via cables. The camera synchronizer 1400 is also connected to camera one 1200, camera two 1300, and computer 1500 via cables, as shown in the attached diagram. Figure 1 As shown, the computer 1500 sends a program to the galvanometer control box 600 to control the galvanometer deflection angle and the dwell and movement time at different angles. At the same time, the galvanometer control box 600 outputs a synchronization signal to the camera synchronizer 1400 when the galvanometer moves to the designated position, controlling the camera to capture images synchronously, and the captured images are displayed on the computer.

[0027] Laser 100 emits laser light, which is deflected by scanning galvanometer 200 and then sequentially passes through biconvex lens 300, aperture 400, and reflector 500. A schematic diagram of the resulting scanning beam is shown in the attached figure. Figure 1 As shown.

[0028] Appendix Figure 2 This is a top view of the dual imager. The dual imager 800 consists of a black cavity cover plate 810 and a black cavity body 820. The black cavity body 820 contains a 3:7 beam splitter 1600, a second reflector 1700, a third reflector 1800, and a fourth reflector 1900.

[0029] A schematic diagram of the dual-imager 800 is attached. Figure 3The dual-imager 800 is manufactured by 3D printing and consists of a black cavity cover plate 810, a through hole 811, a black cavity body 820, an open viewing window 821, a beam splitter slot 822, a fixing through hole 823, a second reflector slot 824, a third reflector slot 825, a fourth reflector slot 826, an observation window 1 827, an observation window 2 828, and a connecting threaded hole 829.

[0030] The size of the temperature field measurement area and the number of scanning planes within one cycle of this system can be adjusted according to the measurement object and specific requirements. In this example, the three-dimensional measurement area is 100×100×20mm. The instantaneous temperature field is obtained by three-dimensional reconstruction using five planar images obtained from scanning within one cycle. Subsequent device parameters correspond to this example.

[0031] In the dual-color image synchronous acquisition module, camera 1200 and camera 21300 are SCMOS cameras; short-pass filter 900 can transmit wavelengths less than 520nm, and band-stop filter 1000 can block wavelengths of 532nm±10nm. Camera 1200, equipped with short-pass filter 900 and band-stop filter 1000, is used to collect the fluorescence intensity of FL27 after laser excitation; long-pass filter 1100 can transmit wavelengths greater than 600nm. Camera 21300, equipped with long-pass filter 1100, is used to collect the fluorescence intensity of KR after laser excitation.

[0032] The laser beam inside laser 100, after being expanded by the Powell prism, reaches a laser surface thickness of approximately 1.3mm on the measurement surface. To allow as much light as possible to enter the dual imager and thus obtain a high-intensity image, the opening window 821 of the dual imager 800 should be larger than 100×100mm. Due to the slot-type design, the optical lenses involved in the dual imager 800 should be rectangular lenses. The dimensions of the beam splitter 1600, reflector 1700, reflector 1800, and reflector 1900 are set at 150×150mm. Since it is necessary to ensure that the light entering the opening window 821 of the dual imager continues to propagate after being split by the 3:7 beam splitter 1600, and the optical lenses are arranged at 45° with the horizontal axis, the opening window 821 is designed to be 106*106mm (106×√2≈149.91<150, which meets the requirements). The beam splitter 1600, mirror 1700, mirror 1800, and mirror 1900 used were all purchased from Beijing Yongxing Perception. The beam splitter 1600 is 1.1mm thick, while mirrors 1700, 1800, and 1900 are aluminum-coated mirrors with a thickness of 2mm. Since the camera lens diameter is 68mm, observation windows 1 (827) and 2 (828) are designed with a diameter of φ=72mm > 68mm to facilitate slight adjustments to the camera position later. The black cavity body 820 of the dual imager 800 is connected to the cover plate 810 via M6 screws and needs to be fixed to the XYZ three-axis displacement stage 6 (3400) (M6 threaded holes, 25mm spacing). Therefore, the base plate has 6.5mm diameter fixing through holes 823 with a spacing of 25mm on three sides.

[0033] After determining the aforementioned key dimensions, the dual-imager 800 was 3D modeled and designed, aiming to minimize its size while meeting the requirements. Black ABS material was used for 3D printing in a single piece, reducing the hassle of later assembly and adjustments, and also lowering costs. Due to the inherent error in 3D printing, to ensure the optical lenses could be inserted into the slots without wobbling, based on experience, the length and width of the beam splitter slot 822, the second reflector slot 824, the third reflector slot 825, and the fourth reflector slot 826 were increased by 1mm during modeling, resulting in 151mm. The slot width was also increased by 0.29mm, designed as 1.39mm and 2.29mm respectively (beam splitter thickness is 1.1mm, reflector thickness is 2mm).

[0034] The dual-color synchronous imaging optical path of the dual-imager 800 is shown in the attached figure. Figure 2As shown, the measurement area is illuminated by a sheet laser, exciting the fluorescent dye and causing it to emit fluorescence at different wavelengths. After passing through the open window 821, the fluorescence image is split into two identical beams by a beam splitter 1600 with a transmission-to-reflection ratio of 3:7. One beam is reflected by the beam splitter onto a left-hand reflecting mirror 1700, which then reflects it to the observation window 827. Similarly, the other beam passes through the beam splitter and is reflected by mirrors 1800 and 1900 to the observation window 828. Thus, cameras 1200 and 1300 can obtain fluorescence images of the same spatial region. Different fluorescence intensity images at different wavelengths can then be obtained by using a short-pass filter 900, a band-stop filter 1000, and a long-pass filter 1100 mounted in front of the lenses. Time synchronization between cameras 1200 and 1300 is controlled by a camera synchronizer 1400.

[0035] Ideally, the propagation lengths of the two optical paths should be identical, and cameras 1200 and 1300 should be placed on the central axis of observation window 828 of observation window 827, respectively. However, due to manufacturing errors in the dual-imager 800, the fluorescence refractive index varies across different wavelengths, causing aberrations in the acquisition system. Furthermore, this design does not eliminate optical imaging aberrations. To obtain images with the highest possible spatial overlap, the placement of cameras 1200 and 1300 will slightly deviate from the central axis, as shown in the attached diagram. Figure 4 As shown.

[0036] Therefore, it is necessary to allow for a certain degree of displacement adjustment of the dual-imager 800, camera one 1200, and camera two 1300 in three-dimensional space, as shown in the attached figure. Figure 5 A three-dimensional motion stage assembly was designed for each. The dual imager 800 is connected to the XYZ three-axis motion stage 3400, which is placed on the optical platform 2000.

[0037] Camera 1 (1200) is fixed at the center of the Z-axis stage 1 (2100), which is fixed on the XY dual-axis stage 1 (2300). Camera 2 (1300) is fixed at the center of the Z-axis stage 2 (2200), which is fixed on the XY dual-axis stage 2 (2400). XY dual-axis stages 1 (2300) and 2 (2400) are fixed on the optical platform 2000. The XYZ three-axis stages, XY-axis stages, and Z-axis stages are all standard purchased products with travel distances of 120×80×50mm, 150×150mm, and 261mm respectively. They can be manually adjusted under a load of ≤20kg and meet the requirements for the dual-imager 800, Camera 1 (1200), and Camera 2 (1300) used in this case.

[0038] As attached Figure 6 The image shown is an image of the calibration board captured by the dual-color image synchronous acquisition module, and the image after spatial algorithm correction. The results show that the original images have slight positional differences. After spatial correction, the overlap between the two images can be reduced to less than one pixel, proving that the designed dual-imager 800 can meet the shooting requirements.

[0039] To ensure that the reflector 500, aperture 400, biconvex lens 300, and scanning galvanometer 200 are coaxially aligned with the optical axis, and that the geometric centers of each component coincide with the optical axis, while simultaneously ensuring that the laser 100 is perpendicular to the positions of the reflector 500, aperture 400, biconvex lens 300, and scanning galvanometer 200, and that the laser emitted from the laser 100 passes through the center of the scanning galvanometer 300 lens for easy optical path adjustment, a displacement stage assembly for the sheet light scanning module was designed, as shown in the attached figure. Figure 7 As shown.

[0040] Laser 100 is fixed at the center of rotary stage 2500, which is fixed on XYZ three-axis displacement stage 2800. Scanning galvanometer 200 is fixed at the center of rotary stage 2600, which is bolted to XYZ three-axis displacement stage 2900. Biconvex lens 300 is fixed inside lens holder 310, which is fixed at the center of rotary stage 2700, which is fixed on XYZ three-axis displacement stage 3000. Aperture 400 is fixed on aperture adapter plate 410, which is fixed on XYZ three-axis displacement stage 4100. Reflector 500 is fixed inside reflector adapter plate 510 via a slot. Reflector adapter plate 510 is fixed at the center of the tilting stage 3300, which is fixed on the XYZ three-axis displacement stage 3200. The XYZ three-axis displacement stage has a travel of 120×80×50mm, the tilting stage has an adjustable angle of 0-65°, and the rotary stage has an adjustable angle of 0-360°; all are standard products purchased from suppliers. The laser 100, scanning galvanometer 200, biconvex lens 300, aperture 400, and reflector 500 used in this case meet the requirements.

[0041] In the sheet-fiber scanning module, laser 100 is a continuous solid-state laser with a wavelength of 532nm and a power of 20W; scanning galvanometer 200 is a single-axis scanning galvanometer with a lens width of 15.9mm and a height of 23.3mm; biconvex lens 300 has a diameter of 200mm, a focal length of 500mm, and is coated with a 532nm anti-reflection coating; frame 310 is model MLNR-8 with a diameter of 200mm; aperture 400 is a custom-made aluminum alloy plate. A schematic diagram and three-view drawing of aperture 400 are attached. Figure 8As shown, the dimensions are 160×80×10mm, with five slits each 3mm wide, and the center-to-center distance between any two slits is 5mm. The aperture 400 has threaded holes on its bottom and sides for easy assembly and connection. The aperture adapter plate 410 is a custom aluminum alloy plate with M6 countersunk holes and M6 threads for easy connection with the aperture 400 and the XYZ three-axis displacement stage 4100. The reflector 500 is a 200×100×2mm aluminum-plated reflector. The galvanometer control box 600 consists of an RTC4 control board, a power supply, and a switch.

[0042] The motion mode of the scanning galvanometer 200 can be set according to requirements. In this example, the galvanometer motion is divided into two modes: static mode and dynamic mode. In static mode, the galvanometer deflects to a specified angle position according to the command, which is used for spatial position calibration of temperature field measurement. In dynamic mode, five angles are set: -1.04°, -0.52°, 0°, 0.52°, and 1.04°. The motion sequence of the galvanometer in the five positions is shown in the attached figure. Figure 9 Since the required camera shooting frequency is 40Hz and the duty cycle is 20%, meaning the time interval between two photos is 25ms and the exposure time is 5ms, to ensure synchronization between the galvanometer deflection and camera shooting, the galvanometer outputs a signal to trigger the camera to shoot during its movement. This signal is a 5V high / low level signal. The time interval between two high-level signals controls the camera's frame rate, and the duration of the high-level signal controls the exposure time. The signal interval is set to 25ms, and the high-level duration is 5ms. When the galvanometer moves to each position, it sends a high-level signal. Simultaneously, the galvanometer stays at that position for 20ms, then moves to the next position after 5ms, ensuring the laser plane is stationary during camera shooting.

[0043] Temperature field images captured by Camera 1 (1200) and Camera 2 (1300) during galvanometer scanning are shown in the attached diagram, along with their spatial and temporal sequences. Figure 10 With a time interval of 25ms between each pair of images and a spatial spacing of 5mm, the temperature field images at five locations are considered as one moment, with a time interval of 125ms between each pair of moments. The three-dimensional temperature field at that moment can be obtained by interpolating and reconstructing the temperature field image within a moment using an algorithm. The transient temperature field can be obtained by reconstructing the temperature field images at multiple moments captured by the camera in sequence.

[0044] In a second aspect, the present invention proposes a method for measuring the three-dimensional temperature field of a fluid using the three-dimensional temperature field measurement system based on Scanning LIF technology described in the above embodiments. According to an embodiment of the present invention, the method includes: (1) Determine the power and wavelength of the laser, the types and concentrations of the two fluorescent dyes in the container to be tested, the size of the three-dimensional measurement area, the frame rate of the camera, the number of temperature field images captured by the camera in one cycle, and the motion mode and deflection angle of the scanning galvanometer.

[0045] Specifically, a 20W continuous laser with a wavelength of 532nm was selected; the two fluorescent dyes in the test container were FL27 and KR, both with a concentration of 300μg / L. The fluorescence intensity of FL27 was positively correlated with temperature, while the fluorescence intensity of KR was negatively correlated with temperature; the size of the three-dimensional measurement area was set to 100×100×20mm; the camera's frame rate was set to 40Hz and the duty cycle to 20%; the camera captured 5 temperature field images per cycle; the galvanometer motion modes were divided into static and dynamic modes, with five deflection angles of -1.04°, -0.52°, 0°, 0.52°, and 1.04°. In static mode, the galvanometer deflects to the specified angle position according to the command, used for spatial position calibration of the temperature field measurement; in dynamic mode, the five angles were set to -1.04°, -0.52°, 0°, 0.52°, and 1.04°, and the movement sequence of the galvanometer in the five positions is shown in the attached figure. Figure 9 .

[0046] (2) Start the laser and adjust the spatial position of the laser, scanning galvanometer, biconvex lens, aperture and reflector in the sheet light scanning module to ensure that the laser passes through the center position of the scanning galvanometer, biconvex lens and reflector, and ensure that the laser area scanned by the laser under the deflection of the scanning galvanometer meets the size of the area to be measured, while the scanning sheet light remains parallel.

[0047] Specifically, first, when the scanning galvanometer is deflected at 0°, adjust the XYZ three-axis displacement stage, rotary stage, and tilting stage so that the laser beam passes sequentially through the scanning galvanometer, biconvex lens, mirror one, and the center of the object being measured, with the laser passing through the slit in the middle of the aperture stop. Then, adjust the galvanometer deflection angle to four positions: -1.04°, -0.52°, 0.52°, and 1.04°, ensuring the laser beam passes through the scanning galvanometer, biconvex lens, and mirror one, respectively, and simultaneously passes through the corresponding positions of the four slits on the left and right sides of the aperture stop. This ensures the laser area scanned by the scanning galvanometer under the deflection of the galvanometer meets the size of the area to be measured. Adjust the angle of the biconvex lens to ensure the scanning beam remains parallel.

[0048] (3) Adjust the spatial position of the camera and dual imager in the dual-color image synchronous acquisition module to ensure that the area captured by the two cameras includes the area to be tested, and that the spatial position of the two cameras is the same.

[0049] Specifically, adjust the XYZ three-axis displacement stage, XY-axis displacement stage, and Z-axis displacement stage below the camera and dual imager to ensure that the area captured by the two cameras includes the area to be measured, and that the spatial positions captured by the two cameras are the same.

[0050] (4) Perform spatial calibration by placing the calibration plate at different locations in the area to be tested and taking images of the calibration plate at different locations using two cameras. Perform spatial calibration based on the shooting results.

[0051] Specifically, the deflection angle of the scanning galvanometer is adjusted to 0°, the calibration plate is moved to coincide with the laser surface, and an image of the calibration plate at this position is captured and stored using a camera. Then, the deflection angle of the scanning galvanometer is adjusted to -1.04°, the calibration plate is moved to coincide with the laser surface at this position, and another image is captured and stored. This process is repeated until the camera records calibration plate images at five angles: -1.04°, -0.52°, 0°, 0.52°, and 1.04°, corresponding to the positions respectively. After capturing these images, the calibration plate is removed. Spatial calibration is then performed on the calibration plate images captured by the two cameras at the five positions.

[0052] (5) Adjust the laser to the maximum power and wait for the light source to stabilize before exciting the two fluorescent dyes in the container to be tested.

[0053] Specifically, the laser was modulated to its maximum power of 20W, and after 15 minutes of waiting for the light source to stabilize, the experiment was started. The laser was used to excite the two fluorescent dyes in the test container.

[0054] (6) Perform temperature calibration by changing the temperature of the fluorescent dye in the container to be tested, and taking pictures of the fluorescence intensity at different temperatures and spatial locations to obtain the fluorescence intensity ratio-temperature relationship curve at different locations.

[0055] Specifically, the system can measure temperatures ranging from 1 to 70°C, while in this example, the temperature range is 25 to 36°C. In this step, first, the temperature of the fluorescent dye in the test solution is ensured to be 25°C. The deflection angle of the scanning galvanometer is adjusted to 0°, and the fluorescence intensity image excited by the laser at this location is captured and stored. Then, the deflection angle of the scanning galvanometer is adjusted to -1.04°, and the fluorescence intensity image excited by the laser at this location is captured and stored. This process is repeated until the camera records and stores fluorescence images excited by the laser at five angles: -1.04°, -0.52°, 0°, 0.52°, and 1.04°. The fluorescent dye in the test container is then heated to 28°C using a heating rod. After the temperature stabilizes, the fluorescence images excited by the laser at five angles: -1.04°, -0.52°, 0°, 0.52°, and 1.04° are recorded and stored. Repeat the above steps, recording the fluorescence intensity at five locations in the test solution when the fluorescent dye is at temperatures of 25℃, 28℃, 31℃, 34℃, and 37℃, and when the galvanometer deflection angles are -1.04°, -0.52°, 0°, 0.52°, and 1.04°, for a total of 25 sets of experimental results. The fluorescence intensity ratio versus temperature curve at each location was calculated by comparing the fluorescence intensity ratios captured by two cameras at different temperatures. These fluorescence intensity ratio versus temperature curves for the five locations were then used for temperature calibration calculations of subsequent experimental images.

[0056] (7) Take experimental images, change the experimental conditions inside the container to be tested, input the control program of the scanning galvanometer according to the required shooting frame rate, and the camera records the fluorescence intensity at different positions in one cycle according to the galvanometer deflection position.

[0057] Specifically, in this example, the camera's frame rate is set to 40Hz and the duty cycle to 20%, meaning the time interval between two photos is 25ms, the exposure time is 5ms, and the scanning galvanometer is set to five deflection angles: -1.04°, -0.52°, 0°, 0.52°, and 1.04°. The sequence of the galvanometer's movement in these five positions is shown in the attached figure. Figure 9 .

[0058] (8) To capture the background image, turn off all light sources and do not change the camera shooting frequency, capture the light intensity image of the experimental background.

[0059] Specifically, all light sources were turned off, the camera was set to shoot at a frame rate of 40Hz and a duty cycle of 20%, and two cameras simultaneously captured and stored the background image of the experimental area.

[0060] (9) Calculation of temperature field experimental results at different locations: After subtracting the light intensity of the background image from the experimental image, spatial calibration is performed using the spatial calibration image, and the temperature field images at different spatial locations are calculated using the fluorescence intensity-temperature relationship curve.

[0061] Specifically, the experimental results at different locations were processed separately. The light intensity of the background image was subtracted from the experimental image, and then the median filtering and spatial calibration were performed. The spatially calibrated images of the two cameras were compared, and the ratio image was cropped to the required area size. The temperature field at that location was calculated through the fluorescence intensity ratio-temperature relationship curve.

[0062] (10) Three-dimensional temperature field interpolation reconstruction: The algorithm is used to interpolate and reconstruct the temperature field images at different locations within a period into a three-dimensional temperature field.

[0063] Specifically, the temperature field images processed at five locations within one period are imported into MATLAB, and cubic convolution interpolation is used to reconstruct the three-dimensional temperature field images from the two-dimensional temperature field images.

[0064] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-dimensional temperature field measurement system based on Scanning LIF technology, characterized in that, The system includes a sheet light scanning module and a dual-color image synchronous acquisition module. The sheet light scanning module is used to excite the fluorescent dye in the test container (700) from below the test container (700). The dual-color image synchronous acquisition module is used to acquire the fluorescence image inside the test container (700). The sheet light scanning module includes a laser (100), a scanning galvanometer (200), a biconvex lens (300), an aperture (400), and a reflector (500) arranged in sequence at intervals. The end of the scanning galvanometer (200) away from the laser (100) and the scanning galvanometer (200) is connected to a galvanometer control box (600). The dual-color image synchronous acquisition module includes a dual-image sensor (800), a short-pass filter (900), a band-stop filter (1000), a long-pass filter (1100), a camera (1200), a camera (1300), a camera synchronizer (1400), and a computer (1500). The camera (1200) and camera (1300) are symmetrically distributed parallel to the axis of the dual-image sensor (800). A short-pass filter (900) and a band-stop filter (1300) are connected sequentially between the dual-image sensor (800) and the camera (1200). The dual imager (800) and the second camera (1300) are connected by a long-pass filter (1100). The other end of the first camera (1200) and the second camera (1300) are connected in parallel with the computer (1500) through the camera synchronizer (1400). The other end of the galvanometer control box (600) is connected in parallel with the camera synchronizer (1400) through the computer (1500). The galvanometer control box (600) is used to control the deflection angle and motion mode of the scanning galvanometer (200).

2. A three-dimensional temperature field measurement system based on Scanning LIF technology according to claim 1, characterized in that, The biconvex lens (300) is fixed inside the frame (310). The optical axes of the reflector (500), aperture (400), biconvex lens (300) and scanning galvanometer (200) are aligned with the central axis. The laser (100) is positioned perpendicular to the central axis.

3. A three-dimensional temperature field measurement system based on Scanning LIF technology according to claim 1, characterized in that, The dual-imager (800) includes a black cavity cover plate (810), a through hole (811), a black cavity body (820), an open viewing window (821), a beam splitter slot (822), a fixed through hole (823), a second reflector slot (824), a third reflector slot (825), a fourth reflector slot (826), an observation window one (827), an observation window two (828), a connecting threaded hole (829), a beam splitter (1600), a second reflector (1700), a third reflector (1800), and a reflector... Mirror 4 (1900), the opening window (821) is located on the front side of the black cavity body (820), the observation window 1 (827) and the observation window 2 (828) are located on the rear side of the black cavity body (820) and are symmetrically distributed, the beam splitter slot (822), the mirror 2 slot (824), the mirror 3 slot (825), the mirror 4 slot (826), the observation window 1 (827), the observation window 2 (828) and the connecting thread The hole (829) is located inside the black cavity body (820), and the fixing through hole (823) is located outside the black cavity body (820) to facilitate the fixation of the dual imager; the black cavity cover plate (810) is connected and fixed to the black cavity body (820), the position of the opening window (821) is consistent with the height of the area to be measured, the beam splitter (1600) is fixed inside the beam splitter slot (822), and the second reflector (1700) is fixed in the second reflector slot (823). Inside 824), the third reflector (1800) is fixed inside the third reflector slot (825), and the fourth reflector (1900) is fixed inside the fourth reflector slot (826). The beam splitter (1600), the second reflector (1700), the third reflector (1800) and the fourth reflector (1900) are all arranged at 45° to the horizontal axis and their central axes coincide with the first observation window (827) and the second observation window (828).

4. A three-dimensional temperature field measurement system based on Scanning LIF technology according to claim 1, characterized in that, It also includes a tilting stage, multiple rotary stages, multiple displacement stages, and an optical platform. A portion of the multiple rotary stages is used to support the dual-color image synchronous acquisition module, and another portion and the tilting stage (3300) are used to support the sheet light scanning module. The multiple displacement stages are used to connect the multiple rotary stages and the optical platform and drive the multiple rotary stages to move. The tilting stage (3300) is used to tilt and adjust the laser direction provided by the sheet light scanning module.

5. A three-dimensional temperature field measurement system based on Scanning LIF technology according to claim 1, characterized in that, The plurality of rotary stages include rotary stage one (2500), rotary stage two (2600), and rotary stage three (2700); the plurality of displacement stages include Z-axis displacement stage one (2100), Z-axis displacement stage two (2200), XY dual-axis displacement stage one (2300), XY dual-axis displacement stage two (2400), XYZ three-axis displacement stage one (2800), XYZ three-axis displacement stage two (2900), XYZ three-axis displacement stage three (3000), XYZ three-axis displacement stage four (3100), XYZ three-axis displacement stage five (3200), and XYZ three-axis displacement stage six (3400).

6. A three-dimensional temperature field measurement system based on Scanning LIF technology according to claim 1, characterized in that, The laser (100) is fixed at the center of the rotating stage (2500), which is fixed on the XYZ three-axis displacement stage (2800). The scanning galvanometer (200) is fixed at the center of the rotating stage (2600), which is fixed on the XYZ three-axis displacement stage (2900), ensuring that the laser (100) and the scanning galvanometer (200) are at the same height, thus ensuring that the laser beam passes through the center of the galvanometer window. The mirror frame (310) is fixed at the center of the rotating stage (2700), which is fixed on the XYZ three-axis displacement stage. On the third (3000) stage; the aperture (400) is fixed on the aperture adapter plate (410), the aperture adapter plate (410) is fixed on the fourth (3100) stage of the XYZ three-axis displacement stage; the first reflector (500) is fixed inside the first reflector adapter plate (510), the first reflector adapter plate (510) is fixed at the center of the inclined worktable (3300) stage, the inclined worktable (3300) is fixed on the fifth (3200) stage of the XYZ three-axis displacement stage, and maintains the same vertical position as the area to be measured in the container to be measured (700); the dual imager (800) is fixed at the center of the sixth (3400) stage of the XYZ three-axis displacement stage.

7. A three-dimensional temperature field measurement system based on Scanning LIF technology according to claim 1, characterized in that, The camera one (1200) is fixed at the center of the Z-axis displacement stage one (2100), the Z-axis displacement stage one (2100) is fixed on the XY dual-axis displacement stage one (2300), the XY dual-axis displacement stage one (2300) is fixed on the optical platform (2000), the lens height of the camera one (1200) is the same as the height of the observation window one (827), the lens height of the camera two (1300) is the same as the height of the observation window two (828), the camera two (1300) is fixed at the center of the Z-axis displacement stage two (2200), the Z-axis displacement stage two (2200) is fixed on the XY dual-axis displacement stage two (2400), the XY dual-axis displacement stage two (2400) is fixed on the optical platform (2000).

8. A three-dimensional temperature field measurement system based on Scanning LIF technology according to claim 1, characterized in that, The camera synchronizer (1400) is connected to camera one (1200), camera two (1300), galvanometer control box (600) and computer (1500) via cables. It is used to receive the synchronization signal output by the galvanometer to control the synchronous shooting of camera one (1200) and camera two (1300). The computer (1500) is connected to camera one (1200), camera two (1300), camera synchronizer (1400) and galvanometer control box (600) via cables. It is used to control the galvanometer deflection and the shooting of camera one (1200) and camera two (1300), and to display the fluorescence image used for storing and processing experimental data.

9. A method for measuring a three-dimensional temperature field using the measurement system as described in any one of claims 1-8, characterized in that, include: (1) Determine the power and wavelength of the laser, the types and concentrations of the two fluorescent dyes in the container to be tested, the size of the three-dimensional measurement area, the frame rate of the camera, the number of temperature field images captured by the camera in one cycle, and the motion mode and deflection angle of the scanning galvanometer. (2) Start the laser and adjust the spatial position of the laser, scanning galvanometer, biconvex lens, aperture and reflector in the sheet light scanning module to ensure that the laser passes through the center position of the scanning galvanometer, biconvex lens and reflector, and ensure that the laser area scanned by the laser under the deflection of the scanning galvanometer meets the size of the area to be measured, while the scanning sheet light remains parallel. (3) Adjust the spatial position of the camera and dual imager in the dual-color image synchronous acquisition module to ensure that the area captured by the two cameras includes the area to be measured, and that the spatial position of the two cameras is the same. (4) Perform spatial calibration by placing the calibration plate at different positions in the area to be tested and taking images of the calibration plate at different positions using two cameras. Perform spatial calibration based on the shooting results. (5) Adjust the laser to the maximum power, wait for the light source to stabilize, and then excite the two fluorescent dyes in the container to be tested; (6) Perform temperature calibration, change the temperature of the fluorescent dye in the container to be tested, and take pictures of the fluorescence intensity at different temperatures and spatial positions. By the ratio of the fluorescence intensity of the two dyes, obtain the fluorescence intensity ratio-temperature relationship curve at different positions. (7) Take experimental images, change the experimental conditions inside the container to be tested, input the required frame rate of the experimental images into the computer to control the deflection of the scanning galvanometer, and the camera one and camera two record the fluorescence intensity at different positions within one cycle according to the deflection position of the galvanometer. (8) Turn off all light sources and take a picture of the light intensity of the experimental background without changing the camera shooting frequency; (9) Calculation of temperature field experimental results at different locations: After subtracting the light intensity of the experimental background image from the light intensity of the experimental image, spatial calibration is performed using the spatial calibration image, and the temperature field images at different spatial locations are calculated using the fluorescence intensity ratio-temperature relationship curve. (10) Three-dimensional temperature field interpolation reconstruction: interpolate and reconstruct the temperature field images at different locations within a period to form a three-dimensional temperature field.

10. The measurement method according to claim 9, characterized in that, The fluorescence intensity of one of the two fluorescent dyes in the test container is positively correlated with temperature, while the fluorescence intensity of the other fluorescent dye is negatively correlated with temperature; or the fluorescence intensity of the two fluorescent dyes is not simultaneously correlated with temperature.

Images