A laser-induced fluorescence-based icing tunnel 3D ice shape measurement method

Abstract

The application provides a laser-induced fluorescence-based icing wind tunnel 3D ice shape measurement method, and according to the laser-induced fluorescence characteristics of water molecules, the laser-induced fluorescence imaging method is adopted to effectively solve the line structure light imaging degradation problem of transparent ice, the cross-section profile measurement of the line structure light of the transparent ice can be realized, and the three-dimensional ice shape measurement can be realized in combination with a scanning device, thereby providing technical support for realizing the time-resolved icing growth process 3D ice shape online measurement in the icing wind tunnel.

Description

Technical Field

[0001] The present invention relates to the technical field of icing wind tunnel testing, and in particular to a 3D ice shape measurement method in an icing wind tunnel based on laser induced fluorescence. Background Art

[0002] Aircraft icing and its protection have always been important research topics in the aviation field. In order to explore the icing mechanism, conduct aerodynamic performance evaluation of aircraft under icing weather conditions, safety assessment, anti-icing / de-icing and other research work, domestic and foreign scholars have carried out a lot of research work in three aspects: CFD numerical calculation, wind tunnel testing, and flight testing. [1-4] Due to the low safety and high cost of flight tests under natural icing conditions, simulated icing tests are currently mainly conducted in icing wind tunnels to conduct branch performance and safety assessments of aircraft under icing conditions, verify the performance of anti-icing / de-icing systems, and verify CFD numerical calculation results. In wind tunnel icing tests, it is generally necessary to measure information such as the thickness and 3D shape of the icing body. Studies have shown that icing is closely related to parameters such as liquid water content, average droplet diameter, temperature, freezing time, flight speed, and angle of attack. [5] To further explore the influence of these parameters on the ice growth process, it is also necessary to conduct online measurement of the 3D ice shape during the ice growth process during the icing wind tunnel test.

[0003] Ice types include transparent ice, translucent mixed ice, and opaque frost ice. To measure the 3D ice shape online during the ice growth process, the above three ice shape measurements must be achieved. [6] According to whether or not the ice is in contact, existing ice shape measurement methods can be divided into contact measurement and non-contact measurement. Contact measurement includes hot knife method and modeling method; non-contact measurement includes: photogrammetry method [7] , Light Knife Technique [8-12] , 3D scanner measurement method

[13] To achieve online measurement of ice shape in an icing wind tunnel, a non-contact measurement method must be used. Existing non-contact measurement methods mostly use imaging to obtain natural images of the ice surface or optical modulation images for three-dimensional shape measurement. The quality of the imaging image directly affects the ice shape measurement results. Experiments show that [11,12] When using the light knife method to measure ice shape, the imaging quality of clear ice and mixed ice is poor, making 3D ice shape measurement difficult. When imaging line structures on frost, mixed, and clear ice surfaces, as transparency increases, the transmittance of the line structured light increases, and the imaging quality degrades, seriously affecting the accuracy of line structured light position extraction.

[0004] Existing optical ice shape measurement methods include: photogrammetry, light knife method, and 3D scanner measurement. [7]Two cameras are used to form a binocular stereo vision measurement system to complete the three-dimensional reconstruction of ice body and the three-dimensional ice shape measurement. In the binocular stereo vision three-dimensional reconstruction, the matching of homonymous pixels in the images taken by two cameras must be solved. When the object is transparent or semi-transparent, it will cause the image quality to degrade, which will lead to the failure of binocular stereo vision matching. Therefore, the three-dimensional measurement of frost ice is realized in the literature [7], but the three-dimensional reconstruction of transparent ice body cannot be realized.

[0005] NASA began to study laser sheet light simulation hot knife for ice cross-section profile measurement in 1993 [8,9] The laser sheet light is projected onto the surface of the ice body, and the deformed laser light bar is generated by the intersection of the laser sheet light and the ice body. The laser light bar reflects the shape of the ice body at the cross-section. The camera is used to take the image of the laser light bar, and the image coordinates of the center line of the laser light bar are extracted. Then, the shape of the laser light bar is calculated by the geometric relationship between the laser plane and the camera, and the cross-section profile of the ice body at the position is obtained. In China, Zhang Long et al.

[10] The binocular line structured light is used to realize the cross-section measurement of frost ice. Wang Bin et al.

[11] The light knife method is used to realize the cross-section profile measurement of ice body.

[0006] The above studies show that the light knife method can well meet the demand of frost ice shape measurement. However, for clear ice and mixed ice with transparent and mirror reflection areas, it is difficult for the camera to take clear laser light bar on the surface of the ice body, and it is difficult to realize the cross-section measurement and three-dimensional shape scanning. Because the mixed ice has a certain degree of transparency, when the camera images, the transmitted light will illuminate the adjacent area of the laser light bar, which will reduce the brightness difference between the laser light bar and the adjacent area, resulting in unclear light bar peak and difficult to accurately extract the center line coordinates of the light bar. In addition, during the icing test, there is also a water film on the surface of the ice body, which makes the ice body become a mirror surface at some angles, which also leads to the failure of the camera to take the laser light bar. In view of this problem, Kang Hanyu et al.

[12] The BM3D denoising method is used to improve the positioning accuracy of the light bar center line, but it cannot fundamentally eliminate the influence of the image quality degradation problem of transparent ice body.

[0007] In recent years, three-dimensional scanners have been applied to the three-dimensional shape scanning of ice body

[13] , and aircraft aerodynamic force evaluation. Commercial three-dimensional scanners usually use point, line, and surface structured light for three-dimensional measurement. The three-dimensional measurement principle based on line structured light is the same as the laser knife cutting method, except that a three-dimensional scanning device is added to obtain multiple measurement results and synthesize the 3D shape. Compared with the laser knife cutting method, the three-dimensional scanner measurement data is more dense, and the 3D shape of the measured object can be digitized. Similarly, the existing commercial three-dimensional scanner uses the imaging of reflected light by the measured object surface (hereinafter referred to as "laser reflection imaging" to distinguish from the "laser excitation radiation imaging" method introduced later) to measure only diffuse reflection surface objects, and cannot measure mirror reflection, transparent objects. Therefore, it is necessary to spray a developing agent on the ice body surface to make it a non-transparent Lambertian surface, and then use a three-dimensional scanner to scan the 3D ice shape.

[0008] In summary, the existing optical ice shape measurement method is interfered by the mirror reflection of the water film on the ice body surface and the transmission of the semi-transparent or transparent ice body, resulting in the camera being unable to capture clear ice body images and unable to achieve three-dimensional measurement of transparent ice bodies. For the light knife method, the existing method uses a reflected light imaging method, and when acquiring a line structured light image, mirror reflection and transmission will degrade the quality of the line structured light image, making it difficult to accurately extract the line structured light position and making it difficult to measure the shape of mixed ice and clear ice.

[0009] [1] Lin Guiping, Bu Xueqin, Shen Xiaobin. Aircraft icing and anti-icing technology [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2016.

[0010] [2] Lee S, Broeren A P, Addy Jr H E, et al. Development of 3D IceAccretion Measurement Method [J]. AIAA Paper, 2012, 2938: 2012.

[0011] [3] Miller D, Potapczuk M, Langhals T. Preliminary Investigation ofIce Shape Sensitivity to Parameter Variations [C] / / 43rd AIAA AerospaceSciences Meeting and Exhibit. American Institute of Aeronautics andAstronautics Reston, Virigina, 2005: 2005-0073.

[0012] [4] Pan Huan, Ai Jianliang. Modeling and simulation of aircraft icing shape prediction[J]. Journal of System Simulation, 2014, 26(1): 221-224.

[0013] [5] Campbell SE, Broeren AP, Bragg M B. Sensitivity of aircraftperformance to icing parameter variations [J]. Journal of Aircraft, 2007, 44(5): 1758-1760.

[0014] [6] Yi Xian, Wang Bin, Li Weibin, et al. Research progress on ice shape measurement methods for aircraft icing[J]. Acta Aeronautica et Aeronautica Sinica. 2017, 38(2):13-24

[0015] [7] Collier P, Dixon L, Fontana D, et al. The use of close rangephotogrammetry for studying ice accretion on aerofoil sections[J].Photogrammetric Record, 1999, 16(94): 671-84.

[0016] [8] Mercer CR, Vargas M, Oldenburg J R. A preliminary study on iceshape tracing with a laser light sheet [J]. Nasa Sti / recon Technical ReportN, 1993, 94.

[0017] [9] Hovenac EA, Vargas M. A laser-based ice shape profilometer for use in icing wind tunnels [J]. Nasa Sti / recon Technical Report N, 1995, 95.

[0018]

[10] Long Z, Longde G, Jianjun Y. Investigation of Ice ShapeMeasurement Technique Based on Laser Sheet and Machine Vision in Icing WindTunnel[C] / / Proceedings of the 2009 Fifth International Conference on Imageand Graphics. IEEE Computer Society, 2009:790-795.

[0019]

[11] Wang Bin, Liu Guihua, Zhang Liping, et al. Ice profile measurement based on line structured light[J]. Experimental Fluid Mechanics, 2016, 30(3): 14-20

[0020]

[12] Kang Hanyu, Liu Guihua, Wang Bin, et al. Rapid extraction method of laser light band centerline on ice surface[J]. Experimental Fluid Mechanics, 2017, 31(5): 81-87

[0021]

[13] Lee S, Broeren AP, Addy Jr HE, et al. Development of 3D IceAccretion Measurement Method [J]. AIAA Paper, 2012, 2938: 2012. Summary of the Invention

[0022] The purpose of the present invention is to address the shortcomings of the existing technology and provide a technical solution for a 3D ice shape measurement method in an icing wind tunnel based on laser induced fluorescence. This solution adopts a laser induced fluorescence imaging method based on the laser induced fluorescence characteristics of water molecules to effectively solve the problem of line structured light imaging degradation of transparent ice bodies. It can realize the measurement of the cross-sectional profile of the line structured light of transparent ice bodies, and then combine with a scanning device to realize three-dimensional ice shape measurement, providing technical support for the time-resolved online measurement of 3D ice shapes in the ice growth process in an icing wind tunnel.

[0023] This solution is achieved through the following technical measures:

[0024] A method for measuring 3D ice shape in an icing wind tunnel based on laser-induced fluorescence comprises the following steps:

[0025] a. Based on the laser-induced fluorescence characteristics of water molecules, a 200-400nm laser light source is selected as the excitation light, and the light source is modulated into a light sheet through an optical system;

[0026] b. Projecting a light sheet onto the surface of the ice, water molecules in the ice undergo an electrochemical reaction with the light sheet, generating fluorescence with a wavelength range of 400-800nm;

[0027] c. Using a camera to capture the fluorescence emitted from the surface of the ice, a light source cutoff filter is placed at the front end of the camera. The cutoff filter can cut off the excitation light so that the camera only receives the fluorescence generated by the surface of the ice;

[0028] d. After the camera receives the fluorescence, the intersection coordinates of the fluorescence and the ice surface are extracted using the fluorescence boundary line extraction method;

[0029] e. Use the line structured light calibration method to calibrate the spatial position relationship between the light sheet and the camera, and obtain the plane equation of the light sheet plane in the camera coordinate system;

[0030] f. Calculate the coordinates of the intersection curve between the ice surface and the light sheet in the current light sheet plane based on the plane equation obtained in step e and the coordinates of the intersection line between the fluorescence and the ice surface obtained in step d;

[0031] g. Use a scanning device to scan the surface of the ice body with a light sheet to obtain a series of ice body surface light sheet images. For each ice body surface light sheet image, use steps d to f to calculate the coordinates of the laser-induced fluorescence interface on the ice body surface in the current light sheet plane. Based on the scanning relationship, the coordinates in each light sheet plane are spliced ​​to obtain the three-dimensional morphology data of the ice body, thereby realizing the three-dimensional morphology measurement of the ice body.

[0032] As a preferred embodiment of this solution: in step a, the wavelength of the light source is 350 nm.

[0033] As a preferred embodiment of this solution: in step g, the scanning device is a translation mechanism based on a one-dimensional guide rail or a fan-shaped refraction mechanism based on a rotating prism.

[0034] As a preferred embodiment of this solution: the camera is an ICCD or EMCCD with low-illumination imaging capability.

[0035] As a preferred embodiment of this solution: during the freezing process, a fluorescent dye is added to the freezing water; the fluorescent dye can emit fluorescence under laser induction.

[0036] As a preferred embodiment of this solution: during the icing wind tunnel test, an ice shape scan is performed at a time interval of t0. During the ice shape scan, in order to avoid the influence of water vapor on the imaging quality during the test, the wind tunnel stops spraying, and measurement is performed only after there are no ice particles in the airflow.

[0037] As a preferred embodiment of this solution: in step d, the fluorescence boundary line extraction method includes the following steps:

[0038] d1. Perform brightness segmentation on the captured ice laser-induced fluorescence image, dividing the image into two areas: brighter and darker.

[0039] d2. Based on the position of the laser, select the bright and dark boundary area close to the laser as the rough positioning area of ​​the fluorescence boundary line;

[0040] d3. Based on the coarse positioning area, take one pixel, calculate the image gradient at the pixel, and calculate the direction y of the fluorescence boundary line based on the gradient;

[0041] d4. Set a rectangular sampling area of ​​m*d along the direction y, where m is the width and d is the height. The width is perpendicular to the direction y of the fluorescence boundary line. Use a gradient-based edge detection method to find the image edge coordinates. After traversing all pixels in the coarse positioning area, obtain the fine positioning coordinates of the fluorescence boundary line, which are the coordinates of the intersection line of the fluorescence and the ice surface.

[0042] As a preferred embodiment of this solution: a fluorescent dye with a smaller liquid surface tension is selected to reduce the interference and influence of the fluorescent dye on the physical process of freezing.

[0043] The beneficial effects of this solution can be seen from the description of the above solution. The present invention can effectively solve the problem of imaging degradation in three-dimensional scanning measurement of transparent ice bodies.

[0044] Compared with the imaging method based on MIR heating, the light source used in the present invention is a cold light source, which will not interfere with the noise of the thermophysical process of the freezing process.

[0045] Compared with the existing commercial 3D scanner method that uses imaging methods based on light reflected from the surface of the object being measured, there is no need to spray developer on the surface of the ice to turn it into a non-transparent Lambertian surface. There is no need to stop the wind tunnel operation during the experiment, and there is no human interference. This avoids the situation in which the icing test is affected by external factors and causes deviations from the actual icing process. It can truly realize real-time online 3D ice shape measurement without external interference.

[0046] The line structured light centerline extraction method proposed in the present invention solves the problem of ice body transmission caused by laser-induced fluorescence. The line structured light centerline can be accurately extracted from the image, and the cross-sectional profile measurement of the transparent ice body can be realized. In combination with the scanning device, the three-dimensional morphology scanning of the ice body can be realized.

[0047] When installing the icing wind tunnel test section, the interference of optical glass was taken into consideration to avoid the interference of fluorescence generated by the glass.

[0048] During the experiment, the method of stopping the spray was adopted to solve the problem of image scattering interference caused by ice particles in the airflow.

[0049] It can be seen that compared with the prior art, the present invention has substantial characteristics and progress, and the beneficial effects of its implementation are also obvious. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a schematic diagram of the laser-induced fluorescence ice shape measurement principle of the present invention.

[0051] Figure 2 Schematic diagram of the imaging results of the present invention.

[0052] Figure 3 This is the equipment layout diagram of Example 1.

[0053] Figure 4 Schematic diagram of the boundary between fluorescence and the ice surface;

[0054] Figure 5 Schematic diagram of the sampling area set in the coarse positioning area of ​​the present invention;

[0055] Figure 6 A schematic diagram of the positioning coordinates of the fluorescent dividing line obtained by the present invention;

[0056] Figure 7 A schematic diagram of searching for an image block similar to an image block to be denoised;

[0057] Figure 8 Schematic diagram for searching and matching similar image blocks.

[0058] In the figure, 1 is the camera, 2 is the filter, 3 is the laser, 4 is the ice body, 5 is the light sheet, 6 is the laser-induced fluorescence, 7 is the cylindrical lens, 8 is the laser-induced fluorescence interface, 9 is the fluorescence boundary line, 10 is the non-laser induced area, 11 is the ice body cross section, 12 is the coarse positioning area, 13 is the sampling area, 14 is the pseudo-denoised image block, 15 is the image block to be matched, and 16 is the fine positioning coordinate. DETAILED DESCRIPTION

[0059] All features disclosed in this specification, or all steps in the disclosed methods or processes, except mutually exclusive features and / or steps, can be combined in any manner.

[0060] Any feature disclosed in this specification (including any appended claims, abstract, and drawings), unless otherwise stated, may be replaced by other equivalent or similar features. In other words, unless otherwise stated, each feature is only an example of a series of equivalent or similar features. Example

[0061] based on Figure 1The laser-induced fluorescence ice shape measurement principle diagram is shown in the figure. The laser light source uses a dye laser with a wavelength of 280nm. An ICCD camera is used for fluorescence imaging. A wavelength cutoff filter below 300nm is set at the front end of the camera to intercept the ultraviolet light reflected from the ice surface. The overall equipment layout is shown in the figure. Figure 3 shown.

[0062] The imaging resolution of ICCD is 2048*2048 pixels and the frame rate is 20fps.

[0063] according to Figure 3 When the measured object is a transparent ice body, the imaging effect is as shown in the following figure. Figure 2 As shown, the image shows a brighter area, indicating laser-induced fluorescence, and a darker area, indicating non-induced fluorescence, resulting in a darker image. The camera can capture the fluorescence generated by the laser sheet entering the ice and within it. Positioning the camera at a specific angle to the laser plane allows it to capture this fluorescence interface, which is the intersection of the laser plane and the ice. This intersection represents the ice's contour. Scanning along a specific direction can obtain 3D surface topography data.

[0064] For images in this area, the existing line structured light extraction algorithm cannot complete the laser sheet light position extraction.

[0065] To address this problem, the present invention specifically proposes a fluorescence boundary line extraction method.

[0066] The steps of the fluorescence boundary line extraction method are as follows:

[0067] d1. Perform brightness segmentation on the captured ice laser-induced fluorescence image, dividing the image into two areas: brighter and darker.

[0068] d2. Based on the position of the laser, select the bright and dark boundary area close to the laser as the rough positioning area of ​​the fluorescence boundary line;

[0069] d3. Based on the coarse positioning area, take one pixel, calculate the image gradient at the pixel, and calculate the direction y of the fluorescence boundary line based on the gradient;

[0070] d4. Set a rectangular sampling area of ​​m*d along the direction y, where m is the width and d is the height. The width is perpendicular to the direction y of the fluorescence boundary line. Use a gradient-based edge detection method to find the image edge coordinates. After traversing all pixels in the coarse positioning area, obtain the fine positioning coordinates of the fluorescence boundary line, which are the coordinates of the intersection line of the fluorescence and the ice surface.

[0071] During laser-induced fluorescence imaging, two frames of images are captured simultaneously: a reference image and a measurement image. When capturing the reference image, the laser is turned off and the substrate signal is captured. When capturing the measurement image, the laser is turned on and the laser-induced fluorescence image is captured. By comparing the two images, the laser-induced fluorescence imaging area can be found, making it easier to locate the laser-induced fluorescence area.

[0072] like Figure 7 As shown in the figure, within the coarse positioning area of ​​the fluorescence boundary line, the image similarity matching method is used to find similar image blocks, and then a weight matrix is ​​constructed based on the pixel values ​​and distances within the image blocks to denoise the current image to enhance the centerline signal-to-noise ratio of the fluorescence boundary line. After the centerline signal-to-noise ratio of the fluorescence boundary line is enhanced, subsequent calculations are performed.

[0073] like Figure 8 As shown in the figure, when searching and matching similar image blocks, the similarity is not determined according to the image coordinate system itself. Instead, the total direction y0 of the image block to be denoised is calculated along the coarse positioning line trajectory, and a sampling area S0 with the same direction as y0 is set. The sampling area Si is set according to the direction of the coarse positioning line along the coarse positioning line trajectory, and the image blocks are extracted for similarity comparison. Figure 8 It can be seen that the set sampling area Si is aligned along the fluorescence dividing line, which has stronger similarity, can find more similar image blocks, and obtain better image boundary denoising effect.

[0074] The line structured light calibration method is used to calibrate the relationship between the line structured light and the camera position, find the laser plane equation, and calculate the three-dimensional coordinates of the current laser-induced fluorescence interface based on the plane equation and the coordinates of the intersection line between the fluorescence and the ice surface.

[0075] The ice body is scanned using a one-dimensional guide rail, and the acquired three-dimensional coordinates are spliced ​​to obtain the three-dimensional morphological data of the ice body.

[0076] The scanning step size of the one-dimensional guide is 1 mm. Example

[0077] The difference from Example 1 is that within the camera field of view, the exterior of the test model is coated with fluorescent paint. When the laser sheet light is irradiated on the fluorescent paint, fluorescence is generated. This fluorescent band is used to assist in determining the fluorescent boundary line of the ice surface. Example

[0078] The difference from Example 1 is that the light source is a 400nm LED light source, which is modulated into a light sheet by a cylindrical mirror. The camera is an EMCCD camera. Example

[0079] The difference from Example 1 is that the camera is a SCMOS camera. Example

[0080] The difference from Example 1 is that the camera is a low-light imaging chip camera, such as a starlight-level camera. Example

[0081] The difference from Example 1 is that in the freezing test, a fluorescent dye is added to the water, and the fluorescent dye generates fluorescence under the excitation of a laser light source, and the fluorescence image is captured using a sCMOS, CMOS, or CCD camera. Example

[0082] The difference from Example 6 is that a fluorescent dye with a smaller liquid surface tension is selected to reduce the interference and influence of the fluorescent dye on the freezing physical process.

[0083] The present invention is not limited to the aforementioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A 3D ice shape measurement method in an icing wind tunnel based on laser-induced fluorescence, characterized by: The following steps are included: a. Based on the laser-induced fluorescence characteristics of water molecules, a 200-400nm laser light source is selected as the excitation light, and the light source is modulated into a light sheet through an optical system; b. Projecting a light sheet onto the surface of the ice, water molecules in the ice undergo an electrochemical reaction with the light sheet, generating fluorescence with a wavelength range of 400-800nm; c. Using a camera to capture the fluorescence emitted from the surface of the ice, a light source cutoff filter is placed at the front end of the camera. The cutoff filter can cut off the excitation light so that the camera only receives the fluorescence generated by the surface of the ice; d. After the camera receives the fluorescence, the intersection coordinates of the fluorescence and the ice surface are extracted using the fluorescence boundary line extraction method; e. Use the line structured light calibration method to calibrate the spatial position relationship between the light sheet and the camera, and obtain the plane equation of the light sheet plane in the camera coordinate system; f. Calculate the coordinates of the intersection curve between the ice surface and the light sheet in the current light sheet plane based on the plane equation obtained in step e and the coordinates of the intersection line between the fluorescence and the ice surface obtained in step d; g. Using a scanning device to scan the surface of the ice body with a light sheet to obtain a series of ice body surface light sheet images; for each ice body surface light sheet image, using steps d to f, calculate the coordinates of the laser-induced fluorescence interface on the ice body surface within the current light sheet plane; based on the scanning relationship, splice the coordinates within each light sheet plane to obtain three-dimensional ice body topography data, thereby achieving three-dimensional ice body topography measurement; In step d, the fluorescence boundary line extraction method includes the following steps: d1. Perform brightness segmentation on the captured ice laser-induced fluorescence image, dividing the image into two areas: brighter and darker. d2. Based on the position of the laser, select the bright and dark boundary area close to the laser as the rough positioning area of ​​the fluorescence boundary line; d3. Based on the coarse positioning area, take one pixel, calculate the image gradient at the pixel, and calculate the direction y of the fluorescence boundary line based on the gradient; d4. Set a rectangular sampling area of ​​m*d along the direction y, where m is the width and d is the height. The width is perpendicular to the direction y of the fluorescence boundary line. Use a gradient-based edge detection method to find the image edge coordinates. After traversing all pixels in the coarse positioning area, obtain the fine positioning coordinates of the fluorescence boundary line, which are the coordinates of the intersection line of the fluorescence and the ice surface.

2. The method for measuring 3D ice shape in an icing wind tunnel based on laser-induced fluorescence according to claim 1, wherein: In step a, the wavelength of the light source is 350 nm.

3. The method for measuring 3D ice shape in an icing wind tunnel based on laser-induced fluorescence according to claim 1, wherein: In step g, the scanning device is a translation mechanism based on a one-dimensional guide rail or a fan-shaped refraction mechanism based on a rotating prism.

4. The method for measuring 3D ice shape in an icing wind tunnel based on laser-induced fluorescence according to claim 1, wherein: The camera is an ICCD or EMCCD with low illumination imaging capability.

5. The method for measuring 3D ice shape in an icing wind tunnel based on laser-induced fluorescence according to claim 1, wherein: During the freezing process, a fluorescent dye is added to the freezing water; the fluorescent dye can emit fluorescence under the induction of laser.

6. The method for measuring 3D ice shape in an icing wind tunnel based on laser-induced fluorescence according to claim 1, wherein: During the icing wind tunnel test, an ice shape scan was performed at a time interval of t0. During the ice shape scan, in order to avoid the influence of water vapor on the imaging quality during the test, the wind tunnel stopped spraying and measurements were performed only after there were no ice particles in the airflow.

7. The method for measuring 3D ice shape in an icing wind tunnel based on laser-induced fluorescence according to claim 5, wherein: Select fluorescent dyes with smaller liquid surface tension to reduce the interference and influence of fluorescent dyes on the physical process of freezing.

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