A multi-layer light source imaging system and method for improving background uniformity of flow field images

Abstract

The present invention discloses a multi-layer light source imaging system and method for improving the uniformity of the background of a flow field image, comprising: a light source transmitting module, a focusing lens, a knife-edge grid module, an imaging screen and an image receiving device, wherein the light source transmitting module comprises: a matrix light source I formed by splicing a plurality of dot matrix light sources I, and a matrix light source II arranged between the splicing gaps of the dot matrix light sources I to form a multi-layer light source with the matrix light source I in space. The present invention adopts a multi-layer light source and an imaging system, adds a light source on another plane corresponding to the light source shielding place, and adopts a multi-layer knife-edge grid module at the imaging position, wherein the knife edges of different planes of the multi-layer knife-edge grid module correspond to light source images of different planes, and ensures that the light source images of different planes are not interfered by the light source images of another plane, thereby improving the uniformity of the background of the schlieren image, and the information of the entire flow field will not be lost.

Description

Technical Field

[0001] The present invention relates to an imaging system, and more specifically, to a multi-layer light source imaging system and method for improving the background uniformity of flow field images. Background Art

[0002] Flow field display technology is one of the effective test technologies in experimental fluid mechanics. It is one of the important means to obtain test data in air flow tests and occupies an important position in test technology. Because the fluids in such tests are mostly transparent media, in order to clearly understand the movement of the fluid, it is necessary to provide a technology that can make the flow visible, which is the flow field display technology. Flow field display technology mainly includes three categories. The first category includes all external material technologies. The external materials must be visible. If the particles of the constituent materials are small enough, it can be considered that the movement of these particles is consistent with the fluid in terms of speed direction and size. Therefore, this display is an indirect method because what is seen is the movement of the external material, not the fluid itself. Since the thermodynamic properties of the external material and the thermodynamic properties of the fluid are usually different, and the change of the thermodynamic state causes relaxation, especially the difference in the mechanical movement of the fluid and the external material, this type of flow field display technology is mainly used in the flow field display at a lower speed. The second type of flow field display technology is based on the characteristic that the density of the fluid changes in the compressible flow field. After the light beam passes through the flow field, it will be deflected according to the density change. The deflected light beam will cause the color or brightness of the photosensitive medium where the light beam passing through the flow field is located to change. If the light beam is not deflected, the image background obtained through the photosensitive medium will be relatively uniform in the ideal situation. In this way, a slight disturbance of the light beam will show the flow field structure characteristics of the test area from the color or brightness change. The third type of flow field technology is a combination of the above two principles in some way, but the external substance injected into the flow field is energy, such as heat energy or discharge energy, and sometimes optical methods are needed to distinguish them from the rest of the fluid. In another case, the released energy is so high that the marked fluid element becomes self-luminous, so it can be directly observed. This method is often used for low-density flow. This technology is not a disturbance-free method because it affects the original flow to a greater or lesser extent depending on the amount of released energy.

[0003] The characteristics of the above three flow field display technologies show that the second type of flow field display technology is more widely used in practice. This type of flow field display technology mainly adopts the shadow or schlieren technology of the "Z"-shaped structure. For example, most domestic wind tunnels are basically equipped with this type of flow field display equipment. The optical elements that determine the size of the test field of view in the "Z"-shaped structure schlieren are mainly collimating spherical reflectors (or lenses) and imaging spherical reflectors (or lenses). However, as the aperture increases, the difficulty of material production and processing of such optical elements increases significantly, and the corresponding cost increases exponentially. When the aperture increases to 800mm (the flow field test field corresponds to 800mm), there are great risks in the material production and processing of such optical elements that meet the flow field requirements. The material aspect is mainly manifested in uniformity and stress streaks, and the processing aspect is mainly manifested in surface accuracy, as well as the deformation of the material caused by its own weight and temperature during the later installation and use. Therefore, this flow field display technology is difficult to achieve when the field of view is greater than 800mm.

[0004] In order to meet the requirements of large field of view flow field display technology, particle image velocimetry (PIV) technology and background schlieren (BOS) technology have been developed at home and abroad. However, both technologies require image processing to obtain the flow field structure, which leads to uncertainty in the obtained flow field structure due to the non-uniqueness of boundary parameters during image processing. In addition, PIV technology is mainly used in flow fields with lower speeds due to particle tracking, while BOS technology also has reasons such as low sensitivity and image resolution. Therefore, in many flow field displays, it is still expected to use flow field display technology that can directly display the flow field structure.

[0005] Therefore, a focused schlieren technology is proposed to realize large-field flow display. However, this technology requires a Fresnel lens optical element. This type of Fresnel lens can only produce products with a maximum diameter of 2m in China, and when it is above 1m, its groove spacing and depth and other quality aspects can no longer meet the requirements of focused schlieren imaging. According to the requirements of conical optical path imaging, the maximum field of view of this technology is about Φ500mm. Therefore, a focused schlieren technology based on light source splicing is proposed. This technology uses a spliced ​​larger-sized matrix light source (referred to as a large matrix light source, and the corresponding knife edge is called a large knife edge grid) to replace the light source and Fresnel lens in the conventional focused schlieren technology. Because the size of the spliced ​​large matrix light source can be realized from several meters to tens of meters or even larger, the corresponding flow field display size can easily be realized from several meters to hundreds of meters. This technology solves the problem of large-field flow display. However, large-field schlieren usually require a large transparent window to isolate the test area and the flow field display system. This window can satisfy the requirement of drawing a certain vacuum in the test area and prevent interference with the flow field display system. However, the glass for larger windows is difficult to manufacture, and smaller window glasses are usually used for splicing. Each piece of glass needs to be connected with a flange. This opaque flange will block part of the light beam from the large matrix light source, causing no light beam to pass through the flow field and enter the focusing lens in some parts of the test area, making it impossible to display the flow field in some parts of the test area, and the black shadow of the flange appears in the flow field image.

[0006] For example, patent application number CN201810209170.9 discloses a direct schlieren imaging system for flow display. In this imaging system, the opaque connecting parts between the source grids will block part of the light beams in the matrix light source I from passing through, causing no light beams to pass through the flow field and enter the focusing lens in some places in the test area, making it impossible to display the flow field in some positions in the test area. The connecting parts appear as black shadows in the flow field image, affecting the overall imaging quality. Summary of the invention

[0007] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0008] In order to achieve these objects and other advantages of the present invention, a multi-layer light source imaging system for improving the background uniformity of a flow field image is provided, comprising: a light source emission module for forming a light beam irradiated to a test area;

[0009] a focusing lens located behind the test area and used to image the test area;

[0010] A knife-edge grid module located on the optical path of the focusing lens and placed at the imaging surface of the light source emitting module, and used for cutting multiple dot matrix light source images of the light source emitting module;

[0011] An imaging screen located in the optical path of the knife-edge grid module and placed at the imaging surface position of the test area for receiving the flow field image;

[0012] An image receiving device is located behind the imaging screen and is used to record the flow field image of the test area. The light source emitting module includes: a matrix light source I formed by splicing a plurality of dot matrix light sources I, and a matrix light source II which is arranged between the splicing gaps of the dot matrix light sources I and is located on different planes of the matrix light source I to form a multi-layer light source with the matrix light source I in space.

[0013] Preferably, the matrix light source II comprises: a support grid arranged behind the matrix light source I and matching the splicing gaps of the plurality of dot matrix light sources I, a high temperature window glass arranged in the grid, and a plurality of dot matrix light sources II uniformly arranged on the front face of the grid;

[0014] Wherein, the number of the dot matrix light sources II is less than the number of the dot matrix light sources I.

[0015] Preferably, the knife-edge grating module comprises: a knife-edge grating I arranged on the optical path of the focusing lens and used to divide the light source image formed by the matrix light source I on the test area;

[0016] The knife-edge grating II is arranged behind the knife-edge grating I on the optical path of the focusing lens and is used to divide the light source image formed by the matrix light source II on the test area.

[0017] Preferably, the imaging screen between the knife-edge grid module and the image receiving device can be replaced by a field lens.

[0018] Preferably, the imaging screen comprises: two pieces of optical glass, a holographic film disposed between the optical glasses;

[0019] Wherein, the surface of the optical glass is coated with an anti-reflection film that is consistent with the wavelength of the light source of the light source emission module.

[0020] Preferably, the matrix light source I is formed by splicing a plurality of low-power LED light sources.

[0021] An imaging method, applied to the multi-layer light source imaging system for improving the background uniformity of flow field images, comprises the following steps:

[0022] Matrix light source I and matrix light source II are arranged in space to form a multi-layer light source to illuminate the test area. The focusing lens images the matrix light source I and the matrix light source II on the plane where the knife-edge grid I and the knife-edge grid II are located respectively. The knife-edge grid I and the knife-edge grid II cut the light source images where the matrix light source II and the matrix light source II are located respectively. At the same time, the focusing lens images the test area on an imaging screen or a field lens. The image receiving device images the imaging screen or the field lens to obtain a flow field image of the test area.

[0023] Preferably, the matrix light source I and the matrix light source II are spatially arranged in the following manner:

[0024] Firstly, a focusing lens is used to image two matrix light sources at different object distances to form corresponding diffuse spots, and the imaging magnification of each matrix light source is calculated.

[0025] Then, according to the lens imaging relationship, the minimum distance between the lamp beads at the edges of the two matrix light sources is inferred. The minimum distance is determined by dividing half of the smaller diffuse spot size by the imaging magnification of the corresponding matrix light source II, and dividing half of the larger diffuse spot size by the imaging magnification of the corresponding matrix light source I, and taking the larger value of the two calculation results;

[0026] Finally, the two matrix light sources are arranged according to the determined minimum distance.

[0027] The present invention includes at least the following beneficial effects: adopting a multi-layer light source and imaging system, adding a light source on another plane corresponding to the place where the light source is blocked, and adopting a multi-layer knife-edge grid at the imaging position, the knife edges of different planes of the multi-layer knife-edge grid correspond to the light source images of different planes, and ensure that the light source images of different planes will not be interfered by the light source image of another plane, thereby improving the uniformity of the background of the schlieren image, and the information of the entire flow field will not be lost.

[0028] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a light path arrangement diagram of the imaging system of the present invention;

[0030] Figure 2 It is a schematic diagram of the structure of the matrix light source II of the present invention;

[0031] Figure 3 This is a schematic diagram of optical path imaging when the imaging screen is used in the present invention;

[0032] Figure 4 This is a schematic diagram of optical path imaging when the field lens is used in the present invention;

[0033] Figure 5 It is a structural schematic diagram of the imaging screen of the present invention;

[0034] Figure 6 This is the relationship diagram between the knife-edge grid I cutting the matrix light source image I and the matrix light source image II;

[0035] Figure 7 This is the relationship diagram between the knife-edge grating II cutting the matrix light source image I and the matrix light source image II;

[0036] Figure 8 It is a light path structure diagram of the matrix light source image I and the matrix light source image II formed by the focusing lens;

[0037] Fig. 9 The flow field image is a shadow produced by the blocking of the support grid in the existing imaging system.

[0038] Figure numerals: 1. Matrix light source I, 101. Lamp bead I, 1011. Lamp bead image point I, 1012. Diffuse spot I, 2. Matrix light source II, 201. Lamp bead II, 2011. Lamp bead image point II, 2012. Diffuse spot II, 21. Support grid, 22. Window glass, 23. Dot matrix light source II, 3. Test area, 4. Focusing lens, 5. Knife-edge grid module, 6. Knife-edge grid I, 7. Knife-edge grid II, 8. Imaging screen, 81. Optical glass, 82. Holographic film, 9. Field lens, 10. Matrix light source image I, 11. Matrix light source image II, 12. Image receiving device. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0040] Figure 1-Figure 5 A multi-layer light source imaging system for improving the background uniformity of a flow field image according to the present invention is shown, comprising: a light source emission module for forming a light beam irradiated to a test area 3;

[0041] A focusing lens 4 located behind the test area 3 and used for imaging the test area 3;

[0042] A knife-edge grid module located on the optical path of the focusing lens 4 and placed at the imaging surface of the light source emitting module, and used for cutting multiple dot matrix light source images of the light source emitting module;

[0043] An imaging screen 8 located in the optical path of the knife-edge grid module and placed at the imaging surface position of the test area 3 for receiving the flow field image;

[0044] An image receiving device 12 is located behind the imaging screen 8 and is used to record the flow field image of the test area 3. The light source emitting module includes: a matrix light source Ⅰ1 formed by splicing a plurality of dot matrix light sources Ⅰ, a matrix light source Ⅱ2 which is arranged between the splicing gaps of the dot matrix light sources Ⅰ and is located on different planes of the matrix light source Ⅰ1 to form a multi-layer light source with the matrix light source Ⅰ1 in space.

[0045] In the conventional flow field imaging process, the shadow of the support grid 21 exists in the schlieren image, such as Fig. 9As shown, the image background is uneven, and part of the flow field information is lost due to shadows. The present invention uses multiple dot matrix light sources I such as LED light sources to be spliced ​​into a larger-sized matrix light source I1 according to certain interval requirements. After the light beam emitted by the matrix light source I1 is irradiated to the test area 3, the light beam of part of the light beam in the matrix light source passing through the test area 3 is collected by the focusing lens 4 in the imaging system. In order to improve the utilization rate of the light source, a condenser is placed in front of each LED light source to reduce the divergence angle of each lamp bead, so that more light beams can be irradiated to the test area 3 and enter the focusing lens 4. In the light beam irradiation path from the matrix light source I1 to the test area 3, non-transparent objects such as the window flange or the support grid 21 will block the light beam from irradiating the test area 3 (at the same time, the window glass 22 on the support grid ensures that the light beam can enter the test area 3, and the window glass 22 is made of high temperature resistant material, so that the window glass 22 can work in the flow field for a long time), and no light beam passes through and enters the focusing lens 4 at some positions of the test area 3. After the light beam passes through the test area 3 and the focusing lens 4, the knife-edge grid Ⅰ6 corresponding to the matrix light source Ⅰ1 cuts each dot matrix light source image to form a schlieren effect, that is, because the density disturbance causes the light beam to be deflected, the light beam that should pass through the knife-edge grid Ⅰ6 cannot pass because of the deflection, and conversely, the light beam that should not pass through the knife-edge grid Ⅰ6 can pass because of the deflection, then the flow field image will change from light to dark, thereby showing the flow field structure of the test area 3. However, due to the obstruction, part of the test area 3 will not have a light beam entering the focusing lens 4, so that this position will be imaged as a black shadow on the flow field image, and the flow field information of this place cannot be displayed. This black shadow not only affects the overall imaging effect, causing the image to be unsightly, but also the flow field structure information where the black shadow is located is lost. A plurality of dot matrix light sources Ⅱ23 are added to the front end surface of the support grid 21 or the window flange to form a matrix light source Ⅱ2, so as to form a multi-layer light source with the matrix light source Ⅰ1 in space. This matrix light source Ⅱ2 realizes the supplementary illumination of the light beam for the test area 3 where no light beam passes through and enters the focusing lens 4. The present invention adopts a multi-layer light source and imaging system, adds a light source on another plane corresponding to the place where the light source is blocked, and adopts a multi-layer knife-edge grid module 5 at the imaging position. The blades of different planes of the multi-layer knife-edge grid module 5 correspond to the light source images of different planes, and ensure that the light source images of different planes are not interfered by the light source image of another plane, thereby improving the uniformity of the background of the schlieren image, and the information of the entire flow field will not be lost.

[0046] In order to realize the flow field display in the field of view of 2.4m*1.2m area, the size of the matrix light source I1 is 4m*2m, 49 dot matrix light sources II23 are arranged on the front end face of the spliced ​​support grid 21, and the focusing lens 4 with a diameter of 350mm images the test area 3 on the imaging screen 8. The knife-edge grid I6 and the knife-edge grid II7 cut the images of the matrix light source I1 and the matrix light source respectively, and the image receiving device 12 shoots the imaging screen 8 to obtain the flow field image of the test area 3.

[0047] At the same time, more than 20,000 1W green LED light sources with a spacing of 16mm are used and spliced ​​into two 2m*2m matrix light sources Ⅰ1. The color spectrum and power of the LED light source in the matrix light source Ⅱ2 are consistent with the LED light source in the matrix light source Ⅰ1, but the spacing is 15mm to ensure that the image obtained by the matrix light source Ⅱ2 through the focusing lens 4 does not affect the image of the matrix light source Ⅰ1.

[0048] When the imaging screen 8 is replaced by the field lens 9, the flow field image is directly imaged on the camera target surface of the image receiving device 12, thereby improving the light beam collection efficiency. The imaging screen 8 made of the holographic film 82 can make the brightness and uniformity of the flow field images at different positions of the imaging screen 8 relatively consistent for the image receiving device 12. The imaging screen 8 uses optical glass 81 and optical glass 81 to clamp the holographic film 82, thereby keeping the holographic film 82 flat. The surfaces of the optical glass 81 and optical glass 81 are coated with an anti-reflection film consistent with the wavelength of the light source, thereby achieving efficient passage of the light beam.

[0049] An imaging method, applied to the multi-layer light source imaging system for improving the background uniformity of flow field images, comprises the following steps:

[0050] The matrix light source Ⅰ1 and the matrix light source Ⅱ2 are arranged in space to form a multi-layer light source to illuminate the test area 3. The focusing lens 4 images the matrix light source Ⅰ1 and the matrix light source Ⅱ2 on the plane positions where the knife-edge grid Ⅰ6 and the knife-edge grid Ⅱ7 are located respectively. The knife-edge grid Ⅰ6 and the knife-edge grid Ⅱ7 cut the light source images where the matrix light source Ⅱ2 and the matrix light source Ⅱ2 are located respectively. At the same time, the focusing lens 4 images the test area 3 on the imaging screen 8 or near the field lens 9. The image receiving device 12 images the imaging screen 8 or the field lens 9 to obtain the flow field image of the test area 3.

[0051] At the same time, in the spatial layout of matrix light source Ⅰ1 and matrix light source Ⅱ2, according to the lens imaging formula (where u is the object distance, v is the image distance, and f is the focal length), and the principle of similar triangles, we can infer the distance relationship between the lamp beads at the edges of the two matrix light sources. The smaller diffuse spot Ⅱ2012 is half the size R2 (corresponding to the diffuse spot Ⅱ22012 of the matrix light source Ⅱ2), divided by the imaging magnification M2 of the matrix light source Ⅱ2, and we get , which represents a distance measure related to the matrix light source II2 in the material space. Similarly, half of the size of the larger diffuse spot I1012, R1 (corresponding to the diffuse spot of the matrix light source I1), divided by the imaging magnification M1 of the matrix light source I1, is obtained .

[0052] The larger value of d1 and d2 is taken as the minimum distance between the lamp beads at the edges of the two matrix light sources. This is because if the distance between the lamp beads at the edges of the two matrix light sources is less than this minimum value, then during the imaging process, the images (diffuse spots) corresponding to the two matrix light sources will interfere with each other, resulting in shadows on the imaging screen 8, affecting the background uniformity and imaging quality of the flow field image.

[0053] Embodiment 1:

[0054] Figure 6 - Figure 8 The optical path structure diagram of the matrix light source Ⅰ1 and the matrix light source Ⅱ2 is imaged by the focusing lens 4. A certain lamp bead Ⅰ101 in the matrix light source Ⅰ1 is imaged on the plane where the knife-edge grid Ⅰ6 is located through the focusing lens 4. The lamp bead image point Ⅰ1011 corresponding to the lamp bead Ⅰ101 in the matrix light source image Ⅰ10 located on the same plane of the knife-edge grid Ⅰ6 is focused, but on the plane where the knife-edge grid Ⅱ7 is located, it is a blurred diffuse spot Ⅰ1012. Similarly, a certain lamp bead Ⅱ201 in the matrix light source Ⅱ2 is imaged on the plane where the knife-edge grid Ⅱ7 is located through the focusing lens 4. The lamp bead image point Ⅱ2011 corresponding to the lamp bead Ⅱ201 in the matrix light source image Ⅱ11 located on the same plane of the knife-edge grid Ⅱ7 is focused, but on the plane where the knife-edge grid Ⅰ6 is located, it is a blurred diffuse spot Ⅱ2012. When the diffuse spot I1012 diffuses to the position of the lamp bead image point II2011, it will be cut by the knife-edge grid II7, and the matrix light source I1 will produce a shadow on the imaging screen 8; similarly, when the diffuse spot II2012 diffuses to the position of the lamp bead image point I1011, it will be cut by the knife-edge grid I6, and a shadow will also be produced on the imaging screen 8. These shadows will cause the flow field background to be uneven and affect the imaging effect. The size of the diffuse spot I1012 and the diffuse spot II2012 is related to the focal length and aperture of the focusing lens 4 and the distance of the matrix light source II2 relative to the focusing lens 4.

[0055] When the focal length of focusing lens 4 is 800mm, the aperture is 300mm, the object distance of matrix light source Ⅰ1 is 3m, and the object distance of matrix light source Ⅱ2 is 2.6m, according to the above-mentioned lens imaging relationship, the corresponding diffuse spot Ⅰ1012 and diffuse spot Ⅱ2012 can be calculated by substituting them into the lens imaging formula to be 32.5mm and 29.3mm respectively, and the imaging magnification of matrix light source Ⅰ1 and matrix light source Ⅱ2 is 0.36 times and 0.5 times respectively. In order to ensure that the two sets of knife-edge grids do not cut non-corresponding light source images, according to the lens imaging relationship, it can be inferred that the minimum distance between the lamp beads at the edge of matrix light source Ⅱ2 and the lamp beads at the edge of matrix light source Ⅰ1 is 29.3 / 2 / 0.36=40.7(mm), and the minimum distance between the lamp beads at the edge of matrix light source Ⅰ1 and the lamp beads at the edge of matrix light source Ⅱ2 is 32.5 / 2 / 0.5=32.5(mm). The maximum value of 40.7mm between 40.7mm and 32.5mm is 40.7mm, which is the minimum distance between the edge of matrix light source Ⅰ1 and the edge of matrix light source Ⅱ2, to ensure that the two sets of knife-edge grids will not cut non-corresponding light source images. This setting can effectively avoid mutual interference due to diffusion of diffuse spots, reduce the possibility of shadows on the imaging screen 8, thereby preventing uneven flow field background and improving imaging effects.

[0056] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A multi-layer light source imaging system for improving the background uniformity of a flow field image, comprising: A light source emission module for forming a light beam to irradiate a test area; a focusing lens located behind the test area and used to image the test area; A knife-edge grid module located on the optical path of the focusing lens and placed at the imaging surface of the light source emitting module, and used for cutting multiple dot matrix light source images of the light source emitting module; An imaging screen located in the optical path of the knife-edge grid module and placed at the imaging surface position of the test area for receiving the flow field image; An image receiving device located behind the imaging screen and used to record the flow field image of the test area is characterized in that the light source transmitting module includes: a matrix light source I formed by splicing a plurality of dot matrix light sources I, a matrix light source II arranged between the splicing gaps of the dot matrix light sources I and located on different planes of the matrix light source I to form a multi-layer light source with the matrix light source I in space; Wherein, the knife-edge grid module comprises: a knife-edge grid I arranged on the optical path of the focusing lens and used to divide the light source image formed by the matrix light source I on the test area; The knife-edge grating II is arranged behind the knife-edge grating I on the optical path of the focusing lens and is used to divide the light source image formed by the matrix light source II on the test area; The imaging screen between the knife-edge grid module and the image receiving device can be replaced by a field lens.

2. The multi-layer light source imaging system for improving the background uniformity of flow field images according to claim 1, characterized in that: The matrix light source II comprises: a support grid arranged behind the matrix light source I and matching the splicing gaps of the plurality of dot matrix light sources I, a high temperature resistant window glass arranged in the grid, and a plurality of dot matrix light sources II evenly arranged on the front face of the grid; Wherein, the number of the dot matrix light sources II is less than the number of the dot matrix light sources I.

3. The multi-layer light source imaging system for improving the background uniformity of flow field images according to claim 1, characterized in that: The imaging screen comprises: two pieces of optical glass, and a holographic film arranged between the optical glasses; Wherein, the surface of the optical glass is coated with an anti-reflection film that is consistent with the wavelength of the light source of the light source emission module.

4. The multi-layer light source imaging system for improving the background uniformity of flow field images according to claim 1, characterized in that: The matrix light source I is formed by splicing a plurality of low-power LED light sources.

5. An imaging method, characterized in that: The multi-layer light source imaging system for improving the background uniformity of a flow field image as described in any one of claims 1 to 4 comprises the following steps: Matrix light source I and matrix light source II are arranged in space to form a multi-layer light source to illuminate the test area. The focusing lens images the matrix light source I and the matrix light source II on the plane positions where the knife-edge grid I and the knife-edge grid II are located respectively. The knife-edge grid I and the knife-edge grid II cut the light source images where the matrix light source II and the matrix light source II are located respectively. At the same time, the focusing lens images the test area on the imaging screen or at the position of the field lens attachment. The image receiving device images the imaging screen or in combination with the field lens, so as to obtain the flow field image of the test area.

6. The imaging method according to claim 5, characterized in that: The spatial layout of matrix light source I and matrix light source II is as follows: Firstly, a focusing lens is used to image two matrix light sources at different object distances to form corresponding diffuse spots, and the imaging magnification of each matrix light source is calculated. Then, according to the lens imaging relationship, the minimum distance between the lamp beads at the edges of the two matrix light sources is inferred. The minimum distance is determined by dividing half of the smaller diffuse spot size by the imaging magnification of the corresponding matrix light source II, and dividing half of the larger diffuse spot size by the imaging magnification of the corresponding matrix light source I, and taking the larger value of the two calculation results; Finally, the two matrix light sources are arranged according to the determined minimum distance.

Images