Schlieren observation system and schlieren measurement method

Abstract

The embodiment of the invention provides a schlieren observation system and a schlieren measurement method. The system comprises a light source assembly; the first reflecting mirror and the second reflecting mirror are oppositely arranged at an interval, and the first reflecting mirror is configured to reflect light rays emitted by the light source assembly and form parallel light rays penetrating through a test flow field between the first reflecting mirror and the second reflecting mirror; and the schlieren imaging structure is arranged corresponding to the second reflector, and the schlieren imaging structure is configured to perform schlieren imaging according to the parallel light rays reflected by the second reflector. According to the invention, a combined scheme of the light source assembly, the first reflector and the second reflector is adopted, so that a traditional expensive laser light source and an achromatic lens can be replaced, and the system cost can be remarkably reduced.

Description

Technical Field

[0001] The embodiments disclosed herein belong to the field of schlieren observation technology, specifically relating to a schlieren observation system and a schlieren measurement method. Background Technology

[0002] Schlieren technology is a relatively traditional optical diagnostic method, mainly used in motion displays.

[0003] Currently, researchers primarily observe flashback in jet premixed flames using direct camera observation. When flashback occurs in a jet premixed flame, the flame root detaches from the nozzle and propagates upstream of the nozzle. The changes that occur within the jet flame and combustion flow field during this process cannot be directly observed with the naked eye or a camera. While commercially available and relatively mature technologies exist for observing the jet flame and combustion flow field using schlieren systems, they are expensive.

[0004] Therefore, there is an urgent need for a new schlieren observation system that can be used to observe and study the flashback of turbulent jet premixed flames, and to determine the flashback location and analyze the flashback mechanism. Summary of the Invention

[0005] The embodiments disclosed herein are intended to at least address one of the technical problems existing in the prior art, and to provide a schlieren observation system and a schlieren measurement method.

[0006] A first aspect of the embodiments of this disclosure provides a schlieren observation system, comprising:

[0007] Light source components;

[0008] A first reflector and a second reflector are arranged at a relative interval. The first reflector is configured to reflect the light emitted by the light source assembly and form parallel light rays that pass through the test flow field between the first reflector and the second reflector.

[0009] A schlieren imaging structure is provided corresponding to the second reflector, and the schlieren imaging structure is configured to perform schlieren imaging based on parallel light rays reflected by the second reflector.

[0010] Optionally, the first reflector may include a concave spherical reflector.

[0011] Optionally, the second reflector may include a concave spherical reflector.

[0012] Optionally, the light source assembly, the first reflector, the second reflector, and the schlieren imaging structure together constitute a Z-shaped optical path reflection structure.

[0013] Optionally, the schlieren imaging structure includes a plane mirror disposed on the reflection path of the second mirror, and a knife edge disposed on the light propagation path between the plane mirror and the second mirror. The knife edge is configured to partially block the parallel light rays reflected by the second mirror, so as to form a schlieren image with uneven brightness on the plane mirror.

[0014] Optionally, the light source assembly includes LED beads and a light shield covering the LED beads, the light shield having a light-emitting hole for forming a point light source.

[0015] Optionally, the blade may include a razor blade.

[0016] Furthermore, it also includes: an image recording device, which is configured correspondingly to the schlieren imaging structure, and the image recording device is used to receive and record the schlieren image of the schlieren imaging structure.

[0017] Optionally, the image recording device includes a high-speed camera.

[0018] A second aspect of the embodiments of this disclosure provides a schlieren measurement method, the method being implemented according to the schlieren observation system described above, comprising:

[0019] The point light source of the light source assembly is reflected by the first reflector to form parallel light rays that pass through the test flow field;

[0020] Parallel light rays are reflected onto the schlieren imaging structure using a second mirror;

[0021] The parallel light rays reflected by the second mirror are received by the schlieren imaging structure and schlieren imaging is performed.

[0022] The beneficial effects of the embodiments of this disclosure include:

[0023] In this invention, a combination of a light source component, a first reflector, and a second reflector is used, which can replace traditional expensive laser light sources and achromatic lenses, and can significantly reduce system costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a schlieren observation system according to an embodiment of the present disclosure;

[0025] Figure 2 This is a schematic flowchart of a schlieren measurement method according to an embodiment of the present disclosure;

[0026] Figure 3 This is a schematic diagram of the tempering process of a turbulent jet premixed flame according to an embodiment of the present disclosure;

[0027] Figure 4This is a schematic diagram of a schlieren image of the high-temperature flow field near the nozzle during the tempering process of a turbulent jet premixed flame according to an embodiment of the present disclosure.

[0028] In the figure, 1 is the light source assembly; 2 is the first reflector; 3 is the second reflector; 4 is the schlieren imaging structure; 5 is the image recording device; 6 is the light ray; 7 is the test flow field; 8 is the flame; 41 is the plane mirror; and 42 is the knife edge. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] The embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. The detailed descriptions and accompanying drawings of the following embodiments are used to exemplarily illustrate the principles of this application, but should not be used to limit the scope of this application; that is, this application is not limited to the described embodiments. In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicating orientation or positional relationships are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. "Vertical" is not strictly vertical, but within the allowable error range. "Parallel" is not strictly parallel, but within the allowable error range.

[0031] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application depending on the specific circumstances.

[0032] like Figure 1 As shown, a schlieren observation system includes a light source assembly 1, a first reflector 2 and a second reflector 3 arranged at relative intervals, and a schlieren imaging structure 4. The first reflector 2 is configured to reflect the light emitted by the light source assembly 1 and form parallel light rays 6 that pass through the test flow field 7 between the first reflector 2 and the second reflector 3.

[0033] The schlieren imaging structure 4 is configured to perform schlieren imaging based on the parallel light rays 6 reflected by the second mirror 3.

[0034] In this invention, the combination of light source component 1 + first reflector 2 + second reflector 3 can replace the traditional expensive laser light source and achromatic lens, which can significantly reduce the system cost.

[0035] In some embodiments, the first reflector 2 includes a concave spherical reflector.

[0036] In some embodiments, the second reflector 3 includes a concave spherical reflector.

[0037] In this invention, a concave spherical reflector is used, which can effectively replace the traditional expensive achromatic lens and significantly reduce the system cost.

[0038] In some embodiments, the light source assembly 1, the first reflector 2, the second reflector 3, and the schlieren imaging structure 4 together constitute a Z-shaped optical path reflection structure. The Z-shaped transmissive optical path configuration has the advantage of a compact structure, and compared to a straight optical path which requires a lens (easily introducing chromatic aberration), the reflective optical path uses a concave reflector to converge the light 6, effectively reducing chromatic aberration problems.

[0039] In some embodiments, the schlieren imaging structure 4 includes a plane mirror 41 disposed on the reflection path of the second mirror 3, and a blade 42 disposed on the light propagation path between the plane mirror 41 and the second mirror 3. The blade 42 is configured to partially block the parallel light rays 6 reflected by the second mirror 3 to form a schlieren image with uneven brightness on the plane mirror 41.

[0040] In some embodiments, the light source assembly 1 includes LED beads and a light shield covering the LED beads, the light shield having a light-emitting hole for forming a point light source.

[0041] In some embodiments, the blade 42 comprises a razor blade. Using a razor blade can effectively partially block the parallel light rays 6 reflected by the second reflector while also significantly reducing system costs.

[0042] In some embodiments, the schlieren observation system further includes an image recording device 5, which is configured corresponding to the schlieren imaging structure 4, and is used to receive and record the schlieren image of the schlieren imaging structure 4.

[0043] In some embodiments, the image recording device 5 includes a high-speed camera.

[0044] In this invention, the changes in the flame 8 and the combustion flow field during the tempering process cannot be observed by the naked eye or by a camera. The schlieren system of this patent can be used to observe the tempering process of the turbulent jet premixed flame 8, and determine the tempering location and analyze the tempering mechanism based on the observation results, while significantly reducing the system cost.

[0045] Specifically, this patent has developed its own schlieren system, such as... Figure 1 As shown, the system mainly includes an optical path and an image recording section, employing a "Z-shaped" optical path design. This transmissive optical path structure is compact and effectively reduces the chromatic aberration problem introduced by using ordinary lenses (biconvex or plano-convex lenses) in a linear optical path. The system mainly includes an LED light source assembly 1, a concave spherical reflector (including a first reflector 2 and a second reflector 3) with a diameter of approximately 108mm and a focal length of approximately 1143mm, a blade 42, a plane mirror 41, and a high-speed camera. The LED light source assembly 1 is made by encapsulating a 10W LED bead in a light shield and powered by two AA batteries. A light-emitting hole with a diameter of approximately 1mm is machined on the light shield corresponding to the center position of the LED bead to generate a point light source. The blade 42 is a common men's razor blade.

[0046] The principle of schlieren technology is as follows: light emitted from a point source reaches the first reflecting mirror 2, is reflected to form parallel light rays 6, and enters the test flow field 7. Due to the non-uniformity of density (or temperature) in the flow field, the parallel light rays 6 are deflected. The deflected light rays 6 are then converged on the blade edge 42 by the second reflecting mirror 3. Because the blade edge 42 partially blocks the light rays 6, a schlieren image with uneven brightness is displayed on the plane mirror 41. In other words, schlieren technology can clearly reveal the internal and external structures of cold turbulence and combustion flow fields that are invisible to the naked eye, which is of great importance for researchers to conduct further analysis.

[0047] Based on experimental observations, this patent uniformly divides the flashback process of the turbulent jet flame 8 into three stages: "before flashback," "during flashback," and "after flashback." The stage before flashback occurs is called "before flashback." When the root of the flame 8 begins to propagate upstream of the nozzle, flashback is considered to have occurred. The flashback stage ends when the flame 8 completely enters the pipe or stops propagating into the pipe; this process is called "during flashback." The stage after flashback ends is called "after flashback."

[0048] Figure 3The image shows the flashback process of a typical hydrogen-rich fuel gas turbulent jet premixed flame 8. At t = 4 ms, the root of flame 8, attached near the burner nozzle, begins to move along one side of the tube wall into the tube, at which point flashback occurs. Note that flashback begins at the root of the right-hand flame 8, indicating a higher propagation velocity. From t = 4 to 24 ms, flame 8 can be seen gradually propagating upstream along the right side of the tube wall. After t > 24 ms, flame 8 exhibits both oscillation and rotation (flipping inwards or outwards) during flashback. At t = 52 ms, flame 8 completely propagates back into the tube, ending the flashback stage. The period after t > 52 ms represents the post-flashback stage, during which flame 8 oscillates continuously at any position within the tube.

[0049] Figure 4 The images show the schlieren images of the high-temperature flow field downstream of the nozzle before and after tempering. From left to right, they represent the pre-tempering, during-tempering, and post-tempering stages, respectively. A significant temperature gradient is observed near the nozzle, as marked by the red circles in the images. It can be seen that in the pre-tempering and during-tempering stages, distinct schlieren fringes appear as the jet leaves the nozzle. The fringes correspond to density changes, indicating a non-uniform temperature field in this region. The schlieren images can clearly distinguish the tempering phenomenon and its location (see [reference]). Figure 4 (As indicated by the yellow arrow), during flashback, the stripes near the nozzle will show a certain angle of deflection or a significant reduction in stripes on one side. As flashback occurs, the stripes near the nozzle can be seen gradually entering the pipe. During flashback, the high-temperature flow field downstream of the nozzle changes significantly. Before flashback, the downstream high-temperature flow field contains a few large-scale vortex structures, and the overall turbulence level is low. As flashback occurs, a large number of smaller-scale vortex structures gradually appear in the downstream high-temperature flow field, especially in the stage after flashback, indicating a significant increase in turbulence. This is closely related to the oscillation and rotation phenomena of flame 8 during flashback.

[0050] By comparing schlieren images and direct-shot images, it was found that the "tempering" stage, from the initiation to the end of tempering, as determined by schlieren images, is basically consistent with the results obtained from direct-shot images. Therefore, significant changes in the high-temperature flow field near the nozzle and downstream can also be used as a method to determine the tempering process.

[0051] refer to Figure 2 A second aspect of the embodiments of this disclosure provides a schlieren measurement method, the method being implemented according to the schlieren observation system described above, comprising:

[0052] S101. The point light source of the light source assembly 1 is reflected by the first reflector 2 to form a parallel light ray 6 that passes through the test flow field 7.

[0053] S102. The parallel light ray 6 is reflected to the schlieren imaging structure 4 using the second reflecting mirror 3.

[0054] S103. The parallel light rays 6 reflected by the second reflector 3 are received through the schlieren imaging structure 4 and schlieren imaging is performed.

[0055] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A schlieren observation system, characterized in that, include: Light source components; A first reflector and a second reflector are arranged at a relative interval. The first reflector is configured to reflect the light emitted by the light source assembly and form parallel light rays that pass through the test flow field between the first reflector and the second reflector. A schlieren imaging structure is provided corresponding to the second reflector, and the schlieren imaging structure is configured to perform schlieren imaging based on parallel light rays reflected by the second reflector.

2. The schlieren observation system according to claim 1, characterized in that, The first reflecting mirror includes a concave spherical reflecting mirror.

3. The schlieren observation system according to claim 1, characterized in that, The second reflector includes a concave spherical reflector.

4. The schlieren observation system according to claim 1, characterized in that, The light source assembly, the first reflector, the second reflector, and the schlieren imaging structure together constitute a Z-shaped optical path reflection structure.

5. The schlieren observation system according to claim 1, characterized in that, The schlieren imaging structure includes a plane mirror disposed on the reflection path of the second mirror, and a knife edge disposed on the light propagation path between the plane mirror and the second mirror. The knife edge is configured to partially block the parallel light rays reflected by the second mirror, so as to form a schlieren image with uneven brightness on the plane mirror.

6. The schlieren observation system according to claim 1, characterized in that, The light source assembly includes LED beads and a light shield covering the LED beads, the light shield having a light-emitting hole for forming a point light source.

7. The schlieren observation system according to claim 5, characterized in that, The blade includes a razor blade.

8. The schlieren observation system according to claim 1, characterized in that, Also includes: An image recording device is provided corresponding to the schlieren imaging structure, and the image recording device is used to receive and record the schlieren image of the schlieren imaging structure.

9. The schlieren observation system according to claim 8, characterized in that, The image recording device includes a high-speed camera.

10. A schlieren measurement method, wherein the method is implemented using the schlieren observation system according to any one of claims 1-9, characterized in that, include: The point light source of the light source assembly is reflected by the first reflector to form parallel light rays that pass through the test flow field; Parallel light rays are reflected onto the schlieren imaging structure using a second mirror; The parallel light rays reflected by the second mirror are received by the schlieren imaging structure and schlieren imaging is performed.

Images