Schlieren system and observation method of flame transition process

Abstract

The embodiment of the invention provides a schlieren system and a flame transition process observation method. The system comprises a light source; the first schlieren mirror and the second schlieren mirror are oppositely arranged at an interval, and the first schlieren mirror is configured to reflect light rays emitted by the light source and form parallel light rays which penetrate through a test flow field between the first schlieren mirror and the second schlieren mirror and push jet flow diffusion flames; the schlieren imaging structure is arranged on a focusing path of the second schlieren mirror; wherein the second schlieren mirror is configured to focus the parallel light which is deflected due to density gradient in the test flow field to the schlieren imaging structure so as to generate a schlieren image capable of observing an intermittent breaking phenomenon in a jet transition process. By means of the schlieren system, the laminar flow and turbulent flow periodical alternating intermittent breaking phenomenon of pushing jet flow flames can be observed, whether flame jet flow enters the turbulent flow stage or not is determined according to disappearance of the intermittent breaking phenomenon of the jet flow in the schlieren image, and then the change characteristics of the flames and the interior of a combustion flow field are achieved.

Description

Technical Field

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

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

[0003] Currently, experimental techniques applied to the transition process of a propulsive jet diffusion flame to turbulence mainly rely on direct imaging with cameras or high-speed cameras. However, these techniques cannot capture the changes that occur inside the flame and combustion flow field during the transition process.

[0004] Therefore, there is an urgent need for a new schlieren system that can be used to observe the transition process of a propulsion jet diffused flame from laminar to turbulent flow, in order to capture the changing characteristics of the flame and combustion flow field during this process. Summary of the Invention

[0005] The embodiments disclosed herein aim to at least solve one of the technical problems existing in the prior art, and provide a schlieren system and a method for observing the flame transition process.

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

[0007] light source;

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

[0009] A schlieren imaging structure, wherein the schlieren imaging structure is disposed in the focusing path of the second schlieren mirror;

[0010] The second schlieren is configured to focus parallel light rays that are deflected by density gradients in the test flow field onto the schlieren imaging structure to generate a schlieren image that can observe the intermittent breakup phenomenon during jet transition.

[0011] Optionally, the first schlieren mirror includes a concave spherical mirror.

[0012] Optionally, the second schlieren mirror includes a concave spherical mirror.

[0013] Optionally, the light source, the first schlieren mirror, the second schlieren mirror, and the schlieren imaging structure together constitute a Z-shaped optical path reflection structure.

[0014] Optionally, the schlieren imaging structure includes a plane mirror disposed on the focusing path of the second schlieren mirror, and a knife edge disposed on the light propagation path between the plane mirror and the second schlieren mirror. The knife edge is configured to partially block the parallel light rays reflected by the second schlieren mirror, so as to form a schlieren image with uneven brightness on the plane mirror.

[0015] Optionally, the light source 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.

[0016] Optionally, the blade may include a razor blade.

[0017] Furthermore, it also includes: a schlieren image recording device, which is configured correspondingly to the schlieren imaging structure, and is used to receive and record the schlieren image of the schlieren imaging structure.

[0018] Optionally, the schlieren image recording device includes a high-speed camera.

[0019] A first aspect of the embodiments of this disclosure provides a method for observing the transition process of a push jet diffusion flame, the method being implemented according to the schlieren system described above, comprising:

[0020] Establish a laminar push jet diffusion flame in the test flow field region;

[0021] Schlieren images of the propulsion jet diffusion flame are recorded using a schlieren imaging structure.

[0022] Based on schlieren images, identify whether there is an intermittent breakup phenomenon with periodic alternation of laminar and turbulent flow;

[0023] When the intermittent fragmentation phenomenon disappears and the jet continues to exhibit turbulent characteristics, it is determined that the flame has entered the turbulent stage.

[0024] The beneficial effects of the embodiments of this disclosure include:

[0025] In this invention, the schlieren system of this application can be used to observe the intermittent breaking phenomenon of the periodic alternation between laminar and turbulent flow in the push jet flame, and the disappearance of the intermittent breaking phenomenon of the jet in the schlieren image can be used to determine whether the flame jet has entered the turbulent stage. In other words, the transition process of the push jet from laminar to turbulent flow is effectively observed, thereby capturing the changing characteristics of the flame and the combustion flow field during this process. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of a schlieren system according to an embodiment of the present disclosure;

[0027] Figure 2This is a flowchart illustrating a method for observing the transition process of a propellant jet diffusion flame according to an embodiment of this disclosure;

[0028] Figure 3 A dynamic feature diagram of a push jet according to an embodiment of this disclosure;

[0029] Figure 4 This is a dynamic characteristic diagram of the push jet at the transition end point of an embodiment of the present disclosure.

[0030] In the figure, 1 is the light source; 2 is the first schlieren mirror; 3 is the second schlieren mirror; 4 is the schlieren imaging structure; 5 is the schlieren 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

[0031] 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.

[0032] 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.

[0033] 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.

[0034] like Figure 1As shown, a schlieren system includes a light source 1, a first schlieren mirror 2 and a second schlieren mirror 3 arranged at relative intervals, and a schlieren imaging structure 4. The first schlieren mirror 2 is configured to reflect the light 6 emitted by the light source 1 and form parallel light rays that pass through the push jet diffuser flame 8 in the test flow field 7 between the first schlieren mirror 2 and the second schlieren mirror 3.

[0035] The schlieren imaging structure 4 is disposed in the focusing path of the second schlieren mirror 3. The second schlieren mirror 3 is configured to focus parallel light rays that are deflected by density gradient in the test flow field 7 onto the schlieren imaging structure 4 to generate a schlieren image that can observe the intermittent breakup phenomenon during the jet transition.

[0036] Specifically, the schlieren imaging structure 4 is configured to perform schlieren imaging on the transition process of the push jet diffusion flame 8 from laminar to turbulent flow based on the parallel light reflected by the second schlieren mirror 3, wherein the disappearance of the intermittent breakup phenomenon of the jet in the schlieren image determines whether the flame jet has entered the turbulent stage.

[0037] In this invention, the schlieren system of this application can be used to observe the intermittent breaking phenomenon of laminar and turbulent periodic alternation in the push jet flame, thus achieving effective observation of the transition process from laminar to turbulent flow in the push jet, thereby capturing the changing characteristics of the flame and combustion flow field during this process. Furthermore, the disappearance of the intermittent breaking phenomenon in the schlieren image can also determine whether the flame jet has entered the turbulent stage. Moreover, the use of a combination of a light source + a first schlieren mirror + a second schlieren mirror can replace traditional expensive laser light sources and achromatic lenses, significantly reducing system costs.

[0038] In some embodiments, the first schlieren 2 includes a concave spherical reflector.

[0039] In some embodiments, the second schlieren mirror 3 includes a concave spherical mirror.

[0040] In this invention, a concave spherical reflector is used, which can effectively replace the traditional expensive achromatic lens and significantly reduce the system cost.

[0041] In some embodiments, the light source 1, the first schlieren mirror 2, the second schlieren mirror 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 lenses (easily introducing chromatic aberration), the reflective optical path uses concave reflectors to converge the light rays 6, effectively reducing chromatic aberration problems.

[0042] In some embodiments, the schlieren imaging structure 4 includes a plane mirror 41 disposed on the focusing path of the second schlieren mirror 3, and a blade 42 disposed on the light propagation path between the plane mirror 41 and the second schlieren mirror 3. The blade 42 is configured to partially block the parallel light rays 6 reflected by the second schlieren mirror 3 to form a schlieren image with uneven brightness on the plane mirror 41.

[0043] In some embodiments, the light source 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.

[0044] 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 schlieren mirror while significantly reducing system costs.

[0045] In some embodiments, the schlieren system further includes a schlieren image recording device 5, which is configured correspondingly to the schlieren imaging structure 4, and is used to receive and record the schlieren image of the schlieren imaging structure 4.

[0046] In some embodiments, the schlieren image recording device 5 includes a high-speed camera.

[0047] 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 transition process of the push jet diffusion flame from laminar to turbulent flow, so as to capture the changing characteristics of the flame and the combustion flow field during this process.

[0048] Specifically, this patent has developed its own schlieren system, such as... Figure 1 As shown, the system mainly includes the optical path and 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 linear optical paths. The system mainly includes an LED light source 1, a concave spherical reflector (including a first schlieren mirror 2 and a second schlieren mirror 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 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.

[0049] The principle of schlieren technology is as follows: light emitted from a point source reaches the first schlieren 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 schlieren 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.

[0050] The transition process from laminar to turbulent flow in a propulsive jet diffusion flame was observed using the aforementioned schlieren system. The dynamic characteristics of jet development during this process are as follows: Figure 3 As shown, A represents the cold jet, and B represents the jet after ignition. It can be seen that under these conditions, both the cold jet and the jet after ignition exhibit intermittent breakup phenomena, meaning the flow sometimes exhibits laminar characteristics and sometimes turbulent characteristics with a consistent frequency. The pusher flame under these conditions possesses characteristics of both. However, it is worth noting that at the end of the transition phase, i.e., when the flame begins to enter the turbulent phase, this intermittent phenomenon disappears, and the jet ejected from the nozzle is in a turbulent state (see...). Figure 4 (A represents a cold jet, and B represents a turbulent jet). After the jet becomes turbulent (the intermittent breakup phenomenon disappears), it interacts directly with the flame, causing mixing and combustion to occur under turbulent conditions. Therefore, the disappearance of the intermittent breakup phenomenon in the jet can be used as a criterion for judging whether a propellant flame has transformed into a turbulent flame.

[0051] This schlieren system demonstrates that the flow during the transition of a jet-diffused flame exhibits both laminar and turbulent characteristics at a consistent frequency, while the flame itself displays characteristics of both. This finding is crucial for analyzing the interaction between the flame and the flow.

[0052] refer to Figure 2 A second aspect of the embodiments of this disclosure provides a method for observing the transition process of a push jet diffusion flame, the method being implemented according to the schlieren system described above, comprising:

[0053] S101. Establish a laminar push jet diffusion flame in the test flow field region.

[0054] S102. Record the schlieren image of the propulsion jet diffusion flame using a schlieren imaging structure.

[0055] S103. Identify the presence of intermittent breakup phenomena with periodic alternation of laminar and turbulent flow based on schlieren images.

[0056] S104. When the intermittent fragmentation phenomenon disappears and the jet continues to exhibit turbulent characteristics, it is determined that the flame has entered the turbulent stage.

[0057] 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 system, characterized in that, include: light source; A first schlieren and a second schlieren are arranged at a relative interval. The first schlieren is configured to reflect the light emitted by the light source and form parallel light rays that pass through the push jet diffuse flame in the test flow field between the first schlieren and the second schlieren. A schlieren imaging structure, wherein the schlieren imaging structure is disposed in the focusing path of the second schlieren mirror; The second schlieren is configured to focus parallel light rays that are deflected by density gradients in the test flow field onto the schlieren imaging structure to generate a schlieren image that can observe the intermittent breakup phenomenon during jet transition.

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

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

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

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

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

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

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

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

10. A method for observing the transition process of a propellant jet diffusion flame, the method being implemented using the schlieren system according to any one of claims 1-9, characterized in that, include: Establish a laminar push jet diffusion flame in the test flow field region; Schlieren images of the propulsion jet diffusion flame are recorded using a schlieren imaging structure. Based on schlieren images, identify whether there is an intermittent breakup phenomenon with periodic alternation of laminar and turbulent flow; When the intermittent fragmentation phenomenon disappears and the jet continues to exhibit turbulent characteristics, it is determined that the flame has entered the turbulent stage.

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