A multi-schlieren effect synergic measuring system

Abstract

The application provides a multi-streak effect cooperative measurement system, which comprises a concave mirror with a random scattered dot pattern, a point light source, a knife edge, a camera and an image acquisition system; the point light source is a point light source formed by a diaphragm limiting light source; the point light source is used for emitting light to the concave mirror, the knife edge is placed near the concave mirror at a distance of 2f f , f is the focal length of the concave mirror, part of the light rays converging at the point of the point light source reflected by the concave mirror is cut to form a knife edge streak effect with light and shade changes, the camera is placed on the side of the knife edge away from the concave mirror and is used for collecting the light ray image cut by the knife edge, and the camera is connected with the image acquisition system. The cooperative measurement system can realize the effect of light and shade changes of a classical knife edge streak technology image, simultaneously obtain the effect of distortion of a background pattern of a background streak technology, combines the knife edge streak technology and the background streak technology, and can quickly qualitatively determine the flow field changes and facilitate quantitative calculation.

Description

Technical Field

[0001] This invention belongs to the field of flow field optical measurement technology, and particularly relates to a multi-strife effect collaborative measurement system. Background Technology

[0002] Schlieren effect refers to the phenomenon of light refraction caused by density gradient in a flow field. As a non-contact optical measurement method for flow fields, schlieren is widely used in the visualization and quantitative measurement of flow with density changes. The classic blade schlieren technique transforms light refraction into changes in brightness on the camera's photosensitive surface, where the light intensity distribution characterizes the magnitude of the density gradient of the measured flow field in the direction perpendicular to the blade. Blade schlieren offers high spatial resolution, but calibration is complex for quantitative measurements and it is significantly affected by light intensity noise. Therefore, blade schlieren is often used for qualitative visualization of flow field density changes.

[0003] Background schlieren emerged and gained popularity around 2000. It converts the deflection of light into the displacement of a pattern on a background plate, and can be used for visualization and quantitative measurement of variable density flows. It offers significant advantages such as convenient calibration and unlimited window size. Background schlieren often utilizes the cross-correlation algorithm in PIV technology to extract displacement. By comparing reference and distorted images with and without the flow field under test, the spatial distribution of displacement distortion in the image is obtained. Further combining calibration information such as the position of optical elements, the two-dimensional refractive index gradient distribution of the flow field under test, integrated along the optical path direction, can be obtained. Compared to blade schlieren, background schlieren requires post-processing of the acquired image to achieve real-time visualization of flow density changes, making it far less clear and concise than blade schlieren. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a multi-stencil effect collaborative measurement system to address the shortcomings of the prior art.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0006] A multi-skin effect collaborative measurement system includes a concave mirror with a random scattered pattern, a point light source, a blade, a camera, and an image acquisition system. The point light source is a point light source formed by an aperture-limited light source. The point light source is used to emit light towards the concave mirror. The blade is placed at a distance of 2f from the concave mirror, where f is the focal length of the concave mirror. The blade is placed at the convergence point formed by the reflection of the point light source by the concave mirror, cutting off part of the light rays at the convergence point to form a blade-like skin effect with varying brightness. The camera is placed on the side of the blade away from the concave mirror to acquire the image of the light rays after being cut by the blade. The camera and the image acquisition system are connected.

[0007] To optimize the above technical solution, the specific measures also include:

[0008] The concave mirror mentioned above is a parabolic mirror, a spherical mirror, or an elliptical mirror; the outer contour of the concave mirror is circular or polygonal, and the random scattered pattern on the concave mirror is printed on the reflective coating layer. The reflective coating layer is located on the surface of the concave mirror and is in direct contact with the air or the outer surface is covered with an anti-scratch coating.

[0009] The random dot pattern on the concave mirror described above consists of random dots of similar size, specifically including the following requirements:

[0010] (1) The shape of the scattered points is one or a mixture of several of the following: circles, triangles, squares, rectangles, and rhombuses. The scattered points are filled in a hollow, semi-hollow, or solid state.

[0011] (2) The size of the random scattered points on the camera imaging surface is within 64 pixels.

[0012] The aforementioned multi-stencil effect collaborative measurement system employs a single-mirror off-axis stencil optical path.

[0013] The specific setup method for the single-mirror off-axis fretting optical path described above is as follows: the center normal vector of the concave mirror, the center normal vector of the camera sensor, and the optical center of the point light source are adjusted to the same plane. The reference point is 2f away from the optical axis of the concave mirror. The camera and the point light source are arranged near the reference point, and the camera and the point light source are as close as possible.

[0014] The aforementioned multi-schlieren effect collaborative measurement system employs a single-mirror coaxial schlieren optical path.

[0015] When the above-mentioned multi-schlieren effect collaborative measurement system adopts a single-mirror coaxial schlieren optical path, the multi-schlieren effect collaborative measurement system includes a plane beam splitter. The center normal vector of the concave mirror, the optical center of the point source, the center normal vector of the camera sensor, and the center of the plane beam splitter are adjusted to the same optical center plane. The plane beam splitter is arranged facing the concave mirror, and its center is placed near 2f away from the normal optical axis of the concave mirror. The axis of rotation is perpendicular to the optical center plane and passes through the center of the plane beam splitter. The normal vector of the plane beam splitter is adjusted to be 45° with the normal vector of the concave mirror. The principal optical axis of the point source illuminates the plane beam splitter at an incident angle of 45°. After the light cone emitted by the point source is reflected by the plane beam splitter, the center line of the light cone coincides with the center normal vector of the concave mirror.

[0016] The beam splitting ratio of the aforementioned planar beam splitter is 50:50.

[0017] The aforementioned blade is placed at the convergence point formed by the reflection of the point light source by the concave mirror, in order to cut part of the light and obtain a blade pattern effect with varying brightness.

[0018] The aforementioned camera includes a convex lens head and a camera sensor. After passing through the convex lens head, light shines on the camera sensor. The camera sensor is connected to the image acquisition system. The camera focuses on a random scattered pattern of a concave mirror. The principal optical axis of the light reflected by the concave mirror coincides with the central normal vector of the camera sensor.

[0019] The image acquisition system captures random scattered patterns of concave reflectors with and without the flow field to be measured. The displacement prediction method is used to calculate the background pattern distortion caused by the flow field to be measured. Furthermore, by calibrating the relative position and distance information of the optical elements, the light deflection angle is calculated and the quantitative distribution of the two-dimensional refractive index gradient along the optical path integral is obtained.

[0020] The present invention has the following advantages:

[0021] The collaborative measurement system of this invention can achieve the effect of brightness and darkness changes in images using classic blade schlieren technology, while simultaneously acquiring the effect of background pattern distortion using background schlieren technology. By combining blade schlieren technology with background schlieren technology, it can quickly qualitatively characterize flow field changes and easily perform quantitative calculations. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the single-mirror coaxial collaborative measurement system of the present invention;

[0023] Figure 2 This is a schematic diagram of the single-mirror off-axis collaborative measurement system of the present invention;

[0024] Figure 3 This is a schematic diagram of the data result post-processing in this invention;

[0025] Figure 4 This is a schematic diagram showing the relationship between light deflection and background displacement during the measurement of the flow field to be measured in this invention.

[0026] The attached figures are labeled as follows: 1. Concave mirror, 11. Scattered pattern, 2. Point light source, 3. Planar beam splitter, 4. Camera, 41. Convex lens head, 42. Camera sensor, 5. Knife edge, 6. Image acquisition system. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0028] Obviously, the accompanying drawings described below are merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios based on these drawings without any inventive effort. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0029] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0030] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms “a,” “an,” “an,” “the,” and similar words used in this application do not indicate quantity limitation and may indicate singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or units (elements) is not limited to the listed steps or units, but may also include steps or units not listed, or may include other steps or units inherent to these processes, methods, products, or devices. The terms “connected,” “linked,” “coupled,” and similar words used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms “multiple” / “several” used in this application refer to two or more. “And / or” describes the relationship between related objects, indicating that three relationships may exist; for example, “A and / or B” can indicate: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following objects are in an "or" relationship. The terms "first," "second," and "third" used in this application are merely to distinguish similar objects and do not represent a specific ordering of the objects.

[0031] like Figure 1This is a schematic diagram of the single-mirror coaxial collaborative measurement system of the present invention, including: a concave mirror 1 with a random scattered pattern 11, a point light source 2, a planar beam splitter 3, a camera 4, a knife edge 5, a single-mirror coaxial schlieren imaging optical path, and an image acquisition system 6; those skilled in the art can select a specific random scattered pattern 11 based on displacement prediction methods, flow field characteristics, flow structure dimensions, etc., to prepare the corresponding concave mirror 1. The measurement method specifically includes the following steps:

[0032] (1) The present invention uses a concave spherical mirror with a focal length of 750mm, selects a circle with a diameter of 1mm as a random scattered pattern 11, and prepares it by spraying; a plane beam splitter 3 with a splitting ratio of 50:50 is used; the center normal vector of the concave mirror 1 with random scattered pattern 11, the optical center of the point light source 2, the center normal vector of the camera sensor 42 and the center of the plane beam splitter 3 are adjusted to the same plane;

[0033] (2) The center of the plane beam splitter 3 is located near the optical axis 2f of the concave mirror 1. Its normal vector is at 45° with the normal vector of the concave mirror 1. The principal optical axis of the point light source 2 illuminates the plane beam splitter 3 at an incident angle of 45°. At this time, half of the light from the point light source 2 passes directly through the plane beam splitter 3, and the other half of the light is reflected by the plane beam splitter 3 onto the concave spherical mirror. The principal optical axis of the incident light cone coincides with the normal vector of the center of the concave mirror 1.

[0034] (2) Half of the light rays reflected from the concave spherical mirror pass directly through the plane beam splitter 3, and the other half are reflected back to the point light source. Use the paper to find the point where the reflected light rays passing through the plane beam splitter 3 converge.

[0035] (3) The blade 5 is placed at the point where the reflected light converges. The blade 5, which is perpendicular to the flow field density gradient, cuts off half of the light entering the camera 4. When there is no flow field to be measured in the measurement system, exactly half of the light enters the camera 4. When there is a flow field to be measured, the light is refracted by the fluid. Part of the light is blocked by the blade 5, and the other part of the light that was originally blocked by the blade 5 passes through the blade 5 and enters the imaging system. Thus, blade schlieren effects with different degrees of brightness are obtained.

[0036] (4) In this invention, the exposure time of camera 4 is adjustable within the range of 1μs to 10sec, the maximum frame rate is 35.6fps, the resolution is 5 million pixels, the focal length of the fixed-focus lens is 50mm, and the focus is manually controlled. Camera 4 is placed at a position away from the direction of the reflector on the blade 5, and the center normal vector of the concave reflector 1 coincides with the center normal vector of the camera sensor 42. Camera 4 is connected to image acquisition system 6 using a transmission line. The distance between camera 4 and concave reflector 1 is adjusted appropriately so that the field of view of camera 4 covers the core area of ​​concave reflector 1. The exposure time and aperture of camera 4 are both adjusted to the maximum. Based on the dot pattern on concave reflector 1 captured by camera 4, the focusing surface of the lens is adjusted until the dots on the concave spherical reflector become clear. The random dot pattern when there is no flow field to be measured is recorded as a reference image. Due to the non-uniform refractive index of the flow field to be measured, the imaging position of the dot pattern is displaced, and the distorted image of the random dot pattern is recorded.

[0037] like Figure 2 This is a schematic diagram of the single-mirror off-axis collaborative measurement system of the present invention, which includes a concave mirror 1 with a random scattered pattern 11, a point light source 2, a knife edge 5, a camera 4, a single-mirror off-axis schlieren imaging optical path, and an image acquisition system 6; the heights of the camera 4 and the point light source 2 are adjusted to ensure that the center normal vector of the concave spherical mirror, the center normal vector of the camera 4 sensor, and the optical center of the point light source 2 are in the same plane; the camera 4 and the point light source 2 are moved horizontally to both sides of the center normal vector 2f of the concave spherical mirror, and the camera 4 and the point light source 2 are as close as possible;

[0038] (5) Turn on the point light source 2, use the paper to find the convergence point of the reflected light of the concave mirror, place the blade 5 at the convergence point of the reflected light, cut off half of the light entering the camera 4, and adjust the distance between the camera 4 and the concave mirror 1 appropriately so that the field of view of the camera 4 covers the core area of ​​the concave mirror 1.

[0039] (6) Connect camera 4 to image acquisition system 6 using a transmission cable. Set the exposure time and aperture of camera 4 to their maximum. Take a picture of the dot pattern on the concave mirror 1 using camera 4. Adjust the lens's focus until the dots on the background pattern become clear. Record images of the random dot pattern with and without the flow field to be measured. Figure 3 , 4 As shown, the displacement prediction method is used to calculate the background pattern movement caused by the flow field under test, and the background pattern displacement vector distribution Δ′ on the imaging plane of camera 4 is obtained; the relative position and distance of the optical elements are calibrated. The near-optical axis assumption is adopted, and it is assumed that the size of the phase object is negligible compared with its distance from the background plate. The relationship between the light deflection angle ε in the x and y directions of the camera sensor and the background pattern displacement Δ′ can be approximately established:

[0040]

[0041] Z d ε is the horizontal distance from the center of the flow field to be measured to the concave mirror. x ε is the angle of deflection of the light ray in the x-direction. y Let Δ' be the angle of deflection of the light ray in the y-direction. x Let Δ' be the displacement of the background pattern in the x-direction of the camera sensor. y This represents the displacement of the background pattern in the y-direction of the camera sensor.

[0042] The background pattern displacement Δ and the pattern displacement Δ on the imaging plane of camera 4 can be related by the magnification M, and its expression is:

[0043]

[0044] Z i The horizontal distance Z from the lens to the camera sensor a The distance is the distance from the center of the flow field to be measured to the lens.

[0045] Deflection angle ε and refractive index gradient The relation is:

[0046]

[0047] The trajectory of the s-ray.

[0048] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0049] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A multi-striped effect synergistic measurement system, characterized in that: The system includes a concave mirror with a random scattered pattern, a point light source, a blade, a camera, and an image acquisition system. The point light source is a point light source formed by an aperture-limited light source. The point light source is used to emit light towards the concave mirror. The blade is placed at a distance of approximately 2f from the concave mirror, where f is the focal length of the concave mirror. The blade is placed at the convergence point formed by the reflection of the point light source by the concave mirror, cutting off part of the light rays at the convergence point to form a blade-like pattern of varying brightness. The camera is placed on the side of the blade away from the concave mirror to acquire images of the light rays after being cut by the blade. The camera and the image acquisition system are connected.

2. The multi-striped effect collaborative measurement system according to claim 1, characterized in that: The concave reflector is a parabolic mirror, a spherical mirror, or an elliptical mirror; the outer contour of the concave reflector is circular or polygonal, and the random scattered pattern on the concave reflector is printed on the reflective coating layer, which is located on the surface of the concave reflector and is in direct contact with the air or covered with an anti-scratch coating on the outer surface.

3. The multi-striped effect collaborative measurement system according to claim 1, characterized in that: The random dot pattern on the concave mirror consists of random dots of similar size, specifically including the following requirements: (1) The shape of the scattered points is one or a mixture of several of the following: circles, triangles, squares, rectangles, and rhombuses. The scattered points are filled in a hollow, semi-hollow, or solid state. (2) The size of the random scattered points on the camera imaging surface is within 64 pixels.

4. The multi-striped effect collaborative measurement system according to claim 1, characterized in that: The multi-stencil effect collaborative measurement system adopts a single-mirror off-axis stencil optical path.

5. The multi-striped effect collaborative measurement system according to claim 4, characterized in that: The specific setup method for the off-axis fretting light path of a single mirror is as follows: the center normal vector of the concave mirror, the center normal vector of the camera sensor, and the optical center of the point light source are adjusted to the same plane. The reference point is 2f away from the optical axis of the concave mirror. The camera and the point light source are arranged near the reference point, and the camera and the point light source are as close as possible.

6. The multi-striped effect collaborative measurement system according to claim 1, characterized in that: The multi-schlieren effect collaborative measurement system adopts a single-mirror coaxial schlieren optical path.

7. The multi-striped effect synergistic measurement system according to claim 6, characterized in that: When the multi-schlieren effect collaborative measurement system adopts a single-mirror coaxial schlieren optical path, the multi-schlieren effect collaborative measurement system includes a planar beam splitter. The center normal vector of the concave mirror, the optical center of the point source, the center normal vector of the camera sensor, and the center of the planar beam splitter are adjusted to the same optical center plane. The planar beam splitter is arranged facing the concave mirror, and its center is placed near 2f away from the normal optical axis of the concave mirror. The axis of rotation is perpendicular to the optical center plane and passes through the center of the planar beam splitter. The normal vector of the planar beam splitter is adjusted to be 45° with the center normal vector of the concave mirror. The principal optical axis of the point source illuminates the planar beam splitter at an incident angle of 45°. After the light cone emitted by the point source is reflected by the planar beam splitter, the center line of the light cone coincides with the center normal vector of the concave mirror.

8. The multi-striped effect collaborative measurement system according to claim 7, characterized in that: The beam splitter of the plane beam splitter has a splitting ratio of 50:

50.

9. A multi-striped effect synergistic measurement system according to claim 5 or 7, characterized in that: The blade is placed at the convergence point formed by the reflection of the point light source by the concave mirror, and is used to cut part of the light to obtain a blade pattern effect with varying brightness; the camera includes a convex lens and a camera sensor. After the light passes through the convex lens, it shines on the camera sensor. The camera sensor is connected to the image acquisition system. The camera focuses on the random scattered pattern of the concave mirror. The principal optical axis of the light reflected by the concave mirror coincides with the central normal vector of the camera sensor.

10. The multi-striped effect collaborative measurement system according to claim 1, characterized in that: The image acquisition system captures random scattered patterns of concave reflectors with and without the flow field to be measured. The displacement prediction method is used to calculate the background pattern distortion caused by the flow field to be measured. Furthermore, by calibrating the relative position and distance information of the optical elements, the light deflection angle is calculated and the quantitative distribution of the two-dimensional refractive index gradient along the optical path integral is obtained.

Images