A supersonic flow field optical flow velocity measurement system

Abstract

The present invention relates to the field of aerospace experimental technology, and in particular to a supersonic flow field optical flow velocity measurement system. The supersonic flow field optical flow velocity measurement system comprises a wind tunnel air source, a high uniformity tracer particle sowing device, a double exposure laser light source, a light guide arm, a sheet light modulation lens group and a cross-frame camera; the main airflow injection port of the high uniformity tracer particle sowing device is connected to the wind tunnel air source; the high uniformity tracer particle sowing device comprises a tracer particle injection port, a cone-lobe mixer, a first honeycomb rectifier, a second honeycomb rectifier and a wind tunnel nozzle; there is a slight difference between the two cavities of the double exposure laser, resulting in different polarization modes, incident angles and energy distributions of the light. The polarization direction, beam combination and energy intensity of the laser are adjusted and controlled by the optical path to meet the light field conservation conditions of the two beams of light as much as possible. The high uniformity tracer particle sowing device can adjust and improve the mixing of particles with the incoming flow and the uniformity of the airflow.

Description

Technical Field

[0001] The invention relates to the field of aerospace experimental technology, and in particular to a supersonic flow field optical flow velocity measurement system. Background Art

[0002] The optical flow measurement method has the advantage of high-resolution flow field structure display. The most classic optical flow field calculation method is the optical flow (HS) algorithm based on global differential method proposed by Horn and Schunck in the 1980s. The introduction of this algorithm marks the beginning of the practical application of the optical flow method. The optical flow method links the two-dimensional velocity field with the image grayscale, and believes that the optical flow field caused by the same moving object should be continuous and smooth, that is, the velocities of adjacent points on the same object are similar, so the optical flow changes projected onto the image should also be smooth. Based on this feature, a method is proposed to use an additional velocity smoothness constraint added to the optical flow field, namely the global smoothness constraint, to transform the calculation problem of the optical flow field into a variational problem, and give a motion estimate with pixel-level resolution.

[0003] Although optical flow velocity field results were obtained in the optical flow velocity field measurement research, the optical flow method requires constant light field conditions. In the existing measurement results, a high-speed camera uses a shooting rate of 10kHz to capture and calculate the mainstream flow field of the order of 1m / s. It is almost impossible to use this scheme to measure the velocity field of a higher speed or even a compressible flow field. Therefore, if you want to perform velocity field measurements based on the optical flow method in a high-speed, compressible flow field, you need to carry out necessary hardware system development. Summary of the invention

[0004] The purpose of the present invention is to provide a supersonic flow field optical flow velocity measurement system, which can solve the problem that the current optical flow method cannot perform velocity field measurement in a high-speed compressible wind tunnel flow field;

[0005] The present invention provides a supersonic flow field optical flow velocity measurement system, which includes a wind tunnel air source, a high-uniformity tracer particle spreading device, a double-exposure laser light source, a light guide arm, a sheet light modulation lens group and a cross-frame camera;

[0006] The main air flow injection port of the high uniformity tracer particle spreading device is connected to the wind tunnel air source;

[0007] The high uniformity tracer particle spreading device comprises a tracer particle injection port, a cone-lobe mixer, a first honeycomb rectifier, a second honeycomb rectifier and a wind tunnel nozzle;

[0008] The main airflow of the wind tunnel air source enters the inner flow channel of the cone-flap mixer, and the tracer particles enter from the tracer particle injection port, and then enter the outer flow channel of the cone-flap mixer. The main airflow and the tracer particles are mixed through the cone-flap mixer; the main airflow mixed with the tracer particles passes through the first honeycomb rectifier and the second honeycomb rectifier and enters the wind tunnel nozzle;

[0009] The double-exposure laser light source emits a laser beam, which passes through the light guide arm and the light sheet modulation lens group, and outputs a double-pulse combined beam laser with the same polarization state. Then, the accelerated main air flow mixed with tracer particles flows to the area illuminated by the laser sheet light source, and two consecutive frames of light flow particle images are captured by the cross-frame camera.

[0010] Preferably, a data processing unit is also included. After obtaining two consecutive frames of optical flow particle images, the data processing unit uses the LK method to first perform a fast initial displacement calculation, and then uses it as the initial condition of the HS algorithm to continue iterating to obtain a high-resolution displacement field result.

[0011] Preferably, the double-exposure laser light source is an illumination device that generates two laser light beams with a set time interval.

[0012] Preferably, the light beams generated by the double-exposure laser light source are two laser light beams S and P with a wavelength of λ0=1024nm;

[0013] After the two laser beams are combined by the polarization beam combining crystal, the two beams enter the laser frequency doubling crystal and become green lasers with a wavelength of λ1=532nm. They pass through the light guide arm and enter the light sheet modulation lens group.

[0014] Preferably, the sheet light modulation lens group comprises a laser polarizer, a 1 / 2 glass plate and a sheet light modulation lens group which are arranged in sequence;

[0015] The laser polarizer converts the polarization of the two beams of light into elliptically polarized light at the same time, and the 1 / 2 glass plate makes the two beams of light become linearly polarized light in the same direction at the same time. Then, the two beams of light pass through the light modulation lens group to keep the polarization directions of the two beams consistent.

[0016] Preferably, the laser polarizer, the 1 / 2 glass plate, and the sheet light modulation lens group are provided with an anti-reflection film;

[0017] The thickness of the antireflection film is h=λ1 / 4=133 nm, and the thickness error is no greater than Δh=2 nm.

[0018] Preferably, when the inner diameter of the wind tunnel air source is D4=50 mm, the middle diameter of the cone-lobed mixer is R0=D4, the total length L≈2×D4, the minor diameter is 0.45×D4≤R1≤0.55×D4, and the major diameter is 1.45×D4≤R2≤1.65×D4;

[0019] The number of cone lobes of the cone-lobed mixer is m=12-16, the outer lobe diameter R3≈2×π×R2 / (2.2×m+2×π), and the inner lobe diameter R4≈2×π×R1 / (1.88×m-2×π).

[0020] Preferably, the side length of the first honeycomb rectifier is preferably s9≈0.1×D4, and the side length of the second honeycomb rectifier is preferably s10≈0.075×D4.

[0021] Beneficial effects:

[0022] There are slight differences between the two cavities of the double-exposure laser, resulting in different polarization modes, incident angles and energy distributions of the light. The light path is adjusted to control the polarization direction, beam combination and energy intensity of the laser to try to meet the light field conservation conditions of the two beams. The high-uniformity tracer particle seeding device can adjust and improve the mixing of particles with the incoming flow and the uniformity of the airflow. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic diagram of a supersonic flow field optical flow velocity measurement system provided for a specific embodiment of the present invention;

[0025] Figure 2 A schematic diagram of a double-exposure laser polarization consistency device provided for a specific embodiment of the present invention;

[0026] Figure 3a A schematic diagram of a highly uniform tracer particle broadcasting device provided for a specific embodiment of the present invention;

[0027] Figure 3b for Figure 3a Section view at “AA”;

[0028] Figure 4 A discretization block diagram of the optical flow composite iterative method provided for a specific embodiment of the present invention.

[0029] Description of reference numerals:

[0030] 1 is a double-exposure YAG laser light source, 2 is a laser light guide arm, 3 is a polarization consistency modulation module, 4 is a wind tunnel air source, 5 is a high-uniformity tracer particle spreading device, 6 is a main air flow injection port, 7 is a tracer particle injection port, 8 is a cone-lobe mixer, 9 is a first honeycomb rectifier, 10 is a second honeycomb rectifier, 11 is a wind tunnel nozzle, 12 is a sheet light illumination area, 13 is an image shooting area, and 14 is a cross-frame camera and lens. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0033] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] like Figures 1 to 4 As shown, this embodiment provides a supersonic flow field optical flow velocity measurement system, which includes a wind tunnel air source, a high-uniformity tracer particle spreading device, a double-exposure laser light source, a light guide arm, a sheet light modulation lens group and a cross-frame camera.

[0035] The main air flow injection port of the high-uniformity tracer particle spreading device is connected to the wind tunnel air source.

[0036] The high-uniformity tracer particle spreading device comprises a tracer particle injection port, a cone-lobe mixer, a first honeycomb rectifier, a second honeycomb rectifier and a wind tunnel nozzle.

[0037] The main airflow of the wind tunnel air source enters the inner flow channel of the cone-flap mixer, and the tracer particles enter from the tracer particle injection port, and then enter the outer flow channel of the cone-flap mixer. The main airflow and the tracer particles are mixed through the cone-flap mixer. The main airflow mixed with the tracer particles passes through the first honeycomb rectifier and the second honeycomb rectifier and enters the wind tunnel nozzle.

[0038] The double-exposure laser light source emits a laser beam, which passes through the light guide arm and the light sheet modulation lens group, and outputs a double-pulse combined beam laser with the same polarization state. Then, the accelerated main air flow mixed with tracer particles flows to the area illuminated by the laser sheet light source, and two consecutive frames of light flow particle images are captured by the cross-frame camera.

[0039] There are slight differences between the two cavities of the double-exposure laser, resulting in different polarization modes, incident angles and energy distributions of the light. The light path is adjusted to control the polarization direction, beam combination and energy intensity of the laser to try to meet the light field conservation conditions of the two beams. The high-uniformity tracer particle seeding device can adjust and improve the mixing of particles with the incoming flow and the uniformity of the airflow.

[0040] In order to further illustrate the above-mentioned supersonic flow field optical flow velocity measurement system, this embodiment provides a

[0041] The present invention will be further described below by taking the FD-03 wind tunnel optical flow velocity measurement as an example in conjunction with the accompanying drawings.

[0042] The present invention relates to a supersonic flow field optical flow velocity measurement system having the following structure.

[0043] The present invention relates to a supersonic flow field optical flow velocity measurement system. First, a double-exposure YAG laser light source 1 is used as an illumination device to generate two laser beams with a specific time interval, such as Figure 2 Two laser beams S and P with a wavelength of λ0=1024nm are generated in the double-exposure YAG laser light source 1. After being combined by the polarization beam combining crystal 1-1, the two beams of light almost overlap and enter the laser frequency doubling crystal 1-2. The frequency doubling is a green laser with a wavelength of λ1=532nm. After passing through the light guide arm 2, it enters the sheet light modulation lens group 3.

[0044] In this embodiment, a laser polarizer 3-1 is first placed in the sheet light modulation lens group 3 to simultaneously polarize the two light beams into elliptically polarized light, and then a 1 / 2 glass plate 3-2 is placed to make the two light beams simultaneously become linearly polarized light in the same direction, and then pass through the sheet light modulation lens group 3-3 to ensure that the polarization directions of the two light beams remain consistent.

[0045] In particular, in order to reduce the light intensity loss during the laser polarization process, an anti-reflection film is coated on the laser polarizer 3-1, the 1 / 2 glass plate 3-2, and the sheet light modulation lens group 3-3. The thickness of the anti-reflection film is preferably h = λ1 / 4 = 133nm, and the thickness error is not greater than Δh = 2nm to maximize the transmittance of the laser beam.

[0046] Develop discontinuous pulsed lighting sources that meet the light field conservation conditions, have sufficient light intensity, and are equipped with corresponding image acquisition equipment.

[0047] The application of optical flow method in velocity field measurement mainly utilizes the light field conservation conditions and additional smoothness constraints, and mainly relies on continuous light sources and high-speed cameras in hardware. Due to hardware limitations, the upper limit of absolute velocity measurement is relatively low. Therefore, it is considered to use the existing double-exposure laser combined with the optical flow method to conduct high-resolution high-speed velocity field measurement research. Due to slight differences between the two cavities of the double-exposure laser, the polarization mode, incident angle of the light, and energy distribution of the light are not the same. It is necessary to design a special optical path to adjust and control the laser polarization direction, beam combination, and energy intensity to try to meet the light field conservation conditions of the two beams.

[0048] A supersonic flow field optical flow velocity measurement system provided in this embodiment is connected to a high uniformity tracer particle sowing device 5 at the rear of the wind tunnel air source 4. The high uniformity tracer particle sowing device 5 is mainly composed of a main airflow injection port 6, a tracer particle injection port 7, a cone-lobe mixer 8, a first honeycomb rectifier 9, and a second honeycomb rectifier 10. The main airflow enters the main airflow injection port 6 in the high uniformity tracer particle sowing device 5 from the wind tunnel air source 4, and then enters the internal flow channel of the cone-lobe mixer 8. The tracer particles enter from the tracer particle injection port 7 and then enter the external flow channel of the cone-lobe mixer 8. The main airflow and the tracer particles are quickly mixed through the cone-lobe mixer 8. Subsequently, the main airflow mixed with the tracer particles passes through the first honeycomb rectifier 9 and the second honeycomb rectifier 10 and enters the wind tunnel nozzle 11. Subsequently, the accelerated main airflow mixed with the tracer particles flows to the area illuminated by the laser sheet light source 12, and the image is captured by the cross-frame camera 14.

[0049] Preferably, the size of the cone-lobe mixer 8 is designed. For the FD-03 wind tunnel, the inner diameter of the wind tunnel air source 4 is D4=50 mm, the middle diameter of the cone-lobe mixer 8 is preferably R0=D4, the total length L≈2×D4, the minor diameter 0.45×D4≤R1≤0.55×D4, the major diameter 1.45×D4≤R2≤1.65×D4, and the preferred number of cone lobes m=12-16. The outer lobe diameter R3≈2×π×R2 / (2.2×m+2×π), the inner lobe diameter R4≈2×π×R1 / (1.88×m-2×π), and the size can be rounded appropriately according to the selection situation.

[0050] Preferably, the honeycomb structure dimensions of the first honeycomb rectifier 9 and the second honeycomb rectifier 10 are designed. The main function of the first honeycomb rectifier 9 is primary rectification, and the honeycomb structure dimension can be coarser. The honeycomb structure is hexagonal, and the side length is preferably s9≈0.1×D4. The main function of the second honeycomb rectifier 10 is secondary rectification, and the honeycomb structure dimension will be smaller, and the side length is preferably s10≈0.075×D4.

[0051] Optical flow calculation requires a dense image grayscale carrier, so it is necessary to improve the tracer particle broadcasting segment in the high-speed, compressible flow field to adapt to the optical flow velocity field calculation.

[0052] The optical flow algorithm needs to perform spatial discrete calculations at pixel resolution, which requires a dense image grayscale field. For velocity field measurement, a dense particle image is required. For a specific small supersonic wind tunnel (FD-03), the mainstream pipe is DN50 in diameter, and the existing particle broadcasting section is directly inserted into the opening on the pipe. The nano powder tracer particle injection through the perforated steel pipe will not only lead to uneven mixing effect, but also cause great interference to the mainstream, which is not conducive to the measurement and calculation of the optical flow velocity field. Therefore, a special particle broadcasting section will be designed to increase the injection section diameter, inject the tracer particles from the annular gap, and add a detachable honeycomb rectifier to adjust and improve the mixing of particles and incoming flow and the uniformity of airflow.

[0053] The working process of a supersonic flow field optical flow velocity measurement system involved in the present invention is as follows.

[0054] First, the main airflow enters the main airflow injection port 6 in the high uniformity tracer particle spreading device 5 from the wind tunnel air source 4, and then enters the internal flow channel of the cone-lobe mixer 8. The tracer particles enter from the tracer particle injection port 7, and then enter the external flow channel of the cone-lobe mixer 8. The main airflow and the tracer particles are quickly mixed through the cone-lobe mixer 8. Then, the main airflow mixed with the tracer particles passes through the first honeycomb rectifier 9 and the second honeycomb rectifier 10, and enters the wind tunnel nozzle 11. The double-exposure YAG laser light source 1 emits a laser beam, which passes through the light guide arm 2 and the sheet light modulation lens group 3, and outputs a double-pulse combined laser with the same polarization state. Then, the accelerated main airflow mixed with the tracer particles flows to the area illuminated by the laser sheet light source 12, and two consecutive frames of optical flow particle images are captured by the cross-frame camera 14.

[0055] After obtaining two consecutive frames of optical flow particle images, a composite iterative method combining the LK algorithm and the HS algorithm is adopted. That is, the LK method is used to perform a fast initial displacement calculation first, and then it is used as the initial condition of the HS algorithm to continue iterating. This can meet the global accuracy while obtaining high-resolution displacement field results.

[0056] Stronger velocity gradients, curls, and shear regions are likely to exist in high-speed, compressible flow fields, and the corresponding optical flow calculation methods need to be improved to meet the local and overall precision control.

[0057] In order to adapt to the measurement of high-speed velocity fields, a double-exposure laser will be used to shoot particle image fields to shorten the time interval between two frames of images and achieve the constraint condition of optical flow conservation. Although the consistency of the two beams of light has been improved, the illumination intensity cannot be completely consistent. It is necessary to develop an adjustment method for illumination consistency in the calculation method and improve the adaptability of the optical flow algorithm to sparse grayscale images and large displacement gradients. In addition, high-speed velocity fields, especially supersonic flow fields, will have strong velocity / displacement gradients, curls, and shear regions. Similarly, because the optical flow calculation method based on the differential method adopts smoothing constraints and uses global constraint control for iteration, the resolution of these regions and structures is improved.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A supersonic flow field optical flow velocity measurement system, characterized in that: It includes a wind tunnel air source, a high-uniformity tracer particle seeding device, a double-exposure laser light source, a light-guiding arm, a sheet light modulation lens group, and a cross-frame camera; The main air flow injection port of the high uniformity tracer particle spreading device is connected to the wind tunnel air source; The high uniformity tracer particle spreading device comprises a tracer particle injection port, a cone-lobe mixer, a first honeycomb rectifier, a second honeycomb rectifier and a wind tunnel nozzle; The main airflow of the wind tunnel air source enters the inner flow channel of the cone-flap mixer, and the tracer particles enter from the tracer particle injection port, and then enter the outer flow channel of the cone-flap mixer. The main airflow and the tracer particles are mixed through the cone-flap mixer; the main airflow mixed with the tracer particles passes through the first honeycomb rectifier and the second honeycomb rectifier and enters the wind tunnel nozzle; The double-exposure laser light source emits a laser beam, which passes through the light guide arm and the light sheet modulation lens group, and outputs a double-pulse combined beam laser with the same polarization state. Then, the accelerated main air flow mixed with tracer particles flows to the area illuminated by the laser sheet light source, and two consecutive frames of light flow particle images are captured by the cross-frame camera.

2. The supersonic flow field optical flow velocity measurement system according to claim 1, characterized in that: The invention also includes a data processing unit. After obtaining two consecutive frames of optical flow particle images, the data processing unit uses the LK method to first perform a fast initial displacement calculation, and then uses it as the initial condition of the HS algorithm to continue iterating and obtain a high-resolution displacement field result.

3. The supersonic flow field optical flow velocity measurement system according to claim 1, characterized in that: The double exposure laser light source is a lighting device that generates two laser beams with a set time interval.

4. The supersonic flow field optical flow velocity measurement system according to claim 3, characterized in that: The light beams generated by the double exposure laser light source are two laser light beams S and P with a wavelength of λ0=1024nm; After the two laser beams are combined by the polarization beam combining crystal, the two beams enter the laser frequency doubling crystal and become green lasers with a wavelength of λ1=532nm. They pass through the light guide arm and enter the light sheet modulation lens group.

5. The supersonic flow field optical flow velocity measurement system according to claim 4, characterized in that: The sheet light modulation lens group comprises a laser polarizing plate, a 1 / 2 glass plate and a sheet light modulation lens group which are arranged in sequence; The laser polarizer converts the polarization of the two beams of light into elliptically polarized light at the same time, and the 1 / 2 glass plate makes the two beams of light become linearly polarized light in the same direction at the same time. Then, the two beams of light pass through the light modulation lens group to keep the polarization directions of the two beams consistent.

6. The supersonic flow field optical flow velocity measurement system according to claim 5, characterized in that: The laser polarizer, the 1 / 2 glass plate, and the sheet light modulation lens group are provided with an anti-reflection film; The thickness of the antireflection film is h=λ1 / 4=133 nm, and the thickness error is no greater than Δh=2 nm.

7. The supersonic flow field optical flow velocity measurement system according to claim 1, characterized in that: When the inner diameter of the wind tunnel air source is D4 = 50 mm, the middle diameter of the cone-lobed mixer is R0 = D4, the total length L ≈ 2 × D4, the small diameter is 0.45 × D4 ≤ R1 ≤ 0.55 × D4, and the large diameter is 1.45 × D4 ≤ R2 ≤ 1.65 × D4; The number of cone lobes of the cone-lobed mixer is m=12-16, the outer lobe diameter R3≈2×π×R2 / (2.2×m+2×π), and the inner lobe diameter R4≈2×π×R1 / (1.88×m-2×π).

8. The supersonic flow field optical flow velocity measurement system according to claim 1, characterized in that: The preferred side length of the first honeycomb rectifier is s9≈0.1×D4, and the preferred side length of the second honeycomb rectifier is s10≈0.075×D4.

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