Single-optical-path double-view PIV (particle image velocimetry) measurement method applicable to vacuum environment

Abstract

The invention discloses a single-light-path double-view P IV measurement method suitable for a vacuum environment, and relates to the technical field of fluid mechanics measurement, and the method comprises the following steps: a laser generator generates a laser beam, the laser beam passes through a vacuum cabin outer light guide arm and a quartz flange on a vacuum cabin through a preset incident angle, and the laser beam passes through the quartz flange; the light is reflected by a reflector in the vacuum chamber, then horizontally enters a light guide arm in the vacuum chamber, and forms a light sheet layer through a light sheet device; according to the invention, the single optical path is combined with the concave reflector to realize double-view coverage, so that the problem that two sets of P IV systems are needed for double measuring points in the vacuum chamber is solved, the system design is simplified, and the cost is reduced; a laser transmission path from the outside to the inside of the cabin is constructed by using a light guide arm and a reflector, and the contradiction between heat dissipation of the laser generator and measurement in the cabin is solved; the light reflection angle is accurately controlled through pitching adjustment, the double-view light intensity requirement is ensured, and the measurement efficiency and reliability are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fluid mechanics measurement, and in particular to a single-light-path dual-field-of-view PIV measurement method suitable for a vacuum environment. Background Art

[0002] In many research and engineering applications, it is necessary to establish a high-speed flow field, and a high-pressure gas source is widely considered to be an effective driving method. The high-pressure gas source passes through the gas delivery system and expands and accelerates inside the nozzle to form a high-speed airflow. However, at the nozzle outlet, the flow of the gas often exhibits non-steady-state characteristics, and there is a steady-state establishment process in the flow channel. In the steady-state flow region, fluid parameters such as gas flow rate, pressure and temperature tend to be stable, and related research and practical applications are often carried out in the steady flow section. In the monitoring of steady flow, it is often necessary to arrange multiple velocity measurement points (at least two) at different positions in the flow channel, and evaluate the steady flow characteristics by comparing the flow rates.

[0003] Particle Image Velocimetry (PIV), a non-contact flow velocity measurement technology, is widely used in fields such as fluid mechanics, aerodynamics, and thermodynamics. Compared to traditional contact measurement methods (such as hot-wire anemometers and pitot tubes), PIV not only significantly reduces disturbance to the flow field but also measures a wider range of flow fields, with higher spatial resolution and a wider velocity measurement range. Therefore, applying PIV to steady flow monitoring is a reliable method.

[0004] The basic principle of PIV is to inversely calculate the velocity distribution of a fluid by tracking the motion trajectories of particles in the flow field. In actual measurement, it is first necessary to introduce specific tiny tracer particles into the flow field to be measured. These particles must be small enough to have good flow-following properties and not cause significant disturbances to the flow field.

[0005] During the measurement process, a high-frequency laser illuminates the area of ​​the flow field to be measured. The laser beam passes through the light sheet, forming a thin light sheet that illuminates the particles within it. A CCD camera, located on the other side of the laser beam, captures the movement of the particles between the two exposures. To obtain accurate velocity data, the time interval between the two exposures is typically in the microsecond range. By comparing the position changes of the particles in the two exposure images, the velocity vector of each point in the flow field can be calculated through correlation analysis, thereby determining the velocity field distribution of the entire measurement area.

[0006] However, the prior art has the following objective shortcomings:

[0007] Steady flow monitoring requires at least two measurement points, but these are often far apart, making a single PIV system incapable of covering both. Therefore, two PIV measurement systems are required. Deploying two PIV systems in a vacuum chamber is more challenging than deploying them in an atmospheric environment.

[0008] The laser generator in the PIV measurement system requires reliable heat dissipation and is therefore located outside the vacuum chamber. The laser light must travel through an external light guide arm, the quartz glass on the chamber wall, a reflector, an internal light guide arm, and a light sheet to reach the area under test. After passing through the light sheet, the laser forms a thin light sheet at a specific beam emission angle. The light intensity distribution varies at different locations within the light sheet, with the intensity being highest at the center of the light sheet and decreasing as the beam angle increases. Given that PIV measurement requires a sufficiently high-intensity laser to illuminate the area under test, only the area near the centerline of the light sheet can be effectively illuminated. Therefore, a single optical path is insufficient for two PIV measurement systems; two separate optical paths are required to illuminate the two test areas, each separated by a certain distance. However, the internal volume of the vacuum chamber is limited, and an excessively long optical path is prone to interference with the test object. Furthermore, the two optical paths must be focused separately during the initial measurement phase, further complicating the system design and increasing equipment cost.

[0009] In view of this, a single-light-path dual-field-of-view PIV measurement method suitable for a vacuum environment is provided to overcome the above problems. Summary of the Invention

[0010] The object of the present invention is to provide a single-light-path dual-field PIV measurement method suitable for a vacuum environment, so as to solve the problems raised in the above background technology.

[0011] To solve the above technical problems, the present invention provides a single-light-path dual-field PIV measurement method suitable for a vacuum environment, comprising the following steps:

[0012] The laser generator generates a laser beam, which passes through the light guide arm outside the vacuum chamber and the quartz flange on the vacuum chamber at a preset incident angle. After being reflected by the reflector inside the vacuum chamber, the laser beam is horizontally incident on the light guide arm inside the vacuum chamber and forms a light sheet layer through the light sheet device.

[0013] The light sheet first covers the second PIV shooting field of view, and then through the reflection and convergence effect of the concave reflector, the reflected light sheet covers the first PIV shooting field of view;

[0014] Two CCD cameras were used to capture two exposure images of the tracer particles in the first PIV field of view and the second PIV field of view, and the velocity field distributions of the two fields of view were calculated by correlation analysis.

[0015] Furthermore, the light guide arm outside the vacuum chamber is connected to the light guide arm inside the vacuum chamber through a quartz flange to form a laser transmission path from outside the vacuum chamber to inside the chamber. A reflector is arranged at the laser incident end of the light guide arm inside the vacuum chamber to reflect the laser beam to the light guide arm inside the vacuum chamber.

[0016] Furthermore, the concave reflector is mounted on a pitch adjustment platform, and the intersection point of the incident light on the concave reflector is changed by adjusting the pitch angle δ, thereby changing the incident angle β, so as to adjust the reflection angle of the light sheet.

[0017] Furthermore, the light sheeter converts the laser beam into a light sheet layer with a beam emission angle, the second PIV shooting field of view is located on a direct light emission path of the light sheet layer, and the first PIV shooting field of view is located on a reflection path of the concave reflector.

[0018] Furthermore, the laser generator is arranged outside the vacuum chamber, and the light guide arm outside the vacuum chamber, the quartz flange, the reflector, the light guide arm inside the vacuum chamber and the light sheet constitute a single laser transmission optical path.

[0019] Furthermore, the pitch adjustment platform precisely adjusts the pitch angle δ of the corresponding concave reflector through a mechanical structure, and the adjustment range is 0°-90°, so as to adapt to the first PIV shooting field of view at different positions.

[0020] Furthermore, the time interval between the two exposures is in the microsecond order, and the velocity vector of each point in the flow field is calculated by comparing the position changes of the tracer particles in the two exposure images.

[0021] Furthermore, the first PIV shooting field of view and the second PIV shooting field of view are located at different positions of the flow channel in the vacuum chamber, and are used to monitor the steady flow characteristics of the high-speed airflow, which is generated by the nozzle.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. Solve the dual-point coverage problem and simplify system design: By combining a single laser optical path with the reflective convergence effect of a concave reflector, one optical path can simultaneously cover two PIV shooting fields of view (the first PIV shooting field of view and the second PIV shooting field of view) that are a certain distance apart. This changes the situation in which the existing technology relies on two PIV systems and two independent optical paths, avoids the space shortage and equipment interference caused by the layout of multiple systems in the vacuum chamber, and significantly reduces the system complexity.

[0024] 2. Optimize the laser transmission path to resolve the contradiction between external heat dissipation and internal measurement: Utilize a single transmission optical path consisting of a light-guide arm outside the vacuum chamber, a quartz flange, a reflector, and a light-guide arm inside the vacuum chamber to place the laser generator that requires heat dissipation outside the chamber while ensuring that the laser is stably incident on the designated area inside the chamber. This not only meets the equipment's heat dissipation requirements but also avoids the technical obstacles of directly installing the laser generator inside the vacuum chamber.

[0025] 3. Precisely adjust the reflection angle to improve optical path flexibility: The pitch angle δ of the concave reflector can be precisely adjusted in the range of 0°-90° through the pitch adjustment platform. This changes the intersection point and incident angle β of the incident light on the concave reflector, enabling flexible adjustment of the reflection direction of the light sheet layer. This ensures that the first PIV shooting field of view at different positions can be effectively illuminated, avoiding the complex operation of focusing multiple optical paths separately in the existing technology, and improving the adaptability and debugging efficiency of the measurement system.

[0026] 4. Utilize the characteristics of light sheet and reflection convergence to ensure the light intensity requirements of dual fields of view: The light sheet layer formed by the light sheet device directly covers the second PIV shooting field of view located on the light output path. At the same time, the light sheet is reflected to the first PIV shooting field of view through the concave reflector's convergence effect. Based on the distribution characteristics of high light intensity in the center of the light sheet layer, it is ensured that the tracer particles in both fields of view can be illuminated by lasers of sufficient intensity, solving the problem of insufficient light intensity at long-distance measuring points under a single optical path, and ensuring the accuracy and reliability of PIV measurement.

[0027] 5. Reduce equipment costs and space occupation: The single optical path design eliminates the laser generator, light guide arm, light sheet and other equipment required for the second PIV system and the supporting optical path in the existing technology, reducing the optical path length and hardware layout in the vacuum chamber, reducing equipment costs and space occupation, while avoiding the signal interference problem that may be caused by multiple systems, and improving the economy and practicality of flow field measurement in a vacuum environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the overall structure of a single-light-path dual-field PIV measurement method suitable for a vacuum environment according to the present invention;

[0029] Figure 2 This is a schematic diagram of the pitch adjustment of a concave reflector in a single-light-path dual-field PIV measurement method suitable for a vacuum environment according to the present invention.

[0030] In the figure: 1. Light sheet; 2. Light guide arm inside the vacuum chamber; 3. Vacuum chamber; 4. Reflector; 5. Quartz flange; 6. Light guide arm outside the vacuum chamber; 7. Laser generator; 8. Nozzle; 9. Flow channel; 10. First PIV shooting field of view; 11. Pitch adjustment platform; 12. Concave reflector; 13. Second PIV shooting field of view; 14. Light sheet. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] See also Figure 1-Figure 2 , the present invention provides a technical solution:

[0033] See Figure 1-Figure 2 As shown, an embodiment of a single-light-path dual-field PIV measurement method suitable for a vacuum environment:

[0034] Application scenarios:

[0035] This embodiment is applied to the steady-flow monitoring scenario of a high-speed flow field within a vacuum chamber. Specifically, a high-speed airflow is generated within a flow channel 9 through a nozzle 8. Flow velocity measurements are performed at two locations within the flow channel 9 (i.e., the first PIV field of view 10 and the second PIV field of view 13) spaced a certain distance apart to assess the steady-flow characteristics of the flow field. The internal volume of the vacuum chamber 3 is limited, and the laser generator 7 needs to be placed outside the vacuum chamber 3 due to heat dissipation requirements.

[0036] Implementation steps:

[0037] Step 1: System setup and initial optical path adjustment:

[0038] A laser generator 7 is fixed outside the vacuum chamber 3 and connected to the quartz flange 5 on the chamber via an external light guide arm 6. One end of the internal light guide arm 2 is connected to the inner side of the quartz flange 5, and the other end is mounted on the light sheet 1. A reflector 4 is provided at the laser incident end of the light guide arm 2 inside the chamber to reflect horizontal laser light back to the light guide arm 2 inside the chamber. A concave reflector 12 is mounted on a pitch adjustment platform 11, located in the light output direction of the light sheet 1. The first PIV field of view 10 and the second PIV field of view 13 are located on the reflection path of the concave reflector 12 and the direct light output path of the light sheet 1, respectively.

[0039] A laser transmission path from the outside of the vacuum chamber 3 to the inside of the chamber is constructed by using the light-guiding arm 6 outside the vacuum chamber and the light-guiding arm 2 inside the vacuum chamber. A single laser transmission optical path is formed by the light-guiding arm 6 outside the vacuum chamber, the quartz flange 5, the reflector 4, the light-guiding arm 2 inside the vacuum chamber and the optical sheet 1, which solves the problem that the laser generator needs to be arranged outside the chamber while laser measurement is required inside the chamber, ensures that the light source outside the vacuum chamber can effectively be incident on the designated area inside the vacuum chamber, provides the basic conditions for subsequent PIV measurement in the chamber, and avoids the problems caused by the difficulty of heat dissipation of the laser generator in the chamber.

[0040] Step 2: Laser emission and preliminary optical path transmission:

[0041] The laser generator 7 generates a laser beam, which passes through the quartz flange 5 at a suitable incident angle through the light guide arm 6 outside the vacuum chamber and reaches the reflector 4 inside the vacuum chamber 3. After being reflected by the reflector 4, the laser beam is horizontally incident on the light guide arm 2 inside the vacuum chamber and is transmitted to the light sheet 1 through the light guide arm 2 inside the vacuum chamber.

[0042] The propagation direction of the laser beam is changed by the reflector 4 so that it is horizontally incident on the light-guiding arm 2 in the vacuum chamber. Combined with the design of the light-guiding arms inside and outside the vacuum chamber, the propagation path of the laser beam inside and outside the vacuum chamber is precisely controlled, ensuring that the laser can be stably and accurately transmitted to the light-sheet device 1 in the chamber, laying the foundation for the subsequent formation of the light-sheet layer and avoiding energy loss and measurement errors caused by path confusion during laser transmission.

[0043] Step 3: Light sheet formation and first field of view coverage:

[0044] After passing through light sheet 1, the laser beam forms a light sheet 14 with a specific beam emission angle. Light sheet 14 initially covers second PIV field of view 13. At this point, the light intensity is highest at the center of light sheet 14. As the beam angle increases, the light intensity gradually decreases. However, because second PIV field of view 13 is located near the centerline of the light sheet, it is effectively illuminated, meeting the light intensity requirements for PIV measurement.

[0045] The light sheet 1 converts the laser beam into a light sheet layer, which directly covers the second PIV shooting field of view 13. The light intensity distribution characteristics of the light sheet layer are used to ensure that the tracer particles in the field of view can be illuminated by laser light of sufficient intensity, providing a clear image basis for particle image acquisition and velocity measurement in the second field of view, and ensuring the accuracy and reliability of the measurement data in this field of view.

[0046] Step 4: Concave mirror adjustment and second field of view coverage:

[0047] Based on the position of the first PIV field of view 10 and the initial angle of the light sheeting layer 14, the pitch angle δ of the concave reflector 12 is adjusted via the pitch adjustment platform 11 within a range of 0°-90°. Assuming that ray AO is any incident light ray, point O is the intersection of incident ray AO and concave reflector 12, OO' is the direction of the normal to the curved reflector at point O, and ray OB is the direction of reflection of ray AO, changing the pitch angle δ will change the intersection point of the incident light ray on the concave reflector 12, thereby changing the incident angle β, causing the light sheeting layer 14 to converge after reflection from the concave reflector 12, accurately covering the first PIV field of view 10.

[0048] The pitch angle of concave reflector 12 is precisely adjusted using a pitch adjustment platform 11. The concave reflector's light-converging effect reflects the light sheet 14 and converges it onto the first PIV field of view 10, achieving coverage of two fields of view separated by a certain distance with a single laser optical path. This eliminates the need for two PIV measurement systems and two optical paths, as is required in existing technologies. This solves the challenges of optical path layout and interference with the test object caused by limited space within the vacuum chamber. It also avoids the complex operation of focusing two optical paths separately, simplifying system design, reducing equipment costs, and the difficulty of debugging during the initial measurement phase.

[0049] Step 5: Particle image acquisition and velocity calculation:

[0050] As light sheet 14 illuminates first and second PIV fields of view 10 and 13, two CCD cameras (not numbered in the figure, representing conventional PIV systems) located within vacuum chamber 3 capture two exposure images of the tracer particles within each field of view. By comparing the positional changes of the particles in the two exposure images and performing correlation analysis, the velocity vector of each point in the flow field within the two fields of view is calculated. This in turn yields the velocity field distributions for the two measurement areas, completing steady-state flow monitoring.

[0051] By using a single optical path to achieve dual-field particle image acquisition, the number of equipment and optical path layout are reduced while ensuring the acquisition of velocity data at two measuring points. This enables efficient and accurate flow field measurement in the limited space of a vacuum chamber. Compared with existing technologies, this method reduces system complexity while ensuring the accuracy and reliability of measurement results, providing strong data support for the assessment of steady-flow characteristics of the flow field.

[0052] Summarize:

[0053] This embodiment utilizes two light-guiding arms (external light-guiding arm 6 and internal light-guiding arm 2) inside and outside the vacuum chamber to successfully guide laser light emitted by a laser generator 7 outside the chamber into a designated area within the chamber, resolving the conflict between the laser generator's heat dissipation requirements and the measurement requirements within the chamber. Using a concave reflector 12 and its pitch adjustment platform 11, the light sheet 14 is reflected and converged, enabling a single laser optical path to cover two PIV fields of view (first PIV field of view 10 and second PIV field of view 13) spaced a certain distance apart.

[0054] To address the existing challenges of steady-flow monitoring, which require two PIV systems, resulting in difficult layout within the vacuum chamber, complex system design, and high equipment costs, this method eliminates the need for two optical paths and two complex PIV systems through a single optical path and dual fields of view design. This reduces the optical path length and the number of devices within the vacuum chamber, lowering the risk of interference with the test piece and simplifying pre-measurement debugging steps such as focusing. Based on the light intensity distribution characteristics of the light sheet and the converging effect of the concave reflector, sufficient light intensity is ensured in both fields of view to meet PIV measurement requirements. This simplifies system design, reduces equipment costs, and improves the efficiency and feasibility of flow field measurement in a vacuum environment.

Claims

1. A single-light-path dual-field PIV measurement method suitable for vacuum environments, characterized in that: The following steps are involved: A laser generator (7) generates a laser beam, which passes through a light guide arm (6) outside the vacuum chamber and a quartz flange (5) on the vacuum chamber (3) at a preset incident angle, is reflected by a reflective mirror (4) inside the vacuum chamber, and then is horizontally incident on the light guide arm (2) inside the vacuum chamber, and forms a light sheet layer (14) through a light sheet device (1); The light sheet layer (14) first covers the second PIV shooting field of view (13), and through the reflection and convergence effect of the concave reflector (12), the reflected light sheet layer (14) covers the first PIV shooting field of view (10); Two CCD cameras are used to collect two exposure images of the tracer particles in the first PIV shooting field of view (10) and the second PIV shooting field of view (13), and the velocity field distribution of the two fields of view is calculated by correlation analysis.

2. The single-optical-path, dual-field-of-view PIV measurement method suitable for a vacuum environment according to claim 1, characterized in that: A light guide arm (6) outside the vacuum chamber is connected to a light guide arm (2) inside the vacuum chamber via a quartz flange (5), forming a laser transmission path from outside the vacuum chamber (3) to inside the chamber. A reflector (4) is provided at the laser incident end of the light guide arm (2) inside the vacuum chamber, and is used to reflect the laser beam to the light guide arm (2) inside the vacuum chamber.

3. The single-optical-path, dual-field-of-view PIV measurement method suitable for a vacuum environment according to claim 1, characterized in that: The concave reflector (12) is mounted on the pitch adjustment platform (11), and the intersection point of the incident light on the concave reflector (12) is changed by adjusting the pitch angle δ, thereby changing the incident angle β, and is used to adjust the reflection angle of the light sheet (14).

4. The single-optical-path, dual-field-of-view PIV measurement method suitable for a vacuum environment according to claim 1, characterized in that: The light sheet device (1) converts the laser beam into a light sheet layer (14) having a beam emission angle, the second PIV shooting field of view (13) is located on a direct light emission path of the light sheet layer (14), and the first PIV shooting field of view (10) is located on a reflection path of a concave reflector (12).

5. The single-optical-path, dual-field-of-view PIV measurement method suitable for a vacuum environment according to claim 1, characterized in that: The laser generator (7) is arranged outside the vacuum chamber (3); the light guide arm (6) outside the vacuum chamber, the quartz flange (5), the reflector (4), the light guide arm (2) inside the vacuum chamber and the optical sheet (1) form a single laser transmission optical path.

6. The single-light-path dual-field PIV measurement method suitable for a vacuum environment according to claim 3, characterized in that: The pitch adjustment platform (11) accurately adjusts the pitch angle δ of the corresponding concave reflector (12) through a mechanical structure, and the adjustment range is 0°-90°, so as to adapt to the first PIV shooting field of view (10) at different positions.

7. The single-optical-path, dual-field-of-view PIV measurement method suitable for a vacuum environment according to claim 1, characterized in that: The time interval between the two exposures is in microseconds. By comparing the position changes of the tracer particles in the two exposure images, the velocity vector of each point in the flow field is calculated.

8. The single-optical-path, dual-field-of-view PIV measurement method suitable for a vacuum environment according to claim 1, characterized in that: The first PIV shooting field of view (10) and the second PIV shooting field of view (13) are located at different positions of the flow channel (9) in the vacuum chamber (3) and are used to monitor the steady flow characteristics of the high-speed airflow generated by the nozzle (8).

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