Acceleration measurement device based on particle image velocimetry

Abstract

The application relates to an acceleration measuring device based on a particle image velocimetry, which comprises at least two CCD cameras, the center points of the mirrors of the two CCD cameras are located on a straight line through a limiting device; a tracer particle generator is used for emitting tracer particles along the direction vertical to the normal of the mirror of the CCD camera; a four-pulse laser is used for sequentially emitting four pulse laser beams along the direction vertical to the direction of the particle flow to illuminate the tracer particles; a control device is connected with the CCD camera and the four-pulse laser respectively, and is used for synchronously controlling the CCD camera and the four-pulse laser, so that the CCD camera acquires the tracer particle images under the irradiation of different pulse lasers in a double-exposure mode, and the speed and acceleration of the particles are acquired based on the tracer particle images. Since the four-pulse laser capable of sending four high-energy pulse lasers at a time is adopted, at least four particle images with a very short time interval are acquired by using two CCD cameras, and then the particle acceleration can be acquired.

Description

Technical Field

[0001] This invention relates to particle image velocimetry (PIV) technology in the field of laser velocimetry, and particularly to an acceleration measurement device based on particle image velocimetry. Background Technology

[0002] Traditional PIV (Pulsed Image Transmission) technology typically uses a pulsed laser with an exposure camera to obtain two consecutive particle images. The particle velocity is then calculated using these two images. By controlling the repetition frequency of this process, usually between 5Hz and 10Hz, a series of data points are obtained. The final particle velocity value is obtained by calculating the average of these multiple velocities. Alternatively, high-frequency PIV technology can be used. This involves employing a high-frequency pulsed laser with a high-speed camera to obtain a large number of particle images with short time intervals within a short period. The particle velocity is then calculated using the two images obtained.

[0003] However, both of the aforementioned PIV technologies have their own characteristics and limitations: The first type of PIV technology uses dual-pulse lasers with generally high single-pulse power, such as 350mJ-1J. Correspondingly, high-resolution exposure CCD cameras can be used, allowing for the measurement of large research objects. However, the frequency and camera transmission speed are limited, and only 5 or 10 pairs of particle images, i.e., 5 or 10 velocity fields, can be obtained per second. Because the time interval between each pair of velocity fields is too long, exceeding 0.1 seconds, there is no temporal correlation between two adjacent velocity fields, making it impossible to calculate the acceleration field from each pair of velocity fields. The second type of high-frequency PIV technology uses high-frequency pulsed lasers with frequencies up to 1kHz, but the single-pulse energy is only 20mJ. Furthermore, the high-speed camera operates under a high frame rate model, and its resolution is constrained by the transmission bandwidth, preventing high-resolution imaging. This results in the system being unable to acquire large-area particle images, and the large amount of data obtained in a short time increases the difficulty of subsequent data processing. Moreover, even when measured at a frequency of 1kHz, the time interval between the two velocity fields reaches 1ms, which is insufficient for high-speed flow and cannot meet the requirement of solving the acceleration field for the time correlation between the two velocity fields. Summary of the Invention

[0004] Therefore, it is necessary to provide an acceleration measurement device based on particle image velocimetry that can measure particle acceleration, addressing the problems mentioned in the background art.

[0005] This application provides an acceleration measurement device based on particle image velocimetry, comprising:

[0006] At least two charge-coupled device (CCD) image sensor cameras, wherein the normals of the mirrors of the two CCD cameras coincide, are used to acquire images of tracer particles, and the two CCD cameras include a first CCD camera and a second CCD camera.

[0007] A limiting device is used to limit the first CCD camera and the second CCD camera to be located on a straight line, and the normals of the mirror surfaces of the first CCD camera and the second CCD camera coincide.

[0008] A tracer particle generator is used to emit tracer particles in a direction perpendicular to the normal of the CCD camera mirror.

[0009] A four-pulse laser is used to sequentially emit four pulsed laser beams in a direction perpendicular to the particle flow to illuminate the tracer particles;

[0010] A control device is connected to the CCD camera and the four-pulse laser respectively, and is used to synchronously control the CCD camera and the four-pulse laser, so that the CCD camera acquires tracer particle images under different pulse laser irradiation, and acquires the particle velocity and acceleration based on the tracer particle images.

[0011] In the particle image velocimetry acceleration measurement device of the above embodiment, a four-pulse laser capable of sending four high-energy laser pulses at once is used, and the time interval between each pair is very short, reaching as short as 200ns. Tracer particles are scattered in the measured airflow using a tracer particle generator, and the tracer particle stream is illuminated by laser emitted by the four-pulse laser. The center points of the mirrors of two CCD cameras are aligned on a straight line by a limiting device, and the tracer particle stream illuminated by the pulsed laser beam is captured to obtain at least four particle images with very short time intervals. The particle velocity is obtained based on the tracer particle images, and then the particle acceleration value is calculated based on the obtained particle velocity values ​​with very short time intervals.

[0012] In one embodiment, the acceleration measurement device based on particle image velocimetry further includes:

[0013] A polarization device is used to combine the emitted light from the four-pulse laser into one or two beams.

[0014] In one embodiment, the polarization device further includes:

[0015] At least four internal polarizing mirrors are disposed on the four-pulse laser for polarization;

[0016] At least one external polarizing mirror is disposed outside the four-pulse laser for combining the emitted light from the four-pulse laser into a single beam and for polarization analysis; and

[0017] At least two beam polarizers are used to split the beam of light into two beams that enter two CCD cameras respectively.

[0018] In one embodiment, based on the tracer particle image, a cross-correlation algorithm is used to obtain the particle velocity, and the particle acceleration is obtained based on the particle velocity.

[0019] In one embodiment, the CCD camera is a dual-exposure CCD camera, used to expose two images in a single continuous exposure.

[0020] In one embodiment, two images are acquired from time T0 using a dual-exposure CCD camera, and the particle velocity v1 is obtained using a cross-correlation algorithm.

[0021] Two images are acquired starting from time T0+Δt using another dual-exposure CCD camera, and the particle velocity v2 is obtained using a cross-correlation algorithm.

[0022] The obtained particle acceleration 'a' is:

[0023]

[0024] In one embodiment, the pulse width of the laser emitted by the four-pulse laser is 6ns-10ns.

[0025] In one embodiment, the exposure time of the first image of the dual-exposure CCD camera is 2µs-1ms, and the exposure time of the second image of the dual-exposure CCD camera is 30ms.

[0026] In one embodiment, the pulse width of the laser emitted by the quad-pulse laser is less than the exposure time of any image from the CCD camera, which is used to take images in a dark room, or a filter is placed above the CCD camera mirror to filter out ambient light in wavelengths other than the pulsed laser.

[0027] In one embodiment, the control device includes at least one synchronization controller connected to the CCD camera and the four-pulse laser, respectively, for controlling the four laser pulses emitted by the four-pulse laser each time to irradiate the tracer particle and be captured by the CCD camera to obtain tracer particle images under different pulse laser irradiation, and to obtain the particle velocity and acceleration based on the tracer particle images. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the structure of an acceleration measurement device based on particle image velocimetry provided in one embodiment of this application.

[0030] Figure 2 This is a schematic diagram of the structure of a polarization device provided in one embodiment of this application.

[0031] Figure 3 This is a schematic diagram showing the time interval between the pulsed laser of the four-pulse laser provided in one embodiment of this application and the exposure and imaging by the CCD camera.

[0032] Figure 4 This is a schematic diagram of an acceleration measurement process based on particle image velocimetry provided in one embodiment of this application. Detailed Implementation

[0033] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0035] When describing positional relationships, unless otherwise specified, when an element such as a layer, film, or substrate is referred to as being "on" another film layer, it may be directly on the other film layer or there may be intermediate film layers. Furthermore, when a layer is referred to as being "below" another layer, it may be directly below it or there may be one or more intermediate layers. It is also understood that when a layer is referred to as being "between" two layers, it may be the only layer between the two layers, or there may be one or more intermediate layers.

[0036] When using the terms “including,” “having,” and “comprising” as described herein, another component may be added unless explicitly qualifying terms such as “only,” “consisting of,” etc. are used. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.

[0037] It should be understood that although the terms “first,” “second,” etc., may be used in this document to describe various elements, these elements should not be limited by these terms.

[0038] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and are not intended to 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 the present invention.

[0039] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only, and are used solely to distinguish one element from another. They should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. For example, a first element may be referred to as a second element without departing from the scope of the invention, and similarly, a second element may be referred to as a first element. In the description of the invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0040] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0041] like Figure 1 As shown, an acceleration measurement device based on particle image velocimetry provided in one embodiment of this application includes:

[0042] At least two CCD cameras, with the center points of the mirrors of the two CCD cameras positioned opposite each other and lying on a straight line, are used to acquire images of the tracer particles.

[0043] In this embodiment, a first CCD camera 41 and a second CCD camera 42 are positioned with their mirror surfaces facing each other. The first CCD camera 41 and the second CCD camera 42 are respectively mounted on a limiting device 43. The limiting device 43 ensures that the center points of the mirror surfaces of the first CCD camera 41 and the second CCD camera 42 are aligned on a straight line. The first CCD camera and the second CCD camera can respectively capture images of tracer particles illuminated by pulsed laser light, ensuring that the images obtained by the first CCD camera 41 and the second CCD camera 42 simultaneously capturing the same stationary object are identical. In this embodiment, the limiting device 43 may include a linear guide rail 431 and a groove 432. The linear guide rail 431 is used to limit the displacement of an object located within the groove 432 to a linear path. The first CCD camera 41 and the second CCD camera 42 are respectively located within the slide groove 432, and can move linearly along the linear guide rail 431 within the slide groove 432, ensuring that the center points of the first CCD camera 41 and the second CCD camera 42 are on the same straight line, and the first CCD camera 41 and the second CCD camera 42 are each equipped with the same lens, such as a 50mm lens, with the same aperture size. The first CCD camera 41 and the second CCD camera 42 are at the same distance from the laser sheet light, thereby ensuring the same field of view.

[0044] The tracer particle generator 10 is used to emit tracer particles in a direction perpendicular to the normal of the CCD camera mirror.

[0045] The tracer particle generator 10 can spray tracer particles along the flow direction of the fluid being measured. Since the particles follow the movement of the object being measured, the measured particle velocity can be considered as the velocity of the object being measured.

[0046] A four-pulse laser 30 is used to sequentially emit four pulsed laser beams along a direction perpendicular to the particle flow direction.

[0047] The quad-pulse laser 30 can emit four high-energy laser pulses with a very short time interval between adjacent pulses. The pulsed lasers can be used by optical elements to form a sheet of light that illuminates the object under test, causing tracer particles in the fluid under test to reflect the light and be captured in an image. In this embodiment, each pulse emitted by the quad-pulse laser 30 is transient, with a pulse width of 6–10 ns and a wavelength of 532 nm.

[0048] The control device 50 is connected to the first CCD camera 41, the second CCD camera 42 and the four-pulse laser 30 respectively, and is used to synchronously control the first CCD camera 41, the second CCD camera 42 and the four-pulse laser 30, so that the first CCD camera 41 and the second CCD camera 42 acquire tracer particle images under different pulse laser irradiation in dual exposure mode, and acquire the particle velocity and acceleration based on the tracer particle images.

[0049] Specifically, in the particle image velocimetry acceleration measurement device in the above embodiments, firstly, by setting the first CCD camera 41 and the second CCD camera 42 on the limiting device 43, the tracer particle generator 10 emits tracer particles along a direction perpendicular to the normal of the mirror surfaces of the first CCD camera 41 and the second CCD camera, so that the tracer particles follow the measured fluid and have the same velocity as the fluid. Then, the control device 50 controls the first CCD camera 41 and the second CCD camera 42 to perform double exposure shooting, and controls the start time of the exposure of the second CCD camera 42 to be after the completion time of the second exposure shooting of the first CCD camera 41. At the same time, the four-pulse laser 30 is controlled to emit four pulse laser beams sequentially along a direction perpendicular to the flow direction of the tracer particles to illuminate the tracer particles, so that the first CCD camera 41 captures tracer particle images under the illumination of the first pulse laser and the second pulse laser, respectively, and the second CCD camera 42 captures tracer particle images under the illumination of the third pulse laser and the fourth pulse laser, respectively. Because the time interval between two consecutive tracer particle images is fixed and extremely short, three tracer particle velocity values ​​can be obtained based on the four acquired tracer particle images. Because the time interval between laser pulses is fixed and extremely short, two tracer particle acceleration values ​​can be obtained based on the three acquired tracer particle velocities, and thus the acceleration value of the measured fluid can be obtained.

[0050] In the particle image velocimetry acceleration measurement device of the above embodiment, a four-pulse laser capable of sending four high-energy laser pulses at once is used, and the time interval between each pair is very short. Tracer particles are scattered in the measured airflow using a tracer particle generator, and the tracer particle stream is illuminated by laser emitted by the four-pulse laser. The center points of the mirrors of two CCD cameras are arranged on a straight line to capture the tracer particle stream illuminated by the pulsed laser beam, thereby obtaining at least four particle images with very short time intervals. The velocity of the particles is obtained based on the tracer particle images, and then the acceleration value of the particles is calculated based on the particle velocity values ​​with very short time intervals.

[0051] Furthermore, in one embodiment of this application, the acceleration measurement device based on particle image velocimetry also includes a polarization device, which can combine the emitted light from a four-pulse laser into one or two beams. The polarization device may include at least four internal polarizers, at least one external polarizer, and at least two beam-splitting polarizers. Each internal polarizer can be disposed on the four-pulse laser to polarize the four pulses respectively; the external polarizer can be disposed outside the four-pulse laser to combine the emitted light into one beam and to analyze the polarization of that beam; the two beam-splitting polarizers can be disposed outside the mirrors of the first CCD camera and the second CCD camera respectively to refract the combined beam emitted by the four-pulse laser into two beams, which are then directed into the first CCD camera and the second CCD camera respectively.

[0052] Specifically, in the polarization device of the above embodiments, such as Figure 2 As shown, the polarization device 60 may include four internal polarizers 61, one external polarizer 62, and a first beam-splitting polarizer 631 and a second beam-splitting polarizer 632. The four internal polarizers 61 are respectively disposed on a four-pulse laser to polarize the first, second, third, and fourth pulse lasers, respectively, and refract them onto the external polarizer 62. The pulse lasers can be combined into a single beam by the polarizer 62. This combined beam is then refracted into two separate beams by the first and second beam-splitting polarizers 631 and 632, respectively, and then directed into the first and second CCD cameras. Therefore, the first and second beam-splitting polarizers 631 and 632 can be positioned on the outer sides of the mirrors of the first and second CCD cameras, respectively. The polarization device 60 can combine the emitted light from the four-pulse laser into one or two beams for different application scenarios. At the same time, it facilitates the two CCD cameras with mirrors facing each other in this application to capture images of the tracer particles irradiated by the four pulses emitted by the four-pulse laser at one time.

[0053] In one embodiment of this application, an acceleration measurement device based on particle image velocimetry is provided. After acquiring a tracer particle image, a cross-correlation algorithm can be used to obtain the particle velocity, and then the particle acceleration can be obtained based on the acquired particle velocity.

[0054] Specifically, in the particle image velocimetry-based acceleration measurement device in the above embodiments, the CCD camera can be a dual-exposure CCD camera, used for continuously exposing two images at once. For example... Figure 3As shown, the image shows a first tracer particle image 411, captured by a first CCD camera during a single exposure at time t1, under the illumination of a first pulsed laser, where the first pulsed laser begins to emit at time t2; a second tracer particle image 412, captured by a second CCD camera during a second exposure, under the illumination of a second pulsed laser, where the second pulsed laser begins to emit at time t3; a third tracer particle image 421, captured by a second CCD camera during a single exposure at time t4, under the illumination of a third pulsed laser, where the third pulsed laser begins to emit at time t5; and a fourth tracer particle image 422, captured by a second CCD camera during a second exposure, under the illumination of a fourth pulsed laser, where the fourth pulsed laser begins to emit at time t6. The tracer particle pair captured in the first tracer particle image 411 during time t2 is denoted as S1, and the tracer particle pair captured in the second tracer particle image 412 during time t3 is denoted as S2. The tracer particle pair captured in the third tracer particle image 421 starting at time t5 is denoted as S3, and the tracer particle pair captured in the fourth tracer particle image 422 starting at time t6 is denoted as S4. Image matching is performed between S1 and S2. Each tracer particle in the image of S1 is displayed using grayscale intensity, and a single-pixel ensemble cross-correlation method is used to find the tracer particle in S2 that corresponds to the image in S1 for matching. Specifically, in the cross-frame image pair of tracer particles, the pixel coordinates of the tracer particle in S1 are (i,j), and the pixel coordinates of the corresponding pixel in S2 whose neighborhood distance is (Δr,Δs) are (i+Δr,j+Δs). Then, all N... f The ensemble correlation function of a pair of tracer particles across frames is expressed by the formula:

[0055]

[0056] In equation (1-1), and These are the gray values ​​of the pixels located in the S1 and S2 images of the nth tracer particle across the frame image pair, respectively. and It is N f The ensemble mean of gray intensity of pixels located in images S1 and S2 across a cross-frame image pair of tracer particles, σ represents the standard deviation of gray intensity:

[0057]

[0058] Get N f After obtaining the ensemble correlation function of each tracer particle across frame image pairs, the ensemble correlation function R is found using a cross-correlation algorithm. Δr,ΔsThe peak value of (i,j) is used to obtain the displacement of the tracer particle between S1 and S2, and finally the velocity v1 of the tracer particle is obtained. Since each pulse emitted by the four-pulse laser is transient, with a pulse width typically 6ns-10ns and a wavelength of 532nm, the exposure time of the first image of the dual-exposure CCD camera is 2us-1ms, and the exposure time of the second image of the dual-exposure CCD camera is 30ms. Therefore, as... Figure 3 As shown, the values ​​of t5-t3 or t6-t5 are very small. Therefore, when Δt is one of t5-t3 or t6-t5, the velocities v1, v2, and v3 obtained from the tracer particles in S1, S2, S3, and S4 can be used. Figure 4 As shown, following the same calculation method as for v1, the velocity v2 of the tracer particle is obtained from the displacement between S2 and S3, and the velocity v3 of the tracer particle is obtained from the displacement between S3 and S4. The acceleration a within this time interval is obtained from the following equation (2-1), where Δt is the time it takes for the acceleration to complete. Let the acceleration of the tracer particle between v1 and v2 be a1, and the acceleration of the tracer particle between v2 and v3 be a2, then:

[0059]

[0060]

[0061]

[0062]

[0063] Furthermore, in one embodiment of the particle image velocimetry acceleration measurement device provided in this application, it is actually possible to obtain two velocity fields and one acceleration field using only three images S1, S2, and S3, or only three images S2, S3, and S4. In this embodiment, it is not necessary to measure all four images each time; two acceleration fields or one acceleration field can be calculated as needed. The pulse width of the laser emitted by the four-pulse laser is less than the exposure time of any image from the CCD camera. The CCD camera is exposed and photographed in a dark room, or a filter can be placed above the CCD camera mirror to filter out ambient light of wavelengths other than the pulsed laser, ensuring that all tracer particles irradiated by any laser pulse are within the exposure time of the CCD camera, such as... Figure 3As shown, the duration of the first laser pulse is entirely included within the first exposure time of the first CCD camera; the duration of the second laser pulse is entirely included within the second exposure time of the first CCD camera; the duration of the third laser pulse is entirely included within the first exposure time of the second CCD camera; and the duration of the fourth laser pulse is entirely included within the second exposure time of the second CCD camera. This configuration ensures that the CCD camera cannot capture tracer particle images before the four-pulse laser emits its pulses, and that each exposure captures a complete tracer particle image under the pulse laser illumination. This facilitates the selection of corresponding tracer particle pairs from the acquired tracer particle images, enabling the calculation of tracer particle velocities using cross-correlation algorithms. Since the time interval between the four-pulse laser pulses is extremely short—meaning the time interval experienced by the tracer particle pairs in the acquired cross-frame images is extremely short—the tracer particle acceleration can be obtained using the acquired tracer particle velocities.

[0064] Furthermore, in one embodiment of the particle image velocimetry acceleration measurement device provided in this application, the control device includes at least one synchronization controller, which is connected to the CCD camera and the four-pulse laser respectively. This controller controls the four laser pulses emitted by the four-pulse laser to irradiate the tracer particle, which is then captured by the CCD camera to obtain tracer particle images under different pulse laser irradiation conditions. Based on these tracer particle images, the particle velocity and acceleration are obtained. In this embodiment, the synchronization controller may include two DG645 units. The DG645 is an eight-channel digital delay pulse generator. The DG645 generates TTL amplitude pulses using high-precision circuitry and digitally controls their delay time for output. It provides four independently controlled pulse outputs, up to eight delay logic conversions, a delay resolution of 5 ps for all channels, and jitter between each channel less than 25 ps. The pulse frequency is up to 10 MHz. The DG645 can be connected to a computer via Ethernet, General Purpose Interface Bus (GPIB), and RS-232 interface. The DG645 offers lower jitter, higher precision, faster trigger frequency, and more output, making it ideal for the timing control of the pulsed laser from a four-pulse laser and the exposure time of the CCD camera, as required in this application.

[0065] Furthermore, in the particle image velocimetry-based acceleration measurement device described in the above embodiments, two DG645 units are respectively connected to a computer to control a dual-exposure CCD camera and a four-pulse laser, enabling them to cooperate to obtain tracer particle images under pulsed laser illumination with extremely short time intervals. A first DG645 is connected to both dual-exposure CCD cameras to control the exposure time interval between the first and second CCD cameras. A second DG645 is connected to the four-pulse laser to control the time interval between the first, second, third, and fourth pulsed lasers. By controlling the pulsed laser emitted by the four-pulse laser to match the exposure time of the two dual-exposure CCD cameras controlled by the first DG645, tracer particle images under four pulsed laser illumination with extremely short time intervals are obtained, thereby acquiring three tracer particle velocity values ​​and two tracer particle acceleration values.

[0066] In the particle image velocimetry acceleration measurement device in the above embodiments, two eight-channel digital delay pulse generators are used to control a dual-exposure CCD camera and a four-pulse laser, respectively, so that the two cooperate with each other to obtain tracer particle images under pulse laser irradiation with extremely short time intervals, thereby obtaining three tracer particle velocity values ​​and two tracer particle acceleration values.

[0067] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An acceleration measurement device based on particle image velocimetry, characterized in that, include: At least two CCD cameras, the normals of the mirrors of the two CCD cameras coincide, are used to acquire images of tracer particles, the two CCD cameras include a first CCD camera and a second CCD camera. A limiting device is used to limit the first CCD camera and the second CCD camera to be located on a straight line, and the normals of the mirror surfaces of the first CCD camera and the second CCD camera coincide. A tracer particle generator is used to emit tracer particles in a direction perpendicular to the normal of the CCD camera mirror. A four-pulse laser is used to sequentially emit four pulsed laser beams along a direction perpendicular to the particle flow to illuminate the tracer particles. The pulse width of the laser emitted by the four-pulse laser is 6ns-10ns. A polarization device is used to polarize and detect the four pulsed laser beams respectively. A control device is connected to both the CCD camera and the four-pulse laser, and is used to synchronously control the CCD camera and the four-pulse laser. This allows the CCD camera to acquire tracer particle images under different pulse laser illuminations, and to obtain the particle velocity based on the tracer particle images using grayscale intensity display and single-pixel ensemble cross-correlation methods. The acceleration is then calculated based on the velocity. The control device includes two DG645 synchronous controllers, which control the pulse timing of the four-pulse laser and the exposure timing of the CCD camera, respectively, ensuring that the duration of the pulse laser is entirely within the exposure time of the CCD camera, and that the minimum time interval between adjacent pulse lasers is 200 ns.

2. The acceleration measurement device based on particle image velocimetry according to claim 1, characterized in that, The first CCD camera and the second CCD camera are at the same distance from the laser sheet light.

3. The acceleration measurement device based on particle image velocimetry according to claim 1, characterized in that, The polarization device further includes: At least four internal polarizing mirrors are respectively disposed on the four-pulse laser for polarization; At least one external polarizing mirror is disposed outside the four-pulse laser for combining the emitted light from the four-pulse laser into a single beam and for polarization analysis; and At least two beam polarizers are used to split the beam of light into two beams that enter two CCD cameras respectively.

4. The acceleration measurement device based on particle image velocimetry according to any one of claims 1-3, characterized in that, Based on the tracer particle image, the particle velocity is obtained using a cross-correlation algorithm, and the particle acceleration is obtained based on the particle velocity.

5. The acceleration measurement device based on particle image velocimetry according to claim 4, characterized in that, The CCD camera is a dual-exposure CCD camera, used to sequentially expose two images.

6. The acceleration measurement device based on particle image velocimetry according to claim 5, characterized in that: Using a dual-exposure CCD camera, two images are acquired starting from time T0, and particle velocities are obtained using a cross-correlation algorithm. ; Based on another double-exposure CCD camera from T0+ Two images are acquired at each time step, and the particle velocity is obtained using a cross-correlation algorithm. ; The obtained particle acceleration 'a' is: 。 7. The acceleration measurement device based on particle image velocimetry according to claim 6, characterized in that, The exposure time for the first image of the dual-exposure CCD camera is 2µs-1ms, and the exposure time for the second image of the dual-exposure CCD camera is 30ms.

8. The acceleration measuring device based on particle image velocimetry according to any one of claims 1-3, characterized in that, The pulse width of the laser emitted by the quad-pulse laser is less than the exposure time of any image of the dual-exposure CCD camera. The dual-exposure CCD camera is used for exposure and shooting in a dark room, or a filter is placed above the mirror of the dual-exposure CCD camera. The filter is used to filter out ambient light in wavelengths other than the pulsed laser.

9. The acceleration measuring device based on particle image velocimetry according to any one of claims 5-7, characterized in that, The control device includes at least one synchronous controller, which is connected to the dual-exposure CCD camera and the four-pulse laser respectively. It is used to control the four laser pulses emitted by the four-pulse laser to irradiate the tracer particles and be captured by the dual-exposure CCD camera to obtain tracer particle images under different pulse laser irradiation, and to obtain the particle velocity and acceleration based on the tracer particle images.

Images