A FLEET speed measurement method and device with point-line fusion marking

Abstract

The present invention discloses a FLEET speed measurement method and device with point-line fusion marking, which relates to the technical field of gas flow field speed measurement. The method includes the following steps: obtaining the position of the gas flow field, and dividing the output laser into line excitation laser and point excitation laser; the line excitation laser is focused in the measurement area to generate a fluorescence marking line; the point excitation laser is modulated into a line beam group, and the line beam group intersects with the fluorescence marking line to obtain fluorescence marking points; obtaining the fluorescence signals of the point-line fusion marking at two consecutive moments to obtain two fluorescence images; extracting the spatial positions of the fluorescence marking line in the two fluorescence images to achieve successful matching of the fluorescence line marking molecular clusters in the two fluorescence images, and using the ratio of the spatial position difference of the fluorescence marking line in the two fluorescence images to the difference between the two different moments to calculate the flow field velocity at the fluorescence marking line. This method uses point-line fusion to enhance the marking, and improves the speed measurement accuracy of the gas flow field by improving the spatial position matching accuracy of the tracer molecules.

Description

Technical Field

[0001] The present invention relates to the technical field of gas flow field velocity measurement, and in particular, to a FLEET velocity measurement method and device with point-line fusion marking. Background Art

[0002] The flow velocity of a fluid is the most fundamental physical quantity of a flow field. The understanding of flow characteristics largely depends on the acquisition of the flow field velocity. Developing gas flow field velocity measurement technology to provide reliable velocity measurement results for experimental aerodynamics is of great significance for the rapid development of advanced aircraft and weaponry and the continuous progress of the propulsion aerodynamics discipline. With the rapid development of modern aviation, aerospace technology, and the aerodynamics discipline, the demand for flow field velocity measurement in hypersonic and near-wall regions of complex models has become more urgent, and at the same time, it has also posed new challenges to flow field velocity measurement technology. Currently, contact measurement technologies such as hot wires and pitot tubes will seriously interfere with the magnetic field in hypersonic complex flow field measurements, and the number of measurement points is limited. Particle Imaging Velocimetry (PIV), Laser Doppler Velocimetry (LDV), and other particle-tracing-based velocity measurement technologies are widely used. However, when measuring the flow field velocity, these technologies need to add tracer particles to the flow field. Affected by the particle addition technology and the followability of the tracer particles themselves, they are more restricted in hypersonic complex flows and even unable to measure. In recent years, the newly developed Femtosecond laser electronic excitation tagging velocimetry (FLEET) technology, which excites and traces the molecules existing in the flow field through a laser, has outstanding advantages such as good followability, non-interference with the flow field, and relatively simple system, and is expected to become a method that can meet the requirements of fine measurement of hypersonic complex flow velocities, complementing the existing technologies. Currently, in the application of the FLEET technology based on line excitation, since the line excitation technology uses a laser beam to excite a fluorescent line in the flow field, and after the fluorescent line moves in the flow field for a certain time, its moving distance is measured to calculate the flow field velocity, it is necessary to match the characteristic positions of the fluorescent lines. However, the front and rear fluorescent lines are almost the same, making it difficult to match the same characteristic positions of the two fluorescent lines, resulting in difficulties in matching the spatial positions of the tracer molecules, thus seriously affecting the velocity measurement accuracy and unable to meet the requirements of scientific research and engineering applications. Summary of the Invention

[0003] To solve the problem of difficult spatial position matching of tracer molecules in existing FLEET technology and improve the velocity measurement accuracy of FLEET technology in velocity measurement of hypersonic complex flow fields, the present invention provides a FLEET velocity measurement method with point-line fusion marking, and the method includes the following steps:

[0004] Obtain the position of the gas flow field to be measured, and divide the laser output by the laser into line excitation laser and point excitation laser, and the intensity of the line excitation laser is greater than the intensity of the point excitation laser;

[0005] The line excitation laser is focused in the measurement area to generate a fluorescence marking line;

[0006] Modulate the point excitation laser into a plurality of line beam groups that are parallel to each other, coplanar, and have equal spacing. The line beam groups intersect with the fluorescence marking line to obtain a number of fluorescence marking points, realizing the point-line fusion marking of the gas flow field;

[0007] Obtain the fluorescence signals of the point-line fusion marking at two successive moments to obtain two fluorescence images;

[0008] Extract the spatial positions of the fluorescence marking line in the two fluorescence images, and successfully match the fluorescence line marking molecular clusters in the two fluorescence images. Use the ratio of the spatial position difference of the fluorescence marking line in the two fluorescence images to the difference between the two different moments to calculate and obtain the flow field velocity at the fluorescence marking line.

[0009] Principle of the present invention: Obtain the position of the gas flow field to be measured, divide the laser beam emitted by the laser into line excitation laser and point excitation laser. The intensity of the line excitation laser is greater than that of the point excitation laser. The line excitation laser and the point excitation laser originate from the same laser beam, and the interference between the line excitation laser and the point excitation laser is small. Therefore, the synchronization and stability of the line excitation laser and the point excitation laser are also better. The line excitation laser is focused in the gas flow field area to generate a fluorescence marking line. The point excitation laser is modulated into a group of line light beams that are parallel to each other, coplanar, and have equal spacing. The multiple light beams in the line light beam group are parallel to each other, coplanar, and have equal spacing. One is to make each light beam of the line light beam group intersect with the fluorescence marking line to obtain several fluorescence marking points, realizing the point-line fusion marking of the gas flow field. The other is to facilitate the extraction of the spatial positions of several fluorescence marking points and subsequent calculation of the gas flow field velocity. Since the intensity of the line excitation laser is greater than that of the point excitation laser, the fluorescence signal intensity at the fluorescence marking points will be enhanced (the fluorescence marking points will be jointly excited by the two light beams) without affecting the signal intensity of the fluorescence marking line. Obtain the fluorescence signals at two successive moments to obtain two fluorescence images. Since the fluorescence signal intensity of the fluorescence marking points is enhanced, it is beneficial to extract the spatial positions of the fluorescence marking lines in the two fluorescence images. Use the ratio of the spatial position difference of the fluorescence marking lines in the two fluorescence images to the difference between the two different moments, and then calculate the flow field velocity at the fluorescence marking lines. Measuring the gas flow field velocity by this method has the following beneficial effects: realizing non-contact accurate measurement of the gas flow field velocity distribution; without adding external tracer particles, with a wide application range; using point-line fusion to enhance marking, improving the spatial position matching accuracy of tracer molecules, and improving the measurement accuracy of the gas flow field velocity.

[0010] Preferably, the method further includes: extracting the spatial positions of the fluorescence marking points in the two fluorescence images, and successfully matching the fluorescence point marking molecular groups in the two fluorescence images. Using the ratio of the spatial position difference of the fluorescence marking points in the two fluorescence images to the difference between the two different moments, calculate the velocity at the fluorescence marking points; based on the matching results of the several fluorescence marking points, correct and constrain the matching results of the fluorescence marking lines in the two fluorescence images; based on the velocity calculation results at the several fluorescence marking points, correct and constrain the flow field velocity results at the fluorescence marking lines.

[0011] Among them, since the fluorescent marker points are independent of each other and the fluorescence signal intensity of the fluorescent marker points is higher than that of other fluorescence signals of the fluorescent marker line except for the fluorescent marker points, it is beneficial to extract the spatial positions of the fluorescent marker points in the two fluorescent images, realize the successful matching of the fluorescent marker points to the molecular clusters in the two fluorescent images, and then use the ratio of the spatial position difference of the fluorescent marker points in the two fluorescent images to the difference between two different moments to calculate the velocity at the fluorescent marker points. Because the line beam group and the fluorescent marker line generate several fluorescent marker points, and several fluorescent marker points are also on the same fluorescent marker line, the spatial position matching result of the fluorescent marker points in the fluorescent image can be used to constrain the spatial position matching result of the fluorescent marker line in the fluorescent image, and the calculated result of the velocity of the fluorescent marker points can be used to constrain the calculated result of the flow field velocity at the fluorescent marker line. Calculating the velocity of the fluorescent marker points is to integrate multiple points on the same fluorescent marker line to more accurately analyze the motion state of the flow field (including velocity, direction, etc.). Using the matching result of the fluorescent marker points to correct and constrain the matching result of the fluorescent marker line is to match the motion state of the fluorescent marker line according to the corresponding position change of the fluorescent marker points, so as to make the calculation of the flow field velocity and the judgment of the motion direction more accurate.

[0012] Preferably, the intensity ratio of the line excitation laser to the point excitation laser is 9:1. Among them, the laser output by the laser is divided into a line excitation laser and a point excitation laser, and the intensity ratio of the line excitation laser to the point excitation laser is 9:1. Only a very small part of the laser energy is used to generate the line beam group, realizing the signal enhancement of the fluorescent marker points, and hardly affecting the length and signal intensity of the fluorescent marker line.

[0013] Preferably, the laser is a femtosecond pulsed laser. Among them, the femtosecond pulsed laser has an ultra-high peak power, can excite N2 molecules in the flow field to generate fluorescence, and the fluorescence lifetime is relatively long. The flow field velocity is calculated by tracing the excited N2 molecules.

[0014] Preferably, the two fluorescent images are collected by a camera in this method. Among them, two fluorescent images are collected by a camera, and then presented by a computer.

[0015] Preferably, the collection of the two fluorescent images by the camera in this method includes: the field of view of the camera can cover all the several fluorescent marker points; the positions of the several fluorescent marker points on the two fluorescent images are independent of each other. Among them, it is ensured that the camera can cover all the excited fluorescent marker points and there is no overlap of each fluorescent marker point on the captured image, so as to meet the subsequent matching of the two fluorescent images according to the fluorescent marker points.

[0016] Preferably, in this method, a timing controller is used to control the acquisition time interval between the two fluorescence images, and to control the time when the laser emits laser pulses and the time when the camera shutter opens to be the same moment. Among them, using the timing controller to control the acquisition time interval between the two fluorescence images can achieve precise control of the time interval. Since the propagation time of the laser pulse can be ignored, the time when the laser pulse excites and labels the molecules existing in the flow field is almost the same as the time when the laser emits laser pulses. Moreover, because the fluorescence image at the initial moment is a straight line, it is more conducive to the feature position matching of the fluorescence images at subsequent moments. At the same time, the fluorescence lifetime of the molecules excited in the flow field is limited. Therefore, it is necessary to control the time when the laser emits laser pulses and the time when the camera shutter opens to be the same moment.

[0017] Preferably, the method further includes: using multiple sets of lasers to respectively generate the line excitation laser and the point excitation laser. Among them, multiple sets of lasers can be used to respectively generate the line excitation laser and the point excitation laser. For example, one set of lasers can be used to generate the line excitation laser, and another set or multiple sets of lasers can be used to generate the point excitation laser to achieve point-line fusion labeling. The effect of enhanced point-line fusion labeling will be better, but more equipment will be used and the optical path control will be more complex.

[0018] Preferably, the multiple sets of lasers emit laser pulses at the same moment. Among them, since the propagation time of the laser pulse can be ignored, if multiple sets of lasers are used to respectively generate the line excitation laser and the point excitation laser, and it is necessary to satisfy that the line excitation laser and the point excitation laser simultaneously label the molecular clusters in the flow field, it is necessary to control the time when the multiple sets of lasers emit laser pulses to be the same.

[0019] To solve the problem of difficult spatial position matching of tracer molecules in the existing FLEET technology and improve the velocity measurement accuracy of the FLEET technology in the velocity measurement of hypersonic complex flow fields, the present invention provides a FLEET velocity measurement device with point-line fusion labeling. The device includes a laser, a beam splitter, a lens, a mirror, a sheet light mirror group, a grating, a timing controller, a camera, and a computer; the laser is used to output a first laser; the beam splitter is used to split the first laser into a line excitation laser and a point excitation laser; the mirror is used to change the transmission direction of the point excitation laser; the sheet light mirror group is used to modulate the point excitation laser reflected by the mirror into sheet laser; the grating is used to modulate the sheet laser into a group of line light beams that are parallel to each other, coplanar, and have equal spacing; the lens is used to converge the line excitation laser to the gas flow field region; the timing controller is used to control the camera to photograph and record the fluorescence signal of point-line fusion labeling in the gas flow field region according to a preset timing sequence to obtain a fluorescence image; the computer is used to process the fluorescence image and calculate the velocity of the gas flow field.

[0020] Among them, the first laser generated by the laser is split into line excitation laser and point excitation laser by a beam splitter. The point excitation laser is reflected by a mirror to change the transmission direction, and the reflected point excitation laser is modulated into a sheet laser by a sheet light mirror group. The sheet laser is modulated by a grating into a group of line light beams that are parallel to each other, coplanar, and have equal spacing. The line excitation laser is focused onto the gas flow field area through a lens, and the line light beam group and the line excitation laser intersect to generate a number of fluorescence marking points. The timing controller controls the camera to capture and record the fluorescence signal marked by the point-line fusion in the gas flow field area according to a preset timing to obtain a fluorescence image. The computer then processes the fluorescence image, and finally calculates and obtains the gas flow field velocity.

[0021] One or more technical solutions provided by the present invention have at least the following technical effects or advantages:

[0022] It can achieve non-contact and accurate measurement of gas velocity distribution; there is no need to add external tracer particles, and the application range is wide; it uses point-line fusion to enhance marking, and by improving the spatial position matching accuracy of tracer molecules, it improves the velocity measurement accuracy of the gas flow field. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of the present invention, and do not limit the embodiments of the present invention;

[0024] Figure 1 It is a schematic flow chart of the FLEET velocity measurement method with point-line fusion marking in the present invention;

[0025] Figure 2 It is a schematic diagram of the FLEET velocity measurement device with point-line fusion marking in the present invention;

[0026] Among them, 1 - gas flow field, 2 - laser, 3 - beam splitter, 4 - line excitation laser, 5 - point excitation laser, 6 - lens, 7 - fluorescence marking line, 8 - mirror, 9 - sheet light mirror group, 10 - sheet laser, 11 - grating, 12 - line light beam group, 13 - fluorescence marking point, 14 - timing controller, 15 - intensified camera, 16 - computer, 17 - fluorescence image at the initial moment, 18 - fluorescence image after a certain time delay. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] In order to more clearly understand the above-mentioned objects, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0028] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways than those specifically described herein, and thus, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0029] Embodiment 1

[0030] Please refer to Figure 1 , Figure 1 which is a schematic flow diagram of a FLEET speed measurement method for point-line fusion marking in the present invention. The method includes the following steps:

[0031] Obtain the position of the gas flow field to be measured, and divide the laser output by the laser into line excitation laser and point excitation laser, where the intensity of the line excitation laser is greater than that of the point excitation laser;

[0032] The line excitation laser is focused in the measurement area to generate a fluorescence marking line;

[0033] Modulate the point excitation laser into a group of line light beams that are parallel to each other, coplanar, and have equal spacing. The group of line light beams intersects with the fluorescence marking line to obtain a number of fluorescence marking points, realizing the point-line fusion marking of the gas flow field;

[0034] Obtain two fluorescence images by acquiring the fluorescence signals of the point-line fusion marking at two successive moments;

[0035] Extract the spatial positions of the fluorescence marking line in the two fluorescence images, and successfully match the fluorescence line marking molecular clusters in the two fluorescence images. Use the ratio of the spatial position difference of the fluorescence marking line in the two fluorescence images to the difference between the two different moments to calculate the flow field velocity at the fluorescence marking line.

[0036] Among them, the fluorescence marking line is coplanar with the line beam group to ensure that multiple fluorescence marking points are formed by intersection, realizing the point-line fusion marking of the gas flow field. For the number of laser beams generated by the line beam group, it can be adjusted according to actual needs, but it is necessary to ensure that all the fluorescence marking points generated by the intersection with the fluorescence marking line can be collected by the camera, and at the same time, there will be no overlap of fluorescence marking points on the fluorescence image. The fluorescence signal intensity of the fluorescence marking points is higher than that of the remaining fluorescence signals of the fluorescence marking line except the fluorescence marking points. Since multiple laser beams of the line beam group intersect with the fluorescence marking line to generate fluorescence marking points, the fluorescence marking points are jointly excited by two laser beams, and the fluorescence signal intensity of the fluorescence marking points will be higher than that of the remaining fluorescence signals of the fluorescence marking line except the fluorescence marking points, which is also convenient for the accurate extraction of the positions of the fluorescence marking points and the fluorescence marking line at different delay times. The line excitation laser for generating the fluorescence marking line and the point excitation laser for generating the line beam group originate from the same optical pulse of the same laser, so they have good synchronization and stability. Since several fluorescence marking points are independent of each other and have obvious characteristics, on the one hand, it can improve the extraction accuracy when extracting the spatial positions of the fluorescence marking points, and on the other hand, it can also improve the matching accuracy when matching the same fluorescence marking point molecular group in two fluorescence images, thereby improving the velocity measurement accuracy of the gas flow field.

[0037] Among them, the method further includes: extracting the spatial positions of the fluorescence marker points in the two fluorescence images. For the extraction method of the fluorescence marker points, other methods such as the PIV algorithm or the optical flow algorithm can be used to achieve the successful matching of the fluorescence point-labeled molecular clusters in the two fluorescence images. Using the ratio of the spatial position difference of the fluorescence marker points in the two fluorescence images to the difference between two different times, the velocity at the fluorescence marker points is calculated; based on the matching results of several fluorescence marker points, the matching results of the fluorescence marker lines in the two fluorescence images are corrected and constrained; based on the calculated results of the velocities at several fluorescence marker points, the flow field velocity results at the fluorescence marker lines are corrected and constrained. Since the fluorescence signal at the fluorescence marker points is jointly excited by two laser beams, and the remaining fluorescence signals of the fluorescence marker lines except the fluorescence marker points are only excited by one laser beam, the fluorescence signal intensity at the fluorescence marker points is higher. Therefore, it is beneficial to extract the spatial positions of the fluorescence marker points in the two fluorescence images and to achieve the successful matching of the same fluorescence marker point molecular clusters in the two fluorescence images. Using the ratio of the spatial position difference of the fluorescence marker points in the two fluorescence images to the difference between two different times, the velocity at the fluorescence marker points is calculated. Because the fluorescence marker points are all on the fluorescence marker lines, the extraction and matching results of the spatial positions of the fluorescence marker lines are corrected and constrained by using the extraction and matching results of the spatial positions of the fluorescence marker points, and the calculated results of the flow field velocities at the fluorescence marker lines are corrected and constrained by using the calculated results of the velocities at the fluorescence marker points, thereby improving the measurement accuracy of the entire gas flow field velocity. Calculating the velocities of several fluorescence marker points and integrating the velocity results of multiple fluorescence marker points on the same fluorescence marker line can more accurately analyze the flow field motion state (velocity, direction, etc.). Using the corresponding position changes of several fluorescence marker points to indicate the motion state of the fluorescence marker line, so that the calculation of the flow field velocity and the judgment of the motion direction at the fluorescence marker line are more accurate.

[0038] Among them, the intensity ratio of the line-excited laser to the point-excited laser is preferably 9:1. The line-excited laser with higher intensity is focused into a fluorescence-labeled line in the gas flow field region, and the point-excited laser with lower intensity is modulated into a group of line beams that are parallel to each other, coplanar, and have equal spacing. The fluorescence-labeled line intersects with the group of line beams to generate several fluorescence-labeled points, realizing the point-line fusion labeling of the gas measurement flow field. Since the point-excited laser only utilizes a very small part of the laser energy, it hardly affects the length and signal intensity of the fluorescence-labeled line. If the intensity of the point-excited laser is too high, it will reduce the intensity of the line-excited laser, resulting in a relatively low signal-to-noise ratio of the collected fluorescence image, and may even fail to excite the generation of the fluorescence-labeled line, affecting the subsequent extraction and matching of the positions of the fluorescence-labeled points and the fluorescence-labeled line. Therefore, it is necessary to ensure that the intensity of the line-excited laser is higher than that of the point-excited laser, and the intensity of the line-excited laser should be sufficient to excite the corresponding molecules in the flow field to generate fluorescence. In the actual process, the intensity ratio of the line-excited laser to the point-excited laser can be adjusted according to the highest power density of the laser itself, and the present invention does not make specific limitations.

[0039] Among them, the laser is preferably a femtosecond pulse laser. A femtosecond laser is a "ultrashort pulse light" generating device that emits light only for a very short time of about 10 -15 seconds. Its main feature is that it has an extremely high peak power. For the model of the femtosecond pulse laser, models such as Astrella-1K-USP, Solstice Ace Ascend 60, or Phidia-1-FS can be selected, and the present invention does not make specific limitations. Because the femtosecond pulse laser has an extremely high peak power, it can excite N2 molecules in the flow field to generate fluorescence, and the fluorescence lifetime is relatively long. Other lasers can also be used to excite other molecules in the flow field for tracing, but it is necessary to make the laser reach a certain laser intensity and match the characteristics of the molecules to be excited in order to excite the generation of fluorescence, and the generated fluorescence lifetime should be relatively long in order to be used for tracing to measure the flow field velocity.

[0040] Among them, two fluorescence images are collected by a camera in this method. The camera is used to collect the fluorescence images and upload them to a computer, and then the computer processes the collected fluorescence images. For the model of the camera, models such as PI-MAX4, Andor-DH334, or Andor-DH720 can be selected and can be selected according to needs, and the present invention does not make specific limitations.

[0041] Among them, two fluorescence images are collected by the camera in this method, including: the camera's field of view can cover all several fluorescence marker points; the positions of the several fluorescence marker points on the two fluorescence images are independent of each other. In the subsequent velocity measurement of the flow field, it is necessary to use several fluorescence marker points to match the two fluorescence images. If the camera cannot collect all the fluorescence marker points and the fluorescence marker points overlap in the two fluorescence images, it will affect the matching of the characteristic positions of the fluorescence marker lines in the two fluorescence images, thereby affecting the subsequent flow field velocity measurement accuracy.

[0042] Among them, in this method, the time interval for collecting two fluorescence images is controlled by a timing controller, and the time when the laser emits laser pulses and the time when the camera's shutter is opened are controlled to be at the same moment. The timing controller can accurately control the time interval for collecting fluorescence images and can be set according to needs. Since the propagation time of the laser pulse can be ignored, the time for the laser pulse to excite and label the molecules existing in the flow field is almost the same as the time when the laser emits the laser pulse. Moreover, because the fluorescence image at the initial moment is a straight line, it is more conducive to the characteristic position matching of the fluorescence images at subsequent moments. At the same time, the fluorescence lifetime of the molecules excited in the flow field is limited. Therefore, it is necessary to control the time when the laser emits the laser pulse and the time when the camera's shutter is opened to be at the same moment. For the specific model of the timing controller, models such as DG645, DG535 or Micropulse can be selected and can be chosen according to actual needs. The present invention does not make specific limitations.

[0043] Among them, the method further includes: using multiple sets of lasers to respectively generate line excitation laser and point excitation laser, and the time when the multiple sets of lasers emit laser pulses is at the same moment. For example, one set of lasers can be used to generate line excitation laser, and another set of lasers can be used to generate point excitation laser. Since the propagation time of the laser pulse can be ignored, if multiple sets of lasers are used to respectively generate line excitation laser and point excitation laser, and it is necessary to satisfy that the line excitation laser and the point excitation laser simultaneously mark the molecular clusters in the flow field, it is necessary to control the time when these two sets of lasers emit laser pulses to be at the same moment. Since another set of lasers is used to generate point excitation laser, the effect of point-line fusion marking enhancement will be better, but more equipment will be used and the optical path control will be more complex. In this embodiment, the gas flow field region to be measured is obtained, the laser output by the laser is divided into line excitation laser and point excitation laser, and the intensity ratio of the line excitation laser and the point excitation laser is 9:1. The line excitation laser generates a fluorescence marking line after focusing in the gas flow field region, and the point excitation laser is modulated into multiple line beam groups that are parallel to each other, coplanar, and have equal spacing. The line beam groups intersect with the fluorescence marking line to obtain a number of fluorescence marking points, realizing the point-line fusion marking of the gas flow field; the timing controller controls the camera to sequentially capture the fluorescence signals of the point-line fusion marking at time t1 and time t2 according to the preset timing to obtain two fluorescence images, which are V1 and V2 respectively. First, the spatial positions of the fluorescence marking points in the fluorescence image V1 are extracted as S1, then the spatial positions S2 of the fluorescence marking points in the fluorescence image V2 are extracted, and the same molecular cluster of the fluorescence marking points is successfully matched in the fluorescence image V1 and the fluorescence image V2. The ratio of (S2 - S1) to (t2 - t1) is the calculation result of the velocity of the fluorescence marking points; the spatial position of the fluorescence marking line in the fluorescence image V1 is extracted as S3, the spatial position S4 of the fluorescence marking line in the fluorescence image V2 is extracted, and the same molecular cluster of the fluorescence marking lines is successfully matched in the fluorescence image V1 and the fluorescence image V2. The ratio of (S4 - S3) to (t2 - t1) is the calculation result of the flow field velocity at the fluorescence marking line. The matching result of the spatial position of the fluorescence marking points is used to constrain the matching result of the spatial position of the fluorescence marking line, and the calculation result of the velocity of the fluorescence marking points is used to constrain the calculation result of the gas flow field velocity at the fluorescence marking line, thereby improving the measurement accuracy of the gas flow field velocity at the entire fluorescence marking line.

[0044] Embodiment 2

[0045] Please refer to Figure 2 , Figure 2It is a schematic diagram of a FLEET speed measurement device with point-line fusion marking in the present invention. The device includes a laser 2, a beam splitter 3, a lens 6, a mirror 8, a sheet light mirror group 9, a grating 11, a timing controller 14, a camera 15 and a computer 16. The laser 2 is used to output a first laser. The beam splitter 3 is used to split the first laser into a line excitation laser 4 and a point excitation laser 5. The mirror 8 is used to change the transmission direction of the point excitation laser 4. The sheet light mirror group 8 is used to modulate the point excitation laser 4 reflected by the mirror 8 into a sheet laser 10. The grating 11 is used to modulate the sheet laser 10 into a group of line light beams 12 that are parallel to each other, coplanar and have equal spacing. The lens 6 is used to converge the line excitation laser 4 to the gas flow field 1 area. The timing controller 14 is used to control the camera 16 to capture and record the fluorescence signal of the point-line fusion marking in the gas flow field 1 area according to a preset timing sequence to obtain a fluorescence image. The computer 16 is used to process the fluorescence image and calculate the speed of the gas flow field 1.

[0046] Among them, determine the area of the gas flow field 1 to be measured. The laser output by the laser 2 is split by the beam splitter 3 into a line excitation laser 4 and a point excitation laser 5. The intensity ratio of the line excitation laser 4 and the point excitation laser 5 is 9:1. The line excitation laser 4 passes through the lens 6 and is focused in the gas flow field 1 area to generate a fluorescence marking line 7. The point excitation laser 5 first passes through the mirror 8 to change the transmission direction. The reflected point excitation laser 5 is modulated by the sheet light mirror group 9 into a sheet laser 10. The sheet laser 10 is then modulated by the grating 11 into a group of line light beams 12 that are parallel to each other, coplanar and have equal spacing. The line light beam group 12 intersects with the fluorescence marking line 7 to generate multiple fluorescence marking points 13 with enhanced signals, realizing the point-line fusion marking of the gas flow field 1. Then, using the timing control 14 according to the set timing sequence, accurately control the camera 15 to capture the fluorescence signals of the point-line fusion marking at two different times successively, obtaining the fluorescence image 17 at the initial time and the fluorescence image 18 after a certain time delay. The computer 16 respectively extracts the spatial coordinate positions of the fluorescence marking points 13 in the fluorescence image 17 at the initial time and the fluorescence image 18 after a certain time delay, obtains the moving displacement of each fluorescence marking point 13, divides the displacement by the acquisition time interval of the two fluorescence images, and calculates the speed of each fluorescence marking point 13. The computer 16 respectively extracts the spatial coordinate positions of the fluorescence marking line 7 in the fluorescence image 17 at the initial time and the fluorescence image 18 after a certain time delay, obtains the moving displacement of the fluorescence marking line 7, divides the displacement by the acquisition time interval of the two fluorescence images, and calculates the flow field speed of the entire fluorescence marking line. The position matching results of several fluorescence marking points 13 correct and constrain the position matching results of the fluorescence marking line 7, and the speed calculation results at several fluorescence marking points 13 correct and constrain the flow field speed calculation results at the fluorescence marking line 7, thereby improving the measurement accuracy of the speed of the entire gas flow field 1.

[0047] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made by those skilled in the art once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present invention.

[0048] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A FLEET speed measurement method with point-line fusion marking, characterized in that, The method includes the following steps: Obtain the position of the gas flow field to be measured, and divide the laser output by the laser into line excitation laser and point excitation laser, wherein the intensity of the line excitation laser is greater than that of the point excitation laser; The line excitation laser is focused in the measurement area to generate a fluorescence marking line; The point excitation laser is modulated into a group of line light beams that are parallel to each other, coplanar and have equal spacing. The group of line light beams intersects with the fluorescence marking line to obtain a number of fluorescence marking points, realizing the point-line fusion marking of the gas flow field; Obtain the fluorescence signals of the point-line fusion marking at two consecutive moments to obtain two fluorescence images; Extract the spatial positions of the fluorescence marking line in the two fluorescence images, and successfully match the fluorescence line marking molecular clusters in the two fluorescence images. Use the ratio of the spatial position difference of the fluorescence marking line in the two fluorescence images to the difference between the two different moments to calculate and obtain the flow field velocity at the fluorescence marking line.

2. The FLEET speed measurement method with point-line fusion marking according to claim 1, characterized in that, The method further includes: extracting the spatial positions of the fluorescence marking points in the two fluorescence images, and successfully matching the fluorescence point marking molecular clusters in the two fluorescence images. Use the ratio of the spatial position difference of the fluorescence marking points in the two fluorescence images to the difference between the two different moments to calculate and obtain the velocity at the fluorescence marking points; based on the matching results of the number of fluorescence marking points, correct and constrain the matching results of the fluorescence marking line in the two fluorescence images; based on the calculation results of the velocities at the number of fluorescence marking points, correct and constrain the flow field velocity results at the fluorescence marking line.

3. The FLEET speed measurement method with point-line fusion marking according to claim 1, characterized in that, The intensity ratio of the line excitation laser to the point excitation laser is 9:

1.

4. The FLEET speed measurement method with point-line fusion marking according to claim 1, wherein The laser is a femtosecond pulse laser.

5. The FLEET speed measurement method with point-line fusion marking according to claim 1, characterized in that, In this method, the two fluorescence images are collected by a camera.

6. The FLEET speed measurement method with point-line fusion marking according to claim 5, characterized in that, The collection of the two fluorescence images by the camera in this method includes: the field of view range of the camera can cover all the number of fluorescence marking points; the positions of the number of fluorescence marking points on the two fluorescence images are independent of each other.

7. A FLEET speed measurement method with point-line fusion marking according to claim 5, characterized in that, In this method, a timing controller is used to control the acquisition time interval of the two fluorescence images, and to control the time when the laser emits laser pulses and the shutter opening time of the camera to be at the same moment.

8. The FLEET speed measurement method with point-line fusion marking according to claim 1, wherein The method further includes: using multiple sets of lasers to respectively generate the line excitation laser and the point excitation laser.

9. A FLEET speed measurement method with point-line fusion marking according to claim 8, characterized in that At the same moment, multiple sets of lasers are used to respectively generate the line excitation laser and the point excitation laser.

10. A FLEET speed measurement device with a point-line fusion marker, characterized in that, The device includes a laser, a beam splitter, a lens, a mirror, a sheet light mirror group, a grating, a timing controller, a camera, and a computer; the laser is used to output a first laser; the beam splitter is used to split the first laser into a line excitation laser and a point excitation laser; the mirror is used to change the transmission direction of the point excitation laser; the sheet light mirror group is used to modulate the point excitation laser reflected by the mirror into a sheet laser; the grating is used to modulate the sheet laser into a group of line light beams that are parallel to each other, coplanar, and have equal spacing; the lens is used to converge the line excitation laser to the gas flow field region; the line excitation laser generates a fluorescence marking line when focused in the measurement region; the group of line light beams intersects with the fluorescence marking line to obtain a number of fluorescence marking points, realizing point-line fusion marking of the gas flow field; the timing controller is used to control the camera to capture and record the fluorescence signal of the point-line fusion marking in the gas flow field region according to a preset timing sequence to obtain a fluorescence image; the computer is used to process the fluorescence image and calculate the velocity of the gas flow field.

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