A molecular marker and scanning based two-dimensional velocity field measurement system and method

Abstract

The application discloses a two-dimensional velocity field measurement system and method based on molecular markers and scanning, and belongs to the field of molecular marker tracing velocity measurement. The application labels a flow field through a high-energy femtosecond laser pulse generated by a femtosecond laser source, and the high-energy femtosecond laser pulse is shot into an optical guide rail with a stepping motor, is finally shot into a multi-focal focusing lens system through a mirror on the optical guide rail, and after being modulated and shot out by the multi-focal focusing lens system, the high-energy femtosecond laser pulse generates a gas fluorescent label with a spatial structure and is shot and acquired by an image enhancement camera. Through a similarity algorithm, a point-to-point corresponding effect is realized after the label moves, and two-component measurement of each single point in a measurement range of a velocity field is completed. Through measurement of different points in a scanning area, two-dimensional two-component velocity measurement of the scanning area in the flow field is completed, and velocity field information with spatial resolution is acquired in a supersonic flow field. The application is suitable for the field of molecular marker tracing velocity measurement, and realizes two-dimensional two-component velocity measurement of a scanning area in a flow field.

Description

Technical Field

[0001] This invention relates to a two-dimensional velocity field measurement system and method based on molecular labeling and scanning, belonging to the field of molecular labeling tracer velocimetry. Background Technology

[0002] With the development of aircraft and engine technologies, flight speeds have reached the supersonic realm. However, due to the extreme complexity of the aerodynamic problems involved in the supersonic domain and the presence of numerous unknown physical phenomena, ground testing remains a crucial means of obtaining aircraft dynamic characteristics and aiding in aircraft design. Currently, however, there are limited measurement methods capable of acquiring spatially resolved velocity field information. While particle image velocimetry can acquire spatially resolved velocity field information, its application in supersonic flow fields is significantly limited by particle tracking and wear and tear on optical windows. New technologies are needed to fill these gaps. Summary of the Invention

[0003] To address the current shortage of measurement methods capable of acquiring spatially resolved velocity field information, the main objective of this invention is to provide a two-dimensional velocity field measurement system and method based on molecular markers and scanning, which acquires spatially resolved velocity field information in a supersonic flow field through molecular markers and mechanical scanning.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] This invention discloses a two-dimensional velocity field measurement system based on molecular labeling and scanning, comprising a femtosecond laser source, a multifocal focusing lens system, an optical rail containing a stepper motor, a synchronization control device, and an image intensifier camera. High-energy femtosecond laser pulses generated by the femtosecond laser source label the flow field and are then incident on the optical rail with the stepper motor. The pulses pass through a mirror on the optical rail and are ultimately incident on the multifocal focusing lens system. After being modulated and emitted by the multifocal focusing lens system, a gaseous fluorescent label with a spatial structure is generated and captured by the image intensifier camera. The timing of the entire system is controlled by the synchronization control device, including the incident time of the femtosecond laser pulse, the start time of the optical rail's movement, and the camera's image capture time.

[0006] Femtosecond lasers are used to generate high-energy femtosecond laser pulses, which induce nitrogen molecules to emit light, and the labeling and velocimetry process in the flow field is realized by using long-life nitrogen fluorescent molecules for labeling.

[0007] A multifocal focusing lens system consists of a beam expander group and a multifocal lens. The beam expander group, composed of concave and convex lenses, is used to amplify the light beam so that the light spot can cover the multifocal lens. The multifocal lens structure is similar to a Fresnel lens, but the focusing increases progressively from the inside out. When a high-energy femtosecond laser passes through this lens, the molecular markers generated will change due to the different focal lengths, thus modulating the morphology of the molecular markers.

[0008] The optical guide rail achieves continuous and stable movement of the markers within the flow field through mechanical movement. The marker spacing corresponds to the quotient of the stepper motor displacement speed and the laser repetition frequency.

[0009] The synchronization control device is used to precisely synchronize the wind tunnel operation time with the laser pulse incident time and the camera shutter opening time. This ensures that the time difference between image acquisition and laser incident time is sufficiently stable.

[0010] Image-enhanced cameras are used to acquire image information and extract the displacement of molecular marker lines.

[0011] This invention discloses a two-dimensional velocity field measurement method based on molecular markers and scanning, comprising the following steps:

[0012] Step 1: High-energy femtosecond laser marks the flow field. The molecular marks generated when passing through the multifocal lens system will change due to the different focal lengths in different areas of the lens, thus achieving modulation of the molecular mark morphology.

[0013] Step 2: The marked gas fluorescence is modulated and captured by an image intensifier camera. The velocity of the scanning area in the flow field is measured in one dimension and two components by calculation.

[0014] Velocity measurement is based on modulated molecular markers and relies on an algorithm to perform point-to-point mapping of the marker lines. To establish coordinates in the flow field, an image recognition algorithm is first used to extract the center lines of the molecular markers as initial markers. Then, two points with the most prominent features, p1(x1,y1) and p2(x2,y2), are selected from the initial markers. Subsequently, the positions p1, p2, and p2 after their movement are obtained from subsequently acquired images. 11 (x 11 ,y 11 ), p 22 (x 22 ,y 22 This allows us to choose any point p on the center line between points p1(x1,y1) and p2(x2,y2). i (x i ,y i Then, the position p of the marker after the movement is obtained through calculation. ii (x ii ,y ii ).

[0015] The specific calculation method is as follows:

[0016] l p1,p2 The length of the centerline of the molecular marker between the two points is given, and the equation of the initial molecular marker centerline is obtained by fitting the equation.

[0017] y i =f(x) i (1)

[0018] Then, by integrating the line lengths, we can obtain the distance from point p1 to p. i Line length:

[0019]

[0020] Similarly, we can obtain p after the movement. 11 to p 22 The equation of the center line and the integral of the line length.

[0021] y ii =f(x) ii (3)

[0022]

[0023] Furthermore, since the distance between the two points is short and the flow field is uniform between these two points, then we have:

[0024]

[0025] The point p is obtained by solving equations (3), (4), (5), and (6). i (x i ,y i The position p after moving ii (x ii ,y ii It can obtain the coordinates of the initial marker position and the marker position after movement at any point on the marker line, and obtain the displacement.

[0026]

[0027] Simultaneously, based on the laser incident time t1 and shutter opening time t2 provided by the synchronization system, the time difference corresponding to this displacement can be obtained:

[0028] Δt=t2-t1(7)

[0029] By calculating the ratio of displacement to time difference, the absolute value of the velocity at any point on the molecular marker line can be obtained:

[0030]

[0031] At the same time, knowing the starting point and the ending point of the marker after movement, the direction of velocity can be obtained:

[0032]

[0033] The corresponding velocity vector is represented as

[0034]

[0035] The above achieves two-component velocity measurement at any marked point within the scanning range;

[0036] Step 3: Perform a two-dimensional scan of the flow field region to achieve two-dimensional velocity measurement of the two components of the scanned region within the flow field.

[0037] High-energy femtosecond laser pulses generated by a femtosecond laser source are injected into an optical guide rail equipped with a stepper motor. The optical guide rail moves a multi-focal-length lens system via the stepper motor, achieving two-dimensional scanning in the flow field region. The initial spacing D of the marking lines is... l The spatial resolution corresponding to the flow direction of the flow field, and the stepper motor speed v s and laser repetition frequency f rep The correspondence is as follows:

[0038]

[0039] The direction of motor movement is opposite to the direction of flow field movement to avoid mutual interference. By measuring different points within the scanning area, two-dimensional, two-component velocity measurement of the scanning area within the flow field is achieved.

[0040] Beneficial effects

[0041] 1. The present invention discloses a two-dimensional velocity field measurement system and method based on molecular markers and scanning. By using Fresnel-like lens structures with different focal lengths, the spatial morphology of molecular markers is modulated, providing a basis for point-to-point correspondence calculation.

[0042] 2. The present invention discloses a two-dimensional velocity field measurement system and method based on molecular markers and scanning. The similarity algorithm is used to achieve point-to-point correspondence after the marker is moved, and to realize two-component measurement of each single point within the velocity field measurement marker range.

[0043] 3. The present invention discloses a two-dimensional velocity field measurement system and method based on molecular markers and scanning, which uses a stepper motor to precisely control the displacement of an optical guide rail and realizes two-dimensional flow field measurement through the scanning process. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of a two-dimensional velocity field measurement system based on molecular markers and scanning disclosed in this invention;

[0045] Among them: 1- Femtosecond laser source, 2- Optical guide rail with stepper motor, 3- Multifocal lens system, 4- Synchronization control device, 5- Image intensifier camera;

[0046] Figure 2 This is a structural diagram of the multifocal lens system in this invention;

[0047] Figure 3 This is a flowchart of a two-dimensional velocity field measurement method based on molecular labeling and scanning disclosed in this invention. Detailed Implementation

[0048] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The technical problems solved by the present invention and its beneficial effects are also described. It should be noted that the described embodiments are only intended to facilitate understanding of the present invention and do not constitute any limitation thereof.

[0049] like Figure 1 , Figure 2 As shown in this embodiment, a two-dimensional velocity field measurement system based on molecular labeling and scanning is disclosed, comprising a femtosecond laser source 1, an optical rail 2 with a stepper motor, a multifocal lens system 3, a synchronization control device 4, and an image intensifier camera 5. The femtosecond laser source 1 generates high-energy femtosecond laser pulses. The pulses are injected into the optical rail 2 with the stepper motor, then into a fixed reflector 1 on one side, reflected into another reflector 2 on the other side of the rail, and finally into the multifocal lens system 3. The reflector 2 and the multifocal lens system are fixed on a base with a stepper motor and move together at a uniform speed to scan the flow field. The femtosecond laser pulses, modulated and emitted by the multifocal lens system 3, generate gaseous fluorescent labels with spatial structures, which are captured by the image intensifier camera. The timing of the entire system is controlled by the synchronization control device, including the incident time of the femtosecond laser pulses, the start time of the optical rail's movement, and the camera's capture time.

[0050] Optical guide rail 2 enables the molecular marker scanning process in different regions of the flow field. A stepper motor drives a multi-focal-length lens system to move, achieving two-dimensional scanning within the flow field region. The initial spacing D between the marker lines... l The spatial resolution corresponding to the flow direction of the flow field (e.g.) Figure 1 ), and the stepper motor speed v s and laser repetition frequency f rep The correspondence is as follows:

[0051]

[0052] The direction of motor movement is opposite to the direction of flow field movement to avoid mutual interference.

[0053] The multifocal lens system 3 is the core of the entire system's measurement. It consists of three lenses: a concave lens, a convex lens, and a multifocal lens. The beam expander group, composed of the concave and convex lenses, is used to amplify the beam so that the light spot can cover the multifocal lens. The multifocal lens has a structure similar to a Fresnel lens, but the focusing increases progressively from the inside out. When the high-energy femtosecond laser passes through this lens, the molecular markers generated will change due to the different focal lengths, thus modulating the morphology of the molecular markers. The final morphology is similar to that shown in the figure (the number of rings and the focal length difference between each ring are determined according to the measurement requirements).

[0054] Velocity measurement is based on modulated molecular markers and is achieved through point-to-point mapping of the marker lines using an algorithm. First, a coordinate system is established in the flow field, such as... Figure 2 As shown, first, select the two points p1(x1,y1) and p2(x2,y2) with the most obvious features from the initial labels. Then, we can obtain the moved positions p of these two points in the subsequently acquired images by the camera. 11 (x 11 ,y 11 ), p 22 (x 22 ,y 22 Then, an image recognition algorithm is used to extract the centerline of the molecular markers, such as... Figure 2 As shown, this allows any point p to be selected on the center line between points p1(x1,y1) and p2(x2,y2). i (x i ,y i Then, the position p of the marker after the movement is obtained through calculation. ii (x ii ,y ii The algorithm is as follows: First, let l... p1,p2 The length of the centerline of the molecular marker between the two points is given, and the equation of the initial molecular marker centerline is obtained by fitting the equation.

[0055] y i =f(x) i (2)

[0056] Then, by integrating the line lengths, we can obtain the distance from point p1 to p. i Line length:

[0057]

[0058] Similarly, we can obtain p after the movement. 11 to p 22 The equation of the center line and the integral of the line length.

[0059] y ii =f(x) ii (4)

[0060]

[0061] Furthermore, since the distance between the two points is relatively short, the flow field can be considered uniform between these two points.

[0062]

[0063] The point p can be solved by combining equations (3), (4), (5), and (6). i (x i ,y i The position p after moving ii (x ii ,y ii In this way, we can obtain the initial and subsequent coordinates of any point on the marker line, and also obtain the displacement.

[0064]

[0065] Simultaneously, based on the laser incident time t1 and shutter opening time t2 provided by the synchronization system, the time difference corresponding to this displacement can be obtained:

[0066] Δt=t2-t1 (8)

[0067] The absolute value of the velocity at any point on the molecular marker line can be obtained by calculating the ratio of displacement to time difference.

[0068]

[0069] Furthermore, knowing the starting point and the ending point of the marker after movement, the direction of velocity can also be obtained:

[0070]

[0071] The corresponding velocity vector can then be expressed as:

[0072]

[0073] Therefore, this invention can realize the two-component velocity measurement of any marked point within the scanning range. By performing a two-dimensional scan of the flow field region, it is possible to realize the two-dimensional two-component velocity measurement of the scanned region within the flow field.

[0074] The field of this invention is an emerging field of molecular marker tracer velocimetry, where there are no mature algorithms yet. This invention aims to provide a multi-dimensional, spatially resolved measurement method for velocity measurement.

[0075] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is merely a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of two-dimensional velocity field measurement based on molecular tagging and scanning, characterized by: Comprising the following steps, Step 1, high-energy femtosecond laser marks the flow field, and the molecular markers generated by the multi-focal lens system will change due to the different focal lengths of different parts of the lens, realizing the modulation of the molecular marker form; Step 2, the marked gas fluorescence is photographed by the image intensifier camera, and the one-dimensional two-component velocity measurement of the scanning area in the flow field is realized by calculation; The implementation method of step 2 is, The speed measurement is based on the modulated molecular markers, and is realized by point-to-point mapping of the marker line by an algorithm; coordinates are established in the flow field, the center line of the molecular marker is extracted as an initial marker by using an image recognition algorithm, then two points p1(x1, y1) and p2(x2, y2) with the most obvious features are selected from the initial marker, and then the moving positions p 11 (x 11 ,y 11 ) and p 22 (x 22 ,y 22 ) of the two points are obtained in the subsequently collected images; that is, any point p i (x i ,y i ) on the center line between the two points p1(x1, y1) and p2(x2, y2) can be taken, and then the position p ii (x ii ,y ii ) of the moving marker is obtained by calculation. The specific calculation method is as follows: the length of the centerline of the molecular label between two points, while fitting the equation of the initial centerline of the molecular label y i = f(x i ) (1) Then the line length integral from point p1 to p i gives the line length: The same reasoning can be used to obtain the moving post-p 11 to p 22 tagged centerline equation and line length integral y ii = f(x ii ) (3) And the distance between the two points is short, and the flow field is uniform between the two points, so According to formula (3), formula (4), formula (5), formula (6) to solve the point p i (x i ,y i ) moved position p ii (x ii ,y ii );The coordinates of the initial mark position and the moved mark position of any point on the mark line can be obtained, and the displacement can be obtained At the same time, according to the laser incidence time t1 and the shutter opening time t2 provided by the synchronization system, the time difference corresponding to the displacement can be obtained: Δt=t2-t1 (7) By calculating the ratio of displacement and time difference, the absolute value of the velocity of any point on the molecular marker line can be obtained: At the same time, the starting point and the terminal position of the marker after moving can obtain the velocity direction: Then the corresponding velocity vector is expressed as The above realizes the two-component velocity measurement of any point in the scanning range of the marker; Step 3, two-dimensional scanning of the flow field area, realizing the two-dimensional two-component velocity measurement of the scanning area in the flow field.

2. A method for measuring two-dimensional velocity field based on molecular tagging and scanning as claimed in claim 1, wherein: The implementation method of step 3 is, The high-energy femtosecond laser pulse generated by the femtosecond laser source is injected into the optical guide rail with a stepping motor, the optical guide rail drives the multi-focus lens system to move through the stepping motor, and two-dimensional scanning in the flow field area is realized, and the initial position interval D of the marking line l Corresponding to the spatial resolution along the flow direction of the flow field, the stepping motor speed v s And the laser repetition frequency f rep The corresponding relationship is as follows: The movement direction of the motor is opposite to the movement direction of the flow field to avoid mutual influence; through the measurement of different points in the scanning area, the two-dimensional two-component velocity measurement of the scanning area in the flow field is realized.

3. A system for molecular tagging and scanning based two-dimensional velocity field measurement for implementing a method of molecular tagging and scanning based two-dimensional velocity field measurement as claimed in claim 1 or 2, characterized in that: It includes femtosecond laser source, multi-focal focusing lens system, optical guide rail containing stepping motor, synchronous control device, image intensifier camera; high-energy femtosecond laser pulses generated by femtosecond laser source mark the flow field, and are shot into the optical guide rail with stepping motor, and finally shot into the multi-focal focusing lens system through the reflecting mirror on the optical guide rail, and after being modulated by the multi-focal focusing lens system, the gas fluorescence marker with spatial structure is generated, and is photographed by the image intensifier camera; The timing of the whole system is controlled by the synchronous control device, including the incidence time of femtosecond laser pulse, the movement starting time of optical guide rail, and the camera shooting time.

4. The two-dimensional velocity field measurement system based on molecular marker and scanning according to claim 3, wherein: The femtosecond laser is used to generate high-energy femtosecond laser pulses, induce nitrogen molecules to emit light, and realize the flow field marking and velocity measurement process by means of long-life nitrogen fluorescence molecular markers; The multi-focal focusing lens system is composed of an expansion lens group and a multi-focal lens; the expansion lens group is composed of a concave lens and a convex lens, which is used to expand the light beam so that the light spot can cover the multi-focal lens; the multi-focal lens is similar in structure to a Fresnel lens, but the focusing increases from the inside to the outside, and the molecular markers generated by high-energy femtosecond laser through the lens will change due to different focal lengths, realizing the modulation of the molecular marker form; The optical guide rail realizes the continuous and stable movement of the marker in the flow field through mechanical movement, and the marker spacing corresponds to the quotient of the displacement speed of the stepping motor and the repetition frequency of the laser; The synchronous control device is used to control the accurate synchronization of the wind tunnel operation time, the laser pulse incidence time and the camera shutter opening time; ensure that the time difference between the image acquisition time and the laser incidence time is stable enough; An image intensifier camera is used to acquire image information from which the displacement of the molecular marker line is extracted.

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