Speed measurement system and method suitable for combined pulse high-enthalpy wind tunnel

Abstract

The invention discloses a speed measurement system and method suitable for a combined pulse high-enthalpy wind tunnel, and belongs to the technical field of aerodynamic tests. The objective of the invention is to improve the speed measurement precision in a high-speed high-enthalpy unsteady flow field. The system comprises a water cooling machine, a femtosecond laser, a reflector I, a time schedule controller, an input power supply, a reflector II, a reflector III, a plano-convex lens, a wind tunnel test section, a computer device and an imaging system. The femtosecond laser is respectively connected with the water cooling machine, the time sequence controller and the input power supply, and the imaging system is respectively connected with the time sequence controller and the computer device; laser emitted by the femtosecond laser irradiates the reflector I to be reflected, then is reflected by the reflector II and the reflector III and then enters the plano-convex lens, emergent laser enters a wind tunnel test section, and the imaging system shoots a test photo of the wind tunnel test section. Effective support is provided for hypersonic pneumatic tests and aircraft design verification.

Description

Technical Field

[0001] This invention belongs to the field of aerodynamic testing technology, specifically relating to a velocity measurement system and method suitable for combined pulse high enthalpy wind tunnels. Background Technology

[0002] With the development of aerospace technology, research on supersonic and hypersonic vehicles has placed higher demands on the accuracy of flow field velocity acquisition in wind tunnel tests. In combined pulsed high-enthalpy wind tunnels, the flow field is typically characterized by high temperature, high pressure, strong unsteadiness, and short test duration, which means that the velocity measurement method must not only have high sensitivity and fast response capabilities, but also minimize disturbance to the original flow.

[0003] Among existing velocity measurement methods, particle image velocimetry (PIV), while mature in conventional flow fields, has significant limitations under combined pulsed high-enthalpy wind tunnel conditions. Due to high temperature, high pressure, and high-speed shearing, tracer particles are difficult to disperse stably and are prone to ablation, aggregation, or rapid loss. Furthermore, particles entering the test section may introduce contamination or alter local flow conditions, thus affecting the reliability of the velocity measurement results and the repeatability of the wind tunnel test. Therefore, traditional particle-based velocimetry methods cannot meet the requirements of non-invasive, highly adaptable velocimetry in such wind tunnels.

[0004] Molecular labeling tracer velocimetry (MTV) avoids particle seeding problems by directly labeling gas molecules and tracking their flow, offering advantages such as non-contact operation and high temporal resolution. In particular, femtosecond laser-induced electron-induced molecular labeling (FLEET) technology uses femtosecond lasers to create fluorescent markers in the air, maintaining good label availability in high-temperature, high-pressure, and high-speed flow fields, thus being considered suitable for high-enthalpy wind tunnel velocimetry scenarios.

[0005] However, in actual experiments in combined pulsed high-enthalpy wind tunnels, image processing using FLEET / MTV still faces several challenges. On the one hand, fluorescence signals are often weak and easily affected by background light, scattered light, and random noise, resulting in insufficient effective signal contrast and difficulty in extracting the center position. On the other hand, factors such as camera installation deviation, imaging distortion, and refraction of the test window can introduce pixel-to-physical distance mapping errors, thereby amplifying systematic deviations in velocity calculations. Furthermore, under unsteady high-speed flow, the morphology and brightness distribution of fluorescent markers can diffuse or be locally missing over time, making traditional threshold segmentation or coarse centroid algorithms prone to unstable positioning, thus increasing the dispersion of velocity results.

[0006] Therefore, a molecular marker-guided velocimetry method is needed for combined pulsed high-enthalpy wind tunnel conditions, forming a more stable and accurate processing flow in key steps such as distance calibration, background suppression, and sub-pixel localization of fluorescence centers, so as to improve the accuracy and repeatability of velocimetry in high-speed, high-enthalpy unsteady flow fields. Summary of the Invention

[0007] The problem this invention aims to solve is to improve the velocity measurement accuracy in high-speed, high-enthalpy unsteady flow fields, and proposes a velocity measurement system and method suitable for combined pulse high-enthalpy wind tunnels.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A velocity measurement system suitable for a combined pulsed high-enthalpy wind tunnel includes a water chiller, a femtosecond laser, a reflector I, a timing controller, an input power supply, a reflector II, a reflector III, a plano-convex lens, a wind tunnel test section, a computer device, and an imaging system.

[0010] The femtosecond laser is connected to a water chiller, a timing controller, and an input power supply, respectively, and the imaging system is connected to the timing controller and a computer device, respectively.

[0011] The laser emitted by the femtosecond laser is reflected by mirror I, and then reflected by mirrors II and III before being incident on a plano-convex lens. The emitted laser is then incident on the wind tunnel test section, and the imaging system takes test photos of the wind tunnel test section.

[0012] Furthermore, the femtosecond laser has a laser frequency of 10 kHz and a center wavelength in the range of 1020–1050 nm.

[0013] Furthermore, the input power supply voltage is 220V and the current is 16A.

[0014] Furthermore, reflectors I, II, and III are all composed of reflectors and universal adjustment frames. By adjusting the knobs on the universal adjustment frames, it is ensured that the laser is always centered on the mirror surface.

[0015] Furthermore, the imaging system consists of a high-speed camera, an image intensifier, and a telephoto lens. The image intensifier is mounted in front of the high-speed camera, and the telephoto lens is mounted in front of the image intensifier. The timing controller is used to control the synchronous operation of the high-speed camera, the image intensifier, and the femtosecond laser in the imaging system.

[0016] A velocity measurement method suitable for combined pulsed high-enthalpy wind tunnels, based on the aforementioned velocity measurement system suitable for combined pulsed high-enthalpy wind tunnels, includes the following steps:

[0017] S1. Construct a velocity measurement system suitable for a combined pulse high-enthalpy wind tunnel;

[0018] S2. Set the image acquisition method. When the timing controller outputs a trigger signal to the femtosecond laser, a femtosecond laser pulse is generated. The imaging system performs multiple exposures according to the set trigger timing sequence, and each exposure acquires an independent image.

[0019] S3. Calculate the scaling factor between pixels and actual physical distances in the imaging system;

[0020] S4. Conduct wind tunnel tests in the wind tunnel test section, collect images during the test, perform image processing, and calculate the flow field velocity during the wind tunnel test.

[0021] Furthermore, the specific implementation method of step S4 includes the following steps:

[0022] S4.1. Following the image acquisition method in step S2, acquire N images;

[0023] S4.2. For each image acquired in step S4.1, calculate the center position of the laser point in the image;

[0024] S4.3. For any adjacent first... The center position of the first laser point and the... The center position of each laser point , ,and < The formula for calculating the flow field velocity in a wind tunnel test is as follows:

[0025] ( , )=k

[0026] ( , )=k

[0027] in, ( , () represents the horizontal velocity. ( , ) represents the vertical velocity, and k is the scaling factor between the pixel and the actual physical distance. For the first The horizontal coordinates of the center position of each laser point For the first The horizontal coordinates of the center position of each laser point For the first The vertical coordinates of the center position of each laser point For the first The vertical coordinates of the center position of each laser point The time interval for generating two adjacent laser points;

[0028] The flow field velocity in the wind tunnel test is calculated for any two adjacent laser points. Then, the average value of the flow field velocities in all wind tunnel tests is taken to obtain the final horizontal velocity. and vertical velocity .

[0029] The beneficial effects of this invention are:

[0030] This invention discloses a velocity measurement method suitable for combined pulsed high-enthalpy wind tunnels. It employs femtosecond laser molecular labeling for velocimetry, achieving non-invasive velocity measurement without particle seeding. This avoids problems such as unstable particle seeding, easy loss, and wind tunnel contamination in high-enthalpy environments. In data processing, this invention first uses a calibration target to acquire and smooth the scale brightness distribution under imaging conditions consistent with actual experiments. Then, it determines the scale edge position based on the brightness gradient extrema and achieves sub-pixel-level positioning through parabolic fitting, thereby obtaining a more accurate pixel-to-physical distance mapping coefficient and reducing the impact of imaging geometric errors on velocity calculation. Addressing the characteristics of weak fluorescence signals and strong background interference in pulsed high-enthalpy wind tunnels, this invention provides a limited processing area... Binary images are obtained through adaptive threshold segmentation, followed by connected component labeling and effective fluorescence region screening. Region constraints are constructed based on the target connected components to suppress background scattering and random noise, thereby improving the contrast of the effective signal. Subsequently, a brightness-weighted sub-pixel centroid algorithm is used to stably extract the center coordinates of the laser marker points on the effective fluorescence image, reducing positioning drift caused by marker diffusion, morphological changes, or local missingness. This forms a complete set of measurement steps from distance calibration and fluorescence image preprocessing to center positioning and velocity calculation. This invention enables the stable acquisition of reliable velocity data in a high-speed, high-temperature, high-pressure, and highly unsteady combined pulsed high-enthalpy wind tunnel flow field, significantly improving the accuracy and consistency of velocity measurement results, and providing effective support for hypersonic aerodynamic testing and aircraft design verification. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of a velocity measurement system suitable for a combined pulse high enthalpy wind tunnel according to the present invention;

[0032] Figure 2 This is a flowchart of a velocity measurement method applicable to a combined pulse high enthalpy wind tunnel according to the present invention; In the figure, 1 is the water chiller, 2 is the femtosecond laser, 3 is the reflector I, 4 is the timing controller, 5 is the input power supply, 6 is the reflector II, 7 is the reflector III, 8 is the plano-convex lens, 9 is the wind tunnel test section, 10 is the computer device, and 11 is the imaging system. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0034] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0035] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 and attached Figure 2 Detailed explanation is as follows:

[0036] Example 1:

[0037] A velocity measurement system suitable for a combined pulsed high-enthalpy wind tunnel includes a water chiller 1, a femtosecond laser 2, a reflector I 3, a timing controller 4, an input power supply 5, a reflector II 6, a reflector III 7, a plano-convex lens 8, a wind tunnel test section 9, a computer device 10, and an imaging system 11.

[0038] The femtosecond laser 2 is connected to the water chiller 1, the timing controller 4, and the input power supply 5 respectively, and the imaging system 11 is connected to the timing controller 4 and the computer device 10 respectively.

[0039] The laser emitted by the femtosecond laser 2 is reflected by the reflector I3, and then reflected by the reflector II6 and the reflector III7 before being incident on the plano-convex lens 8. The emitted laser is then incident on the wind tunnel test section 9, and the imaging system 11 takes test photos of the wind tunnel test section 9.

[0040] Furthermore, the femtosecond laser 2 has a laser frequency of 10 kHz and a center wavelength in the range of 1020–1050 nm.

[0041] Furthermore, the input power supply 5 has a voltage of 220V and a current of 16A.

[0042] Furthermore, reflectors I3, II6, and III7 are all composed of reflectors and universal adjustment frames. By adjusting the knobs on the universal adjustment frames, it is ensured that the laser is always in the center of the mirror surface.

[0043] Furthermore, the imaging system 11 consists of a high-speed camera, an image intensifier, and a telephoto lens. The image intensifier is installed at the front end of the high-speed camera, and the telephoto lens is installed at the front end of the image intensifier. The timing controller 4 is used to control the synchronous operation of the high-speed camera, the image intensifier, and the femtosecond laser 2 in the imaging system 11.

[0044] Furthermore, the water chiller 1 provides a stable cooling water circulation for the femtosecond laser 2, removing the heat generated during operation and maintaining a constant laser temperature; preventing performance instability or damage due to overheating; and also providing temperature monitoring and alarm functions to ensure long-term stable and safe operation of the femtosecond laser. The main function of the femtosecond laser 2 is to output high-peak-power pulsed laser light to excite air molecules and achieve molecular fluorescence signal radiation. The femtosecond laser 2 needs to have high repetition rate, high energy, and stable output. The reflector I 3 reflects the pulsed laser light emitted by the femtosecond laser 2 onto the reflector II 6. The input power supply 5 provides a stable power supply to the input femtosecond laser 2 to meet the high power requirements of the femtosecond laser operation. Independent power lines and grounding design ensure the stability and anti-interference of power transmission. The reflector II 6 and the reflector III 7 mainly reflect the pulsed laser light output by the femtosecond laser onto the plano-convex lens 8. The plano-convex lens 8 focuses the laser beam onto the flow field region to be measured, exciting molecules or gas atoms in the flow field to generate fluorescence signals. The wind tunnel test section 9 must have an optical window. The optical glass of the window must have high transmittance (especially in the femtosecond laser wavelength range) and excellent optical uniformity to ensure distortion-free laser pulse transmission; it must also have high thermal shock resistance and a laser damage threshold to avoid thermal stress cracks or ablation caused by high-energy lasers, ensuring the stability and safety of the velocimetry optical path. The computer device 10 is used to acquire and record images during the experiment and for image processing. The imaging system 11 consists of a high-speed camera, an image intensifier, and a telephoto lens. The image intensifier's main function is to amplify the fluorescence signal intensity; it is installed at the front end of the high-speed camera, and the enhanced image is imaged on the high-speed camera's chip. The timing controller 4 is mainly responsible for precise timing control to coordinate the synchronous operation of the laser, high-speed camera, and other experimental equipment.

[0045] Example 2:

[0046] A velocity measurement method suitable for a combined pulsed high-enthalpy wind tunnel, based on the velocity measurement system for a combined pulsed high-enthalpy wind tunnel described in Example 1, is characterized by comprising the following steps:

[0047] S1. Construct a velocity measurement system suitable for a combined pulse high-enthalpy wind tunnel;

[0048] S2. Set the image acquisition method. When the timing controller 4 outputs a trigger signal to the femtosecond laser 2, a femtosecond laser pulse is generated. The imaging system 11 performs multiple exposures according to the set trigger timing sequence, and each exposure acquires an independent image.

[0049] Furthermore, the timing control is used to control the pulse output of the femtosecond laser and to enable the camera to record laser feature points separately during multiple independent exposures. Specifically, after the pulse signal generator outputs a trigger signal to the femtosecond laser, a femtosecond laser pulse is generated. The camera performs multiple exposures according to the set trigger timing, acquiring an independent image for each exposure. During each exposure, the image intensifier performs gated opening and closing according to different delays. The first gated opening occurs after a very short time t0. The second gated opening occurs at t0+... The rear door controls the opening. Assuming a total of n images are captured, then in the last capture, the image intensifier at time t0... Afterwards, the door is opened via gate control, and the time for each gate opening by the image intensifier is t. e .

[0050] Since each frame exposure corresponds to only one laser pulse or one laser point signal, each image contains only the laser point information corresponding to a single moment. By advancing a sequence of multiple frames over time, it is possible to analyze the distribution of points, velocity fields, or the trajectory of markers in the flow field as they change over time.

[0051] S3. Calculate the scaling factor between pixels and actual physical distances in imaging system 11;

[0052] Furthermore, a calibration target with a known scale spacing was placed in the same shooting position and imaging parameters as in the actual experiment to acquire high-resolution images. , These represent the pixel coordinates in the horizontal and vertical directions of the image, respectively; A rectangular region R covering the scale lines is extracted from the data, and the grayscale values ​​of this region are averaged in the direction perpendicular to the scale lines to generate a one-dimensional brightness distribution function.

[0053]

[0054] Where y1 is the starting pixel coordinate (upper boundary) of the rectangular region R in the vertical direction, y2 is the ending pixel coordinate (lower boundary) of the rectangular region R in the vertical direction, and H=y2-y1+1 is the height R of the rectangular region, that is, the number of pixel rows participating in the averaging process.

[0055] For one-dimensional brightness signals One-dimensional Gaussian smoothing is performed to obtain a smooth signal, suppressing high-frequency noise and improving the reliability of gradient calculation.

[0056] *

[0057] in, It is a one-dimensional Gaussian kernel function. It is the standard deviation of the Gaussian kernel, which controls the filtering strength;

[0058] Then, taking the first derivative of the smoothed signal, we get:

[0059] ;

[0060] The two edges of the scale line are at the first derivative of the smoothed signal. The gradient maxima / minimum points are represented in the image, serving as the initial location of the edge; after the brightness signal is smoothed, the first derivative of the smoothed signal is... Near the edge of the scale line, a sharp peak shape with approximately symmetrical and smooth variation will appear. For continuous signals, this peak can be approximated by a second-order Taylor expansion near the extreme point. The form of the second-order Taylor expansion is a quadratic function. Therefore, the signal in the neighborhood of the gradient peak can be regarded as a local distribution that approximately conforms to a parabolic curve.

[0061] Based on this, at each gradient peak Three sampling points were selected nearby. , , Fitting a quadratic function = Where a, b, and c are the parameters of the quadratic function, and its vertex is:

[0062]

[0063] in, This is the precise sub-pixel position of the edge; this step is performed separately on the left and right edges of each tick mark to obtain... and The center of the scale line is the average value of the left and right edges:

[0064] ;

[0065] The center coordinates are obtained from the center positions of the two scale lines. and The pixel spacing between them is N= The actual distance between these two scale lines is The proportionality constant k can be obtained. .

[0066] S4. Conduct wind tunnel tests in wind tunnel test section 9, collect images during the test, perform image processing, and calculate the flow field velocity during the wind tunnel test.

[0067] Furthermore, the specific implementation method of step S4 includes the following steps:

[0068] S4.1. Following the image acquisition method in step S2, acquire N images;

[0069] S4.2. For each image acquired in step S4.1, calculate the center position of the laser point in the image;

[0070] Furthermore, the maximum bounding rectangle of the laser point is extracted, and the binarization threshold T is calculated by maximizing the inter-class variance. First, the normalized probability in radians is calculated. , = ,in Let N be the number of pixels with a grayscale value of t, where t represents every possible grayscale value in the image, and N be the total number of pixels in the image. For a possible threshold T, the weights of class 1 (background) and class 2 (foreground) are respectively... and =1- Calculate the mean of the classes; the mean of class 1 (background) is... = The mean of class 2 (foreground) is = ,in This represents the grayscale range of the image. Calculate the between-class variance. Finally, by calculating the inter-class variance at all possible thresholds T, the threshold that maximizes the inter-class variance is selected. Then based on To achieve image binarization, i.e. That is, all grayscale values ​​are greater than or equal to The pixel is set as the foreground (class 2), smaller than The pixels are set as the background (Class 1).

[0071] Then roughly locate the position of the laser point, and... Perform local maximum detection to find The approximate center position of the laser dot is obtained by taking the average of all pixels with a value of 1. .

[0072] The edges of the laser points are extracted, with regions exhibiting significant gradient changes identified as edge points. Connected regions surrounding the laser points are obtained from the edge detection results, and then the maximum bounding rectangle E is extracted based on the minimum bounding box of this region. The four boundaries of this rectangle are... , , , ,( , ), representing the coordinates of all edge pixels in the connected region of the laser point. Then, a mask is constructed based on a rectangle formed by these four points. .

[0073] Get a clean image =I M ;

[0074] against Calculate the center of the laser point at the sub-pixel level. First, calculate the total brightness S of the image. Calculate the weighted sum in the x and y directions. = and = Where R1 is the height of the image and C1 is the width of the image, the coordinates of the center position of the laser point are: ,in , .

[0075] for , , , The center point coordinates of any image in the dataset are calculated using the method described above, resulting in... .

[0076] S4.3. For any adjacent first... The center position of the first laser point and the... The center position of each laser point , ,and < The formula for calculating the flow field velocity in a wind tunnel test is as follows:

[0077] ( , )=k

[0078] ( , )=k

[0079] in, ( , () represents the horizontal velocity. ( , ) represents the vertical velocity, and k is the scaling factor between the pixel and the actual physical distance. For the first The horizontal coordinates of the center position of each laser point For the first The horizontal coordinates of the center position of each laser point For the first The vertical coordinates of the center position of each laser point For the first The vertical coordinates of the center position of each laser point The time interval for generating two adjacent laser points.

[0080] The flow field velocity in the wind tunnel test is calculated for any two adjacent laser points. Then, the average value of the flow field velocities in all wind tunnel tests is taken to obtain the final horizontal velocity. and vertical velocity .

[0081] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0082] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A velocity measurement system suitable for use in a combined impulse high-enthalpy wind tunnel, characterized in that, Includes a water chiller (1), a femtosecond laser (2), a reflector I (3), a timing controller (4), an input power supply (5), a reflector II (6), a reflector III (7), a plano-convex lens (8), a wind tunnel test section (9), a computer device (10), and an imaging system (11); The femtosecond laser (2) is connected to the water chiller (1), the timing controller (4), and the input power supply (5) respectively, and the imaging system (11) is connected to the timing controller (4) and the computer device (10) respectively. The laser emitted by the femtosecond laser (2) is reflected by the reflector I (3), and then reflected by the reflector II (6) and the reflector III (7) before being incident on the plano-convex lens (8). The emitted laser is then incident on the wind tunnel test section (9), and the imaging system (11) takes test photos of the wind tunnel test section (9).

2. A velocity measurement system suitable for use in a combined pulse high-enthalpy wind tunnel according to claim 1, characterized in that, The femtosecond laser (2) has a laser frequency of 10 kHz and a center wavelength in the range of 1020–1050 nm.

3. A velocity measurement system suitable for a combined pulsed high-enthalpy wind tunnel according to claim 2, characterized in that, The input power supply (5) has a voltage of 220V and a current of 16A.

4. A velocity measurement system suitable for a combined pulsed high-enthalpy wind tunnel according to claim 3, characterized in that, Reflector I (3), Reflector II (6), and Reflector III (7) are all composed of a reflector and a universal adjustment frame. By adjusting the knob on the universal adjustment frame, the laser is ensured to be in the center of the mirror surface.

5. A velocity measurement system suitable for a combined pulsed high-enthalpy wind tunnel according to claim 4, characterized in that, The imaging system (11) consists of a high-speed camera, an image intensifier and a telephoto lens. The image intensifier is installed at the front end of the high-speed camera and the telephoto lens is installed at the front end of the image intensifier. The timing controller (4) is used to control the synchronous operation of the high-speed camera, the image intensifier and the femtosecond laser (2) in the imaging system (11).

6. A velocity measurement method suitable for a combined pulsed high-enthalpy wind tunnel, implemented based on a velocity measurement system suitable for a combined pulsed high-enthalpy wind tunnel as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Construct a velocity measurement system suitable for a combined pulse high-enthalpy wind tunnel; S2. Set the image acquisition method. When the timing controller (4) outputs a trigger signal to the femtosecond laser (2), a femtosecond laser pulse is generated. The imaging system (11) performs multiple exposures according to the set trigger timing sequence, and each exposure acquires an independent image. S3. Calculate the scaling factor between pixels and actual physical distance in the imaging system (11); S4. Conduct wind tunnel tests in the wind tunnel test section (9), collect images during the test, perform image processing, and calculate the flow field velocity in the wind tunnel test.

7. The velocity measurement method applicable to a combined pulse high-enthalpy wind tunnel according to claim 6, characterized in that, The specific implementation method of step S4 includes the following steps: S4.

1. Following the image acquisition method in step S2, acquire N images; S4.

2. For each image acquired in step S4.1, calculate the center position of the laser point in the image; S4.

3. For any adjacent first... The center position of the first laser point and the... The center position of each laser point , ,and < The formula for calculating the flow field velocity in a wind tunnel test is as follows: ( , )=k ； ( , )=k ； in, ( , () represents the horizontal velocity. ( , ) represents the vertical velocity, and k is the scaling factor between the pixel and the actual physical distance. For the first The horizontal coordinates of the center position of each laser point For the first The horizontal coordinates of the center position of each laser point For the first The vertical coordinates of the center position of each laser point For the first The vertical coordinates of the center position of each laser point The time interval for generating two adjacent laser points; The flow field velocity in the wind tunnel test is calculated for any two adjacent laser points. Then, the average value of the flow field velocities in all wind tunnel tests is taken to obtain the final horizontal velocity. and vertical velocity .

Images