Folding wing unfolding angle identification method based on high-speed photography in wind tunnel test

Abstract

The invention provides a folding wing unfolding angle identification method based on high-speed photography in a wind tunnel test. The method comprises the following steps: measuring the distance from a wing tip of a folding wing to the center of a rotating shaft before the test, arranging a camera in front of an observation window on the outer side of a wind tunnel, arranging a plane scale calibration target, and calculating a conversion factor between a camera pixel scale and a physical scale; performing a wind tunnel blowing test and high-speed camera shooting; and calculating an expansion angle and an angular velocity based on image recognition. Compared with a method for installing an angle sensor and a linear tension sensor, the technology does not need to add any part on the airfoil, so that the mass and rotational inertia attributes of the airfoil are not changed, the original flow field distribution is not changed, and the test authenticity can be ensured to the maximum extent.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of aerodynamics, and particularly relates to a folding wing unfolding angle image recognition method based on high-speed photography for a folding wing unfolding wind tunnel test. BACKGROUND

[0002] The folding wing design of an aircraft wing surface is an effective means of considering the high-density loading of a carrier aircraft and the high aerodynamic performance of an aircraft. A key point for the feasibility of the folding wing design is whether the folding wing can quickly unfold to a specified angle and lock under the action of the aerodynamic load in real flight. This needs to be examined through the folding wing unfolding test under the blowing condition in the wind tunnel. However, the current wind tunnel test measurement method needs to install additional mechanisms and uses an invasive measurement method, which changes the original flow distribution in the flow field in the wind tunnel and affects the reliability of the test. At the same time, the sampling frequency of these sensors is low, and the measurement accuracy is easily disturbed by the impact. Therefore, it is necessary to develop an image recognition technology for the unfolding angle of the folding wing based on high-speed photography, which does not affect the flow field distribution and can obtain high time and space resolution of the unfolding angle information. SUMMARY

[0003] The purpose of the present application is to provide a folding wing unfolding wind tunnel test method, which can take high-speed photographs of the wing unfolding process through the observation window on the side of the wind tunnel without changing the flow field distribution around the test model and affecting the authenticity of the test, and then identify the unfolding position of the folding wing based on the images to obtain the wing unfolding angle and angular velocity information over time.

[0004] The technical scheme of the present application is: A folding wing unfolding angle recognition method based on high-speed photography in a wind tunnel test, comprising the following steps: 1) Preparation before test 1.1) Measure the distance from the folding wing tip to the center of the rotating shaft, and spray white spray on the folding wing tip to ensure that the folding wing tip has a high enough contrast with other parts of the aircraft; 1.2) Install the aircraft model with the folding wing in the wind tunnel, and set an observation window opposite the folding wing position on the side of the wind tunnel, and set a camera in front of the observation window outside the wind tunnel; 1.3) Arrange a planar scale calibration target within the depth of field of the camera, and calculate the conversion factor between the pixel size and the physical size of the camera η ; 1.4) Run the folding wing wing surface unfolding action and high-speed photography process once before the test, and estimate the sampling frequency of the high-speed camera according to the unfolding time and the displacement of the wing surface in the photographic image; 2) Perform wind tunnel blowing test and camera high-speed photography The wind tunnel is opened to blow, and after the flow field is stable, the high-speed photography is started, and at the same time, the folded wing surface is unfolded, so as to obtain the wing surface images at different time; 3) calculating the unfolding angle and angular velocity based on image recognition 3.1) obtaining the displacement of the folded wing tip in the image by using the image cross-correlation algorithm According to all the images obtained by the camera at different time, the tracking window is set to track the position of the folded wing tip, and the image cross-correlation method is used to calculate the displacement of the folded wing tip in the image. N 3.2) calculating the angle and angular velocity of the wing surface unfolding according to the spatial relationship between the displacement of the folded wing tip in the image and the folding angle.

[0005] The feature is that after the camera is set in front of the observation window outside the wind tunnel in step 1.2), the position and focal length of the camera are adjusted to ensure that the folded wing surface is within the depth of field of the camera during the whole process of folding and unfolding to the position, and can be clearly imaged.

[0006] The feature is that the planar scale calibration target in step 1.3) is a chessboard grid plate.

[0007] The feature is that in step 1.4), the displacement of the wing surface in each two images is required to be greater than 2 pixels to ensure that the measurement accuracy meets the requirements of angle recognition calculation.

[0008] The feature is that the algorithm for calculating the displacement of the folded wing tip in the image in step 3.1) is as follows: 3.1.1) the size of the tracking window is given, the position of the tracking window at the first time is given , the bias of the tracking window is initialized , the offset in the window is , and the displacement is ; then, the number of images is given , and the following steps 3.1.2)-3.1.7) are executed in a loop to obtain the displacement of the wing tip in the image at all time: 3.1.2) for the k th image, if , the displacement acceleration is given , otherwise ; 3.1.3) the tracking window position at the th time is preset as ; 3.1.4) the image in the tracking window at the th time is extracted and enhanced to obtain the pixel matrix ; 3.1.5) the pixel matrix ​cross-correlation coefficient Obtain the in-window offset corresponding to the maximum cross-correlation coefficient. ; 3.1.6) Calculate the first Displacement of the wingtip within the image at any given time and given the first Window bias at time ; 3.1.7) Amendment to section [number missing] Constantly track the window's position and set .

[0009] The characteristic is that the loop of steps 3.1.2)-3.1.7) ends when k=N-1.

[0010] The feature is that, by executing steps 3.1.2)-3.1.7), the displacement of the wingtip within the image at all times is obtained. , The result is more robust and the displacement calculation results are smoother.

[0011] The characteristic is that step 3.2) specifically comprises: Based on the relationship between displacement and angle conversion, the real-time deployment displacement of the wingtip within the image is: The projection of the displacement onto the phase plane passing through the axis of rotation ; Given the time interval between two consecutive frames Scale conversion factor from pixel space to physical space η , angle size Wingspan of a folding wing and its projection length in the phase plane The relationship is, ; Wingtip displacement within the image at all times , Then the first The angle of unfolding at each moment and angular velocity The calculation formula is:

[0012] .

[0013] The advantages of this invention are: For wind tunnel tests of aircraft wing deployment, this invention can obtain deployment angle information with high temporal and spatial resolution. Compared to methods that install angle sensors or linear tension sensors, this technology does not require any additional components on the wing, thus not changing the wing's mass and moment of inertia properties, nor altering the original flow field distribution, and can maximize the authenticity of the test. Attached Figure Description

[0014] Figure 1 A schematic diagram of the high-speed photography setup for wind tunnel testing of wing deployment.

[0015] Figure 2 This is a graph showing the relationship between the wingtip displacement and the deployment angle within the image.

[0016] Figure 3 This is a schematic diagram of the cross-correlation algorithm for displacement images within the wingtip image.

[0017] Figure 4 The results of the wing deployment angle and angular velocity obtained using this method after a certain experiment. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0019] The present invention provides a method for identifying the deployment angle of a folding wing based on high-speed photography in a wind tunnel test, comprising the following steps: 1) Preparation before the experiment 1.1) Measure the distance from the wingtip of the folding wing to the center of the rotation axis, and spray the wingtip of the folding wing with white spray to ensure that the wingtip of the folding wing presents a sufficiently high contrast relative to other parts of the aircraft.

[0020] 1.2) Install the aircraft model with folding wings in the wind tunnel. Place an observation window on the side of the wind tunnel directly opposite the folding wing position. Place a camera in front of the observation window on the outside of the wind tunnel. Figure 1 As shown. Adjust the camera position and focal length to ensure that the folding wing surface remains within the camera's depth of field throughout the entire folding and unfolding process, allowing for clear imaging, as shown. Figure 2 As shown.

[0021] 1.3) Arrange planar calibration targets (e.g., checkerboard-patterned flat surfaces) within the camera's depth of field and calculate the conversion factor between the camera's pixel scale and the physical scale. η .

[0022] 1.4) Before the test, run the folding wing surface deployment action and high-speed photography process once. Estimate the sampling frequency of the high-speed camera based on the deployment time and the displacement of the wing surface in the photographed image to ensure that the wing surface displacement is greater than 2 pixels in every two frames to ensure measurement accuracy.

[0023] 2) Conduct wind tunnel blowing tests and high-speed camera photography. The wind tunnel was turned on to blow air, and after the flow field stabilized, high-speed photography was started. At the same time, the folded wing surface was deployed to obtain images of the wing surface at different times.

[0024] 3) Calculate the unfolding angle and angular velocity based on image recognition. 3.1) Obtain the displacement of the folding wingtip within the image using an image cross-correlation algorithm. Based on all the images captured by the camera N Images at specific times are used to track the wingtip position of the folding wing using a tracking window. Image cross-correlation is then used to calculate the displacement of the wingtip within the image. A schematic diagram of the wingtip displacement recognition algorithm is shown below. Figure 3 As shown: 3.1.1) Given the tracking window size and the position of the tracking window at time 1. Initialize the bias of the tracking window. Offset within the window Displacement Then, given Repeat the following steps: 3.1.2) For the first k Zhang picture, if Given the displacement acceleration Otherwise .

[0025] 3.1.3) Preset the first The position of the tracking window is .

[0026] 3.1.4) Extract the first The image within the window is constantly tracked and enhanced to obtain a pixel matrix. .

[0027] 3.1.5) Calculate the pixel matrix cross-correlation coefficient Obtain the in-window offset corresponding to the maximum cross-correlation coefficient. .

[0028] 3.1.6) Calculate the first Displacement of the wingtip within the image at any given time and given the first Window bias at time .

[0029] 3.1.7) Amendment to section [number missing] Constantly track the window's position and set .

[0030] By repeating the above loop, the displacement of the wingtip within the image at all times can be obtained. , Compared to identifying the centroid position of the wingtip, the cross-correlation algorithm is more robust and can obtain smoother displacement results.

[0031] 3.2) Calculate the unfolding angle and angular velocity. in accordance with Figure 2 The relationship between displacement and angle conversion, the real-time deployment displacement of the wingtip within the image is .

[0032] ; Given the time interval between two consecutive frames Scale conversion factor from pixel space to physical space η , angle size ,length , , ; Wingtip displacement within the image at all times , Then the first The angle of unfolding at each moment and angular velocity The calculation formula is:

[0033] .

[0034] Figure 4 The changes in wing deployment angle and angular velocity obtained using this method after a wind tunnel test of wing deployment are shown. It is evident that this method can analyze the acceleration process during wing deployment and the vibration process after deployment.

Claims

1. A method for identifying the deployment angle of a folding wing in a wind tunnel test based on high-speed photography, comprising the following steps: 1) Preparation before test 1.1) Measure the distance from the folding wing tip to the center of the rotating shaft, and spray white paint on the folding wing tip to ensure that the folding wing tip has a high enough contrast with other parts of the aircraft. 1.2) Install the aircraft model with folding wings in the wind tunnel, set an observation window on the side of the wind tunnel opposite the folding wing position, and set a camera in front of the observation window outside the wind tunnel. 1.3) Arrange a planar scale calibration target within the depth of field of the camera, compute the conversion factor between the camera pixel scale and the physical scale 1.4) Run the folding wing surface unfolding action and high-speed photography process once before the test, and estimate the sampling frequency of the high-speed camera according to the time length of unfolding to the position and the displacement of the wing surface in the photographic image. ; 2) Conduct wind tunnel blowing test and camera high-speed photography Turn on the wind tunnel to blow, and after the flow field is stable, start high-speed photography, and at the same time, unfold the folding wing surface to obtain wing surface images at different times. 3) Calculate the unfolding angle and angular velocity based on image recognition 3.1) Use the image cross-correlation algorithm to obtain the displacement of the folding wing tip in the image 3.2) Calculate the angle and angular velocity of the wing surface unfolding according to the spatial relationship between the displacement of the folding wing tip in the image and the folding angle. Based on all the images captured by the camera N For each moment in the image, a tracking window is set to track the position of the folding wingtip, and the displacement of the folding wingtip within the image is calculated using the image cross-correlation method. Step 1.2) After setting the camera in front of the observation window outside the wind tunnel, adjust the camera position and focal length to ensure that the folding wing surface is within the depth of field of the camera during the entire process of folding and unfolding to the position, and can be clearly imaged.

2. The method for identifying the deployment angle of a folding wing in wind tunnel tests based on high-speed photography according to claim 1, characterized in that, Step 1.3) The planar scale calibration target is a checkerboard plate.

3. The method of claim 2, wherein the method is characterized by: Step 1.4) Ensure that the wing surface displacement in each two frames of images is greater than 2 pixels to ensure that the measurement accuracy meets the requirements of angle recognition calculation.

4. The method of claim 3, wherein the method is characterized by: The algorithm for calculating the displacement of the folding wing tip in the image in step 3.1) is as follows:

5. The method of claim 4, wherein the method is characterized by: When k = N-1, end the loop of steps 3.1.2)-3.1.7). 3.1.1) Given the tracking window size, given the position of the tracking window at the 1st time instant , initialize the bias of the tracking window , the offset within the window , the displacement ; then, given , loop the following steps 3.1.2) - 3.1.7) to get the displacement of the wing tip within the image at all time instants: 3.1.2) For the first k picture, if then give the displacement acceleration , otherwise let ; 3.1.3) preset the first the time tracking window position is ; 3.1.4) extracting the first the image within the time tracking window, and performing enhancement processing to obtain a pixel matrix ; 3.1.5) calculating the pixel matrix the cross-correlation coefficient , obtaining the offset within the window corresponding to the maximum cross-correlation coefficient ; 3.1.6) Calculate the first Displacement of the wingtip within the image at any given time and given the first Window bias at time ; 3.1.7) Corrected Section The position of the time tracking window is and set .

6. The method of claim 5, wherein the method is characterized by: Step 3.2) is as follows:

7. The method of claim 6, wherein the method is used in a wind tunnel test. By performing the loop of steps 3.1.2) - 3.1.7) the displacement of the wing tip within the image at all instants is obtained , ) results in a higher robustness and smoother displacement results.

8. The method of claim 7, wherein the method is used in a wind tunnel test. ​ According to the displacement amount and angle conversion relationship, the real-time unfolding displacement amount of the wing tip in the image is The projection of the displacement amount in the phase plane passing through the rotation shaft ； known time interval between two consecutive images , scale conversion factor from pixel space to physical space ​ , angle size , span length of the folding wing and its projection length in the complex plane , ； The amount of displacement of the wing tip within the image at all times , The calculation formula of the spread angle of the first time and the angular velocity of the first time is: ​ 。

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