Aircraft engine inlet flow field detection method based on positron annihilation technology

Abstract

The present invention discloses a method for detecting the flow field of an aero-engine inlet duct based on a positron annihilation technology. The method comprises the following steps: installing a wind tunnel tube in an annular gamma photon detector, installing a fairing at one end of the wind tunnel tube away from the annular gamma photon detector, and connecting one end of the wind tunnel to a wind tunnel blower; arranging an inlet duct bracket in the wind tunnel tube; fixing the inlet duct to be detected on the inlet duct bracket; planting cotton threads on a silica gel plate in a linear array manner; preparing a radionuclide-labeled aqueous solution to be adsorbed on the cotton threads; fixing the silica gel plate in an inner cavity of the inlet duct to be detected; starting the wind tunnel blower, collecting gamma photon pairs generated by positron annihilation on the cotton threads in the inlet duct through the annular gamma photon detector, and storing the collected gamma photon pairs as three-dimensional sinusoidal graphs; performing interpolation processing on the three-dimensional sinusoidal graphs to expand data; and performing three-dimensional image iterative reconstruction based on the processed three-dimensional sinusoidal graphs to obtain a clear flow field state in the inner cavity of the aero-engine inlet duct.

Description

Technical Field

[0001] The present invention relates to an aircraft engine air inlet flow field detection technology, and in particular to an aircraft engine air inlet flow field detection method based on positron annihilation technology. Background Art

[0002] As a crucial component of aircraft engines, the inlet duct exhibits numerous complex flow phenomena, including shock waves, expansion waves, shock wave reflection, shock wave-boundary layer interference, and flow separation. This makes the aerodynamic loads and aerodynamic heat distribution within the inlet duct more complex than those of the external flow. When conducting inlet flow field state experiments, the starting performance of the inlet duct is typically assessed using test results obtained using pressure sensors, thermal flow sensors, and various flow field visualization techniques, including wall filament visualization and oil flow analysis.

[0003] The wire method, a widely used flow visualization method, involves planting one end of a thread made of a specific material on the surface of a model, while the other end drifts with the airflow, to reflect the flow field's current state. However, the traditional wire method also has its drawbacks. It cannot detect flow fields within metal cavities, opaque devices, or those with demanding internal pressure and velocity conditions.

[0004] As a nondestructive detection method, positron annihilation technology has broad application prospects in biomedicine, materials science, and engineering. The gamma photons produced by positron annihilation are electrically neutral and possess strong penetrating power and anti-interference capabilities, effectively preventing the effects of environmental fluctuations on detection. This makes gamma photon imaging a powerful tool for overcoming the vulnerability of traditional detection methods to specific factors, enabling nondestructive testing of opaque cavities in a variety of environments. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an aero-engine inlet flow field detection method based on positron annihilation technology.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a method for detecting the flow field of an aircraft engine intake duct based on positron annihilation technology, comprising the following steps:

[0007] Step 1: Install the wind tunnel tube in the annular gamma photon detector, install a fairing at the end of the wind tunnel tube away from the annular gamma photon detector, seal the inner wall of the wind tunnel tube with the outer wall of the fairing, and connect the end of the wind tunnel tube away from the annular gamma photon detector to the wind tunnel blower;

[0008] Step 2: Place the inlet bracket in the wind tunnel tube within the portion of the annular gamma photon detector.

[0009] Step 3: Fix the inlet duct to be tested on the inlet duct bracket, and make the line connecting the openings at both ends of the inlet duct to be tested parallel to the center line of the wind tunnel tube;

[0010] Step 4: Take a piece of cotton thread and divide it into multiple segments with a length of 8-20 mm. Plant them on the silicone plate in a linear array.

[0011] Step 5: Prepare a radionuclide-labeled aqueous solution and adsorb it onto cotton thread;

[0012] Step 6: Fix the silica gel plate on which the cotton thread adsorbs the radionuclide labeled aqueous solution in the inner cavity of the air inlet to be tested;

[0013] Step 7: Start the wind tunnel blower and use the annular gamma photon detector to collect the gamma photon pairs generated by the positron annihilation on the cotton thread in the inlet duct and store them as a three-dimensional sinusoidal diagram;

[0014] Step 8: Interpolate the three-dimensional sinogram to expand the data;

[0015] Step 9: Perform iterative 3D image reconstruction based on the processed 3D sinogram and add a Beltrami filter during the iterative process to obtain a clear flow field state of the aircraft engine inlet cavity. The implementation process is as follows:

[0016] (1) The MLEM algorithm is used to iteratively reconstruct the image based on the interpolated sinusoidal graph. The iterative formula is:

[0017]

[0018] in, and Represents the results of reconstructed images at iterations k+1 and k, respectively, i represents the i-th response line, a ij represents the probability that the j-th pixel is detected by the i-th response line;

[0019] (2) A Beltrami filter is added in each image iteration to stimulate flow in the direction of smaller resolution in the image, removing noise while maintaining the edge information of the image. The expression of Beltrami flow is:

[0020]

[0021] in, Represents the derivative of the image gray value with respect to time t, is the gradient vector of the image, g represents the metric tensor of the image manifold, and div is the divergence operator;

[0022] (3) Let the total number of iterations be N. In the nth iteration, where n = 1, 2, ..., N, the reconstructed image obtained is X n After the iteration is completed, Beltrami image flow filtering is performed, and the number of filtering is Nn. The number of filtering decreases with the increase of the number of MLEM iterations. Finally, after completing all iterations, the final flow field reconstruction image X is obtained. N .

[0023] As a preferred solution, the implementation process of step 8 is as follows:

[0024] (1) Perform bicubic interpolation on the coincident event sinogram to increase the number of coincident events. The kernel function of bicubic interpolation is:

[0025]

[0026] (2) Assume that the coordinates of the 16 pixels around the pixel to be interpolated in the sine graph are (i-1, j-1), (i-1, j), (i-1, j+1), (i-1, j+2), (i, j-1), (i, j), (i, j+1), (i, j+2), (i+1, j-1), (i+1, j), (i+1, j+1), (i+1, j+2), (i+2, j-1), (i+2, j), (i+2, j+1), (i+2, j+2); substitute their abscissas into x in formula (1) to obtain the weight of this pixel in the interpolation;

[0027] (3) Assume that the coordinates of the pixel to be interpolated in the sine graph are (i+a, j+b), and calculate the weight values ​​of the 16 surrounding pixels in the horizontal and vertical directions to obtain the grayscale value of the interpolated point;

[0028] The grayscale value f(i+a, j+b) of the interpolation point (i+a, j+b) is obtained by formula (2):

[0029] f(i+a, j+b)=A×B×C (2);

[0030] Among them, A, B, and C are obtained by the following formula:

[0031]

[0032] (4) According to formula (3), the grayscale information of the point to be interpolated is obtained through the grayscale values ​​of the pixels at the surrounding 16 points.

[0033] As a preferred solution, the upper portion of the air inlet support can be deflected around an axis parallel to the center line of the wind tunnel tube to adjust the angle between it and the horizontal plane.

[0034] As a preferred solution, the spacing between the silk thread arrays on the silica gel plate is 10-15 mm, and the silk threads are cotton threads with a diameter of 0.8-1.2 mm, which are degreased with a caustic soda solution.

[0035] As a preferred solution, the concentration of the radionuclide in the radionuclide-labeled aqueous solution is 7-12 mci / L.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention's method for detecting flow fields in an aero-engine inlet duct dissolves and adsorbs radionuclides with short half-lives and low activity onto a thread. After the object to be detected is placed in the thread, the thread changes with the movement of the flow field. The positrons in the radionuclides on the thread annihilate with the surrounding electrons, generating a pair of gamma photons. This gamma photon pair is then captured by a detector to achieve non-destructive detection imaging of the flow field state in the opaque cavity. The collected three-dimensional sinusoidal image is interpolated using bicubic interpolation to expand the number of coincident events and improve imaging quality. This method solves the problem of short acquisition time, rapid flow field changes, a small number of collected coincident events, and poor imaging results during dynamic detection. Furthermore, a Beltrami filter is added to the iterative image reconstruction to suppress artifacts and noise in the image reconstruction, further significantly improving the quality of the flow field reconstruction image.

[0038] In addition, in the air inlet flow field detection device adopted by the present invention, a fairing is set in the wind tunnel tube to ensure the constant airflow velocity, and cotton thread is planted on the silicone plate as a silk thread module. Compared with the traditional operation method of planting on the model, the silk thread module is simpler and more convenient to operate, and can be recycled to reduce economic costs.

[0039] Since the upper part of the air inlet bracket can be deflected around an axis parallel to the center line of the wind tunnel tube to adjust the angle between it and the horizontal plane, it is possible to study the changes in the air inlet flow field at different angles, providing a reliable basis for flow field analysis and air inlet structure design. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a schematic diagram of the structure of an aircraft engine inlet flow field detection device;

[0041] Figure 2 It is a schematic diagram of the structure of the silicone plate;

[0042] Figure 3 This is the flow chart of the interpolation-filtering iterative reconstruction algorithm for the inlet flow field;

[0043] In the figure: 1 wind tunnel blower, 2 fairing, 3 wind tunnel tube, 4 gamma photon detector, 5 air inlet to be tested, 6 upper part of air inlet bracket, 7 angle piece, 8 air inlet bracket base, 9 silicone plate. DETAILED DESCRIPTION

[0044] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0045] like Figure 1-3 As shown, the technical problem to be solved by the present invention is to provide an aircraft engine inlet flow field detection method based on positron annihilation technology.

[0046] To solve the above technical problems, the technical solution adopted by the present invention is: a method for detecting the flow field of an aircraft engine intake duct based on positron annihilation technology, comprising the following steps:

[0047] Step 1: Install the wind tunnel tube 3 in the annular γ photon detector 4, install the fairing 2 at the end of the wind tunnel tube 3 away from the annular γ photon detector 4, seal the inner wall of the wind tunnel tube 3 with the outer wall of the fairing 2, and connect the end of the wind tunnel tube 3 away from the annular γ photon detector 4 to the wind tunnel blower 1;

[0048] Step 2: placing the air inlet bracket in the wind tunnel tube 3 within the portion of the annular gamma photon detector 4;

[0049] Step 3: Fix the air inlet duct 5 to be tested on the air inlet duct bracket, and make the line connecting the openings at both ends of the air inlet duct 5 to be tested parallel to the center line of the wind tunnel tube 3;

[0050] The upper portion 6 of the air intake support can be deflected about an axis parallel to the centerline of the wind tunnel tube 3 to adjust its angle with the horizontal plane. (As shown in the figure, angle pieces 7 of varying angles can be used to connect the air intake support base 8 to the upper portion 6 of the air intake support to facilitate flow field testing at various locations.)

[0051] Step 4: Take a piece of cotton thread with a diameter of 1.0 mm and degreased with caustic soda solution, divide it into multiple segments with a length of 12 mm, and plant them on the silica gel plate 9 in a linear array with a spacing of 13 mm.

[0052] Step 5: Prepare a radionuclide-labeled aqueous solution with a radionuclide concentration of 10 mci / L and adsorb it onto a cotton thread;

[0053] Step 6: Fix the silica gel plate 9 on which the cotton thread adsorbs the radionuclide labeled aqueous solution into the inner cavity of the air inlet 5 to be tested;

[0054] Step 7: Start the wind tunnel blower 1, collect the gamma photon pairs generated by the positron annihilation on the cotton thread in the air inlet through the annular gamma photon detector 4, and store them as a three-dimensional sinusoidal diagram;

[0055] Step 8: Interpolate the three-dimensional sinusoidal graph and expand the data, as follows;

[0056] (1) Perform bicubic interpolation on the coincident event sinogram to increase the number of coincident events. The kernel function of bicubic interpolation is:

[0057]

[0058] (2) Assume that the coordinates of the 16 pixels around the pixel to be interpolated in the sine graph are (i-1, j-1), (i-1, j), (i-1, j+1), (i-1, j+2), (i, j-1), (i, j), (i, j+1), (i, j+2), (i+1, j-1), (i+1, j), (i+1, j+1), (i+1, j+2), (i+2, j-1), (i+2, j), (i+2, j+1), (i+2, j+2); substitute their abscissas into x in formula (1) to obtain the weight of this pixel in the interpolation;

[0059] (3) Assume that the coordinates of the pixel to be interpolated in the sine graph are (i+a, j+b), and calculate the weight values ​​of the 16 surrounding pixels in the horizontal and vertical directions to obtain the grayscale value of the interpolated point;

[0060] The grayscale value f(i+a, j+b) of the interpolation point (i+a, j+b) is obtained by formula (2):

[0061] f(i+a, j+b)=A×B×C (2);

[0062] Among them, A, B, and C are obtained by the following formula:

[0063] A=[S(1+a)S(a)S(1-a)S(2-a)],

[0064]

[0065] C=[S(1+b)S(b)S(1-b)S(2-b)] T

[0066] (4) According to formula (3), the grayscale information of the point to be interpolated is obtained through the grayscale values ​​of the pixels at the surrounding 16 points.

[0067] Step 9: Perform iterative 3D image reconstruction based on the processed 3D sinogram. In the iterative process, add the Beltrami filter to obtain a clear flow field state of the aircraft engine inlet cavity. The specific process is as follows:

[0068] (1) The MLEM algorithm is used to iteratively reconstruct the image based on the interpolated sinusoidal graph. The iterative formula is:

[0069]

[0070] in, and Represents the results of reconstructed images at iterations k+1 and k, respectively, i represents the i-th response line, a ij represents the probability that the j-th pixel is detected by the i-th response line;

[0071] (2) A Beltrami filter is added in each image iteration to stimulate flow in the direction of smaller resolution in the image, removing noise while maintaining the edge information of the image. The expression of Beltrami flow is:

[0072]

[0073] in, Represents the derivative of the image gray value with respect to time t, is the gradient vector of the image, g represents the metric tensor of the image manifold, and div is the divergence operator;

[0074] (3) Let the total number of iterations be N. In the nth iteration (n=1, 2, ..., N), the reconstructed image obtained is X n After the iteration is completed, Beltrami image flow filtering is performed, and the number of filtering is Nn. The number of filtering decreases with the increase of the number of MLEM iterations. Finally, after completing all iterations, the final flow field reconstruction image X is obtained. N .

[0075] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some embodiments of its application, and are not intended to limit the present invention. It should be noted that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for detecting the flow field of an aero-engine intake duct based on positron annihilation technology, comprising the following steps: Step 1: Install the wind tunnel tube in the annular gamma photon detector, install a fairing at the end of the wind tunnel tube away from the annular gamma photon detector, seal the inner wall of the wind tunnel tube with the outer wall of the fairing, and connect the end of the wind tunnel tube away from the annular gamma photon detector to the wind tunnel blower; Step 2: Place the inlet bracket in the wind tunnel tube within the portion of the annular gamma photon detector. Step 3: Fix the air intake to be tested on the air intake bracket, and make the line connecting the openings at both ends of the air intake to be tested parallel to the center line of the wind tunnel tube; Step 4: Take a piece of cotton thread and divide it into multiple segments with a length of 8-20 mm. Plant them on the silicone plate in a linear array. Step 5: Prepare a radionuclide-labeled aqueous solution and adsorb it onto cotton thread; Step 6: Fix the silica gel plate on which the cotton thread adsorbs the radionuclide labeled aqueous solution in the inner cavity of the air inlet to be tested; Step 7: Start the wind tunnel blower and use the annular gamma photon detector to collect the gamma photon pairs generated by the positron annihilation on the cotton thread in the inlet duct and store them as a three-dimensional sinusoidal diagram; Step 8: Interpolate the three-dimensional sinusoidal graph to expand the data; Step 9: Perform iterative 3D image reconstruction based on the processed 3D sinogram and add a Beltrami filter during the iterative process to obtain a clear flow field state of the aircraft engine inlet cavity. The implementation process is as follows: (1) The MLEM algorithm is used to iteratively reconstruct the image based on the interpolated sinusoidal graph. The iterative formula is: in, and Represents the results of reconstructed images at iterations k+1 and k, respectively, i represents the i-th response line, a ij represents the probability that the j-th pixel is detected by the i-th response line; (2) A Beltrami filter is added in each image iteration to stimulate flow in the direction of smaller resolution in the image, removing noise while maintaining the edge information of the image. The expression of Beltrami flow is: in, Represents the derivative of the image gray value with respect to time t, is the gradient vector of the image, g represents the metric tensor of the image manifold, and div is the divergence operator; (3) Let the total number of iterations be N. In the nth iteration, where n = 1, 2, ..., N, the reconstructed image obtained is X n After the iteration is completed, Beltrami image flow filtering is performed, and the number of filtering is Nn. The number of filtering decreases with the increase of the number of MLEM iterations. Finally, after completing all iterations, the final flow field reconstruction image X is obtained. N .

2. The method for detecting the flow field of an aircraft engine intake duct based on positron annihilation technology according to claim 1, characterized in that: The implementation process of step 8 is as follows: (1) Perform bicubic interpolation on the coincident event sinogram to increase the number of coincident events. The kernel function of bicubic interpolation is: (2) Assume that the coordinates of the 16 pixels around the pixel to be interpolated in the sine graph are (i-1, j-1), (i-1, j), (i-1, j+1), (i-1, j+2), (i, j-1), (i, j), (i, j+1), (i, j+2), (i+1, j-1), (i+1, j), (i+1, j+1), (i+1, j+2), (i+2, j-1), (i+2, j), (i+2, j+1), (i+2, j+2); substitute their abscissas into x in formula (1) to obtain the weight of this pixel in the interpolation; (3) Assume that the coordinates of the pixel to be interpolated in the sine graph are (i+a, j+b), and the weight values ​​of the 16 surrounding pixels in the horizontal and vertical directions are calculated to obtain the grayscale value of the interpolated point. The grayscale value f(i+a, j+b) of the interpolated point (i+a, j+b) is calculated by formula (2): f(i+a,j+b)=A×B×C (2); Among them, A, B, and C are obtained by the following formula: (4) According to formula (3), the grayscale information of the point to be interpolated is obtained through the grayscale values ​​of the pixels at the surrounding 16 points.

3. The method for detecting the flow field of an aircraft engine intake duct based on positron annihilation technology according to claim 1, characterized in that: The upper portion of the air inlet support can be deflected around an axis parallel to the center line of the wind tunnel tube to adjust the angle between the upper portion and the horizontal plane.

4. The method for detecting the flow field of an aircraft engine intake duct based on positron annihilation technology according to claim 1, characterized in that: The spacing between the silk thread arrays on the silica gel plate is 10-15 mm, and the silk threads are cotton threads with a diameter of 0.8-1.2 mm, which are degreased with a caustic soda solution.

5. The method for detecting the flow field of an aircraft engine intake duct based on positron annihilation technology according to claim 1, characterized in that: The concentration of the radionuclide in the radionuclide-labeled aqueous solution is 7-12 mci / L.

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