Speed field measurement system and method for scramjet engine in strong flame combustion environment

Abstract

The present application relates to a kind of strong flame combustion environment under scramjet speed field measurement system and method, belong to aerospace engine testing and flow field measurement technical field, comprising: first camera, second camera, particle generator, engine combustion chamber and sheet light beam;Through system construction, regulate timing to realize the extremely short exposure of nanosecond level of double camera wrong time, and the light of laser double cavity is respectively matched with the exposure period of double camera;Again, calibration image is collected to solve perspective conversion matrix and error matrix, and flow field image is synchronously collected and preprocessed is completed;Subsequently, through cross-correlation algorithm, original velocity field is solved, and after outlier rejection, bilinear interpolation and error matrix correction, actual velocity field is obtained by combining calibration coefficient conversion.The measurement method of the present application can accurately capture and analyze the dynamic change of the flow field inside the combustion chamber under the strong flame combustion environment, which provides important support for the research and development of scramjet.

Description

Technical Field

[0001] This invention relates to a velocity field measurement system and method for a scramjet engine under intense flame combustion conditions, belonging to the field of aerospace engine testing and flow field measurement technology. Background Technology

[0002] As the core power unit for achieving hypersonic flight, the performance of the scramjet engine directly determines the range, speed, and maneuverability of the aircraft. The combustion chamber of the engine contains an extremely complex hypersonic reaction flow field. The key to the success of the entire technology lies in the rapid mixing and stable combustion of fuel with the incoming airflow within a very short residence time, releasing enormous amounts of heat. In this process, precise measurement of the steady and unsteady flow velocities inside the combustion chamber constitutes an indispensable core element for understanding and optimizing the combustion process.

[0003] However, traditional contact probes are currently unsuitable for velocity measurements in high-temperature, high-speed, and high-flow-field environments, while existing particle image velocimetry (PIV) methods based on single-camera dual-frame mode have limitations in resisting strong background light interference. Due to the intense combustion within scramjet engines, hardware limitations prevent general-purpose dual-frame cameras from achieving extremely short exposures to filter out flame background light. Furthermore, while existing single-frame extremely short-exposure cameras are technically mature, current registration and data correction algorithms are lacking, hindering effective velocity field measurements under intense combustion conditions. This makes it difficult to meet the precise measurement requirements of the internal flow field morphology within scramjet engine combustion chambers, thus restricting subsequent optimization of the combustion chamber structure. Summary of the Invention

[0004] This invention aims to solve the technical problems of insufficient resistance to strong background light interference in existing single-camera dual-frame PIV methods and the difficulty of achieving extremely short exposures to filter out flame noise with general dual-frame cameras, which leads to the inability to accurately measure the flow field velocity inside the combustion chamber. It proposes a velocity field measurement system and method for scramjet engines under strong flame combustion environment.

[0005] The technical solution of the present invention:

[0006] A velocity field measurement system for a scramjet engine under intense flame combustion conditions includes: a first camera, a second camera, a particle generator, an engine combustion chamber, and a sheet-like light beam;

[0007] Optical observation windows are respectively provided on the side and upper part of the engine combustion chamber; the first camera and the second camera are both horizontally arranged outside the optical observation windows on the side of the engine combustion chamber, and 532nm filters are installed in front of the lenses of the first camera and the second camera; the first camera is set facing the test area of ​​the engine combustion chamber, and the second camera is set at a small angle relative to the first camera; the first camera and the second camera are both communicatively connected to the image processing unit; a 532nm dual-cavity pulsed laser is arranged near the engine combustion chamber, and a reflector group and a sheet beam shaping device are arranged sequentially on its output optical path; the laser output by the 532nm dual-cavity pulsed laser is reflected by the reflector group and then vertically incident into the engine combustion chamber from the optical observation window at the upper part of the engine combustion chamber, and then expanded into a sheet beam by the sheet beam shaping device, which covers and illuminates the test area inside the engine combustion chamber; the 532nm dual-cavity pulsed laser is electrically connected to the timing controller; the particle generator is installed upstream of the scramjet engine and is used to release tracer particles into the flow field of the engine combustion chamber.

[0008] A method for measuring the velocity field of a scramjet engine under intense flame combustion conditions, applicable to a scramjet engine velocity field measurement system under intense flame combustion conditions, includes the following steps:

[0009] S1. Optical observation windows are respectively installed on the side and upper part of the scramjet engine combustion chamber; two cameras are horizontally arranged outside the side optical observation window, and 532nm filters are installed in front of the lenses of both cameras. The first camera is set directly facing the test area of ​​the engine combustion chamber, and the second camera is set at a small angle relative to the first camera; a 532nm dual-cavity pulsed laser is set near the engine combustion chamber. The laser output from the laser is reflected by a mirror and then vertically incident into the engine combustion chamber through the upper optical observation window. A sheet beam shaping device is set at the end of the laser incident beam to expand the laser into a sheet beam to illuminate the test area; a particle generator is installed upstream of the scramjet engine.

[0010] S2. Adjust the exposure timing of the two cameras so that the second camera starts exposure immediately after the first camera finishes its exposure. The exposure time interval between the two cameras is on the nanosecond level, and the single-frame exposure time of both cameras is less than 1μs. Adjust the dual-cavity emission time of the dual-cavity pulsed laser so that the emission time of the first cavity of the laser falls within the exposure time window of the first camera, and the emission time of the second cavity of the laser falls within the exposure time window of the second camera. Set the emission time interval of the dual-cavity laser to dt, in seconds.

[0011] S3. Start the particle generator, dual-cavity pulsed laser, first camera, and second camera. After the flow field inside the engine combustion chamber stabilizes, the two cameras acquire an image sequence synchronously at the same frequency. The image sequence is represented as follows: Where n is the total number of image sequences, The nth frame image captured by the first camera. The nth frame image is captured by the second camera; the image sequence is saved after the acquisition is completed.

[0012] S4. Place a dot calibration plate covering the entire measurement area on the plane where the area to be measured is located. Take pictures of the first dot calibration image and the second dot calibration image using the first camera (1) and the second camera (2) respectively, and represent them as follows: , Identify the center coordinates of the dots in two dot calibration images, and obtain a one-to-one correspondence between the first set of center coordinates and the second set of center coordinates, represented as follows: , Where r is the total number of circular dots. Let r be the coordinates of the first center of the circle corresponding to the r-th point. Let H be the coordinates of the second center of the r-th circular point. The perspective transformation matrix H, which maps the image from the second camera (2) to the image from the first camera (1), is calculated using the least squares method. A speckle pattern covering the entire measurement area is placed on the plane containing the area to be measured. The first speckle image and the second speckle image are captured by the first camera (1) and the second camera (2) respectively, and are represented as follows: , Place a calibration ruler on the plane where the area to be measured is located, and calculate the conversion factor k between the spatial length of the image of the first camera (1) and the image pixels, with the unit being m / pixel; S5. Using the perspective transformation matrix H to... Perform a perspective transformation to obtain the second speckle image after perspective transformation. The image cross-correlation algorithm is used to calculate... and Error matrix between , , Let be a real number matrix, where a is the length of the error matrix and b is the width of the error matrix; S6. Preprocess the acquired image sequence and calculate the time-averaged images of the first camera (1) and the second camera (2). , Through H Perform image transformation to obtain the registered time-averaged image. ; for the acquired image sequence All image frames acquired by the second camera (2) are transformed by H, and all image frames acquired by the first camera (1) and the second camera (2) are respectively subtracted. , Finally, the preprocessed image is obtained. ,in The image of the nth frame from the first camera (1) after preprocessing. The image of the nth frame of the second camera (2) after preprocessing; S7. Based on the cross-correlation algorithm, the velocity field of the preprocessed flow field image pair is calculated to obtain the original velocity field. , , u is the lateral velocity vector matrix, v is the longitudinal velocity vector matrix;

[0013] S8. Remove vectors whose length and direction exceed the preset threshold in the original velocity field vector, and then perform bilinear interpolation to obtain the velocity vector matrix;

[0014] S9. Subtract the pixel displacement error matrix from the velocity vector matrix to obtain the high-precision pixel velocity field;

[0015] S10. Based on the calibration coefficient and the time interval between the output of the dual-cavity laser, the high-precision pixel velocity field is converted into the actual physical velocity field.

[0016] Specifically, in step S1, the tracer particles used in the particle generator are white alumina powder.

[0017] Specifically, in step S4, Hough transform is used to identify the center coordinates of the dots in the two dot calibration plate images.

[0018] Specifically, in step S5, the cross-correlation calculation coordinate matrix and calculation window size used when calculating the pixel displacement error matrix are the same as those used in step S7 to solve the original velocity location.

[0019] Specifically, in step S9, the formula for calculating the high-precision pixel velocity field is as follows:

[0020]

[0021] .

[0022] Specifically, in step S10, the conversion formula for the actual physical velocity field is:

[0023]

[0024] . Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the system setup for the present invention;

[0026] Figure 2 A schematic diagram of the dot calibration plate;

[0027] Figure 3 This is a schematic diagram of a speckle pattern;

[0028] Figure 4 Timing diagram for PIV dual-camera system;

[0029] Figure 5 This is a flowchart of the velocity field solution algorithm of the present invention;

[0030] In the diagram, 1-first camera, 2-second camera, 3-particle generator, 4-engine combustion chamber, 5-sheet beam. Detailed Implementation

[0031] To make the technical solutions and advantages in the embodiments of this application clearer, the following description is provided in conjunction with the appendix. Figure 1 - Appendix Figure 5 The exemplary embodiments of this application will be described in further detail.

[0032] Example 1:

[0033] A velocity field measurement system for a scramjet engine under intense flame combustion conditions includes: a first camera 1, a second camera 2, a particle generator 3, an engine combustion chamber 4, and a sheet-like light beam 5;

[0034] Optical observation windows are respectively provided on the side and upper part of the engine combustion chamber 4; the first camera 1 and the second camera 2 are both horizontally arranged outside the optical observation windows on the side of the engine combustion chamber 4, and a 532nm filter is installed in front of the lens of the first camera 1 and the second camera 2; the first camera 1 is set directly facing the area to be measured in the engine combustion chamber 4, and the second camera 2 is set at a small angle relative to the first camera 1; the first camera 1 and the second camera 2 are both communicatively connected to the image processing unit; the 532nm dual-cavity pulsed laser is arranged near the engine combustion chamber 4. The output optical path is sequentially equipped with a mirror group and a sheet beam shaping device; the laser output from the 532nm dual-cavity pulsed laser is reflected by the mirror group and then vertically incident into the interior of the engine combustion chamber 4 through the optical observation window at the top of the engine combustion chamber 4. It is then expanded into a sheet beam 5 by the sheet beam shaping device. The sheet beam 5 covers and illuminates the test area inside the engine combustion chamber 4; the 532nm dual-cavity pulsed laser is electrically connected to the timing controller; the particle generator 3 is installed upstream of the scramjet engine and is used to release tracer particles into the flow field of the engine combustion chamber 4.

[0035] Example 2:

[0036] A method for measuring the velocity field of a scramjet engine under intense flame combustion conditions, applicable to the velocity field measurement system for a scramjet engine under intense flame combustion conditions described in Example 1, includes the following steps:

[0037] S1, System Setup

[0038] An optical observation window is installed on the side of the scramjet engine's combustion chamber. Two cameras are horizontally positioned outside the window, with 532nm filters installed in front of their lenses. The first camera faces the area under test, while the second camera is positioned at a small angle relative to the first. An optical observation window is installed above the combustion chamber to allow 532nm laser light to enter. A 532nm dual-cavity pulsed laser is placed near the combustion chamber and reflected by a mirror to the upper part of the scramjet engine, then incident vertically downwards. A fixed sheet laser shaping device is installed in the final stage to spread the laser light into a sheet that illuminates the entire area under test. A particle generator, using white alumina powder, is installed upstream of the scramjet engine.

[0039] S2, System Timing Adjustment

[0040] Adjust the system timing so that the second camera starts exposing immediately after the first camera finishes exposing, and the exposure time of the two cameras is staggered by a very small time interval (nanosecond level). Set the exposure time of the first camera and the second camera to be less than 1μs. Adjust the light emission time of the first cavity and the second cavity of the dual-cavity pulsed laser so that the laser from the first cavity falls within the exposure time of the first camera, and the laser from the second cavity falls within the exposure time of the second camera. Set the time interval of the dual-cavity laser to dt[s].

[0041] S3, Experimental Image Acquisition

[0042] To begin the experiment, the particle generator was turned on, along with the dual-cavity pulsed laser and two cameras. Once the flow field stabilized, the two cameras simultaneously acquired image sequences at the same frequency. After the experiment is completed, save the images and turn off the laser, two cameras, and particle generator.

[0043] S4, Calibration Image Acquisition

[0044] A dotted calibration plate, filling the entire measurement area, is placed on a flat surface in the area to be measured. The first and second cameras then capture and record the images. , A speckle pattern, filling the entire measurement area, is placed on a plane in the area to be measured. The first and second cameras capture and record the images. , Place a steel ruler on the plane of the area to be measured, and calculate the spatial length and image pixel conversion factor k [m / pixel] in the first camera image.

[0045] S5. Image Transformation Relationship Calculation

[0046] Select the dot calibration plate image respectively , The origin center is determined, and the Hough transform is used to calculate the coordinates of the circle centers, ultimately obtaining the first set of circle center coordinates and the second set of circle center coordinates. , Here, r is the total number of circular dots, and and The midpoints correspond in order. The set is calculated using the least squares method. to the set The perspective transformation matrix H.

[0047] S6. Error Matrix Calculation

[0048] The image is transformed by the perspective transformation matrix H. Transform to image Image cross-correlation algorithm is used to calculate the image With images Error matrix between , That is, setting the calculation coordinate matrix. , The calculation window size is .

[0049] S7, Image Preprocessing

[0050] Perform experimental image preprocessing and calculate the time-averaged images from the first and second cameras. Through H ,right Perform image transformation to obtain the registered time-averaged image. .right All B-frame images are transformed using H, and all images in A and B frames are subtracted respectively. , Finally, the preprocessed image is obtained. .

[0051] S8. Solving the original velocity field

[0052] Draw a mask for the region to be calculated and solve for the velocity field. Set up a cross-correlation calculation coordinate matrix. , Set the window size for the two-dimensional cross-correlation calculation to [size missing]. The original velocity field was calculated. , Here, the lattice coordinates are... , Completely consistent with step S6.

[0053] S9, Velocity Field Post-processing

[0054] Post-processing of the velocity field is performed. Vectors with lengths and directions exceeding a certain threshold are removed. Then, bilinear interpolation is performed to update the velocity vector matrix. .

[0055] S10, Error Correction

[0056] For the velocity vector matrix Subtract the error matrix , Finally, high-precision velocity fields at each moment were obtained. , ,Right now:

[0057]

[0058]

[0059] Where u' is the horizontal high-precision pixel velocity vector matrix, and v' is the vertical high-precision pixel velocity vector matrix. The lateral velocity vector error matrix is... The longitudinal velocity vector error matrix;

[0060] S11, Speed ​​Conversion

[0061] Based on the calibration coefficient k[m / pixel] and the time interval dt[s], the actual velocity field at each moment is calculated. [m / s], [m / s], that is:

[0062]

[0063]

[0064] in, This is the actual physical velocity vector matrix in the transverse direction. The actual physical velocity vector matrix in the longitudinal direction. For calibration coefficients, For time intervals.

Claims

1. A velocity field measurement system for a scramjet engine under intense flame combustion conditions, characterized in that, include: First camera (1), second camera (2), particle generator (3), engine combustion chamber (4), and sheet beam (5); Optical observation windows are provided on the side and upper part of the engine combustion chamber (4); the first camera (1) and the second camera (2) are both horizontally arranged outside the optical observation windows on the side of the engine combustion chamber (4), and 532nm filters are installed in front of the lenses of the first camera (1) and the second camera (2); the first camera (1) is set facing the test area of ​​the engine combustion chamber (4), and the second camera (2) is set at a small angle relative to the first camera (1); the first camera (1) and the second camera (2) are both connected to the image processing unit; a 532nm dual-cavity pulsed laser is arranged near the engine combustion chamber (4), and a reflector group and a sheet light shaping device are arranged in sequence on its output optical path; The laser output from the 532nm dual-cavity pulsed laser is reflected by a set of mirrors and then incident vertically into the engine combustion chamber (4) through the optical observation window at the top of the combustion chamber (4). The laser beam is then expanded into a sheet beam (5) by a sheet beam shaping device. The sheet beam (5) covers and illuminates the area to be tested inside the engine combustion chamber (4). The 532nm dual-cavity pulsed laser is electrically connected to a timing controller. The particle generator (3) is installed upstream of the scramjet engine and is used to release tracer particles into the flow field of the engine combustion chamber (4).

2. A method for measuring the velocity field of a scramjet engine under intense flame combustion conditions, applicable to the velocity field measurement system for a scramjet engine under intense flame combustion conditions as described in claim 1, characterized in that, Includes the following steps: S1. Optical observation windows are respectively set on the side and upper part of the scramjet engine combustion chamber (4); two cameras are horizontally arranged outside the side optical observation window, and 532nm filters are installed in front of the lenses of the two cameras. The first camera (1) is set facing the test area of ​​the engine combustion chamber (4), and the second camera (2) is set at a small angle relative to the first camera (1); a 532nm dual-cavity pulsed laser is set near the engine combustion chamber (4). The laser output by the laser is reflected by a mirror and then vertically incident into the engine combustion chamber (4) through the upper optical observation window. A sheet beam shaping device is set at the end of the laser incident light path to expand the laser into a sheet beam (5) to illuminate the test area; a particle generator (3) is installed upstream of the scramjet engine. S2. Adjust the exposure timing of the two cameras so that the second camera (2) starts exposure immediately after the first camera (1) finishes exposure. The exposure time interval between the two cameras is at the nanosecond level, and the single frame exposure time of both cameras is less than 1μs. Adjust the dual-cavity emission time of the dual-cavity pulsed laser so that the emission time of the first cavity of the laser falls within the exposure time window of the first camera (1), and the emission time of the second cavity of the laser falls within the exposure time window of the second camera (2). Set the emission time interval of the dual-cavity laser to dt, with the unit being s. S3. Start the particle generator (3), dual-cavity pulsed laser, first camera (1), and second camera (2). After the flow field inside the engine combustion chamber (4) stabilizes, the two cameras acquire image sequences synchronously at the same frequency. The image sequence is represented as follows: Where n is the total number of image sequences, The nth frame image captured by the first camera (1), The nth frame image is acquired by the second camera (2), and the image sequence is saved after acquisition; S4. Place a dot calibration plate covering the entire measurement area on the plane where the area to be measured is located. Take pictures of the first dot calibration image and the second dot calibration image using the first camera (1) and the second camera (2) respectively, and represent them as follows: , Identify the center coordinates of the dots in two dot calibration images, and obtain a one-to-one correspondence between the first set of center coordinates and the second set of center coordinates, represented as follows: , Where r is the total number of circular dots. Let r be the coordinates of the first center of the circle corresponding to the r-th point. Let H be the coordinates of the second center of the r-th circular point. The perspective transformation matrix H, which maps the image from the second camera (2) to the image from the first camera (1), is calculated using the least squares method. A speckle pattern covering the entire measurement area is placed on the plane containing the area to be measured. The first speckle image and the second speckle image are captured by the first camera (1) and the second camera (2) respectively, and are represented as follows: , Place a calibration ruler on the plane where the area to be measured is located, and calculate the conversion factor k between the spatial length of the image of the first camera (1) and the image pixels, with the unit being m / pixel; S5. Using the perspective transformation matrix H to... Perform a perspective transformation to obtain the second speckle image after perspective transformation. The image cross-correlation algorithm is used to calculate... and Error matrix between , , Let be a real number matrix, where a is the length of the error matrix and b is the width of the error matrix; S6. Preprocess the acquired image sequence and calculate the time-averaged images of the first camera (1) and the second camera (2). , Through H Perform image transformation to obtain the registered time-averaged image. ; for the acquired image sequence All image frames acquired by the second camera (2) are transformed using H, and all image frames acquired by the first camera (1) and the second camera (2) are respectively subtracted. , Finally, the preprocessed image is obtained. ,in The image of the nth frame from the first camera (1) after preprocessing. The image of the nth frame of the second camera (2) after preprocessing; S7. Based on the cross-correlation algorithm, the velocity field of the preprocessed flow field image pair is calculated to obtain the original velocity field. , , u is the lateral velocity vector matrix, v is the longitudinal velocity vector matrix; S8. Remove vectors whose length and direction exceed the preset threshold in the original velocity field vector, and then perform bilinear interpolation to obtain the velocity vector matrix; S9. Subtract the pixel displacement error matrix from the velocity vector matrix to obtain the high-precision pixel velocity field; S10. Based on the calibration coefficient and the time interval between the output of the dual-cavity laser, the high-precision pixel velocity field is converted into the actual physical velocity field.

3. The method for measuring the velocity field of a scramjet engine under intense flame combustion conditions according to claim 2, characterized in that, In step S1, the tracer particles used in the particle generator (3) are white alumina powder.

4. The method for measuring the velocity field of a scramjet engine under intense flame combustion conditions according to claim 2, characterized in that, In step S4, Hough transform is used to identify the center coordinates of the dots in the two dot calibration plate images.

5. The method for measuring the velocity field of a scramjet engine under intense flame combustion conditions according to claim 2, characterized in that, In step S5, the cross-correlation calculation coordinate matrix and calculation window size used when calculating the pixel displacement error matrix are the same as those used in step S7 to solve the original velocity location.

6. The method for measuring the velocity field of a scramjet engine under intense flame combustion conditions according to claim 2, characterized in that, In step S9, the formula for calculating the high-precision pixel velocity field is as follows: ； ； Where u' is the horizontal high-precision pixel velocity vector matrix, and v' is the vertical high-precision pixel velocity vector matrix. The lateral velocity vector error matrix is... This is the longitudinal velocity vector error matrix.

7. The method for measuring the velocity field of a scramjet engine under intense flame combustion conditions according to claim 6, characterized in that, In step S10, the conversion formula for the actual physical velocity field is: ； ； in, This is the actual physical velocity vector matrix in the transverse direction. The actual physical velocity vector matrix in the longitudinal direction. For calibration coefficients, For time intervals.

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