Method and system for measuring time-averaged velocity field in scramjet combustion chamber

Abstract

The present invention discloses a method and system for measuring the time-averaged velocity field of a scramjet combustion chamber, belonging to the technical field of average velocity field measurement. The present invention constructs a measurement system, matches the exposure frame number of a high-speed camera with the cavity number of a laser, collects time-series images for pre-processing, obtains the pre-processed time-series images, divides them into grid slices for cross-correlation calculation, and obtains the time-series velocity based on the spatial and pixel conversion coefficients; constructs a velocity model based on a Gaussian mixture model algorithm, and obtains a probability matrix of a data point belonging to a correct velocity vector based on an expectation maximization algorithm; and calculates the time-averaged velocity field based on the correct velocity vector and the error velocity vector judgment conditions. The present invention effectively improves the efficiency and accuracy of measuring the time-averaged velocity field distribution and can be applied to measuring the time-averaged velocity field.

Description

Technical Field

[0001] The invention relates to a method and a system for measuring a time-averaged velocity field in a scramjet combustion chamber, and belongs to the technical field of average velocity field measurement. Background Art

[0002] Measuring the flow field inside a scramjet combustion chamber is crucial for improving engine performance and optimizing design. Accurate flow field measurements can effectively understand the velocity, temperature, and pressure fields of the airflow, as well as the vortex characteristics during combustion, thereby evaluating the fuel-air mixing effect and combustion efficiency in the combustion chamber. Flow field data can help identify potential design issues, optimize nozzle and combustion chamber shapes, and injection strategies, thereby improving the engine's thrust output and combustion stability. Measuring and understanding the morphology of the internal velocity field is crucial. Accurately understanding the flow characteristics inside the combustion chamber can provide a deep understanding of airflow acceleration, turbulence, and the interaction between airflow and walls. Flow characteristic data is of great value in optimizing airflow distribution, reducing flow losses, and avoiding flow instability. Especially in the hypersonic and high-temperature environments of scramjet engines, measuring the internal velocity field can help determine whether adverse phenomena such as airflow separation and vortexes exist in the combustion chamber, thereby providing an important basis for further optimizing the scramjet combustion chamber design and helping to improve the overall performance and reliability of the engine.

[0003] Particle image velocimetry (PIV) is a commonly used flow field velocity visualization measurement technology that is widely used in various measurement scenarios. It mainly relies on fully spreading tracer particles in the flow field, using a sheet laser beam to illuminate the tracer particles in the test area, using a high-speed camera to continuously shoot two frames of images at a very short time interval, and calculating the displacement through image algorithms to obtain the velocity field. The key to its application lies in the uniformity of particle spreading and the background light interference caused by other factors in the test area. When performing PIV measurement inside the combustion chamber of a scramjet engine, the following challenges are faced: (1) There is complex three-dimensional flow such as strong turbulence inside the combustion chamber, and the tracer particles dropped upstream are difficult to be evenly distributed through the test area; (2) There is background light interference from flame combustion in the combustion chamber, and the laser intensity scattered by the tracer particles has a weak signal-to-noise ratio, which seriously interferes with the subsequent image algorithm solution; (3) The sheet laser beam is strongly scattered when it is incident on the combustion chamber wall, which has a certain impact on the measurement inside the combustion chamber, that is, it reduces the signal-to-noise ratio of the laser intensity scattered by the tracer particles.

[0004] In summary, a method and system for measuring the time-averaged velocity field in the scramjet combustion chamber are needed. Summary of the Invention

[0005] A brief overview of the present invention is provided below to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify key or important aspects of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is simply to present certain concepts in a simplified form as a prelude to the more detailed description discussed later.

[0006] In view of this, in order to solve the problem in the prior art that the traditional method for measuring the time-averaged velocity field inside the combustion chamber of a scramjet engine has large measurement errors due to background light interference, the present invention provides a method and system for measuring the time-averaged velocity field in the combustion chamber of a scramjet engine.

[0007] Technical solution 1 is as follows: A method for measuring the time-averaged velocity field in a scramjet combustion chamber comprises the following steps:

[0008] S1. Build a measurement system for a scramjet combustion chamber equipped with a timing signal generator using a laser, a high-speed camera, a lens with a filter, and a particle generator.

[0009] S2. Adjust the measurement system's acquisition timing and the laser's two-cavity light emission timing, set the time interval, and match the high-speed camera's exposure frame rate with the laser's cavity number to obtain a matching result.

[0010] S3. Start the measurement test. At time t0, turn on the particle generator. At time t1, turn on the laser and high-speed camera. Collect time series images based on the matching results. After the acquisition, turn off the laser, high-speed camera, and particle generator. Save the time series images to the computer.

[0011] Specifically: Time series images are represented as , where A and B represent the frame numbers of the high-speed camera, and n represents the image sequence number. Represents n A-frame and B-frame images;

[0012] S4. In a calm state, place a steel ruler on the smooth surface of the laser sheet so that it overlaps the laser surface. Calculate the spatial-to-pixel conversion factor.

[0013] Specifically, the space-to-pixel conversion factor is expressed as P, with the unit being m / pixel, where m / pixel means meters per pixel;

[0014] S5. Pre-processing the collected time series images to obtain pre-processed time series images;

[0015] S6. Divide the pre-processed time series image into grid slices for cross-correlation calculation to obtain the particle displacement within the grid slices, and obtain the time series velocity based on the space-to-pixel conversion coefficient;

[0016] S7. Calculate the vorticity field based on the time series velocity, generate a Gaussian matrix, construct a velocity model using the Gaussian mixture model algorithm, and obtain updated model parameters of the velocity model using the expectation-maximization algorithm, thereby obtaining a probability matrix that the data point belongs to the correct velocity vector;

[0017] S8. Calculate the time-averaged velocity field based on the probability matrix, the correct velocity vector, and the incorrect velocity vector judgment conditions.

[0018] Furthermore, in S1, a quartz glass observation window is provided on the side wall of the scramjet combustion chamber, a quartz glass groove is provided on the upper wall of the scramjet combustion chamber, and a laser sheet light incident window is provided on the upper portion of the scramjet combustion chamber. A laser is emitted by a laser, shaped into a sheet light beam with a thickness of less than 1 mm, and then vertically incident from the quartz glass groove to the area to be measured.

[0019] Furthermore, in said S2, the acquisition timing is adjusted, that is, the high-speed camera is in a double-frame acquisition mode, and after the A frame of the high-speed camera is exposed, the B frame of the high-speed camera is exposed;

[0020] The laser cavity A light emission moment is included in the A frame exposure of the high-speed camera, and the laser light emission time interval dt is set. Its unit is s, where s represents seconds. The laser cavity B light emission moment is included in the B frame exposure of the high-speed camera.

[0021] Furthermore, in said S5, the time average image of frame A is calculated and B-frame temporal average image ;

[0022] A frame time average image Expressed as:

[0023] ;

[0024] B-frame temporal average image Expressed as:

[0025] ;

[0026] For all time series images of frame A and frame B, subtract the time average image of frame A and B-frame temporal average image ,Right now 、 , is the A-frame time series image after pre-processing, The B-frame time series image after pre-processing is obtained. ;

[0027] Furthermore, in S6, the pre-processed time series image is divided into K×L grid slices, where K represents rows and L represents columns. A cross-correlation calculation is performed on each grid slice to calculate the particle displacement within the grid slice. The specific steps are as follows:

[0028] Slice the first image , the second image slice Perform two-dimensional Fourier transform respectively to obtain the first image slice , the second image slice The two-dimensional Fourier transform result of ;

[0029] First image slice , the second image slice The two-dimensional Fourier transform result of 、 Expressed as:

[0030] ;

[0031] ;

[0032] Perform conjugate multiplication on the two-dimensional Fourier transform results to obtain the conjugate matrix ;

[0033] Conjugate Matrix Expressed as:

[0034]

[0035] Conjugate matrix Perform two-dimensional inverse Fourier transform to obtain cross-correlation results ;

[0036] Cross-correlation results Expressed as:

[0037] ;

[0038] Finding cross-correlation results The sub-pixel position of the maximum value relative to the center is obtained, that is, the particle displacement in the corresponding grid slice is obtained, and the particle displacement in all grid slices is traversed and calculated, that is, the velocity vector field at time t is obtained. , the speed unit is converted into m / s by using the space and pixel conversion coefficient P and the laser light time interval dt. m / s means meter per second, and the converted speed vector field is obtained ( , );

[0039] The converted velocity vector field ( , ) is expressed as:

[0040] ;

[0041] ;

[0042] According to the converted velocity vector field, the velocity vector field in the time series is traversed and calculated to obtain the time series velocity .

[0043] Furthermore, in said S7, the vortex field is obtained according to the time series velocity calculation. , thus obtaining the time series vorticity field ;

[0044] vorticity field Expressed as:

[0045] ;

[0046] in, Represents the x-axis velocity matrix To perform derivation, Velocity matrix in the y-axis direction Perform derivatives;

[0047] The velocity horizontal coordinate matrix X, the x-axis direction velocity matrix , velocity ordinate matrix Y, y-axis velocity matrix , vorticity matrix Pack and merge into a Gaussian matrix ;

[0048] Gaussian matrix Expressed as:

[0049] ;

[0050] According to the Gaussian mixture model algorithm, the Gaussian matrix The data points in the velocity model , where each data point is represented by a weighted sum of multiple Gaussian distributions;

[0051] Velocity Model Expressed as:

[0052] ;

[0053] in, It is High-speed distribution weights, satisfying , For the The probability density of a high-speed distribution, whose mean is , the covariance matrix is , is a Gaussian matrix Middle data points, i.e. ;

[0054] Define two categories of correct velocity vector and wrong velocity vector, namely =2, then the velocity model Expressed as:

[0055] ;

[0056] Estimate the velocity model using the expectation maximization algorithm of 、 and .

[0057] The E-step process in the expectation-maximization algorithm is as follows: Calculate the posterior probability, that is, the probability that each data point belongs to the Gaussian distribution;

[0058] Posterior probability Expressed as:

[0059] ;

[0060] The M-step process in the expectation maximization algorithm is as follows: According to the posterior probability , update speed model Parameters of the model are updated.

[0061] The updated model parameters are expressed as:

[0062] ;

[0063] ;

[0064] ;

[0065] According to the updated model parameters, substitute them into the velocity model , obtain the probability matrix of the data point belonging to the correct velocity vector .

[0066] Furthermore, in said S7, the correct velocity vector and the wrong velocity vector judgment condition are expressed as follows: Set the time matrix , set the threshold , if the probability matrix The element value is greater than the threshold , then it is considered that this moment is the correct velocity vector, and the time matrix The corresponding position at this moment is set to 1, otherwise it is 0, which is an error velocity vector;

[0067] According to the correct velocity vector and the error velocity vector judgment conditions, the time average velocity field is calculated. , that is, obtaining the time-averaged velocity distribution;

[0068] ;

[0069] ;

[0070] ;

[0071] in, is the velocity matrix after conversion in the x-axis direction The average speed, is the velocity matrix after conversion in the y-axis direction average speed.

[0072] Technical Solution 2 is as follows: A system for measuring the time-averaged velocity field in a scramjet combustion chamber, used to implement the method for measuring the time-averaged velocity field in a scramjet combustion chamber described in Technical Solution 1, comprising a light-sheet shaping device, a high-speed camera, a lens equipped with a filter, a laser, a particle generator, and a timing signal generator;

[0073] The laser is connected to a light sheet shaping device, and the light sheet beam outlet of the light sheet shaping device is directed toward the quartz glass groove on the upper wall of the scramjet combustion chamber;

[0074] The front end of the high-speed camera is provided with a lens equipped with a filter, and the lens equipped with the filter faces the quartz glass observation window on the side wall of the scramjet engine combustion chamber;

[0075] The timing signal generator is connected to the laser and the high-speed camera respectively;

[0076] The particle generator is arranged upstream of the scramjet combustion chamber.

[0077] The beneficial effects of the present invention are as follows: the present invention solves the problem of being unable to effectively measure the velocity field in a scramjet engine due to noise interference from various factors. The present invention effectively measures the time-averaged velocity field distribution inside the scramjet engine by coupling particle image velocimetry and a Gaussian mixture model algorithm. The present invention introduces a Gaussian mixture model algorithm to screen and eliminate large-area noise vectors, thereby improving the efficiency and accuracy of measuring the time-averaged velocity field distribution. The present invention can still effectively obtain the time-averaged velocity field distribution under complex conditions of multi-physical phenomenon coupling, and has important guiding significance for the optimization of the shape of the scramjet engine combustion chamber and the fuel injection method. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0079] Figure 1 Schematic diagram of a flow chart of a method for measuring the time-averaged velocity field in a scramjet combustion chamber;

[0080] Figure 2 This is a schematic diagram of the structure of the measurement system for the time-averaged velocity field in the scramjet combustion chamber;

[0081] Figure 3 This is a schematic diagram of the working timing control of the measurement system;

[0082] Figure 4 Schematic diagram of the process of solving the time-averaged velocity field based on the Gaussian mixture model.

[0083] Description of the figures: 1. Light-sheet shaping device; 2. High-speed camera; 3. Lens with filter; 4. Laser; 5. Particle generator; 6. Scramjet combustion chamber; 7. Timing signal generator; 8. Quartz glass tank; 9. Quartz glass observation window. DETAILED DESCRIPTION

[0084] To make the technical solutions and advantages of the embodiments of the present invention more clearly understood, exemplary embodiments of the present invention are further described in detail below with reference to the accompanying drawings. It should be noted that the embodiments described are only a portion of the embodiments of the present invention, and are not an exhaustive list of all embodiments. It should be noted that the embodiments of the present invention and the features thereof may be combined with each other unless they conflict.

[0085] Example 1: Reference Figures 1-4 The present embodiment is described in detail. The method for measuring the time-averaged velocity field in the scramjet combustion chamber includes the following steps:

[0086] S1. Build a measurement system for a scramjet combustion chamber equipped with a timing signal generator using a laser, a high-speed camera, a lens with a filter, and a particle generator.

[0087] S2. Adjust the measurement system's acquisition timing and the laser's two-cavity light emission timing, set the time interval, and match the high-speed camera's exposure frame rate with the laser's cavity number to obtain a matching result.

[0088] S3. Start the measurement test. At time t0, turn on the particle generator. At time t1, turn on the laser and high-speed camera. Collect time series images based on the matching results. After the acquisition, turn off the laser, high-speed camera, and particle generator. Save the time series images to the computer.

[0089] Specifically: Time series images are represented as , where A and B represent the frame numbers of the high-speed camera, and n represents the image sequence number. Represents n A-frame and B-frame images;

[0090] S4. In a calm state, place a steel ruler on the smooth surface of the laser sheet so that it overlaps the laser surface. Calculate the spatial-to-pixel conversion factor.

[0091] Specifically, the space-to-pixel conversion factor is expressed as P, with the unit being m / pixel, where m / pixel means meters per pixel;

[0092] S5. Pre-processing the collected time series images to obtain pre-processed time series images;

[0093] S6. Divide the pre-processed time series image into grid slices for cross-correlation calculation to obtain the particle displacement within the grid slices, and obtain the time series velocity based on the space-to-pixel conversion coefficient;

[0094] S7. Calculate the vorticity field based on the time series velocity, generate a Gaussian matrix, construct a velocity model using the Gaussian mixture model algorithm, and obtain updated model parameters of the velocity model using the expectation-maximization algorithm, thereby obtaining a probability matrix that the data point belongs to the correct velocity vector;

[0095] S8. Calculate the time-averaged velocity field based on the probability matrix, the correct velocity vector, and the incorrect velocity vector judgment conditions.

[0096] Furthermore, in S1, a quartz glass observation window is provided on the side wall of the scramjet combustion chamber, a quartz glass groove is provided on the upper wall of the scramjet combustion chamber, and a laser sheet light incident window is provided at the upper portion of the scramjet combustion chamber. A 527 nm wavelength dual-cavity pulse laser is used to emit laser light, which is shaped into a sheet-shaped beam with a thickness of less than 1 mm and then vertically incident from the quartz glass groove to the area to be measured.

[0097] Specifically, a quartz glass window provided on the side wall of the scramjet engine combustion chamber facilitates shooting by the high-speed camera 2, and a laser sheet light incident window provided on the upper portion facilitates the incidence of laser light in the form of sheet light. In this embodiment, a 527nm wavelength dual-cavity pulse laser 4 and a lens 3 equipped with a filter are used, and the wavelength of the filter is 527nm.

[0098] Furthermore, in said S2, the acquisition timing is adjusted, that is, the high-speed camera is in a double-frame acquisition mode, and after the A frame of the high-speed camera is exposed, the B frame of the high-speed camera is exposed;

[0099] The laser cavity A light emission moment is included in the A frame exposure of the high-speed camera, and the laser light emission time interval dt is set. Its unit is s, where s represents seconds. The laser cavity B light emission moment is included in the B frame exposure of the high-speed camera.

[0100] Furthermore, in said S5, the time average image of frame A is calculated and B-frame temporal average image ;

[0101] A frame time average image Expressed as:

[0102] ;

[0103] B-frame temporal average image Expressed as:

[0104] ;

[0105] For all time series images of frame A and frame B, subtract the time average image of frame A and B-frame temporal average image ,Right now 、 , is the A-frame time series image after pre-processing, The B-frame time series image after pre-processing is obtained. ;

[0106] Furthermore, in S6, the pre-processed time series image is divided into K×L grid slices, where K represents rows and L represents columns. A cross-correlation calculation is performed on each grid slice to calculate the particle displacement within the grid slice. The specific steps are as follows:

[0107] Slice the first image , the second image slice Perform two-dimensional Fourier transform respectively to obtain the first image slice , the second image slice The two-dimensional Fourier transform result of ;

[0108] First image slice , the second image slice The two-dimensional Fourier transform result of 、 Expressed as:

[0109] ;

[0110] ;

[0111] Perform conjugate multiplication on the two-dimensional Fourier transform results to obtain the conjugate matrix ;

[0112] Conjugate Matrix Expressed as:

[0113] ;

[0114] Conjugate matrix Perform two-dimensional inverse Fourier transform to obtain cross-correlation results ;

[0115] Cross-correlation results Expressed as:

[0116] ;

[0117] Finding cross-correlation results The sub-pixel position of the maximum value relative to the center is obtained, that is, the particle displacement in the corresponding grid slice is obtained, and the particle displacement in all grid slices is traversed and calculated, that is, the velocity vector field at time t is obtained. , the speed unit is converted into m / s by using the space and pixel conversion coefficient P and the laser light time interval dt. m / s means meter per second, and the converted speed vector field is obtained ( , );

[0118] The converted velocity vector field ( , ) is expressed as:

[0119] ;

[0120] ;

[0121] According to the converted velocity vector field, the velocity vector field in the time series is traversed and calculated to obtain the time series velocity .

[0122] Furthermore, in said S7, the vortex field is obtained according to the time series velocity calculation. , thus obtaining the time series vorticity field ;

[0123] vorticity field Expressed as:

[0124] ;

[0125] in, Represents the x-axis velocity matrix To perform derivation, Velocity matrix in the y-axis direction Perform derivatives;

[0126] The velocity horizontal coordinate matrix X, the x-axis direction velocity matrix , velocity ordinate matrix Y, y-axis velocity matrix , vorticity matrix Pack and merge into a Gaussian matrix ;

[0127] Gaussian matrix Expressed as:

[0128] ;

[0129] According to the Gaussian mixture model algorithm (GMM), the Gaussian matrix The data points in the velocity model , where each data point is represented by a weighted sum of multiple Gaussian distributions;

[0130] Velocity Model Expressed as:

[0131] ;

[0132] in, It is High-speed distribution weights, satisfying , For the The probability density of a high-speed distribution, whose mean is , the covariance matrix is , is a Gaussian matrix Middle data points, i.e. ;

[0133] Define two categories of correct velocity vector and wrong velocity vector, namely =2, then the velocity model Expressed as:

[0134] ;

[0135] Estimate the velocity model using the Expectation Maximization (EM) algorithm of 、 and .

[0136] The E-step process in the expectation-maximization algorithm is as follows: Calculate the posterior probability, that is, the probability that each data point belongs to the Gaussian distribution;

[0137] Posterior probability Expressed as:

[0138] ;

[0139] The M-step process in the expectation maximization algorithm is as follows: According to the posterior probability , update speed model Parameters of the model are updated.

[0140] The updated model parameters are expressed as:

[0141] ;

[0142] ;

[0143] ;

[0144] According to the updated model parameters, substitute them into the velocity model , obtain the probability matrix of the data point belonging to the correct velocity vector .

[0145] Furthermore, in said S7, the correct velocity vector and the wrong velocity vector judgment condition are expressed as follows: Set the time matrix , set the threshold , if the probability matrix The element value is greater than the threshold , then it is considered that this moment is the correct velocity vector, and the time matrix The corresponding position at this moment is set to 1, otherwise it is 0, which is an error velocity vector;

[0146] According to the correct velocity vector and the error velocity vector judgment conditions, the time average velocity field is calculated. , that is, obtaining the time-averaged velocity distribution;

[0147] ;

[0148] ;

[0149] ;

[0150] in, is the velocity matrix after conversion in the x-axis direction The average speed, is the velocity matrix after conversion in the y-axis direction average speed.

[0151] Example 2: Reference Figure 2This embodiment is described in detail. The system for measuring the time-averaged velocity field in the scramjet combustion chamber is used to implement the method for measuring the time-averaged velocity field in the scramjet combustion chamber described in Example 1. The system includes a light sheet shaping device 1, a high-speed camera 2, a lens equipped with a filter 3, a laser 4, a particle generator 5, and a timing signal generator 7.

[0152] The laser 4 is connected to the light sheet shaping device 1, and the light sheet beam outlet of the light sheet shaping device 1 is directed toward the quartz glass groove 8 on the upper wall of the scramjet combustion chamber 6;

[0153] The front end of the high-speed camera 2 is provided with a lens 3 equipped with a filter, and the lens 3 equipped with a filter faces the quartz glass observation window 9 on the side wall of the scramjet engine combustion chamber 6;

[0154] The timing signal generator 7 is connected to the laser 4 and the high-speed camera 2 respectively;

[0155] The particle generator 5 is arranged upstream of the scramjet combustion chamber 6 .

[0156] Specifically, the tracer particles of the particle generator 5 can be titanium dioxide particles.

[0157] Although the present invention has been described with respect to a limited number of embodiments, it will be apparent to those skilled in the art, having benefit of the foregoing description, that other embodiments are contemplated within the scope of the invention thus described. Furthermore, it should be noted that the language used in this specification has been selected primarily for readability and didactic purposes, rather than for the purpose of explaining or limiting the subject matter of the present invention. Consequently, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is intended to be illustrative rather than restrictive of the scope of the invention, which is defined by the appended claims.

Claims

1. A method for measuring the time-averaged velocity field in a scramjet combustion chamber, characterized in that: The following steps are involved: S1. Build a measurement system for a scramjet combustion chamber equipped with a timing signal generator using a laser, a high-speed camera, a lens with a filter, and a particle generator. S2. Adjust the measurement system's acquisition timing and the laser's two-cavity light emission timing, set the time interval, and match the high-speed camera's exposure frame rate with the laser's cavity number to obtain a matching result. S3. Start the measurement test. At time t0, turn on the particle generator. At time t1, turn on the laser and high-speed camera. Collect time series images based on the matching results. After the acquisition, turn off the laser, high-speed camera, and particle generator. Save the time series images to the computer. Specifically: Time series images are represented as , where A and B represent the frame numbers of the high-speed camera, and n represents the image sequence number. Represents n A-frame and B-frame images; S4. In a calm state, place a steel ruler on the smooth surface of the laser sheet so that it overlaps the laser surface. Calculate the spatial-to-pixel conversion factor. Specifically, the space-to-pixel conversion factor is expressed as P, with the unit being m / pixel, where m / pixel means meters per pixel; S5. Pre-processing the collected time series images to obtain pre-processed time series images; S6. Divide the pre-processed time series image into grid slices for cross-correlation calculation to obtain the particle displacement within the grid slices, and obtain the time series velocity based on the space-to-pixel conversion coefficient; S7. Calculate the vorticity field based on the time series velocity, generate a Gaussian matrix, construct a velocity model using the Gaussian mixture model algorithm, and obtain updated model parameters of the velocity model using the expectation-maximization algorithm, thereby obtaining a probability matrix that the data point belongs to the correct velocity vector; S8. Calculate the time-averaged velocity field based on the probability matrix, the correct velocity vector, and the incorrect velocity vector judgment conditions.

2. The method for measuring the time-averaged velocity field of a scramjet combustion chamber according to claim 1, characterized in that: In S1, a quartz glass observation window is provided on the side wall of the scramjet combustion chamber, a quartz glass groove is provided on the upper wall of the scramjet combustion chamber, and a laser sheet light incident window is provided at the upper portion of the scramjet combustion chamber. A laser is emitted by a laser, shaped into a sheet light beam with a thickness of less than 1 mm, and then vertically incident from the quartz glass groove to the area to be measured.

3. The method for measuring the time-averaged velocity field of a scramjet combustion chamber according to claim 2, characterized in that: In S2, the acquisition timing is adjusted, that is, the high-speed camera is in a double-frame acquisition mode, and after the A frame of the high-speed camera is exposed, the B frame of the high-speed camera is exposed; The laser cavity A light emission moment is included in the A frame exposure of the high-speed camera, and the laser light emission time interval dt is set. Its unit is s, where s represents seconds. The laser cavity B light emission moment is included in the B frame exposure of the high-speed camera.

4. The method for measuring the time-averaged velocity field of a scramjet combustion chamber according to claim 3, characterized in that: In the step S5, the time average image of frame A is calculated. and B-frame temporal average image ; A frame time average image Expressed as: ； B-frame temporal average image Expressed as: ； For all time series images of frame A and frame B, subtract the time average image of frame A and B-frame temporal average image ,Right now 、 , is the A-frame time series image after pre-processing, The B-frame time series image after pre-processing is obtained. ; 5. The method for measuring the time-averaged velocity field of a scramjet combustion chamber according to claim 4, characterized in that: In S6, the pre-processed time series image is divided into K×L grid slices, where K represents rows and L represents columns. A cross-correlation calculation is performed on each grid slice to calculate the particle displacement within the grid slice. The specific steps are as follows: Slice the first image , the second image slice Perform two-dimensional Fourier transform respectively to obtain the first image slice , the second image slice The two-dimensional Fourier transform result of ; First image slice , the second image slice The two-dimensional Fourier transform result of 、 Expressed as: ； ； Perform conjugate multiplication on the two-dimensional Fourier transform results to obtain the conjugate matrix ; Conjugate Matrix Expressed as: ； Conjugate matrix Perform two-dimensional inverse Fourier transform to obtain cross-correlation results ; Cross-correlation results Expressed as: ； Finding cross-correlation results The sub-pixel position of the maximum value relative to the center is obtained, that is, the particle displacement in the corresponding grid slice is obtained, and the particle displacement in all grid slices is traversed and calculated, that is, the velocity vector field at time t is obtained. , the speed unit is converted into m / s by using the space and pixel conversion coefficient P and the laser light time interval dt. m / s means meter per second, and the converted speed vector field is obtained ( , ); The converted velocity vector field ( , ) is expressed as: ； ； According to the converted velocity vector field, the velocity vector field in the time series is traversed and calculated to obtain the time series velocity .

6. The method for measuring the time-averaged velocity field of a scramjet combustion chamber according to claim 5, characterized in that: In S7, the vortex field is obtained according to the time series velocity calculation. , thus obtaining the time series vorticity field ; vorticity field Expressed as: ； in, Represents the velocity matrix in the x-axis direction To perform derivation, Represents the velocity matrix in the y-axis direction Perform derivatives; The velocity horizontal coordinate matrix X, the x-axis direction velocity matrix , velocity ordinate matrix Y, y-axis velocity matrix , vorticity matrix Pack and merge into a Gaussian matrix ; Gaussian matrix Expressed as: ； According to the Gaussian mixture model algorithm, the Gaussian matrix The data points in the velocity model , where each data point is represented by a weighted sum of multiple Gaussian distributions; Velocity Model Expressed as: ； in, It is High-speed distribution weights, satisfying , For the The probability density of a high-speed distribution, whose mean is , the covariance matrix is , is a Gaussian matrix Middle data points, i.e. ; Define two categories of correct velocity vector and wrong velocity vector, namely =2, then the velocity model Expressed as: ； Estimate the velocity model using the expectation maximization algorithm of 、 and ; The E-step process in the expectation-maximization algorithm is as follows: Calculate the posterior probability, that is, the probability that each data point belongs to the Gaussian distribution; Posterior probability Expressed as: ； The M-step process in the expectation maximization algorithm is as follows: According to the posterior probability , update speed model Parameters of the model are updated. The updated model parameters are expressed as: ； ； ； According to the updated model parameters, substitute them into the velocity model , obtain the probability matrix of the data point belonging to the correct velocity vector .

7. The method for measuring the time-averaged velocity field of a scramjet combustion chamber according to claim 6, characterized in that: In the above S8, the correct velocity vector and the error velocity vector judgment condition are expressed as follows: Set the time matrix , set the threshold , if the probability matrix The element value is greater than the threshold , then it is considered that this moment is the correct velocity vector, and the time matrix The corresponding position at this moment is set to 1, otherwise it is 0, which is an error velocity vector; According to the correct velocity vector and the error velocity vector judgment conditions, the time average velocity field is calculated. , that is, obtaining the time-averaged velocity distribution; ； ； ； in, is the velocity matrix after conversion in the x-axis direction The average speed, is the velocity matrix after conversion in the y-axis direction average speed.

8. A system for measuring the time-averaged velocity field in a scramjet combustion chamber, characterized in that: A method for measuring the time-averaged velocity field of a scramjet combustion chamber according to any one of claims 1 to 7, comprising a light sheet shaping device (1), a high-speed camera (2), a lens equipped with a filter (3), a laser (4), a particle generator (5), and a timing signal generator (7); The laser (4) is connected to a sheet light shaping device (1), and the sheet light beam outlet of the sheet light shaping device (1) faces the quartz glass groove (8) on the upper wall of the scramjet engine combustion chamber (6); The front end of the high-speed camera (2) is provided with a lens (3) equipped with a filter, and the lens (3) equipped with a filter faces a quartz glass observation window (9) on the side wall of the scramjet engine combustion chamber (6); The timing signal generator (7) is connected to the laser (4) and the high-speed camera (2) respectively; The particle generator (5) is arranged upstream of the scramjet engine combustion chamber (6).

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