A method for testing engine plume radiation oscillation characteristics

Abstract

A rocket engine exhaust radiation oscillation characteristic test method adopts a high-speed infrared thermal imager to measure the global exhaust radiation brightness temperature, acquires the global exhaust time sequence thermal image with high frame frequency, adopts a Fourier transform method to convert the measured time domain exhaust radiation thermal image into a frequency domain, and analyzes the spectrum intensity distribution of different regions of the exhaust radiation field.The present application can more accurately capture the time domain variation of the exhaust radiation field structure and energy distribution characteristics, convert the measured time domain exhaust radiation thermal image into a frequency domain, analyze the spectrum intensity distribution of different regions of the exhaust radiation field, and better monitor the running state of the engine.

Description

Technical Field

[0001] This invention relates to the field of infrared radiation testing, and more specifically to a method for testing the radiation oscillation characteristics of engine exhaust plumes. Background Technology

[0002] Rocket engine exhaust plume radiation characteristics data are crucial foundational data for applications such as engine combustion state diagnosis, performance evaluation, and target identification. The combustion products in the rocket engine exhaust plume undergo vibration and rotational transitions, generating infrared radiation in specific wavelengths. These infrared radiation signals exhibit different characteristics and patterns in the time and frequency domains. The oscillation characteristics of the exhaust plume radiation in the frequency domain can infer the operating state of the engine combustion chamber; therefore, the oscillation characteristics of the exhaust plume radiation in the frequency domain have significant application value.

[0003] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art. Summary of the Invention

[0004] The purpose of this invention is to provide a method for testing the radiation oscillation characteristics of rocket engine exhaust plumes, which can more accurately capture the temporal changes in the structure and energy distribution characteristics of the exhaust plume radiation field, convert the measured temporal exhaust plume radiation thermogram to the frequency domain, analyze the spectral intensity distribution in different regions of the exhaust plume radiation field, and better monitor the engine's operating status.

[0005] To achieve the above objectives, the present invention provides a method for testing the radiation oscillation characteristics of rocket engine exhaust plume, comprising the following steps:

[0006] Step S1: The rocket engine to be tested is installed on the test stand. Based on the field of view, image plane width, focal length, and axial length of the exhaust flame of the rocket engine to be tested, the arrangement position and detection pitch angle of the high-speed infrared thermal imager are determined to ensure that the detection line of sight is perpendicular to the axial direction of the exhaust flame of the engine and that the exhaust flame is entirely within the field of view of the high-speed infrared thermal imager.

[0007] Step S2: Turn on the high-speed infrared thermal imager and conduct the test run according to the test run procedure. Collect data on the infrared thermal image of the exhaust flame during the entire process from engine start-up to shutdown. After the test run is completed, turn off the high-speed infrared thermal imager and obtain the infrared radiation thermal image dataset that changes over time.

[0008] Step S3: Convert the infrared radiation thermal image dataset of the tail flame obtained in step S2 from the time domain to the frequency domain to obtain the frequency modes of the tail flame radiation field, and analyze the oscillation characteristics of the tail flame radiation in the frequency domain.

[0009] Step S1 includes the following steps:

[0010] Step S1.1: Install the engine under test on the test bench and use flow field simulation to estimate the axial length L of the exhaust flame of the engine under test. plume ;

[0011] Step S1.2: Based on the field of view θ, image plane width d, focal length q, and exhaust plume axial length L of the high-speed thermal imager... plume Determine the arrangement distance D of the high-speed thermal imager perpendicular to the axial direction of the exhaust plume:

[0012]

[0013]

[0014] Step S1.3: The lens axis of the high-speed thermal imager is perpendicular to the tail flame axis, and the intersection point is located at 1 / 2 of the tail flame axial length. This determines the horizontal arrangement position of the high-speed infrared thermal imager in the direction of the tail flame axis.

[0015] Step S1.1 includes the following steps:

[0016] Step S1.1.1: Use CEA thermodynamic calculation software to calculate the engine nozzle parameters based on the engine prototype parameters;

[0017] Step S1.1.2: Using the engine nozzle parameters as input for the exhaust flow field simulation, the CFD flow field simulation method is used to calculate the exhaust flow field distribution, obtaining the temperature, pressure, and component mole fraction of the exhaust flow field. When the temperature of the exhaust center axis develops to be equal to the ambient temperature, it is taken as the cutoff position of the exhaust axial length. The distance from the engine nozzle position to the axial temperature cutoff position is the exhaust axial length L. plume .

[0018] In step S2, the engine starts at time t0 and shuts down at time t. n During this time period, the collected infrared thermal image dataset is M, where M = {T} k ,L k,i,j}(k=1,2,3...N;i=1,2,3...a;j=1,2,3...b), where N is the total number of infrared thermal images acquired, N=(t n -t0)·F, where a is the number of pixels horizontally in the image, b is the number of pixels vertically in the image, and T k To acquire the time corresponding to the k-th image, L k,i,j Let be the radiance temperature of pixel (i,j) in the k-th image.

[0019] Step S3 includes the following steps:

[0020] Step S3.1: Extract the temporal radiation brightness temperature of each pixel (i,j) in the infrared radiation thermal image dataset and convert it to the frequency domain;

[0021] Step S3.2: Combine the spectral intensity of each pixel into a new image. Each frequency corresponds to one image, that is, the frequency mode distribution at that frequency.

[0022] Step S3.3: Analyze the exhaust radiation field under different frequency modes, extract the spectral intensity of different regions such as the core region and boundary layer in the exhaust radiation field, and compare the absolute value ΔU(f) of the difference in the mean spectral intensity of different regions to evaluate the magnitude of the oscillation amplitude.

[0023]

[0024] in, The mean spectral intensity of the core region of the exhaust radiation field under the f-frequency domain mode; The mean spectral intensity of the exhaust radiation field in the boundary layer region under the f-frequency domain mode is given.

[0025] Step S3.1 includes the following steps:

[0026] Step S3.1.1: Extract the radiance value of each pixel (i,j) and construct a radiance temperature sequence N along the time distribution. i,j =(L 1,i,j ,L 2,i,j ,L 3,i,j ...L N,i,j );

[0027] Step S3.1.2: Transform the temporal radiative brightness temperature of each pixel to the frequency domain using a Fourier transform. The calculation formula is as follows:

[0028] Among them, U i,j (f) represents the spectral intensity of pixel (i,j), where f is the frequency.

[0029] Before using a high-speed infrared thermal imager to test the radiation oscillation characteristics of rocket engine exhaust plumes, the high-speed infrared thermal imager must be calibrated in advance.

[0030] Methods for calibrating high-speed infrared thermal imagers include:

[0031] A high-temperature blackbody and a high-speed infrared thermal imager are arranged, with the high-speed infrared thermal imager having a frame rate F of 1000Hz.

[0032] During calibration, the distance between the blackbody furnace and the lens is the same as the experimental measurement distance, the surface of the blackbody furnace aperture and the pixel surface are perpendicular to the lens axis, and the frame rate of the high-speed infrared thermal radiation meter is kept the same as the experimental frame rate.

[0033] Set different blackbody furnace temperatures T black Based on Planck's blackbody radiation law, calculate the radiance E at this temperature. black (T black );

[0034] High-speed infrared thermal imager was used to image different temperatures T black The blackbody furnace performs infrared thermal image acquisition and reads the DN of the infrared thermal image. black Values, resulting in a series of values ​​related to T black Corresponding thermal image DN black For a series of T black and E black The calibration curve is obtained by fitting the data.

[0035] DN black =A1×E black (T black )+A2

[0036] In the formula, A1 and A2 are the calibration coefficients of the high-speed infrared thermal imager.

[0037] The present invention has the following beneficial effects:

[0038] 1. A high-speed infrared thermal imager is used to measure the global radiation brightness temperature of the exhaust flame. The high frame rate thermal image of the exhaust flame is acquired in a time-series manner. The obtained high frame rate thermal image captures the temporal changes of the exhaust flame radiation field structure, energy distribution and other characteristics more accurately.

[0039] 2. The Fourier transform method is used to convert the measured time-domain exhaust flame radiation thermogram to the frequency domain, and the spectral intensity distribution of different regions of the exhaust flame radiation field is analyzed. This provides a new approach to analyzing exhaust flame radiation characteristics from the frequency domain perspective and can provide a basis for engine combustion chamber condition diagnosis. Attached Figure Description

[0040] Figure 1 This is a flowchart of a method for testing the radiation oscillation characteristics of rocket engine exhaust plumes provided by the present invention.

[0041] Figure 2 This is a schematic diagram of the experimental equipment layout. Detailed Implementation

[0042] The following is based on Figure 1 and Figure 2 The preferred embodiments of the present invention will be described in detail below.

[0043] Existing research on rocket engine exhaust radiation measurement primarily involves measuring the radiation intensity and spectrum at different times from a fixed location on a ground-based test platform, analyzing the time-domain variation of the radiation intensity. However, no reports have been found regarding measurement methods for the oscillation characteristics of exhaust radiation, leaving a gap in the methods for measuring and processing the oscillating radiation characteristics of rocket engine exhaust in the frequency domain. Measuring the oscillation characteristics of rocket engine exhaust radiation requires addressing issues such as methods for acquiring the global high-frequency radiation characteristics of the exhaust and methods for time-frequency domain conversion of the exhaust radiation field. Therefore, it is necessary to provide a method for measuring and processing the oscillation characteristics of rocket engine exhaust radiation, thereby providing data for establishing the correlation between engine combustion chamber pressure and radiation oscillation, for monitoring engine operating status and performance evaluation.

[0044] This invention provides a method for testing the radiation oscillation characteristics of rocket engine exhaust plumes. It employs a high-speed infrared thermal imager to acquire high-frequency global radiation thermal images of the exhaust plume, converts the time-domain radiation thermal image to the frequency domain, and analyzes the spectral intensity of the exhaust plume radiation field. For example... Figure 1 As shown, the method for testing the radiation oscillation characteristics of rocket engine exhaust plume provided by the present invention specifically includes the following steps:

[0045] Step S1: Before the experiment, set up a high-temperature blackbody and a high-speed infrared thermal imager, calibrate the high-speed infrared thermal imager, and obtain the calibration coefficient of the high-speed infrared thermal imager.

[0046] In step S1, the acquisition frame frequency F of the high-speed infrared thermal imager is 1000Hz.

[0047] The high-speed infrared thermal imager calibration process in step S1 further includes the following steps:

[0048] Step S1.1 During calibration, the distance between the blackbody furnace and the lens is the same as the experimental measurement distance. The surface of the aperture of the blackbody furnace and the surface of the pixel are perpendicular to the lens axis. The frame rate of the high-speed infrared thermal radiation meter is the same as that of the experiment.

[0049] Step S1.2: Set different blackbody furnace temperatures T black Based on Planck's blackbody radiation law, calculate the radiance E at this temperature. black (T black );

[0050] Step S1.3: Use a high-speed infrared thermal imager to image different temperatures T black The blackbody furnace performs infrared thermal image acquisition and reads the DN of the infrared thermal image. black Values, resulting in a series of values ​​related to T black Corresponding thermal image DN black For a series of T black and E blackThe calibration curve is obtained by fitting the data.

[0051] DN black =A1×E black (T black )+A2

[0052] In the formula, A1 and A2 are the calibration coefficients of the high-speed infrared thermal imager;

[0053] Step S2, as follows Figure 2 As shown, the rocket engine under test 1 is installed on the test stand. Based on the field of view, image plane width, focal length, and axial length of the tail flame of the rocket engine under test, the arrangement position and detection pitch angle of the high-speed infrared thermal imager 2 are determined to ensure that the detection line of sight is perpendicular to the axial direction of the tail flame of the engine and that the entire tail flame is within the field of view of the high-speed infrared thermal imager.

[0054] Step S2 further includes the following steps:

[0055] Step S2.1: Install the engine under test 1 on the test bench. Based on parameters such as engine nozzle diameter, propellant type and ratio, use flow field simulation to estimate the axial length L of the exhaust flame of the engine under test. plume Specifically, it includes the following steps:

[0056] Step S2.1.1: Engine prototype parameters such as engine nozzle diameter, nozzle expansion ratio, combustion chamber pressure, propellant composition and ratio are calculated using CEA thermodynamic calculation software to calculate engine nozzle parameters, including nozzle temperature, pressure, component mole fraction, specific heat ratio, Mach number, etc.

[0057] Step S2.1.2: Using the engine nozzle parameters as input for the exhaust flow field simulation, the CFD flow field simulation method is employed to calculate the exhaust flow field distribution, obtaining the temperature, pressure, and component mole fraction of the exhaust flow field. When the temperature along the central axis of the exhaust reaches the same level as the ambient temperature, this point can be considered the cutoff point for the axial length of the exhaust. The distance from the engine nozzle position to the axial temperature cutoff point is the axial length L of the exhaust. plume ;

[0058] Step S2.2: Based on the field of view θ, image plane width d, focal length q, and tail flame axial length L of the high-speed thermal imager 2 plume Determine the arrangement distance D of the high-speed thermal imager perpendicular to the axial direction of the exhaust plume:

[0059]

[0060]

[0061] Step S2.3: The lens axis of the high-speed thermal imager is perpendicular to the tail flame axis, and the intersection point is located at 1 / 2 of the tail flame axial length. This determines the horizontal arrangement position of the high-speed infrared thermal imager in the direction of the tail flame axis.

[0062] Step S3: Turn on the high-speed infrared thermal imager and conduct the test run according to the test run procedure. Collect data on the infrared thermal image of the exhaust flame during the entire process from engine start-up to shutdown. After the test run is completed, turn off the high-speed infrared thermal imager and obtain the infrared radiation thermal image dataset that changes over time.

[0063] In step S3, the engine start-up time is t0, and the engine shutdown time is t... n During this time period, the collected infrared thermal image dataset is M.

[0064] M = {T k ,L k,i,j}(k=1,2,3...N;i=1,2,3...a;j=1,2,3...b), where N is the total number of infrared thermal images acquired, N=(t n -t0)·F, where a is the number of pixels horizontally in the image, b is the number of pixels vertically in the image, and T k To acquire the time corresponding to the k-th image, L k,i,j Let be the radiance temperature of pixel (i,j) in the k-th image;

[0065] Step S4: Convert the time-series infrared thermal image dataset of the exhaust flame obtained in step S3 from the time domain to the frequency domain to obtain the frequency modes of the exhaust flame radiation field, and analyze the oscillation characteristics of the exhaust flame radiation in the frequency domain.

[0066] Step S4 further includes the following steps:

[0067] Step S4.1: Extract the temporal radiation brightness temperature of each pixel (i,j) in the infrared radiation thermal image dataset and convert it to the frequency domain. This specifically includes:

[0068] Step S4.1.1: Extract the radiance value of each pixel (i,j) and construct a radiance temperature sequence N along the time distribution. i,j =(L 1,i,j ,L 2,i,j ,L 3,i,j... L N,i,j );

[0069] Step S4.1.2: Transform the temporal radiative brightness temperature of each pixel to the frequency domain using a Fourier transform. The calculation formula is as follows:

[0070] Among them, U i,j (f) represents the spectral intensity of pixel (i,j), where f is the frequency;

[0071] Step S4.2: Combine the spectral intensity of each pixel into a new image. Each frequency corresponds to one image, that is, the frequency mode distribution at that frequency.

[0072] Step S4.3: Analyze the exhaust radiation field under different frequency modes, extract the spectral intensity of different regions such as the core region and boundary layer in the exhaust radiation field, and compare the absolute value ΔU(f) of the difference in the mean spectral intensity of different regions to evaluate the magnitude of the oscillation amplitude.

[0073]

[0074] in, The mean spectral intensity of the core region of the exhaust radiation field under the f-frequency domain mode; The mean spectral intensity of the exhaust radiation field in the boundary layer region under the f-frequency domain mode is given.

[0075] In one embodiment of the present invention, a method for testing the radiation oscillation characteristics of engine exhaust flame is provided, comprising the following steps:

[0076] S1. Before the experiment, set up a high-temperature blackbody and a high-speed infrared thermal imager, calibrate the infrared thermal imager, and obtain the calibration coefficient of the high-speed infrared thermal imager.

[0077] Before the experiment, the high-speed infrared thermal imager was calibrated. The distance between the blackbody furnace and the lens was the same as the experimental measurement distance. The surface of the aperture and the pixel of the blackbody furnace were perpendicular to the lens axis. The frame rate of the high-speed infrared thermal radiation meter was 1000Hz, which was the same as the experiment.

[0078] Set different blackbody temperatures T black Based on Planck's blackbody radiation law, calculate the radiance E at this temperature. black (T black High-speed infrared thermal imager was used to image different temperatures T. black The blackbody furnace performs infrared thermal image acquisition and reads the DN of the infrared thermal image. black Values, resulting in a series of values ​​related to T black Corresponding thermal image DN black For a series of T black and E black The calibration curve is obtained by fitting the data.

[0079] DN black =A1×E black (T black )+A2

[0080] In the formula, A1 and A2 are the calibration coefficients of the high-speed infrared thermal imager;

[0081] S2. The rocket engine to be tested is installed on the test stand. Based on the field of view and tail flame size of the high-speed infrared thermal imager, the arrangement position and detection pitch angle of the high-speed thermal imager are determined to ensure that the detection line of sight is perpendicular to the axial direction of the engine tail flame and that the entire tail flame is within the field of view of the high-speed thermal imager.

[0082] The engine under test is mounted on the engine test stand, and the high-speed infrared thermal imager shows that the engine under test is located within the plane of the engine test stand.

[0083] Based on parameters such as engine nozzle diameter, propellant type and ratio, flow field simulation is used to estimate the axial length of the engine exhaust plume under test, as detailed below:

[0084] The engine tested in this embodiment uses perchloric acid as an oxidant and terminal hydroxybutadiene as fuel. Using CEA thermodynamic calculation software, based on the Gibbs free energy minimum criterion and one-dimensional isentropic flow, the engine nozzle parameters, including nozzle temperature, pressure, component mole fraction, specific heat ratio, Mach number, etc., are calculated.

[0085] A computational domain grid for the exhaust plume flow field was constructed, with an axial length 1000 times the nozzle diameter and a radial dimension 100 times the nozzle diameter. Boundary conditions for the exhaust plume flow field were determined: pressure, velocity, and multi-component inlet conditions were applied at the nozzle outlet; uniform pressure, velocity, temperature, and atmospheric parameters were applied at the inlet; the pressure far field was characterized by inlet parameters. A kW turbulence model was selected; and CFD flow field simulation was used to calculate the exhaust plume flow field distribution, obtaining the temperature, pressure, and component mole fractions of the exhaust plume flow field.

[0086] Based on the simulation results of the exhaust flow field, the temperature distribution along the axial direction of the exhaust flow field is extracted. When the axial temperature no longer fluctuates significantly and decreases to the ambient temperature, this point can be taken as the cutoff point for the axial length of the exhaust. The starting point of the exhaust axis is the nozzle exit. The distance between the cutoff point of the exhaust axis length and the nozzle exit determines the axial length L of the exhaust. plume ;

[0087] In this embodiment, the field of view of the high-speed thermal imager is θ, the image plane width is d, the focal length is q, and the axial length of the exhaust flame is L. plume The arrangement distance D of the high-speed thermal imager perpendicular to the axial direction of the exhaust plume is determined by the following formula:

[0088]

[0089]

[0090] The lens axis of the high-speed thermal imager is perpendicular to the tail flame axis, and the intersection point is located at 1 / 2 of the tail flame length. This determines the horizontal arrangement position of the high-speed infrared thermal imager in the direction of the tail flame axis and the detection pitch angle.

[0091] S3. Turn on the high-speed infrared thermal imager and conduct the test run according to the test run procedure. Collect data on the infrared thermal image of the exhaust flame during the entire process from engine start-up to shutdown. After the test run is completed, turn off the infrared thermal imager and obtain the infrared radiation thermal image dataset that changes over time.

[0092] First, turn on the high-speed infrared thermal imager, set the frame rate to 1000Hz, the pixel count to 256×256, and the detection spectral band to 2.7~2.9μm;

[0093] When the engine is started and the exhaust flame is emitted from the nozzle, the high-speed thermal imager begins to collect data simultaneously. After the engine is shut off, the high-speed infrared thermal imager stops collecting data. In this embodiment, a total of 10 seconds of data was collected. The collected infrared thermal image set M is then exported from the computer, where M = {T}. k ,L k,i,j}(k=1,2,3...N;i=1,2,3...a;j=1,2,3...b), where N is the total number of infrared thermal images acquired, N=10000, the number of horizontal pixels in the image is a=256, the number of vertical pixels in the image is b=256, T k To acquire the time corresponding to the k-th image, L k,i,j Let be the radiance temperature of pixel (i,j) in the k-th image;

[0094] S4. The time-series infrared thermal image dataset of the exhaust flame obtained in step S3 is transformed from the time domain to the frequency domain to obtain the frequency modes of the exhaust flame radiation field, and the oscillation characteristics of the exhaust flame radiation are analyzed in the frequency domain.

[0095] S4.1 Extract the temporal radiative brightness temperature of each pixel (i,j) in the image set and convert it to the frequency domain;

[0096] S4.1.1 Extract the radiance value of each pixel (i,j) and construct a radiance temperature sequence N along the time distribution. i,j =(L 1,i,j ,L 2,i,j ,L 3,i,j ...L N,i,j );

[0097] S4.1.2. The temporal radiative brightness temperature of each pixel is transformed to the frequency domain using a Fourier transform. The calculation formula is as follows:

[0098] Among them, U i,j (f) represents the spectral intensity of pixel (i,j), where f is the frequency;

[0099] S4.2 Combine the spectral intensity of each pixel into a new image, with each frequency corresponding to one image, i.e., the frequency mode distribution at that frequency;

[0100] S4.3 Analyze the exhaust plume radiation field under different frequency modes, extract the spectral intensity of different regions such as the core region and boundary layer in the exhaust plume radiation field, and compare the absolute difference ΔU(f) of the mean spectral intensity of different regions:

[0101] in, The mean spectral intensity of the core region of the exhaust radiation field under the f-frequency domain mode; The mean spectral intensity of the exhaust radiation field in the boundary layer region under the f-frequency domain mode is given.

[0102] The present invention has the following beneficial effects:

[0103] 1. A high-speed infrared thermal imager is used to measure the global radiation brightness temperature of the exhaust flame. The high frame rate thermal image of the exhaust flame is acquired in a time-series manner. The obtained high frame rate thermal image captures the temporal changes of the exhaust flame radiation field structure, energy distribution and other characteristics more accurately.

[0104] 2. The Fourier transform method is used to convert the measured time-domain exhaust flame radiation thermogram to the frequency domain, and the spectral intensity distribution of different regions of the exhaust flame radiation field is analyzed. This provides a new approach to analyzing exhaust flame radiation characteristics from the frequency domain perspective and can provide a basis for engine combustion chamber condition diagnosis.

[0105] It should be noted that, in the embodiments of the present invention, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the embodiments. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0106] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0107] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for testing the radiation oscillation characteristics of rocket engine exhaust plume, characterized in that, Includes the following steps: Step S1: The rocket engine to be tested is installed on the test stand. Based on the field of view, image plane width, focal length, and axial length of the exhaust flame of the rocket engine to be tested, the arrangement position and detection pitch angle of the high-speed infrared thermal imager are determined to ensure that the detection line of sight is perpendicular to the axial direction of the exhaust flame of the engine and that the exhaust flame is entirely within the field of view of the high-speed infrared thermal imager. Step S2: Turn on the high-speed infrared thermal imager and conduct the test run according to the test run procedure. Collect data on the infrared thermal image of the exhaust flame during the entire process from engine start-up to shutdown. After the test run is completed, turn off the high-speed infrared thermal imager and obtain the infrared radiation thermal image dataset that changes over time. Step S3: Convert the infrared radiation thermal image dataset of the tail flame obtained in step S2 from the time domain to the frequency domain to obtain the frequency modes of the tail flame radiation field, and analyze the oscillation characteristics of the tail flame radiation in the frequency domain.

2. The method for testing the radiation oscillation characteristics of rocket engine exhaust plume as described in claim 1, characterized in that, Step S1 includes the following steps: Step S1.1: Install the engine under test on the test bench and use flow field simulation to estimate the axial length of the exhaust flame of the engine under test. ; Step S1.2: Based on the field of view of the high-speed thermal imager Image plane width ,focal length and the axial length of the tail flame Determine the placement distance of the high-speed thermal imager perpendicular to the axial direction of the exhaust plume. : Step S1.3: The lens axis of the high-speed thermal imager is perpendicular to the exhaust flame axis, and the intersection point is located within the axial length of the exhaust flame. This determines the horizontal placement of the high-speed infrared thermal imager along the exhaust plume axis.

3. The method for testing the radiation oscillation characteristics of rocket engine exhaust plumes as described in claim 2, characterized in that, Step S1.1 includes the following steps: Step S1.1.1: Use CEA thermodynamic calculation software to calculate the engine nozzle parameters based on the engine prototype parameters; Step S1.1.2: Using the engine nozzle parameters as input for the exhaust flow field simulation, the CFD flow field simulation method is used to calculate the exhaust flow field distribution, obtaining the temperature, pressure, and component mole fraction of the exhaust flow field. When the temperature along the central axis of the exhaust reaches the same level as the ambient temperature, this is taken as the cutoff point for the axial length of the exhaust. The distance from the engine nozzle position to the axial temperature cutoff point is the axial length of the exhaust. .

4. The method for testing the radiation oscillation characteristics of rocket engine exhaust plume as described in claim 3, characterized in that, In step S2, the engine starts at time t0 and shuts down at time t. n During this period, the collected infrared thermal image dataset is , ,in, This represents the total number of infrared thermal images acquired. 'a' represents the number of pixels horizontally in the image, and 'b' represents the number of pixels vertically in the image. To acquire the time corresponding to the k-th image, For the k-th image The radiative brightness temperature corresponding to each pixel.

5. The method for testing the radiation oscillation characteristics of rocket engine exhaust plume as described in claim 4, characterized in that, Step S3 includes the following steps: Step S3.1: Extract each pixel from the infrared thermal imaging dataset. The time-domain radiative brightness temperature is calculated and converted to the frequency domain. Step S3.2: Combine the spectral intensity of each pixel into a new image. Each frequency corresponds to one image, that is, the frequency mode distribution at that frequency. Step S3.3: Analyze the exhaust flame radiation field under different frequency modes, extract the spectral intensity at different regions in the exhaust flame radiation field, and compare the absolute value of the difference between the mean spectral intensity at different regions. Used to assess the magnitude of oscillations: in, for Mean spectral intensity of the core region of the exhaust flame radiation field under frequency domain modes; for Mean spectral intensity of the boundary layer region of the exhaust flame radiation field in the frequency domain mode.

6. The method for testing the radiation oscillation characteristics of rocket engine exhaust plume as described in claim 5, characterized in that, Step S3.1 includes the following steps: Step S3.1.1: Extract each pixel. The radiance values ​​are used to construct a time-distributed radiance temperature sequence. ; Step S3.1.2: Transform the temporal radiative brightness temperature of each pixel to the frequency domain using a Fourier transform. The calculation formula is as follows: in, For pixels spectral intensity, For frequency.

7. The method for testing the radiation oscillation characteristics of rocket engine exhaust plume as described in claim 6, characterized in that, Before using a high-speed infrared thermal imager to test the radiation oscillation characteristics of rocket engine exhaust plumes, the high-speed infrared thermal imager must be calibrated in advance.

8. The method for testing the radiation oscillation characteristics of rocket engine exhaust plume as described in claim 7, characterized in that, Methods for calibrating high-speed infrared thermal imagers include: The setup includes a high-temperature blackbody and a high-speed infrared thermal imager, with the high-speed infrared thermal imager's acquisition frame rate... 1000Hz; During calibration, the distance between the blackbody furnace and the lens is the same as the experimental measurement distance, the surface of the blackbody furnace aperture and the pixel surface are perpendicular to the lens axis, and the frame rate of the high-speed infrared thermal radiation meter is kept the same as the experimental frame rate. Set different blackbody furnace temperatures Based on Planck's blackbody radiation law, calculate the radiance at this temperature. ; High-speed infrared thermal imager was used to measure different temperatures. The blackbody furnace performs infrared thermal image acquisition and reads the infrared thermal images. Value, to obtain a series of values Corresponding thermal image For a series and The calibration curve is obtained by fitting the data. In the formula, , This represents the calibration coefficients for the high-speed infrared thermal imager.

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