A ramjet engine direct connection test method based on working condition adaptive regulation and control

Abstract

This invention belongs to the field of ramjet engine direct-drive testing technology. It provides a ramjet engine direct-drive testing method based on operating condition adaptation and control, comprising: during the ramjet engine direct-drive test, gradually adjusting test parameters, performing operating condition scanning, recording combustion chamber pressure fluctuation data under each operating condition, and determining oscillation-sensitive areas; performing multiple repeated tests on each operating condition within the oscillation-sensitive area to identify the probability of pressure oscillation occurring under each operating condition within each oscillation-sensitive area, and determining high-probability pressure oscillation operating conditions; extracting high-probability pressure oscillation operating conditions, and using Fast Fourier Transform to extract the dominant frequency of the direct-drive test oscillation; this invention can effectively avoid engine shutdown, structural damage, and other failures caused by oscillations in actual flight, ensuring engine flight safety and operational stability.

Description

Technical Field

[0001] This invention belongs to the field of ramjet engine direct connection test technology, specifically a ramjet engine direct connection test method based on operating condition adaptation and control. Background Technology

[0002] Ramjet engines, as high-performance power plants, possess advantages such as high thrust, high thrust-to-weight ratio, and high flight speed, and are widely used in aerospace equipment such as missiles and spacecraft. These engines operate in harsh environments of high temperature, high pressure, and high speed. The coupling between the combustion process and acoustic oscillations can easily induce pressure oscillations in the combustion chamber. If the oscillation amplitude is too large, it can lead to engine shutdown, structural damage, or even flight malfunctions, seriously threatening the flight safety and operational stability of the equipment. Therefore, accurately identifying the engine pressure oscillation characteristics and defining the flight vibration damping window are core and critical aspects of ramjet engine research and development and testing.

[0003] Direct-drive testing, as the primary method for ground simulation testing of ramjet engines, is widely used for mechanistic studies of engine combustion chamber performance and combustion processes due to its advantages such as high air utilization, convenient operation, short test cycle, and good economy. It can effectively reduce R&D costs and technical risks. However, existing direct-drive testing methods still have many shortcomings in practical applications and cannot meet the precision requirements of engineering applications: On the one hand, traditional direct-drive testing often uses qualitative or semi-quantitative methods to identify pressure oscillation sensitive areas, which is insufficient in terms of quantitative accuracy of pressure oscillation intensity under various operating conditions. Moreover, the test condition scanning often deviates from the similarity simulation requirements of real flight conditions, resulting in deviations between the test results and the oscillation characteristics in real flight. At the same time, there is a lack of effective fitting and verification methods, resulting in poor verifiability and engineering applicability of the test data. On the other hand, direct-drive testing usually uses rigid upstream boundaries and semi-closed downstream boundaries, which are significantly different from the open boundary characteristics in real flight. This boundary difference can lead to acoustic modal frequency shifts and oscillation amplitude amplification, resulting in acoustic boundary distortion. In the existing technology, there is a lack of effective means of identifying and correcting boundary distortion, which makes it impossible to accurately restore the oscillation characteristics of the direct connection test results to the actual flight conditions. This results in deviations in the vibration damping window calibrated based on the test results, making it difficult to effectively avoid various faults caused by oscillations in actual flight.

[0004] Therefore, the present invention provides a direct-drive test method for ramjet engines based on operating condition adaptation and control. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0006] The technical solution adopted by this invention to solve its technical problem is: During the direct-drive test of the ramjet engine, the test parameters were gradually adjusted to perform a working condition scan, and the combustion chamber pressure fluctuation data under each working condition was recorded to determine the oscillation sensitive area. Repeated tests were conducted on each working condition within the oscillation-sensitive area to identify the probability of pressure oscillation occurring under each working condition within each oscillation-sensitive area, and to determine the working conditions with high probability of pressure oscillation. By performing modal identification on high-probability operating condition oscillations of pressure oscillations, the main frequency of the direct-drive test oscillations is extracted using fast Fourier transform, and equivalent real flight data is obtained by using combustion-acoustic coupling high-fidelity CFD simulation to determine the theoretical frequency of acoustic modal oscillations and to determine whether the direct-drive test produces acoustic boundary distortion. If the direct connection test produces acoustic boundary distortion, determine the direct connection boundary correction coefficient, and based on the direct connection boundary correction coefficient, determine the oscillation sensitive area that is closer to the actual flight.

[0007] As a further aspect of the present invention: the process of determining the oscillation-sensitive region is as follows: The test parameters include the incoming Mach number and fuel equivalence ratio; the oscillation amplitude of the operating conditions is determined by analyzing the combustion chamber pressure fluctuation data under each operating condition. The least squares method is used to fit the quadratic response surface formula of oscillation amplitude with Mach number and equivalence ratio. MATLAB is used to plot the oscillation amplitude contour map of the Mach number-equivalence ratio plane. In the contour map, a contour line is drawn with a preset oscillation amplitude limit. The area beyond the contour line is recorded as the oscillation sensitive area.

[0008] As a further aspect of the present invention: the process for determining the oscillation amplitude of the aforementioned operating condition is as follows: Pressure sensors are evenly arranged along the combustion chamber axis. Pressure values ​​are collected using the pressure sensors at the sampling frequency required by the test. The sampling time is preset, and the sampling time is the same for each working condition. The test parameters under each working condition are recorded. Based on any operating condition, the collection time is divided into several sampling points according to equal time intervals. By analyzing and processing the pressure values, the average instantaneous pressure in the combustion chamber at the sampling point and the average steady-state pressure under the current operating condition are obtained. Based on the instantaneous pressure in the combustion chamber at the sampling point and the mean steady-state pressure under the current operating conditions, the root mean square of the pressure oscillation under the current operating conditions is calculated. The oscillation amplitude under the current operating condition is obtained by comparing the root mean square of the pressure oscillation with the mean steady-state pressure.

[0009] As a further aspect of the present invention: the process for determining the average instantaneous pressure in the combustion chamber at the sampling point and the average steady-state pressure under the current operating conditions is as follows: Record the sensor installation position, measure the distance between the pressure sensor and the combustion chamber inlet starting from the combustion chamber inlet, normalize the pressure sensor position to the 0-1 range, calculate the shape function value of the pressure sensor, and obtain the modal weight of the pressure sensor by normalizing the absolute value of the shape function value. The pressure values ​​of all pressure sensors at the sampling point are extracted, and the instantaneous pressure in the combustion chamber at the sampling point is calculated by combining the modal weights of the pressure sensors, thus generating a time-domain pressure signal. The average of the instantaneous pressures in the combustion chamber at all sampling points within the collection period is summed to obtain the average steady-state pressure under the current operating conditions.

[0010] As a further aspect of the present invention: the process of identifying high-probability pressure oscillation conditions is as follows: Based on any operating condition test, extract the oscillation amplitude corresponding to the current operating condition to determine whether pressure oscillation has occurred; The percentage of pressure oscillations occurring in the total number of tests under the current operating condition is recorded as the probability value of oscillation occurrence under the current operating condition. If the probability of oscillation is greater than or equal to the probability threshold of oscillation, the corresponding working condition is recorded as a high-probability working condition of pressure oscillation.

[0011] As a further aspect of the present invention: the process of determining whether pressure oscillation occurs is as follows: If the oscillation amplitude is greater than or equal to the preset oscillation amplitude limit, then pressure oscillation is determined to have occurred; if the oscillation amplitude is less than the preset oscillation amplitude limit, then pressure oscillation is determined not to have occurred.

[0012] As a further aspect of the present invention: the process of extracting the main frequency of the direct-connection test oscillation using Fast Fourier Transform is as follows: The time-domain pressure signal is preprocessed by high-pass filtering to separate the pressure oscillation component, and threshold filtering with 3-level decomposition of db4 wavelet basis is used to remove wind tunnel noise and sensor electronic noise. A fast Fourier transform is performed on the preprocessed time-domain pressure signal to calculate the amplitude spectrum of the time-domain pressure signal. The frequency point with the largest amplitude in the amplitude spectrum of the time-domain pressure signal is extracted as the main frequency of the direct connection test oscillation.

[0013] As a further aspect of the present invention: the process of determining the theoretical frequency of acoustic modal oscillation is as follows: A simulation model was established, boundary conditions were set, an adaptive time step was adopted, multiple pressure monitoring points were evenly arranged in the combustion chamber along the axis, and the pressure time series data of the monitoring points were stored. The simulation sampling frequency was consistent with the sampling frequency of the direct connection test. DC removal processing was performed on the pressure time series of each monitoring point to extract the simulated pressure oscillation component; a fast Fourier transform was performed on the preprocessed simulated pressure oscillation component to obtain the simulated amplitude spectrum, and the frequency point with the largest amplitude in the simulated amplitude spectrum was extracted as the theoretical frequency of the acoustic modal oscillation.

[0014] As a further aspect of the present invention: the process of determining whether the direct connection test produces acoustic boundary distortion is as follows: The frequency deviation value of the acoustic modal oscillation is obtained by taking the absolute value of the difference between the main frequency of the direct connection test oscillation and the theoretical frequency of the acoustic modal oscillation. The frequency deviation value of the acoustic modal oscillation is then compared with the theoretical frequency of the acoustic modal oscillation to obtain the frequency deviation ratio of the acoustic modal oscillation. If the frequency deviation ratio of the acoustic modal oscillation is greater than the frequency deviation ratio threshold, it indicates that the direct connection test produces acoustic boundary distortion; otherwise, it indicates that the direct connection test does not produce acoustic boundary distortion.

[0015] As a further aspect of the present invention: the process of determining the oscillation-sensitive region that more closely approximates actual flight is as follows: The direct connection boundary correction coefficient is obtained by comparing the ratio of the main frequency of the direct connection test oscillation to the theoretical frequency of the acoustic modal oscillation. The direct boundary correction coefficient is multiplied with the quadratic response surface formula to obtain the corrected quadratic response surface formula. Based on the corrected quadratic response surface formula, the fitting result of the oscillation amplitude is corrected. MATLAB is used to plot the contour map of the oscillation amplitude after the Mach number-equivalent ratio plane correction to determine the oscillation sensitive area that is closer to the actual flight.

[0016] The beneficial effects of this invention are as follows: 1. This invention not only accurately quantifies the pressure oscillation intensity under various operating conditions, but also intuitively defines the oscillation-sensitive area, ensuring that the test results closely match the oscillation characteristics of actual flight and possess quantifiable and verifiable engineering attributes. Multiple repeated tests are conducted on the operating conditions within the sensitive area, and the probability of oscillation occurrence is statistically analyzed based on the oscillation amplitude limit, further distinguishing between high-probability and low-probability oscillation conditions. This effectively eliminates the random interference of single tests, focusing on core high-risk operating conditions. This not only improves the reliability of oscillation risk identification but also reduces the workload of subsequent simulation analysis and other processes, laying a precise and reliable experimental data foundation for the calibration of the engine's actual flight vibration damping window.

[0017] 2. This invention uses frequency deviation ratio quantification to determine the acoustic boundary distortion problem in direct-drive tests. For cases where distortion exists, a direct-drive boundary correction coefficient is determined based on the ratio of the test dominant frequency to the theoretical frequency. This coefficient is then combined with the quadratic response surface formula to correct the oscillation amplitude fitting result and plot the corrected contour map. This not only compensates for the frequency shift and oscillation amplitude amplification caused by the rigid semi-enclosed boundary of the direct-drive test, but also accurately calibrates the oscillation sensitive area that is closer to actual flight. Ultimately, this provides a reliable basis for defining the vibration damping window for ramjet engine flight, effectively avoiding engine shutdown, structural damage, and other failures caused by oscillations in actual flight, and ensuring engine flight safety and operational stability. Attached Figure Description

[0018] The invention will now be further described with reference to the accompanying drawings.

[0019] Figure 1 This is a flowchart of the steps of a direct-drive test method for a ramjet engine based on operating condition adaptation and control according to an embodiment of the present invention; Figure 2 This is a system block diagram of a direct-drive test system for a ramjet engine based on operating condition adaptation and control, according to an embodiment of the present invention. Detailed Implementation

[0020] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0021] Example 1 Please see Figure 1 As shown in the embodiment of the present invention, a direct-drive test method for a ramjet engine based on operating condition adaptation and control includes the following steps: Step 1: During the direct-drive test of the ramjet engine, the test parameters are gradually adjusted to perform a working condition scan, and the combustion chamber pressure fluctuation data under each working condition is recorded to determine the oscillation sensitive area; The test parameters include the incoming Mach number and the fuel equivalence ratio; It should be noted that the operating condition scan of the direct connection test is based on a similar simulation of the flight operating condition to ensure that the test results can reflect the oscillation characteristics in real flight. Pressure sensors are evenly arranged along the combustion chamber axis, and their installation positions are recorded. The distance between the pressure sensors and the combustion chamber inlet is measured starting from the combustion chamber inlet. The pressure sensor positions are normalized to the 0-1 range, and then calculated using the formula... Calculate the shape function value of the pressure sensor In the formula, x represents the distance between the pressure sensor and the combustion chamber inlet, and the modal weights of the pressure sensor are obtained by normalizing the absolute value of the shape function. Pressure values ​​are collected using pressure sensors at the sampling frequency required by the test. The sampling duration is preset, and the sampling duration is the same for each working condition. The test parameters under each working condition are recorded. Based on any operating condition, the acquisition time is divided into several sampling points according to equal time intervals. The pressure values ​​of all pressure sensors at each sampling point are extracted, and combined with the modal weights of the pressure sensors, the results are obtained using the formula: The instantaneous pressure in the combustion chamber at the kth sampling point was calculated. Generate a time-domain pressure signal, where, This represents the modal weight of the i-th pressure sensor. This represents the pressure value of the i-th pressure sensor; The average of the instantaneous pressures in the combustion chamber at all sampling points within the collection period is summed to obtain the average steady-state pressure under the current operating conditions. Based on the average instantaneous pressure and steady-state pressure under current operating conditions within the combustion chamber at the sampling point, through... The root mean square of the pressure oscillation under the current operating condition was calculated. In the formula, Indicates the number of sampling points. This represents the average steady-state pressure under the current operating conditions. The oscillation amplitude under the current operating condition is obtained by comparing the root mean square of the pressure oscillation with the mean steady-state pressure. The least squares method was used to fit the quadratic response surface formula of oscillation amplitude with Mach number and equivalence ratio. The oscillation amplitude contour map of the Mach number-equivalence ratio plane was plotted using MATLAB. In the contour map, a contour line was drawn with a preset oscillation amplitude limit. The area beyond the contour line was recorded as the oscillation sensitive area. It should be noted that the oscillation amplitude limit was set by those skilled in the art based on historical experience. After fitting, the fitting accuracy needs to be verified, and the coefficient of determination is required. A value greater than 0.9 indicates that the fit between the fitting results and the experimental data is >90%; Step 2: Conduct repeated tests on each working condition within the oscillation-sensitive area to identify the probability of pressure oscillation occurring under each working condition within each oscillation-sensitive area, and determine the working conditions with high probability of pressure oscillation. Based on any operating condition test, extract the oscillation amplitude corresponding to the current operating condition. If the oscillation amplitude is greater than or equal to the preset oscillation amplitude limit, it is determined that pressure oscillation has occurred; if the oscillation amplitude is less than the preset oscillation amplitude limit, it is determined that pressure oscillation has not occurred. The percentage of pressure oscillations occurring in the total number of tests under the current operating condition is recorded as the probability value of oscillation occurrence under the current operating condition. If the probability value of oscillation is greater than or equal to the probability threshold of oscillation, the corresponding working condition is recorded as a high probability working condition of pressure oscillation. If the probability of oscillation is less than the probability threshold of oscillation, the corresponding working condition is recorded as a low probability working condition of pressure oscillation. The technical solution of this invention is as follows: During the direct-drive test of a ramjet engine, test parameters are gradually adjusted to perform a condition scan, and combustion chamber pressure fluctuation data under each condition are recorded to determine the oscillation-sensitive area. Multiple repeated tests are conducted on each condition within the oscillation-sensitive area to identify the probability of pressure oscillation occurring under each condition within each oscillation-sensitive area, thus determining the high-probability pressure oscillation condition. This invention not only accurately quantifies the pressure oscillation intensity of each condition but also intuitively defines the oscillation-sensitive area, ensuring that the test results closely match the oscillation characteristics of actual flight and possess quantifiable and verifiable engineering attributes. Multiple repeated tests are conducted on the conditions within the sensitive area, and the probability of oscillation occurrence is statistically analyzed based on the oscillation amplitude limit, further distinguishing between high-probability and low-probability oscillation conditions. This effectively eliminates the random interference of a single test, focusing on core high-risk conditions, improving the reliability of oscillation risk identification, and reducing the workload of subsequent simulation analysis and other processes. This lays a precise and reliable test data foundation for the calibration of the engine's actual flight vibration damping window.

[0022] Example 2 Please see Figure 1 As shown in the embodiment of the present invention, a direct-drive test method for a ramjet engine based on operating condition adaptation and control further includes the following steps: Step 3: Extract high-probability pressure oscillation conditions, use Fast Fourier Transform to extract the main frequency of the direct-drive test oscillation, use combustion-acoustic coupling high-fidelity CFD simulation to obtain equivalent real flight data, determine the theoretical frequency of acoustic modal oscillation, and determine whether the direct-drive test produces acoustic boundary distortion. The time-domain pressure signal is preprocessed by high-pass filtering to separate the pressure oscillation component, and threshold filtering with 3-level decomposition of db4 wavelet basis is used to remove wind tunnel noise and sensor electronic noise. A fast Fourier transform is performed on the preprocessed time-domain pressure signal to calculate the amplitude spectrum of the time-domain pressure signal. The frequency point with the largest amplitude in the amplitude spectrum of the time-domain pressure signal is extracted as the main frequency of the direct connection test oscillation. Establish a simulation model: Geometric Model: The combustion chamber geometry model is completely consistent with that of the direct-drive test, including the axial length L, radial radius R, cavity structure (if any), and fuel injector layout, ensuring geometric consistency between simulation and experiment; Mesh Generation: A structured mesh is used, with the axial mesh resolution of the combustion chamber meeting the acoustic modal wavelength resolution requirements, ensuring the capture of the spatial distribution of acoustic oscillations; The wall boundary layer uses a finer mesh to meet the wall resolution requirements of Large Eddy Simulation (LES); Turbulence Model: Large Eddy Simulation (LES) is used, with the WALE model selected for the subgrid model to accurately simulate the small-scale structure of turbulent flow; Combustion Model: A simplified EDC model is used to accurately simulate the combustion heat release process; Acoustic Coupling Model: An acoustic disturbance transmission equation is introduced to couple the fluctuations of combustion heat release with the acoustic modes of the combustion chamber, simulating the generation and development of thermoacoustic oscillations; Set boundary conditions: Upstream boundary: Set as a soft boundary, using a pressure inlet boundary, with inlet Mach number, total temperature, and total pressure consistent with actual flight conditions; simultaneously, inlet acoustic impedance is set to simulate the soft boundary characteristics of the actual air intake, contrasting with the rigid boundary of the direct-connection test; Downstream boundary: Set as an open jet boundary, using a pressure outlet boundary, with outlet pressure being the ambient pressure of actual flight; simultaneously, outlet acoustic impedance is set to simulate the open jet boundary of actual flight, with sound pressure approaching 0; Wall boundary: Set as an adiabatic wall or isothermal wall, with wall temperature consistent with the combustion chamber wall temperature of actual flight; An adaptive time step is adopted to ensure that the time resolution meets the sampling requirements of acoustic oscillation; the calculation duration is ≥100 acoustic oscillation cycles to ensure that the simulation reaches a stable thermoacoustic oscillation state; multiple pressure monitoring points are evenly arranged axially in the combustion chamber to store the pressure time series data of the monitoring points, and the simulation sampling frequency is consistent with the sampling frequency of the direct connection test. DC removal processing was performed on the pressure time series of each monitoring point to extract the simulated pressure oscillation component; a fast Fourier transform was performed on the preprocessed simulated pressure oscillation component to obtain the simulated amplitude spectrum, and the frequency point with the largest amplitude in the simulated amplitude spectrum was extracted as the theoretical frequency of the acoustic modal oscillation. The frequency deviation value of the acoustic modal oscillation is obtained by taking the absolute value of the difference between the main frequency of the direct connection test oscillation and the theoretical frequency of the acoustic modal oscillation. The frequency deviation value of the acoustic modal oscillation is then compared with the theoretical frequency of the acoustic modal oscillation to obtain the frequency deviation ratio of the acoustic modal oscillation. If the frequency deviation ratio of the acoustic modal oscillation is greater than the frequency deviation ratio threshold, it indicates that the direct connection test produces acoustic boundary distortion. If the frequency deviation ratio of the acoustic modal oscillation is less than or equal to the frequency deviation ratio threshold, it indicates that the direct connection test did not produce acoustic boundary distortion. Step 4: If the direct connection test produces acoustic boundary distortion, determine the direct connection boundary correction coefficient. Based on the direct connection boundary correction coefficient, determine the oscillation sensitive area that is closer to the actual flight. It should be noted that the rigid upstream boundary and semi-enclosed downstream boundary of the direct connection test will cause the acoustic modal frequency to shift and amplify the oscillation amplitude. The correction coefficient needs to make the modal frequency and oscillation amplitude of the direct connection test closer to the open boundary characteristics of actual flight. The direct connection boundary correction coefficient is obtained by comparing the ratio of the main frequency of the direct connection test oscillation to the theoretical frequency of the acoustic modal oscillation. The direct boundary correction coefficient is multiplied with the quadratic response surface formula to obtain the corrected quadratic response surface formula. Based on the corrected quadratic response surface formula, the fitting result of the oscillation amplitude is corrected. MATLAB is used to plot the contour map of the oscillation amplitude after the Mach number-equivalent ratio plane correction to determine the oscillation sensitive area that is closer to the actual flight. It should be noted that the boundary distortion of the direct connection test will amplify the oscillation. After correction, it can accurately identify which operating conditions will cause oscillation in actual flight, which can be used to calibrate the vibration damping window for flight and avoid oscillation failures during actual flight, such as engine shutdown or structural damage. The technical solution of this invention is as follows: High-probability pressure oscillation conditions are extracted; the dominant frequency of the direct-drive test oscillation is extracted using Fast Fourier Transform; equivalent real flight data is obtained using combustion-acoustic coupled high-fidelity CFD simulation; the theoretical frequency of the acoustic modal oscillation is determined; and it is determined whether the direct-drive test produces acoustic boundary distortion. If the direct-drive test produces acoustic boundary distortion, a direct-drive boundary correction coefficient is determined; based on the direct-drive boundary correction coefficient, an oscillation-sensitive region closer to real flight is determined. This invention uses frequency deviation ratio quantification to determine the acoustic boundary distortion problem of the direct-drive test. For cases where distortion exists, the direct-drive boundary correction coefficient is determined based on the ratio of the test dominant frequency to the theoretical frequency. This coefficient is then combined with the quadratic response surface formula to correct the oscillation amplitude fitting result and plot the corrected contour map. This not only compensates for the frequency shift and oscillation amplitude amplification problems caused by the rigid semi-closed boundary of the direct-drive test, but also accurately calibrates an oscillation-sensitive region more closely resembling real flight. Ultimately, this provides a reliable basis for defining the vibration damping window for ramjet engine flight, effectively avoiding engine stalling, structural damage, and other faults caused by oscillation in real flight, ensuring engine flight safety and operational stability.

[0023] Example 3 Based on the same inventive concept as the direct-drive test method for ramjet engines based on operating condition adaptation and control in the foregoing embodiments, such as Figure 2 As shown, this application provides a direct-drive test system for ramjet engines based on operating condition adaptation and control, wherein the system specifically includes: Oscillation-sensitive area determination module: During the direct-drive test of the ramjet engine, the test parameters are gradually adjusted to perform a working condition scan, and the combustion chamber pressure fluctuation data under each working condition is recorded to determine the oscillation-sensitive area; Probability analysis module: Performs repeated tests on each working condition within the oscillation sensitive area to identify the probability of pressure oscillation occurring under each working condition within each oscillation sensitive area, and determines the working conditions with high probability of pressure oscillation. Distortion Detection Module: Extracts high-probability pressure oscillation conditions, uses Fast Fourier Transform to extract the main frequency of direct-drive test oscillation, and uses combustion-acoustic coupling high-fidelity CFD simulation to obtain equivalent real flight data, determines the theoretical frequency of acoustic modal oscillation, and judges whether the direct-drive test produces acoustic boundary distortion. Correction processing module: If the direct connection test produces acoustic boundary distortion, determine the direct connection boundary correction coefficient, and based on the direct connection boundary correction coefficient, determine the oscillation sensitive area that is closer to the actual flight.

[0024] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A direct-drive test method for a ramjet engine based on operating condition adaptation and control, characterized in that: include: During the direct-drive test of the ramjet engine, the test parameters were gradually adjusted to perform a working condition scan, and the combustion chamber pressure fluctuation data under each working condition was recorded to determine the oscillation sensitive area. Repeated tests were conducted on each working condition within the oscillation-sensitive area to identify the probability of pressure oscillation occurring under each working condition within each oscillation-sensitive area, and to determine the working conditions with high probability of pressure oscillation. High-probability pressure oscillation conditions are extracted, and the main frequency of the direct-drive test oscillation is extracted using fast Fourier transform. Equivalent real flight data is obtained by combustion-acoustic coupling high-fidelity CFD simulation to determine the theoretical frequency of acoustic modal oscillation and to determine whether the direct-drive test produces acoustic boundary distortion. If the direct connection test produces acoustic boundary distortion, determine the direct connection boundary correction coefficient, and based on the direct connection boundary correction coefficient, determine the oscillation sensitive area that is closer to the actual flight.

2. The direct-drive test method for a ramjet engine based on operating condition adaptation and control according to claim 1, characterized in that: The process of determining the oscillation-sensitive region is as follows: The test parameters include the incoming Mach number and fuel equivalence ratio; the oscillation amplitude of the operating conditions is determined by analyzing the combustion chamber pressure fluctuation data under each operating condition. The least squares method is used to fit the quadratic response surface formula of oscillation amplitude with Mach number and equivalence ratio. MATLAB is used to plot the oscillation amplitude contour map of the Mach number-equivalence ratio plane. In the contour map, a contour line is drawn with a preset oscillation amplitude limit. The area beyond the contour line is recorded as the oscillation sensitive area.

3. The direct-drive test method for a ramjet engine based on operating condition adaptation and control according to claim 2, characterized in that: The process for determining the oscillation amplitude under the aforementioned operating condition is as follows: Pressure sensors are evenly arranged along the combustion chamber axis. Pressure values ​​are collected using the pressure sensors at the sampling frequency required by the test. The sampling time is preset, and the sampling time is the same for each working condition. The test parameters under each working condition are recorded. Based on any operating condition, the collection time is divided into several sampling points according to equal time intervals. By analyzing and processing the pressure values, the average instantaneous pressure in the combustion chamber at the sampling point and the average steady-state pressure under the current operating condition are obtained. Based on the instantaneous pressure in the combustion chamber at the sampling point and the mean steady-state pressure under the current operating conditions, the root mean square of the pressure oscillation under the current operating conditions is calculated. The oscillation amplitude under the current operating condition is obtained by comparing the root mean square of the pressure oscillation with the mean steady-state pressure.

4. The direct-drive test method for a ramjet engine based on operating condition adaptation and control according to claim 3, characterized in that: The process for determining the average instantaneous pressure in the combustion chamber at the sampling point and the average steady-state pressure under the current operating conditions is as follows: Record the sensor installation position, measure the distance between the pressure sensor and the combustion chamber inlet starting from the combustion chamber inlet, normalize the pressure sensor position to the 0-1 range, calculate the shape function value of the pressure sensor, and obtain the modal weight of the pressure sensor by normalizing the absolute value of the shape function value. The pressure values ​​of all pressure sensors at the sampling point are extracted, and the instantaneous pressure in the combustion chamber at the sampling point is calculated by combining the modal weights of the pressure sensors, thus generating a time-domain pressure signal. The average of the instantaneous pressures in the combustion chamber at all sampling points within the collection period is summed to obtain the average steady-state pressure under the current operating conditions.

5. The direct-drive test method for a ramjet engine based on operating condition adaptation and control according to claim 4, characterized in that: The process for identifying high-probability pressure oscillation conditions is as follows: Based on any operating condition test, extract the oscillation amplitude corresponding to the current operating condition to determine whether pressure oscillation has occurred; The percentage of pressure oscillations occurring in the total number of tests under the current operating condition is recorded as the probability value of oscillation occurrence under the current operating condition. If the probability of oscillation is greater than or equal to the probability threshold of oscillation, the corresponding working condition is recorded as a high-probability working condition of pressure oscillation.

6. The direct-drive test method for a ramjet engine based on operating condition adaptation and control according to claim 5, characterized in that: The process for determining whether pressure oscillation has occurred is as follows: If the oscillation amplitude is greater than or equal to the preset oscillation amplitude limit, then pressure oscillation is determined to have occurred; if the oscillation amplitude is less than the preset oscillation amplitude limit, then pressure oscillation is determined not to have occurred.

7. The direct-drive test method for a ramjet engine based on operating condition adaptation and control according to claim 5, characterized in that: The process of extracting the main oscillation frequency of the direct-connection test using Fast Fourier Transform is as follows: The time-domain pressure signal is preprocessed by high-pass filtering to separate the pressure oscillation component, and threshold filtering with 3-level decomposition of db4 wavelet basis is used to remove wind tunnel noise and sensor electronic noise. A fast Fourier transform is performed on the preprocessed time-domain pressure signal to calculate the amplitude spectrum of the time-domain pressure signal. The frequency point with the largest amplitude in the amplitude spectrum of the time-domain pressure signal is extracted as the main frequency of the direct connection test oscillation.

8. The direct-drive test method for a ramjet engine based on operating condition adaptation and control according to claim 7, characterized in that: The process of determining the theoretical frequency of acoustic modal oscillation is as follows: A simulation model was established, boundary conditions were set, an adaptive time step was adopted, multiple pressure monitoring points were evenly arranged in the combustion chamber along the axis, and the pressure time series data of the monitoring points were stored. The simulation sampling frequency was consistent with the sampling frequency of the direct connection test. DC removal processing was performed on the pressure time series of each monitoring point to extract the simulated pressure oscillation component; A fast Fourier transform is performed on the preprocessed simulated pressure oscillation components to obtain the simulated amplitude spectrum. The frequency point with the largest amplitude in the simulated amplitude spectrum is extracted as the theoretical frequency of the acoustic modal oscillation.

9. The direct-drive test method for a ramjet engine based on operating condition adaptation and control according to claim 8, characterized in that: The process for determining whether the direct connection test produces acoustic boundary distortion is as follows: The frequency deviation value of the acoustic modal oscillation is obtained by taking the absolute value of the difference between the main frequency of the direct connection test oscillation and the theoretical frequency of the acoustic modal oscillation. The frequency deviation value of the acoustic modal oscillation is then compared with the theoretical frequency of the acoustic modal oscillation to obtain the frequency deviation ratio of the acoustic modal oscillation. If the frequency deviation ratio of the acoustic modal oscillation is greater than the frequency deviation ratio threshold, it indicates that the direct connection test produces acoustic boundary distortion; otherwise, it indicates that the direct connection test does not produce acoustic boundary distortion.

10. The direct-drive test method for a ramjet engine based on operating condition adaptation and control according to claim 8, characterized in that: The process of determining the oscillation-sensitive region that more closely approximates actual flight is as follows: The direct connection boundary correction coefficient is obtained by comparing the ratio of the main frequency of the direct connection test oscillation to the theoretical frequency of the acoustic modal oscillation. The direct boundary correction coefficient is multiplied with the quadratic response surface formula to obtain the corrected quadratic response surface formula. Based on the corrected quadratic response surface formula, the fitting result of the oscillation amplitude is corrected. MATLAB is used to plot the contour map of the oscillation amplitude after the Mach number-equivalent ratio plane correction to determine the oscillation sensitive area that is closer to the actual flight.

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