Combustion field velocity measurement system and method based on laser-induced impact ripple shadow imaging

Abstract

The invention discloses a combustion field velocity measurement system and method based on laser-induced impact ripple shadow imaging, and belongs to the field of combustion diagnosis and optical measurement, the system comprises a laser focusing system, a double-optical-path schlieren optical path, a camera and an image processing unit, local plasma is generated through laser induction, impact waves are triggered, and the laser-induced impact ripple shadow imaging is realized. And a shock wave propagation process is captured by combining a double-optical-path schlieren optical path system, so that the velocity field of the combustion field is accurately measured. According to the double-optical-path schlieren optical path, the measurement sensitivity of the system is successfully improved by three times by means of two times of deflection of light in a flow field. And the camera and the image processing unit realize + / -3% speed measurement precision in combustion flow field measurement through image processing and model construction. The method provides important technical support for performance optimization and reliability evaluation of the aerospace engine.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of combustion diagnosis and optical measurement, and particularly relates to a combustion field velocity measurement system and method based on laser-induced shock wave schlieren imaging. BACKGROUND

[0002] With the rapid development of aerospace technology, the research and development of high-performance engines have become the focus of international competition. There is a complex high-temperature and high-pressure combustion environment in the combustion chamber of high-performance propulsion systems such as aerospace engines, and the flow field velocity distribution directly affects the combustion efficiency, stability and emission characteristics. Accurate measurement of the combustion field velocity is of great significance for optimizing the design of the combustion chamber, improving the combustion efficiency, reducing pollution emissions and ensuring flight safety.

[0003] Traditional contact measurement methods such as thermocouples and pressure sensors are difficult to work stably in high-temperature and high-pressure combustion environments for a long time, and will interfere with the flow field, resulting in distorted measurement results. In recent years, with the development of optical diagnosis technology, non-contact optical measurement methods have gradually become the mainstream of combustion field velocity measurement. However, the particle image velocimetry (PIV) technology faces problems such as high-temperature decomposition of tracer particles and uneven distribution in high-temperature combustion environments, and particles have some interference with combustion reactions. Laser Doppler velocimetry (LDV) can only obtain point measurement results, making it difficult to achieve full-field velocity distribution measurement. Molecular tracer techniques such as laser-induced fluorescence (LIF) are limited by the selection of tracer molecules and signal intensity.

[0004] In the research of aerospace engines, there are complex phenomena such as shock waves, boundary layers and combustion reaction coupling in the combustion field, and existing measurement methods face severe challenges. The temperature gradient is large, the pressure fluctuation is strong, and the chemical reaction is intense, making it difficult for conventional measurement techniques to obtain accurate data, so it is urgent to develop on-site combustion field velocity measurement techniques. SUMMARY

[0005] To solve the above technical problems, the present application provides a combustion field velocity measurement system based on laser-induced shock wave schlieren imaging, comprising:

[0006] laser focusing system, double optical path schlieren light path and camera and image processing unit;

[0007] The laser focusing system is used to generate high-energy density laser pulses and focus them into the combustion flow field to produce plasma breakdown effect and induce shock waves;

[0008] The double optical path schlieren light path is used to capture the density gradient caused by the shock wave, and the sensitivity is multiplied by the double optical path design;

[0009] The camera and the image processing unit are used for dynamically capturing the shock wave propagation process and inversely calculating the combustion field velocity distribution through an algorithm.

[0010] Preferably, the laser focusing system comprises:

[0011] A single-pulse all-solid-state laser is used to generate high-energy density laser pulses.

[0012] A first mirror is used to change the direction of laser propagation.

[0013] A first concave lens is used to focus the laser into the combustion flow field.

[0014] A DG645 timing controller is used to control the synchronization triggering of the laser, halogen lamp and high-speed camera.

[0015] Preferably, the double-optical-path schlieren optical path comprises:

[0016] A halogen lamp is used to provide a wide-spectrum continuous light source.

[0017] A second concave lens is used to collimate the divergent light source into a parallel light beam.

[0018] A slit is used to limit the width of the light beam and improve the spatial coherence of the light source.

[0019] A beam splitter prism is used to separate and combine the optical paths.

[0020] A second mirror and a third mirror are used to form a double-optical-path optical path.

[0021] A knife edge is used to realize schlieren imaging and convert phase gradients into intensity changes.

[0022] A third concave lens is used for imaging.

[0023] Preferably, the camera and the image processing unit comprise:

[0024] A high-speed camera is used to capture schlieren images of the shock wave propagation process.

[0025] A data processing unit is used to process image data and realize the inverse calculation and visual output of the combustion field velocity.

[0026] In another aspect, the present application also provides a combustion field velocity measurement method based on laser-induced shock wave schlieren imaging, which is applied to a combustion field velocity measurement system based on laser-induced shock wave schlieren imaging.

[0027] A laser focusing system is used to generate high-energy density laser pulses and focus them into the combustion flow field, generating plasma breakdown effect and inducing shock waves.

[0028] The density gradient caused by the shock wave is captured by a double-path schlieren optical path;

[0029] The propagation process of the shock wave is dynamically captured by a camera and an image processing unit, and the velocity distribution of the combustion field is inversed by an algorithm.

[0030] Preferably, the process of generating plasma breakdown effect and inducing shock wave comprises:

[0031] A single-pulse all-solid-state laser is used to generate high-energy density laser pulses;

[0032] A first mirror is used to change the direction of laser propagation;

[0033] A first concave lens is used to focus the laser into the combustion flow field;

[0034] A DG645 time sequence controller is used to control the synchronous triggering of the laser, halogen lamp and high-speed camera.

[0035] Preferably, the step of dynamically capturing the propagation process of the shock wave by the camera and the image processing unit, and inversing the velocity distribution of the combustion field by the algorithm comprises:

[0036] A high-speed camera is used to capture the schlieren image of the propagation process of the shock wave;

[0037] A data processing unit is used to process the image data and realize the inverse calculation and visual output of the combustion field velocity.

[0038] Preferably, the step of processing the image data by the data processing unit and realizing the inverse calculation and visual output of the combustion field velocity comprises:

[0039] An image preprocessing module is used to eliminate the non-uniformity of the light field by background correction, suppress noise by Gaussian filtering, enhance the contrast of the shock wave front by histogram equalization, and complete spatial calibration based on pixel-physical space mapping;

[0040] An edge extraction module is used to perform edge detection by Canny operator, generate image gradient field and apply non-maximum suppression, extract candidate edge point set by double-threshold processing, optimize edge continuity combined with region connectivity analysis, filter out interference structures based on geometric morphological features, and finally perform Gaussian fitting on the gradient profile of each front point to realize sub-pixel level precision positioning;

[0041] An edge point set fitting module is used to fit the edge point set by weighted least squares method, minimize the sum of squares of residuals by iterative calculation, and determine the parameters of the major axis length, direction and center position of the ellipsoid equation.

[0042] In another aspect, the present application also provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method when executing the computer program.

[0043] In another aspect, the present application also provides a computer readable storage medium storing a computer program, wherein the computer program is executable by a processor to implement the method.

[0044] Compared with the prior art, the present application has the following advantages and technical effects:

[0045] The combustion field velocity measurement system and method based on laser-induced shock wave schlieren imaging provided by the present application realizes non-contact measurement of the high-temperature combustion field of an aerospace engine, and overcomes the flow field interference problem and high-temperature environment limitation of traditional probe-type measurement. Compared with traditional optical measurement technologies, such as PIV, which requires the addition of easily ablated tracer particles, the present application uses laser-induced shock wave as a controllable and directional disturbance source, and combines with high-sensitivity schlieren imaging technology, so that the flow field velocity information can be obtained by analyzing the propagation characteristics of the shock wave in the combustion field, and the combustion environment of up to 3000K has good adaptability. Through the cooperation of nanosecond pulse laser and high-speed camera, the system can realize the time resolution of microsecond level, and can realize multi-scale measurement from millimeter to centimeter level by adjusting the parameters, and the spatial resolution can reach 0.1 mm, so that the two-dimensional velocity field distribution in the measurement plane can be obtained, and the complex flow characteristics can be captured. BRIEF DESCRIPTION OF DRAWINGS

[0046] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. The accompanying drawings do not constitute an inappropriate limitation on the present application. In the drawings:

[0047] Figure 1 The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. The accompanying drawings do not constitute an inappropriate limitation on the present application. In the drawings:

[0048] Figure 2 The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. The accompanying drawings do not constitute an inappropriate limitation on the present application. In the drawings:

[0049] Figure 3 The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. The accompanying drawings do not constitute an inappropriate limitation on the present application. In the drawings:

[0050] 1, single-pulse all-solid-state laser; 2, first mirror; 3, first convex lens; 4, combustion flow field; 5, DG645 time sequence controller; 6, halogen lamp; 7, second convex lens; 8, slit; 9, light splitting prism; 10, second mirror; 11, data processing unit; 12, third mirror; 13, blade; 14, third convex lens; 15, high-speed camera. Detailed Implementation

[0051] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0052] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0053] Example 1

[0054] like Figure 1 As shown, this embodiment provides a combustion field velocity measurement system based on laser-induced shock ripple imaging, comprising:

[0055] Laser focusing system, dual-path ripple optical path and camera and image processing unit;

[0056] The laser focusing system is used to generate high-energy-density laser pulses and focus them onto the combustion flow field, thereby generating a plasma breakdown effect and inducing a shock wave.

[0057] The dual-path schlieren optical path is used to capture the density gradient caused by the shock wave, and the sensitivity is multiplied by the dual-path design;

[0058] The camera and image processing unit are used to dynamically capture the propagation process of the shock wave and to invert the velocity distribution of the combustion field through an algorithm.

[0059] The laser focusing system includes a single-pulse all-solid-state laser 1, a first reflecting mirror 2, a first concave lens 3, and a DG645 timing controller 5. The single-pulse all-solid-state laser 1 is an Nd:YAG laser with a working wavelength of 1064 nm, a pulse width of 8 ns, and a single-pulse energy of 300 mJ, used to generate high-energy-density laser pulses. The first reflecting mirror 2 is a high-reflectivity mirror with a reflectivity greater than 99%, used to change the laser propagation direction. The first concave lens 3 is made of quartz with a focal length of 100 mm, used to focus the laser onto the combustion flow field 4. The focused spot diameter is approximately 1 mm, sufficient to generate a plasma breakdown effect in the combustion flow field. The DG645 timing controller 5 has 8 independent output channels with a time resolution of 5 ps, used to precisely control the synchronous triggering of the laser, halogen lamp, and high-speed camera, ensuring the system's timing coordination.

[0060] The double optical path schlieren optical system includes a halogen lamp 6, a second concave lens 7, a slit 8, a beam splitter prism 9, a second mirror 10, a third mirror 12, a knife edge 13, and a third concave lens 14. The halogen lamp 6 is a 150 W quartz halogen lamp with a color temperature of 5600 K, which provides a wide-spectrum continuous light source to ensure the illumination stability of the schlieren system. The second concave lens 7 has a focal length of 150 mm, which is used to collimate the divergent light emitted by the halogen lamp into a parallel light beam to control the beam divergence angle and uniformity. The slit 8 has an adjustable width, typically set to 0.2 mm, which is used to limit the beam width and improve the spatial coherence to achieve high-precision spatial filtering. The beam splitter prism 9 is a 50:50 beam splitting ratio cube prism, which is used to separate and combine the optical paths to achieve accurate multiplexing of the optical paths. The second mirror 10 and the third mirror 12 are both high-precision mirrors with a surface flatness better than λ / 10, which are used to form a double optical path to make the light pass through the combustion flow field twice to enhance the system sensitivity. The knife edge 13 is a stainless steel precision knife edge with an edge flatness better than 1 μm, which is installed on a precision displacement stage and can accurately adjust the amount of light cutting, which is used to convert the phase gradient into intensity variation to improve the contrast. The third concave lens 14 has a focal length of 200 mm, which is used to project the schlieren image onto the sensor of the high-speed camera to control the magnification and correct the optical aberration.

[0061] The camera and image processing unit includes a high-speed camera 15 and a data processing unit 11. The high-speed camera 15 is a CMOS sensor with a resolution of 1024x1024 pixels, a maximum frame rate of 10 5 fps, and an exposure time as short as 500 ns, which is used to capture the schlieren images of the shock wave propagation process to provide nanosecond-level time resolution. The data processing unit 11 is a high-performance computing workstation, which is used to process image data and implement the inversion calculation and visualization output of the combustion field velocity.

[0062] Example Two

[0063] As shown in Figure 2 , the present embodiment provides a combustion field velocity measurement method based on laser-induced shock wave schlieren imaging, which includes:

[0064] Set the DG645 timing controller 5, set the laser trigger channel as the main trigger source, and set the high-speed camera 15 trigger delay to between 0.5 μs and 10 μs to capture different stages of shock wave propagation. Set the single-pulse solid-state laser 1 to have an energy of 300 mJ, and set the high-speed camera 15 frame rate to 20000 fps and the exposure time to 1 μs. Adjust the position of the first concave lens 3 so that the laser focal point is located at a predetermined position of the combustion flow field 4. Use the single-pulse solid-state laser to generate a high-energy density laser pulse, which is focused by the first mirror 2 and the first concave lens and then irradiated into the combustion flow field 3 to generate plasma breakdown effect and induce a shock wave.

[0065] Using the background light emitted by the halogen lamp 6, the optical path sensitivity is adjusted by the blade 13 and the second reflecting mirror 10. A high-speed camera synchronously records the schlieren image during the propagation of the shock wave, thus acquiring the schlieren image of the shock wave propagation. The continuous light emitted by the halogen lamp 6 is collimated by the second concave lens 7 and passes through the slit 8 to form a thin beam. This beam passes through the combustion flow field 4 after passing through the beam splitter prism 9. Due to the density gradient caused by the shock wave propagation, the light is deflected. The deflected light is reflected by the second reflecting mirror 10 and passes through the combustion flow field 4 again, achieving dual-path propagation and further enhancing the deflection effect. The light is then recombined by the beam splitter prism 9, modulated by the blade 13 to convert the phase gradient into an intensity change, and finally imaged onto the high-speed camera 15 by the third concave lens 14. Under the control of the DG645 timing controller 5, the high-speed camera captures the schlieren image sequence during the shock wave propagation process with a preset delay time.

[0066] The data processing unit 11 receives the image sequence acquired by the high-speed camera 15, extracts the shock wave edge information, and performs the following image processing operations, such as... Figure 3 As shown:

[0067] First, image preprocessing is performed. Background correction is used to eliminate light field inhomogeneity, Gaussian filtering is used to suppress noise, histogram equalization is used to enhance the contrast of the shock wave front, and spatial calibration is performed based on pixel-physical space mapping with a typical resolution of 0.05 mm / pixel.

[0068] Subsequently, shock wave edge extraction was performed: edge detection was conducted using the Canny operator with a low threshold of 20 and a high threshold of 60, generating an image gradient field and applying non-maximum suppression; a candidate edge point set was extracted using dual threshold processing, and edge continuity was optimized by combining regional connectivity analysis; the shock wave leading edge was screened based on geometric morphological features to eliminate interfering structures; finally, Gaussian fitting was performed on the gradient profile of each leading edge point to achieve sub-pixel level precision positioning.

[0069] Finally, edge point set fitting is performed: the weighted least squares method is used to fit the shock wave edge, and the objective function is constructed. Where a, b, c, and d are the parameters of the ellipsoid equation. The weighting factor is used; the principal axis length, direction, and center position parameters of the ellipsoid equation are determined by minimizing the sum of squared residuals through iterative calculation; the fitting results are used for subsequent shock wave propagation velocity calculation and flow field velocity inversion.

[0070] The shock wave propagation equation is established, taking into account the propagation characteristics of the shock wave in the combustion flow field, such as... Figure 3 As shown, it includes:

[0071] The propagation equation of shock waves in a stationary medium is used to establish a spherical shock wave propagation model based on the Sedov-Taylor self-similar solution, and the relationship between the shock wave radius and time is defined. where a is the energy-dependent coefficient and β is the self-similarity index; the Rankine-Hugoniot conservation relations are combined to calculate the density ratio , pressure ratio and temperature ratio , where γ is the ratio of specific heat and M is the Mach number; the actual sound speed and state parameters are determined by analyzing the shock position data at multiple times.

[0072] The effect of the combustion flow field velocity on the shock propagation is corrected by vector composition of the combustion flow field velocity and the intrinsic velocity of the shock A correction model of the propagation velocity in the local coordinate system is established; for an anisotropic flow field, a radial non-uniform correction function is constructed to solve the distortion of the shock shape and the change of the front curvature caused by the flow field velocity by iteration with the continuity equation.

[0073] Based on the temperature and pressure distributions of the combustion flow field, the shock propagation velocity is related by the sound speed formula , where R is the gas constant and M is the molecular weight; the shock propagation velocity is determined according to the calculated sound speed and the measured shock Mach number; the refractive index compensation algorithm is introduced to eliminate the interference of the temperature gradient on the schlieren imaging, where k is the gas refractive index constant; the coupling relationship between the temperature and pressure fields and the shock propagation is described by a second-order partial differential equation system.

[0074] Based on the established shock propagation equation, the flow field velocity is calculated by inversion, as shown in Figure 3

[0075] A mathematical relationship model of the shock velocity and the combustion flow field velocity is established; a propagation model of the shock velocity and the flow field velocity is established , where is the shock velocity in a stationary medium, is the flow field velocity vector, is the unit vector of the propagation direction; the problem is converted into a linear equation system by spatial discretization , and the divergence constraint is introduced to ensure the continuity of the flow field.

[0076] The Levenberg-Marquardt algorithm is used to solve the nonlinear inversion problem: the objective function is constructed; the initial guess of the flow field velocity is set; the residual vector is calculated; the Jacobian matrix ​Solve the incremental equation where is the damping factor; update the flow field velocity estimate ; set the convergence criterion as or reach the maximum iteration number, 50 times; apply physical constraints to the intermediate results to ensure that the velocity field satisfies the fluid mechanics velocity field continuity.

[0077] Introduce Tikhonov regularization to improve the stability of inversion: modify the objective function as where is the regularization parameter, is the difference operator matrix. Use the L-curve method to determine the optimal regularization parameter , balance the data fitting degree and the smoothness of the solution; implement a multi-scale regularization strategy, gradually transition from large scale to small scale in the iteration process, with an initial value of 0.1 and a final value of 0.01; introduce physical knowledge-based constraint conditions, such as the curl constraint and the boundary condition; finally output the two-dimensional velocity field distribution of the combustion flow field that satisfies the continuity equation and momentum conservation.

[0078] In this embodiment, the velocity field reconstruction and visualization step includes: deploying multiple measurement points in the measurement area based on the geometric characteristics of the flow field using a non-uniform grid strategy, increasing the point density in high gradient areas, and setting the minimum point spacing to be no less than 1 / 10 of the diameter of the shock wave; using a radial basis function interpolation algorithm to reconstruct the velocity vector of the measurement points, constructing an interpolation function of the form, introducing local polynomial correction to preserve the divergence-free constraint, and applying the mirror point method to the boundary area; calculating the vector and scalar representation of the reconstructed velocity field on a regular grid to generate the velocity magnitude distribution and the direction distribution , using an adaptive strategy to draw the vector field and non-uniform contour lines, and adding key feature markers to assist in identifying flow field characteristics.

[0079] The technical effects of this embodiment are:

[0080] The combustion field velocity measurement system and method based on laser-induced shock wave schlieren imaging provided by the embodiment realizes non-contact measurement of the high-temperature combustion field of an aerospace engine, and overcomes the flow field interference problem and high-temperature environment limitation of traditional probe-type measurement. Compared with traditional optical measurement technologies, such as PIV, which needs to add easily ablated tracer particles, the embodiment uses laser-induced shock wave as a controllable and directional disturbance source, and combines high-sensitivity schlieren imaging technology, so that the flow field velocity information can be obtained by analyzing the propagation characteristics of the shock wave in the combustion field, and the combustion environment of up to 3000K has good adaptability. Through the cooperation of nanosecond pulse laser and high-speed camera, the system can realize time resolution of microsecond level, and can realize multi-scale measurement from millimeter to centimeter level by adjusting parameters, and the spatial resolution can reach 0.1 mm, so that the two-dimensional velocity field distribution in the measurement plane can be obtained, and the complex flow characteristics can be captured.

[0081] Currently, schlieren imaging mostly uses single-optical-path schlieren light paths, such as transmission-type schlieren light paths and reflection-type schlieren light paths, which results in low detection sensitivity. The double-optical-path schlieren light path system used in the embodiment realizes twice transmission of light in the combustion flow field, thereby significantly improving the response sensitivity of the system to flow field changes. The light source enters the flow field through a condenser lens, a slit and a beam splitter, is reversed by a reflecting mirror and passes through the flow field again, and finally completes imaging through a beam splitter, a knife edge and an imaging objective lens. According to optical theory analysis, the sensitivity of the double-optical-path schlieren light path system of the embodiment can be expressed as: wherein R is the radius of the spherical mirror, and f is the focal length of the plane mirror. The sensitivity is about 3 times higher than that of the traditional single-optical-path system, and the micro velocity change of ±1.5 m / s can be accurately captured.

[0082] Only one lens and one beam splitter are needed to replace the double-lens design in the single-optical-path system, which not only simplifies the optical system, but also reduces the space occupation by about 40%. The beam splitter prism and the reflecting mirror are combined to realize double transmission of light through the flow field, and the number of optical elements is reduced by about 30% compared with the double-lens design required by the traditional single-optical-path system, which directly reduces the system material cost and assembly complexity. This design not only reduces the total cost of optical components by about 45%, but also reduces the light energy loss by reducing the number of optical interfaces, and improves the system integration and anti-vibration performance, so that the system has significant economic advantages in manufacturing, debugging and maintenance. The overall stability is improved, and it is especially suitable for high-vibration aerospace engine test environment.

[0083] The inversion algorithm of the embodiment has a unique advantage in using double optical path schlieren imaging data. By simultaneously considering the propagation law of the shock wave in the stationary medium, the influence of the flow field velocity on the shock wave propagation, and the correction of the temperature and pressure distribution, a high-precision shock wave propagation equation is established. Combined with the Levenberg-Marquardt optimization algorithm and the Tikhonov regularization method, the embodiment constructs a stable and efficient inversion calculation framework. Double sampling of shock wave propagation provides more abundant flow field information, so that the algorithm can more accurately separate the inherent propagation characteristics of the shock wave and the influence of the flow field, significantly reduces the mathematical ill-conditioning in the inversion process, and makes the calculation result still maintain a high precision of ± 3% under the condition of noise.

[0084] In another aspect, the embodiment further provides an electronic device, including a memory, a processor, and a computing program stored in the memory and executable on the processor, and the processor implements the method when executing the computing program.

[0085] In another aspect, the embodiment further provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the method.

[0086] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A combustion field velocity measurement system based on laser-induced shockwave schlieren imaging, characterized by, The system comprises: a laser focusing system, a double-path schlieren optical path and a camera and image processing unit; the laser focusing system is used to generate high-energy-density laser pulses and focus them into the combustion flow field to generate plasma breakdown effect and induce shock wave; the double-path schlieren optical path is used to capture the density gradient caused by the shock wave and multiply the sensitivity by the double-path design; the camera and image processing unit are used to dynamically capture the shock wave propagation process and inversely calculate the combustion field velocity distribution by algorithm.

2. The system of claim 1, wherein, The laser focusing system comprises: a single-pulse all-solid-state laser for generating high-energy-density laser pulses; a first mirror for changing the laser propagation direction; a first concave lens for focusing the laser into the combustion flow field; a DG645 time sequence controller for controlling the synchronous triggering of the laser, halogen lamp and high-speed camera.

3. The system of claim 1, wherein, The double-path schlieren optical path comprises: a halogen lamp for providing a wide-spectrum continuous light source; a second concave lens for collimating the divergent light source into a parallel light beam; a slit for limiting the light beam width and improving the spatial coherence of the light source; a beam splitter prism for separating and combining the light paths; a second mirror and a third mirror for forming a double-path optical path; a knife for realizing schlieren imaging and converting phase gradient into intensity change; a third concave lens for imaging.

4. The system of claim 1, wherein, The camera and image processing unit comprises: a high-speed camera for capturing schlieren images of the shock wave propagation process; a data processing unit for processing image data and realizing inverse calculation and visual output of the combustion field velocity.

5. A method for combustion field velocity measurement based on laser-induced shockwave schlieren imaging, characterized in that, The method applied to the system of any one of claims 1-4 comprises: generating high-energy-density laser pulses by the laser focusing system and focusing them into the combustion flow field to generate plasma breakdown effect and induce shock wave; capturing the density gradient caused by the shock wave by the double-path schlieren optical path; dynamically capturing the shock wave propagation process by the camera and image processing unit and inversely calculating the combustion field velocity distribution by algorithm.

6. The method of claim 5, wherein, The process of generating plasma breakdown effect and inducing shock wave comprises: generating high-energy-density laser pulses by the single-pulse all-solid-state laser; changing the laser propagation direction by the first mirror; focusing the laser into the combustion flow field by the first concave lens; controlling the synchronous triggering of the laser, halogen lamp and high-speed camera by the DG645 time sequence controller.

7. The method of claim 5, wherein, The step of dynamically capturing the shock wave propagation process by the camera and image processing unit and inversely calculating the combustion field velocity distribution by algorithm comprises: capturing schlieren images of the shock wave propagation process by the high-speed camera; processing image data and realizing inverse calculation and visual output of the combustion field velocity by the data processing unit.

8. The method of claim 5, wherein, The step of processing image data and realizing inverse calculation and visual output of the combustion field velocity by the data processing unit comprises: eliminating light field inhomogeneity by background correction, suppressing noise by Gaussian filtering, enhancing shock wave front contrast by histogram equalization and completing spatial calibration based on pixel-physical space mapping by the image preprocessing module. The shock wave edge extraction module performs edge detection by a Canny operator, generates an image gradient field and applies non-maximum suppression, adopts double threshold processing to extract a candidate edge point set, optimizes edge continuity in combination with region connectivity analysis, screens shock wave fronts based on geometric morphological features, eliminates interference structures, and finally performs Gaussian fitting on a gradient profile of each front point to achieve sub-pixel level precision positioning. The edge point set fitting module adopts a weighted least squares method to fit the edge point set, minimizes residual sum of squares through iterative calculation, and determines parameters of the major axis length, direction and center position of the ellipsoid equation.

9. An electronic device comprising a memory, a processor, and a computing program stored in the memory and executable on the processor, characterized in that, The processor implements the method of any one of claims 5-8 when executing the computing program.

10. A computer-readable storage medium storing a computer program, the computer program comprising instructions that, when executed by a computer, cause the computer to perform the method of any one of claims 1 to 9. The computer program implements the method of any one of claims 5-8 when executed by the processor.

Images