Aero-engine test-bed ground vortex test method and device

Abstract

The present application belongs to the field of aero-engine ground test technology, and provides an aero-engine test stand ground vortex test method and device. The method coats a brightening coating on the fan blades, rotating cap cover and inlet duct inner wall of the engine, and sets a background plate and a side high-speed camera on both sides of the inlet duct, wherein the background plate is opposite to the side high-speed camera and is in the field of view of the side high-speed camera, and the surface of the background plate is provided with a high-density random speckle pattern; the front high-speed camera is arranged opposite to the inlet duct to construct a double-view high-speed imaging system. When the engine is stably operated at a target speed, the double cameras are synchronously triggered to shoot image sequences; the cross-correlation calculation is performed based on the side image and the vortex-free background speckle pattern to generate a ground vortex center trajectory and fit a development curve; and the ground vortex centroid and cross-sectional area are determined based on the front image through a gray scale weighting method. The method does not need to invade the flow field, and can realize the synchronous quantification of the spatial evolution and cross-sectional morphology of the ground vortex.

Description

Technical Field

[0001] This invention belongs to the field of aero-engine ground testing technology, and relates to a ground vortex testing method and device for aero-engine test bench. Background Technology

[0002] During ground testing of aero engines, due to the limited height of the test stand above the ground, ground vortices form under the air intake under specific operating conditions due to the ground boundary layer effect. These ground vortices are characterized by being transient, weak in intensity, and having no fixed occurrence pattern. Once sucked into the engine, they will cause distortion of the intake airflow field, leading to compressor stall, surge, or even engine shutdown. They may even entrain foreign objects from the ground, causing blade damage and seriously threatening test safety.

[0003] Since the occurrence of ground vortices depends on a variety of factors such as engine speed, ambient wind speed, and ground roughness, their occurrence time and spatial location are highly uncertain. Traditional contact measurement methods (such as hot-wire anemometers and pressure probes) are difficult to deploy and easily interfere with the flow field. Conventional video monitoring has a low frame rate and poor contrast, and can only achieve qualitative observation, but cannot capture its rapid evolution process.

[0004] Although some studies in recent years have attempted to predict the generation and development of ground eddies through numerical simulation, the accuracy of the simulation models has not been effectively verified due to the lack of high-precision experimental data.

[0005] Furthermore, visual measurement techniques are considered ideal for observing ground vortices due to their non-contact and full-field visualization advantages. However, most publicly available images or videos of ground vortices are taken with ordinary cameras under natural light, resulting in problems such as insufficient frame rate (usually below 100 fps), low signal-to-noise ratio, and weak contrast between the vortex and the background. Especially at high humidity levels, ground vortices appear only as faint white, misty structures, easily confused with ground reflections, water vapor, or shadows, making manual identification difficult and automated quantitative analysis almost impossible. Summary of the Invention

[0006] To address the shortcomings of existing technologies, such as the lack of personalization of ground vortex observations, missing parameters, low signal-to-noise ratio, and incomplete information from a single perspective, this invention discloses a ground vortex testing method for aero-engine test benches. This method can achieve high-precision, synchronous, and quantitative extraction of multidimensional dynamic parameters of ground vortices and establish their mapping relationship with engine operating conditions, providing a reliable experimental basis for inlet distortion assessment.

[0007] Specifically, the method includes the following steps:

[0008] S1. A brightening coating is applied to the engine fan blades, rotating hood, and inner wall of the air intake. A background plate and a side high-speed camera are respectively installed on both sides of the air intake. The background plate is located directly opposite the side high-speed camera and within its field of view. The surface of the background plate is provided with a speckle pattern.

[0009] S2. A dual-view high-speed imaging system is set up on the test stand, wherein the front high-speed camera faces the engine air intake, and the focal plane of the side high-speed camera coincides with the vertical center section of the air intake, and its field of view covers the section and the boundary area between it and the ground.

[0010] S3. During engine testing, when the target speed is reached and the engine is running stably, the front high-speed camera and the side high-speed camera are simultaneously triggered to capture image sequences.

[0011] S4. Based on the image sequence captured by the side high-speed camera and the speckle map without vortex background, perform cross-correlation calculation to generate the ground vortex center trajectory, and fit the ground vortex center trajectory to obtain the ground vortex development curve.

[0012] Meanwhile, based on the image sequence captured by the frontal high-speed camera, the ground vortex centroid and ground vortex cross-sectional area are determined by gray-scale weighting.

[0013] Further, in step S1, the brightening coating is formed by a matte white water-based paint with a thickness of less than 0.1 mm; the speckle pattern is a random speckle pattern with a speckle density of not less than 80%, and the diameter of a single speckle occupies 1 to 5 pixels of the image.

[0014] Further, in step S1, reference lines are drawn at 45°, 135°, 225° and 315° circumferential positions of the air intake, respectively. The reference lines extend from the engine fan inlet to the air intake inlet, and are used to initially determine the positional movement of the ground vortex.

[0015] Furthermore, in step S2, the frame rate and exposure time of the side high-speed camera are set according to the engine's maximum intake speed and intake duct diameter, and the frame rate and exposure time of the front high-speed camera are set according to the fan speed, number of blades, and camera resolution.

[0016] Further, in step S4, cross-correlation calculations are performed to generate the ground vortex center trajectory, and the ground vortex center trajectory is fitted to obtain the ground vortex development curve, including:

[0017] S401. Perform cross-correlation calculation between the vortex-free background speckle map and the image sequence captured by the side high-speed camera, divide each image into multiple local regions and calculate the corresponding spatial displacement vector for each region.

[0018] S402. For each image, construct a displacement amplitude field using its corresponding spatial displacement vector, and extract high gradient regions through adaptive threshold segmentation.

[0019] S403. Extract the skeleton of the high gradient region to generate the ground vortex center trajectory;

[0020] S404. Perform time averaging on the ground vortex center trajectory corresponding to multiple consecutive frames of images at the same target rotation speed to obtain the average center trajectory, and fit the average center trajectory to obtain the ground vortex development curve.

[0021] Furthermore, in step S4, the vortex-free background speckle image is a background speckle image pre-captured by the side high-speed camera when the engine is not running and there are no ground vortices.

[0022] Further, in step S4, the ground vortex centroid and ground vortex cross-sectional area are determined by the gray-scale weighted method, including:

[0023] S411. Perform grayscale normalization on the image sequence captured by the front high-speed camera, remove the background image without vortex, and generate a weighted map reflecting the distribution of ground vortex intensity.

[0024] S412. Perform adaptive threshold segmentation on the weighted map to extract the ground vortex region, and filter out the non-vortex part of the ground vortex region with an area smaller than a set threshold.

[0025] S413. The ground eddy centroid is calculated from the weighted map using the gray-scale weighting method.

[0026] S414. Calculate the cross-sectional area of ​​the ground vortex based on the number of pixels in the ground vortex region and the calibration coefficient of the front high-speed camera.

[0027] In an improved embodiment of the above-mentioned ground vortex testing method for aero-engine test benches, the method further includes:

[0028] S6. Based on the ground vortex development curve, the ground vortex centroid, the ground vortex cross-sectional area, and the target rotational speed, evaluate the impact of the ground vortex on the uniformity of engine intake.

[0029] Further, in step S6, the impact of ground vortices on engine intake uniformity is evaluated, including:

[0030] S61. Based on the ground vortex cross-sectional area and the known cross-sectional area of ​​the air intake, calculate the ratio of the ground vortex cross-sectional area to the air intake cross-sectional area.

[0031] Based on the positions of the ground vortex centroid and the air intake center, calculate the offset of the ground vortex centroid relative to the air intake center;

[0032] The ground vortex moving speed is calculated based on the time series of the ground vortex center trajectory. Combined with the average axial velocity of the air intake corresponding to the target rotational speed, the ratio of the ground vortex moving speed to the average axial velocity of the air intake is calculated.

[0033] S62. Establish a speed-distortion relationship curve based on the ratio, the offset, and the ratio to determine the intake safety margin.

[0034] This invention also provides a ground vortex testing device for an aero-engine test stand, comprising:

[0035] A high-speed front camera is mounted directly in front of the engine, with a field of view covering the entire air intake.

[0036] A high-speed side camera is installed on the side of the test stand, and its field of view covers the cross section and the area where it meets the ground.

[0037] The front LED light source and the side LED light source are arranged on the same side as the front high-speed camera and the side high-speed camera, respectively, to provide flicker-free and uniform illumination;

[0038] Background plate, with a speckle pattern on its surface, is vertically mounted directly opposite the field of view of the side high-speed camera;

[0039] A synchronization controller is electrically connected to the front high-speed camera and the side high-speed camera respectively, and is used to synchronously trigger shooting;

[0040] The computer is communicatively connected to the front high-speed camera, the side high-speed camera, and the synchronization controller, and is configured to perform image acquisition, cross-correlation analysis, vortex structure extraction, parameter fitting, and intake distortion assessment.

[0041] This invention constructs a dual-view collaborative ground-based vortex optics testing system by applying a brightening coating to key rotating components of the engine and the inner wall of the air intake, and by strategically arranging high-speed side cameras and a high-density random speckle background plate on both sides of the air intake. This system has the following significant technical advantages:

[0042] 1. The development trajectory of the ground vortex in the height direction is captured by a side high-speed camera, and its inlet cross-sectional morphology is obtained by a front high-speed camera. The two complement each other to carry out dual-view collaborative observation, so as to realize the synchronous extraction of spatial trajectory and cross-sectional parameters.

[0043] 2. By combining a brightening coating, a high-density random speckle background, and a flicker-free LED light source, the signal-to-noise ratio and edge sharpness of ground vortex structure images are significantly improved;

[0044] 3. By using cross-correlation algorithms and gray-scale weighting methods, image pixel information is converted into quantifiable engineering parameters such as the physical displacement, cross-sectional area, and moving speed of ground eddies;

[0045] 4. The method of the present invention does not require intrusion into the flow field or modification of the engine structure, is applicable to real test environments, and can directly output intake safety margin assessment indicators such as cross-sectional area ratio, center of mass offset, and velocity ratio. Attached Figure Description

[0046] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of the ground vortex testing device for an aero-engine test stand according to the present invention;

[0048] Figure 2 A schematic diagram of ground vortex in an aero-engine;

[0049] Figure 3 This is a flowchart of the ground vortex testing method for an aero-engine test stand according to the present invention;

[0050] Among them, 1. Front high-speed camera; 2. Front LED light source; 3. Side high-speed camera; 4. Side LED light source; 5. Background plate; 6. Synchronization controller; 7. Computer; 8. Engine fan inlet; 9. Air intake; 10. Ground vortex. Detailed Implementation

[0051] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0052] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features of the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0053] This invention discloses a ground vortex testing method for an aero-engine test stand, which involves, as follows: Figure 1 The ground vortex testing device shown is implemented, see [link / reference]. Figure 1As shown, the device includes a front high-speed camera 1, a front LED light source, a side high-speed camera 3, a side LED light source 4, a background plate 5, a synchronization controller 6, a computer 7, an engine fan inlet 8, and an air intake duct 9. The position of the ground vortex 10 after entering the engine is shown in the diagram. Figure 2 As shown.

[0054] The system includes a frontal high-speed camera 1 mounted directly in front of the engine's air intake, covering the entire air intake area; a side high-speed camera 3 mounted on the side of the test stand, covering the cross-section and its boundary with the ground; a frontal LED light source 2 and a side LED light source 4, arranged on the same side as the frontal high-speed camera 1 and the side high-speed camera 3, respectively, providing flicker-free uniform illumination; a background plate 5 with a speckle pattern on its surface, vertically mounted opposite the field of view of the side high-speed camera 3; a synchronization controller 6 electrically connected to the frontal high-speed camera 1 and the side high-speed camera 3 for synchronously triggering shooting; and a computer 7 communicatively connected to the frontal high-speed camera 1, the side high-speed camera 3, and the synchronization controller 6, configured to perform image acquisition, cross-correlation analysis, vortex structure extraction, parameter fitting, and air intake distortion assessment.

[0055] Specifically, when installing the ground vortex testing device, the upper boundary of the field of view of the side high-speed camera 3 should include the outer edge of the engine air intake, and the lower boundary should include the intersection line of the vertical center section of the air intake and the ground platform. The intersection line can be drawn as a straight line using white paint. The front high-speed camera 1 can be positioned 2-5 meters directly in front of the engine. The field of view of this high-speed camera should exactly include the air intake, and the focal plane should be aligned with the fan blades.

[0056] The frame rate and exposure time of the side high-speed camera 3 are set according to the engine's maximum intake speed and intake duct diameter, while the frame rate and exposure time of the front high-speed camera 1 are set according to the fan speed, number of blades, and camera resolution.

[0057] Specifically, the exposure time and frame rate of the side high-speed camera 3 can be estimated based on the maximum air intake speed of the test stand. If the camera resolution is r×c, where r is the number of pixels in the horizontal direction and c is the number of pixels in the vertical direction, and the maximum air intake speed of the test stand is v and the air intake diameter is d, then the shooting frame rate of the side high-speed camera 3 can be calculated. Calculate and set the exposure time according to formula (1). Calculate and set according to formula (2), where, and These are empirical values, typically integers between 1 and 5.

[0058] Formula (1);

[0059] Formula (2).

[0060] The exposure time and frame rate of the front high-speed camera can be determined based on the expected fan speed during the test run. If the fan speed is A and the number of blades is s, then the shooting frame rate of the front high-speed camera is... The selection range and exposure time are determined according to formula (3). Calculate and set according to formula (4), where, and These are empirical values, typically integers between 1 and 5.

[0061] Formula (3);

[0062] Formula (4).

[0063] Among them, the front LED light source 2 and the side LED light source 4 are flicker-free white light, and are on the same side as the high-speed camera, so they do not affect the camera shooting. After illumination, the gray value of the area with the white brightening coating sprayed on the camera image is between 180 and 220.

[0064] The method provided in this invention can achieve high-precision, synchronous, and quantitative extraction of multidimensional dynamic parameters of ground vortices, and establish a mapping relationship between these parameters and engine operating conditions, providing a reliable experimental basis for inlet distortion assessment. Specifically, as... Figure 3 As shown, the ground eddy test method includes the following steps:

[0065] S1. A brightening coating is applied to the engine fan blades, rotating hood, and inner wall of the air intake. A background plate and a side high-speed camera are respectively installed on both sides of the air intake. The background plate is located directly opposite the side high-speed camera and within its field of view. The surface of the background plate is provided with a speckle pattern.

[0066] S2. A dual-view high-speed imaging system is set up on the test stand, wherein the front high-speed camera faces the engine air intake, and the focal plane of the side high-speed camera coincides with the vertical center section of the air intake, and its field of view covers the section and the boundary area between it and the ground.

[0067] S3. During engine testing, when the target speed is reached and the engine is running stably, the front high-speed camera and the side high-speed camera are simultaneously triggered to capture image sequences.

[0068] S4. Based on the image sequence captured by the side high-speed camera and the speckle map without vortex background, perform cross-correlation calculation to generate the ground vortex center trajectory, and fit the ground vortex center trajectory to obtain the ground vortex development curve.

[0069] Meanwhile, based on the image sequence captured by the frontal high-speed camera, the ground vortex centroid and ground vortex cross-sectional area are determined by gray-scale weighting.

[0070] In one embodiment of step S1, the brightening coating is used to enhance the contrast between the engine and the ground vortex in the captured image. The brightening coating is formed by a matte white water-based paint with a thickness of less than 0.1 mm. The speckle pattern is a high-density random speckle pattern with a speckle density of not less than 80%, and the diameter of a single speckle occupies 1 to 5 pixels of the image. When preparing the speckle pattern on the background plate, speckle generation software can be used to generate the speckle pattern, which is then water-based transferred onto the background plate after printing.

[0071] In one embodiment of step S1, to initially determine and record the location and dynamic changes of the ground vortex, the air intake can be marked in detail. Four key locations around the air intake—45°, 135°, 225°, and 315°—are selected as the base points for drawing reference lines. These angles are chosen because they are evenly distributed around the circumference, providing omnidirectional visual coverage and ensuring that the ground vortex can be accurately captured regardless of its direction.

[0072] When drawing reference lines, first determine the reference points. A precision protractor or digital angle measuring instrument can be used to accurately locate the positions of the four angles on the inner wall of the air intake. To ensure accuracy, measurements can begin at the edge of the air intake and extend along its surface to the fan inlet area. Next, draw the reference lines using high-temperature resistant, high-contrast paint or stickers at the selected angle positions, ensuring the lines are clearly visible and resistant to wear. Each reference line should directly connect the fan inlet and the air intake inlet, forming a continuous straight line throughout the entire observation area. This helps to quickly locate the approximate position of the ground vortex during subsequent analysis.

[0073] During testing, image sequences captured at different time points using a high-speed camera, combined with the speckle pattern on the background and the pre-defined reference lines, can effectively track the trajectory of ground vortices. Analysis software can automatically identify and quantify vortex activity near the intersections of each reference line, thereby assessing the variation of ground vortices relative to a fixed coordinate system. In this embodiment of the invention, the reference line-assisted design not only enables the preliminary determination of the movement of ground vortices but also provides reliable data support for further in-depth research.

[0074] In one embodiment of step S2, after the ground vortex testing device is assembled, the frontal high-speed camera 1 and the side high-speed camera 3 are calibrated respectively. Specifically, a checkerboard calibration plate is placed in the field of view of the side camera, with the calibration plate coinciding with the vertical center section of the air intake. Two-dimensional calibration is performed within the field of view to obtain the first calibration coefficient. Within the field of view of the front camera, a checkerboard calibration plate is placed inside the engine intake duct. The calibration plate is in contact with the apex of the hood and coincides with the fan plane. Two-dimensional calibration is performed within the field of view to obtain the second calibration coefficient η.

[0075] In one embodiment of step S3, during engine testing, the light source and high-speed camera are turned on. When the target speed is reached and the engine is running stably, the front high-speed camera 1 and the side high-speed camera 3 are triggered by the synchronization controller 6 to synchronously acquire image sequences and synchronously record the engine speed.

[0076] In one embodiment of step S4, the image sequences of all states captured by the side high-speed camera 3 can be cross-correlated with the background image. Then, the image center is defined as the origin (coordinates 0, 0), and the coordinates of the centerline of the ground vortex structure are extracted. The centerline coordinates of all ground vortex images at the same rotational speed are averaged to obtain the time-averaged distribution of the ground vortex curve. Simultaneously, the ground vortex curve can be fitted to obtain the fitting formula, which is the average curve equation of the ground vortex. Specifically, cross-correlation calculation is performed to generate the trajectory of the ground vortex center, and the ground vortex development curve is obtained by fitting the trajectory of the ground vortex center, including:

[0077] S401. Perform cross-correlation calculation between the vortex-free background speckle map and the image sequence captured by the side high-speed camera, divide each image into multiple local regions and calculate the corresponding spatial displacement vector for each region.

[0078] S402. For each image, construct a displacement amplitude field using its corresponding spatial displacement vector, and extract high gradient regions through adaptive threshold segmentation.

[0079] S403. Extract the skeleton of the high gradient region to generate the ground vortex center trajectory;

[0080] S404. Perform time averaging on the ground vortex center trajectory corresponding to multiple consecutive frames of images at the same target rotation speed to obtain the average center trajectory, and fit the average center trajectory to obtain the ground vortex development curve.

[0081] The vortex-free background speckle image is a background speckle image pre-captured by the side high-speed camera when the engine is not running and there are no ground vortices. .

[0082] In practice, the image center is defined as the origin (coordinates 0, 0). The acquired image sequence, including the background speckle image acquired when the engine did not generate ground vortices, is used. speckle pattern after the engine generates ground vortices Perform the following processing:

[0083] First, all images are preprocessed as follows: grayscale normalization is performed, and then median filtering (window size 5×5) is used to suppress random noise;

[0084] Secondly, when performing cross-correlation calculation using formula (5), the preprocessed image is first divided into several non-overlapping or partially overlapping integration windows. The window size is usually chosen to be 16×16 pixels or 32×32 pixels. The cross-correlation function is then calculated for each sub-block:

[0085] Formula (5);

[0086] Take the cross-correlation function The largest This serves as the local speckle displacement.

[0087] Secondly, based on the first calibration coefficient Convert pixel displacement into spatial displacement It can be expressed by formula (6):

[0088] Formula (6);

[0089] The amplitude field of spatial displacement is expressed by formula (7):

[0090] Formula (7);

[0091] Then, adaptive threshold segmentation is used to binarize the amplitude field image, extracting high displacement gradient regions to obtain a binary map of the ground vortex influence area. The main framework region of the binary vortex area is then extracted, representing the centerline trajectory of the ground vortex in space. The time-averaged coordinates of the ground vortex centerlines across multiple frames under the same rotational speed are calculated, and a polynomial is used for fitting to obtain the average development curve equation of the ground vortex.

[0092] In addition, the ground vortex image sequence can be used in conjunction with the first calibration coefficient. The velocity of the vortex core is calculated frame by frame using the differential method to obtain its velocity curve. Based on the velocity curves of different images, the velocity pulsation, the change over time, and the average velocity value at each point can be analyzed. By combining the velocity curves of different states with the rotational speed distribution, the rotational speed-average velocity curve can be obtained, which can be used to evaluate the development history of the ground vortex.

[0093] Specifically, firstly, the point of maximum displacement on the centerline is defined as the vortex core position. For time intervals in an image sequence The instantaneous velocity is calculated frame by frame using formula (8) for two adjacent frames. :

[0094] Formula (8);

[0095] Then, the average transmission velocity was obtained when calculating the instantaneous velocity in all image sequences. The velocity pulsation intensity is calculated using formula (9) based on the average transmission velocity:

[0096] Formula (9).

[0097] In another embodiment of step S4, for the image sequence captured by the frontal high-speed camera 1, a gray-scale weighted method can be applied to determine the coordinates of the ground vortex centroid and extract the ground vortex boundary. The sum of the number of pixels within the boundary multiplied by the square of the calibration coefficient is the ground vortex cross-sectional area. By averaging the cross-sectional areas under the same condition, a curve is generated showing the relationship between the cross-sectional area and rotational speed at multiple rotational speeds, thus obtaining the rotational speed-average cross-sectional area curve. Specifically, determining the ground vortex centroid and ground vortex cross-sectional area using the gray-scale weighted method includes:

[0098] S411. Perform grayscale normalization on the image sequence captured by the front high-speed camera, remove the background image without vortex, and generate a weighted map reflecting the distribution of ground vortex intensity.

[0099] S412. Perform adaptive threshold segmentation on the weighted map to extract the ground vortex region, and filter out the non-vortex part of the ground vortex region with an area smaller than a set threshold.

[0100] S413. The ground eddy centroid is calculated from the weighted map using the gray-scale weighting method.

[0101] S414. Calculate the cross-sectional area of ​​the ground vortex based on the number of pixels in the ground vortex region and the calibration coefficient of the front high-speed camera.

[0102] In practical implementation, firstly, the image sequence captured by the front high-speed camera 1 can be normalized in grayscale, and the background can be subtracted using the image without vortex. Since the grayscale of the ground vortex area is significantly lower than that of the white brightening coating background, the ground vortex can be segmented using the grayscale weighting method and formula (10):

[0103] Formula (10);

[0104] Then, connected ground vortex regions are extracted from the weighted image to eliminate non-dominant vortex structures. Similarly, the pixel coordinates of the centroid can be calculated using the gray-scale weighting method with formula (11):

[0105] The following formula (11);

[0106] Finally, the cross-sectional area of ​​the ground vortex region is calculated using the number of pixels at the vortex region boundary. The second calibration coefficient η is calculated using formula (12):

[0107] The following formula (12).

[0108] In an improved embodiment of the above-mentioned ground vortex testing method for aero-engine test benches, the method further includes: S6, evaluating the impact of the ground vortex on engine intake uniformity based on the ground vortex development curve, the ground vortex centroid, the ground vortex cross-sectional area, and the target rotational speed. Specifically, this includes the following steps:

[0109] S61. Based on the ground vortex cross-sectional area and the known cross-sectional area of ​​the air intake, calculate the ratio of the ground vortex cross-sectional area to the air intake cross-sectional area.

[0110] Based on the positions of the ground vortex centroid and the air intake center, calculate the offset of the ground vortex centroid relative to the air intake center;

[0111] The ground vortex moving speed is calculated based on the time series of the ground vortex center trajectory. Combined with the average axial velocity of the air intake corresponding to the target rotational speed, the ratio of the ground vortex moving speed to the average axial velocity of the air intake is calculated.

[0112] S62. Establish a speed-distortion relationship curve based on the ratio, the offset, and the ratio to determine the intake safety margin.

[0113] In practical implementation, on the one hand, the engine intake duct image captured by the frontal high-speed test camera 1 can be used as a basis to divide the intake duct cross-section into several sub-regions. Then, using the extracted cross-sectional area of ​​the ground vortex and its centroid position, the spatial distribution of the ground vortex within the intake duct cross-section can be determined, and local areas within the intake duct affected by the ground vortex can be identified as potential intake distortion areas.

[0114] On the other hand, the intake distortion region can be compared with the total cross-sectional area of ​​the intake duct to construct equivalent characterization indicators for ground vortex-induced intake distortion. These indicators include the ratio of the ground vortex cross-sectional area to the intake duct cross-sectional area, the offset of the ground vortex centroid relative to the intake duct center, and the relative relationship between the ground vortex velocity and the average axial velocity at the intake duct inlet. Through the analysis of these indicators, the degree of influence of ground vortex on engine intake uniformity can be quantitatively assessed.

[0115] Furthermore, the above process can be repeated under different engine speeds and test conditions to compare and analyze the obtained intake distortion evaluation indicators. By analyzing the correspondence between ground vortex parameters and engine speed, the trend of ground vortex-induced intake distortion changing with operating conditions can be obtained, which can be used to evaluate the intake safety margin of the engine under test bench conditions.

[0116] The method of this invention constructs a dual-view collaborative ground-based vortex optics testing system by coating key rotating components of the engine and the inner wall of the air intake with a brightening coating, and by rationally arranging side high-speed cameras and a high-density random speckle background plate on both sides of the air intake. This method and system have the following technical advantages compared to existing technologies:

[0117] (1) By capturing the flow field deformation in the vertical center section of the air intake through a high-speed side camera, and performing cross-correlation analysis with the speckle map without vortex background, the spatial displacement field of the ground vortex can be accurately extracted and the center trajectory can be generated. By performing time averaging and fitting on multiple frames of trajectory, a stable ground vortex development curve can be obtained, overcoming the defect that traditional single-view observation cannot obtain information on the evolution of vortex height direction.

[0118] (2) Use a high-speed front camera to obtain a full view of the air intake inlet, and calculate the coordinates of the ground vortex centroid and the physical cross-sectional area by gray-scale weighting method to avoid subjective interpretation error; combined with the inherent geometric parameters of the air intake (such as center position and total cross-sectional area), the two key distortion indicators of cross-sectional area ratio and centroid offset can be directly output.

[0119] (3) Calculate the moving speed of the ground vortex center trajectory based on the time series and associate it with the average axial velocity of the inlet corresponding to the current engine speed to obtain the speed ratio parameter; integrate the cross-sectional area ratio, the centroid offset and the speed ratio to construct the speed-distortion relationship curve, provide an objective and quantifiable basis for the intake uniformity assessment of the engine test, and significantly improve the ground vortex risk early warning capability.

[0120] (4) The present invention uses matte white water-based paint as a brightening coating (thickness < 0.1 mm), which not only enhances the uniformity of reflection in the target area, but also avoids the coating being too thick and affecting the aerodynamic shape; the background plate uses high-density random speckle (dot density ≥ 80%, diameter 1–5 pixels) to ensure that the cross-correlation algorithm has a high signal-to-noise ratio and sub-pixel displacement resolution; the frame rate and exposure time of the dual cameras are adaptively set according to the engine operating parameters (such as intake speed and fan speed) to effectively suppress motion blur and ensure image quality.

[0121] (5) In addition, by setting reference lines at 45°, 135°, 225° and 315° around the air intake, extending from the fan inlet to the air intake inlet, the orientation can be quickly marked in the image, which helps to preliminarily judge the circumferential position migration trend of the ground vortex and improves the testing efficiency.

[0122] Obviously, those skilled in the art should understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations of the embodiments of the present invention are possible for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A ground vortex testing method for an aero-engine test stand, characterized in that, include: A brightening coating is applied to the engine fan, rotating hood, and inner wall of the air intake. A background plate and a side high-speed camera are respectively installed on both sides of the air intake. The background plate is located directly opposite the side high-speed camera and within its field of view. The surface of the background plate is provided with a speckle pattern. A dual-view high-speed imaging system is set up on the test stand. The front high-speed camera faces the air intake, and the focal plane of the side high-speed camera coincides with the vertical center section of the air intake, and its field of view covers the vertical center section of the air intake and the boundary area between it and the ground. During engine testing, once the target speed is reached and the engine is running stably, the image sequence captured by the front high-speed camera and the side high-speed camera is triggered simultaneously. Based on the image sequence and speckle pattern captured by the lateral high-speed camera, cross-correlation calculation is performed to generate the ground vortex center trajectory, and the ground vortex development curve is obtained by fitting the ground vortex center trajectory. This includes: performing cross-correlation calculation on the speckle pattern and the image sequence captured by the lateral high-speed camera; dividing each image into multiple local regions and calculating the corresponding spatial displacement vector for each; constructing a displacement amplitude field for each image using its corresponding spatial displacement vector, and extracting high-gradient regions through adaptive threshold segmentation; extracting the skeleton of the high-gradient regions to generate the ground vortex center trajectory; and performing time averaging on the ground vortex center trajectories corresponding to multiple consecutive frames of images at the same target rotational speed to obtain the average center trajectory, and fitting the average center trajectory to obtain the ground vortex development curve. Meanwhile, based on the image sequence captured by the frontal high-speed camera, the ground vortex centroid and ground vortex cross-sectional area are determined by gray-scale weighting.

2. The ground vortex testing method for an aero-engine test stand according to claim 1, characterized in that, The brightening coating is formed by a matte white water-based paint with a thickness of less than 0.1 mm; the speckle pattern is a random speckle pattern with a speckle density of not less than 80%, and the diameter of a single speckle occupies 1 to 5 pixels of the image.

3. The ground vortex testing method for an aero-engine test stand according to claim 1, characterized in that, Reference lines are drawn at 45°, 135°, 225° and 315° circumferential positions of the air intake, extending from the engine fan inlet to the air intake inlet, to preliminarily determine the positional movement of the ground vortex.

4. The ground vortex testing method for an aero-engine test stand according to claim 1, characterized in that, The frame rate and exposure time of the side high-speed camera are set according to the engine's maximum intake speed and intake duct diameter, while the frame rate and exposure time of the front high-speed camera are set according to the fan speed, number of blades, and resolution.

5. The ground vortex testing method for an aero-engine test stand according to claim 1, characterized in that, The speckle pattern is a background speckle image pre-captured by the side high-speed camera when the engine is not running and there is no ground vortex.

6. The ground vortex testing method for an aero-engine test stand according to claim 1, characterized in that, The ground vortex centroid and ground vortex cross-sectional area were determined using a gray-scale weighted method, including: The image sequence captured by the frontal high-speed camera is subjected to grayscale normalization and speckle pattern removal to generate a weighted map reflecting the distribution of ground vortex intensity. The weighted map is subjected to adaptive threshold segmentation to extract the ground vortex region, and the non-vortex part of the ground vortex region with an area smaller than a set threshold is filtered out. The ground eddy centroid was calculated from the weighted map using a gray-scale weighting method. The ground vortex cross-sectional area is calculated based on the number of pixels in the ground vortex region and the calibration coefficient of the frontal high-speed camera.

7. The ground vortex testing method for an aero-engine test stand according to claim 1, characterized in that, Also includes: Based on the ground vortex development curve, the ground vortex centroid, the ground vortex cross-sectional area, and the target rotational speed, the impact of the ground vortex on the engine intake uniformity is evaluated.

8. The ground vortex testing method for an aero-engine test stand according to claim 7, characterized in that, The impact of ground vortices on engine intake uniformity was assessed, including: Based on the ground vortex cross-sectional area and the air intake cross-sectional area, calculate the ratio of the ground vortex cross-sectional area to the air intake cross-sectional area. Based on the positions of the ground vortex centroid and the air intake center, calculate the offset of the ground vortex centroid relative to the air intake center; The ground vortex moving speed is calculated based on the time series of the ground vortex center trajectory. Combined with the average axial velocity of the air intake corresponding to the target rotational speed, the ratio of the ground vortex moving speed to the average axial velocity of the air intake is calculated. A speed-distortion relationship curve is established based on the ratio, the offset, and the ratio to determine the intake safety margin.

9. A ground vortex testing device for an aero-engine test stand, used to implement the ground vortex testing method for an aero-engine test stand as described in any one of claims 1 to 8, characterized in that, include: A high-speed front camera (1) is installed in front of the engine, with a field of view covering the entire air intake (9). A side high-speed camera (3) is installed on the side of the test stand, and its field of view covers the vertical center section of the air intake and the area where it meets the ground. The front LED light source (2) and the side LED light source (4) are arranged on the same side as the front high-speed camera (1) and the side high-speed camera (3), respectively, to provide flicker-free uniform illumination; Background plate (5), with speckle pattern on its surface, is vertically mounted directly opposite the field of view of the side high-speed camera (3); The synchronization controller (6) is electrically connected to the front high-speed camera (1) and the side high-speed camera (3) respectively, and is used to synchronously trigger shooting; The computer (7) is communicatively connected to the front high-speed camera (1), the side high-speed camera (3) and the synchronization controller (6), and is configured to perform image capture, cross-correlation calculation, ground hole extraction, trajectory fitting and intake distortion assessment.

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