Air inlet channel flow field panoramic measurement system and method based on multiple cameras and background schlieren

Abstract

The invention discloses an air inlet channel flow field panoramic measurement system based on multiple cameras and background schlieren. The measurement system comprises a multi-camera imaging module, a pulse illumination module, a synchronization system and a computing platform. And a plurality of cameras in the multi-camera imaging module synchronously collect background plate images and output the background plate images to the computing platform. And the calculation platform performs cross-correlation calculation on the two frames of background images with / without flow field disturbance to obtain a displacement field, and performs two-dimensional flow field chromatography reconstruction on the multi-camera view angle displacement field based on the calibrated imaging parameters to obtain a density gradient field of the flow field in the binary supersonic air inlet. A miniature background schlieren system is adopted to replace a single-point measurement pressure measurement system, large-view two-dimensional reconstruction of a flow field in an air inlet channel is achieved, the system is simple in structure, high in reliability and high in expansibility, and a plurality of cameras are arranged in an optical access channel so that measurement of flow in a larger range of the flow field can be achieved.

Description

Technical Field

[0001] This invention relates to the field of flow measurement methods, and in particular to a panoramic measurement system and method for inlet flow field based on multiple cameras and background schlieren. Background Technology

[0002] Supersonic inlets are a crucial component of aero-engines, and their stable and efficient operation is vital for flight safety and performance. The supersonic inlet contains a complex shock wave system, the distribution of which is closely related to the inlet's actual operating state. Therefore, the measurement and reconstruction of the supersonic inlet shock wave system can often be used to determine and monitor the inlet's operating state and to stabilize the aero-engine. Currently, flow field monitoring within aero-engine inlets typically relies on point measurements of wall pressure using multiple discretely distributed pressure sensors. Analysis of the wall pressure intensity and frequency domain, combined with prior knowledge of the inlet's design, allows for the assessment of the inlet's operating state.

[0003] The aforementioned methods for monitoring the operational status of inlet test components based on wall pressure point measurements often provide only extremely limited pressure information at specific points, significantly restricting the reliability of inlet operational status assessment and jeopardizing flight safety. In particular, once the inlet enters surge, the resulting wall separation bag renders traditional wall pressure-based inlet flow monitoring methods ineffective in reflecting the true operational status of the inlet test component. Therefore, a new technical solution is needed to address these technical problems. Summary of the Invention

[0004] Purpose of the invention: To address the above shortcomings, this invention provides a panoramic measurement system for the air intake flow field based on multiple cameras and background schlieren. By replacing the single-point pressure measurement system with a multi-camera background schlieren system, a large-field-of-view two-dimensional reconstruction of the flow field inside the air intake is achieved, solving the problems of insufficient pressure information monitoring coverage and inability to reflect the true working state of the air intake test piece in the existing pressure measurement system.

[0005] The present invention also provides a measurement method using the above-described panoramic measurement system for inlet flow field based on multiple cameras and background schlieren.

[0006] Technical solution: To solve the above problems, the present invention employs a panoramic measurement system for the air intake flow field based on multiple cameras and background schlieren, comprising:

[0007] An air intake test piece, a multi-camera imaging module located on one side of the air intake test piece, and a pulse illumination module located on the other side of the air intake test piece and facing the multi-camera imaging module.

[0008] The air intake test piece includes an inlet, an outlet, and an inner channel. The multi-camera imaging module and the pulse illumination module are located on both sides of the inner channel. The multi-camera imaging module has several cameras arranged along the extension direction of the inner channel. The pulse illumination module includes a background plate facing the camera and a light source located on the back of the background plate.

[0009] Furthermore, the air intake test piece has windows on both sides, and the multi-camera imaging module includes a multi-camera imaging module mounting bracket covering one side window, a multi-camera imaging module housing covering the outside of the multi-camera imaging module mounting bracket, and a camera positioning bracket located between the multi-camera imaging module mounting bracket and the multi-camera imaging module housing; the camera positioning bracket extends along the extension direction of the air intake channel, and several cameras are mounted on the camera positioning bracket from front to back, with the camera opening positions determined by the inner surface of the air intake.

[0010] Furthermore, the front end of the housing of the multi-camera imaging module is a windward surface, and this windward surface is a wedge that gradually expands outward from front to back.

[0011] Furthermore, the camera's main optical axis is perpendicular to the sidewall of the air intake test piece and the background plate; the camera's field of view... Satisfy the following formula:

[0012] ;

[0013] in For the length of the flow field to be measured, Number of cameras; Spacing between two adjacent cameras Satisfy the following formula:

[0014] .

[0015] Furthermore, the pulse lighting module includes a pulse lighting module mounting bracket covering the window on the other side, LED heat dissipation silicone, LEDs, and a background plate installed sequentially from the outside to the inside of the pulse lighting module mounting bracket.

[0016] Furthermore, the front end of the pulse lighting module mounting bracket is a windward surface, and this windward surface is a wedge that gradually expands outward from front to back.

[0017] Furthermore, the background plate is an irregular speckle pattern printed on transparent film by inkjet printing, and the background plate is used for background schlieren imaging.

[0018] Furthermore, it also includes a synchronization system, which includes a signal generator that emits a pulsed rectangular wave signal to simultaneously trigger the multi-camera imaging module and the pulsed illumination module, enabling several cameras and light sources to work synchronously.

[0019] The technical solution of the measurement method using the binary supersonic inlet flow field measurement system provided by the present invention includes the following steps:

[0020] Step 1: Using Zhang's calibration method, calibrate each camera individually to determine the camera's intrinsic parameters. Then, place the multi-camera calibration target at the background plate position and simultaneously acquire images of the calibration target using multiple cameras to determine the multi-camera extrinsic parameters.

[0021] Step 2: When there is no incoming flow in the air intake, multiple cameras simultaneously acquire background images as reference images; after the flow field in the air intake is established, multiple cameras simultaneously acquire background images as background images under disturbance.

[0022] Step 3: Use the background image acquired by each camera under no-flow condition as a reference image, and combine it with the background image acquired by the same camera after the flow field is established to form an image pair. Perform cross-correlation calculation to obtain the single-camera displacement field. ;

[0023] Step 4: Based on the two-dimensional distribution characteristics of the flow field in the two-dimensional supersonic inlet, the density field is simplified to a two-dimensional density field, and the inverse equation is solved: The density gradient field inside the binary supersonic inlet is solved, and then the two-dimensional shock wave system inside the binary supersonic inlet is reconstructed.

[0024] In the formula The angle of light refraction. For perspective The relevant tomographic projection matrix was obtained from the system calibration. The gradient of the density field, u is .

[0025] Furthermore, step 4 specifically includes:

[0026] Considering the imaging angle For single-camera displacement field The influence of establishing a single-camera displacement field Angle of light deflection Relationship:

[0027] ;

[0028] Based on the pinhole imaging model, establish the pixel coordinates of the original background image ( , Between ) and imaging perspective relation

[0029] Obtain the angle of light refraction Reconstruction model:

[0030] ;

[0031] Considering the imaging angle Image displacement The influence of refractive index field when establishing large field-of-view imaging. With deflection angle Relationship:

[0032] ;

[0033] In the formula Let be the angle between the refractive index field gradient vector and the line of sight. For environmental refractive index;

[0034] The relationship between density field and refractive index was established using the Gladstone-Dale equation and obtained based on ray optics. Perspective Interrelationship The imaging model of the BOS system embedded in the intake wall was obtained:

[0035] ;

[0036] The above equation can be linearly discretized as follows:

[0037] ;

[0038] In the formula For perspective The relevant tomographic projection matrix was obtained from the system calibration. The density gradient is given by the equation. Based on the two-dimensional distribution characteristics of the flow field in the two-dimensional supersonic inlet, the density field is simplified to a two-dimensional density field. The above equation is then solved inversely to obtain the density gradient field within the two-dimensional supersonic inlet. The density gradient field within the two-dimensional supersonic inlet is thus obtained.

[0039] Beneficial effects: Compared with the prior art, the significant advantage of this invention is that it uses multi-camera background schlieren technology to replace the traditional single-point supersonic inlet flow field monitoring method based on wall pressure measurement points, which can realize the reconstruction and monitoring of the two-dimensional shock wave system in the entire field of the inlet. Attached Figure Description

[0040] Figure 1 This is a system schematic diagram of the present invention;

[0041] Figure 2 This is a schematic diagram of the structure of the air intake test piece, the multi-camera imaging module, and the pulse illumination module in the system of this invention.

[0042] Figure 3 This is a schematic diagram of the structure of the multi-camera imaging module of the present invention;

[0043] Figure 4 This is a schematic diagram of the pulse lighting module of the present invention;

[0044] Figure 5 This is a schematic diagram of the system parameters of the present invention;

[0045] Figure 6 This is a flowchart of the measurement method reconstruction of the present invention.

[0046] In the diagram: 1. Multi-camera imaging module mounting bracket; 2. Camera positioning bracket; 3. Miniature camera; 4. Camera driver board; 5. Multi-camera imaging module housing; 6. Pulse illumination module mounting bracket; 7. LED thermal silicone; 8. LED light source; 9. Background board. Detailed Implementation

[0047] like Figure 1 As shown in this embodiment, a binary supersonic inlet flow field measurement system based on multi-camera background schlieren imaging is presented. This system consists of three parts: a multi-camera imaging module, a pulse illumination module, and a synchronization system. Among them, as... Figure 2 As shown, the multi-camera imaging module and the pulse illumination module are respectively mounted opposite each other on both sides of the air intake test piece.

[0048] like Figure 3 The diagram shows a multi-camera imaging module, comprising a mounting bracket 1, a camera positioning bracket 2, a miniature camera 3, a camera driver board 4, and a housing 5. The miniature camera is mounted within the camera positioning bracket, and its position and viewing angle are determined by the bracket. The camera opening position within the positioning bracket is determined by the inner surface of the air intake. The main optical axis of the miniature camera is perpendicular to the side wall of the air intake test piece and perpendicular to the background plate of the pulse illumination module. (The last sentence appears to be incomplete and possibly refers to further details.) Figure 4 As shown. The field of view of a miniature camera. The following formula must be satisfied:

[0049]

[0050] in, For the length of the flow field to be measured, The number of cameras in a multi-camera imaging module, and the spacing between the cameras in a miniature camera. The following formula must be satisfied:

[0051]

[0052] The camera positioning bracket 2 and the camera drive board 4 are mounted on the multi-camera imaging module mounting bracket 1 and combined with the multi-camera imaging module housing 5 to form an integrated module. The windward surface of the multi-camera imaging module is wedge-shaped, and its wedge angle is determined by the inlet Mach number of the inlet wind tunnel test. The wedge shape of the multi-camera imaging module housing is used to prevent the formation of a normal shock wave on the windward surface inside the wind tunnel, thereby avoiding excessive stress on the model and affecting the inlet flow field.

[0053] like Figure 5 The diagram shows a pulsed illumination module, which includes a pulsed illumination module mounting bracket 6, LED thermal silicone 7, LED light source 8, and a background plate 9, all stacked sequentially. The background plate 9 can also be covered with a light-diffusing plate to achieve a uniform surface lighting effect for the LED light. The windward side of the pulsed illumination module mounting bracket 6 is also wedge-shaped, with its wedge angle determined by the inlet Mach number of the wind tunnel test. This wedge structure is used to prevent the formation of a normal shock wave on the windward side inside the wind tunnel. The background plate 9 consists of irregular speckle patterns inkjet-printed on transparent film; this background plate 9 is used for background schlieren imaging.

[0054] The synchronization system includes a signal generator that emits pulsed rectangular wave signals to simultaneously trigger the multi-camera imaging module and the pulse illumination module. Furthermore, the pulse signals emitted by the synchronization system can be simultaneously output to other measurement systems, such as a dynamic pressure acquisition system, to achieve time synchronization between multiple systems.

[0055] as follows Figure 6 The present invention provides a method for measuring the flow field inside a binary supersonic inlet based on multi-camera background schlieren, comprising the following steps:

[0056] Step 1: Multi-camera calibration. The specific steps are as follows: First, perform single-camera calibration using Zhang's calibration method to calibrate each camera in the multi-camera imaging module and determine the camera's intrinsic parameters. Second, perform multi-camera spatial calibration by placing the calibration ruler at the background plate position and simultaneously acquiring images of the calibration ruler from multiple cameras to determine the multi-camera extrinsic parameters.

[0057] Step 2: Acquisition of background images across the entire field. Specifically, the following steps are performed: First, with no incoming flow in the air intake, the multi-camera imaging module simultaneously acquires background images as reference images. Second, after the flow field within the air intake is established, the multi-camera imaging module simultaneously acquires background images as background images under disturbance conditions.

[0058] Step 3: Single-camera displacement field reconstruction. Specifically, the background image acquired by each camera in the multi-camera imaging module is reconstructed using displacement field reconstruction. The background image acquired by each camera under no-flow conditions is used as a reference image, and this image is paired with the background image acquired by that camera after the flow field is established. Cross-correlation calculations are then performed to obtain the single-camera displacement field. .

[0059] Step 4: Two-dimensional flow field tomography reconstruction of the binary supersonic inlet. The specific operation is as follows: First, consider the imaging angle. Image displacement The influence of image shift when establishing large field-of-view imaging With deflection angle Relationship:

[0060]

[0061] Based on the single-camera displacement field in step 3, and using the above formula, the single-camera light deflection angle can be obtained. Then, based on the image pixel coordinates ( , Between ) and imaging perspective relation Substituting into the above formula, we obtain the light deflection angle under large field-of-view imaging ( Reconstruction model:

[0062]

[0063] Secondly, consider the imaging angle. Image displacement The influence of refractive index field when establishing large field-of-view imaging. With deflection angle Relationship:

[0064]

[0065] In the formula Let be the angle between the refractive index field gradient vector and the line of sight. Finally, the relationship between the density field and the refractive index is established using the Gladstone-Dale equations. Simultaneously, based on ray optics, the following is obtained... Perspective Interrelationships, simplifying the refractive index field With deflection angle The relationship yields the imaging model of the BOS system embedded in the inlet wall:

[0066]

[0067]

[0068] The above equation can be linearly discretized as follows:

[0069]

[0070] In the formula For perspective The relevant tomographic projection matrix was obtained from the system calibration. Let be the gradient of the density field. Based on the two-dimensional distribution characteristics of the flow field in a two-dimensional supersonic inlet, the density field is simplified to a two-dimensional density field. The above linear discretization equation is then solved inversely to obtain the gradient density field within the two-dimensional supersonic inlet. The density gradient field within the two-dimensional supersonic inlet is thus obtained.

Claims

1. A panoramic measurement system for the air intake flow field based on multiple cameras and background schlieren, characterized in that, include: An air intake test piece, a multi-camera imaging module located on one side of the air intake test piece, and a pulse illumination module located on the other side of the air intake test piece and facing the multi-camera imaging module. The air intake test piece includes an inlet, an outlet, and an inner channel. The multi-camera imaging module and the pulse illumination module are located on both sides of the inner channel. The multi-camera imaging module has several cameras arranged along the extension direction of the inner channel. The pulse illumination module includes a background plate facing the camera and a light source located on the back of the background plate.

2. The panoramic measurement system for the air intake flow field based on multiple cameras and background schlieren as described in claim 1, characterized in that: The air intake test piece has windows on both sides. The multi-camera imaging module includes a multi-camera imaging module mounting bracket covering one side window, a multi-camera imaging module housing covering the outside of the multi-camera imaging module mounting bracket, and a camera positioning bracket located between the multi-camera imaging module mounting bracket and the multi-camera imaging module housing. The camera positioning bracket extends along the extension direction of the air intake channel, and several cameras are mounted on the camera positioning bracket from front to back. The position of the camera opening is determined by the inner surface of the air intake.

3. The panoramic measurement system for the air intake flow field based on multiple cameras and background schlieren as described in claim 2, characterized in that: The front end of the housing of the multi-camera imaging module is a windward surface, and this windward surface is a wedge that gradually expands outward from front to back.

4. The panoramic measurement system for the air intake flow field based on multiple cameras and background schlieren as described in claim 3, characterized in that: The camera's main optical axis is perpendicular to the side wall of the air intake test piece and the background plate; the camera's field of view... Satisfy the following formula: ； in For the length of the flow field to be measured, Number of cameras; Spacing between two adjacent cameras Satisfy the following formula: 。 5. The panoramic measurement system for inlet flow field based on multiple cameras and background schlieren as described in any one of claims 2 to 4, characterized in that: The pulse lighting module includes a pulse lighting module mounting bracket covering the window on the other side, LED heat dissipation silicone, LEDs, and a background plate installed sequentially from the outside to the inside of the pulse lighting module mounting bracket.

6. The panoramic measurement system for inlet flow field based on multiple cameras and background schlieren as described in claim 5, characterized in that: The front end of the pulse lighting module mounting bracket is the windward side, and this windward side is a wedge that gradually expands outward from front to back.

7. The panoramic measurement system for inlet flow field based on multiple cameras and background schlieren as described in claim 6, characterized in that: The background plate is an irregular speckle pattern printed on transparent film by inkjet printing, and the background plate is used for background schlieren imaging.

8. The panoramic measurement system for the air intake flow field based on multiple cameras and background schlieren as described in claim 1, characterized in that: It also includes a synchronization system, which includes a signal generator that emits a pulsed rectangular wave signal to simultaneously trigger the multi-camera imaging module and the pulsed illumination module, enabling several cameras and light sources to work synchronously.

9. A measurement method using the inlet flow field panoramic measurement system based on multiple cameras and background schlieren as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Using Zhang's calibration method, calibrate each camera individually to determine the camera's intrinsic parameters. Then, place the multi-camera calibration target at the background plate position and simultaneously acquire images of the calibration target using multiple cameras to determine the multi-camera extrinsic parameters. Step 2: With no airflow into the intake duct, multiple cameras simultaneously acquire background images as reference images; After the flow field inside the air intake is established, multiple cameras simultaneously acquire background images, which are used as background images under disturbance. Step 3: Use the background image acquired by each camera under no-flow condition as a reference image, and combine it with the background image acquired by the same camera after the flow field is established to form an image pair. Perform cross-correlation calculation to obtain the single-camera displacement field. ; Step 4: Based on the two-dimensional distribution characteristics of the flow field in the two-dimensional supersonic inlet, the density field is simplified to a two-dimensional density field, and the inverse equation is solved: The density gradient field inside the binary supersonic inlet is solved, and then the two-dimensional shock wave system inside the binary supersonic inlet is reconstructed. In the formula The angle of light refraction. For perspective The relevant tomographic projection matrix is ​​obtained from system calibration. The gradient of the density field, u is .

10. The measurement method as described in claim 9, characterized in that, Step 4 specifically includes: Considering the imaging angle For single-camera displacement field The influence of single-camera displacement field Angle of light deflection Relationship: ； Based on the pinhole imaging model, establish the pixel coordinates of the original background image ( , Between ) and imaging perspective relation Obtain the angle of light refraction Reconstruction model: ； Considering the imaging angle Image displacement The influence of refractive index field when establishing large field-of-view imaging. With deflection angle Relationship: ； In the formula Let be the angle between the refractive index field gradient vector and the line of sight. For environmental refractive index; The relationship between density field and refractive index was established using the Gladstone-Dale equation and obtained based on ray optics. Perspective Interrelationship The imaging model of the BOS system embedded in the intake wall was obtained: ； The above equation can be linearly discretized as follows: ； In the formula For perspective The relevant tomographic projection matrix is ​​obtained from system calibration. The density gradient field is given by the following equation: Based on the two-dimensional distribution characteristics of the flow field in the two-dimensional supersonic inlet, the density field is simplified to a two-dimensional density field. The above equation is solved inversely to obtain the density gradient field inside the two-dimensional supersonic inlet.

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