A three-dimensional space velocity field measurement device and method suitable for helicopter nozzle

Abstract

The present invention discloses a three-dimensional space velocity field measurement device and method suitable for helicopter nozzles, belonging to the field of aerodynamic test and testing technology. The present invention solves the problem of complex layout and low calculation efficiency of the traditional three-dimensional velocity field measurement device and method in the prior art; the present invention builds a scanning measurement device, calibrates the laser plane and calibrates the internal and external parameters of the double-exposure camera, uses a chessboard calibration plate to construct a standard space plane grid, controls the high-precision translation stage to move to the specified position through a computer, triggers each component through a digital pulse signal generator and synchronously controls two double-exposure cameras to collect particle images when the nozzle jet is flowing; determines the three-dimensional velocity field based on the particle image, and obtains the three-dimensional space velocity field of the nozzle jet. The present invention effectively provides high-precision and high-resolution velocity field data, realizes the accurate measurement of the three-dimensional space velocity field of the helicopter nozzle, and can be applied to measure the three-dimensional space velocity field of the helicopter nozzle.

Description

Technical Field

[0001] The invention relates to a three-dimensional space velocity field measuring device and method, in particular to a three-dimensional space velocity field measuring device and method suitable for a helicopter nozzle, and belongs to the technical field of aerodynamic test and experiment. Background Art

[0002] The design of helicopter nozzles directly affects the aerodynamic performance and thrust distribution of the aircraft. Accurate spatial velocity field measurement methods can provide high-precision test data and provide a scientific basis for the optimization design of nozzles. Through accurate velocity field measurement, noise sources can be identified and reduced, thereby improving the environmental adaptability of helicopters. In addition, understanding the spatial velocity field characteristics of the nozzle can optimize the geometry and material selection of the nozzle, and improve the thrust efficiency and fuel economy of the helicopter. It can also predict the performance attenuation of the nozzle in high temperature and high pressure environments and conduct material durability analysis.

[0003] The measurement of the spatial velocity field can provide necessary data for aerodynamic characteristics analysis, helping nozzle designers understand the impact of the jet on the overall aerodynamic performance of the helicopter. Through subsequent analysis, flow control technology can be studied and developed to further improve the helicopter's control performance and stability.

[0004] Compared with the traditional two-dimensional measurement method that can only provide limited plane data, the three-dimensional measurement method can obtain more comprehensive velocity field information and reveal complex flow structures and jet behaviors. Moreover, the three-dimensional space velocity field data helps to deeply understand the turbulent structure, vortex distribution and velocity field characteristics, and provide scientific support for improving nozzle design. In addition, the development of three-dimensional measurement technology can significantly improve the accuracy and resolution of velocity field measurement, capture more detailed flow information, and reduce measurement errors.

[0005] In the existing technology, traditional hot wire anemometers can only provide point measurement data, making it difficult to obtain large-scale, continuous velocity field information, and are easily disturbed in high-speed, high-temperature velocity fields. Common non-contact measurement methods such as particle image velocimetry (PIV) measure the velocity field by tracking the movement of suspended particles in the velocity field, and can measure two-dimensional velocity fields. Classic three-dimensional velocity field measurement methods such as tomographic particle image velocimetry (Tomographic PIV) require more than six high-speed cameras and a complex synchronous trigger system to ensure synchronization of images acquired from different angles, which increases the complexity and cost of the test layout, and has a large amount of calculations, a long processing time, high requirements for computing resources and technology, and high limitations.

[0006] In summary, a three-dimensional spatial velocity field measurement device and method suitable for a helicopter nozzle is needed to simplify and optimize the system layout, reduce the amount of calculation, and obtain large-scale and continuous velocity field information. Summary of the invention

[0007] A brief overview of the present invention is provided below in order to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify key or important parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to a more detailed description discussed later.

[0008] In view of this, in order to solve the problem that the traditional three-dimensional velocity field measurement device and method in the prior art have complex layout and low calculation efficiency, the present invention provides a three-dimensional space velocity field measurement device and method suitable for a helicopter nozzle.

[0009] The first technical solution is as follows: a three-dimensional space velocity field measuring device suitable for a helicopter nozzle, comprising a first image acquisition device, a second image acquisition device, a laser, a reflector, a beam expander, a high-precision translation stage, a digital pulse signal generator and a computer;

[0010] The first image acquisition device and the second image acquisition device are connected to the computer respectively, the first image acquisition device and the second image acquisition device both include a double exposure camera, a filter and a lens, and the lenses of the first image acquisition device and the second image acquisition device are facing the nozzle of the nozzle;

[0011] The digital pulse signal generator is connected to the laser, the first image acquisition device, the second image acquisition device and the computer respectively, the emission end of the laser faces the reflector, and the digital pulse signal generator is used to trigger the double exposure camera of the first image acquisition device and the second image acquisition device to acquire images and trigger the laser to emit a laser beam;

[0012] The reflector is arranged on a moving plate of a high-precision translation stage, a beam expander is arranged above the reflector, and the reflector and the beam expander are used to expand the laser beam emitted by the laser into a laser plane perpendicular to the nozzle of the nozzle, and a flow field area is arranged on the laser plane;

[0013] The high-precision translation stage is used to move the first image acquisition device, the second image acquisition device and the reflector;

[0014] The computer is used for processing and storing data and controlling the movement of the high-precision translation stage.

[0015] Technical solution 2 is as follows: A three-dimensional space velocity field measurement method suitable for a helicopter nozzle includes the following steps:

[0016] S1. Build the measuring device and adjust the optical path;

[0017] S2. Calibrate the laser plane and calibrate the internal and external parameters of the double exposure camera;

[0018] S3. Control the high-precision translation stage to move to the specified position through a computer, trigger each component through a digital pulse signal generator and synchronously control two double-exposure cameras to collect particle images during the nozzle jet;

[0019] S4. According to the internal and external parameters of the double-exposure camera and the particle image, a three-dimensional velocity field based on the particle image is determined to obtain the three-dimensional spatial velocity field of the nozzle jet.

[0020] Furthermore, in S1, the installation position of the image acquisition device and the position of the laser are determined according to the nozzle position of the helicopter, the laser beam emitted by the laser is formed into a laser plane in the measurement area through a reflector and a beam expander, the position of each component is adjusted so that the laser plane is perpendicular to the nozzle of the nozzle, and the reflector, beam expander and image acquisition device are fixedly connected and installed on a high-precision translation stage.

[0021] Furthermore, in S2, a world coordinate system on the laser plane and a camera coordinate system with the optical center of the double-exposure camera as the origin are established, a checkerboard calibration plate is placed in the laser plane so that it is parallel to the laser plane, and two images of the checkerboard calibration plate under the double-exposure viewing angles are collected and recorded as the first image and the second image respectively. and the second image ;

[0022] The chessboard calibration plate is rotated to collect images at an angle in the pitch direction, and a pixel coordinate system is established. The internal and external parameters of the double-exposure camera are obtained by the Zhang Zhengyou calibration method. The internal parameters are: , , the external parameters are , ,in, The pixel coordinate system The focal length of the direction, The pixel coordinate system The focal length of the direction, is the radial distortion parameter, is the image principal point coordinate, R is the rotation matrix from the world coordinate system to the camera coordinate system, t The translation vector from the world coordinate system to the camera coordinate system.

[0023] Furthermore, the step S3 specifically includes the following steps:

[0024] S31. In the nozzle spray test, while waiting for the flow to reach a steady state, the particles are spread through the particle generator;

[0025] S32. Through the preset translation stage control program in the computer, the high-precision translation stage is controlled to move in the depth direction, and the moving distance is , wait for the high-precision translation stage to be in place, and then feed back the current position to the computer;

[0026] S33. The computer gives a trigger signal, and the digital pulse signal generator synchronously triggers the dual-exposure cameras in the two image acquisition devices. Under synchronous control, when the laser emits light for the first time, the two dual-exposure cameras start the first exposure acquisition. Frame image, after a preset delay time After t, the laser emits light again, and the two dual-exposure cameras perform the second exposure acquisition. Frame image, complete the acquisition of particle images in the flow field at the current position;

[0027] S34. Follow step S33 and loop n times to obtain n groups of the current depth position. Frame image and Frame image;

[0028] S35. Repeat steps S32 to S34 until the depth position is the total width of the jet area in the depth direction. , respectively obtain the double exposure camera in the first image acquisition device Frame image first sequence group and Frame image first sequence group , the double exposure camera in the second image acquisition device Frame image second sequence group and Frame image second sequence group , where each element in each image sequence group contains n images collected continuously.

[0029] Furthermore, the step S4 specifically includes the following steps:

[0030] S41. Based on the four corner points on the checkerboard calibration plate, a rectangular area is constructed to establish a velocity field plane grid;

[0031] S42. Obtain a transformation matrix group from the camera coordinate system to the world coordinate system according to the velocity field plane grid parameters and the corner point coordinates;

[0032] S43. Perform background removal on two types of frame images captured by the double-exposure cameras of the two image acquisition devices to obtain background-removed images of two types of frame images of the two image acquisition devices;

[0033] S44. Based on the background removal image and triangulation principle, the three-dimensional space velocity field is calculated;

[0034] In S41, based on the first image and the second image , all the corner points on the checkerboard calibration plate are detected by the corner point detection method, and the four corner points at the top, bottom, left and right edges are selected, namely the first corner point A, the second corner point B, the third corner point C and the fourth corner point D, and a rectangular area E is constructed based on the four corner points in the first image and the second image The image coordinates in and the internal and external parameters of the double exposure camera are used to obtain the three-dimensional coordinates of the four corner points in the camera coordinate system, which are the three-dimensional coordinates of the first corner point. , 3D coordinates of the second corner point , 3D coordinates of the third corner point and the 3D coordinates of the fourth corner point , integrate to get the three-dimensional coordinates of the four corner points of the camera coordinate system { , , , };

[0035] Calculate the transverse unit vector of the plane of the checkerboard calibration plate and the longitudinal unit vector ;

[0036] Transverse direction unit vector It is expressed as:

[0037] = / ;

[0038] Longitudinal unit vector It is expressed as:

[0039] = / ;

[0040] Defining the Grid G The row spacing is , the column spacing is , divide the plane of the rectangular area E into equidistant rectangular cells, where Indicates the number of rows in the grid. Indicates the number of columns of the grid, get the grid G The three-dimensional coordinates of each point , = + ;

[0041] In the above S42, if in the world coordinate system, according to the three-dimensional coordinates of the first corner point Infer the world coordinates of the other three corner points and integrate them to get the world coordinate system. , = , = , = ,in, is the world coordinate of the first corner point, is the world coordinate of the second corner point, is the world coordinate of the third corner point, is the world coordinate of the fourth corner point, is the current position of the laser plane in the depth direction, The spacing of each chessboard grid of the chessboard calibration board, is the number of vertical chessboard squares between the first corner point A and the second corner point B, is the number of horizontal chessboard squares between the first corner point A and the third corner point C;

[0042] According to the three-dimensional coordinates of the four corner points of the camera coordinate system { , , , } and the three-dimensional coordinates of the four corner points of the world coordinate system { , , , }, the rotation and translation matrix from the camera coordinate system to the world coordinate system is obtained through the Genlo-Kabsch algorithm , the distance of the laser plane in the depth direction The initial value is 0 and the maximum value is , for any current laser plane position in the depth direction , , get the transformation matrix group from the camera coordinate system to the world coordinate system ;

[0043] In S43, for Frame image first sequence group , The first group of images of the first sequence group of frame images The n images in are represented as , take the average value to get the first background image ,Will The first group of images of the first sequence group of frame images All elements of the ,get The first group of frames removes the background image , = ,right Frame image first sequence group , Frame image first sequence group , Frame image second sequence group and Frame image second sequence group The above processing is performed on all elements in the first image acquisition device to obtain the first double exposure camera Frame background removal image sequence group and first Frame background removal image sequence group and a double exposure camera in the second image acquisition device Frame background removal image sequence group and second Frame background removal image sequence group ;

[0044] In S44, for Frame The first image in the first group of background-removed images and Frame The first image in the first group of background-removed images , through the grid G The three-dimensional coordinates of each point and the internal and external parameters of the double exposure camera, and then the projection to Image coordinates of the first image in the first set of background-removed images in the frame , through the method of image digital correlation, the corresponding points of the same name for each grid point are obtained. Image coordinates of the first image in the first set of background-removed images in the frame ;

[0045] After the above processing is performed on the n groups of images collected by the first image acquisition device when z=0, the images projected to The first set of n sets of image coordinates on the background-free image and the projection to The first set of n sets of image coordinates on the background image of the frame are removed, and the mean of the two sets of n sets of image coordinates is taken to obtain the first Coordinates of the frame average image and first Coordinates of the frame average image ;

[0046] The above processing is performed on n groups of images collected by the second image acquisition device when z=0 and the average is taken to obtain the second Coordinates of the frame average image and second Coordinates of the frame average image ;

[0047] According to the internal and external parameters of the double exposure camera, the second Coordinates of the frame average image and second Coordinates of the frame average image Based on the principle of triangulation, the delay time in the camera coordinate system is obtained. The grid G ​​after t The three-dimensional coordinates of each point ;

[0048] The first transformation matrix from the camera coordinate system to the world coordinate system , get the grid G ​​in the world coordinate system The initial 3D coordinates of each point and the delay time The grid after t G The three-dimensional coordinates of each point , = + , = + ,in, Represents the rotation relationship between the camera coordinate system and the world coordinate system. Indicates the position of the origin of the camera coordinate system relative to the origin of the world coordinate system;

[0049] Then the three-dimensional velocity field is , ;

[0050] Get the position of any current laser plane in the depth direction The three-dimensional velocity field , the integration gets the depth direction from 0 to The three-dimensional velocity field .

[0051] The beneficial effects of the present invention are as follows: In the field of aerodynamic test and testing technology, the present invention proposes a method suitable for measuring the three-dimensional spatial velocity field of a helicopter nozzle, including building a scanning measurement system, using a checkerboard calibration plate for plane calibration to construct a standard spatial plane grid, using two double-exposure cameras to synchronously collect particle images, calculating the three-dimensional velocity field of each plane in the depth direction, and finally merging to generate a complete three-dimensional spatial velocity field; the present invention realizes the accurate measurement of the three-dimensional spatial velocity field of the helicopter nozzle, and solves the problem that the traditional measurement method can only provide limited plane data and is difficult to obtain a large range of continuous velocity field information; through accurate velocity field measurement, the scientific basis of the helicopter nozzle design is improved, the geometry and material selection of the nozzle are optimized, the thrust efficiency and fuel economy of the helicopter are improved, and support is provided for the research and development of flow control technology, and the control performance and stability of the helicopter are significantly improved; the present invention also simplifies the test layout, reduces the amount of calculation and test cost, provides high-precision and high-resolution velocity field data, captures more abundant flow information, and reduces measurement errors. Therefore, the present invention has important application value in the optimization design of helicopter nozzles and aerodynamic research. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0053] Figure 1 It is a structural schematic diagram of a three-dimensional space velocity field measurement device suitable for helicopter nozzle;

[0054] Figure 2 This is a schematic diagram of the corner points of the chessboard calibration board;

[0055] Figure 3 The figure is a flow chart of a three-dimensional velocity field measurement method suitable for helicopter nozzles.

[0056] Description of the drawings: 1. First image acquisition device; 2. Second image acquisition device; 3. Laser; 4. Reflector; 5. Beam expander; 6. High-precision translation stage; 7. Digital pulse signal generator; 8. Computer; 9. Nozzle nozzle; 10. Laser plane; 11. Flow field area. DETAILED DESCRIPTION

[0057] In order to make the technical solutions and advantages of the embodiments of the present invention more clearly understood, the exemplary embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than an exhaustive list of all the embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0058] Example 1: Reference Figure 1 The present embodiment is described in detail, a three-dimensional space velocity field measuring device suitable for a helicopter nozzle includes a first image acquisition device 1, a second image acquisition device 2, a laser 3, a reflector 4, a beam expander 5, a high-precision translation stage 6, a digital pulse signal generator 7 and a computer 8;

[0059] The first image acquisition device 1 and the second image acquisition device 2 are connected to a computer 8 respectively, and both the first image acquisition device 1 and the second image acquisition device 2 include a double exposure camera, a filter and a lens, and the lenses of the first image acquisition device 1 and the second image acquisition device 2 face toward the nozzle 9;

[0060] The digital pulse signal generator 7 is connected to the laser 3, the first image acquisition device 1, the second image acquisition device 2 and the computer 8 respectively. The emission end of the laser 3 faces the reflector 4. The digital pulse signal generator 7 is used to trigger the double exposure cameras of the first image acquisition device 1 and the second image acquisition device 2 to capture images and trigger the laser 3 to emit a laser beam.

[0061] The reflector 4 is arranged on a movable plate of a high-precision translation stage 6, and a beam expander 5 is arranged above the reflector 4. The reflector 4 and the beam expander 5 are used to expand the laser beam emitted by the laser 3 into a laser plane 10 perpendicular to the nozzle 9 of the nozzle, and a flow field area 11 is arranged on the laser plane 10;

[0062] The high-precision translation stage 6 is used to move the first image acquisition device 1, the second image acquisition device 2 and the reflector 4, thereby changing the position of the laser plane 10;

[0063] The computer 8 is used to process and store data and control the movement of the high-precision translation stage 6 .

[0064] Example 2: Reference Figure 1-Figure 3 The present embodiment is described in detail. A three-dimensional space velocity field measurement method applicable to a helicopter nozzle specifically comprises the following steps:

[0065] S1. Build the measuring device and adjust the optical path;

[0066] S2. Calibrate the laser plane and calibrate the internal and external parameters of the double exposure camera;

[0067] S3. Control the high-precision translation stage to move to the specified position through a computer, trigger each component through a digital pulse signal generator and synchronously control the two double-exposure cameras in the first image acquisition device and the second image acquisition device to collect particle images when the nozzle jet is in motion;

[0068] S4. According to the internal and external parameters of the double-exposure camera and the particle image, a three-dimensional velocity field based on the particle image is determined to obtain the three-dimensional spatial velocity field of the nozzle jet.

[0069] Furthermore, in S1, the installation position of the image acquisition device and the position of the laser are determined according to the nozzle position of the helicopter, and the laser beam emitted by the laser is formed into a high-precision laser plane in the measurement area through a reflector and a beam expander. In order to ensure the accuracy of the measurement, the position of each component is adjusted so that the laser plane is perpendicular to the nozzle of the nozzle, and the reflector, beam expander and image acquisition device are fixed together through guide rails, wrench sliders and other components to ensure that the relative positions between the components remain unchanged and are adjustable, and are installed on a high-precision translation stage.

[0070] Specifically, after the components are installed on the high-precision translation stage 6, and the laser plane 10 is made perpendicular to the moving direction of the high-precision translation stage 6, the positions of the reflector 4 and the beam expander 5 are adjusted so that the laser plane 10 is positioned at the starting position of the flow field area 11. At this time, the position of the laser plane 10 in the depth direction is defined as z=0; matte black camera paint is sprayed on the surface of the nozzle to suppress the degradation of image quality caused by the reflection on the surface of the helicopter model, the focal length of the lens in the image acquisition device is adjusted to make the image clear, and the aperture is opened to the maximum to ensure the best image contrast; based on the Schiempflug principle, the lens and the chip of the double exposure camera in the image acquisition device can be angled to increase the depth of field of the lens, so that when the optical axis of the camera is not perpendicular to the laser plane 10, all images in the laser plane 10 are clear.

[0071] Furthermore, in S2, a world coordinate system on the laser plane and a camera coordinate system with the optical center of the double-exposure camera as the origin are established, a checkerboard calibration plate is placed in the laser plane so that it is parallel to the laser plane, and images of the checkerboard calibration plate under the perspectives of the two double-exposure cameras are collected and recorded as first images and second images respectively. and the second image ;

[0072] The chessboard calibration plate is rotated to collect images at an angle in the pitch direction, and a pixel coordinate system is established. The internal and external parameters of the double-exposure camera are obtained by the Zhang Zhengyou calibration method. The internal parameters are: , , the external parameters are , ,in, The pixel coordinate system The focal length of the direction, The pixel coordinate system The focal length of the direction, is the radial distortion parameter, is the image principal point coordinate, R is the rotation matrix from the world coordinate system to the camera coordinate system, t is the translation vector from the world coordinate system to the camera coordinate system;

[0073] Specifically, the size of the checkerboard calibration plate accounts for more than 85% of the field of view.

[0074] Furthermore, the step S3 specifically includes the following steps:

[0075] S31. In the nozzle spray test, while waiting for the flow to reach a steady state, the particles are spread through the particle generator;

[0076] S32. Through the preset translation stage control program in the computer, the high-precision translation stage is controlled to move in the depth direction, and the moving distance is , wait for the high-precision translation stage to be in place, and then feed back the current position to the computer;

[0077] S33. The computer gives a trigger signal, and the digital pulse signal generator synchronously triggers the dual-exposure cameras in the two image acquisition devices. Under synchronous control, when the laser emits light for the first time, the two dual-exposure cameras start the first exposure acquisition. Frame image, after a preset delay time After t, the laser emits light again, and the two dual-exposure cameras perform the second exposure acquisition. Frame image, complete the acquisition of particle images in the flow field at the current position;

[0078] S34. Follow step S33 and loop n times to obtain n groups of the current depth position. Frame image and Frame image;

[0079] S35. Repeat steps S32 to S34 until the depth position is the total width of the jet area in the depth direction. , respectively obtain the double exposure camera in the first image acquisition device Frame image first sequence group and Frame image first sequence group , the double exposure camera in the second image acquisition device Frame image second sequence group and Frame image second sequence group , where each element in each image sequence group contains n images collected continuously.

[0080] Specifically, the preferred particles should have the characteristics of moderate particle size (generally 1-10 microns), high reflectivity, uniform distribution, density close to that of fluid, and chemical inertness. Commonly used preferred particles include polystyrene particles and oil fume particles;

[0081] refer to Figure 1 , the red arrow direction marked above the high-precision translation stage 6 moves in the depth direction;

[0082] In order to ensure the delay accuracy, t, Frame image and The displacement of particles in the frame image in the horizontal and vertical directions should not exceed 5 pixels.

[0083] Furthermore, the step S4 specifically includes the following steps:

[0084] S41. Based on the four corner points on the checkerboard calibration plate, a rectangular area is constructed to establish a velocity field plane grid;

[0085] S42. Obtain a transformation matrix group from the camera coordinate system to the world coordinate system according to the velocity field plane grid parameters and the corner point coordinates;

[0086] S43. Perform background removal on two types of frame images captured by the double-exposure cameras of the two image acquisition devices to obtain background-removed images of two types of frame images of the two image acquisition devices;

[0087] S44. Based on the background removal image and triangulation principle, the three-dimensional space velocity field is calculated;

[0088] In S41, based on the first image and the second image , all the corner points on the checkerboard calibration plate are detected by the corner point detection method, and the four corner points at the top, bottom, left and right edges are selected, namely the first corner point A, the second corner point B, the third corner point C and the fourth corner point D, and a rectangular area E is constructed based on the four corner points in the first image and the second image The image coordinates in and the internal and external parameters of the double exposure camera are used to obtain the three-dimensional coordinates of the four corner points in the camera coordinate system, which are the three-dimensional coordinates of the first corner point. , 3D coordinates of the second corner point , 3D coordinates of the third corner point and the 3D coordinates of the fourth corner point , integrate to get the three-dimensional coordinates of the four corner points of the camera coordinate system { , , , };

[0089] Calculate the transverse unit vector of the plane of the checkerboard calibration plate and the longitudinal unit vector ;

[0090] Transverse direction unit vector It is expressed as:

[0091] = / ;

[0092] Longitudinal unit vector It is expressed as:

[0093] = / ;

[0094] Defining the Grid G The row spacing is , the column spacing is , divide the plane of the rectangular area E into a series of equidistant rectangular cells, where Indicates the number of rows in the grid. Indicates the number of columns in the grid Get the grid G The three-dimensional coordinates of each point , = + ;

[0095] In S42, since the checkerboard calibration plate is parallel to the laser plane and perpendicular to the ground, for the four corner points, if in the world coordinate system, the three-dimensional coordinates of the first corner point are Infer the world coordinates of the other three corner points and integrate them to get the world coordinate system. , = , = , = ,in, is the world coordinate of the first corner point, is the world coordinate of the second corner point, is the world coordinate of the third corner point, is the world coordinate of the fourth corner point, is the current position of the laser plane in the depth direction, The spacing of each chessboard grid of the chessboard calibration board, is the number of vertical chessboard squares between the first corner point A and the second corner point B, is the number of horizontal chessboard squares between the first corner point A and the third corner point C;

[0096] According to the three-dimensional coordinates of the four corner points of the camera coordinate system { , , , } and the three-dimensional coordinates of the four corner points of the world coordinate system { , , , }, the rotation and translation matrix from the camera coordinate system to the world coordinate system is obtained through the Genlo-Kabsch algorithm , the distance of the laser plane in the depth direction The initial value is 0 and the maximum value is , for any current laser plane position in the depth direction , , get the transformation matrix group from the camera coordinate system to the world coordinate system ;

[0097] In S43, for Frame image first sequence group , The first group of images of the first sequence group of frame images The n images in are represented as , take the average value to get the first background image ,Will The first group of images of the first sequence group of frame images All elements of the ,get The first group of frames removes the background image , = ,right Frame image first sequence group , Frame image first sequence group , Frame image second sequence group and Frame image second sequence group The above processing is performed on all elements in the first image acquisition device to obtain the first double exposure camera Frame background removal image sequence group and first Frame background removal image sequence group and a double exposure camera in the second image acquisition device Frame background removal image sequence group and second Frame background removal image sequence group ;

[0098] In S44, for Frame The first image in the first group of background-removed images and Frame The first image in the first group of background-removed images , through the grid G The three-dimensional coordinates of each point and the internal and external parameters of the double exposure camera, and then the projection to Image coordinates of the first image in the first set of background-removed images in the frame , through the method of image digital correlation, the corresponding points of the same name for each grid point are obtained. Image coordinates of the first image in the first set of background-removed images in the frame ;

[0099] For n groups of images (i.e. Frame first to go to the background image and Frame image first removes the background image ) After the above processing, the projection to The first set of n sets of image coordinates on the background-free image and the projection to The first set of n sets of image coordinates on the background image of the frame are removed, and the mean of the two sets of n sets of image coordinates is taken to obtain the first Coordinates of the frame average image and first Coordinates of the frame average image ;

[0100] For n groups of images (i.e. Frame 2 to remove background image and Frame image second background removal image ) and take the average value to get the second Coordinates of the frame average image and second Coordinates of the frame average image ;

[0101] According to the internal and external parameters of the double exposure camera, the second Coordinates of the frame average image and second Coordinates of the frame average image Based on the triangulation principle, the delay time in the camera coordinate system is obtained. The grid G ​​after t The three-dimensional coordinates of each point ;

[0102] At this time, the grid G The three-dimensional coordinates of each point and the delay time The grid G ​​after t The three-dimensional coordinates of each point , are all in the camera coordinate system. To calculate the real velocity field, it is necessary to convert it into three-dimensional coordinates in the world coordinate system. According to the first transformation matrix from the camera coordinate system to the world coordinate system , get the grid G ​​in the world coordinate system The initial 3D coordinates of each point and the delay time The grid G ​​after t The three-dimensional coordinates of each point , = + , = + ,in, Represents the rotation relationship between the camera coordinate system and the world coordinate system. Indicates the position of the origin of the camera coordinate system relative to the origin of the world coordinate system;

[0103] Then the three-dimensional velocity field is , ;

[0104] Similarly, the position of any current laser plane in the depth direction is obtained The three-dimensional velocity field , the integration gets the depth direction from 0 to The three-dimensional velocity field .

[0105] Although the present invention has been described according to a limited number of embodiments, it will be apparent to those skilled in the art, with the benefit of the above description, that other embodiments may be envisioned within the scope of the invention thus described. In addition, it should be noted that the language used in this specification is selected primarily for readability and teaching purposes, rather than for explaining or defining the subject matter of the present invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is illustrative, not restrictive, with respect to the scope of the present invention, which is defined by the appended claims.

Claims

1. A three-dimensional space velocity field measurement device suitable for helicopter nozzle, characterized in that: It comprises a first image acquisition device (1), a second image acquisition device (2), a laser (3), a reflector (4), a beam expander (5), a high-precision translation stage (6), a digital pulse signal generator (7) and a computer (8); The first image acquisition device (1) and the second image acquisition device (2) are respectively connected to a computer (8), the first image acquisition device (1) and the second image acquisition device (2) both comprising a double exposure camera, a filter and a lens, and the lenses of the first image acquisition device (1) and the second image acquisition device (2) are facing the nozzle (9) of the nozzle; The digital pulse signal generator (7) is connected to the laser (3), the first image acquisition device (1), the second image acquisition device (2) and the computer (8) respectively. The emission end of the laser (3) faces the reflector (4). The digital pulse signal generator (7) is used to trigger the double exposure cameras of the first image acquisition device (1) and the second image acquisition device (2) to acquire images and to trigger the laser (3) to emit a laser beam. The reflector (4) is arranged on a movable plate of a high-precision translation stage (6), a beam expander (5) is arranged above the reflector (4), the reflector (4) and the beam expander (5) are used to expand the laser beam emitted by the laser (3) into a laser plane (10) perpendicular to the nozzle (9), and a flow field area (11) is arranged on the laser plane (10); The high-precision translation stage (6) is used to move the first image acquisition device (1), the second image acquisition device (2) and the reflector (4); The computer (8) is used to process and store data and control the movement of the high-precision translation stage (6).

2. A three-dimensional space velocity field measurement method suitable for helicopter nozzles, characterized in that: The three-dimensional space velocity field measuring device for a helicopter nozzle as claimed in claim 1 comprises the following steps: S1. Build the measuring device and adjust the optical path; S2. Calibrate the laser plane and calibrate the internal and external parameters of the double exposure camera; S3. Control the high-precision translation stage to move to the specified position through a computer, trigger each component through a digital pulse signal generator and synchronously control two double-exposure cameras to collect particle images during the nozzle jet; S4. According to the internal and external parameters of the double-exposure camera and the particle image, a three-dimensional velocity field based on the particle image is determined to obtain the three-dimensional spatial velocity field of the nozzle jet.

3. A three-dimensional space velocity field measurement method suitable for a helicopter nozzle according to claim 2, characterized in that: In S1, the installation position of the image acquisition device and the position of the laser are determined according to the nozzle position of the helicopter, the laser beam emitted by the laser is formed into a laser plane in the measurement area through a reflector and a beam expander, the position of each component is adjusted so that the laser plane is perpendicular to the nozzle of the nozzle, and the reflector, beam expander and image acquisition device are fixedly connected and installed on a high-precision translation stage.

4. A three-dimensional space velocity field measurement method suitable for a helicopter nozzle according to claim 3, characterized in that: In S2, a world coordinate system on the laser plane and a camera coordinate system with the optical center of the double-exposure camera as the origin are established, a checkerboard calibration plate is placed in the laser plane so that it is parallel to the laser plane, and images of the checkerboard calibration plate under the perspectives of the two double-exposure cameras are collected and recorded as first images respectively. and the second image ; The chessboard calibration plate is rotated to collect images at an angle in the pitch direction, and a pixel coordinate system is established. The internal and external parameters of the double-exposure camera are obtained by the Zhang Zhengyou calibration method. The internal parameters are: , , the external parameters are , ,in, The pixel coordinate system The focal length of the direction, The pixel coordinate system The focal length of the direction, is the radial distortion parameter, is the image principal point coordinate, R is the rotation matrix from the world coordinate system to the camera coordinate system, t The translation vector from the world coordinate system to the camera coordinate system.

5. A three-dimensional space velocity field measurement method suitable for a helicopter nozzle according to claim 4, characterized in that: The S3 specifically includes the following steps: S31. In the nozzle spray test, while waiting for the flow to reach a steady state, the particles are spread through the particle generator; S32. Through the preset translation stage control program in the computer, the high-precision translation stage is controlled to move in the depth direction, and the moving distance is , wait for the high-precision translation stage to be in place, and then feed back the current position to the computer; S33. The computer gives a trigger signal, and the digital pulse signal generator synchronously triggers the dual-exposure cameras in the two image acquisition devices. Under synchronous control, when the laser emits light for the first time, the two dual-exposure cameras start the first exposure acquisition. Frame image, after a preset delay time After t, the laser emits light again, and the two dual-exposure cameras perform the second exposure acquisition. Frame image, complete the acquisition of particle images in the flow field at the current position; S34. Follow step S33 and loop n times to obtain n groups of the current depth position. Frame image and Frame image; S35. Repeat steps S32 to S34 until the depth position is the total width of the jet area in the depth direction. , respectively obtain the double exposure camera in the first image acquisition device Frame image first sequence group and Frame image first sequence group , the double exposure camera in the second image acquisition device Frame image second sequence group and Frame image second sequence group , where each element in each image sequence group contains n images collected continuously.

6. A three-dimensional space velocity field measurement method suitable for a helicopter nozzle according to claim 5, characterized in that: The S4 specifically includes the following steps: S41. Based on the four corner points on the checkerboard calibration plate, a rectangular area is constructed to establish a velocity field plane grid; S42. Obtain a transformation matrix group from the camera coordinate system to the world coordinate system according to the velocity field plane grid parameters and the corner point coordinates; S43. Perform background removal on two types of frame images captured by the double-exposure cameras of the two image acquisition devices to obtain background-removed images of two types of frame images of the two image acquisition devices; S44. Based on the background removal image and triangulation principle, the three-dimensional space velocity field is calculated; In S41, based on the first image and the second image , all the corner points on the checkerboard calibration plate are detected by the corner point detection method, and the four corner points at the top, bottom, left and right edges are selected, namely the first corner point A, the second corner point B, the third corner point C and the fourth corner point D, and a rectangular area E is constructed based on the four corner points in the first image and the second image The image coordinates in and the internal and external parameters of the double exposure camera are used to obtain the three-dimensional coordinates of the four corner points in the camera coordinate system, which are the three-dimensional coordinates of the first corner point. , 3D coordinates of the second corner point , 3D coordinates of the third corner point and the 3D coordinates of the fourth corner point , integrate to get the three-dimensional coordinates of the four corner points of the camera coordinate system { , , , }; Calculate the transverse unit vector of the plane of the checkerboard calibration plate and the longitudinal unit vector ; Transverse direction unit vector It is expressed as: = / ； Longitudinal unit vector It is expressed as: = / ； Defining the Grid G The row spacing is , the column spacing is , divide the plane of the rectangular area E into equidistant rectangular cells, where Indicates the number of rows in the grid. Indicates the number of columns in the grid Get the grid G The three-dimensional coordinates of each point , = + ; In the above S42, if in the world coordinate system, according to the three-dimensional coordinates of the first corner point Infer the world coordinates of the other three corner points and integrate them to get the world coordinate system. , = , = , = ,in, is the world coordinate of the first corner point, is the world coordinate of the second corner point, is the world coordinate of the third corner point, is the world coordinate of the fourth corner point, is the current position of the laser plane in the depth direction, The spacing of each chessboard grid for the chessboard calibration board, is the number of vertical chessboard squares between the first corner point A and the second corner point B, is the number of horizontal chessboard squares between the first corner point A and the third corner point C; According to the three-dimensional coordinates of the four corner points of the camera coordinate system { , , , } and the three-dimensional coordinates of the four corner points of the world coordinate system { , , , }, the rotation and translation matrix from the camera coordinate system to the world coordinate system is obtained through the Genlo-Kabsch algorithm , the distance of the laser plane in the depth direction The initial value is 0 and the maximum value is , for any current laser plane position in the depth direction , , get the transformation matrix group from the camera coordinate system to the world coordinate system ; In S43, for Frame image first sequence group , The first group of images of the first sequence group of frame images The n images in are represented as , take the average value to get the first background image ,Will The first group of images of the first sequence group of frame images All elements of the ,get The first group of frames removes the background image , = ,right , Frame image first sequence group , Frame image second sequence group and Frame image second sequence group The above processing is performed on all elements in the first image acquisition device to obtain the first double exposure camera Frame background removal image sequence group and first Frame background removal image sequence group and a double exposure camera in the second image acquisition device Frame background removal image sequence group and second Frame background removal image sequence group ; In S44, for Frame The first image in the first group of background-removed images and Frame The first image in the first group of background-removed images , through the grid G The three-dimensional coordinates of each point and the internal and external parameters of the double exposure camera, and then the projection to Image coordinates of the first image in the first set of background-removed images. , through the method of image digital correlation, the corresponding points of the same name for each grid point are obtained. Image coordinates of the first image in the first set of background-removed images. ; After the above processing is performed on the n groups of images collected by the first image acquisition device when z=0, the images projected to The first set of n sets of image coordinates on the background-free image and the projection to The first set of n sets of image coordinates on the background image of the frame, and the average of the two sets of n sets of image coordinates, get the first Coordinates of the frame average image and first Coordinates of the frame average image ; The above processing is performed on n groups of images collected by the second image acquisition device when z=0 and the average is taken to obtain the second Coordinates of the frame average image and second Coordinates of the frame average image ; According to the internal and external parameters of the double exposure camera, the second Coordinates of the frame average image and second Coordinates of the frame average image Based on the principle of triangulation, the delay time in the camera coordinate system is obtained. The grid G ​​after t The three-dimensional coordinates of each point ; The first transformation matrix from the camera coordinate system to the world coordinate system , get the grid G ​​in the world coordinate system The initial 3D coordinates of each point and the delay time The grid G ​​after t The three-dimensional coordinates of each point , = + , = + ,in, Represents the rotation relationship between the camera coordinate system and the world coordinate system. Indicates the position of the origin of the camera coordinate system relative to the origin of the world coordinate system; Then the three-dimensional velocity field is , ; Get the position of any current laser plane in the depth direction The three-dimensional velocity field , the integration gets the depth direction from 0 to The three-dimensional velocity field .

Images