Small-scale vortex measurement device and method for water tunnel experiment integrating PTV and SPIV technologies

Abstract

The invention discloses a PTV and SPIV technology fused small-scale vortex measurement device and method for a water tunnel experiment, the device comprises a support mechanism, a mounting plate, a shooting mechanism and a water tunnel test mechanism, the shooting mechanism is mounted on the mounting plate, the mounting plate is mounted on the support mechanism, and the water tunnel test mechanism is arranged at the upper part of the shooting mechanism; the method comprises the following steps: calibrating; scattering the tracer particles; adjusting and shooting synchronous parameters; dividing a vortex region; carrying out PTV post-treatment; performing PIV (particle image velocimetry) post-treatment; performing space-time coupling averaging; a PTV and PIV fusion technology is adopted; the SPIV is used for calculating a 2D-3C velocity field; according to the invention, PTV and PIV technologies are fused, and advantage complementation is realized through partition cooperation; the method comprises the following steps: accurately measuring a vortex core by using PTV, covering the whole field by combining PIV, seamlessly splicing data through a precision algorithm and a space-time averaging technology, and establishing an SPIV algorithm based on a self-compiled program to calculate a 2D-3C velocity field, thereby realizing the reconstruction of the whole velocity field; and reliable experimental data support is efficiently provided for research and development of the underwater vehicle.

Description

Technical Field

[0001] This invention relates to the field of non-contact flow field measurement technology in experimental fluid mechanics, and relates to a small-scale vortex measurement device and method for water tunnel experiments that integrates PTV and SPIV technologies. Background Technology

[0002] With the deepening of fluid dynamics research, the accurate measurement of small-scale vortices in complex flow fields has become a key challenge. Stereoscopic particle imaging velocimetry and particle tracking velocimetry, as mainstream non-contact optical velocimetry methods, each have their own advantages and limitations.

[0003] While SPIV, through high-density tracer particles and cross-correlation algorithms, can output a gridded Eulerian velocity field and possesses high spatiotemporal resolution, its measurement nature dictates that the velocity vector is an average result within the query window. This inherently limits the method's ability to capture high-frequency, high-gradient flow structures with scales close to or smaller than the query window, particularly making it difficult to accurately resolve the micro-vortex structures in tip gap flows with small gaps. PTV, based on individual identification and cross-frame matching of low-density particles, directly acquires Lagrange trajectory information, achieving higher accuracy in local pulsating velocity measurements. However, its sparse particle distribution leads to insufficient flow field coverage, with data points being discrete and randomly distributed, making it difficult to provide a continuous gridded velocity field across the entire field of view. Existing single technologies cannot simultaneously achieve high resolution and a continuous gridded velocity field across the entire field of view: SPIV's inherent characteristics, such as the query window spatial averaging effect, optical system hardware resolution, and tracer particle dynamic response hysteresis, mask small-scale vortex structures, while PTV's particle sparsity limits its macroscopic descriptive capabilities. In complex flow scenarios, to accurately capture small-scale eddies, it is urgent to develop a measurement method that integrates the advantages of PTV and SPIV, retaining the local high-precision measurement capability of PTV while possessing the full-field coverage advantage of SPIV.

[0004] To address the aforementioned issues, this invention proposes a measurement device and method that integrates PTV and SPIV, aiming to overcome the limitations of single technologies and achieve high-precision full-field measurement of small-scale vortices, providing high-precision experimental data for complex vortex flow fields, especially small-scale vortex flow fields. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a small-scale vortex measurement device for water tunnel experiments that integrates PTV and SPIV technologies.

[0006] The objective of this invention is achieved as follows: a small-scale vortex measurement device for water tunnel experiments integrating PTV and SPIV technologies, comprising a support mechanism (1), a mounting plate (2), an imaging mechanism (3), and a water tunnel testing mechanism (4), wherein the imaging mechanism (3) is fixedly mounted on the mounting plate (2), the mounting plate (2) is fixedly mounted on the support mechanism (1), and the water tunnel testing mechanism (4) is disposed on the upper part of the imaging mechanism (3);

[0007] The water tunnel testing mechanism (4) includes a horizontally arranged rectangular fixing frame (401). A glass box (402) is fixedly bonded to the inner side of the rectangular fixing frame (401) with glass glue. A first fixing post (403) is fixedly provided on one side of the glass box (402). A baffle (404) is fixedly connected to the end of the first fixing post (403). The first fixing post (403) is located on the outside of the glass box (402), and the baffle (404) is located on the outside of the glass box (402). Inside the glass box (402), a second fixed column (405) is fixedly connected to the other side of the glass box (402). A hydrofoil (406) is fixedly connected to the end of the second fixed column (405). The second fixed column (405) is located on the other side of the glass box (402), and the hydrofoil (406) is located inside the glass box (402). A pinhole flow is formed between the hydrofoil (406) and the baffle (404). The axis of the hydrofoil (406) is perpendicular to the direction of water flow.

[0008] The mounting plate (2) is placed horizontally directly below the water tunnel test mechanism (4). The mounting plate (2) has a first fixing rod (301) fixed at each end of the shooting mechanism (3). A high-speed camera (302) is fixed at the end of the first fixing rod (301). A fixing seat (304) of the shooting mechanism (3) is fixed in the middle of the mounting plate (2). A second fixing rod (305) is fixed at the upper end of the fixing seat (304). A fixing plate (306) is fixedly connected to the top of the second fixing rod (305). A laser (303) is fixedly mounted on one side of the fixing plate (306). The laser ( 303) The hydrofoil (406) is vertically aligned with the inside of the water tunnel test mechanism (4). The laser (303) is used to generate sheet laser to irradiate particles on the vertical plane of the main flow direction. Two high-speed cameras (302) are symmetrically distributed on both sides of the laser (303) and are installed at the same height with the mounting plate (2) at a 45-degree angle. The two high-speed cameras (302) and the laser (303) are collinear, and the straight line formed is parallel to the water flow direction inside the water tunnel test mechanism (4). The flow field measurement area is set along the water flow direction to cover the downstream of the tip vortex flow from the blade tip gap of the hydrofoil (406) to the tip vortex flow direction within a range of 120 mm.

[0009] Furthermore, the bottom of the rectangular mounting bracket (401) is fixedly connected to an adapter plate (407), and the bottom of the adapter plate (407) is fixedly provided with two water prisms (408). The two water prisms (408) are in the shape of a right triangle with an inverted 45-degree cross section, and the two water prisms (408) are respectively fixed on both sides of the laser (303).

[0010] Furthermore, the support mechanism (1) includes an X-axis housing (101), an X-axis motor lead screw (102) is provided at one end and inside the X-axis housing (101), and a first movable seat (103) connected to the X-axis motor lead screw (102) is movably mounted on the X-axis housing (101).

[0011] Furthermore, a Z-axis housing (104) is fixedly installed on the first movable seat (103), and a Z-axis motor lead screw (105) is provided at one end and inside the Z-axis housing (104). A second movable seat (106) connected to the Z-axis motor lead screw (105) is movably installed on the Z-axis housing (104).

[0012] Furthermore, a Y-axis housing (107) is fixedly installed on the second movable seat (106), and a Y-axis motor lead screw (108) is provided at one end and inside the Y-axis housing (107). The mounting plate (2) connected to the Y-axis motor lead screw (108) is movably installed on the Y-axis housing (107); a connecting plate (109) is provided on the back of the Z-axis housing (104), and a reinforcing plate (110) is welded between the connecting plate (109) and the first movable seat (103).

[0013] A method for measuring small-scale eddies in water tunnel experiments that integrates PTV and SPIV technologies includes the following steps:

[0014] S1. Two high-speed cameras (302) are used to take multiple pictures to establish the mapping relationship between the camera image plane and the physical space and obtain the object-image ratio;

[0015] S2. The tracer particles are dispersed into the water tunnel test mechanism (4) through the pre-drilled hole on the glass box (402); the external circulating water pump is turned on to make the fluid flow in the water tunnel test mechanism (4), thereby ensuring that the tracer particles are more evenly distributed.

[0016] S3. Connect two high-speed cameras (302) using a BNC cable, set the trigger mode of the high-speed camera (302) to ensure that the two high-speed cameras (302) can synchronously capture high-speed images, adjust the laser intensity of the laser (303) and the aperture, sampling frequency and exposure time of the two high-speed cameras (302) to synchronously capture high-speed images of the evolution process of the pinhole vortex and obtain the original image.

[0017] S4. Based on the particle rotation features in the original image, the vortex structure region is selected for segmentation processing, laying the foundation for subsequent high-precision analysis;

[0018] S5. Process high-speed camera images of the vortex tube region based on particle tracking velocimetry method to obtain two-dimensional velocity field characteristics;

[0019] S6. In the non-vortex tube region, the traditional particle image velocimetry method is used to calculate the average displacement vector of the particle population through the cross-correlation function of two consecutive frames of images, and to reconstruct the gridded two-dimensional velocity field.

[0020] S7. Spatial interpolation and averaging are performed on the two-dimensional velocity field after particle tracking and velocimetry processing to obtain a gridded velocity field. The grid size is consistent with the particle image velocimetry output. On this basis, the transient velocity field results in the gridded velocity field are time-averaged to eliminate transient disturbances. The particle image velocimetry processing results are time-averaged to obtain an average velocity field that eliminates transient disturbances.

[0021] S8. Based on the fusion technology of particle image velocimetry and particle tracking velocimetry, the two-dimensional velocity field features and the gridded velocity field are used to construct a full-field two-dimensional field through world coordinate unification and regional stitching matching algorithm;

[0022] S9. The full-field two-dimensional field of the two high-speed cameras (302) is post-processed and calculated using Matlab based on the three-dimensional particle image velocimetry algorithm to obtain the 2D-3C velocity field results.

[0023] Furthermore, the steps for constructing the full-field two-dimensional field using the world coordinate unification and region stitching matching algorithm in S8 are as follows:

[0024] With the world coordinates unified and the calibration plate as a reference, the first and second homography matrices of the two high-speed cameras (302) are solved respectively. Both the first and second homography matrices are 3×3 homogeneous matrices. The particle velocity of particle tracking measurement and the velocity of particle image measurement grid are unified to the same world coordinate system, and a regular grid with the same spacing as the original particle image measurement grid is constructed in the world coordinate system.

[0025] Particle tracking velocities are gridded. For any grid node, the velocities of surrounding particle tracking velocities are mapped to the node using a Gaussian weighted average, thus obtaining the particle tracking velocities interpolated velocity field corresponding to the particle image velocities grid.

[0026] The boundaries of the particle image velocimetry and particle tracking velocimetry regions are linearly and gradually merged to generate a mask to distinguish the particle tracking velocimetry processing region from the particle image velocimetry processing region. A transition zone is set within three times the spacing width inside and outside the boundary, and the weights in the transition zone decrease linearly to achieve seamless stitching of the two types of velocities.

[0027] Furthermore, the formula for calculating the Gaussian weighted average is as follows:

[0028] ;

[0029] in, The sample of particle velocities obtained from particle tracking measurements is collected within a local window of radius, and... , Represented as grid spacing, Represented as a grid node, Represented as particle world coordinates.

[0030] The linear decrease in weights within the transition band is calculated as follows:

[0031] ;

[0032] in, Represented as weights within the transition band, and on the boundary line Core area outer area , It is represented as a defined distance function, which is the shortest distance from node G to the mask boundary.

[0033] Furthermore, the two high-speed cameras (302) output full-field two-dimensional fields that are aligned with the world coordinate system and maintain the standard particle image velocimetry data format after fusion, which are used for subsequent 2D-3C velocity field calculations.

[0034] Furthermore, the post-processing calculation steps in S9 based on the 3D particle image velocimetry algorithm are as follows:

[0035] The two-dimensional velocity fields acquired by the two high-speed cameras are combined to calculate the 2D-3C velocity field. The specific formula is as follows:

[0036] ;

[0037] ;

[0038] ;

[0039] Let the velocity components of high-speed camera A and high-speed camera B in the X direction be u1 and u2, respectively, and their velocity components in the Y direction be v1 and v2, respectively. Let α1 and α2 be the camera mounting angles, both 45°. Then the final three-dimensional velocity components u, v, and w are:

[0040] ;

[0041] ;

[0042] ;

[0043] The three-dimensional velocity vector on each grid node is calculated point by point, and a complete 2D-3C velocity field is finally constructed. The output 2D-3C velocity field data is in standard SPIV format and can be directly used for subsequent flow field analysis tasks such as vorticity analysis, turbulent structure identification, and vortex trajectory tracking.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] This invention innovatively integrates particle tracking velocimetry and stereo particle image velocimetry technologies, and constructs a new measurement paradigm with partitioned collaborative processing. It effectively overcomes the inherent limitations of single technologies. It accurately utilizes PTV technology to perform high-precision, high-resolution particle trajectory tracking in key microscale regions such as the vortex core to capture details of dramatic velocity gradient changes. At the same time, it uses SPIV technology to provide a full-field coverage, stable and efficient continuous gridded velocity field distribution in the peripheral macroscopic flow field region. This complementary fusion strategy fundamentally solves the technical contradiction of difficulty in balancing high resolution and large field of view in traditional measurement methods, laying a solid methodological foundation for the accurate analysis of complex flow field structures.

[0046] Based on the fusion paradigm, this invention achieves seamless splicing and smooth transition of two heterogeneous velocity field data through a series of sophisticated algorithms, including world coordinate unification, PTV scattered point gridding, and linear gradual fusion of regional boundaries. This overcomes the bottleneck of single SPIV technology's inability to capture microscale vortices. Furthermore, it introduces spatiotemporal coupled averaging technology to perform dual averaging of the transient velocity field in both time and space dimensions, effectively suppressing random turbulence disturbances and measurement noise, and greatly enhancing the expression of the stable morphology and intrinsic characteristics of the core vortex structure. The final output of a unified, complete, and high-fidelity 2D-3C velocity field retains the particle-level resolution provided by PTV while possessing the full-field continuity of SPIV, significantly improving the accuracy of capturing microscale vortex structures and the reliability of the overall flow field data.

[0047] This invention represents a revolutionary measurement method and constitutes a complete, high-precision experimental measurement device capable of automated scanning and precise positioning. It enables high-precision full-field measurement of small-scale vortices in water tunnel experiments, providing an unprecedentedly powerful tool for deeply revealing the physical mechanisms of complex flows such as tip gap vortices. The highly reliable experimental data it produces can be directly used to verify and improve computational fluid dynamics models, providing crucial and reliable experimental data and solid technical support for the optimized design, vibration reduction, noise reduction, and performance improvement of underwater vehicles and high-performance turbomachinery, thus possessing significant engineering application value. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0049] Figure 1 This is a schematic diagram of the front structure of the present invention.

[0050] Figure 2 This is a schematic diagram of the rear view structure of the present invention.

[0051] Figure 3 This is a partial structural front view of the present invention.

[0052] Figure 4 This is a rear view schematic diagram of part of the structure of the present invention.

[0053] Figure 5 This is a schematic diagram of the support mechanism of the present invention.

[0054] Figure 6 This is a schematic diagram of the steps of using the present invention.

[0055] Figure 7 A schematic diagram showing the segmentation of the vortex region for the method of using this invention.

[0056] Figure 8 This is a schematic diagram illustrating the calculation principle of particle image tracking technology in the application method of the present invention.

[0057] Figure 9 This is a schematic diagram illustrating the spatial coupling averaging principle of the method of use of the present invention.

[0058] Figure 10 This is a schematic diagram illustrating the PTV and SPIV fusion technology of the present invention.

[0059] In the diagram, 1. Support mechanism; 101. X-axis housing; 102. X-axis motor lead screw; 103. First moving seat; 104. Z-axis housing; 105. Z-axis motor lead screw; 106. Second moving seat; 107. Y-axis housing; 108. Y-axis motor lead screw; 109. Connecting plate; 110. Reinforcing plate; 2. Mounting plate; 3. Imaging mechanism; 301. First fixed rod; 302. High-speed camera; 303. Laser; 304. Fixed seat; 305. Second fixed rod; 306. Fixed plate; 4. Water tunnel testing mechanism; 401. Rectangular fixed frame; 402. Glass box; 403. First fixed column; 404. Baffle; 405. Second fixed column; 406. Hydrofoil; 407. Adapter plate; 408. Water prism. Detailed Implementation

[0060] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] like Figure 1-5 As shown, a small-scale vortex measurement device for water tunnel experiments integrating PTV and SPIV technologies includes a support mechanism 1, a mounting plate 2, an imaging mechanism 3, and a water tunnel test mechanism 4. The imaging mechanism 3 is fixedly mounted on the mounting plate 2, the mounting plate 2 is fixedly mounted on the support mechanism 1, and the water tunnel test mechanism 4 is located on the upper part of the imaging mechanism 3.

[0062] The water tunnel testing mechanism 4 includes a horizontally arranged rectangular fixing frame 401. A glass box 402 is fixedly bonded to the inner side of the rectangular fixing frame 401 with glass glue. A first fixing post 403 is fixedly installed on one side of the glass box 402. A baffle 404 is fixedly connected to the end of the first fixing post 403. The first fixing post 403 is located on the outside of the glass box 402, and the baffle 404 is located inside the glass box 402. A second fixing post 405 is fixedly connected to the other side of the glass box 402. A hydrofoil 406 is fixedly connected to the end of the second fixing post 405. The second fixing post 405 is located on the other outside of the glass box 402, and the hydrofoil 406 is located inside the glass box 402. A pinhole flow is formed between the hydrofoil 406 and the baffle 404, and the axis of the hydrofoil 406 is perpendicular to the direction of water flow.

[0063] Mounting plate 2 is placed horizontally directly below water tunnel testing mechanism 4. First fixing rods 301 from the imaging mechanism 3 are fixedly mounted at both ends of mounting plate 2. A high-speed camera 302 is fixedly mounted at the end of the first fixing rod 301. A fixing seat 304 from the imaging mechanism 3 is fixedly mounted in the middle of mounting plate 2. A second fixing rod 305 is fixedly mounted at the upper end of the fixing seat 304. A fixing plate 306 is fixedly connected to the top of the second fixing rod 305. A laser 303 is fixedly mounted on one side of the fixing plate 306. The laser 303 is vertically aligned with the water. Inside the water tunnel test mechanism 4, a hydrofoil 406 and a laser 303 are used to generate sheet lasers to irradiate particles on the plane perpendicular to the mainstream flow direction. Two high-speed cameras 302 are symmetrically distributed on both sides of the laser 303 and are installed at the same height with the mounting plate 2 at a 45-degree angle. The two high-speed cameras 302 and the laser 303 are collinear, and the straight line formed is parallel to the water flow direction inside the water tunnel test mechanism 4. The flow field measurement area is set along the water flow direction to cover the downstream flow of the tip vortex flow within a 120 mm range from the tip gap of the hydrofoil 406 to the tip vortex flow direction range.

[0064] Laser 303 is a Photonics-DM30-527-Nd / YLF with a repetition rate of 3kHz, capable of generating sheet lasers with a thickness of 1±0.1mm; high-speed camera 302 is a Phantom-M310 with a CMOS sensor as the recording medium, featuring high speed, low power consumption and clear images, with a maximum recording speed of 100,000 frames per second (fps), which fully meets the needs of leaf tip gap flow research. In this experiment, the acquisition frequency of both high-speed cameras 302 was set to 18000Hz, and the resolution was 256×256.

[0065] In this embodiment, preferably, the bottom of the rectangular fixing frame 401 is fixedly connected to the adapter plate 407, and the bottom of the adapter plate 407 is fixedly provided with two water prisms 408. The two water prisms 408 are in the shape of a right triangle with an inverted 45-degree cross section, and the two water prisms 408 are respectively fixed on both sides of the laser 303.

[0066] It should be noted that the water prism 408 is designed to eliminate the cross-interface refraction effect caused when the high-speed camera 302 captures images of the interior of the water tunnel test mechanism 4.

[0067] In this embodiment, preferably, the support mechanism 1 includes an X-axis housing 101, an X-axis motor lead screw 102 is provided at one end and inside the X-axis housing 101, and a first movable seat 103 connected to the X-axis motor lead screw 102 is movably mounted on the X-axis housing 101.

[0068] It should be noted that the X-axis motor lead screw 102 is set to realize power output, and the lead screw drives the first moving seat 103 to move and adjust on the X-axis housing 101, so that the shooting mechanism 3 can move and adjust on the X-axis.

[0069] In this embodiment, preferably, a Z-axis housing 104 is fixedly installed on the first movable seat 103, a Z-axis motor lead screw 105 is provided at one end and inside the Z-axis housing 104, and a second movable seat 106 connected to the Z-axis motor lead screw 105 is movably installed on the Z-axis housing 104.

[0070] It should be noted that the Z-axis motor lead screw 105 is set to realize power output, and the second moving seat 106 is moved and adjusted on the Z-axis housing 104 by the lead screw, so that the shooting mechanism 3 can be moved and adjusted on the Z-axis.

[0071] In this embodiment, preferably, a Y-axis housing 107 is fixedly installed on the second movable seat 106, a Y-axis motor lead screw 108 is provided at one end and inside the Y-axis housing 107, and a mounting plate 2 connected to the Y-axis motor lead screw 108 is movably installed on the Y-axis housing 107.

[0072] It should be noted that the Y-axis motor lead screw 108 is set to realize power output, and the lead screw drives the mounting plate 2 to move and adjust on the Y-axis housing 107, so that the shooting mechanism 3 can move and adjust on the Y-axis.

[0073] In this embodiment, preferably, a connecting plate 109 is provided on the back of the Z-axis housing 104, and a reinforcing plate 110 is welded between the connecting plate 109 and the first movable seat 103;

[0074] It should be noted that the Z-axis housing 104 is fixedly installed by the connecting plate 109 to maintain the vertical stability of the Z-axis housing 104, and the reinforcing plate 110 can ensure the reinforced connection of the Z-axis housing 104 on the first moving seat 103, thus ensuring the stability and balance of the Z-axis housing 104 during use.

[0075] refer to Figure 6-10 A method for using a small-scale vortex measurement device for water tunnel experiments that integrates PTV and SPIV technologies includes the following steps:

[0076] S1. Two high-speed cameras 302 are used to take multiple pictures to establish the mapping relationship between the camera image plane and the physical space, and to obtain the object-to-image ratio;

[0077] This embodiment employs a double-sided, double-sided dot matrix target for multiple calibration operations. By translating and rotating the calibration plate, multi-view imaging is simulated. This is equivalent to moving the high-speed camera 302 while keeping the calibration plate fixed, thereby constructing a set of viewpoints covering various spatial directions and avoiding ill-conditioned matrix problems caused by insufficient viewpoints. By comparing the scaling and perspective changes of the calibration plate dot matrix in the horizontal and vertical directions under different viewpoints, the mapping relationship between the camera image plane and physical space is established, thereby completing the transformation from the camera coordinate system to the calibration plate coordinate system. This allows for the acquisition of the key object-to-image ratio, providing a geometric basis for subsequent velocity field reconstruction and velocity field analysis.

[0078] S2. The tracer particles are dispersed into the water tunnel test mechanism 4 through the pre-drilled holes on the glass box 402; the external circulating water pump is turned on to make the fluid flow in the water tunnel test mechanism 4, thereby ensuring that the tracer particles are more evenly distributed.

[0079] The reserved hole is set on the upper part or side of the glass box 402 for the external circulating water pump to input the fluid into the glass box 402. In addition to transporting the fluid, the circulating water pump can also make the tracer particles more evenly distributed.

[0080] The tracer particles are hollow glass beads with a diameter of 100±8µm. The density of the tracer particles is very close to that of water, and they can remain suspended in water. The tracer particle concentration is 5-10 particles per cubic millimeter. The tracer particles can ensure that there are enough particles in the field of view of the high-speed camera 302 to accurately reflect the flow field information, while avoiding the difficulty of image recognition due to excessive particle density.

[0081] S3. Connect two high-speed cameras 302 using a BNC cable, set the trigger mode of the high-speed cameras 302 to ensure that the two high-speed cameras 302 can synchronously capture high-speed video images, adjust the laser intensity of the laser 303 and the aperture, sampling frequency and exposure time of the two high-speed cameras 302, synchronously capture high-speed video of the evolution process of the pinhole vortex, and obtain the original image.

[0082] BNC cable is a type of cable with strong signal transmission stability, which can ensure that the two high-speed cameras 302 can achieve precise synchronous shooting, providing a time-consistent image data source for subsequent three-dimensional reconstruction of flow field data;

[0083] S4. Based on the particle rotation features in the original image, the vortex structure region is selected for segmentation processing, laying the foundation for subsequent high-precision analysis;

[0084] For vortex region segmentation, the particle rotation feature region in the original image is generated based on particle image velocimetry and subsequently represented as PIV, which initially determines the approximate location of the vortex structure. Combined with particle tracking velocimetry, the subsequent representation is represented by the PTV algorithm. Based on the observation results of the vortex region, the image of a vortex tube structure with a diameter of about 2mm in the water tunnel is selected for segmentation and processing. The segmented region is combined with the PTV algorithm for fine analysis of the region, laying the foundation for subsequent high-precision vortex structure identification and velocity field extraction.

[0085] S5. Process high-speed camera images of the vortex tube region based on particle tracking velocimetry method to obtain two-dimensional velocity field characteristics;

[0086] S6. In the non-vortex tube region, the traditional particle image velocimetry method is used to calculate the average displacement vector of the particle population through the cross-correlation function of two consecutive frames of images, and to reconstruct the gridded two-dimensional velocity field.

[0087] S7. Spatial interpolation and averaging are performed on the two-dimensional velocity field after particle tracking and velocimetry processing to obtain a gridded velocity field. The grid size is consistent with the particle image velocimetry output. On this basis, the transient velocity field results in the gridded velocity field are time-averaged to eliminate transient disturbances. The particle image velocimetry processing results are time-averaged to obtain an average velocity field that eliminates transient disturbances.

[0088] PTV post-processing involves performing particle tracking and velocimetry on the segmented vortex region image to obtain high-precision tracer particle motion information. Continuous image frames within the vortex region are processed to identify and accurately locate the center coordinates of individual tracer particles. Based on the principles of continuity and spatial proximity of tracer particle motion within short time intervals, tracer particle matching is performed between adjacent image frames, successfully constructing the time-series trajectory of a single tracer particle. Based on the successfully matched tracer particle trajectories, the movement of the tracer particles within known precise time intervals is calculated. Displacement within And apply the basic velocity formula The instantaneous velocity vector of each tracked particle at the corresponding moment is directly calculated. The discrete velocity vector data corresponding to the spatial position of each tracked particle are then reconstructed into a continuous and dense two-dimensional velocity vector field within the vortex region through appropriate mathematical interpolation methods. This PTV processing workflow can achieve fine motion tracking at the particle level within a selected region, effectively capturing the unique local high gradient velocity change characteristics of micro-scale vortex structures, and providing a high-resolution local velocity data foundation for subsequent fusion analysis.

[0089] Post-processing of PIV: Non-vortex regions, i.e., areas not analyzed by PTV, are processed using the traditional PIV method. By dividing two consecutive frames into overlapping grids, the cross-correlation function of the tracer particle grayscale images in each window is calculated to determine the average displacement vector of the tracer particle population. Based on the relationship between displacement and inter-frame time interval, local velocity information can be obtained, thereby reconstructing the gridded two-dimensional velocity field of the entire region. The basic calculation formula for PIV is as follows:

[0090] ;

[0091] in, Indicates at image coordinates The velocity vector at that point This represents the average displacement vector of the tracer particle at that location. The time interval between two adjacent frames is represented by the image frame. By sliding the window across the entire image region sequentially, performing the cross-correlation matching described above, and calculating the velocity, a complete gridded two-dimensional velocity field distribution map can be generated.

[0092] Although PIV has certain limitations in resolving small-scale structures, it still has a stable and efficient velocity field extraction capability in macroscopic regions. It can complement the PTV analysis results to construct a complete flow field information distribution map. This partitioning and fusion strategy allows each region of the image to use the algorithm most suitable for its scale characteristics, improving the overall measurement accuracy and reliability.

[0093] Spatiotemporal coupled averaging is performed on the PTV velocity fields acquired by each high-speed camera 302, with spatial dimensional coupling averaging. Based on the spatial distribution and motion correlation of tracer particles in the velocity field, velocity information at different spatial locations is integrated. By analyzing the trajectory and velocity vector of tracer particles in the spatial domain, the velocities of tracer particles in similar spatial correlations are averaged to weaken the influence of local spatial disturbances and highlight the true characteristics of the steady-state vortex structure in spatial distribution. This lays a solid foundation for subsequent accurate analysis of the vortex spatial morphology and velocity field characteristics. Spatial averaging is used to converge the dispersed and disturbed tracer particle motion characteristics towards a more regular shape that conforms to the steady-state vortex spatial structure. On this basis, the transient velocity field results are time-averaged to eliminate transient disturbances. The PIV processing results are also time-averaged to obtain an average velocity field with transient disturbances eliminated.

[0094] S8. Based on the fusion technology of particle image velocimetry and particle tracking velocimetry, the two-dimensional velocity field features and the gridded velocity field are used to construct a full-field two-dimensional field through world coordinate unification and regional stitching matching algorithm;

[0095] The PIV and PTV fusion technology, based on the processing results of PIV and PTV, fuses PIV and PTV through a world coordinate unification and region stitching matching algorithm. It integrates the perspective data of two high-speed cameras 302, completes the boundary matching and full-field stitching of the PTV region and PIV region under a unified world coordinate system, and finally constructs a complete two-dimensional velocity field covering the entire field.

[0096] S9. The full-field two-dimensional field of the two high-speed cameras 302 is post-processed and calculated using Matlab based on the three-dimensional particle image velocimetry algorithm to obtain the 2D-3C velocity field results.

[0097] Furthermore, the steps for constructing the full-field two-dimensional field using the world coordinate unification and region stitching matching algorithm in S8 are as follows:

[0098] With the world coordinate system unified and the calibration plate as a reference, the first and second homography matrices of the two high-speed cameras 302 are solved respectively. Both the first and second homography matrices are 3×3 homogeneous matrices. The particle velocity of particle tracking measurement and the velocity of particle image measurement grid are unified to the same world coordinate system, and a regular grid with the same spacing as the original particle image measurement grid is constructed in the world coordinate system.

[0099] Particle tracking velocities are gridded. For any grid node, the velocities of surrounding particle tracking velocities are mapped to the node using a Gaussian weighted average, thus obtaining the particle tracking velocities interpolated velocity field corresponding to the particle image velocities grid.

[0100] The boundaries of particle image velocimetry and particle tracking velocimetry regions are linearly and gradually merged to generate a mask to distinguish the particle tracking velocimetry processing region from the particle image velocimetry processing region. A transition zone is set within three times the spacing width inside and outside the boundary, and the weight decreases linearly within the transition zone to achieve seamless stitching of the two types of velocities.

[0101] All PTV particle velocities and PIV mesh velocities are unified to the world coordinate system, ensuring that the velocity vectors at the same physical point share the same spatial reference. The formula for calculating world coordinates from image coordinates is shown below:

[0102] ;

[0103] PTV scatter meshing, constructing a mesh with the same spacing as the original PIV mesh within the world coordinate system. The regular grid, Represented as grid spacing, grid nodes are denoted as For any node Centered on this node, Collect all PTV particle velocity samples within a local window of radius. ,Right now The world coordinates of the sample are ,Right now A Gaussian weighted average is used to map samples to nodes. , Take 1.5 This method suppresses long-range noise while preserving local fine-scale structure, thereby obtaining a PTV interpolated velocity field that corresponds one-to-one with the PIV grid in the same world coordinate system. This provides a grid-based reference for subsequent region fusion. The specific calculation formula is as follows:

[0104] ;

[0105] ;

[0106] The boundaries between the PIV and PTV regions are linearly and gradually blended. To achieve seamless region stitching, a mask function is designed. With linearly gradual weights Divide functional areas and generate masks To distinguish between high-resolution areas and background areas, For nodes Located in the PTV processing area; For the remaining areas; and on the boundary lines Core area outer area Define the distance function For nodes The closest distance to the mask boundary; 3 both inside and outside the boundary. A transition band is set within the width, and the weight within the transition band is... A linear decrease yields the fusion speed, thus enabling the core region to achieve this. Preserve small-scale details from PTV; transition area The speed changes continuously; the outer area The PIV speed is used throughout. The specific calculation formula is as follows:

[0107] ;

[0108]

[0109] The output images are generated by two high-speed cameras (302), each outputting two full-field two-dimensional fields in the world coordinate system. and The coordinate system features of both are fully aligned with the original PIV grid, thus maintaining the standard PIV data format, which can be directly used for subsequent three-dimensional SPIV calculations. The world coordinate unification and regional stitching matching algorithm realizes the reconstruction of 2D velocity field based on the fusion of PTV and PIV. It not only retains the high-resolution information of small-scale structures, but also ensures the continuity and integrity of the flow field structure over a large area, laying a reliable foundation for subsequent 2D-3C velocity field analysis.

[0110] Furthermore, the two high-speed cameras 302, after fusion, output full-field two-dimensional fields that are aligned with the world coordinate system and maintain the standard particle image velocimetry data format, which are used for subsequent 2D-3C velocity field calculations.

[0111] Furthermore, the steps of the 3D particle image velocimetry algorithm in S9 are as follows:

[0112] Two-dimensional velocity field preprocessing, for the fused two-dimensional velocity field and Temporal averaging was performed to reduce the impact of transient disturbances and measurement noise on subsequent 2D-3C velocity field synthesis; stable two-dimensional velocity field data were obtained from the perspectives of high-speed camera A and high-speed camera B, respectively.

[0113] The geometric projection formula synthesizes the three-dimensional velocity components. Using the geometric projection formula combined with the angular relationships obtained from calibration, and based on the camera arrangement angles, let the tilt angles of the two high-speed cameras 302 relative to the x-axis be... and By using the geometric relationship along the line of sight, the three-dimensional velocity components of the flow field are inverted and calculated. , , Finally, the reconstruction included , , Complete 2D-3C velocity field with three directional components;

[0114] Furthermore, the geometric projection formula for synthesizing three-dimensional velocity components is as follows:

[0115] ;

[0116] ;

[0117] ;

[0118] in: , These are the velocity components in the x-direction of high-speed camera A and high-speed camera B, respectively. , These are the velocity components in the y-direction for high-speed camera A and high-speed camera B, respectively. The velocity component in the x-direction; The velocity component in the y-direction; The velocity component in the z-direction (perpendicular to the laser sheet's optical plane); and Both are 45°; , , This constitutes the final three-dimensional velocity vector;

[0119] After simplification, we get:

[0120] ;

[0121] ;

[0122] ;

[0123] A 2D-3C velocity field is constructed by calculating the three-dimensional velocity vector on each grid node point by point based on the above synthesis formula, and finally constructing a complete 2D-3C velocity field.

[0124] The final output 2D-3C velocity field data is in standard SPIV format and can be directly used for subsequent flow field analysis tasks such as vorticity analysis, turbulent structure identification, and vortex trajectory tracking.

[0125] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A small-scale vortex measurement device for water tunnel experiments integrating PTV and SPIV technologies, characterized in that: It includes a support mechanism (1), a mounting plate (2), a shooting mechanism (3) and a water tunnel testing mechanism (4). The shooting mechanism (3) is fixedly mounted on the mounting plate (2), the mounting plate (2) is fixedly mounted on the support mechanism (1), and the water tunnel testing mechanism (4) is located on the upper part of the shooting mechanism (3). The water tunnel testing mechanism (4) includes a horizontally arranged rectangular fixing frame (401). A glass box (402) is fixedly bonded to the inner side of the rectangular fixing frame (401) with glass glue. A first fixing post (403) is fixedly provided on one side of the glass box (402). A baffle (404) is fixedly connected to the end of the first fixing post (403). The first fixing post (403) is located on the outside of the glass box (402), and the baffle (404) is located on the outside of the glass box (402). Inside the glass box (402), a second fixed column (405) is fixedly connected to the other side of the glass box (402). A hydrofoil (406) is fixedly connected to the end of the second fixed column (405). The second fixed column (405) is located on the other side of the glass box (402), and the hydrofoil (406) is located inside the glass box (402). A pinhole flow is formed between the hydrofoil (406) and the baffle (404). The axis of the hydrofoil (406) is perpendicular to the direction of water flow. The mounting plate (2) is placed horizontally directly below the water tunnel test mechanism (4). The mounting plate (2) has a first fixing rod (301) fixed at each end of the shooting mechanism (3). A high-speed camera (302) is fixed at the end of the first fixing rod (301). A fixing seat (304) of the shooting mechanism (3) is fixed in the middle of the mounting plate (2). A second fixing rod (305) is fixed at the upper end of the fixing seat (304). A fixing plate (306) is fixedly connected to the top of the second fixing rod (305). A laser (303) is fixedly mounted on one side of the fixing plate (306). The laser ( 303) The hydrofoil (406) is vertically aligned with the inside of the water tunnel test mechanism (4). The laser (303) is used to generate sheet laser to irradiate particles on the vertical plane of the main flow direction. Two high-speed cameras (302) are symmetrically distributed on both sides of the laser (303) and are installed at the same height with the mounting plate (2) at a 45-degree angle. The two high-speed cameras (302) and the laser (303) are collinear, and the straight line formed is parallel to the water flow direction inside the water tunnel test mechanism (4). The flow field measurement area is set along the water flow direction to cover the downstream of the tip vortex flow from the blade tip gap of the hydrofoil (406) to the tip vortex flow direction within a range of 120 mm.

2. The small-scale vortex measurement device for water tunnel experiments integrating PTV and SPIV technologies according to claim 1, characterized in that: The bottom of the rectangular mounting bracket (401) is fixedly connected to an adapter plate (407). Two water prisms (408) are fixedly installed at the bottom of the adapter plate (407). The two water prisms (408) are in the shape of a right triangle with an inverted 45-degree cross section. The two water prisms (408) are respectively fixed on both sides of the laser (303).

3. The small-scale vortex measurement device for water tunnel experiments integrating PTV and SPIV technologies according to claim 1, characterized in that: The support mechanism (1) includes an X-axis housing (101), an X-axis motor lead screw (102) is provided at one end and inside the X-axis housing (101), and a first movable seat (103) connected to the X-axis motor lead screw (102) is movably mounted on the X-axis housing (101).

4. The small-scale vortex measurement device for water tunnel experiments integrating PTV and SPIV technologies according to claim 3, characterized in that: A Z-axis housing (104) is fixedly installed on the first movable seat (103). A Z-axis motor lead screw (105) is provided at one end and inside the Z-axis housing (104). A second movable seat (106) connected to the Z-axis motor lead screw (105) is movably installed on the Z-axis housing (104).

5. The small-scale vortex measurement device for water tunnel experiments integrating PTV and SPIV technologies according to claim 4, characterized in that: A Y-axis housing (107) is fixedly installed on the second movable seat (106). A Y-axis motor lead screw (108) is provided at one end and inside the Y-axis housing (107). The mounting plate (2) connected to the Y-axis motor lead screw (108) is movably installed on the Y-axis housing (107). A connecting plate (109) is provided on the back of the Z-axis housing (104). A reinforcing plate (110) is welded between the connecting plate (109) and the first movable seat (103).

6. A method for measuring small-scale eddy currents in water tunnel experiments that integrates PTV and SPIV technologies, comprising the method described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Two high-speed cameras (302) are used to take multiple pictures to establish the mapping relationship between the camera image plane and the physical space and obtain the object-image ratio; S2. The tracer particles are dispersed into the water tunnel test mechanism (4) through the pre-drilled hole on the glass box (402); the external circulating water pump is turned on to make the fluid flow in the water tunnel test mechanism (4), thereby ensuring that the tracer particles are more evenly distributed. S3. Connect two high-speed cameras (302) using a BNC cable, set the trigger mode of the high-speed camera (302) to ensure that the two high-speed cameras (302) can synchronously capture high-speed images, adjust the laser intensity of the laser (303) and the aperture, sampling frequency and exposure time of the two high-speed cameras (302) to synchronously capture high-speed images of the evolution process of the pinhole vortex and obtain the original image. S4. Based on the particle rotation features in the original image, the vortex structure region is selected for segmentation processing, laying the foundation for subsequent high-precision analysis; S5. Process high-speed camera images of the vortex tube region based on particle tracking velocimetry method to obtain two-dimensional velocity field characteristics; S6. In the non-vortex tube region, the traditional particle image velocimetry method is used to calculate the average displacement vector of the particle population through the cross-correlation function of two consecutive frames of images, and to reconstruct the gridded two-dimensional velocity field. S7. Spatial interpolation and averaging are performed on the two-dimensional velocity field after particle tracking and velocimetry processing to obtain a gridded velocity field. The grid size is consistent with the particle image velocimetry output result. On this basis, time averaging is performed on the transient velocity field result in the gridded velocity field to eliminate transient disturbances. Time averaging is performed on the particle image velocimetry processing result to obtain an average velocity field that eliminates transient disturbances. S8. Based on the fusion technology of particle image velocimetry and particle tracking velocimetry, the two-dimensional velocity field features and the gridded velocity field are used to construct a full-field two-dimensional field through world coordinate unification and regional stitching matching algorithm; S9. The full-field two-dimensional field of the two high-speed cameras (302) is post-processed and calculated using Matlab based on the three-dimensional particle image velocimetry algorithm to obtain the 2D-3C velocity field results.

7. The method for measuring small-scale eddies in water tunnel experiments integrating PTV and SPIV technologies according to claim 6, characterized in that: The steps for constructing a full-field two-dimensional field using the world coordinate unification and region stitching matching algorithm in S8 are as follows: With the world coordinate system unified and the calibration plate as a reference, the first and second homography matrices of the two high-speed cameras (302) are solved respectively. Both the first and second homography matrices are 3×3 homogeneous matrices. The particle velocity of particle tracking measurement and the velocity of particle image measurement grid are unified to the same world coordinate system, and a regular grid with the same spacing as the original particle image measurement grid is constructed in the world coordinate system. Particle tracking velocities are gridded. For any grid node, the velocities of surrounding particle tracking velocities are mapped to the node using a Gaussian weighted average, thus obtaining the particle tracking velocities interpolated velocity field corresponding to the particle image velocities grid. The boundaries of the particle image velocimetry and particle tracking velocimetry regions are linearly and gradually merged to generate a mask to distinguish the particle tracking velocimetry processing region from the particle image velocimetry processing region. A transition zone is set within three times the spacing width inside and outside the boundary, and the weights in the transition zone decrease linearly to achieve seamless splicing of the two types of velocities.

8. The method for measuring small-scale eddies in water tunnel experiments integrating PTV and SPIV technologies according to claim 7, characterized in that: The formula for calculating the Gaussian weighted average is as follows: ； in, The sample of particle velocities obtained from particle tracking measurements is collected within a local window of radius, and... , Represented as grid spacing, Represented as a grid node, Represented as particle world coordinates. The linear decrease in weights within the transition band is calculated as follows: ； in, Represented as weights within the transition band, and on the boundary line Core area outer area , It is represented as a defined distance function, which is the shortest distance from node G to the mask boundary.

9. The method for measuring small-scale eddies in water tunnel experiments integrating PTV and SPIV technologies according to claim 8, characterized in that: The two high-speed cameras (302) output full-field two-dimensional fields that are aligned with the world coordinate system and maintain the standard particle image velocimetry data format after fusion, which are used for subsequent 2D-3C velocity field calculations.

10. The method for measuring small-scale eddies in water tunnel experiments integrating PTV and SPIV technologies according to claim 8, characterized in that: The post-processing calculation steps in S9 based on the 3D particle image velocimetry algorithm are as follows: The two-dimensional velocity fields acquired by the two high-speed cameras are combined to calculate the 2D-3C velocity field. The specific formula is as follows: ； ； ； Let the velocity components of high-speed camera A and high-speed camera B in the X direction be u1 and u2, respectively, and their velocity components in the Y direction be v1 and v2, respectively. Let α1 and α2 be the camera mounting angles, both 45°. Then the final three-dimensional velocity components u, v, and w are: ； ； ； The three-dimensional velocity vector on each grid node is calculated point by point, and a complete 2D-3C velocity field is finally constructed. The output 2D-3C velocity field data is in standard SPIV format and can be directly used for subsequent flow field analysis tasks such as vorticity analysis, turbulent structure identification, and vortex trajectory tracking.

Images