A test device and method for synchronously measuring spray far-field droplet size and droplet transient velocity distribution

Abstract

The application discloses a kind of test device and method for synchronously measuring spray far-field droplet particle size and droplet instantaneous velocity distribution, and the test device includes spray visualization system, high-speed imaging system and computer;Image acquisition is carried out to the spray in spray visualization system using high-speed imaging system, and the image collected can also be processed by computer while controlling each unit of system.Based on the test device, the application also proposes a test method for synchronously measuring spray far-field droplet particle size and droplet instantaneous velocity distribution, adopts the algorithm for splitting discrete droplet, each droplet in spray image is split into connected region, and the center and diameter of droplet are calculated;Based on the discrete droplet segmented, the instantaneous velocity of discrete droplet is calculated using the algorithm for measuring instantaneous velocity of discrete liquid pairing, the center position of same droplet at different time is connected, and the movement track of droplet in spray process is obtained;Further, the technical purpose of synchronously measuring far-field region discrete droplet particle size and instantaneous velocity distribution is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of spray multiphase flow test, and particularly relates to a test device and method for synchronously measuring droplet size and instantaneous velocity distribution of spray far field, and particularly relates to high time and space resolution imaging of an effective measurement area of spray far field, a droplet segmentation algorithm in the image, a discrete droplet pairing algorithm, and real-time synchronous accurate measurement of droplet size and droplet velocity. BACKGROUND

[0002] Spray processes are widely used in various industrial processes, mainly including fuel injection of power systems, medical nasal spray, spray drying and coating related to drug preparation, agricultural spray (herbicides and pesticides, etc.) and cosmetic spray (perfume, moisturizing water and hair gel, etc.). A deep understanding of the size and velocity distribution of discrete droplets generated by the spray process is the basis for solving the heat and mass transfer problems related to spray multiphase flow, which can fundamentally optimize the related processes. Therefore, synchronous measurement of the size and instantaneous velocity of discrete droplets in the spray far field is of great significance.

[0003] At present, the mature methods for quantitative measurement of the spray far field mainly include: phase Doppler interferometry (PDI) measurement of single-point droplet velocity and size, particle image velocimetry (PIV) measurement of the average velocity field of the interrogation window in the plane, and planar laser-induced fluorescence (PLIF) measurement of the composition.

[0004] Among them, PDI can realize synchronous measurement of droplet size and velocity, but it has the disadvantages of single-point testing and high price. Synchronous experimental measurement of droplet size and velocity has always been a difficult technology in multiphase flow test, and a low-cost, high-time-efficiency measurement method needs to be developed, and the measurement accuracy needs to be improved. SUMMARY

[0005] In view of the shortcomings of the existing measurement technology and method, the present application provides a test device and method for synchronously measuring droplet size and instantaneous velocity distribution of spray far field. The present application realizes high time and space resolution imaging of the spray far field by using LED dot matrix light source and camera control method, and realizes synchronous measurement of the size and instantaneous velocity distribution of discrete droplets in the far field region based on segmentation of discrete droplets and pairing measurement of instantaneous velocity.

[0006] The present application realizes the above purpose through the following technical scheme.

[0007] A test method for synchronously measuring droplet size and instantaneous velocity distribution of spray far field, comprising the following steps:

[0008] Step 1: collecting spray images of spray far field droplets;

[0009] Step 2: Each droplet in the spray image is segmented into connected regions using a segmentation algorithm for discrete droplets, and the center and diameter of the droplet are calculated;

[0010] Step 3: Based on the discrete droplets segmented in Step 2, the instantaneous velocity of the discrete droplets is calculated using a discrete droplet pair measurement algorithm, and the instantaneous velocity of the discrete droplets is calculated. The center positions of the same droplet at different times are connected to obtain the motion trajectory of the droplet in the spray process.

[0011] Further, the method for segmenting discrete droplets in Step 2 is:

[0012] S1) Convert the original image to a gray image matrix I g , and perform two-dimensional median filtering to obtain matrix I m ;

[0013] Preferably, each output pixel contains the median value of the n x n region around the corresponding pixel in I g when performing median filtering, n is greater than 5 times the average diameter of the droplet;

[0014] S2) Binary processing matrix I m , obtain matrix I b ;

[0015] S3) Calculate the Euclidean distance between each pixel point in matrix I b and the nearest non-zero pixel, and obtain matrix I d ;

[0016] S4) Perform watershed transformation on matrix I d to separate the droplets in contact with each other in the image, and obtain a new binary matrix I b，2 ;

[0017] S5) Determine the connected regions from the binary matrix I b，2 ;

[0018] S6) Obtain the light intensity distribution at the corresponding position in matrix I g according to the coordinates of the connected regions, and filter out the connected regions corresponding to the droplets outside the mirror according to the droplet light intensity calibration result;

[0019] S7) Calculate the center of mass position and equivalent circle diameter of each connected region using the image matrix algorithm, which corresponds to the center (C) and diameter (D) of each droplet.

[0020] Further, the method for calibrating the light intensity of the droplet in S6 is:

[0021] The nozzle outlet is defined as the Cartesian coordinate system z = 0 position, the point diameter and the point interval point array ruler are placed in the z = 0 plane, and the actual size of each pixel point in the field of view and the uniformity of the light intensity distribution are calibrated; the liquid used in the spray test is used to generate liquid drops with the same volume at different positions on the liquid drop light intensity calibration board, the z = 0 plane of the liquid drop light intensity calibration board is placed in the focusing plane, and the quantitative relationship between the average light intensity and the light intensity standard deviation of the seat liquid drop and the distance between the center of the seat liquid drop and the focusing plane is calibrated.

[0022] Further, the algorithm for measuring the instantaneous velocity of the discrete liquid pair in step 3 comprises the following steps:

[0023] S1) determining the center C of the target liquid drop i at time 1 i，1 The center C of the candidate liquid drop j at time 2 j，2 The determination criterion of the candidate liquid drop is the relative displacement d ij = |C i，1 -C j，2 | < A1.max(v i，0 ), wherein max(v i，0 ) is the maximum value of the instantaneous velocity of the discrete liquid drop at time 0; the constant A1 > 1;

[0024] S2) determining the center C of the adjacent liquid drop k of the target liquid drop i at time 1 k(i)，1 The determination criterion of the adjacent liquid drop is the center corresponding to the adjacent Thiessen polygon of the target liquid drop;

[0025] S3) determining the center C of the candidate liquid drop l of the adjacent liquid drop k at time 2 l(k)，2 The determination criterion of the candidate is d k(i)r(k) = |C k(i),1 -C l(k),2 | < A2.max(v i,0 ); the constant A2 > 1

[0026] S4) determining the quasi-rigid condition of the adjacent liquid drop k and the candidate liquid drop l, i.e. |d ij -d k(i)l(k) | < A3.max(v i，0 ); the constant A3 < 0.3;

[0027] S5) iteratively calculating the pairing probability of the candidate liquid drop j and the target liquid drop i wherein the superscript n represents the iteration step number, P ij represents the pairing probability of the liquid drop j and the liquid drop i; before iteration, the pairing probability of each candidate liquid drop is the same, When the adjacent liquid drop k and the candidate liquid drop l meet the quasi-rigid condition, the pairing probability P k(i)l(k) is added to The pairing probability P The total pairing probability of all candidate droplets of the droplet i is normalized; constants A4 < 1, A5 > 2;

[0028] S6) after the selection iteration is completed, P ij The corresponding droplet j is successfully paired, and the instantaneous velocity v i of the droplet i is calculated as follows: ij Δt, wherein Δt is a time interval;

[0029] S7), when multiple discrete droplets at the time t are paired with the same droplet at the time t, only the pairing combination with the minimum relative displacement is retained: connecting the center positions of the same droplet at different times to obtain the motion trajectory of the discrete spray droplet;

[0030] Further, the acceleration a i of the droplet is calculated according to the change of the instantaneous velocity of the same droplet at adjacent times: i Δt.

[0031] A test device for synchronously measuring the droplet size and the instantaneous velocity distribution of a spray in a far field, comprising: a spray visualization system, a high-speed imaging system and a computer;

[0032] The spray visualization system mainly comprises a main cavity, a plurality of visualization windows are arranged on the main cavity; a nozzle is arranged in the main cavity, and the nozzle is connected to a spray control device through a signal line;

[0033] The high-speed imaging system mainly comprises a high-speed digital camera, a position control unit of the camera and an LED dot matrix light source; a long-focus microscope lens is arranged on the high-speed digital camera, the high-speed digital camera and the long-focus microscope lens are arranged towards the visualization window, and the LED dot matrix light source is located between the visualization window and the long-focus microscope lens; the high-speed digital camera and the LED dot matrix light source are arranged on the position control unit of the camera, and the position of the camera is adjusted through the position control unit of the camera;

[0034] The computer is connected to the spray control device, the high-speed digital camera and the position control unit of the camera through signal lines.

[0035] Further, a plurality of sensors are arranged in the main cavity, the sensors include temperature, pressure and humidity sensors, and the sensors are connected to the computer through signal lines to collect temperature, pressure and humidity data in the main cavity;

[0036] Further, an air extraction device and a waste liquid recovery device are arranged in the main cavity 1;

[0037] Further, the position control unit of the camera comprises an x linear electric control straight guide rail and a y linear electric control straight guide rail;

[0038] Further, the y linear electric control straight guide rail comprises two vertical rods and a horizontal plate between the two vertical rods, and the camera is mounted on the horizontal plate; the two ends of the horizontal plate can move up and down along the vertical rods under the cooperation of the driving motor and the guide rail, thereby driving the camera to change the position in the y direction; the x linear electric control straight guide rail comprises an optical guide rail arranged on the horizontal plate, and the camera is arranged on the optical guide rail and moves along the optical guide rail under the cooperation of the driving motor and the guide rail, thereby driving the camera to move left and right relative to the visualization window.

[0039] The beneficial effects of the present application are:

[0040] 1) The test device for synchronously measuring the droplet size and the instantaneous velocity distribution of the spray far field provided by the present application proposes a technology for quickly and accurately obtaining the droplet image with high time and space resolution in the spray far field region;

[0041] 2) The test method for synchronously measuring the droplet size and the instantaneous velocity distribution of the spray far field provided by the present application proposes to use the watershed algorithm to reduce the influence of droplet coincidence in the image on the droplet size distribution; and proposes to filter out the droplets outside the mirror depth through droplet light intensity calibration;

[0042] 3) The test method for synchronously measuring the droplet size and the instantaneous velocity distribution of the spray far field provided by the present application proposes an algorithm for calculating the instantaneous velocity of the droplet by pairing adjacent discrete droplets;

[0043] 4) The test device and method for synchronously measuring the droplet size and the instantaneous velocity distribution of the spray far field provided by the present application realize the synchronous measurement of the droplet size and the droplet velocity in the spray far field at different time and in different regions, and can further analyze the changes of the droplet size and the instantaneous velocity of the droplet with time and position in the spray process. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 It is a test device structure schematic diagram of the spray droplet size and instantaneous velocity distribution provided by the present application;

[0045] Figure 2 It is a dot matrix scale structure schematic diagram provided by the present application;

[0046] Figure 3 It is a droplet light intensity calibration plate structure schematic diagram provided by the present application;

[0047] Figure 4 It is a camera field of view adjustment schematic diagram provided by the present application;

[0048] Figure 5 It is a droplet pairing algorithm schematic diagram provided by the present application;

[0049] Figure 6is a liquid droplet segmentation effect schematic diagram provided by the present application;

[0050] Figure 7 is a liquid droplet particle size distribution schematic diagram provided by the present application;

[0051] Figure 8 is a liquid droplet instantaneous velocity schematic diagram provided by the present application;

[0052] Figure 9 is a liquid droplet motion trajectory schematic diagram provided by the present application;

[0053] In the figure, 1 is a main cavity, 2 is a visualization window, 3 is a nozzle, 4 is a spray control device, 5 is a sensor, 6 is a high-speed digital camera, 7 is a long-focus microscope lens, 8 is a dot matrix light source, 9 is an optical guide rail, 10 is an x linear electric control straight guide rail, 11 is a y linear electric control straight guide rail, 12 is a computer, 13 is a lamp bead, 14 is a dot diameter and dot interval dot matrix scale, 15 is a liquid droplet light intensity calibration plate, 16 is a position on the center line with a distance of 1 / 2 spray penetration distance L_s from the nozzle, 17 is a spray profile, and 18 is a field of view side length. DETAILED DESCRIPTION

[0054] The present application will be further described below in combination with the drawings and specific embodiments, but the protection scope of the present application is not limited thereto.

[0055] As Figure 1 shown in a kind of synchronous measurement spray far-field liquid droplet particle size and liquid droplet instantaneous velocity distribution test device, comprising: spray visualization system, high-speed imaging system, calculation analysis control module;Each system specific structure is as follows:

[0056] Spray visualization system mainly includes main cavity (1), is provided with multiple visualization windows (2) on main cavity (1);Nozzle (3) is arranged in main cavity (1), nozzle (3) is sequentially connected spray control device (4) and computer 12 by signal line;Main cavity 1 is also provided with multiple sensors 5, and the sensor 5 includes temperature, pressure, humidity sensor, and sensor 5 is all connected computer 12 by signal line, for collecting the temperature, pressure, humidity data in main cavity 1;In addition, main cavity 1 is also provided with exhaust device and waste liquid recovery device;

[0057] The high-speed imaging system mainly comprises a high-speed digital camera (6), a position control unit of the camera, and an LED dot matrix light source 8. The high-speed digital camera 6 is provided with a long-focus microscope lens 7, and the high-speed digital camera 6 and the long-focus microscope lens 7 are arranged towards the visualization window 2. The control unit of the high-speed digital camera 6 is connected to the computer 12 through a signal line. The position control unit of the camera comprises an x linear electric control straight guide rail 10 and a y linear electric control straight guide rail 11. As shown in the drawings, in order to adjust the position of the camera during the test, the y linear electric control straight guide rail 11 comprises two vertical rods and a horizontal plate between the two vertical rods, and the camera is mounted on the horizontal plate. The two ends of the horizontal plate can move up and down along the vertical rods under the cooperation of the driving motor and the guide rail, thereby driving the camera to change the position in the y direction. The x linear electric control straight guide rail 10 comprises an optical guide rail 9 arranged on the horizontal plate, and the camera is arranged on the optical guide rail 9 and moves along the optical guide rail 9 under the cooperation of the driving motor and the guide rail, thereby driving the camera to move left and right relative to the visualization window 2. The LED dot matrix light source 8 is composed of a plurality of lamp beads 13, and the LED dot matrix light source 8 is located between the visualization window 2 and the long-focus microscope lens 7. In this embodiment, the plurality of lamp beads 13 are arranged in a matrix or in a ring.

[0058] In this embodiment, the driving motors of the x linear electric control straight guide rail 10 and the y linear electric control straight guide rail 11 are connected to the computer 12 through signal lines, and the position of the camera is adjusted according to the instructions issued by the computer 12.

[0059] The computer 12 is connected to each system and can control the spray generation, spray flow, electric control guide rail accurate position, high-speed digital camera shooting, and digital image transmission. The computer can perform real-time analysis on the digital image and adjust the control strategy of each system. More specifically, the computer 12 is built-in with a calculation and analysis control module, which comprises computer hardware and related program codes of test methods.

[0060] In this embodiment, the nozzle is a double-fluid nozzle, and the pressure of the gas phase is 4 bar, the liquid is an HPMC solution with a concentration of 4%, and the flow rate is 20 g / min, which are controlled by the computer.

[0061] In this embodiment, the size and position of the LED dot matrix light source frame and the number and position of the lamp beads (13) are adjusted according to the size of the field of view. A diffusion plate is arranged in front of the LED dot matrix light source to ensure uniform distribution of light intensity in the entire field of view.

[0062] Preferably, the spatial resolution of the camera should reach 50 pixel / mm.

[0063] Preferably, the time resolution of the camera should reach 10000 fps.

[0064] Preferably, the adjustment accuracy of the electric control guide rail is better than 1 mm.

[0065] The above system in the experimental process:

[0066] The nozzle 3 outlet is defined as the Cartesian coordinate system z = 0 position, the high-speed digital camera 6 is focused on the z = 0 plane, high time and space resolution imaging is realized; since the optical guide rail 9 is fixedly connected with the x linear electric control straight rail 10 and the y linear electric control straight rail 11, the position of the camera field of view in the x and y directions can be adjusted through the electric control rail, so that the entire spray area is accurately and fully covered and the light intensity distribution is the same;

[0067] Further, the camera control method in the system is that: the right lower corner of the initial shooting field of view is set as a position (16) on the center line, which is 1 / 2 spray penetration distance L s from the nozzle 1, when the inside and outside regions of the spray profile (17) are contained in the shooting field of view at the same time, the shooting position is effective; the shooting position is translated by 1 / 2 field of view side length (18) upward, downward, leftward and rightward from the initial position in turn, the next effective shooting position is searched, as shown in Figure 4 , and so on, until the effective test area covers the entire spray profile;

[0068] Based on the above-mentioned test device for synchronously measuring the droplet size and the instantaneous velocity distribution of the spray in the far field, the application further provides a test method for synchronously measuring the droplet size and the instantaneous velocity distribution of the spray in the far field, comprising the following steps:

[0069] Step 1: based on the above-mentioned test device, the high-speed imaging system collects the spray image in the spray visualization system;

[0070] Step 2: using the algorithm for segmenting discrete droplets, each droplet in the spray image is segmented into a connected region, and the center and diameter of the droplet are calculated;

[0071] The method for segmenting discrete droplets is:

[0072] S1) converting the original image into a gray image matrix I g , performing two-dimensional median filtering to obtain a matrix I m ;

[0073] Preferably, when the median filtering is performed, each output pixel contains the median value of the n*n region around the corresponding pixel in I g , and n is greater than 5 times the average diameter of the droplet;

[0074] S2) binarizing the matrix I m to obtain a matrix I b ;

[0075] S3) calculating the Euclidean distance between each pixel point in the matrix I b and the nearest non-zero pixel to obtain a matrix Id ;

[0076] S4) performing watershed transform on matrix I d to separate the droplets in contact with each other in the image, obtaining a new binary matrix I b，2 ; the present application improves the accuracy of droplet segmentation from images by using the watershed and image moment coupling algorithm and droplet light intensity calibration, and can realize fast and accurate imaging of spray far field at different times and in different regions, and synchronous and accurate measurement of droplet size and droplet velocity.

[0077] S5) determining the connected regions from the binary matrix I b，2 ;

[0078] S6) obtaining the light intensity distribution of the corresponding position in matrix I g according to the coordinates of the connected regions, and filtering out the connected regions corresponding to the droplets outside the mirror depth according to the droplet light intensity calibration result; in the present embodiment, the method of droplet light intensity calibration is as follows: a determination point diameter and a point interval dot array scale (14) are placed on the z=0 plane, and the actual size and light intensity distribution uniformity of each pixel point in the field of view are calibrated; the same liquid as used in the spray test is used to generate seat droplets with the same volume at different positions on the droplet light intensity calibration plate (15), and the same high-speed imaging system parameters as used in the test are used to place the z=0 plane of the droplet light intensity calibration plate in the focusing plane, and the quantitative relationship between the average light intensity and the light intensity standard deviation of the seat droplet surface and the distance between the center of the seat droplet and the focusing plane is calibrated.

[0079] S7) using the image moment algorithm to calculate the centroid position of each connected region and the equivalent circle diameter with the same area as the connected region, corresponding to the center (C) and diameter (D) of each droplet;

[0080] Step 3, based on the discrete droplets segmented in step 2, the instantaneous velocity of the discrete droplets is calculated by using the discrete liquid pairing measurement instantaneous velocity algorithm, as shown in Figure 8 ; connecting the center positions of the same droplet at different times can obtain the motion trajectory of the droplet in the spray process, as shown in Figure 9 .

[0081] The discrete liquid pairing measurement instantaneous velocity algorithm is shown in Figure 5 , which includes the following steps:

[0082] S1) determining the candidate droplet j (center C i，1 ) of the target droplet i (center C j，2 ) at time 2; the determination criterion of the candidate droplet is the relative displacement d ij = |C i，1 -C j，2 | < A1·max(v i，0 ), wherein max(vi，0 ) is the maximum value of the instantaneous velocity of the discrete droplet at time 0; preferably, constant A1 > 1;

[0083] S2) determining the neighboring droplet k (center C k(i)，1 ) of the target droplet i at time 1; the criterion for determining the neighboring droplet is that the center corresponding to the neighboring Voronoi polygon of the target droplet i;

[0084] S3) determining the candidate droplet l (center C l(k)，2 ) of the neighboring droplet k at time 2; the criterion for determining the candidate is that d k(i)l(k) = |C k(i)，1 -C l(k)，2 | < A2 max(v i，0 ); preferably, constant A2 > 1

[0085] S4) determining the quasi-rigid condition of the neighboring droplet k and the candidate droplet l, i.e., |d ij -d k(i)l(k) | < A3 max(v i，0 ); preferably, constant A3 < 0.3

[0086] S5) iteratively calculating the pairing probability of the candidate droplet j and the target droplet i wherein the superscript n represents the iteration step number, P ij represents the pairing probability of the droplet j and the droplet i; before iteration, the pairing probability of each candidate droplet is the same, When the neighboring droplet k and the candidate droplet l meet the quasi-rigid condition, their pairing probability P k(i)l(k) is added to the pairing probability of the droplet j after each iteration step The total pairing probability of all candidate droplets of the target droplet i needs to be normalized;

[0087] Preferably, constant A4 < 1 and A5 > 2;

[0088] S6) selecting the droplet j corresponding to P ij after iteration completion as the successful pairing, and the instantaneous velocity v i of the droplet i = d ij / Δt, wherein Δt is the time interval;

[0089] S7), when multiple discrete droplets at time 1 are paired with the same droplet at time 2, only the pairing combination with the smallest relative displacement is retained: connecting the center positions of the same droplet at different time points to obtain the motion trajectory of the discrete spray droplet, as shown in Figure 9 Further, according to the change of the instantaneous velocity of the same droplet at adjacent time points, the acceleration a i of the droplet can be calculated = Δv i / Δt.

[0090] In the present case experiment, the high-speed camera shooting speed is 5000 fps, the window area size is 1024x1024 pixel, and the actual size of each pixel point obtained by cooperating with the long-focus microscope lens is 20 μm; the average light intensity and light intensity standard deviation of the droplet surface decrease with the increase of the distance between the droplet center and the focusing plane, the average light intensity and light intensity standard deviation of the droplet in the focusing plane are standardized for other positions, and 0.6 and 0.8 are taken as the average light intensity threshold and light intensity standard deviation threshold of the connected region corresponding to the droplet outside the filter lens depth, respectively;

[0091] Figure 6 The spray original picture and the droplet segmentation effect are shown at a certain time when the spray is stable, which is shot at a distance of 10 cm from the nozzle and 8 cm from the spray center line; Figure 7 The corresponding Sauter mean diameter of the droplet is 142.7 μm for the cumulative droplet diameter density distribution function calculated by 100 pictures at the position;

[0092] In the present embodiment, the above-mentioned test method for synchronously measuring the droplet size and the instantaneous velocity distribution of the spray in the far field is written in the form of a program in the calculation and analysis control module, so that the droplet size and the instantaneous velocity of the spray in the far field at different times and in different regions can be synchronously and real-timely measured, and the changes of the droplet size and the instantaneous velocity of the spray with time and position in the spray process can be analyzed.

[0093] The above embodiments are only used to illustrate the design idea and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and the protection scope of the present application is not limited to the above-mentioned embodiments. Therefore, any equivalent changes or modifications made according to the principles and design ideas disclosed by the present application are within the protection scope of the present application.

Claims

1. A test method for simultaneously measuring the droplet size and the instantaneous velocity distribution of a spray in the far field, characterized in that The method comprises the following steps: Step 1: collecting a spray image of spray far-field droplets; Step 2: using an algorithm for segmenting discrete droplets, segmenting each droplet in the spray image into a connected region, and calculating the center and diameter of the droplet; the method for segmenting discrete droplets in step 2 is as follows: S1) converting the original image into a grey scale matrix I g , performing a two-dimensional median filtering to obtain a matrix I m ; Each output pixel contains I g The median value in an n x n region around the corresponding pixel, n being larger than 5 times the average droplet diameter. S2) binarizing the matrix I m , obtaining a matrix I b ; S3) Computing the matrix I b the Euclidean distance between each pixel and the nearest non-zero pixel, obtaining the matrix I d ; S4) performing a watershed transform on the matrix I d to separate mutually touching droplets in the image, obtaining a new binary matrix I b,2 ; S5) determining connected regions from the binary matrix I b,2 S5) determining connected regions from the binary matrix I S6) According to the coordinates of the connected region, obtain matrix I g According to the light intensity calibration result of the liquid drops, filter out the connected region corresponding to the liquid drops outside the mirror depth. S7) using an image moment algorithm to calculate the centroid position of each connected region and an equivalent circle diameter equal to the area of the connected region, corresponding to the center C and diameter D of each droplet; Step 3: based on the discrete droplets segmented in step 2, using an algorithm for pairing discrete droplets to measure the instantaneous velocity to calculate the instantaneous velocity of the discrete droplets, connecting the center positions of the same droplet at different times to obtain the movement trajectory of the droplet in the spray process; the algorithm for pairing discrete droplets to measure the instantaneous velocity in step 3 comprises the following steps: S1) determining the target droplet i center C at time 1 i,1 the candidate droplet j center C at time 2 j,2 ; the candidate droplet decision criterion is the relative displacement d ij = |C i,1 - C j,2 | < A1 • max(v i,0 ), where max(v i,0 ) is the maximum value of the discrete droplet instantaneous velocity at time 0; the constant A1 > 1; S2) determining the center C of the adjacent droplet k of the target droplet i at time 1 k(i),1 ; the determination criterion of the adjacent droplet is the center corresponding to the adjacent Thiessen polygon of the target droplet i; S3) determine the candidate droplet I center C at time 2 for the adjacent droplet k at time 1 l(k),2 ; the candidate determination criterion is d k(i)l(k) = |C k(i),1 - C l(k),2 | < A2- max(v i,0 ); constant A2 > 1 S4) determining the quasi-rigidity condition of the adjacent droplet k and the candidate droplet 1, i.e. |d ij -d k(i)l(k) |<A3·max(v i,0 ); constant A3 < 0.3; S5) Iteratively calculate the pairing probability of candidate droplet j and target droplet i where the superscript n represents the iteration step number, P ij represents the pairing probability of droplet j and droplet i; the pairing probability of each candidate droplet before iteration is the same, When adjacent droplet k and candidate droplet l meet the quasi-rigid condition, their pairing probability P k(i)l(k) The superposition is taken into account The pairing probability after each iteration step The total pairing probability of all candidate droplets of target droplet i needs to be normalized; constant A4<1, A5>2; S6) Select P after iteration is complete ij Corresponding droplet j is successfully paired, droplet i instantaneous velocity v i = d ij / Δt, where Δt is the time interval; S7), when multiple discrete droplets in time 1 are paired with the same droplet in time 2, only the pairing combination with the smallest relative displacement is retained: connecting the center positions of the same droplet at different times to obtain the movement trajectory of the discrete spray droplets.

2. A test method for simultaneous measurement of droplet size and droplet velocity distribution in the far field of a spray according to claim 1, characterized in that The method for calibrating the light intensity of the droplets in S6 is as follows: The outlet of the nozzle 3 is defined as the z=0 position of the Cartesian coordinate system, a point diameter and a point spacing dot array scale (14) are placed on the z=0 plane, and the actual size of each pixel point in the field of view and the uniformity of the light intensity distribution are calibrated; using the liquid used in the spray test, generate a volume of seat droplets at different positions on the droplet light intensity calibration plate (15) surface, place the z=0 plane of the droplet light intensity calibration plate in the focusing plane, and calibrate the quantitative relationship between the average light intensity and the light intensity standard deviation of the seat droplet surface and the distance between the center of the seat droplet and the focusing plane.

3. A test method for simultaneous measurement of droplet size and droplet velocity distribution in the far field of a spray according to claim 1, characterized in that The droplet acceleration a is calculated from the change in the instantaneous velocity of the same droplet at adjacent time instants i = Δv i / Δt.

4. A test apparatus for testing the method of claim 1 for simultaneous measurement of spray droplet size and droplet velocity distribution in the far field, characterized in that It comprises: a spray visualization system, a high-speed imaging system and a computer; The spray visualization system mainly comprises a main cavity (1), a plurality of visualization windows (2) are arranged on the main cavity (1); a nozzle (3) is arranged in the main cavity (1), and the nozzle (3) is connected with a spray control device (4) through a signal line; The high-speed imaging system mainly comprises a high-speed digital camera (6), a position control unit of the camera and an LED dot array light source (8); a long-focus microscope lens (7) is arranged on the high-speed digital camera (6), the high-speed digital camera (6) and the long-focus microscope lens (7) are arranged towards the visualization window (2), and the LED dot array light source (8) is located between the visualization window (2) and the long-focus microscope lens (7); the high-speed digital camera (6) and the LED dot array light source (8) are arranged on the position control unit of the camera, and the position of the camera is adjusted through the position control unit of the camera; The computer (12) is connected with the spray control device (4), the high-speed digital camera (6) and the position control unit of the camera through signal lines.

5. A test apparatus for simultaneous measurement of droplet size and droplet velocity distribution in the far field of a spray according to claim 4, characterized in that The main cavity (1) is also provided with a plurality of sensors (5), and the sensors (5) comprise temperature, pressure and humidity sensors; the sensors (5) are connected with the computer (12) through signal lines, and are used to collect temperature, pressure and humidity data in the main cavity (1).

6. A test apparatus for simultaneous measurement of droplet size and droplet velocity distribution in the far field of a spray according to claim 4, characterized in that The main cavity (1) is also provided with an air extraction device and a waste liquid recovery device.

7. A test apparatus for simultaneous measurement of droplet size and droplet velocity distribution in the far field of a spray according to claim 4, characterized in that The position control unit of the camera comprises an x linear electric control straight line guide rail (10) and a y linear electric control straight line guide rail (11).

8. A test apparatus for simultaneous measurement of droplet size and droplet velocity distribution in the far field of a spray according to claim 7, characterized in that The y linear electric control straight guide rail (11) comprises two vertical rods and a horizontal plate between the two vertical rods, and a camera is mounted on the horizontal plate; the two ends of the horizontal plate can move up and down along the vertical rods under the cooperation of the driving motor and the guide rail, thereby driving the change of the position of the camera in the y direction; the x linear electric control straight guide rail (10) comprises an optical guide rail (9) arranged on the horizontal plate, and the camera is arranged on the optical guide rail (9) and moves along the optical guide rail (9) under the cooperation of the driving motor and the guide rail, thereby driving the left and right movement of the camera relative to the visualization window (2).

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