Ultrasonic flowmeter positioning method and system for elbow-shaped flow channel

Abstract

The invention discloses an ultrasonic flowmeter positioning method for an elbow-shaped flow channel, which comprises the following steps of: building a model experiment table of an inlet section of a pump station to be tested, which takes the elbow-shaped flow channel as a water inlet flow channel, arranging PIV (Particle Image Velocimetry) testing equipment, and defining a three-dimensional rectangular coordinate system of the inlet section of the elbow-shaped flow channel in the model experiment table; sequentially performing PIV two-dimensional flow field measurement on each section to be measured by using PIV testing equipment to obtain a two-dimensional flow velocity vector of each section to be measured; performing two-dimensional interpolation on the two-dimensional flow velocity vector of each section to be measured to obtain a two-dimensional flow velocity field of the flow measurement section, and introducing a continuity equation as a physical constraint to perform three-dimensional interpolation on the two-dimensional flow velocity field to realize three-dimensional flow field reconstruction of the flow measurement section; respectively calculating the turbulent kinetic energy at each position in the flow measurement section according to the reconstructed three-dimensional flow field, and taking the position with the minimum turbulent kinetic energy as the mounting position of the ultrasonic flowmeter. According to the method, a complex three-dimensional flow field in the elbow-shaped flow channel is reconstructed through PIV, and an experimental basis is provided for selection of the mounting position of the ultrasonic flowmeter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultrasonic flowmeter installation positioning, and particularly relates to an ultrasonic flowmeter positioning method and system for an elbow-shaped flow passage. BACKGROUND

[0002] The elbow-shaped water inlet passage has the advantages of good hydraulic performance and reliable operation, and is widely applied to large pump stations.

[0003] The elbow-shaped water inlet passage is an irregular passage with variable rectangular contraction, and is composed of an inlet section, a curved section and an outlet section. The inlet section is a rectangular flow cross-section tapered pipe with a constant width and a height that changes uniformly along the passage; the flow cross-section of the curved section is gradually changed from a rectangle to a circle, and the cross-sectional area gradually decreases along the passage; the outlet section is a tapered conical pipe, and the outlet is connected with the seat ring of the pump. The shape and size of the flow passage cross-section of the elbow-shaped water inlet passage change continuously from the inlet section to the outlet section, which introduces flow complexity and disturbance in addition to the main flow, and the flow field distribution is relatively complex. The flow velocity and direction of the elbow-shaped water inlet passage of the large pump station change along the passage, and the fluid flow cannot be fully developed. The asymmetric inflow characteristic of the edge unit as the most edge-side operating unit under different unit combination operating conditions of the pump station will lead to the asymmetric distribution of the inlet flow velocity of the elbow-shaped water inlet passage, further leading to the complex distribution of the flow field. The distribution of the flow state inside the passage has a direct impact on the measurement accuracy of the ultrasonic flowmeter: the uneven, asymmetric, backflow and deflection of the flow state may lead to unstable ultrasonic wave propagation, and further affect the flow measurement accuracy. Therefore, selecting a suitable installation measurement position in the elbow-shaped flow passage is the key to improving the measurement accuracy of the ultrasonic flowmeter.

[0004] At present, there is no feasible experimental method to provide experimental basis for the selection of the installation position of the ultrasonic flowmeter in the elbow-shaped flow passage. SUMMARY

[0005] The present application aims to at least solve one of the technical problems in the related art to some extent.

[0006] To this end, the present application aims to provide an ultrasonic flowmeter positioning method and system for an elbow-shaped flow passage, which reconstructs the complex three-dimensional flow characteristics inside the elbow-shaped flow passage by using a single camera PIV, provides an experimental basis for the optimal installation position selection of the ultrasonic flowmeter, and has important significance for ensuring the flow measurement accuracy of the ultrasonic flowmeter in the large pump station.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0008] The first aspect of the present application provides an ultrasonic flowmeter positioning method for an elbow-shaped flow passage, comprising:

[0009] Step S1, build a model test bench of the inlet section of the elbow-shaped flow channel as the water inlet flow channel of the pump station to be tested, and set up a PIV test device;

[0010] Define the three-dimensional rectangular coordinate system xyz of the inlet section of the elbow-shaped flow channel in the model test bench, wherein the direction parallel to the center line of the inlet section of the elbow-shaped flow channel is taken as the x-axis, the direction parallel to the width direction of the inlet end of the elbow-shaped flow channel is taken as the z-axis, and the y-axis positive direction is perpendicular to the xz plane and upward along the water depth, and the coordinate origin is located at the bottom of the inlet section of the elbow-shaped flow channel close to the inlet end; the flow velocity in the main flow direction in the elbow-shaped flow channel is defined as v, the flow velocity in the y-axis positive direction is defined as u, and the flow velocity in the z-axis positive direction is defined as w;

[0011] The PIV test device comprises a transparent water tank, a laser and a single camera, and the elbow-shaped flow channel is arranged in the transparent water tank;

[0012] The inlet section of the elbow-shaped flow channel is set as a flow measurement section, and a in the XY plane and b in the XZ plane are determined at different Z coordinates in the flow measurement section;

[0013] Step S2, use the PIV test device to sequentially perform PIV two-dimensional flow field measurement on each test section to obtain the two-dimensional flow velocity vector of each test section;

[0014] Step S3, first perform two-dimensional interpolation on the two-dimensional flow velocity vector of each test section to obtain the two-dimensional flow velocity field of the flow measurement section; then introduce the continuity equation as a physical constraint to perform three-dimensional interpolation on the two-dimensional flow velocity field to reconstruct the three-dimensional flow field of the flow measurement section;

[0015] Step S4, calculate the turbulent kinetic energy at each position in the flow measurement section according to the reconstructed three-dimensional flow field, and take the position with the minimum turbulent kinetic energy as the installation position of the ultrasonic flowmeter.

[0016] In some embodiments, the model test bench comprises the elbow-shaped flow channel, a vertical axial flow pump, a water outlet pipe, a connecting pipe and a circulating pool connected in sequence to form a circulating loop, the elbow-shaped flow channel is made of transparent material, and tracer particles are added to the fluid in the circulating loop;

[0017] Mark each test section on the side wall of the transparent water tank to ensure that the plane where the laser generated by the laser is coincident with the test section.

[0018] In some embodiments, in step S2, when performing PIV two-dimensional flow field measurement on any test XY section, it comprises:

[0019] Step S211, adjust the position of the laser installed above the elbow-shaped flow channel so that the sheet light formed by the laser is coincident with the current test XY section;

[0020] Step S212, set up the camera on the side of the elbow-shaped flow channel, make the camera clear imaging and ensure that the camera imaging plane is parallel to the current XY cross section to be measured, place the chessboard calibration board at the current XY cross section to be measured and shoot the chessboard calibration image under the condition that the laser is turned off;

[0021] Step S213, for the current XY cross section to be measured, shoot a group of continuous XY cross section particle images;

[0022] Step S214, average the continuous XY cross section particle images to obtain an average particle image containing background information, subtract the average particle image containing background information from each particle image in the continuous XY cross section particle images respectively to obtain continuous XY cross section particle images with background light interference removed;

[0023] Step S215, perform PIV calculation on the continuous XY cross section particle images with background light interference removed to obtain the two-dimensional flow velocity vector of each node in the current XY cross section to be measured in pixel unit, and combine the chessboard calibration image shot in step S212 to obtain the two-dimensional flow velocity vector (v, u) of each node in the current XY cross section to be measured.

[0024] In some embodiments, in step S2, when performing PIV two-dimensional flow field measurement on any XZ cross section to be measured, the imaging plane of the camera is horizontal and has an angle with the XZ cross section to be measured, the perspective correction is performed on the XZ cross section particle image shot by the camera by using the chessboard calibration method, and the two-dimensional flow velocity vector (v, w) of each node in the XZ cross section to be measured is obtained based on the corrected XZ cross section particle image.

[0025] In some embodiments, in step S2, when performing PIV two-dimensional flow field measurement on any XZ cross section to be measured, the method comprises:

[0026] Step S221, adjust the position of the laser installed on one side of the elbow-shaped flow channel so that the sheet of light formed by the laser coincides with the current XZ cross section to be measured;

[0027] Step S222, set up the camera above the elbow-shaped flow channel, make the camera clear imaging and ensure that the camera imaging plane is horizontal, place the chessboard calibration board at the current XZ cross section to be measured under the condition that the laser is turned off, make the camera be at different shooting angles and shooting positions relative to the chessboard calibration board, and shoot multiple chessboard calibration images;

[0028] Step S223, for the current XZ cross section to be measured, obtain a group of continuous XZ cross section particle images;

[0029] Step S224, detecting the corner points of the checkerboard calibration board in each checkerboard calibration image, mapping each detected corner point to a three-dimensional rectangular coordinate system of the inlet section of the elbow-shaped flow channel, and calculating a perspective transformation matrix; applying the perspective transformation matrix to the continuous XZ cross-section particle images to eliminate distortion caused by the inconsistency between the camera imaging plane and the XZ cross-section to be measured, and obtaining the corrected continuous XZ cross-section particle images;

[0030] Step S225, averaging the corrected continuous XZ cross-section particle images to obtain an average particle image containing background information, and subtracting the calculated average particle image containing background information from each particle image in the corrected continuous XZ cross-section particle images to obtain continuous XZ cross-section particle images with background light interference removed;

[0031] Step S226, performing PIV calculation on the continuous XZ cross-section particle images with background light interference removed to obtain two-dimensional flow velocity vectors of each node in the current XZ cross-section in pixel units, and combining the checkerboard calibration image photographed in step S222 to obtain two-dimensional flow velocity vectors (v, w) of each node in the current XZ cross-section.

[0032] In some embodiments, in step S3, when the continuity equation is introduced as a physical constraint for three-dimensional interpolation of the two-dimensional flow velocity field, the target value of the change of the average flow velocity along the flow process on each YZ cross-section of the elbow-shaped flow channel in the flow measurement section is defined, and by minimizing the deviation between the adjusted velocity field and the initial three-dimensional interpolation result, it is ensured that the final reconstruction result meets the physical constraint.

[0033] The second aspect of the present application provides an ultrasonic flowmeter positioning system for an elbow-shaped flow channel, comprising:

[0034] A model test bench is built for the inlet section of a pump station to be measured with an elbow-shaped flow channel as the inlet flow channel; a three-dimensional rectangular coordinate system xyz of the inlet section of the elbow-shaped flow channel in the model test bench is defined, wherein the x-axis is parallel to the center line direction of the inlet section of the elbow-shaped flow channel, the z-axis is parallel to the width direction of the inlet end of the elbow-shaped flow channel, the y-axis is perpendicular to the xz plane and points upward along the water depth, and the coordinate origin is located at the bottom of the inlet section of the elbow-shaped flow channel near the inlet end; the flow velocity in the main flow direction in the elbow-shaped flow channel is defined as v, the flow velocity in the positive y-axis direction is defined as u, and the flow velocity in the positive z-axis direction is defined as w;

[0035] A PIV test device includes a transparent water tank, a laser, and a single camera, and the elbow-shaped flow channel is arranged in the transparent water tank;

[0036] The two-dimensional velocity vector acquisition unit is configured to set the inlet section of the elbow-shaped flow channel as the flow measurement section, determine a XY sections to be measured under different Z coordinates and b XZ sections to be measured under different Y coordinates within the flow measurement section, and use the PIV test equipment to sequentially perform PIV two-dimensional flow field measurement on each section to be measured to obtain the two-dimensional velocity vector of each section to be measured.

[0037] The three-dimensional flow field reconstruction unit is configured to first perform two-dimensional interpolation on the two-dimensional velocity vectors of each section to be measured to obtain the two-dimensional velocity field of the measurement section; then, the continuity equation is introduced as a physical constraint to perform three-dimensional interpolation on the two-dimensional velocity field to realize the three-dimensional flow field reconstruction of the measurement section.

[0038] The positioning unit is configured to calculate the turbulent kinetic energy at each location within the flow measurement section based on the reconstructed three-dimensional flow field, and to use the location with the minimum turbulent kinetic energy as the installation location of the ultrasonic flow meter.

[0039] Compared with the prior art, the present invention has the following characteristics and beneficial effects:

[0040] This invention, based on a single-camera PIV experiment, reconstructs the three-dimensional flow field inside an elbow-shaped channel using a slicing method. Specifically, it conducts bidirectional flow field measurement experiments at the inlet section of the elbow-shaped channel and uses three-dimensional interpolation to refine the sparse grid formed by the bidirectional two-dimensional flow field to obtain the three-dimensional velocity vectors of each node in the coordinate system. Simultaneously, a continuity equation is introduced as a physical constraint to optimize the missing velocity components at each target grid point, resulting in more accurate reconstruction results. The high-precision three-dimensional flow field ensures the accuracy of ultrasonic flow meter positioning, thereby improving the measurement accuracy of the ultrasonic flow meter in the elbow-shaped channel. This invention provides experimental basis for selecting the installation location of ultrasonic flow meters in complex flow channels such as elbow-shaped channels. It is of great significance for ensuring the flow measurement accuracy of ultrasonic flow meters in large pumping stations. Attached Figure Description

[0041] Figure 1 This is the overall flow chart of the ultrasonic flow meter positioning method for elbow-shaped flow channels provided in the first aspect embodiment of the present invention;

[0042] Figure 2 yes Figure 1 A schematic diagram of the structure of the model experimental platform built in the provided positioning method;

[0043] Figure 3 In the middle (a) and (b) respectively Figure 1 A schematic diagram of the xz and xy coordinates constructed in the provided positioning method;

[0044] Figure 4 yes Figure 1 A schematic diagram of the PIV test equipment set in the provided positioning method.

[0045] Fig. 1 is a schematic diagram of a model test bench for elbow-shaped flow channel;

[0046] 100, model test bench, 110, elbow-shaped flow channel, 111, inlet end, 112, outlet end, 120, vertical axial flow pump, 130, water outlet pipe, 140, connecting pipe, 150, circulating pool; I, inlet section, II, curved section, III, outlet section;

[0047] 200, PIV test equipment, 210, transparent water tank, 220, laser, 230, camera. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0049] On the contrary, the present application covers any alternative, modification, equivalent method and scheme defined by the claims on the essence and scope of the present application. Further, in order to make the public better understand the present application, some specific details are described in detail in the following detailed description of the present application. The present application can also be completely understood without the description of these details by those skilled in the art.

[0050] Referring to Figure 1 The first aspect embodiment of the present application provides a positioning method for an ultrasonic flowmeter for an elbow-shaped flow channel, comprising the following steps:

[0051] Step S1, for the pump station to be measured with the elbow-shaped flow channel as the water inlet flow channel, a model test bench 100 for the inlet section is built, and a PIV test equipment 200 is set, wherein:

[0052] Referring to Figure 2 and Figure 3The model experiment table 100 comprises an elbow-shaped flow channel 110, a vertical axial flow pump 120, a water outlet pipe 130, a connecting pipe 140 and a circulating pool 150 which are sequentially connected to form a circulating loop, wherein the elbow-shaped flow channel 110 is made of transparent material, and is sequentially divided into an inlet section I, a curved section II and an outlet section III along the water flow direction; the outlet end 112 of the elbow-shaped flow channel 110 is connected with one end of the water outlet pipe 130 through the vertical axial flow pump 120; the other end of the water outlet pipe 130 is connected with the circulating pool 150 through the connecting pipe 140; the circulating pool 150 is connected with the inlet end 111 of the elbow-shaped flow channel 110; and tracer particles are added in the fluid of the circulating loop; the width and height of the inlet end 111 of the elbow-shaped flow channel 110 are respectively B and H; a three-dimensional rectangular coordinate system xyz of the inlet section I is constructed, the x-axis is parallel to the center line direction of the inlet section I of the elbow-shaped flow channel 110, the water flow direction is defined as the positive direction of the x-axis, the z-axis is parallel to the width direction of the inlet end 111 of the elbow-shaped flow channel 110, and the y-axis is perpendicular to the xz plane and points upward along the water depth; and the coordinate origin is located at the bottom of the inlet section I close to the inlet end 111; the flow velocity in the main flow direction of the elbow-shaped flow channel 110 is defined as v, the flow velocity in the positive direction of the y-axis is defined as u, and the flow velocity in the positive direction of the z-axis is defined as w;

[0053] Referring to Figure 4 , the PIV test equipment 200 comprises a transparent water tank 210, a laser 220 and a single camera 230; the elbow-shaped flow channel 110 is arranged in the transparent water tank 210, and the elbow-shaped flow channel 110 and the fluid in the transparent water tank 210 are independent of each other; the laser 220 and the camera 230 are both arranged near the elbow-shaped flow channel 110, and the camera 230 is controlled by a synchronizer (not shown in the figure) to collect the frequency;

[0054] The inlet section I of the elbow-shaped flow channel 110 is set as a measuring section; a total of a XY cross sections under different Z coordinates and b XZ cross sections under different Y coordinates are determined in the measuring section, and the determined cross sections are marked on the side wall of the transparent water tank 210, so that the plane where the laser generated by the laser 220 coincides with the cross sections to be measured;

[0055] In step S2, the PIV test equipment is used to sequentially perform PIV two-dimensional flow field measurement on the cross sections to be measured, so as to obtain the two-dimensional flow velocity vectors of the cross sections to be measured;

[0056] In step S3, the two-dimensional flow velocity vectors of the cross sections to be measured obtained in step S2 are first subjected to two-dimensional interpolation to obtain a two-dimensional flow velocity field of the measuring section; then, the continuity equation is introduced as a physical constraint to perform three-dimensional interpolation on the two-dimensional flow velocity field, so as to reconstruct a three-dimensional flow field of the measuring section;

[0057] Step S4, the turbulence kinetic energy at each position in the flow measuring section is calculated according to the three-dimensional flow field reconstructed in step S3, and the position with the minimum turbulence kinetic energy is taken as the installation position of the ultrasonic flowmeter.

[0058] In some embodiments, step S1, a certain large pump station to be tested with an elbow-shaped flow channel as the inlet flow channel is taken as a typical pump station, and a model test platform 100 of the inlet section of the typical pump station is built according to the principle of hydraulic similarity, and the basic characteristics of the elbow-shaped inlet flow channel in the actual project are strictly reproduced. In the model test platform 100 of the embodiment, there are four elbow-shaped flow channels that are parallel and symmetrically distributed, which are sequentially denoted as 1#-4# elbow-shaped flow channels. The 1# and 4# elbow-shaped flow channels are located at the side, respectively, and the outlet ends 112 of each elbow-shaped flow channel are connected to a vertical axial flow pump 120. Referring to Figure 2 Among them, 1# and 4# elbow-shaped flow channels are side units, and since they are symmetrically distributed, only the 1# elbow-shaped flow channel can be used to carry out the inlet flow pattern PIV experiment, which can represent the distribution of the inlet flow pattern in the corresponding elbow-shaped flow channel of the 4# side unit under the symmetric operating condition. A transparent water tank 210 is built outside the elbow-shaped flow channel of the side unit to be tested for PIV experiment, a laser 220 is arranged above the elbow-shaped flow channel, and a single camera 230 is arranged on the side of the elbow-shaped flow channel. By reducing the refraction error of the laser between different media, the propagation direction of the laser beam is stabilized, thereby improving the accuracy of the PIV measurement.

[0059] It should be noted that the relatively simple geometric conditions of the inlet section of the elbow-shaped flow channel can provide a relatively stable flow field and a reliable sound wave propagation environment for the ultrasonic flowmeter, and the complex flow characteristics of the curved section will introduce significant errors. Therefore, the ultrasonic transducers are installed in the inlet section of the elbow-shaped flow channel, and the PIV experiment is only carried out on the inlet section of the elbow-shaped flow channel.

[0060] Further, in step S1, the laser 220 in the PIV test equipment 200 adopts a sheet light source. After the model test platform 100 and the PIV test equipment 200 are built, a plurality of XY sections under different Z coordinates and a plurality of XZ sections under different Y coordinates need to be determined, and each to-be-tested section is marked on the transparent water tank 210 outside the elbow-shaped flow channel 110 to ensure that the plane where the laser is located is accurately overlapped with the to-be-tested section to be shot. The number of a and b is set according to the test accuracy of PIV. In this embodiment, a to-be-tested section is taken every 4 cm in the inlet section I.

[0061] It can be understood that the embodiment of the present application is aimed at the elbow-shaped inlet flow channel commonly used in large pump stations, which is different from the traditional circular or square straight pipe and is an irregular flow channel with variable rectangular contraction. Therefore, a corresponding three-dimensional rectangular coordinate system needs to be constructed according to the flow channel center line and the main dimensions of the flow channel to determine the directions of the XY section and the XZ section, which is convenient for subsequent PIV two-dimensional flow field calculation.

[0062] In some embodiments, step S2 specifically comprises:

[0063] Step S21, PIV flow field measurement is carried out on a XY section.

[0064] Step S211, the position of the laser 220 installed above the elbow-shaped flow channel 110 is adjusted so that the sheet of light formed by the laser precisely coincides with the XY section to be measured.

[0065] Step S212, the position of the camera 230 placed on the side of the elbow-shaped flow channel 110 by the tripod is adjusted to ensure clear shooting while ensuring that the imaging plane of the camera is parallel to the XY section to be measured. In the case where the laser 220 is turned off, a chessboard calibration plate is placed at the XY section to be measured, specifically, the chessboard calibration plate is placed into the elbow-shaped flow channel 110 from the inlet end 111 of the elbow-shaped flow channel 110 and fixed at the corresponding XY section to be measured by a clamp, the corner points and size of the chessboard calibration plate are known, and a chessboard calibration image is shot and stored for subsequent conversion of pixel coordinates.

[0066] Step S213, the camera 230 is connected with the synchronizer, and the synchronizer emits a signal to control the camera 230 to continuously collect to obtain a set of continuous XY section particle images. The specific operation is as follows: the camera 230 is controlled to collect 2 current XY section particle images continuously, and then paused for 1 second, the sampling time of each frame is 0.002 seconds, and the single sampling time is 1800 frames. The synchronizer can control the camera 230 to obtain flow field data for a longer period of time in a single collection process, so as to obtain more accurate average flow field information.

[0067] Step S214, the matlab software is used to average the set of continuous 1800 frames of XY section particle images collected in step S213 respectively to obtain an average particle image containing background information, and then each particle image in the set of continuous XY section particle images is subtracted from the average particle image containing background information calculated, so as to effectively remove the interference of background light and obtain more accurate particle information.

[0068] Step S215, PIV calculation is performed on the continuous XY section particle images after removing the interference of background light to obtain the two-dimensional flow velocity vector of each node in the XY section to be measured in pixel unit, and the pixel unit is converted into real unit by combining the chessboard calibration image shot in step S212 to obtain the two-dimensional flow velocity vector (v, u) of each node in the XY section to be measured in real unit.

[0069] Step S216, for the remaining XY sections to be measured, the operations of steps S211 to S215 are repeated to carry out PIV flow field measurement.

[0070] Step S22, PIV flow field measurement is carried out on the b XZ sections:

[0071] Step S221, the laser 220 is installed on one side of the elbow-shaped flow channel 110, and the position of the laser 220 is adjusted so that the sheet of light formed by the laser is accurately overlapped with the current XZ section to be measured.

[0072] Step S222, the camera 230 is placed above the elbow-shaped flow channel 110, and the position of the camera 230 is adjusted to ensure clear shooting and ensure that the imaging plane of the camera is horizontal. The optimal angle of the camera should be controlled to be parallel to the current XZ section to be measured (the angle between the horizontal plane and the center line of the inlet section I of the elbow-shaped flow channel 110). Since the outlet end 112 of the elbow-shaped flow channel 110 is connected with the vertical axial flow pump 120, the optimal condition for camera installation cannot be met, so the camera 230 can only be controlled to be horizontal. Subsequently, perspective transformation correction is performed on the continuous images obtained by shooting to eliminate the distortion caused by the angle between the imaging plane of the camera and the section to be measured. In the case that the laser 220 is turned off, a chessboard calibration plate (the chessboard calibration plate and its placement method are the same as step S212) is placed at the current XZ section to be measured, and the camera 230 is placed at different shooting angles and positions relative to the chessboard calibration plate. A plurality of chessboard calibration images are stored for subsequent pixel coordinate conversion and perspective transformation correction of the images.

[0073] Step S223, the camera 230 is connected with the synchronizer, and the synchronizer emits signals to control the camera 230 to continuously collect a group of continuous XZ section particle images. The specific operation is as follows: the camera 230 is controlled to collect 2 current XZ section particle images continuously, and then paused for 1 second, the sampling time of each frame is 0.002 seconds, and the single sampling time is 1800 frames. The synchronizer can control the camera 230 to obtain flow field data for a longer period of time in a single collection process, so as to obtain more accurate average flow field information.

[0074] Step S224, perspective transformation correction is performed on the XZ section particle image using the chessboard calibration image:

[0075] The corner points of the checkerboard calibration plate in each checkerboard calibration image are detected by an existing corner point recognition image processing algorithm; the camera is calibrated by using MATLAB to calculate the internal and external parameters of the camera; four corner points are selected from the corresponding checkerboard calibration image, which are usually the four corner points of the checkerboard calibration plate, and the coordinates of these points are known; the four selected corner points in the checkerboard calibration image are mapped to the three-dimensional orthogonal coordinate system of the elbow-shaped runner inlet section; the perspective transformation matrix is calculated by using MATLAB; and the calculated perspective transformation matrix is applied to the captured continuous XZ sectional particle images, specifically, the pixel coordinates of the XZ sectional particle images captured in step S223 are multiplied by the above-mentioned perspective transformation matrix to correct the distorted particle images to a new rectangular plane, so as to eliminate the distortion caused by the camera angle tilt, and a set of corrected continuous XZ sectional particle images are obtained.

[0076] In step S225, the set of corrected continuous (1800 frames) XZ sectional particle images are averaged respectively by using MATLAB software to obtain an average image containing background information, and each image in the set of continuous XZ sectional particle images is subtracted from the calculated average image containing background information, so that the interference of background light can be effectively removed, and more accurate particle information can be obtained.

[0077] In step S226, PIV calculation is performed on the continuous XZ sectional particle images after the interference of background light is removed, so that two-dimensional flow velocity vectors of each node in the current to-be-measured XZ section in pixel units are obtained; and pixel units are converted into real units in combination with the calibration image captured in step S222, so that two-dimensional flow velocity vectors (v, w) of each node in the current to-be-measured XZ section in real units are obtained.

[0078] It can be understood that, considering that the imaging plane of the camera is horizontal when the XZ section is captured, and the to-be-measured XZ section is not horizontal and not parallel to the imaging plane, a certain distortion is generated. The chessboard calibration method is used for perspective correction of the XZ sectional particle images in the embodiment of the application. Before the XZ sectional particle images at different Y coordinates are collected, the prepared checkerboard is first fixed on the to-be-measured XZ section at the corresponding Y coordinate, and the position of the camera is adjusted to ensure clear shooting. After the checkerboard image at this time is captured, the perspective transformation matrix is calculated by using MATLAB. Under the premise that the camera parameters remain unchanged, the checkerboard is removed and the XZ sectional series particle images at the Y coordinate are captured. Finally, the perspective transformation matrix calculated is used for perspective transformation of the particle images, so that geometric correction of the images is realized.

[0079] In some embodiments, step S3 specifically comprises:

[0080] In step S31, two-dimensional interpolation is performed on each point in the a XY sections to obtain the flow velocity information v of the X direction and the Y direction of the to-be-measured node i、u i ; two-dimensional interpolation is performed on each point in the b XZ sections to obtain the X-direction and Z-direction flow velocity information v j 、w j ; since the known flow velocity information points in the PIV experiment are dense enough in the section, when performing two-dimensional interpolation on the XY section and the XZ section, a common spline interpolation can be selected to obtain the flow velocity information of the target grid point, specifically, the flow velocity information v i 、u i of several same (x, y) coordinates in the XY section under different Z coordinates, and the flow velocity information v j 、w j of several same (x, z) coordinates in the XZ section under different Y coordinates. Each measurement section is missing the third velocity component, such as XY missing w and XZ missing v, which needs to be completed in the subsequent interpolation of the third velocity component.

[0081] Step S32, three-dimensional interpolation refinement is performed on the three-dimensional grid composed of the a XY sections and the b XZ sections after interpolation to obtain the three-dimensional flow velocity information at the unknown nodes, and the three-dimensional flow field reconstruction inside the elbow-shaped flow passage is realized. Due to the existence of additional flow complexity and disturbance in the elbow-shaped flow passage in addition to the main flow, the flow field distribution is relatively complex. Direct three-dimensional interpolation of the flow velocity information on the a XY sections and the b XZ sections may produce large errors. Therefore, the continuity equation needs to be introduced as a physical constraint in the interpolation process to optimize the missing flow velocity component of each target grid point to obtain the reconstructed three-dimensional flow field inside the elbow-shaped flow passage. Specifically, the target value of the change of the average flow velocity along the flow process on each YZ section of the elbow-shaped flow passage in the flow measurement section should be defined. After interpolation, further optimization processing is performed to minimize the deviation between the adjusted velocity field and the initial three-dimensional interpolation result, so as to ensure that the final reconstruction result meets the above physical constraint condition. The continuity equation calculation formula is as follows:

[0082]

[0083] wherein v ' , u ' , w ' represent the three-dimensional flow velocity meeting the physical constraint;

[0084] Step S33, the turbulent kinetic energy k at each position in the flow measurement section is calculated through the reconstructed three-dimensional flow field inside the elbow-shaped flow passage, and the turbulent kinetic energy k is an important physical quantity for measuring the intensity of turbulent flow, and the calculation formula is as follows:

[0085]

[0086] wherein is the time average of the velocity fluctuation components in three directions (x, y, z).

[0087] k can quantify the flow stability of different regions in the flow measurement section, and the section with the minimum turbulent kinetic energy represents the most stable region in the flow field, so selecting this section as the installation position of the ultrasonic flowmeter can maximize the flow measurement accuracy.

[0088] It can be understood that the embodiment of the application is a single-camera-based PIV experiment, which reconstructs the three-dimensional flow field inside the elbow-shaped flow passage in a slicing manner, specifically, by carrying out a bidirectional flow field measurement experiment on the inlet section of the elbow-shaped flow passage, and by using three-dimensional interpolation to encrypt the sparse grid formed by the bidirectional two-dimensional flow field to obtain the three-dimensional velocity vector of each node in the coordinate system, and by introducing the continuity equation as a physical constraint to optimize the missing flow velocity component of each target grid point, so that the reconstruction result is more accurate; the high-precision three-dimensional flow field ensures the accuracy of the ultrasonic flowmeter positioning, thereby improving the measurement accuracy of the ultrasonic flowmeter in the elbow-shaped flow passage.

[0089] The second aspect embodiment of the application provides an ultrasonic flowmeter positioning system for an elbow-shaped flow passage, comprising:

[0090] A model experiment table is built for the inlet section of the pump station to be measured, which has an elbow-shaped flow passage as the inlet flow passage; a three-dimensional rectangular coordinate system xyz of the inlet section of the elbow-shaped flow passage in the model experiment table is defined, wherein the x-axis is parallel to the center line direction of the inlet section of the elbow-shaped flow passage, the z-axis is parallel to the width direction of the inlet end of the elbow-shaped flow passage, and the y-axis is perpendicular to the xz plane and points upward along the water depth, and the coordinate origin is located at the bottom of the inlet section of the elbow-shaped flow passage close to the inlet end; the flow velocity in the main flow direction in the elbow-shaped flow passage is defined as v, the flow velocity in the positive direction of the y-axis is defined as u, and the flow velocity in the positive direction of the z-axis is defined as w;

[0091] A PIV test device comprises a transparent water tank, a laser, and a single camera, and the elbow-shaped flow passage is arranged in the transparent water tank;

[0092] A two-dimensional flow velocity vector acquisition unit is configured to set the inlet section of the elbow-shaped flow passage as a flow measurement section, determine a plurality of XY sections to be measured at different Z coordinates and a plurality of XZ sections to be measured at different Y coordinates within the flow measurement section, and use the PIV test device to sequentially perform PIV two-dimensional flow field measurement on each of the measured sections to obtain the two-dimensional flow velocity vector of each of the measured sections;

[0093] A three-dimensional flow field reconstruction unit is configured to first perform two-dimensional interpolation on the two-dimensional flow velocity vector of each of the measured sections to obtain a two-dimensional flow velocity field of the flow measurement section; then introduce a continuity equation as a physical constraint to perform three-dimensional interpolation on the two-dimensional flow velocity field to reconstruct the three-dimensional flow field of the flow measurement section;

[0094] The positioning unit is configured to calculate the turbulent kinetic energy at each position in the flow measuring section according to the reconstructed three-dimensional flow field, and take the position with the minimum turbulent kinetic energy as the installation position of the ultrasonic flowmeter.

[0095] It should be noted that the foregoing embodiment of the method for positioning the ultrasonic flowmeter for the elbow-shaped flow passage is also applicable to the embodiment of the system for positioning the ultrasonic flowmeter for the elbow-shaped flow passage, and will not be repeated here.

[0096] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0097] Although the embodiments of the present application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. An ultrasonic flow meter positioning method for elbow flow conduits, characterized by, The application relates to a method for determining the installation position of an ultrasonic flowmeter. The method comprises the following steps: S1, a model test table of an inlet section of a pump station to be tested with an elbow-shaped flow channel as a water inlet flow channel is built, and a PIV test device is arranged; A three-dimensional rectangular coordinate system xyz of the inlet section of the elbow-shaped flow channel in the model test table is defined, wherein the x-axis is parallel to the center line direction of the inlet section of the elbow-shaped flow channel, the z-axis is parallel to the width direction of the inlet end of the elbow-shaped flow channel, the y-axis positive direction is perpendicular to the xz plane and upward along the water depth, and the coordinate origin is located on the bottom of the inlet section of the elbow-shaped flow channel close to the inlet end; the flow velocity in the main flow direction of the elbow-shaped flow channel is defined as v, the flow velocity in the y-axis positive direction is defined as u, and the flow velocity in the z-axis positive direction is defined as w; The PIV test device comprises a transparent water tank, a laser and a single camera, and the elbow-shaped flow channel is arranged in the transparent water tank; The inlet section of the elbow-shaped flow channel is arranged as a flow measurement section, a total of a XY cross sections under different Z coordinates and a total of b XZ cross sections under different Y coordinates are determined in the flow measurement section; S2, the PIV two-dimensional flow field measurement of each cross section is sequentially carried out by using the PIV test device, and the two-dimensional flow velocity vector of each cross section is obtained; S3, the two-dimensional flow velocity vector of each cross section is subjected to two-dimensional interpolation, and the two-dimensional flow velocity field of the flow measurement section is obtained; subsequently, the continuity equation is introduced as a physical constraint to carry out three-dimensional interpolation on the two-dimensional flow velocity field, and the three-dimensional flow field reconstruction of the flow measurement section is realized; 2. The ultrasonic flow meter positioning method of claim 1, wherein, S4, the turbulent kinetic energy of each position in the flow measurement section is calculated according to the reconstructed three-dimensional flow field, and the position with the minimum turbulent kinetic energy is taken as the installation position of the ultrasonic flowmeter. The model test table comprises the elbow-shaped flow channel, a vertical axial flow pump, a water outlet pipe, a connecting pipe and a circulating pool which are sequentially connected to form a circulating loop, the elbow-shaped flow channel is made of transparent material, and tracer particles are added in the fluid of the circulating loop; 3. The ultrasonic flow meter positioning method of claim 1, wherein, The determined cross sections are marked on the side wall of the transparent water tank, and it is ensured that the plane where the laser generated by the laser is coincident with the cross sections to be measured. In S2, the PIV two-dimensional flow field measurement of any XY cross section comprises the following steps: S211, the position of the laser arranged above the elbow-shaped flow channel is adjusted, so that the sheet light formed by the laser is coincident with the current XY cross section to be measured; S212, the camera is arranged on the side of the elbow-shaped flow channel, so that the camera can clearly image and ensure that the imaging plane of the camera is parallel to the current XY cross section to be measured; under the condition that the laser is turned off, a chessboard calibration plate is placed at the current XY cross section to be measured and a chessboard calibration image is shot; S213, a group of continuous XY cross section particle images of the current XY cross section to be measured are shot; S214, the continuous XY cross section particle images are averaged to obtain an average particle image containing background information, and each particle image in the continuous XY cross section particle images is subtracted by the average particle image containing background information to obtain continuous XY cross section particle images without background light interference; Step S215, PIV calculation is performed on the continuous XY cross-section particle images after the background light interference is removed, to obtain the two-dimensional flow velocity vector of each node in the current XY cross-section in pixel unit, and the two-dimensional flow velocity vector (v, u) of each node in the current XY cross-section is obtained by combining the chessboard calibration image photographed in step S212.

4. The ultrasonic flow meter positioning method of claim 1, wherein, In step S2, when performing PIV two-dimensional flow field measurement on any to-be-measured XZ cross-section, the imaging plane of the camera is horizontal and has an angle with the to-be-measured XZ cross-section, the perspective correction is performed on the to-be-measured XZ cross-section particle image photographed by the camera by using the chessboard calibration method, and the two-dimensional flow velocity vector (v, w) of each node in the to-be-measured XZ cross-section is obtained based on the corrected to-be-measured XZ cross-section particle image.

5. The ultrasonic flow meter positioning method of claim 1, wherein, In step S2, when performing PIV two-dimensional flow field measurement on any to-be-measured XZ cross-section, the imaging plane of the camera is horizontal and has an angle with the to-be-measured XZ cross-section, the perspective correction is performed on the to-be-measured XZ cross-section particle image photographed by the camera by using the chessboard calibration method, and the two-dimensional flow velocity vector (v, w) of each node in the to-be-measured XZ cross-section is obtained based on the corrected to-be-measured XZ cross-section particle image. Step S221, the position of the laser installed on one side of the elbow-shaped flow channel is adjusted so that the sheet of light formed by the laser coincides with a to-be-measured XZ cross-section; Step S222, the camera is erected above the elbow-shaped flow channel, the camera is clear imaging and the imaging plane of the camera is horizontal, the chessboard calibration plate is placed at the to-be-measured XZ cross-section under the condition that the laser is turned off, the camera is at different shooting angles and shooting positions relative to the chessboard calibration plate, and multiple chessboard calibration images are photographed; Step S223, a group of continuous XZ cross-section particle images of the to-be-measured XZ cross-section are obtained; Step S224, the corner points of the chessboard calibration plate in each chessboard calibration image are detected, each detected corner point is mapped to the three-dimensional rectangular coordinate system of the inlet section of the elbow-shaped flow channel, and the perspective transformation matrix is calculated, the perspective transformation matrix is applied to the continuous XZ cross-section particle images, the distortion caused by the inconsistency between the imaging plane of the camera and the to-be-measured XZ cross-section is eliminated, and the corrected continuous XZ cross-section particle images are obtained; Step S225, the corrected continuous XZ cross-section particle images are averaged to obtain an average particle image containing background information, each particle image in the corrected continuous XZ cross-section particle images is subtracted by the calculated average particle image containing background information, and the continuous XZ cross-section particle images after the background light interference is removed are obtained; Step S226, PIV calculation is performed on the continuous XZ cross-section particle images after the background light interference is removed, to obtain the two-dimensional flow velocity vector of each node in the current XZ cross-section in pixel unit, and the two-dimensional flow velocity vector (v, w) of each node in the current XZ cross-section is obtained by combining the chessboard calibration image photographed in step S222.

6. The ultrasonic flow meter positioning method of claim 1, wherein, In step S3, when the continuity equation is introduced as a physical constraint for three-dimensional interpolation of the two-dimensional flow velocity field, the target value of the change of the average flow velocity of each YZ cross-section of the elbow-shaped flow channel along the flow process is defined, the deviation between the adjusted velocity field and the initial three-dimensional interpolation result is minimized, and it is ensured that the final reconstruction result meets the physical constraint.

7. An ultrasonic flowmeter positioning system for elbow-shaped flow channels, characterized in that, It comprises: A model test bench is built for the inlet section of a pump station to be tested with an elbow-shaped flow channel as the water inlet flow channel; a three-dimensional rectangular coordinate system xyz of the inlet section of the elbow-shaped flow channel in the model test bench is defined, wherein the x-axis is parallel to the center line direction of the inlet section of the elbow-shaped flow channel, the z-axis is parallel to the width direction of the inlet end of the elbow-shaped flow channel, and the y-axis is perpendicular to the xz plane and positive in the upward water depth direction, and the coordinate origin is located at the bottom of the inlet section of the elbow-shaped flow channel close to the inlet end; the flow velocity in the main flow direction in the elbow-shaped flow channel is defined as v, the flow velocity in the positive y-axis direction is defined as u, and the flow velocity in the positive z-axis direction is defined as w; A PIV test device includes a transparent water tank, a laser, and a single camera, and the elbow-shaped flow channel is arranged in the transparent water tank; A two-dimensional flow velocity vector acquisition unit is configured to set the inlet section of the elbow-shaped flow channel as a flow measurement section, determine a plurality of to-be-tested XY cross sections at different Z coordinates and a plurality of to-be-tested XZ cross sections at different Y coordinates in the flow measurement section, and sequentially perform PIV two-dimensional flow field measurement on each to-be-tested cross section by using the PIV test device to obtain the two-dimensional flow velocity vector of each to-be-tested cross section; A three-dimensional flow field reconstruction unit is configured to first perform two-dimensional interpolation on the two-dimensional flow velocity vector of each to-be-tested cross section to obtain a two-dimensional flow velocity field of the flow measurement section, and then perform three-dimensional interpolation on the two-dimensional flow velocity field by introducing a continuity equation as a physical constraint to realize three-dimensional flow field reconstruction of the flow measurement section; A positioning unit is configured to calculate the turbulent kinetic energy at each position in the flow measurement section according to the reconstructed three-dimensional flow field, and determine the position with the minimum turbulent kinetic energy as the installation position of the ultrasonic flowmeter.

8. The ultrasonic flow meter positioning system of claim 7, wherein, The model test bench includes the elbow-shaped flow channel, a vertical axial flow pump, a water outlet pipe, a connecting pipe, and a circulating pool connected in sequence to form a circulating loop, the elbow-shaped flow channel is made of transparent material, and tracer particles are added to the fluid in the circulating loop; The determined to-be-tested cross sections are marked on the side wall of the transparent water tank to ensure that the plane where the laser generated by the laser is coincides with the to-be-tested cross section.

9. The ultrasonic flow meter positioning system of claim 7, wherein, When the two-dimensional flow velocity vector acquisition unit performs PIV two-dimensional flow field measurement on any to-be-tested XZ cross section, the imaging plane of the camera is horizontal and has an included angle with the to-be-tested XZ cross section, the perspective correction is performed on the to-be-tested XZ cross section particle image captured by the camera by using a chessboard calibration method, and the two-dimensional flow velocity vector of each node in the to-be-tested XZ cross section is obtained based on the corrected to-be-tested XZ cross section particle image.

10. The ultrasonic flow meter positioning system of claim 7, wherein, When the three-dimensional flow field reconstruction unit performs three-dimensional interpolation on the two-dimensional flow velocity field by introducing a continuity equation as a physical constraint, the target value of the change of the average flow velocity along the flow path on each YZ cross section of the elbow-shaped flow channel in the flow measurement section is defined, the deviation between the adjusted velocity field and the initial three-dimensional interpolation result is minimized, and it is ensured that the final reconstruction result meets the physical constraint.

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