Ultrasonic flowmeter positioning method and system for elbow flow channel

Abstract

The application discloses a positioning method for an ultrasonic flowmeter for an elbow-shaped flow channel, and comprises the following steps: building a model experiment table of an inlet section of a pump station to be measured with an elbow-shaped flow channel as a water inlet flow channel, setting a PIV test device, and defining a three-dimensional rectangular coordinate system of the inlet section of the elbow-shaped flow channel in the model experiment table; using the PIV test device to sequentially perform PIV two-dimensional flow field measurement on each to-be-measured cross section to obtain two-dimensional flow velocity vectors of each to-be-measured cross section; performing two-dimensional interpolation on the two-dimensional flow velocity vectors of each to-be-measured cross section to obtain a two-dimensional flow velocity field of a flow measuring section, 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 measuring section; and calculating turbulent kinetic energy at each position in the flow measuring section according to the reconstructed three-dimensional flow field, and taking a position with minimum turbulent kinetic energy as an installation position of the ultrasonic flowmeter. The application reconstructs a complex three-dimensional flow field inside the elbow-shaped flow channel through PIV, and provides an experimental basis for selection of the installation position of the ultrasonic flowmeter.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic flow meter installation and positioning technology, and specifically to an ultrasonic flow meter positioning method and system for elbow-shaped flow channels. Background Technology

[0002] The elbow-shaped water inlet channel is similar in shape to the human elbow joint and has the advantages of good hydraulic performance and reliable operation. It is widely used in large pumping stations.

[0003] The elbow-type inlet channel is an irregularly shaped, tapering rectangular channel consisting of three parts: an inlet section, a bend section, and an outlet section. The inlet section is a rectangular, tapering pipe with a constant width and a uniformly varying height along the flow path. The bend section's cross-section gradually transitions from rectangular to circular, with the cross-sectional area gradually decreasing along the flow path. The outlet section is a tapering conical pipe that connects to the pump's seat ring at the outlet. The constantly changing cross-sectional shape and size of the elbow-type inlet channel from inlet to outlet introduce flow complexity and disturbances beyond the main flow, resulting in a complex flow field distribution. In large pumping stations, the magnitude and direction of the water flow velocity in the elbow-type inlet channel vary along the flow path, preventing the fluid flow from fully developing. Furthermore, the asymmetrical inflow characteristics of the outermost unit in the combined operation of different pumping units within the station further complicate the flow field distribution due to its asymmetrical inflow characteristics. The flow pattern distribution within the flow channel directly affects the measurement accuracy of the ultrasonic flow meter: non-uniformity, asymmetry, backflow, and flow deviation can all lead to unstable ultrasonic wave propagation, thus affecting the measurement accuracy. Therefore, selecting a suitable installation and measurement position within the elbow-shaped flow channel is crucial for improving the measurement accuracy of the ultrasonic flow meter.

[0004] Currently, there is no feasible experimental method to provide experimental basis for selecting the installation location of ultrasonic flow meters with complex flow channels such as elbow-shaped flow channels. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the related art.

[0006] Therefore, the purpose of this invention is to provide a method and system for locating ultrasonic flow meters in elbow-shaped flow channels. By reconstructing the complex three-dimensional flow characteristics inside the elbow-shaped flow channel using a single-camera PIV, it provides experimental basis for selecting the optimal installation position of the ultrasonic flow meter, which is of great significance for ensuring the flow measurement accuracy of ultrasonic flow meters in large pumping stations.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of this invention provides a method for locating an ultrasonic flow meter for an elbow-shaped flow channel, comprising:

[0009] Step S1: Build a model test platform for the inlet section of the pump station under test, with an elbow-shaped flow channel as the inlet flow channel, and set up PIV test equipment.

[0010] Define a three-dimensional rectangular coordinate system xyz for the inlet section of the elbow-shaped flow channel in the model experimental platform, where the x-axis is the direction parallel to the center line of the inlet section of the elbow-shaped flow channel, the z-axis is the direction parallel to the width of the inlet end of the elbow-shaped flow channel, and the positive y-axis is perpendicular to the xz plane and upward along the water depth. The origin of the coordinate system is located at the bottom of the inlet section of the elbow-shaped flow channel near the inlet end. Define the flow velocity in the main flow direction of the elbow-shaped flow channel as v, the flow velocity in the positive y-axis direction as u, and the flow velocity in the positive z-axis direction as w.

[0011] The PIV testing equipment includes a transparent water tank, a laser, and a single camera, with the elbow-shaped flow channel disposed inside the transparent water tank;

[0012] The inlet section of the elbow-shaped flow channel is set as the flow measurement section, and within the range of the flow measurement section, a XY sections to be measured under different Z coordinates and b XZ sections to be measured under different Y coordinates are determined.

[0013] Step S2: Use the PIV testing equipment to perform PIV two-dimensional flow field measurements on each test section in sequence to obtain the two-dimensional velocity vector of each test section;

[0014] Step S3: First, perform two-dimensional interpolation on the two-dimensional velocity vectors of each cross section to be measured to obtain the two-dimensional velocity field of the measuring section; then, introduce the continuity equation 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 measuring section.

[0015] Step S4: Calculate the turbulent kinetic energy at each location within the flow measurement section based on the reconstructed three-dimensional flow field, and take the location with the minimum turbulent kinetic energy as the installation location of the ultrasonic flow meter.

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

[0017] Mark the determined cross-sections to be tested on the side wall of the transparent water tank to ensure that the plane of the laser generated by the laser coincides with the cross-section to be tested.

[0018] In some embodiments, step S2, when performing a two-dimensional flow field measurement of any XY section to be measured using PIV, includes:

[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 coincides with an XY section to be measured.

[0020] Step S212: Set up the camera on the side of the elbow-shaped flow channel, make the camera clearly image and ensure that the camera imaging plane is parallel to the XY section to be measured. With the laser off, place the checkerboard calibration plate at the XY section to be measured and take a checkerboard calibration image.

[0021] Step S213: Take a set of continuous XY cross-sectional particle images for the current XY cross-section to be tested;

[0022] Step S214: Average the continuous XY cross-sectional particle images to obtain an average particle image containing background information. Subtract the calculated average particle image containing background information from each particle image in the continuous XY cross-sectional particle images to obtain a continuous XY cross-sectional particle image with background light interference removed.

[0023] Step S215: Perform PIV calculation on the continuous XY cross-section particle image after removing background light interference to obtain the two-dimensional flow velocity vector of each node in the current XY cross-section under test in pixel units. Combined with the checkerboard calibration image taken in step S212, obtain the two-dimensional flow velocity vector (v, u) of each node in the current XY cross-section under test.

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

[0025] In some embodiments, step S2, when performing a two-dimensional PIV flow field measurement on any XZ section to be measured, includes:

[0026] Step S221: Adjust the position of the laser installed on one side of the elbow-shaped flow channel so that the sheet light formed by the laser coincides with an XZ section to be measured.

[0027] Step S222: Set up the camera above the elbow-shaped flow channel to make the camera clearly image and ensure that the camera imaging plane is horizontal. With the laser off, place the checkerboard calibration plate at the current XZ section to be measured, so that the camera is at different shooting angles and shooting positions relative to the checkerboard calibration plate, and take multiple checkerboard calibration images.

[0028] Step S223: Obtain a set of continuous XZ cross-section particle images for the current XZ cross-section to be measured;

[0029] Step S224: Detect the corner points of the checkerboard calibration plate in each checkerboard calibration image, map each detected corner point to the three-dimensional rectangular coordinate system of the inlet section of the elbow-shaped flow channel and calculate the perspective transformation matrix, apply the perspective transformation matrix to the continuous XZ cross-section particle image to eliminate the distortion caused by the inconsistency between the camera imaging plane and the XZ cross-section to be measured, and obtain the corrected continuous XZ cross-section particle image.

[0030] Step S225: Average the corrected continuous XZ cross-section particle image to obtain an average particle image containing background information. Subtract the calculated average particle image containing background information from each particle image in the corrected continuous XZ cross-section particle image to obtain a continuous XZ cross-section particle image with background light interference removed.

[0031] Step S226: Perform PIV calculation on the continuous XZ cross-section particle image after removing background light interference to obtain the two-dimensional flow velocity vector of each node in the current XZ cross-section under test in pixel units. Combined with the checkerboard calibration image taken in step S222, obtain the two-dimensional flow velocity vector (v, w) of each node in the current XZ cross-section under test.

[0032] In some embodiments, in step S3, when introducing a continuity equation as a physical constraint to perform three-dimensional interpolation on the two-dimensional velocity field, a target value for the change of the average velocity along the flow path on each YZ section of the elbow-shaped channel within the flow measurement section is defined. By minimizing the deviation between the adjusted velocity field and the initial three-dimensional interpolation result, the final reconstruction result is ensured to meet the physical constraint.

[0033] A second aspect of the present invention provides an ultrasonic flowmeter positioning system for elbow-shaped flow channels, comprising:

[0034] The model test bench is constructed for the inlet section of a pump station under test that uses an elbow-shaped flow channel as its inlet channel. A three-dimensional rectangular coordinate system xyz is defined for the inlet section of the elbow-shaped flow channel in the model test bench. The x-axis is parallel to the centerline of the inlet section of the elbow-shaped flow channel, the z-axis is parallel to the width of the inlet end of the elbow-shaped flow channel, and the positive y-axis is perpendicular to the xz plane and extends upwards along the water depth. The origin of the coordinate system is located at the bottom of the inlet section of the elbow-shaped flow channel near the inlet end. The velocity in the main flow direction within the elbow-shaped flow channel is defined as v, the velocity in the positive y-axis direction is defined as u, and the velocity in the positive z-axis direction is defined as w.

[0035] The PIV testing equipment includes a transparent water tank, a laser, and a single camera, with the elbow-shaped flow channel located inside 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] In the picture:

[0046] 100. Model experimental platform; 110. Elbow-shaped flow channel; 111. Inlet end; 112. Outlet end; 120. Vertical axial flow pump; 130. Water outlet pipe; 140. Connecting pipe; 150. Circulation tank; I. Inlet section; II. Bend section; III. Outlet section.

[0047] 200. PIV testing equipment; 210. Transparent water tank; 220. Laser; 230. Camera. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application.

[0049] Conversely, this application covers any alternatives, modifications, equivalent methods, and schemes made within the spirit and scope of this application as defined by the claims. Furthermore, to provide the public with a better understanding of this application, certain specific details are described in detail below. However, this application can be fully understood by those skilled in the art even without these detailed descriptions.

[0050] See Figure 1 The first aspect of the present invention provides a method for locating an ultrasonic flow meter for an elbow-shaped flow channel, comprising the following steps:

[0051] Step S1: For the pump station under test that uses an elbow-shaped flow channel as the inlet flow channel, construct a model test bench 100 for its inlet section and set up a PIV test device 200, wherein:

[0052] See Figure 2 and Figure 3(a) and (b) show a model experimental platform 100, comprising an elbow-shaped flow channel 110, a vertical axial flow pump 120, an outlet pipe 130, a connecting pipe 140, and a circulation tank 150 connected in sequence to form a circulation loop. The elbow-shaped flow channel 110 is made of transparent material and is divided into an inlet section I, a curved section II, and an outlet section III along the direction of water flow. The outlet end 112 of the elbow-shaped flow channel 110 is connected to one end of the outlet pipe 130 via the vertical axial flow pump 120. The other end of the outlet pipe 130 is connected to the circulation tank 150 via the connecting pipe 140. The circulation tank 150 is connected to the inlet end 111 of the elbow-shaped flow channel 110. The fluid in the circulation loop... Tracer particles are added; let the width and height of the inlet end 111 of the elbow-shaped flow channel 110 be B and H respectively, construct a three-dimensional rectangular coordinate system xyz for the inlet section I, with the direction parallel to the center line of the inlet section I of the elbow-shaped flow channel 110 as the x-axis, and define the direction along the water flow as the positive direction of the x-axis, the direction parallel to the width of the inlet end 111 of the elbow-shaped flow channel 110 as the z-axis, and the direction perpendicular to the xz plane and upward along the water depth as the positive direction of the y-axis, with the origin of the coordinate system located at the bottom of the inlet section I near the inlet end 111; define the flow velocity in the main flow direction within the elbow-shaped flow channel 110 as v, the flow velocity in the positive direction of the y-axis as u, and the flow velocity in the positive direction of the z-axis as w;

[0053] See Figure 4 The PIV testing equipment 200 includes a transparent water tank 210, a laser 220, and a single camera 230. An elbow-shaped flow channel 110 is set inside the transparent water tank 210. The fluids inside the elbow-shaped flow channel 110 and the transparent water tank 210 are independent of each other. The laser 220 and the camera 230 are both mounted near the elbow-shaped flow channel 110. The acquisition frequency of the camera 230 is controlled by a synchronizer (not shown in the figure).

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

[0055] Step S2: Use the PIV testing equipment to perform PIV two-dimensional flow field measurements on each test section in sequence to obtain the two-dimensional velocity vector of each test section;

[0056] Step S3: First, perform two-dimensional interpolation on the two-dimensional velocity vectors of each cross section to be measured obtained in step S2 to obtain the two-dimensional velocity field of the measuring section; then, introduce the continuity equation 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 measuring section.

[0057] Step S4: Calculate the turbulent kinetic energy at each location within the flow measurement section based on the three-dimensional flow field reconstructed in step S3, and take the location with the minimum turbulent kinetic energy as the installation location of the ultrasonic flow meter.

[0058] In some embodiments, step S1 involves using a large-scale pumping station with an elbow-shaped inlet channel as a typical pumping station. A model experimental platform 100 is constructed based on the principle of hydraulic similarity to strictly reproduce the basic characteristics of the elbow-shaped inlet channel in actual engineering. In this embodiment, the model experimental platform 100 has four parallel and symmetrically distributed elbow-shaped channels, sequentially designated as elbow-shaped channels 1# to 4#. Elbow-shaped channels 1# and 4# are located on the sides, and the outlet end 112 of each elbow-shaped channel is connected to a vertical axial flow pump 120. (See also...) Figure 2 Both elbow-shaped flow channels #1 and #4 are side units. Due to their symmetrical distribution, only the #1 elbow-shaped flow channel can be used for inlet flow pattern PIV experiments, which can represent the distribution of inlet flow patterns inside the elbow-shaped flow channel of the #4 side unit under symmetrical operation conditions. A transparent water tank 210 is built outside the elbow-shaped flow channel of the side unit where the PIV experiment is to be conducted. A laser 220 is placed above the elbow-shaped flow channel, and a single camera 230 is placed 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 ensured to be stable, thereby improving the accuracy of PIV measurement.

[0059] It should be noted that the relatively simple geometry of the elbow-shaped flow channel inlet section provides a relatively stable flow field and reliable acoustic wave propagation environment for the ultrasonic flow meter, while the complex flow characteristics of the curved section introduce significant errors. Therefore, the ultrasonic transducers are all installed in the inlet section of the elbow-shaped flow channel, and this invention only conducts PIV experiments on the inlet section of the elbow-shaped flow channel.

[0060] Further, in step S1, the laser 220 in the PIV testing equipment 200 uses a sheet light source. After the model experimental platform 100 and the PIV testing equipment 200 are built, it is necessary to determine a XY sections under different Z coordinates and b XZ sections under different Y coordinates. Each section to be tested 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 coincides precisely with the section to be tested to be photographed. The number of a and b is set according to the testing accuracy of PIV. In this embodiment, a section to be tested is taken every 4 cm within the inlet section I.

[0061] It is understood that the embodiments of the present invention are aimed at the elbow-shaped water inlet channel commonly found in large pumping stations. This channel is different from the traditional circular or square straight pipe. It is an irregular channel with variable rectangular contraction. It is necessary to construct a corresponding three-dimensional rectangular coordinate system based on its channel centerline and its main dimensions to determine the XY section and XZ section direction, which is convenient for subsequent PIV two-dimensional flow field calculation.

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

[0063] Step S21: Perform PIV flow field measurements on a XY cross sections:

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

[0065] Step S212: Adjust the position of the camera 230, which is placed on the side of the elbow-shaped flow channel 110 via a tripod, to ensure clear imaging and that the camera's imaging plane is parallel to the current XY section to be measured. With the laser 220 off, place a checkerboard calibration plate at the current XY section to be measured. Specifically, the checkerboard calibration plate can be inserted into the elbow-shaped flow channel 110 from the inlet end 111 and fixed at the corresponding XY section to be measured using a clamp. The corner points and dimensions of the checkerboard calibration plate are known. Take a picture of the checkerboard calibration and store it for subsequent pixel coordinate conversion.

[0066] Step S213: Connect camera 230 to a synchronizer. The synchronizer sends a signal to control camera 230 to continuously acquire a set of continuous XY cross-sectional particle images. Specifically, camera 230 continuously acquires two images of the current XY cross-section particle data, then pauses for one second. Each frame has a sampling duration of 0.002 seconds, and a single sampling duration is 1800 frames. The synchronizer can adjust camera 230 to acquire flow field data over a longer period during a single acquisition, thereby obtaining more accurate average flow field information.

[0067] Step S214: Use MATLAB software to average the 1800 consecutive XY cross-sectional particle images acquired in step S213 to obtain an average particle image containing background information. Then, subtract the calculated average particle image containing background information from each particle image in the set of consecutive XY cross-sectional particle images to effectively remove the interference of background light and obtain more accurate particle information.

[0068] Step S215: Perform PIV calculation on the continuous XY cross-sectional particle image after removing background light interference to obtain the two-dimensional velocity vector of each node in the current XY cross-section under test in pixel units. Combined with the checkerboard calibration image taken in step S212, convert the pixel units to real units to obtain the two-dimensional velocity vector (v, u) of each node in the current XY cross-section under test in real units.

[0069] Step S216: For the remaining XY sections to be measured, repeat the operations of steps S211 to S215 to carry out PIV flow field measurements.

[0070] Step S22: Perform PIV flow field measurements on b XZ cross sections:

[0071] Step S221: Install the laser 220 on one side of the elbow-shaped flow channel 110, and adjust the position of the laser 220 so that the sheet light formed by the laser precisely coincides with an XZ section to be measured.

[0072] Step S222: Place the camera 230 above the elbow-shaped flow channel 110, adjust the position of the camera 230 to ensure clear imaging, 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 XZ section to be measured (the angle with the horizontal plane is the angle between the center line of the inlet section I of the elbow-shaped flow channel 110 and the horizontal plane). Since the outlet end 112 of the elbow-shaped flow channel 110 is connected to the vertical axial flow pump 120, the optimal conditions for camera installation are not met. Therefore, 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 camera imaging plane and the section to be measured. With the laser 220 off, a checkerboard calibration plate is placed at the XZ section to be measured (the checkerboard calibration plate and its placement method are the same as in step S212), so that the camera 230 is at different shooting angles and shooting positions relative to the checkerboard calibration plate, and multiple checkerboard calibration images are stored for subsequent pixel coordinate transformation and perspective transformation correction of the images.

[0073] Step S223: Connect camera 230 to a synchronizer. The synchronizer sends a signal to control camera 230 to continuously acquire a set of continuous XZ cross-sectional particle images. Specifically, camera 230 continuously acquires two images of the current XZ cross-section particle data, then pauses for one second. Each frame has a sampling duration of 0.002 seconds, and a single sampling duration is 1800 frames. The synchronizer can adjust camera 230 to acquire flow field data over a longer period during a single acquisition, thereby obtaining more accurate average flow field information.

[0074] Step S224: Use the checkerboard calibration image to perform perspective transformation correction on the XZ section particle image:

[0075] Using existing corner detection image processing algorithms, the corner points of the checkerboard calibration plate in each checkerboard calibration image are detected. Camera calibration is performed using MATLAB, and the camera's intrinsic and extrinsic parameters are calculated. Four corner points are selected from the corresponding checkerboard calibration image, usually the four corner points of the checkerboard calibration plate, whose coordinates are known. The four corner points selected in the checkerboard calibration image are mapped to the three-dimensional rectangular coordinate system of the elbow-shaped flow channel inlet section. The perspective transformation matrix is ​​calculated using MATLAB. The calculated perspective transformation matrix is ​​applied to the captured continuous XZ cross-sectional particle images. Specifically, the pixel coordinates of the XZ cross-sectional particle images acquired in step S223 are multiplied by the above perspective transformation matrix to correct the distorted particle images to a new rectangular plane, thereby eliminating the distortion caused by the camera angle tilt, and obtaining a set of corrected continuous XZ cross-sectional particle images.

[0076] Step S225: Use MATLAB software to average a set of corrected continuous (1800 frames) XZ cross-sectional particle images to obtain an average image containing background information. Then, subtract the calculated average image containing background information from each image in this set of continuous XZ cross-sectional particle images to effectively remove the interference of background light and obtain more accurate particle information.

[0077] Step S226: Perform PIV calculation on the continuous XZ cross-section particle image after removing background light interference to obtain the two-dimensional velocity vector of each node in the current XZ cross-section under test in pixel units. Combined with the calibration image taken in step S222, convert the pixel units to real units to obtain the two-dimensional velocity vector (v, w) of each node in the current XZ cross-section under test in real units.

[0078] It is understandable that, considering the camera's imaging plane is horizontal when capturing the XZ cross-section, while the XZ cross-section under test is not horizontal, the two are not parallel, resulting in some distortion. This embodiment of the invention employs a checkerboard calibration method to perform perspective correction on the XZ cross-section particle images. Before acquiring XZ cross-section particle images at different Y coordinates, a pre-fabricated checkerboard is first fixed on the XZ cross-section under test at the corresponding Y coordinate, and the camera position is adjusted to ensure clear imaging. After capturing the checkerboard image at this point, the perspective transformation matrix is ​​calculated using MATLAB. While keeping the camera parameters unchanged, the checkerboard is removed, and a series of XZ cross-section particle images are captured at that Y coordinate. Finally, the calculated perspective transformation matrix is ​​used to perform perspective transformation on the particle images, thereby achieving geometric correction of the images.

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

[0080] Step S31: Perform two-dimensional interpolation on each point in the a XY cross sections to obtain the flow velocity information v in the X and Y directions at the node to be measured. iu i Two-dimensional interpolation is performed at each point in the b XZ sections to obtain the flow velocity information v in the X and Z directions at the node to be measured. j w j Since the information points of known flow velocities within the cross-section obtained from the PIV experiment are sufficiently dense, when performing two-dimensional interpolation on the XY and XZ cross-sections, the more common spline interpolation can be selected to obtain the flow velocity information of the target grid points. Specifically, this involves obtaining the flow velocity information v at several identical (x,y) coordinates within the XY cross-section under different Z coordinates. i u i And flow velocity information v at several identical (x,z) coordinates within the XZ section under different Y coordinates. j w j Each measurement section lacks a third velocity component; for example, XY lacks w, and XZ lacks v. The third velocity component needs to be supplemented in subsequent interpolation.

[0081] Step S32: Refine the 3D mesh composed of a XY sections and b XZ sections after interpolation to obtain 3D velocity information at unknown nodes, thus reconstructing the 3D flow field inside the elbow-shaped channel. Due to the additional flow complexity and disturbances besides the main flow within the elbow-shaped channel, the flow field distribution is quite complex. Directly interpolating the velocity information on a XY sections and b XZ sections may produce significant errors. Therefore, a continuity equation needs to be introduced as a physical constraint during interpolation to optimize the missing velocity components at each target mesh point, obtaining the reconstructed 3D flow field inside the elbow-shaped channel. Specifically, a target value for the variation of the average velocity along the flow path on each YZ section of the elbow-shaped channel within the measurement section should be defined. After interpolation, further optimization is performed to minimize the deviation between the adjusted velocity field and the initial 3D interpolation result, ensuring that the final reconstruction result meets the above physical constraints. The formula for calculating the continuity equation is as follows:

[0082]

[0083] Among them, v ' u ' w ' Represents the three-dimensional flow velocity that satisfies physical constraints;

[0084] Step S33: Using the reconstructed three-dimensional flow field inside the elbow-shaped channel, calculate the turbulent kinetic energy k at each location within the measurement section. Turbulent kinetic energy k is an important physical quantity for measuring turbulence intensity, and the calculation formula is as follows:

[0085]

[0086] in, The time average of the velocity fluctuation components in the three directions (x, y, z);

[0087] k can quantify the flow stability in different regions within the flow measurement section. The section with the lowest turbulent kinetic energy represents the most stable region in the flow field. Therefore, selecting this section as the installation location for the ultrasonic flow meter can maximize the flow measurement accuracy.

[0088] Yes, it is understood that this invention provides a single-camera-based PIV experiment, which uses a slicing method to reconstruct the three-dimensional flow field inside the elbow-shaped channel. Specifically, by conducting a bidirectional flow field measurement experiment at the inlet section of the elbow-shaped channel, and using three-dimensional interpolation to refine the sparse grid formed by the bidirectional two-dimensional flow field, the three-dimensional velocity vectors of each node in the coordinate system are obtained. At the same time, a continuity equation is introduced as a physical constraint to optimize the missing velocity components of each target grid point, making the reconstruction results more accurate. The high-precision three-dimensional process ensures the accuracy of ultrasonic flow meter positioning, thereby improving the measurement accuracy of ultrasonic flow meter in the elbow-shaped channel.

[0089] A second aspect of the present invention provides an ultrasonic flowmeter positioning system for elbow-shaped flow channels, comprising:

[0090] The model test bench is constructed for the inlet section of the pump station under test, which uses an elbow-shaped flow channel as the inlet channel. A three-dimensional rectangular coordinate system xyz is defined for the inlet section of the elbow-shaped flow channel in the model test bench. The x-axis is parallel to the centerline of the inlet section of the elbow-shaped flow channel, the z-axis is parallel to the width of the inlet end of the elbow-shaped flow channel, and the positive y-axis is perpendicular to the xz plane and upwards along the water depth. The origin of the coordinate system is located at the bottom of the elbow-shaped flow channel inlet section near the inlet end. The velocity in the main flow direction within the elbow-shaped flow channel is defined as v, the velocity in the positive y-axis direction is defined as u, and the velocity in the positive z-axis direction is defined as w.

[0091] The PIV testing equipment includes a transparent water tank, a laser, and a single camera, with an elbow-shaped flow channel set inside the transparent water tank;

[0092] The two-dimensional velocity vector acquisition unit is configured to set the inlet section of the elbow-shaped flow channel as the 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 measurement section, and use the PIV test equipment to perform PIV two-dimensional flow field measurement on each section to be measured in sequence to obtain the two-dimensional velocity vector of each section to be measured.

[0093] 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.

[0094] 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.

[0095] It should be noted that the foregoing explanation of an embodiment of an ultrasonic flow meter positioning method for an elbow-shaped flow channel also applies to an ultrasonic flow meter positioning system for an elbow-shaped flow channel in this embodiment, and will not be repeated here.

[0096] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0097] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for locating an ultrasonic flow meter in an elbow-shaped flow channel, characterized in that, include: Step S1: Build a model test platform for the inlet section of the pump station under test, with an elbow-shaped flow channel as the inlet flow channel, and set up PIV test equipment. Define a three-dimensional rectangular coordinate system xyz for the inlet section of the elbow-shaped flow channel in the model experimental platform, where the x-axis is the direction parallel to the center line of the inlet section of the elbow-shaped flow channel, the z-axis is the direction parallel to the width of the inlet end of the elbow-shaped flow channel, and the positive y-axis is perpendicular to the xz plane and upward along the water depth. The origin of the coordinate system is located at the bottom of the inlet section of the elbow-shaped flow channel near the inlet end. Define the flow velocity in the main flow direction of the elbow-shaped flow channel as v, the flow velocity in the positive y-axis direction as u, and the flow velocity in the positive z-axis direction as w. The PIV testing equipment includes a transparent water tank, a laser, and a single camera, with the elbow-shaped flow channel disposed inside the transparent water tank; The inlet section of the elbow-shaped flow channel is set as the flow measurement section, and within the range of the flow measurement section, a XY sections to be measured under different Z coordinates and b XZ sections to be measured under different Y coordinates are determined. Step S2: Use the PIV testing equipment to perform PIV two-dimensional flow field measurements on each test section in sequence to obtain the two-dimensional velocity vector of each test section; Step S3: 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 measuring section; then, introduce the continuity equation 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 measuring section. Step S4: Calculate the turbulent kinetic energy at each location within the flow measurement section based on the reconstructed three-dimensional flow field, and take the location with the minimum turbulent kinetic energy as the installation location of the ultrasonic flow meter.

2. The ultrasonic flow meter positioning method according to claim 1, characterized in that, The model experimental platform includes an elbow-shaped flow channel, a vertical axial flow pump, a water outlet pipe, a connecting pipe, and a circulation tank connected in sequence to form a circulation loop. The elbow-shaped flow channel is made of transparent material, and tracer particles are added to the fluid in the circulation loop. Mark the determined cross-sections to be tested on the side wall of the transparent water tank to ensure that the plane of the laser generated by the laser coincides with the cross-section to be tested.

3. The ultrasonic flow meter positioning method according to claim 1, characterized in that, In step S2, when performing a two-dimensional PIV flow field measurement on any XY section to be measured, the following steps are included: Step S211: Adjust the position of the laser installed above the elbow-shaped flow channel so that the sheet light formed by the laser coincides with an XY section to be measured. Step S212: Set up the camera on the side of the elbow-shaped flow channel, make the camera clearly image and ensure that the camera imaging plane is parallel to the XY section to be measured. With the laser off, place the checkerboard calibration plate at the XY section to be measured and take a checkerboard calibration image. Step S213: Take a set of continuous XY cross-sectional particle images for the current XY cross-section to be tested; Step S214: Average the continuous XY cross-sectional particle images to obtain an average particle image containing background information. Subtract the calculated average particle image containing background information from each particle image in the continuous XY cross-sectional particle images to obtain a continuous XY cross-sectional particle image with background light interference removed. Step S215: Perform PIV calculation on the continuous XY cross-section particle image after removing background light interference to obtain the two-dimensional flow velocity vector of each node in the current XY cross-section under test in pixel units. Combined with the checkerboard calibration image taken in step S212, obtain the two-dimensional flow velocity vector (v, u) of each node in the current XY cross-section under test.

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

5. The ultrasonic flow meter positioning method according to claim 1, characterized in that, In step S2, when performing PIV two-dimensional flow field measurement on any XZ section to be measured, the following steps are included: Step S221: Adjust the position of the laser installed on one side of the elbow-shaped flow channel so that the sheet light formed by the laser coincides with an XZ section to be measured. Step S222: Set up the camera above the elbow-shaped flow channel to make the camera clearly image and ensure that the camera imaging plane is horizontal. With the laser off, place the checkerboard calibration plate at the current XZ section to be measured, so that the camera is at different shooting angles and shooting positions relative to the checkerboard calibration plate, and take multiple checkerboard calibration images. Step S223: Obtain a set of continuous XZ cross-section particle images for the current XZ cross-section to be measured; Step S224: Detect the corner points of the checkerboard calibration plate in each checkerboard calibration image, map each detected corner point to the three-dimensional rectangular coordinate system of the inlet section of the elbow-shaped flow channel and calculate the perspective transformation matrix, apply the perspective transformation matrix to the continuous XZ cross-section particle image to eliminate the distortion caused by the inconsistency between the camera imaging plane and the XZ cross-section to be measured, and obtain the corrected continuous XZ cross-section particle image. Step S225: Average the corrected continuous XZ cross-section particle image to obtain an average particle image containing background information. Subtract the calculated average particle image containing background information from each particle image in the corrected continuous XZ cross-section particle image to obtain a continuous XZ cross-section particle image with background light interference removed. Step S226: Perform PIV calculation on the continuous XZ cross-section particle image after removing background light interference to obtain the two-dimensional flow velocity vector of each node in the current XZ cross-section under test in pixel units. Combined with the checkerboard calibration image taken in step S222, obtain the two-dimensional flow velocity vector (v, w) of each node in the current XZ cross-section under test.

6. The ultrasonic flow meter positioning method according to claim 1, characterized in that, In step S3, when the continuity equation is introduced as a physical constraint to perform three-dimensional interpolation on the two-dimensional velocity field, the target value of the change of the average velocity along the flow path on each YZ section of the elbow-shaped channel within the flow measurement section is defined. By minimizing the deviation between the adjusted velocity field and the initial three-dimensional interpolation result, the final reconstruction result is ensured to meet the physical constraint.

7. An ultrasonic flowmeter positioning system for elbow-shaped flow channels, characterized in that, include: The model test bench is constructed for the inlet section of a pump station under test that uses an elbow-shaped flow channel as its inlet channel. A three-dimensional rectangular coordinate system xyz is defined for the inlet section of the elbow-shaped flow channel in the model test bench. The x-axis is parallel to the centerline of the inlet section of the elbow-shaped flow channel, the z-axis is parallel to the width of the inlet end of the elbow-shaped flow channel, and the positive y-axis is perpendicular to the xz plane and extends upwards along the water depth. The origin of the coordinate system is located at the bottom of the inlet section of the elbow-shaped flow channel near the inlet end. The velocity in the main flow direction within the elbow-shaped flow channel is defined as v, the velocity in the positive y-axis direction is defined as u, and the velocity in the positive z-axis direction is defined as w. The PIV testing equipment includes a transparent water tank, a laser, and a single camera, with the elbow-shaped flow channel located inside the transparent water tank; 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. 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. 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.

8. The ultrasonic flowmeter positioning system according to claim 7, characterized in that, The model experimental platform includes an elbow-shaped flow channel, a vertical axial flow pump, a water outlet pipe, a connecting pipe, and a circulation tank connected in sequence to form a circulation loop. The elbow-shaped flow channel is made of transparent material, and tracer particles are added to the fluid in the circulation loop. Mark the determined cross-sections to be tested on the side wall of the transparent water tank to ensure that the plane of the laser generated by the laser coincides with the cross-section to be tested.

9. The ultrasonic flowmeter positioning system according to claim 7, characterized in that, When the two-dimensional velocity vector acquisition unit performs PIV two-dimensional flow field measurement on any XZ section to be measured, the imaging plane of the camera is horizontal and has an angle with the XZ section to be measured. The particle image of the XZ section to be measured captured by the camera is corrected by perspective using the checkerboard calibration method. Based on the corrected particle image of the XZ section to be measured, the two-dimensional velocity vector of each node in the XZ section to be measured is obtained.

10. The ultrasonic flowmeter positioning system according to claim 7, characterized in that, When the three-dimensional flow field reconstruction unit introduces the continuity equation as a physical constraint to perform three-dimensional interpolation of the two-dimensional velocity field, it defines the target value of the change of the average velocity along the flow path on each YZ section of the elbow-shaped channel within the flow measurement section. By minimizing the deviation between the adjusted velocity field and the initial three-dimensional interpolation result, it ensures that the final reconstruction result meets the physical constraint.

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