Methods and systems for selecting drag-reducing materials in water conveyance projects

Abstract

This invention discloses a method and system for selecting drag-reducing materials in water conveyance projects. The selection method includes: S1 applying the drag-reducing material to be tested onto a test sample and placing it in a water conveyance test section; S2 adjusting the average flow velocity of the cross-section of the water conveyance test section until the water flow enters the square resistance zone, and calculating the comprehensive roughness of the water conveyance test section while maintaining a constant flow state; S3 calculating the roughness of the test sample coated with drag-reducing material; S4 acquiring a two-dimensional planar flow field along the water flow direction in the water conveyance test section, and obtaining the near-wall average flow velocity and vertical velocity gradient of the test sample coated with drag-reducing material from the vertical velocity distribution; S5 obtaining the drag-reducing effect of the drag-reducing material based on the roughness, near-wall average flow velocity, and vertical velocity gradient of the test sample before and after applying the drag-reducing material; S6 repeating S1 to S5 until the drag-reducing effect of all the drag-reducing materials to be tested is obtained, and then selecting drag-reducing materials that meet the design requirements based on the design requirements of the water conveyance project.

Description

Technical Field

[0001] This invention relates to a method for selecting materials in water conveyance projects, specifically to a method and system for selecting drag-reducing materials in water conveyance projects. Background Technology

[0002] Constructing long-distance water transfer projects is the most effective and direct means to address the severe spatial and temporal unevenness of water resource distribution; it is a veritable "lifeline project." Water conveyance capacity is one of the most important indicators for evaluating the water resource allocation function of a water network. How to ensure and improve the water conveyance capacity of long-distance water transfer projects is a key issue in ensuring the strategic effectiveness of the national water network and safeguarding national water resource security. Conducting drag reduction research and engineering renovations to reduce the resistance of channels and pipelines is of great significance for improving the water conveyance capacity of water network projects, saving project investment, enhancing project efficiency, and improving urban water supply security.

[0003] By spraying or pasting drag-reducing materials onto the flow surfaces of water conveyance structures, it is possible to reduce water conveyance resistance and improve water conveyance capacity. In recent decades, drag-reducing materials for water conveyance projects have been continuously innovated. Currently, commonly used drag-reducing materials include dozens of types such as PVC geomembranes, SK single-component polymer coatings, YEC epoxy protective coatings, fluorine-modified polymer roughness-reducing protective coatings, and nano-adhesives. However, faced with such a wide variety of drag-reducing materials, project management units often compare options based on price. But for water conveyance projects tens or even hundreds of kilometers long, improper selection of drag-reducing materials can lead to significant construction costs without effectively improving water conveyance capacity. Therefore, there is an urgent need to establish a method and system for quantitatively evaluating the effectiveness of drag-reducing materials, thereby enabling the selection of appropriate materials. Summary of the Invention

[0004] In view of the above-mentioned shortcomings in the prior art, the method and system for selecting drag-reducing materials in water conveyance projects provided by the present invention solves the problem that the prior art cannot effectively select drag-reducing materials according to the design requirements of water conveyance channels.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0006] Firstly, a method for selecting drag-reducing materials in water conveyance projects is provided, comprising the following steps:

[0007] S1. Select the drag-reducing material to be tested and apply it to the test sample. Then place the test sample in the water transmission test section.

[0008] S2. Adjust the average flow velocity of the water conveyance test section until the water flow enters the resistance square region, and calculate the comprehensive roughness of the water conveyance test section while maintaining a constant flow state:

[0009]

[0010] in, h f This refers to head loss along the route; l This refers to the length of the water transport route. R The hydraulic radius; n 综 This is the overall roughness value; V The average flow velocity across the cross-section of the box culvert test section;

[0011] S3. Calculate the roughness of the test sample coated with drag-reducing material based on the overall roughness value:

[0012]

[0013] in, and The wetted perimeter of the selected system's acrylic wall surface and the wetted perimeter of the test sample wall surface are respectively; n 1 represents the roughness of the transparent wall surface of the selected system; n 2 represents the roughness of the test sample coated with drag-reducing material;

[0014] S4. Collect the two-dimensional planar flow field along the water flow direction of the water conveyance test section, and obtain the near-wall average flow velocity and vertical velocity gradient of the test sample coated with drag-reducing material from the vertical velocity distribution.

[0015] S5. Obtain the drag reduction effect of the drag reduction material based on the roughness, near-wall average flow velocity, and vertical flow velocity gradient of the test sample before and after applying the drag reduction material.

[0016] S6. Repeat steps S1 to S5 until the drag reduction effect of all the drag reduction materials to be tested is obtained. Then, based on the design requirements of the water conveyance project, select the drag reduction materials that meet the design requirements.

[0017] Furthermore, step S4 further includes:

[0018] A two-dimensional planar flow field along the water flow direction was collected in the water conveyance test section. The instantaneous flow field of the two-dimensional planar flow field was averaged by position, and the flow velocity was averaged along the water flow direction to obtain the instantaneous velocity distribution perpendicular to the wall surface of the drag-reducing material.

[0019] in, x The instantaneous flow direction and position, with a maximum value of X ; U A For instantaneous flow field; u y The instantaneous flow velocity distribution is perpendicular to the wall surface of the test sample coated with drag-reducing material;

[0020] The flow velocity was averaged over time to obtain the result.y directional distribution of time-averaged flow velocity:

[0021] in, T For time, For along y The time-averaged flow velocity with directional distribution;

[0022] The average flow rate at a distance of 5 mm from the wall of the test sample coated with drag-reducing material was used. As the near-wall average flow velocity;

[0023] According to along y Calculation of time-averaged flow velocity with directional distribution y The velocity gradient in the direction of y = 15 mm. As a vertical velocity gradient.

[0024] Furthermore, step S5 further includes:

[0025] The degree of roughness reduction of the drag-reducing material was calculated based on the roughness of the test sample before and after applying the drag-reducing material and the average flow velocity near the wall. The degree of increase in average flow velocity near the wall ,

[0026] in n 2 and The roughness of the test sample before and after applying drag-reducing material are respectively. and The near-wall average flow velocities of the test sample before and after applying drag-reducing material are respectively:

[0027] The drag reduction scores corresponding to the roughness reduction of the drag reduction material, the increase of the near-wall average flow velocity, and the vertical velocity gradient are obtained by referring to the table. All drag reduction scores are then weighted to obtain the comprehensive drag reduction score of the drag reduction material.

[0028] Based on the comprehensive drag reduction score, the drag reduction effect of the drag reduction material can be obtained by referring to the table.

[0029] Furthermore, the weighted calculation formula for all drag reduction scores is as follows:

[0030] M = 0.5A + 0.25B + 0.25C

[0031] Where M is the overall drag reduction score; A, B and C are the drag reduction scores corresponding to the degree of roughness reduction of the drag-reducing material, the degree of increase of the near-wall average flow velocity, and the vertical flow velocity gradient, respectively.

[0032] Furthermore, the roughness reduction degree of the drag-reducing material includes four levels, with the first to fourth levels being respectively... <0.05, 0.05≤ <0.1, 0.1≤ <0.2 and 0.2≤ ;

[0033] The increase in near-wall average velocity is divided into four levels, with the first to fourth levels being 1≤ <1.2、1.2≤ <1.5, 1.5≤ <2.0 and 2.0≤ ;

[0034] The vertical velocity gradient includes four levels, the first to the fourth levels are as follows: ≥70 s -1 30s -1 ≤ <70s -1 5s -1 ≤ <30 s -1 and <5 s -1 ;

[0035] The drag reduction scores for the corresponding levels of roughness reduction, near-wall average velocity increase, and vertical velocity gradient are the same.

[0036] Furthermore, when the Reynolds number Re of the water conveyance test section is ≥ 1 × 10⁻⁶ 6 At this point, the water flow enters the square-resistance region; the formula for calculating the Reynolds number is:

[0037]

[0038] in, d The hydraulic diameter of the water conveyance test section; ν Let be the kinematic viscosity coefficient of water.

[0039] Secondly, a selection system for selecting drag-reducing materials in water conveyance projects is provided, comprising a water pump for a water storage device, a water conveyance test section, and a test template for applying drag-reducing materials; the test template matches the bottom dimensions of the water conveyance test section; a water intake pipe and a transition pipe are sequentially arranged between the water storage device and the water conveyance test section, and the water pump is used to transport water from the water storage device to the water intake pipe.

[0040] A backwater gate is installed at the outlet of the water conveyance test section, and the backwater gate is connected to a return water channel, with a measuring weir at the end of the return water channel; valves and electromagnetic flow meters are installed on the water intake pipeline, and a differential pressure sensor for collecting the pressure difference of the water conveyance test section and a 2D-PIV system for two-dimensional planar flow field are installed in the water conveyance test section.

[0041] Furthermore, the water supply test section has a square structure and is a transparent pipe, preferably made of plexiglass. The top plate of the water supply test section is connected to the extension of its side wall by a connector, and a sealing element is provided between the top plate and the extension.

[0042] The beneficial effects of this invention are as follows: First, several test specimens of drag-reducing materials are made. The test specimens are placed in the water conveyance test section, and the resistance index of each specimen is measured (including three resistance indexes: roughness, average flow velocity in the near-wall region, and vertical velocity gradient near the wall). The resistance index of each drag-reducing specimen is then quantitatively compared with the resistance index of the original water conveyance material specimen. Based on the drag-reducing effect of this invention, the drag-reducing level of each drag-reducing material is evaluated, thereby achieving the optimal selection of drag-reducing materials.

[0043] The method and system for selecting drag-reducing materials are simple to operate and have clear physical meaning. Through quantitative measurement and analysis, the material with the best drag-reducing effect can be quickly selected for water conveyance projects, which improves work efficiency, saves project investment, and enhances water conveyance benefits. Attached Figure Description

[0044] Figure 1 This is a flowchart illustrating the selection method for drag-reducing materials in water conveyance projects.

[0045] Figure 2 This is a schematic diagram of the system for selecting drag-reducing materials in water conveyance projects.

[0046] Figure 3 for Figure 2 A cross-sectional view along the AA direction.

[0047] Figure 4 for Figure 2 A cross-sectional view along the BB direction.

[0048] Figure 5 This is a partial 3D view of the system for selecting drag-reducing materials in water conveyance projects.

[0049] The components include: 1. Water storage device (including water pump); 2. Water intake pipeline; 3. Gradient pipeline; 4. Water delivery test section; 41. Top plate; 42. Sealing components; 5. Backwater gate; 6. Measuring weir; 7. Test template; 8. 2D-PIV system. Detailed Implementation

[0050] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0051] refer to Figure 1 , Figure 1 A flowchart illustrating the selection method for drag-reducing materials in water conveyance projects is shown; for example... Figure 1 As shown, the method includes steps S1 to S6.

[0052] In step S1, the drag-reducing material to be tested is selected and applied to the test sample 7. Then the test sample 7 is placed in the water transmission test section 4.

[0053] In step S2, the average flow velocity of the cross-section of the water conveyance test section 4 is adjusted until the water flow enters the resistance square region, and the overall roughness of the water conveyance test section 4 is calculated while maintaining a constant flow state.

[0054]

[0055] in, h f This refers to head loss along the route; l This refers to the length of the water transport route. R The hydraulic radius; n 综 This is the roughness value; V The average flow velocity across the cross-section of the box culvert test section;

[0056] In implementation, this scheme is preferably used when the Reynolds number Re of water conveyance test section 4 is ≥ 1 × 10⁻⁶. 6 At this point, the water flow enters the square-resistance region; the formula for calculating the Reynolds number is:

[0057]

[0058] in, d The hydraulic diameter of water conveyance test section 4; ν Let be the kinematic viscosity coefficient of water.

[0059] In step S3, the roughness of the test sample 7 coated with drag-reducing material is calculated based on the overall roughness:

[0060]

[0061] in, and The wetted perimeter of the transparent wall surface of the selected system and the wetted perimeter of the test sample wall surface are respectively used. n 1 represents the roughness of the transparent wall surface of the selected system; n 2 represents the roughness of the test sample coated with drag-reducing material; this scheme preferably uses a transparent pipe for the water conveyance test section 4, with its wall made of plexiglass, where the roughness of the plexiglass wall is a known value. n 1 = 0.009;

[0062] In step S4, a two-dimensional planar flow field along the water flow direction of the water conveyance test section 4 is collected, and the near-wall average flow velocity and vertical velocity gradient of the test sample 7 coated with drag-reducing material are obtained from the vertical velocity distribution.

[0063] In one embodiment of the present invention, step S4 further includes:

[0064] A two-dimensional planar flow field was collected in the direction of water flow in section 4 of the water conveyance test. The instantaneous flow field of the two-dimensional planar flow field was averaged by position, and the flow velocity was averaged along the direction of water flow to obtain the instantaneous velocity distribution perpendicular to the wall surface of the drag-reducing material:

[0065] in, x The instantaneous flow direction and position, with a maximum value of X ; U A For instantaneous flow field; u y The instantaneous flow velocity distribution is perpendicular to the wall surface of the test sample coated with drag-reducing material;

[0066] The flow velocity was averaged over time to obtain the result. y directional distribution of time-averaged flow velocity:

[0067] in, T For time, For along y The time-averaged flow velocity with directional distribution;

[0068] The average flow rate at a distance of 5 mm from the wall of test sample 7 coated with drag-reducing material was used. As the near-wall average flow velocity;

[0069] According to along y Calculation of time-averaged flow velocity with directional distribution y The velocity gradient in the direction of y = 15 mm. As a vertical velocity gradient.

[0070] In step S5, the drag reduction effect of the drag reduction material is obtained based on the wall roughness, near-wall average flow velocity, and vertical flow velocity gradient before and after the drag reduction material is applied to the test sample 7.

[0071] In implementation, step S5 of this solution preferably further includes:

[0072] Based on the roughness and near-wall average flow velocity of test sample 7 before and after applying the drag-reducing material, calculate the degree of roughness reduction of the drag-reducing material. The degree of increase in average flow velocity near the wall ,

[0073] in n 2 and The roughness values ​​are those of test sample 7 before and after applying the drag-reducing material. and The near-wall average flow velocities before and after applying drag-reducing material to test sample 7 are respectively:

[0074] The drag reduction scores corresponding to the degree of roughness reduction, the increase in near-wall average velocity, and the vertical velocity gradient of the drag-reducing material are obtained from a table. All drag reduction scores are then weighted to obtain the comprehensive drag reduction score of the drag-reducing material. The formula for weighting all drag reduction scores is as follows:

[0075] M = 0.5A + 0.25B + 0.25C

[0076] Where M is the overall drag reduction score; A, B and C are the drag reduction scores corresponding to the degree of roughness reduction of the drag-reducing material, the degree of increase of the near-wall average flow velocity, and the vertical flow velocity gradient, respectively.

[0077] Based on the comprehensive drag reduction score, the drag reduction effect of the drag reduction material can be obtained by referring to the table.

[0078] In this scheme, the roughness and near-wall average flow velocity of the test sample before the drag-reducing material is applied can be obtained by using steps S1 to S4 of this scheme after the test sample 7 is placed in the water delivery test section 4.

[0079] In step S6, steps S1 to S5 are repeated until the drag reduction effect of all the drag reduction materials to be tested is obtained. Then, based on the design requirements of the water conveyance project, drag reduction materials that meet the design requirements are selected.

[0080] In one embodiment of the present invention, the roughness reduction degree of the drag-reducing material includes four levels, the first to fourth levels being respectively... <0.05, 0.05≤ <0.1, 0.1≤ <0.2 and 0.2≤ ;

[0081] The increase in near-wall average velocity is divided into four levels, with the first to fourth levels being 1≤ <1.2、1.2≤ <1.5, 1.5≤ <2.0 and 2.0≤ ;

[0082] The vertical velocity gradient includes four levels, the first to the fourth levels are as follows: ≥70 s -1 30 s -1 ≤ <70 s -1 5 s -1 ≤ <30 s -1 and <5 s -1 ;

[0083] The drag reduction scores for the corresponding levels of roughness reduction, near-wall average velocity increase, and vertical velocity gradient are the same.

[0084] like Figure 2-3 As shown, the drag-reducing material selection system in the water conveyance project includes a water storage device 1, a water conveyance test section 4, and a test template 7 for applying drag-reducing materials. The water storage device 1 is equipped with a water pump and a flat water grid. The test template 7 matches the bottom dimensions of the water conveyance test section 4. A water intake pipe 2 and a transition pipe 3 are sequentially arranged between the water storage device 1 and the water conveyance test section 4. The water pump is used to transport water from the water storage device 1 to the water intake pipe 2. The water flows from the water inlet bell mouth from the water storage device 1 into the water intake pipe 2, and the diameter of the water intake pipe 2 is 350mm.

[0085] A backwater gate 5 is installed at the outlet of the water conveyance test section 4 to ensure that the water conveyance test section 4 is under pressure; the backwater gate 5 is connected to a return water channel, and a measuring weir 6 is installed at the end of the return water channel for testing the system flow rate; valves and electromagnetic flow meters are installed on the water intake pipe 2, and a differential pressure sensor for collecting the pressure difference of the water conveyance test section 4 and a 2D-PIV system 8 for two-dimensional planar flow field are installed in the water conveyance test section 4.

[0086] like Figure 4 As shown, the water supply test section 4 has a square structure and is a transparent pipe made of plexiglass. It is 10m long and has a net cross-sectional dimension of 0.4×0.5m (width×height). The top plate 41 of the water supply test section 4 is connected to the extension of its side wall by a connector, and a sealing element 42 is provided between the top plate 41 and the extension.

[0087] When selecting drag-reducing materials, a test template 7, 0.4m wide and 10m long, needs to be fabricated. The thickness of the test template 7 should be less than 0.1m. The materials used in its fabrication are the same as those used in the water conveyance project's cross-section. The front of the test template 7 is coated with the drag-reducing material to be tested (following the construction process of the drag-reducing material being tested). The top plate 41 of the water conveyance test section 4 is detachable, facilitating the placement of the test template 7.

[0088] like Figure 5 As shown, the 2D-PIV system 8 of this scheme is installed on the top of the water conveyance test section 4, with the measurement profile 6.5m from the inlet section of the water conveyance test section 4 and 10cm from the side wall. The sheet light source is directed from the top plate 41 to the measurement profile through the light guide arm. The CCD camera is positioned perpendicular to the side wall, and the height of the CCD camera is adjusted so that the bottom edge of the camera image coincides with the drag-reducing material wall (i.e., the bottom surface of the box culvert test section).

[0089] In summary, the selection method of this scheme, through quantitative measurement and analysis, can quickly select the material with the best drag reduction effect for water conveyance projects, thereby improving work efficiency.

Claims

1. A method for selecting drag-reducing materials in water conveyance projects, characterized in that, The method comprises the steps of: S1, selecting a drag-reducing material to be tested, and brushing the drag-reducing material on a test sample, and then placing the test sample in a water conveying test section which is a transparent pipeline made of organic glass; S2, adjusting the average flow velocity of the cross section of the water conveying test section until the water flow enters the resistance square region, and calculating the comprehensive roughness value of the water conveying test section under the condition of constant flow; wherein, h f is the head loss along the length of the pipe; l is the length of the pipe; R is the hydraulic radius; n 综 is the composite roughness value; V is the average velocity of flow over the cross section of the box culvert test section; S3, calculating the roughness of the test sample with the drag-reducing material according to the comprehensive roughness value; wherein, and Lw and Lw2 are the wetted perimeter length of the transparent wall of the water conveyance test section and the test panel, respectively; n 1 is the roughness of the transparent wall of the water conveyance test section; n 2 is the roughness of the test panel coated with the drag-reducing material; S4, collecting the two-dimensional plane flow field of the water conveying test section along the water flow direction, and obtaining the near-wall time-averaged flow velocity and the vertical flow velocity gradient of the test sample with the drag-reducing material from the vertical distribution of the flow velocity; the step S4 further comprises: collecting the two-dimensional plane flow field of the water conveying test section along the water flow direction, and performing position averaging on the instantaneous flow field of the two-dimensional plane flow field, and averaging the flow velocity along the water flow direction to obtain the instantaneous flow velocity distribution perpendicular to the wall surface direction of the test sample with the drag-reducing material; wherein x is the instantaneous flow field streamwise position, maximum value X ; U A is the instantaneous flow field; u y is the instantaneous flow velocity profile normal to the wall of the test panel coated with drag reducing material; The time-averaged velocity distribution is obtained by time-averaging the velocity field y Time-averaged velocity distribution wherein T is time, is the time-averaged flow velocity distributed along y the direction. The time-averaged velocity at 5 mm from the wall of the test panel coated with the drag-reducing material as the near-wall time-averaged velocity; According to along y Calculation of time-averaged flow velocity with directional distribution y Direction, i.e., the velocity gradient perpendicular to the wall surface of the test sample coated with drag-reducing material and at a distance of 15 mm from the wall surface of the test sample coated with drag-reducing material. As a vertical velocity gradient; S5, obtaining the drag-reducing effect of the drag-reducing material according to the roughness, the near-wall time-averaged flow velocity and the vertical flow velocity gradient of the test sample before and after brushing the drag-reducing material; the step S5 further comprises: According to the roughness and the near-wall time-averaged velocity before and after the drag-reducing material is painted on the test template, the roughness reduction degree of the drag-reducing material is calculated and the increase degree of the near-wall time-averaged velocity , wherein n 2 and are the roughness of the test panel before and after the drag reduction material is applied, respectively, and are the near-wall time-averaged velocity of the test panel before and after the drag reduction material is applied, respectively. obtaining the drag-reducing score corresponding to the roughness reduction degree, the near-wall time-averaged flow velocity increase degree and the vertical flow velocity gradient of the drag-reducing material by looking up a table, and weighting all the drag-reducing scores to obtain the comprehensive drag-reducing score of the drag-reducing material; obtaining the drag-reducing effect of the drag-reducing material by looking up a table according to the comprehensive drag-reducing score; S6, repeating the steps S1-S5 until the drag-reducing effects of all the drag-reducing materials to be tested are obtained, and then selecting a drag-reducing material meeting the design requirements based on the design requirements of the water conveying project.

2. The method for selecting a drag reduction material for a water conveyance project according to claim 1, wherein The calculation formula of weighting all the drag-reducing scores is: M=0.5A+0.25B+0.25C wherein M is the comprehensive drag-reducing score; A, B and C are respectively the drag-reducing scores corresponding to the roughness reduction degree, the near-wall time-averaged flow velocity increase degree and the vertical flow velocity gradient of the drag-reducing material.

3. The method for selecting a drag reduction material for a water conveyance project according to claim 1, wherein The roughness reduction of the drag reduction material includes four levels, the first to fourth levels are <0.05, 0.05≤ <0.1, 0.1≤ <0.2 and 0.2≤ ; The increase in the near-wall time-averaged flow velocity includes four levels, the first to fourth levels are 1 <1.2, 1.2 <1.5, 1.5 <2.0 and 2.0 ; The vertical flow velocity gradient includes four levels, the first to fourth levels are respectively ≥ 70 s -1 , 30 s -1 ≤ < 70 s -1 , 5 s -1 ≤ < 30 s -1 and < 5 s -1 ; The drag-reducing scores corresponding to the same level of the roughness reduction degree, the near-wall time-averaged flow velocity increase degree and the vertical flow velocity gradient are the same.

4. The method for selecting a drag reduction material for a water conveyance project according to claim 1, wherein When the Reynolds number Re of the water delivery test section is greater than or equal to 1 x 10 6 When the Reynolds number Re of the water delivery test section is greater than or equal to 1 x 10 When the Reynolds number Re of the water delivery test section is greater than or equal to 1 x 10 wherein, d Dh is the hydraulic diameter of the water delivery test section; The device comprises a water storage device, a water pump, a water conveying test section and a test sample for brushing a drag-reducing material; the test sample is matched with the size of the bottom surface of the water conveying test section; a water leading pipeline and a gradual change pipeline are sequentially arranged between the water storage device and the water conveying test section, and the water pump is used to convey water in the water storage device to the water leading pipeline; is the kinematic viscosity of water.

5. A selection system for the selection method of the resistance reducing material applied to the water conveyance project according to any one of claims 1 to 4, characterized in that, a water retaining gate is arranged at the outlet of the water conveying test section, the water retaining gate is connected with a backwater channel, and a water measuring weir is arranged at the tail of the backwater channel; a valve and an electromagnetic flowmeter are arranged on the water leading pipeline, and the water conveying test section is provided with a differential pressure sensor for collecting the differential pressure of the water conveying test section and a 2D-PIV system for collecting the two-dimensional plane flow field. The water conveying test section is in a square structure and is a transparent pipeline; the top plate of the water conveying test section is connected with the extension of the side wall through a connecting piece, and a sealing piece is arranged between the top plate and the extension.

6. The selection system of claim 5, wherein, ​

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