Mixed-flow water turbine top cover silt wear test device and design method thereof

Abstract

The invention relates to the technical field of model tests, in particular to a mixed-flow water turbine top cover silt wear test device and a design method thereof.The test device comprises a connecting part, a runner crown model and a top cover model; a flow channel, a liquid inlet, a liquid outlet and an overflow port are formed in the connecting part; the runner crown model comprises a rotating disc and a rotating shaft; the lower surface of the rotating disc is arranged at the overflow port; the top cover model comprises an outer ring part, a transition connection part and an inner ring part; the outer ring part is sleeved outside the rotating disc; the inner ring part is sleeved outside the rotating shaft; and the transition connecting part is connected between the top of the outer ring part and the top of the inner ring part. The test device is simple in structure and low in manufacturing cost, can better simulate the flowing condition of the sediment-containing water flow in the top cover flow channel, studies the abrasion problem of the sediment-containing water flow to the top cover by using a test developing method, and is high in reliability, and the test result is more persuasive.

Description

Technical Field

[0001] The invention relates to the technical field of model tests, and in particular to a Francis turbine top cover sediment wear test device and a design method thereof. Background Art

[0002] In a mixed-flow turbine generator set, the top cover is an important part of the water guide mechanism. It not only plays the role of drainage of the water guide mechanism, but also supports the guide vanes, transmission mechanism, guide vane bearings and other auxiliary devices, and prevents water from overflowing. The flow surface of the top cover is generally equipped with a stainless steel anti-wear surface, but the non-flow surface is eroded by the impact of water flow and sediment, which not only reduces the strength of the top cover, but also causes water seepage in the plant when it is severely damaged. The sediment wear and damage of the turbine is a very complex physical process, which involves multi-disciplinary issues such as multiphase flow, sediment wear, tribology, materials science and surface protection, and has the characteristics of multiphase, microscopic, transient and random. At present, there is no corresponding test device to simulate the sediment wear of the top cover. Summary of the invention

[0003] In view of this, the present invention provides a Francis turbine top cover sediment wear test device and a design method thereof, aiming to perform a simulation test on the top cover sediment wear to facilitate targeted research.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A test device for the sand wear of a Francis turbine top cover comprises a connecting part, a runner crown model and a top cover model; the connecting part has a flow channel, and the two ends of the connecting part respectively have a liquid inlet and a liquid outlet connected to the flow channel, and the top of the connecting part also has an overflow connected to the flow channel; the runner crown model comprises a rotating disc and a rotating shaft; the lower surface of the rotating disc is arranged at the overflow, and a gap is provided between the edge of the rotating disc and the edge of the overflow; the rotating shaft is connected to the top of the rotating disc, and the rotating disc is connected to the top of the rotating disc. The shaft is used for transmission connection with the rotating drive mechanism; the top cover model includes an outer ring part, a transition connection part and an inner ring part; the outer ring part is sleeved on the outside of the rotating disk with a gap therebetween, and the bottom of the outer ring part is sealed and connected to the top of the connection part; the inner ring part is sleeved on the outside of the rotating shaft, and the bottom of the inner ring part is sealed and assembled with the top of the rotating disk; the transition connection part is connected between the top of the outer ring part and the top of the inner ring part, and there is a gap between the transition connection part and the rotating disk.

[0006] In some optional embodiments, a plurality of test blocks are further included; the test blocks are detachably mounted on the inner wall of the top cover model; when there are more than two test blocks, the test blocks are arranged along the circumference of the top cover model; a groove is provided on the inner wall of the top cover model corresponding to the installation position of the test block, the test block is installed in the groove, and the depth of the groove is consistent with the thickness of the test block.

[0007] In some optional embodiments, when there are more than two test blocks, the materials of the test blocks are the same or different.

[0008] In some optional embodiments, the flow channel in the connecting portion gradually expands from the liquid inlet to the liquid outlet, and the overflow port is completely connected to the flow channel.

[0009] A design method for a Francis turbine top cover sediment wear test device comprises the following steps: establishing an assembly model of a runner crown and a real turbine top cover to obtain a three-dimensional model of a real turbine top cover flow passage; shortening the rotation radius of the three-dimensional model of the real turbine top cover flow passage to obtain a three-dimensional model of a test top cover flow passage; and designing a three-dimensional model of a main part of a test device according to the three-dimensional model of the test top cover flow passage.

[0010] In some optional embodiments, when designing the three-dimensional model of the main part of the test device, a groove and a test block detachably installed in the groove are also designed on the inner wall of the top cover; when there are more than two test blocks, the groove and the test blocks are designed to be arranged along the circumference of the top cover.

[0011] In some optional embodiments, the rotation radius of the three-dimensional model of the top cover flow channel of the real machine is shortened, and the step of obtaining the three-dimensional model of the top cover flow channel of the test includes: intercepting the two-dimensional flow channel surface of the three-dimensional model of the top cover flow channel of the real machine to obtain the two-dimensional cross-section of the top cover flow channel of the real machine; shortening the distance from the two-dimensional cross-section of the top cover flow channel of the real machine to the rotation axis while ensuring that the two-dimensional cross-sectional shape and size of the top cover flow channel of the real machine remain unchanged to obtain the two-dimensional cross-section of the test top cover flow channel; and obtaining the three-dimensional model of the test top cover flow channel based on the rotation restoration of the two-dimensional cross-section of the test top cover flow channel.

[0012] In summary, compared with the prior art, the present invention has the following advantages and beneficial effects: the test device described in the embodiment of the present application has a simple structure and low manufacturing cost, can better simulate the flow of silt-containing water flow in the top cover flow channel, and uses the experimental method to study the wear problem of the top cover caused by the silt-containing water flow, with high reliability and more convincing test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the three-dimensional structure of the test device described in Example 1 of the present invention.

[0014] Figure 2 It is a schematic diagram of the front view cross-section structure of the test device described in Example 1 of the present invention.

[0015] Figure 3 for Figure 2 Schematic diagram of the enlarged structure of area A in the middle.

[0016] Figure 4 It is a schematic diagram of the three-dimensional structure of the connecting part in the test device described in Example 1 of the present invention.

[0017] Figure 5 It is a schematic diagram of the cross-sectional structure of the connection part in the test device described in Example 1 of the present invention when viewed from above.

[0018] Figure 6 It is a schematic diagram of the three-dimensional structure of the crown model of the rotating wheel in the test device described in Example 1 of the present invention.

[0019] Figure 7 It is a schematic diagram of the top view of the three-dimensional structure of the top cover model in the test device described in Example 1 of the present invention.

[0020] Figure 8 It is a bottom-view stereoscopic structural schematic diagram of the top cover model in the test device described in Example 1 of the present invention.

[0021] Fig. 9 This is a cross section of the assembly model of the crown and top cover of the real machine's wheel.

[0022] Fig.10 It is a cross-sectional comparison diagram of the three-dimensional model of the real machine top cover flow channel and the three-dimensional model of the experimental top cover flow channel.

[0023] Fig.11 A comparison chart of the 3D model of the real machine top cover flow channel and the 3D model of the test top cover flow channel.

[0024] Fig.12 Schematic diagram of the comparison section between the test top cover flow channel and the real machine top cover flow channel.

[0025] Fig.13 This is a comparison chart of the simulated flow velocity distribution of the test top cover flow channel and the real machine top cover flow channel comparison section.

[0026] The meanings of the numbers in the figure are: connecting part 1, liquid inlet 11, liquid outlet 12, overflow port 13, runner crown model 2, rotating disk 21, rotating shaft 22, top cover model 3, outer ring part 31, transition connecting part 32, inner ring part 33, test block 4, three-dimensional model of real machine runner crown 5, three-dimensional model of real machine top cover 6, three-dimensional model of real machine top cover flow channel 7, three-dimensional model of test top cover flow channel 8, rotating shaft 9. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with specific implementation methods.

[0028] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0029] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there are any descriptions of "first", "second" and the like, they are only used for the purpose of distinguishing technical features and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0030] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0031] Embodiment 1

[0032] The flow of water in the flow passage of a Francis turbine is a complex three-dimensional flow. Common research methods include theoretical analysis, numerical simulation analysis based on computer technology, and experimental device simulation analysis. At present, people do not have a deep understanding of the movement law of sediment-laden water flow. The use of theoretical analysis and numerical simulation analysis is mainly qualitative research. To further deepen the research, it is necessary to carry out research on experimental device simulation analysis.

[0033] The present application embodiment introduces a Francis turbine top cover sediment wear test device, such as Figure 1 and Figure 2 As shown, the test device mainly includes a connecting part 1, a runner crown model 2 and a top cover model 3.

[0034] Among them, Figure 4 and Figure 5 As shown, the connecting part 1 has a flow channel, and the two ends of the connecting part 1 respectively have a liquid inlet 11 and a liquid outlet 12 connected to the flow channel, and the top of the connecting part 1 also has an overflow port 13 connected to the flow channel. The connecting part 1 is connected to a liquid supply device for supplying sediment-containing water flow through its liquid inlet 11.

[0035] like Figure 6As shown, the wheel crown model 2 includes a rotating disc 21 and a rotating shaft 22.

[0036] like Figure 2 and Figure 3 As shown, the lower surface of the rotating disc 21 is arranged at the overflow port 13 of the connecting part 1, and there is a gap between the edge of the rotating disc 21 and the edge of the overflow port 13 for the sediment-containing water flow to pass through. The rotating shaft 22 is connected to the top of the rotating disc 21, and the rotating shaft 22 is used for transmission connection with the rotating drive mechanism, so as to drive the rotating disc 21 to rotate under the action of the rotating drive mechanism, thereby simulating the rotation of the crown on the wheel, that is, the rotating disc 21 is used to replace the crown on the real machine wheel in the embodiment of the present application. The line shape and size of the upper wall of the rotating disc 21 in the test device should be consistent with the line shape and size of the upper wall of the real machine wheel crown, so as to restore the actual situation of the real machine wheel crown as much as possible.

[0037] like Figure 7 and Figure 8 As shown, the top cover model 3 includes an outer ring portion 31 , a transition connection portion 32 and an inner ring portion 33 .

[0038] like Figure 2 and Figure 3 As shown, the outer ring part 31 is sleeved outside the rotating disc 21 and there is a gap between the two to allow the silt-containing water flow to pass through. The bottom of the outer ring part 31 is sealed and connected to the top of the connecting part 1, for example, by bolts and sealing strips to prevent the silt-containing water flow from leaking from the connection between the outer ring part 31 and the connecting part 1. The inner ring part 33 is sleeved outside the rotating shaft 22, and the bottom of the inner ring part 33 is sealed and assembled with the top of the rotating disc 21, for example, by a sealed bearing to prevent the silt-containing water flow from leaking from the connection between the inner ring part 33 and the rotating disc 21. The transition connecting part 32 is connected between the top of the outer ring part 31 and the top of the inner ring part 33, and there is a gap between the transition connecting part 32 and the upper wall of the rotating disc 21, which is the main part of the top cover flow channel for the silt-containing water flow to fill in between.

[0039] The method for simulating the flow of sediment-laden water flow in the top cover flow channel by the test device described in the embodiment of the present application is as follows:

[0040] The silt-containing water flows into the connecting part 1 from the liquid inlet 11 and fills its flow channel before being discharged from the liquid outlet 12. A part of the silt-containing water flow in the flow channel will enter the top cover flow channel along the gap and gradually fill it up. Driven by the rotating drive mechanism, the rotating disc 21 of the runner crown model 2 starts to rotate, so that the flow state of the silt-containing water flow in the top cover flow channel is consistent with the flow state of the silt-containing water flow in the top cover flow channel of the real machine. After the test device has been running for a certain period of time (for example, one hundred hours), the supply of the silt-containing water flow is stopped and the rotating drive mechanism is shut down, after which the top cover model 3 can be removed to check the wear of its inner wall.

[0041] The test device described in the embodiment of the present application has a simple structure and low manufacturing cost. It can better simulate the flow of silt-containing water flow in the top cover flow channel. The test method is used to study the wear problem of the top cover caused by the silt-containing water flow. It has high reliability and the test results are more convincing.

[0042] In order to test the wear of the top cover model 3 made of different materials by the sediment-containing water flow, as an optional implementation, the test device described in the embodiment of the present application may also include a plurality of test blocks 4.

[0043] like Figure 8 As shown, the test block 4 can be detachably mounted on the inner wall of the top cover model 3, for example, the two can be connected by bolts, or by snap-fitting, interference fitting and other connection methods.

[0044] Since the flow characteristics such as flow velocity and pressure in the top cover flow channel are consistent along the circumferential direction, when there are more than two test blocks 4, the test blocks 4 are arranged along the circumferential direction of the top cover model 3 to ensure that each test block 4 has the same wear condition when impacted by the sediment-containing water flow. The materials of these test blocks 4 can be the same to facilitate repeated verification of the wear condition, or they can be different so that test blocks 4 of multiple materials can be tested at one time.

[0045] In order to reduce the impact of the test block 4 on the overall linear shape of the top cover flow channel after installation, a groove is provided on the inner wall of the top cover model 3 corresponding to the installation position of the test block 4, and the test block 4 is installed in the groove. The groove has the same size as the corresponding test block 4, and in particular, the depth of the groove needs to be consistent with the thickness of the test block 4, so that after the test block 4 is installed in the groove, the two can be tightly connected as a whole, the surface is flat, and the water flow is avoided from being affected.

[0046] In addition, in order to ensure that the flow of the silt-laden water flow entering the connection part 1 is consistent with the flow of the silt-laden water flow in the runner of the real machine, as Figure 5As shown, the flow channel in the connecting portion 1 can be designed to be an arc-shaped outward expansion type that gradually expands from the liquid inlet 11 to the liquid outlet 12, and the overflow port 13 is completely connected to the flow channel. This design can avoid the occurrence of vortices in the flow channel that affect the flow pattern of the sediment-containing water flow in the top cover flow channel.

[0047] Embodiment 2

[0048] The present application embodiment introduces a design method for a Francis turbine top cover sediment wear test device, which includes the following steps:

[0049] (1) Establish the assembly model of the real machine rotor crown and the real machine top cover to obtain the 3D model of the real machine top cover flow channel

[0050] According to the design drawings, a 3D model of the real machine wheel crown and a 3D model of the real machine top cover are established through 3D modeling software, and the assembly model of the real machine wheel crown and the real machine top cover is obtained after assembling the two. Fig. 9 As shown, there is a gap between the three-dimensional model 5 of the real machine's wheel crown and the three-dimensional model 6 of the real machine's top cover after assembly. The gap is the three-dimensional model 7 of the flow channel of the real machine's top cover. Therefore, the three-dimensional model of the flow channel of the real machine's top cover can be obtained based on the assembly model of the real machine's wheel crown and the real machine's top cover.

[0051] (2) Shorten the rotation radius of the three-dimensional model of the real machine top cover flow channel to obtain the three-dimensional model of the test top cover flow channel

[0052] The top cover of a Francis turbine is a large plate with a huge volume and relatively complex shape. Its shape is just like a ring-shaped reinforced box. When designing the test, the size scaling of the test device must be considered to reduce the test cost.

[0053] It is known that the flow channel of the real machine top cover is a three-dimensional ring. The two-dimensional flow channel surface of the three-dimensional model of the flow channel of the real machine top cover is intercepted by three-dimensional modeling software to obtain the two-dimensional cross section of the flow channel of the real machine top cover. Fig.10 As shown, under the premise of ensuring that the two-dimensional cross-sectional shape and size of the real machine top cover flow channel remain unchanged, the distance from the two-dimensional cross-sectional area of ​​the real machine top cover flow channel to the rotation axis 9 is shortened to obtain the two-dimensional cross-sectional area of ​​the test top cover flow channel. Fig.11 As shown, based on the two-dimensional cross-section of the test top cover flow channel, a three-dimensional model 8 of the test top cover flow channel is obtained through the rotation and restoration operation of the three-dimensional modeling software, so as to reduce the size of the top cover flow channel without affecting the flow state, ensure that the size and wall profile of the top cover flow channel of the test device are consistent with the top cover flow channel of the real machine, and further ensure that the flow state of the silt-containing water flow in the test top cover flow channel is consistent with the actual flow state of the silt-containing water flow in the top cover flow channel of the real machine.

[0054] (3) Design the 3D model of the main part of the test device based on the 3D model of the test cover flow channel

[0055] Based on the three-dimensional model of the test top cover flow channel, the edges of the three-dimensional model of the test top cover flow channel were thickened by three-dimensional modeling software to obtain the three-dimensional models of the crown part and the top cover part of the runner in the test device.

[0056] In the test device, a connecting part needs to be designed to supply silt-laden water flow to the top cover flow channel. As an optional implementation, the connecting part can be designed as a box body with a flow channel, and the two ends of the box body respectively have a liquid inlet and a liquid outlet connected to the flow channel. At the same time, the upper surface of the box body also has an overflow port connected to the flow channel for supplying silt-laden water flow to the top cover flow channel. In addition to the box body, the shape of the connecting part can also be designed to be other shapes, as long as it can supply silt-laden water flow to the top cover flow channel. After determining the shape of the connecting part, a three-dimensional model of the connecting part of the test device can be established through three-dimensional modeling software.

[0057] The three-dimensional model of the crown part and the top cover part of the test device is assembled with the three-dimensional model of the connecting part of the test device according to the content described in Example 1 to obtain the three-dimensional model of the main part of the test device.

[0058] (3.1) Design a 3D model of the main part of the test device including the test block

[0059] When designing the three-dimensional model of the main part of the test device in step (3), it is also possible to consider designing a replaceable test block on the inner wall of the top cover to observe the wear patterns of different materials and the wear resistance of different materials caused by the silt-laden water flow in the top cover flow channel.

[0060] Consider machining a groove on the top cover to install the test block. The groove should be the same size as the test block. In particular, the depth of the groove should be consistent with the thickness of the test block, so that the two can be tightly connected after the test block is installed in the groove, and the surface is flat to avoid affecting the water flow. After testing a test block of one material, you can replace the test block of another material for testing to ensure that the conditions of the previous and subsequent tests are consistent, and then observe the wear of each test block.

[0061] To improve the efficiency of the comparative test, multiple test blocks can be installed on the top cover at the same time. These test blocks are arranged along the circumference of the top cover to ensure that each test block has the same wear condition when impacted by the silt-laden water flow. The materials of these test blocks can be the same to facilitate repeated verification of wear conditions, or they can be different so that test blocks of multiple materials can be tested at one time.

[0062] (4) Verify the accuracy of the test top cover flow path relative to the real machine top cover flow path through simulation

[0063] The three-dimensional model of the test top cover flow channel and the three-dimensional model of the real machine top cover flow channel are imported into the CFD software for mesh calculation, and the mesh model of the test top cover flow channel and the mesh model of the real machine top cover flow channel are obtained respectively. The mesh model of the test top cover flow channel and the mesh model of the real machine top cover flow channel are respectively subjected to CFD simulation under the same target research flow condition, and the simulation results of the test top cover flow channel and the real machine top cover flow channel under the target research flow condition are obtained, mainly including the simulated flow velocity distribution and the simulated pressure distribution.

[0064] like Fig.12 As shown, a small section at the same position of the test top cover flow channel and the real machine top cover flow channel can be selected as a comparison section when performing CFD simulation. Since the rotation radius of the test top cover flow channel is inconsistent with the rotation radius of the real machine top cover flow channel, the rotation angular velocity of the test top cover flow channel should be set higher than the rotation angular velocity of the real machine top cover flow channel when performing CFD simulation, so as to make the comparison section of the test top cover flow channel and the real machine top cover flow channel have the same rotation linear velocity as much as possible, thereby ensuring that the comparison section of the test top cover flow channel and the real machine top cover flow channel is CFD simulated under the same target research flow condition as much as possible, so that the simulation results of the test top cover flow channel and the simulation results of the real machine top cover flow channel are comparable.

[0065] Compare the simulation results of the test top cover flow channel with the simulation results of the real machine top cover flow channel, for example, compare the simulated flow velocity distribution of the test top cover flow channel with the real machine top cover flow channel, such as Fig.13 As shown, if the flow rates and trends of the two are similar, it means that the test device designed based on steps (1)-(3) has almost the same physical properties as the real machine. Therefore, the real machine can be replaced by studying the test device, thereby simplifying the research process and reducing research costs.

[0066] The above is the design method of the test device for the top cover of a Francis turbine. After the design is completed, the main part of the test device can be made: the top cover, the upper crown of the runner and the connecting part, as well as the possible test blocks, are obtained by, for example, numerical control machining according to the three-dimensional model of the main part of the test device. After machining, they are assembled in place to serve as the main part of the test device described in Example 1. Other parts of the test device, such as the liquid supply device for supplying the sediment-containing water flow and the motor for driving the upper crown of the runner to rotate, are all commonly used laboratory devices and can be assembled as needed.

[0067] The main part of the test device in the embodiment of the present application is shortened based on the top cover flow channel of the real machine, has a small size and low production cost. Since the main part of the test device is obtained by computer three-dimensional modeling, the three-dimensional model of the main part of the test device can be numerically simulated and analyzed under corresponding working conditions, and the actual operation conditions can be numerically simulated and predicted by computer technology, and can be compared and verified with the numerical simulation analysis results of the real machine model to verify the rationality and authenticity of the test device and ensure high simulation reliability.

[0068] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0069] The above preferred embodiments shall not be regarded as limiting the present invention, and the protection scope of the present invention shall be subject to the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications shall also be regarded as the protection scope of the present invention.

Claims

1. A Francis turbine top cover sediment wear test device, characterized in that: It comprises a connecting part (1), a wheel crown model (2) and a top cover model (3); The connecting part (1) has a flow channel in it, and the two ends of the connecting part (1) respectively have a liquid inlet (11) and a liquid outlet (12) connected to the flow channel, and the top of the connecting part (1) also has an overflow port (13) connected to the flow channel; The rotating wheel crown model (2) comprises a rotating disc (21) and a rotating shaft (22); the lower surface of the rotating disc (21) is arranged at the overflow port (13), and a gap is provided between the edge of the rotating disc (21) and the edge of the overflow port (13); the rotating shaft (22) is connected to the top of the rotating disc (21), and the rotating shaft (22) is used for transmission connection with a rotation driving mechanism; The top cover model (3) comprises an outer ring part (31), a transition connection part (32) and an inner ring part (33); the outer ring part (31) is sleeved outside the rotating disc (21) with a gap therebetween, and the bottom of the outer ring part (31) is sealedly connected to the top of the connection part (1); the inner ring part (33) is sleeved outside the rotating shaft (22), and the bottom of the inner ring part (33) is sealedly assembled to the top of the rotating disc (21); the transition connection part (32) is connected between the top of the outer ring part (31) and the top of the inner ring part (33), and there is a gap between the transition connection part (32) and the rotating disc (21).

2. A Francis turbine top cover sediment wear test device as claimed in claim 1, characterized in that: It also includes several test blocks (4); The test block (4) is detachably mounted on the inner wall of the top cover model (3); when there are more than two test blocks (4), the test blocks (4) are arranged along the circumference of the top cover model (3); A groove is provided on the inner wall of the top cover model (3) corresponding to the installation position of the test block (4), the test block (4) is installed in the groove, and the depth of the groove is consistent with the thickness of the test block (4).

3. A Francis turbine top cover sediment wear test device as claimed in claim 2, characterized in that: When there are two or more test blocks (4), the materials of the test blocks (4) are the same or different.

4. A Francis turbine top cover sediment wear test device as claimed in claim 1, characterized in that: The flow channel in the connecting portion (1) gradually expands from the liquid inlet (11) to the liquid outlet (12), and the overflow port (13) is completely connected to the flow channel.

5. A design method for a Francis turbine top cover sediment wear test device, characterized in that: The steps include: Establish the assembly model of the wheel crown and the real machine top cover, and obtain the three-dimensional model of the flow channel of the real machine top cover; Shorten the rotation radius of the three-dimensional model of the top cover flow channel of the real machine to obtain the three-dimensional model of the top cover flow channel of the test machine; The three-dimensional model of the main part of the test device is designed according to the three-dimensional model of the test top cover flow channel.

6. The design method of a Francis turbine top cover sediment wear test device as claimed in claim 5, characterized in that: When designing the three-dimensional model of the main part of the test device, a groove and a test block detachably mounted in the groove are also designed on the inner wall of the top cover; When there are more than two test blocks, the grooves and the test blocks are designed to be arranged along the circumference of the top cover.

7. The design method of a Francis turbine top cover sediment wear test device as claimed in claim 5, characterized in that: The steps of shortening the rotation radius of the three-dimensional model of the top cover flow channel of the real machine and obtaining the three-dimensional model of the top cover flow channel of the test machine include: Cutting the two-dimensional flow channel surface of the three-dimensional model of the flow channel of the top cover of the real machine to obtain the two-dimensional cross section of the flow channel of the top cover of the real machine; Under the premise of ensuring that the two-dimensional cross-sectional shape and size of the flow channel on the top cover of the real machine remain unchanged, the distance from the two-dimensional cross-sectional area of ​​the flow channel on the top cover of the real machine to the rotation axis is shortened to obtain the two-dimensional cross-sectional area of ​​the flow channel on the top cover of the test machine; The three-dimensional model of the experimental top cover flow channel is obtained based on the two-dimensional cross-section rotation restoration of the experimental top cover flow channel.

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