Tail water pipe, tail water pipe protection device and design method of tail water pipe protection device

Abstract

The invention discloses a draft tube, a draft tube protection device and a design method of the draft tube protection device. The draft tube comprises the draft tube protection device. The section shape of the draft tube protection device is determined through the draft tube protection device design method. The design method of the draft tube protection device comprises the following steps: establishing a coordinate system; drawing lines; rotating the lines to obtain a plane area; rotating the plane area to obtain a rotating curved surface body; and manufacturing the draft tube protection device. According to the draft tube protection device, a flow field is weakened, large-scale adherent vortexes are damaged to be changed into small-scale adherent vortexes, then the small-scale adherent vortexes are dissipated along with water flow, and spiral vortex strips can be weakened and gradually dissipated, so that the pressure pulsation amplitude in the draft tube is effectively reduced, a water turbine runs more safely and stably under the small-flow working condition, and the service life of the water turbine is prolonged. Vibration and noise are weakened, and the probability of safety accidents such as machine lifting, chamber sweeping and blade breakage is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of tailwater pipes, and in particular to a tailwater pipe, a tailwater pipe protection device and a design method thereof. Background Art

[0002] As the proportion of new energy sources gradually increases, the role of hydropower is gradually changing from power generation to flexible regulation of new energy sources. Due to their intermittent and random nature, wind and solar energy may have a certain impact on the stable operation of the power grid when directly integrated into the power system. Hydropower has the advantages of fast response speed, sustainable energy supply, and energy storage, so the three are used to form a water-wind-solar complementary system. Most conventional turbine units currently operate at an opening of 50% to 100%, but in the water-wind-solar complementary system, hydropower units are required to adjust the guide vane opening at any time and frequently undergo transition processes, which requires hydropower to operate more under small flow conditions, so higher requirements are placed on operational stability.

[0003] The operation of a turbine under low flow conditions may cause large-scale blade vortices, spiral vortices in the tailwater pipe, and low-frequency and high-amplitude pressure pulsations, which can easily cause safety accidents such as excessive vibration, lifting, sweeping, and blade breakage. For example, at the Dongqing Power Station, when the turbine was operating under non-design conditions, the pressure pulsation and vibration of the unit were significantly enhanced. The low-head and low-load operating conditions of the Jishixia Hydropower Station intensified the vibration and produced vacuum vortices in the tailwater pipe. When the Dongwushi and Zhuzhuang power stations were operating under low load, the turbines produced severe noise accompanied by large swings of the main shaft. In order to improve the regulation capacity of the hydropower station and quickly respond to changes in the grid load, it has become a technical problem to be solved to study how to reduce the amplitude of pressure pulsations under low flow conditions and during the transition process, thereby improving the hydraulic stability of the unit. Summary of the invention

[0004] The technical problem to be solved by the present invention is how to reduce the pressure pulsation amplitude under low flow conditions and in the transition process. The purpose is to provide a tailwater pipe, a tailwater pipe protection device and a design method thereof to solve the above-mentioned problem.

[0005] The present invention is achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for designing a tailwater protection device, comprising the following steps:

[0007] S100: Establish a rectangular coordinate system with the front view of the straight cone section of the tailwater pipe as the base surface and the intersection of the tailwater pipe generatrix and the tailwater pipe inlet section as the origin;

[0008] S200: Based on the rectangular coordinate system, draw the generatrix y of the straight cone section of the tailwater pipe 1 and design curve y 2 ;

[0009] S300: Rotate the design curve y based on the origin 2 To the busbar y of the straight cone section of the tailwater pipe 1 Overlap to obtain the tailwater pipe straight cone section busbar y 1 and design curve y 2 Enclose a closed plane area;

[0010] S400: Rotate the plane region with the central axis of the draft tube as the center to obtain a rotational curved surface;

[0011] S500: A draft tube protection device is manufactured based on a rotating curved surface.

[0012] In a possible design, in step S100, there are two intersections between the tailwater pipe busbar and the tailwater pipe inlet section, and any one of the intersections is used as the origin of the rectangular coordinate system, with the positive direction of the y-axis pointing upward and the positive direction of the x-axis pointing rightward.

[0013] In a possible design, in step S200, the tailwater pipe straight cone section generatrix y is drawn along the tailwater pipe generatrix 1 , tailwater pipe straight cone section busbar y 1 The vertex is the origin of the rectangular coordinate system.

[0014] In a possible design, in step S200, a design curve y is drawn 2 The following steps are involved:

[0015] S210: Select the curve design formula:

[0016]

[0017] Among them, s is the height of the design curve, c is a parameter related to the period of the sin trigonometric function, and l is the length of the generatrix of the straight cone section of the tailwater pipe;

[0018] S220: Select the values ​​of s and c, where both s and c shall not be less than 0.1 times l and shall not exceed 0.2 times l, and s shall not exceed 1 / 3 of the diameter of the tailwater pipe inlet section;

[0019] S230: Draw the design curve y on the rectangular coordinate system 2 ;

[0020] Steps S210-S220 can be interchanged with step S100. The curve drawn in step S230 includes two straight lines and an arc, and the two straight lines are connected by the arc to form a continuous design curve y. 2 .

[0021] In a possible design, in step S220, s and c select multiple sets of values ​​respectively to obtain multiple design curves y 2Accordingly, a plurality of plane regions are obtained in step S300, and a plurality of rotational curved surfaces are obtained in step S400.

[0022] In a possible design, in step S300, the tailwater pipe straight cone section busbar y 1 and design curve y 2 After overlap, the design curve y 2 The two straight lines are respectively connected to the generatrix y 1 Overlap, in y 2 <y<y 1 Area, design curve y 2 The arc line and the generatrix y of the straight cone section of the tailwater pipe 1 Enclosed plane area.

[0023] In a possible design, (the tailwater pipe protection device design method) further includes the following steps between step S400 and step S500:

[0024] S01: repeat steps S200-S400 to obtain multiple rotational curved surfaces;

[0025] S02: Simulate multiple rotational curved surfaces separately to obtain the required rotational curved surface;

[0026] Wherein, step S02 includes the following steps:

[0027] S021: Import turbine model parameters, or create new model parameters;

[0028] S022: Import the parameters of one of the rotational surfaces;

[0029] S023: simulation experiment;

[0030] S024: record experimental data;

[0031] S025: Repeat steps S022-S024 until all rotating curved surfaces are simulated;

[0032] S026: Compare experimental data and obtain the desired body of revolution.

[0033] In a second aspect, the present invention provides a tailwater pipe protection device, which is constructed in an annular shape and has a cross-sectional shape determined by the tailwater pipe protection device design method.

[0034] In one possible design, the tailwater pipe protection device has a relative outer surface and an inner surface, the outer surface is used to connect the tailwater pipe, and the inner surface is constructed as a water-passing curved surface. Along the direction of water flow, the water-passing curved surface is divided into a water inlet section, a curved surface section and a water-passing section connected in sequence, and the water inlet section and the water-passing section are respectively provided with bolts for connecting the tailwater pipe.

[0035] In a third aspect, the present invention provides a tailwater pipe, comprising a pipe body and the tailwater pipe protection device, wherein the tailwater pipe protection device is detachably arranged on the pipe body.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] The tailwater pipe protection device weakens the flow field, destroys large-scale wall-attached vortices and turns them into small-scale wall-attached vortices, which then dissipate with the water flow. The spiral vortex belts can also be weakened and gradually dissipate. Based on this, the pressure pulsation amplitude inside the tailwater pipe is effectively reduced, and the turbine runs safer and more smoothly under small flow conditions, vibration and noise are reduced, and the probability of safety accidents such as lifting the machine, sweeping the barrel, and blade breakage is also greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0039] Figure 1 The present invention is a flow chart of a design method of a tailwater pipe protection device.

[0040] Figure 2 It is a front view schematic diagram of the straight cone section of the tailwater pipe.

[0041] Figure 3 for Figure 2 Schematic diagram of establishing a rectangular coordinate system.

[0042] Figure 4 To draw the generatrix y of the straight cone section of the tailwater pipe on the rectangular coordinate system 1 Schematic diagram of .

[0043] Figure 5 To draw the generatrix y of the straight cone section of the tailwater pipe on the rectangular coordinate system 1 and design curve y 2 Schematic diagram of .

[0044] Figure 6 After rotation, the straight cone section of the tailwater pipe has a generatrix y 1 and design curve y 2 Schematic diagram of overlap.

[0045] Figure 7 Schematic diagram of a body of revolution.

[0046] Figure 8 The figure is a structural schematic diagram of a tailwater pipe protection device.

[0047] Fig. 9 The figure is a schematic diagram of the assembly of a tailwater pipe with a tailwater pipe protection device installed on the tailwater pipe.

[0048] Fig.10 It is a schematic diagram comparing the pressure pulsation amplitudes in the existing tailwater pipe and the tailwater pipe.

[0049] Fig.11 is a flowchart of steps S01 and S02. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0051] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is apparent to one of ordinary skill in the art that these specific details are not necessarily employed to practice the present invention. In other embodiments, in order to avoid obscuring the present invention, well-known structures, circuits, materials, or methods are not specifically described.

[0052] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment," "an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. In addition, it will be appreciated by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0053] In the description of the present invention, the directions or positional relationships indicated by terms such as “front”, “rear”, “left”, “right”, “up”, “down”, “vertical”, “horizontal”, “high”, “low”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the scope of protection of the present invention.

[0054] Embodiment 1:

[0055] The operation of the turbine under low flow conditions may cause large-scale blade vortices, spiral vortex belts in the tailwater pipe, and low-frequency and high-amplitude pressure pulsations. Specifically, the large-scale vortex is close to the inner wall of the tailwater pipe, and it is difficult to dissipate and will remain in the tailwater pipe for a long time. The spiral vortex belt is located in the center of the tailwater pipe, but when the flow rate decreases, the spiral vortex belt will move toward the inner wall of the tailwater pipe. Furthermore, different flow fields are superimposed on each other to produce pressure pulsations, which in turn causes vibration and noise in the turbine under low flow conditions. In severe cases, it may also cause safety accidents such as lifting of the machine, sweeping of the barrel, and blade breakage.

[0056] Therefore, this embodiment proposes a tailwater pipe protection device, which weakens the flow field, destroys large-scale wall-attached vortices and turns them into small-scale wall-attached vortices, which then dissipate with the water flow. The spiral vortex belt can also be weakened and gradually dissipate. Based on this, the pressure pulsation amplitude inside the tailwater pipe is effectively reduced, and the operation of the turbine under small flow conditions is safer and more stable, vibration and noise are reduced, and the probability of safety accidents such as lifting the machine, sweeping the barrel, and blade breakage is also greatly reduced.

[0057] Specifically: Figure 1-Figure 11 As shown, a method for designing a tailwater pipe protection device comprises the following steps:

[0058] S100: Establish a rectangular coordinate system with the front view of the straight cone section of the tailwater pipe as the base surface and the intersection of the tailwater pipe generatrix and the tailwater pipe inlet section as the origin;

[0059] S200: Based on the rectangular coordinate system, draw the generatrix y of the straight cone section of the tailwater pipe 1 and design curve y 2 ;

[0060] S300: Rotate the design curve y based on the origin 2 To the busbar y of the straight cone section of the tailwater pipe 1 Overlap to obtain the tailwater pipe straight cone section busbar y 1 and design curve y 2 Enclose a closed plane area;

[0061] S400: rotating the plane region with the central axis of the draft tube as the center to obtain a rotational curved surface body; repeating the above steps to obtain multiple rotational curved surface bodies;

[0062] S500: The tailwater pipe protection device is manufactured based on the required rotational curved surface.

[0063] In short, the design method of the tailwater protection device includes the following steps: establishing a coordinate system; drawing lines (two lines, one of which is equivalent to the reference line and the other is a curve); rotating the lines to obtain a plane area; rotating the plane area to obtain a rotational curved surface. This is steps S100-S400. According to the obtained rotational curved surface, step S500 can be performed to manufacture and obtain the tailwater protection device.

[0064] Among them, for step S100, if Figure 2 As shown, the base surface is constructed as a closed quadrilateral similar to an isosceles trapezoid, the tailwater tube inlet section is located at the top, the interface between the tailwater tube straight cone section and the bent axis end is located at the bottom, and there are two tailwater tube generatrixes, which are respectively located on both sides of the base surface. Therefore, in step S100, there are two intersections between the tailwater tube generatrix and the tailwater tube inlet section, and any one of the intersections is used as the origin of the rectangular coordinate system, with the positive direction of the y-axis pointing upward and the positive direction of the x-axis pointing rightward.

[0065] Based on this, the difference between the two rectangular coordinate systems lies in the different positions of the origins. In step S300, the design curve y 2 Rotate and connect with the tailwater pipe straight cone section generatrix y 1 When the design curve y 2 The angle of rotation is different. At the same time, the straight cone section of the tailwater pipe generatrix y 1 and design curve y 2 The end points coincide with each other, and after the two are rotated and coincided, it can be confirmed that the plane area is on the generatrix y of the straight cone section of the tailwater pipe 1 The position on the tailwater pipe is determined, that is, the position of the tailwater pipe protection device on the tailwater pipe is determined, which reduces the variables in the subsequent simulation process and is also convenient for accurately installing the tailwater pipe protection device on the tailwater pipe.

[0066] Furthermore, if a rectangular coordinate system is established with any point on the base surface as the origin, theoretically, the generatrix y of the straight cone section of the tailwater pipe can also be drawn. 1 and design curve y 2 , but the problem is:

[0067] First, for step S300, the design curve y 2 After rotation and translation, it can be aligned with the straight cone section busbar y of the tailwater pipe. 1 The overlap process is cumbersome, increases the workload, and is prone to errors, which in turn affects subsequent steps.

[0068] Second, the tailwater pipe straight cone section busbar y 1 and design curve y 2 The overlapped area is different, so the plane area is on the generatrix y of the straight cone section of the tailwater pipe. 1 The position on the tailwater pipe is also different. Accordingly, the position of the tailwater pipe protection device on the tailwater pipe is an adjustable variable, which further increases the workload of the simulation.

[0069] Therefore, the origin of the rectangular coordinate system is selected as the intersection of the tailwater pipe generatrix and the tailwater pipe inlet section.

[0070] For step S200, draw the straight cone section generatrix y of the tailwater pipe 1 and design curve y 2 , tailwater pipe straight cone section busbar y 1 The location indicates the location of the inner wall of the tailwater pipe. The design curve y 2 The straight cone section of the tailwater pipe is constructed as a curve so that the generatrix y 1 and design curve y 2 After overlapping, a plane area can be formed.

[0071] Specifically, in a possible implementation, in step S200, a tailwater pipe straight cone section busbar y is drawn along the tailwater pipe busbar 1 , tailwater pipe straight cone section busbar y 1 The vertex of is the origin of the rectangular coordinate system. Based on the above design scheme, according to the different positions of the origin, the tailwater tube straight cone section generatrix y is drawn along the tailwater tube generatrix intersecting with the origin. 1 That's it.

[0072] In a possible implementation, in step S200, a design curve y is drawn. 2 The following steps are involved:

[0073] S210: Select the curve design formula:

[0074]

[0075] Among them, s is the height of the design curve, c is a parameter related to the period of the sin trigonometric function, and l is the length of the generatrix of the straight cone section of the tailwater pipe;

[0076] S220: Select the values ​​of s and c, where both s and c shall not be less than 0.1 times l and shall not exceed 0.2 times l, and s shall not exceed 1 / 3 of the diameter of the tailwater pipe inlet section;

[0077] S230: Draw the design curve y on the rectangular coordinate system 2 ;

[0078] Steps S210-S220 can be interchanged with step S100. The curve drawn in step S230 includes two straight lines and an arc, and the two straight lines are connected by the arc to form a continuous design curve y. 2 .

[0079] Based on the above design scheme, the design curve y can be drawn on the x-axis of the rectangular coordinate system through the curve formula 2, and the length of the straight cone section of the tailwater pipe limits the range of s and c. In other words, l is a constant, and s and c can be selected and combined with different values. Therefore, the design curve y 2 With multiple linear shapes, different plane areas are formed in step S300, and different rotational curved surfaces are obtained in S400. Then, in order to achieve the best effect, multiple simulations can be performed and the results can be compared to obtain the best design curve y 2 .

[0080] For the design curve y 2 , the shape and position of the arc will be different if the parameter values ​​are different, so it is necessary to select different values ​​to confirm the best result. 2 The arc part does not coincide with the straight cone section of the tailwater pipe. 1 Therefore, after step S300 is implemented, the busbar y of the straight cone section of the tailwater pipe 1 With the design curve y 2 They do not completely overlap to obtain a closed plane area.

[0081] It is easy to understand that the selection of curve design formulas and parameter values, as well as the establishment of a rectangular coordinate system can be performed before drawing lines, and the order of implementation can be changed, so those skilled in the art can select a specific implementation order as needed.

[0082] In step S220, s and c select multiple sets of values ​​respectively to obtain multiple design curves y 2 Accordingly, multiple plane regions are obtained in step S300, and multiple rotational curved surfaces are obtained in step S400. Based on this, the number of rotational curved surfaces is also increased, and the staff can select the rotational curved surface with the best effect through experiments to ensure that the turbine works stably and smoothly under low flow conditions.

[0083] For step S300, Figure 6 As shown, in step S300, the tailwater pipe straight cone section busbar y 1 With the design curve y 2 After overlap, the design curve y 2 The two straight lines are respectively connected to the generatrix y 1 Overlap, in y 2 <y<y 1 Area, design curve y 2 The arc line and the generatrix y of the straight cone section of the tailwater pipe 1 Enclosed plane area.

[0084] Based on this, due to the straight cone section of the tailwater pipe generatrix y 1 and design curve y 2 The vertices of coincide at the origin of the rectangular coordinate system, so only the design curve y needs to be rotated2 This can make the two overlap, reduce the operation steps and intermediate variables, and help improve the speed and accuracy of the design.

[0085] Further, if Fig.11 As shown, the tailwater pipe protection device design method further includes the following steps between step S400 and step S500:

[0086] S01: repeat steps S200-S400 to obtain multiple rotational curved surfaces;

[0087] S02: Simulate experiments on multiple rotational curved surfaces separately to obtain the required rotational curved surface.

[0088] Based on the above design, since s and c can select multiple sets of values, the design curve y 2 With diversity, in order for the tailwater pipe protection device to achieve a better protection effect, steps S01 and S02 are designed on the basis of steps S100-S400, which on the one hand ensure the better performance of the tailwater pipe protection device, and on the other hand collect data to facilitate subsequent improvement, maintenance and the like.

[0089] Wherein, step S02 includes the following steps:

[0090] S021: Import turbine model parameters, or create new model parameters;

[0091] S022: Import the parameters of one of the rotational surfaces;

[0092] S023: simulation experiment;

[0093] S024: record experimental data;

[0094] S025: Repeat steps S022-S024 until all rotating curved surfaces are simulated;

[0095] S026: Compare experimental data and obtain the desired body of revolution.

[0096] Based on this, the parameters in step S021 are determined according to the actual turbine used, and steps S022-S025 are performed on any suitable computing terminal, reducing the actual machine test, which can not only speed up the efficiency of the experiment, but also reduce the design cost. In step S026, the optimal rotational curved surface is generally selected, and if necessary, any rotational curved surface can also be selected.

[0097] This embodiment introduces a tailwater tube protection device based on the tailwater tube protection device design method. The tailwater tube protection device is constructed in a ring shape and its cross-sectional shape is determined by the tailwater tube protection device design method.

[0098] Based on this, the tailwater pipe protection device design method can not only confirm the shape of the tailwater pipe protection device, but also determine the position of the tailwater pipe protection device on the tailwater pipe, thereby killing two birds with one stone and facilitating the staff to accurately install the tailwater pipe protection device.

[0099] Accordingly, the shape of the tailwater tube protection device is confirmed by the tailwater tube protection device design method, and those skilled in the art may manufacture it in any suitable manner.

[0100] In one possible implementation, the tailwater pipe protection device has a relative outer surface and an inner surface, the outer surface is used to connect the tailwater pipe, and the inner surface is constructed as a water-passing curved surface. Along the water flow direction, the water-passing curved surface is divided into a water inlet section, a curved surface section and a water-passing section connected in sequence, and the water inlet section and the water-passing section are respectively provided with bolts for connecting the tailwater pipe.

[0101] Based on the above design, the water inlet section and the water passage section are relatively stable and have a small curvature, so it is convenient to open a hole structure such as a screw hole, so as to facilitate the subsequent fixing of the draft tube protection device by bolts. At the same time, the processing of the curved surface section is reduced, and the shape of the curved surface section is protected to ensure the ability of the draft tube protection device to weaken the vortex, thereby achieving the purpose of reducing the pressure pulsation amplitude.

[0102] Optionally, a concave weight-reducing groove is provided on the outer surface. Based on this, on the basis of ensuring that the tailwater tube protection device will not be deformed by pressure during operation, a weight-reducing groove is provided on the tailwater tube protection device to reduce the weight of the tailwater tube protection device.

[0103] This embodiment also introduces a tailwater pipe, the tailwater pipe includes a pipe body and the tailwater pipe protection device, the tailwater pipe protection device is detachably arranged on the pipe body. Based on this, whether to install the tailwater pipe protection device is selected according to the actual flow rate, which is flexible and convenient to use, and also makes the structure of the tailwater pipe more adaptable to the working flow, making the tailwater pipe work more stable and reliable.

[0104] Embodiment 2:

[0105] When the length of the straight cone section of the turbine tailwater tube is 1.2 m, s and c are 0.12 m and 0.15 m respectively. Figure 1-Figure 9 As shown, the cross-sectional shape of the tailwater tube protection device is confirmed according to the tailwater tube protection device design method described in Example 1, and then the tailwater tube protection device is manufactured.

[0106] At this time, the tailwater pipe protection device is installed at point A, which is 0.3D below the tailwater pipe inlet section, and D is the diameter of the tailwater pipe inlet section. Fig.10As shown, after the tailwater pipe protection device is installed, the pressure pulsation amplitude of the tailwater pipe at point A drops from 2704.6Pa to 2212.7Pa, with a maximum drop of 22.2%, which is a significant drop and effectively protects the tailwater pipe.

[0107] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for designing a tailwater pipe protection device, characterized in that: It includes the following steps: S100: Taking the front view of the straight conical section of the draft tube as the base plane, and taking the intersection point of the draft tube busbar and the inlet section of the draft tube as the origin, establish a rectangular coordinate system; S200: Taking the rectangular coordinate system as the reference, draw the draft tube straight conical section busbar y1 and the design curve y2; S300: Rotate the design curve y2 around the origin until it coincides with the draft tube straight conical section busbar y1, and obtain the closed planar region enclosed by the draft tube straight conical section busbar y1 and the design curve y2; S400: Rotate the planar region around the central axis of the draft tube to obtain a rotating surface body; S500: Make a draft tube protection device based on the rotating surface body.

2. The method for designing a tailwater pipe protection device according to claim 1, characterized in that: In step S100, there are two intersection points between the draft tube busbar and the inlet section of the draft tube. Taking any one of the intersection points as the origin of the rectangular coordinate system, the upward direction is the positive direction of the y-axis, and the rightward direction is the positive direction of the x-axis.

3. The method for designing a tailwater pipe protection device according to claim 2, characterized in that: In step S200, draw the draft tube straight conical section busbar y1 along the draft tube busbar, and the vertex of the draft tube straight conical section busbar y1 is the origin of the rectangular coordinate system.

4. The method for designing a tailwater pipe protection device according to claim 3, characterized in that: In step S200, drawing the design curve y2 includes the following steps: S210: Select a curve design formula: where s is the convex height of the design curve, c is a parameter related to the period of the sin trigonometric function, and l is the length of the draft tube straight conical section busbar; S220: Select the respective values of s and c. Among them, both s and c shall not be less than 0.1 times of l and shall not exceed 0.2 times of l, and s shall not exceed 1 / 3 of the diameter of the draft tube inlet section; S230: Draw the design curve y2 on the rectangular coordinate system; Among them, steps S210 - S220 can be interchanged with step S100. The curve drawn in step S230 includes two straight lines and an arc, and the two straight lines are connected by the arc to form a continuous design curve y2.

5. The method for designing a tailwater pipe protection device according to claim 4, characterized in that: In step S220, multiple groups of values are respectively selected for s and c to obtain multiple design curves y2. Correspondingly, multiple planar regions are obtained in step S300, and multiple rotating surface bodies are obtained in step S400.

6. The method for designing a tailwater pipe protection device according to claim 4, characterized in that: In step S300, after the draft tube straight conical section busbar y1 coincides with the design curve y2, the two straight lines of the design curve y2 respectively coincide with the draft tube straight conical section busbar y1. In the region where y2 < y < y1, the arc of the design curve y2 and the draft tube straight conical section busbar y1 enclose a closed planar region.

7. The method for designing a draft tube protection device according to any one of claims 1 to 6, characterized in that: It also includes the following steps located between step S400 and S500: S01: Repeat steps S200 - S400 to obtain multiple rotating surface bodies; S02: Conduct simulation experiments on multiple rotating surface bodies respectively to obtain the required rotating surface body; Among them, step S02 includes the following steps: S021: Import the water turbine model parameters, or, create new model parameters; S022: Import the parameters of one of the rotating surface bodies; S023: Conduct a simulation experiment; S024: Record the experimental data; S025: Repeat steps S022 - S024 until all rotating surface bodies are simulated; S026: Compare the experimental data and obtain the required rotating surface body.

8. A tailwater pipe protection device, characterized in that: It is constructed as an annular shape and the cross-sectional shape is determined by the draft tube protection device design method described in any one of claims 1 - 7.

9. The tailwater pipe protection device according to claim 8, characterized in that: The tailwater pipe protection device has a relative outer surface and an inner surface, the outer surface is used to connect the tailwater pipe, and the inner surface is constructed as a water-passing curved surface. Along the water flow direction, the water-passing curved surface is divided into a water inlet section, a curved surface section and a water-passing section connected in sequence, and the water inlet section and the water-passing section are respectively provided with bolts for connecting the tailwater pipe.

10. A tailwater pipe, characterized in that: It comprises a pipe body and the tailwater pipe protection device according to claim 8 or 9, wherein the tailwater pipe protection device is detachably arranged on the pipe body.

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