Diversion structure for draft tube of water turbine

Abstract

According to the draft tube flow guide structure for the water turbine, a triangular flow guide grid is arranged at an inlet of a draft tube, a circular flow guide grid is further arranged in the triangular flow guide grid, and a plurality of flow guide plates are further evenly arranged on the inner wall of the rear half section of a straight cone section of the draft tube in the circumferential direction. According to the draft tube flow guide structure for the water turbine, the problem that in the prior art, the efficiency of a water turbine set is reduced due to increased pressure oscillation and draft tube loss caused by a vortex band is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of water turbine structures and relates to a tailwater pipe guide structure for a water turbine. Background Art

[0002] Hydropower generation often needs to operate under non-design conditions, which will increase flow instability and reduce turbine efficiency. When the fluid enters the runner, as the rotating vortex structure evolves, periodic pressure pulsations will occur in the tailwater pipe, which may threaten the performance of the turbine. In order to change the water flow state in the tailwater pipe, eliminate the circulation, and reduce the impact of the vortex belt, the method of adding air to the tailwater pipe and adding guide plates to the tailwater pipe is usually adopted. However, the air replenishment method is not easy to control the air replenishment position and air replenishment amount, and it will also affect the pressure pulsation.

[0003] Under partial load operation of the turbine, low-frequency oscillations relative to the runner frequency appear in the draft tube of the turbine, affecting the power output of the turbine and reducing efficiency. Under partial load conditions, the residual vortex entering the draft tube has a large tangential velocity in the area close to the wall, resulting in the formation of a low-speed area in the center of the straight cone section of the draft tube. At the same time, the high shear force between the recirculation zone and the vortex zone is more likely to form a vortex belt, increase pressure oscillations, increase the loss of the draft tube, and reduce the efficiency of the turbine unit. Therefore, it is urgent to propose a new type of internal guide plate of the draft tube to alleviate the distribution of the flow field in the draft tube, thereby reducing the generation of vortex belts and improving the efficiency of the turbine. Summary of the invention

[0004] The purpose of the present invention is to provide a draft tube guide structure for a water turbine, which solves the problem in the prior art of increased pressure oscillation and loss of the draft tube caused by vortex bands, thereby reducing the efficiency of the water turbine unit.

[0005] The technical solution adopted by the present invention is a tailwater pipe guide structure for a turbine, including a triangular guide grid arranged at the inlet of the tailwater pipe, a circular guide grid arranged inside the triangular guide grid, and a plurality of guide plates evenly arranged along the circumferential direction on the inner wall of the rear half of the straight cone section of the tailwater pipe.

[0006] The present invention is also characterized in that: The triangular guide grid at the tailwater pipe inlet is an inscribed triangle at the tailwater pipe inlet and is an equilateral triangle.

[0007] The ratio of the side length L1 of the equilateral triangle of the triangular guide fence to the outlet diameter D of the turbine runner is L1 / D= / 2.

[0008] The ratio of the height H1 of the triangular guide grid to the outlet diameter of the turbine runner is H1 / D=1 / 1, and the height of the circular guide grid is the same as that of the triangular guide grid.

[0009] The cross section of the circular guide fence is the inscribed circle of the triangle of the triangular guide fence, and the ratio of the diameter d of the circular guide fence to the outlet diameter D of the turbine runner is d / D=1 / 2.

[0010] The ratio of the distance H2 between the end of the guide plate close to the triangular guide fence and the triangular guide fence to the turbine runner outlet diameter D is H2 / D=1 / 10.

[0011] The ratio of the guide plate height H3 to the turbine runner outlet diameter D is H3 / D=1 / 2.

[0012] The ratio of the length L2 of the guide plate extending from the inner wall of the tailwater tube toward the center of the tailwater tube to the outlet diameter D of the turbine runner is L2 / D=1 / 4.

[0013] The guide plate is hinged on the inner wall of the tailwater pipe, and the guide plate is also connected to an angle adjustment device, and the other end of the angle adjustment device extends out of the tailwater pipe and is located outside the tailwater pipe; A plurality of shaft rods are embedded and evenly rotated in the circumferential direction on the side wall of the rear half of the straight cone section of the tailwater pipe, and the shaft rods coincide with the generatrix of the tailwater pipe installation position, and the guide plate is fixed to the side of the shaft rod located in the tailwater pipe. The angle adjustment device includes an adjustment plate installed on the side of the shaft rod located outside the tailwater pipe, the adjustment plate is parallel to the corresponding guide plate and is located in the same plane, an adjustment rod is connected to the adjustment plate, and also includes a fixed bracket, an annular fixing plate is arranged above the fixed bracket, the annular fixing plate is sleeved on the plane of the adjusting rod corresponding to the tailwater pipe, an adjustment box is fixedly arranged on the annular fixing plate, the other end of the adjusting rod passes through the adjusting box and is connected to an adjustment handle, and slide rails are correspondingly arranged on the two end surfaces of the adjusting rod passing through the adjusting box, and a slider cooperating with the slide rails is arranged on the adjusting rod, and when the adjusting rod slides left and right in the slide rail, the adjustment plate drives the shaft rod to rotate, thereby driving the guide plate to rotate a certain angle.

[0014] When the adjustment rod is located in the middle position of the slide rail, the guide plate is perpendicular to the side wall of the tailwater pipe, and the adjustment angle is 0°. When the adjustment rod is located at the left and right ends of the slide rail, the adjustment angles of the guide plate are -45° and 45° respectively. One side of the adjustment box where the adjustment handle is set is located below the slide rail and corresponding scale lines of -45°, -25°, 0°, 25° and 45° are set. When the adjustment handle is located at the corresponding scale position, the guide plate is adjusted to the corresponding angle.

[0015] The beneficial effects of the present invention are: After the guide grid is arranged at the inlet of the tailwater pipe, the vortex belt is in the guide grid, which reduces the eccentric effect of the vortex belt and the circumferential velocity of the water flow, and reduces the backflow at the inlet of the tailwater pipe; the pressure distribution at the straight cone section of the tailwater pipe is made more uniform, and the impact of the vortex belt on the side wall of the straight cone section is reduced, so that the streamline of the straight cone section is in a stable distribution state, and the vibration generated by the vortex belt of the tailwater pipe is reduced to a certain extent, and the resonance of the unit caused by the vortex belt of the tailwater pipe is further reduced.

[0016] The present invention provides a rotatable guide plate at the rear half of the straight cone section of the tailwater pipe, and adjusts the angle of the guide plate according to the change of the guide vane opening of the unit, which can effectively weaken the pressure oscillation after the water flow passes through the guide grid, reduce the pressure pulsation in the tailwater pipe, slow down the formation of the vortex belt, alleviate and suppress the vortex near the inner wall of the tailwater pipe, and reduce the vortex core in the center of the straight cone section of the tailwater pipe, that is, reduce the size of the low-pressure area, improve the performance of the tailwater pipe, reduce the loss of water flow energy, and achieve the purpose of improving the operating efficiency of the turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of a draft tube flow guide structure for a water turbine according to the present invention; Figure 2 yes Figure 1 A top view of the AA section in FIG. Figure 3 yes Figure 1 A top view of the BB section in FIG. Figure 4 It is a structural schematic diagram of an angle adjustment device in a draft tube flow guide structure for a water turbine according to the present invention; Figure 5 It is a schematic diagram of one side of a regulating box in a tailwater pipe guide structure for a water turbine according to the present invention.

[0018] In the figure: 1. tailwater pipe, 2. triangular guide fence, 3. circular guide fence, 4. guide plate, 5. adjustment box, 6. shaft rod, 7. adjustment plate, 8. adjustment rod, 9. fixing bracket, 10. annular fixing plate, 11. adjustment handle, 12. slide rail. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Example 1 The present invention is used for the tailwater pipe guide structure of a water turbine, and its structure is as follows Figure 1-3 As shown, a triangular guide grid 2 is arranged at the inlet of the tailwater pipe 1, a circular guide grid 3 is also arranged inside the triangular guide grid 2, and a plurality of guide plates 4 are evenly arranged along the circumferential direction on the inner wall of the rear half of the straight cone section of the tailwater pipe 1, and the inner wall of the tailwater pipe 1 close to the guide plate 4 and the side away from the inner wall of the tailwater pipe 1 are parallel to the generatrix of the tailwater pipe 1 corresponding to the setting position thereof.

[0021] like Figure 4-5 As shown, the guide plate 4 is hinged on the inner wall of the tailwater pipe 1, and the guide plate 4 is also connected to an angle adjustment device, and the other end of the angle adjustment device extends out of the tailwater pipe 1 and is located outside the tailwater pipe 1; A plurality of shafts 6 are evenly rotated and embedded in the side wall of the rear half of the straight cone section of the tailwater tube 1 in the circumferential direction, and the shafts 6 coincide with the generatrix of the installation position of the tailwater tube 1. The guide plate 4 is fixed to the side of the shaft 6 located inside the tailwater tube 1. The angle adjustment device includes an adjustment plate 7 installed on the side of the shaft 6 located outside the tailwater tube 1. The adjustment plate 7 is parallel to the corresponding guide plate 4 and is located in the same plane. An adjustment rod 8 is connected to the adjustment plate 7, and also includes a fixing bracket 9. An annular fixing plate 10 is arranged above the fixing bracket 9. The annular fixing plate 10 is sleeved on the plane of the tailwater pipe 1 corresponding to the adjusting rod 8, an adjusting box 5 is fixedly arranged on the annular fixing plate 10, the other end of the adjusting rod 8 passes through the adjusting box 5 and is connected with an adjusting handle 11, and the two end surfaces of the adjusting box 5 passing through the adjusting rod 8 are correspondingly provided with slide rails 12, and the adjusting rod 8 is provided with a slider matched with the slide rail 12. When the adjusting rod 8 slides left and right in the slide rail 12, the adjusting plate 7 drives the shaft rod 6 to rotate, thereby driving the guide plate 4 to rotate a certain angle, and the fixing bracket 9 is fixed at the work site according to the actual situation on site.

[0022] When the adjusting rod 8 is located in the middle position of the slide rail 12, the guide plate 4 is perpendicular to the side wall of the tailwater pipe 1, and the adjustment angle is 0° at this time. When the adjusting rod 8 is located at the left and right ends of the slide rail 12, the adjustment angles of the guide plate 4 are -45° and 45° respectively. One side of the adjusting box 5 is provided with an adjusting handle 11, and correspondingly -45°, -25°, 0°, 25° and 45° scale lines are provided below the slide rail 12. When the adjusting handle 11 is located at the corresponding scale position, the guide plate 4 is adjusted to the corresponding angle.

[0023] The working principle of this embodiment is as follows: When the turbine operates normally, the fluid enters the draft tube 1 along the turbine runner outlet, and flows through the triangular guide fence 2 and the circular guide fence 3, reducing the circumferential velocity of the water flow and the probability of generating eccentric vortex belts, so that the flow state in the straight cone section of the draft tube 1 is stable, and the pressure of the straight cone section of the draft tube 1 tends to be evenly distributed between the baffles, reducing the low-speed area in the center of the straight cone section.

[0024] A guide plate 4 with an adjustable angle is arranged in the rear half of the straight cone section of the tailwater pipe 1. The angle of the guide plate is adjusted according to the different guide vane openings of the unit. Under the optimal opening condition, the guide plate 4 is perpendicular to the wall of the tailwater pipe 1 at 90°. At this time, the adjustment angle of the guide plate 4 is 0°. Then, according to the working conditions, the guide plate 4 is rotated 45° clockwise and 45° counterclockwise to weaken the pressure oscillation after the water flow passes through the triangular guide grid 2 and the circular guide grid 3, reduce the pressure pulsation in the tailwater pipe, slow down the formation of the vortex belt, relieve and suppress the vortex near the inner wall of the tailwater pipe, and at the same time reduce the vortex core in the center of the straight cone section of the tailwater pipe, that is, reduce the size of the low-pressure area, improve the performance of the tailwater pipe, reduce the loss of water flow energy, and achieve the purpose of improving the operation efficiency of the turbine.

[0025] Example 2 On the basis of Example 1, three guide plates 4 are evenly arranged along the circumferential direction on the inner wall of the rear half of the straight cone section of the tailwater pipe 1.

[0026] Example 3 The present invention is used for the tailwater pipe guide structure of a water turbine, and its structure is as follows Figure 1-3 As shown, a triangular guide grid 2 is arranged at the inlet of the tailwater pipe 1, a circular guide grid 3 is arranged inside the triangular guide grid 2, and a plurality of guide plates 4 are evenly arranged along the circumferential direction on the inner wall of the rear half of the straight cone section of the tailwater pipe 1.

[0027] like Figure 4-5 As shown, the guide plate 4 is hinged on the inner wall of the tailwater pipe 1, and the guide plate 4 is also connected to an angle adjustment device, and the other end of the angle adjustment device extends out of the tailwater pipe 1 and is located outside the tailwater pipe 1; A plurality of shafts 6 are evenly and uniformly embedded in the side wall of the rear half of the straight cone section of the tailwater tube 1 in the circumferential direction, and the shafts 6 coincide with the generatrix of the installation position of the tailwater tube 1. The guide plate 4 is fixed to the side of the shaft 6 located inside the tailwater tube 1. The angle adjustment device includes an adjustment plate 7 installed on the side of the shaft 6 located outside the tailwater tube 1. The adjustment plate 7 is parallel to the corresponding guide plate 4 and is located in the same plane. An adjustment rod 8 is connected to the adjustment plate 7, and also includes a fixed bracket 9. An annular fixing plate 10 is arranged above the fixed bracket 9. The annular fixing plate 10 is sleeved on the plane of the corresponding adjusting rod 8 of the tailwater tube 1. An adjustment box 5 is fixedly arranged on the annular fixing plate 10. The other end of the adjusting rod 8 passes through the adjusting box 5 and is connected with an adjusting handle 11. The two end surfaces of the adjusting box 5 through which the adjusting rod 8 is passed are correspondingly provided with slide rails 12. The adjusting rod 8 is provided with a slider matched with the slide rail 12. When the adjusting rod 8 slides left and right in the slide rail 12, the adjustment plate 7 drives the shaft 6 to rotate, thereby driving the guide plate 4 to rotate a certain angle.

[0028] When the adjusting rod 8 is located in the middle position of the slide rail 12, the guide plate 4 is perpendicular to the side wall of the tailwater pipe 1, and the adjustment angle is 0° at this time. When the adjusting rod 8 is located at the left and right ends of the slide rail 12, the adjustment angles of the guide plate 4 are -45° and 45° respectively. One side of the adjusting box 5 is provided with an adjusting handle 11, and correspondingly -45°, -25°, 0°, 25° and 45° scale lines are provided below the slide rail 12. When the adjusting handle 11 is located at the corresponding scale position, the guide plate 4 is adjusted to the corresponding angle.

[0029] The triangular guide fence 2 at the inlet of the tailwater pipe 1 is an inscribed triangle at the inlet of the tailwater pipe 1 and is an equilateral triangle.

[0030] The working principle of this embodiment is as follows: When the turbine operates normally, the fluid enters the draft tube 1 along the turbine runner outlet, and flows through the triangular guide fence 2 and the circular guide fence 3, reducing the circumferential velocity of the water flow and the probability of generating eccentric vortex belts, so that the flow state in the straight cone section of the draft tube 1 is stable, and the pressure of the straight cone section of the draft tube 1 tends to be evenly distributed between the baffles, reducing the low-speed area in the center of the straight cone section.

[0031] A guide plate 4 with an adjustable angle is arranged in the rear half of the straight cone section of the tailwater pipe 1. The angle of the guide plate is adjusted according to the different guide vane openings of the unit. Under the optimal opening condition, the guide plate 4 is perpendicular to the wall of the tailwater pipe 1 at 90°. At this time, the adjustment angle of the guide plate 4 is 0°. Then, according to the working conditions, the guide plate 4 is rotated 45° clockwise and 45° counterclockwise to weaken the pressure oscillation after the water flow passes through the triangular guide grid 2 and the circular guide grid 3, reduce the pressure pulsation in the tailwater pipe, slow down the formation of the vortex belt, relieve and suppress the vortex near the inner wall of the tailwater pipe, and at the same time reduce the vortex core in the center of the straight cone section of the tailwater pipe, that is, reduce the size of the low-pressure area, improve the performance of the tailwater pipe, reduce the loss of water flow energy, and achieve the purpose of improving the operation efficiency of the turbine.

[0032] Example 4 Based on Example 3, the ratio of the side length L1 of the equilateral triangle of the triangular guide fence 2 to the outlet diameter D of the turbine runner is L1 / D= / 2.

[0033] The ratio of the height H1 of the triangular guide fence 2 to the outlet diameter of the turbine runner is H1 / D=1 / 1, and the height of the circular guide fence 3 is the same as the height of the triangular guide fence 2.

[0034] Example 5 On the basis of Example 4, the cross section of the circular guide fence 3 is the inscribed circle of the triangle of the triangular guide fence 2, and the ratio of the diameter d of the circular guide fence 3 to the outlet diameter D of the turbine runner is d / D=1 / 2.

[0035] Example 6 On the basis of Example 5, the ratio of the distance H2 between the end of the guide plate 4 close to the triangular guide fence 2 and the triangular guide fence 2 to the outlet diameter D of the turbine runner is H2 / D=1 / 10.

[0036] The ratio of the height H3 of the guide plate 4 to the outlet diameter D of the turbine runner is H3 / D=1 / 2.

[0037] The ratio of the length L2 of the guide plate 4 extending from the inner wall of the tailwater tube 1 toward the center of the tailwater tube 1 to the outlet diameter D of the turbine runner is L2 / D=1 / 4.

[0038] Example 7 On the basis of Example 6, the present invention is used for the tailwater pipe guide structure of the turbine, and its structure is as follows Figure 1-3As shown, a triangular guide grid 2 is arranged at the inlet of the tailwater pipe 1, a circular guide grid 3 is arranged inside the triangular guide grid 2, and three guide plates 4 are evenly arranged along the circumferential direction on the inner wall of the rear half of the straight cone section of the tailwater pipe 1.

[0039] like Figure 4-5 As shown, the guide plate 4 is hinged on the inner wall of the tailwater pipe 1, and the guide plate 4 is also connected to an angle adjustment device, and the other end of the angle adjustment device extends out of the tailwater pipe 1 and is located outside the tailwater pipe 1; Three shafts 6 are evenly rotated and embedded in the side wall of the rear half of the straight cone section of the tailwater tube 1 in the circumferential direction, that is, the three shafts 6 are distributed at 120 degrees around the circumference of the tailwater tube 1, and the shafts 6 coincide with the generatrix of the installation position of the tailwater tube 1. The guide plate 4 is fixed to the side of the shaft 6 located inside the tailwater tube 1, and the angle adjustment device includes an adjustment plate 7 installed on the side of the shaft 6 located outside the tailwater tube 1, and the adjustment plate 7 is parallel to the corresponding guide plate 4 and located in the same plane, and an adjustment rod 8 is connected to the adjustment plate 7, and a fixing bracket 9 is also included. An annular fixing plate 10 is arranged above the fixing bracket 9, and the annular fixing plate 10 is sleeved on the plane of the tailwater pipe 1 corresponding to the adjusting rod 8. An adjusting box 5 is fixedly arranged on the annular fixing plate 10, and the other end of the adjusting rod 8 passes through the adjusting box 5 and is connected with an adjusting handle 11. The two end surfaces of the adjusting box 5 through which the adjusting rod 8 is passed are correspondingly provided with slide rails 12, and the adjusting rod 8 is provided with a slider that cooperates with the slide rail 12. When the adjusting rod 8 slides left and right in the slide rail 12, the adjusting plate 7 drives the shaft rod 6 to rotate, thereby driving the guide plate 4 to rotate a certain angle.

[0040] The two end surfaces of the adjustment box 5 through which the adjustment rod 8 passes are provided with corresponding slide rail fixing grooves, and a slide rail 12 is fixedly provided at the bottom of the slide rail fixing groove. A slider is provided at a position corresponding to the slide rail 12 below the adjustment rod 8, and the slider is slidably connected in the slide rail 12. Driven by the slider, the adjustment rod 8 moves left and right in the slide rail fixing groove, driving the adjustment plate 7, thereby driving the shaft rod 6 to rotate, so that the guide plate 4 rotates a certain angle.

[0041] When the adjusting rod 8 is located in the middle position of the slide rail 12, the guide plate 4 is perpendicular to the side wall of the tailwater pipe 1, and the adjustment angle is 0° at this time. When the adjusting rod 8 is located at the left and right ends of the slide rail 12, the adjustment angles of the guide plate 4 are -45° and 45° respectively. One side of the adjusting box 5 is provided with an adjusting handle 11, and correspondingly -45°, -25°, 0°, 25° and 45° scale lines are provided below the slide rail 12. When the adjusting handle 11 is located at the corresponding scale position, the guide plate 4 is adjusted to the corresponding angle.

[0042] The working principle of this embodiment is as follows: When the turbine operates normally, the fluid enters the draft tube 1 along the turbine runner outlet, and flows through the triangular guide fence 2 and the circular guide fence 3, reducing the circumferential velocity of the water flow and the probability of generating eccentric vortex belts, so that the flow state in the straight cone section of the draft tube 1 is stable, and the pressure of the straight cone section of the draft tube 1 tends to be evenly distributed between the baffles, reducing the low-speed area in the center of the straight cone section.

[0043] A guide plate 4 with an adjustable angle is arranged in the rear half of the straight cone section of the tailwater pipe 1. The angle of the guide plate is adjusted according to the different guide vane openings of the unit. Under the optimal opening condition, the guide plate 4 is perpendicular to the wall of the tailwater pipe 1 at 90°. At this time, the adjustment angle of the guide plate 4 is 0°. Then, according to the working conditions, the guide plate 4 is rotated 45° clockwise and 45° counterclockwise to weaken the pressure oscillation after the water flow passes through the triangular guide grid 2 and the circular guide grid 3, reduce the pressure pulsation in the tailwater pipe, slow down the formation of the vortex belt, relieve and suppress the vortex near the inner wall of the tailwater pipe, and at the same time reduce the vortex core in the center of the straight cone section of the tailwater pipe, that is, reduce the size of the low-pressure area, improve the performance of the tailwater pipe, reduce the loss of water flow energy, and achieve the purpose of improving the operation efficiency of the turbine.

[0044] Example 8 On the basis of Example 7, the tailwater guide structure for the turbine in Example 7 was simulated on ANSYS. After the test, before the guide grid was set at the inlet of the tailwater pipe, the circumferential velocity of the water flow was relatively large, the vortex belt in the tailwater pipe was widely distributed, and the vortex belt gradually extended close to the tailwater pipe wall, and there was a certain backflow at the inlet. After the inlet guide grid was set, the vortex belt was in the guide grid, which reduced the eccentric effect of the vortex belt and the circumferential velocity of the water flow, and reduced the backflow at the inlet of the tailwater pipe; the pressure distribution at the straight cone section of the tailwater pipe was more uniform, and the impact of the vortex belt on the side wall of the straight cone section was reduced, so that the streamlines of the straight cone section were in a stable distribution state, which to a certain extent reduced the vibration generated by the vortex belt of the tailwater pipe, and further reduced the resonance of the unit caused by the vortex belt of the tailwater pipe.

[0045] Example 9 On the basis of Example 7, the combination of the slide rail 12 and the slider is set as an electric slide rail, the slide rail base of the electric slide rail is set in the slide rail fixing groove, the slider of the electric slide rail is fixed under the adjusting rod and slides in the slide rail base of the electric slide rail, and the angle adjustment is achieved by electric control. At this time, the adjustment handle 11 is used as a scale indicator needle, and the adjustment position can be clearly known according to the indication.

[0046] Example 10 On the basis of Example 7, if it is an ordinary manually adjustable slide rail, the slider is moved on the slide rail by manually adjusting the adjusting handle 11, and then limit holes are provided on both sides of each scale line corresponding to one side of the adjusting handle 11 of the adjusting box 5. When the adjusting handle 11 is adjusted to the corresponding scale, the adjusting handle 11 is positioned to move left and right by fixing the limit pin in the limit hole.

Claims

1. A draft tube guide structure for a water turbine, characterized in that: The invention comprises a triangular flow guide grid (2) arranged at the inlet of a tailwater pipe (1), a circular flow guide grid (3) being arranged inside the triangular flow guide grid (2), and a plurality of flow guide plates (4) being evenly arranged along the circumferential direction on the inner wall of the rear half of the straight cone section of the tailwater pipe (1).

2. The draft tube guide structure for a water turbine according to claim 1, characterized in that: The triangular guide fence (2) at the inlet of the tailwater pipe (1) is an inscribed triangle at the inlet of the tailwater pipe (1) and is an equilateral triangle.

3. The draft tube guide structure for a water turbine according to claim 2, characterized in that: The ratio of the side length L1 of the equilateral triangle of the triangular guide fence (2) to the outlet diameter D of the turbine runner is L1 / D= / 2.

4. The draft tube guide structure for a water turbine according to claim 3, characterized in that: The ratio of the height H1 of the triangular guide fence (2) to the outlet diameter of the turbine runner is H1 / D=1 / 1, and the height of the circular guide fence (3) is the same as the height of the triangular guide fence (2).

5. The draft tube guide structure for a water turbine according to claim 4, characterized in that: The cross section of the circular guide fence (3) is the inscribed circle of the triangle of the triangular guide fence (2), and the ratio of the diameter d of the circular guide fence (3) to the outlet diameter D of the turbine runner is d / D=1 / 2.

6. The draft tube guide structure for a water turbine according to claim 5, characterized in that: The ratio of the distance H2 between one end of the guide plate (4) close to the triangular guide fence (2) and the triangular guide fence (2) to the outlet diameter D of the turbine runner is H2 / D=1 / 10.

7. The draft tube flow guide structure for a water turbine according to claim 6, characterized in that: The ratio of the height H3 of the guide plate (4) to the outlet diameter D of the turbine runner is H3 / D=1 / 2.

8. The draft tube flow guide structure for a water turbine according to claim 7, characterized in that: The ratio of the length L2 of the guide plate (4) extending from the inner wall of the tailwater tube (1) towards the center of the tailwater tube (1) to the outlet diameter D of the turbine runner is L2 / D=1 / 4.

9. The draft tube flow guide structure for a water turbine according to claim 1, characterized in that: The guide plate (4) is hinged on the inner wall of the tailwater pipe (1), and the guide plate (4) is also connected to an angle adjustment device, and the other end of the angle adjustment device extends out of the tailwater pipe (1) and is located outside the tailwater pipe (1); A plurality of shafts (6) are evenly rotated and embedded in the side wall of the rear half of the straight cone section of the tailwater tube (1) in a circumferential direction, the shafts (6) coincide with the generatrix of the installation position of the tailwater tube (1), the guide plate (4) is fixed on the side of the shaft (6) located inside the tailwater tube (1), the angle adjustment device comprises an adjustment plate (7) installed on the side of the shaft (6) located outside the tailwater tube (1), the adjustment plate (7) is parallel to the corresponding guide plate (4) and is located in the same plane, the adjustment plate (7) is connected to an adjustment rod (8), and also comprises a fixing bracket (9), and an annular fixing plate is arranged above the fixing bracket (9). (10), the annular fixing plate (10) is sleeved on the plane of the tailwater pipe (1) corresponding to the adjusting rod (8), an adjusting box (5) is fixedly arranged on the annular fixing plate (10), the other end of the adjusting rod (8) passes through the adjusting box (5) and is connected to an adjusting handle (11), and the two end surfaces of the adjusting box (5) through which the adjusting rod (8) is passed are correspondingly provided with slide rails (12), and the adjusting rod (8) is provided with a slider that cooperates with the slide rail (12), and when the adjusting rod (8) slides left and right in the slide rail (12), the adjusting plate (7) drives the shaft rod (6) to rotate, thereby driving the guide plate (4) to rotate a certain angle.

10. The draft tube flow guide structure for a water turbine according to claim 9, characterized in that: When the adjusting rod (8) is located at the middle position of the slide rail (12), the guide plate (4) is perpendicular to the side wall of the tailwater pipe (1), and the adjustment angle is 0°. When the adjusting rod (8) is located at the left and right ends of the slide rail (12), the adjustment angles of the guide plate (4) are respectively -45° and 45°. A side surface of the adjusting box (5) on which the adjusting handle (11) is provided is located below the slide rail (12) and has corresponding scale lines of -45°, -25°, 0°, 25° and 45°. When the adjusting handle (11) is located at a corresponding scale position, the guide plate (4) is adjusted to a corresponding angle.

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