A novel draft tube rectifying and energy harvesting device for a low-load operating water turbine

Abstract

The present invention relates to a novel tailwater pipe rectifying and energy collecting device for a low-load operating turbine, comprising a volute, wherein fixed guide vanes, movable guide vanes and turbine blades are respectively connected to the interior of the volute; the rear end of the volute is connected to the tailwater pipe, a plurality of grooves are provided on the inner wall of the straight cone section of the tailwater pipe, a guide plate is connected to the interior of the horizontal diffusion section of the tailwater pipe, a guide cover is provided on the guide plate, and an adjustable air supply guide grid device is provided in the guide cover; the adjustable air supply guide grid device comprises a central hub body, guide grid blades, a fixed straight cone pipe and a blade adjustment mechanism, a plurality of guide grid blades are evenly distributed on the outer periphery of the central hub body, the outer ring of the guide grid blades is connected to the fixed straight cone pipe, and the outer side of the fixed straight cone pipe is provided with a blade adjustment mechanism; an engine room is provided in the horizontal diffusion section of the tailwater pipe, the engine room is connected to the tailwater pipe through a fixed shaft, and the engine room is connected to the blades of the energy recovery device.

Description

Technical Field

[0001] The invention relates to a novel tailwater pipe rectifying and energy collecting device for a low-load operating water turbine, and is applied in the technical field of water turbine rectifying and energy collecting. Background Art

[0002] As is known to all, in recent years, my country's electricity demand has increased and the power system has developed rapidly. However, the power system has the problem of large and frequent load fluctuations. More power stations are needed to regulate the power system. Therefore, pumped storage power stations play an important role in peak-shaving and valley-filling, frequency and phase regulation, and emergency standby of the power grid.

[0003] The draft tube is a critical energy recovery component in a hydro turbine, and its performance directly determines the overall efficiency of the turbine unit. The efficiency and stability of the draft tube are primarily determined by the internal flow characteristics. Typically, the flow inside the draft tube is highly complex, with varying pressure gradients in different directions, accompanied by horseshoe vortices and scalloped vortices in the wake and flow channel. The flow exhibits strong vorticity, resulting in highly complex three-dimensional unsteady viscous fluid motion, making it difficult to simulate and test using advanced technology and equipment. To modify this vortex and improve flow stability, research on turbulent boundary layers on grooved surfaces began as early as the 1970s and 1980s, focusing on the drag reduction properties and mechanisms of grooved surfaces. Grooved surfaces reduce drag by induced secondary vortices interacting with streamwise vortices, retaining low-speed fluid within the grooves. This reduces the efficiency of momentum exchange between high- and low-speed fluids, thereby reducing drag. Grooved surfaces can suppress the sudden onset of coherent structures and shorten the timescales of their ejection and sweep, thereby achieving drag reduction. The grooved surface not only increases the laminar boundary layer area, but also increases the Reynolds number for the transition from laminar flow to turbulent flow by about 4 times, thereby reducing the resistance of the flat plate boundary layer.

[0004] At the same time, in pumped-storage power plants, to meet the two main operating conditions of pumping and power generation, the pump-turbine needs to rotate forward and backward, and start and stop frequently. This results in complex operating conditions. Especially when operating far from rated conditions, the flow pattern near the runner becomes turbulent, easily forming unstable vortices that cause high-frequency pulsation in the unit and even lead to cavitation and fatigue damage on the blades, as well as vibration in the unit's plant. This situation is highly detrimental to the efficient, safe, and stable operation of pumped-storage units. In recent years, the capacity of my country's pumped-storage units has gradually increased, placing even higher demands on unit stability. Effective measures are urgently needed to suppress these instabilities. For similar problems, other types of turbines typically employ measures such as air injection through the main shaft center hole, top cover, or tailwater pipe, or by extending the runner discharge cone or adding guide plates to the straight cone section of the tailwater pipe. However, these measures are very limited for pump-turbines with numerous and frequently changing operating conditions.

[0005] Patent publication number CN103982361B discloses a tailwater tube for a hydraulic turbine, specifically a rectifier tube with front and rear openings installed within the tailwater tube's channel to suppress the generation and impact of eccentric vortexes. However, the tailwater tube vortex first appears near the runner outlet, and the device's location can only affect the vortex at the end of the vortex. Furthermore, the device requires a fixed rod connected to the tailwater tube wall. This additional component increases structural complexity, and the connecting rod located in the flow field also affects the flow within the tailwater tube. The second connection method, in which the connecting rod is fixed to the ground, increases the sealing effort required to separate the flow from the outside world. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a new tailwater pipe rectifying and energy collecting device for low-load operating turbines. By making a unitized arrangement structure for the auxiliary equipment and electrical and control equipment of the gas turbine, it is beneficial to the unitized construction of the unit and shortens the construction period.

[0007] The technical solutions of the present invention are as follows:

[0008] A novel tailwater pipe rectifying and energy collecting device for a low-load operating turbine comprises a volute, wherein fixed guide vanes, movable guide vanes and turbine blades are connected to the interior of the volute respectively; the rear end of the volute is connected to the tailwater pipe, a plurality of grooves are provided on the inner wall of the straight cone section of the tailwater pipe, a guide plate is connected to the interior of the horizontal diffusion section of the tailwater pipe, a guide cover is provided on the guide plate, and an adjustable air supply guide grid device is provided in the guide cover; the adjustable air supply guide grid device comprises a central hub body, guide grid blades, a fixed straight cone pipe and a blade adjustment mechanism, a plurality of guide grid blades are evenly distributed on the outer periphery of the central hub body, the outer ring of the guide grid blades is connected to the fixed straight cone pipe, and the outside of the fixed straight cone pipe is provided with a blade adjustment mechanism; an engine room is provided inside the horizontal diffusion section of the tailwater pipe, the engine room is connected to the tailwater pipe through a fixed shaft, and the engine room is connected to the blades of the energy recovery device.

[0009] The groove is a groove of a rectangular structure, and the groove is evenly distributed on the inner wall surface of the straight cone section of the tailwater pipe; the relationship between the width a of the groove and the depth h of the groove is a=(1~2)*h, and the length of the groove is the same as the length of the straight cone section of the tailwater pipe.

[0010] A pressure sensor is provided at the straight cone section of the tailwater pipe inlet, an angular displacement sensor is provided on the movable guide vane, a speed sensor is provided on the main shaft inside the horizontal diffusion section of the tailwater pipe, a flow sensor is provided inside the volute, and the regulating air supply guide grid device is electrically connected to the control system.

[0011] The circumferential coverage ratio of the grooves is 50% of the entire circumference, and the angle between two adjacent grooves is 7.2°.

[0012] The deflector is fixed inside the horizontal diffusion section of the tailwater pipe through a deflector plate. The deflector is a trumpet-shaped structure and plays a role in collecting water flow and improving power generation efficiency.

[0013] The fixed shaft has a hollow structure inside, and transmits the torque generated by the blades of the energy recovery device to the external generator.

[0014] The energy recovery device has three blades in total, and the energy recovery device blades are specifically axial flow blades.

[0015] The central hub body is a spindle-shaped structure, and the axis of the central hub body coincides with the center line of the straight cone section of the tailwater pipe.

[0016] The guide gate blades consist of an airfoil and a shaft section. One radial end of the guide gate blade is connected to the central hub body via a bearing, while the outer edge of the other end is connected to a fixed straight tapered tube via a bearing. When not connected to the blade adjustment mechanism, the guide gate blades can freely rotate along the centerline of their shaft section. The cross-section of the guide gate blades follows the NACA series standard airfoil profile. The guide gate blades effectively guide the water flow in the horizontal diffuser section of the draft tube, improving the flow pattern and providing timely air supply based on the pressure state in the horizontal diffuser section. This not only eliminates vortices in the runner outlet during turbine operation, but also pre-swirls the runner inlet water during pump operation, improving pump performance.

[0017] The blade adjustment mechanism includes operating arms, connecting rods, and a control ring. The control ring is evenly distributed with several operating arms that mate with the guide vane blades. The operating arms are connected to the control ring via connecting rods. The operating arms and guide vane blades are fixed to the extended shaft section of a fixed straight tapered tube, and transmission is then achieved via the connecting rods and control ring to adjust the opening of the guide vane blades.

[0018] The present invention has the following beneficial effects:

[0019] 1. This invention achieves drag reduction by providing grooves in the direct-chassis section of the draft tube. The blades of the energy recovery device recover draft tube energy, thereby improving turbine efficiency. The device is also equipped with an adjustable air supply guide grid, which not only secures the axial-flow energy recovery device with a guide shield but also improves the flow pattern in the draft tube. This addresses the technical problem in the prior art of pump-turbines operating under deviated operating conditions, such as turbulent flow near the runner, which causes high-frequency pressure pulsation in the turbine and fatigue damage to the runner, hindering the efficient, safe and stable operation of the pumped-storage unit.

[0020] 2. This invention is easy to install, economical to maintain, and available in a wide range of materials. It improves the stability and efficiency of hydropower units with different water heads and operating conditions, enhancing the operational stability of the entire hydropower unit, extending the unit's lifespan, reducing equipment maintenance, and lowering maintenance costs for the hydropower system, thus saving costs. Furthermore, this invention improves water utilization, which has important engineering practical significance in today's increasingly scarce resources.

[0021] 3. The present invention makes full use of the energy lost in the tailwater pipe, improves the power generation efficiency of the turbine, and provides a new solution for improving the flow state of the pump-turbine and other reversible turbines and conventional turbines in pumped storage power stations. The flow state of water in the flow channel near the runner of the pump-turbine under different load conditions is significantly improved, the tailwater vortex is significantly eliminated, the vibration of the unit and the fatigue damage resistance of the runner are greatly improved, and pre-rotation is generated on the water flow at the runner inlet under the pump working condition, thereby improving the flow state of water in the flow channel and improving the operating performance of the pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a side structural schematic diagram of the present invention;

[0023] Figure 2 It is a schematic diagram of the top view of the structure of the present invention;

[0024] Figure 3 It is a schematic diagram of the three-dimensional structure of the present invention;

[0025] Figure 4 This is the frequency domain diagram of the pressure pulsation in the draft tube of a traditional hydraulic turbine;

[0026] Figure 5 This is a frequency domain diagram of the pressure pulsation of the turbine tailwater tube of the present invention;

[0027] Figure 6 It is a structural schematic diagram of the air supply guide grid regulating device in the present invention;

[0028] Figure 7 Schematic diagram of the connection structure between the guide grid blades and the blade adjustment mechanism in the present invention;

[0029] Figure 8 Schematic diagram of the structure of the guide grid blade in the present invention;

[0030] Figure 9 It is the working flow chart of the control system in the present invention.

[0031] The reference numerals in the figures are as follows:

[0032] 1. Volute; 2. Fixed guide vanes; 3. Movable guide vanes; 4. Turbine blades; 5. Grooves; 6. Draft tube; 7. Guide plate; 8. Guide cover; 9. Energy recovery device blades; 10. Nacelle; 11. Fixed shaft; 12. Center hub body; 13. Guide gate blades; 14. Fixed straight tapered tube; 15. Blade adjustment mechanism; 151. Operating arm; 152. Connecting rod; 153. Control ring; 16. Main shaft. DETAILED DESCRIPTION

[0033] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] See also Figures 1 to 9 The novel tailwater pipe rectifying and energy collecting device for low-load turbine operation includes a volute 1, wherein the interior of the volute 1 is respectively connected to a fixed guide vane 2, a movable guide vane 3 and a turbine blade 4; the rear end of the volute 1 is connected to a tailwater pipe 6, wherein a plurality of grooves 5 are provided on the inner wall of the straight cone section of the tailwater pipe 6, and a guide plate 7 is connected to the interior of the horizontal diffusion section of the tailwater pipe 6, wherein a guide cover 8 is provided on the guide plate 7, and an air supply guide grid device is provided in the guide cover 8; the air supply guide grid device includes A central hub body 12, guide grid blades 13, a fixed straight tapered tube 14 and a blade adjustment mechanism 15. Several guide grid blades 13 are evenly distributed on the outer periphery of the central hub body 12. The outer ring of the guide grid blades 13 is connected to the fixed straight tapered tube 14. The blade adjustment mechanism 15 is provided on the outside of the fixed straight tapered tube 14. A cabin 10 is provided inside the horizontal diffusion section of the tailwater pipe 6. The cabin 10 is connected to the tailwater pipe 6 through a fixed shaft 11. The cabin 10 is connected to the energy recovery device blades 9.

[0035] The groove 5 is a rectangular groove, evenly distributed on the inner wall of the straight cone section of the tailwater pipe 6. The relationship between the width a of the groove 5 and the depth h of the groove 5 is a=(1-2)*h, and the length of the groove 5 is the same as the length of the straight cone section of the tailwater pipe 6. The width of the groove 5 is set to 128mm, and the depth of the groove 5 is set to 100mm. Under low flow conditions, the tailwater pipe 6 generates an eccentric vortex. The secondary vortex in the groove 5 interacts with the eccentric vortex, keeping the low-speed fluid in the groove 5, thereby achieving the effect of eliminating vortex.

[0036] A pressure sensor is provided in the straight cone section at the inlet of the tailwater pipe 6, an angular displacement sensor is provided on the movable guide vane 3, a speed sensor is provided on the main shaft 16 inside the horizontal diffusion section of the tailwater pipe 6, the main shaft 16 is connected to the turbine runner through a pin, a flow sensor is provided inside the volute 1, and the regulating air supply guide grid device is electrically connected to the control system.

[0037] The results show that after the grooves 5 are installed, the vortex bands in the tailwater tube 6 are effectively eliminated. Before the installation of the grooves 5, a single spiral vortex band with a relatively strong spiral strength existed in the straight cone section of the tailwater tube 6. There were also obvious eccentric vortex bands. The eccentricity of the vortex bands increased towards the lower end of the tailwater tube 6, and the shape was extremely unstable. After the grooves 5 were installed, the vortex bands were basically eliminated, with only a very small amount of vortex bands remaining at the inlet of the tailwater tube 6. This shows that the installation of the grooves 5 in the straight cone section of the tailwater tube 6 has a significant effect on improving the vortex bands in the tailwater tube 6.

[0038] The circumferential ratio covered by the grooves 5 is 50% of the entire circumference, and the angle between two adjacent grooves 5 is 7.2°.

[0039] Table 1 shows the monitoring and calculation of the turbine efficiency under low flow conditions. It can be seen from the table that the installation of groove 5 in the straight cone section has little effect on the unit efficiency, with the difference before and after being 0.62%. It can be considered that the installation of groove 5 has almost no effect on the turbine efficiency and will not affect the normal operation of the turbine.

[0040] Table 1 Efficiency of turbine before and after installation of groove 5 under low flow conditions

[0041]

[0042] Figure 4 、 Figure 5 The following are frequency domain diagrams of the pressure pulsation at each measuring point in the tailwater pipe 6 under low flow conditions, respectively, for the traditional tailwater pipe 6 and the scheme with the groove 5. The frequency domain diagram with the groove 5 added shows that the main frequency of the tailwater pipe 6 is low-frequency pressure pulsation, with a corresponding frequency of approximately 1.56 Hz, and a maximum pressure pulsation amplitude of 20.868 kPa. At DT1 near the runner outlet, there is a more obvious secondary frequency of 40.6062 Hz (13 times the rotation frequency fn, i.e., the blade frequency), but at DT2-DT6, which is a little further away, the pressure pulsation has no obvious secondary frequency. At the monitoring point DT6 in the diffuser section near the outlet, due to the rectification effect, the pressure pulsation amplitude is not much different, indicating that the water flow has basically returned to smoothness here.

[0043] Table 2 shows the maximum pressure pulsation amplitude corresponding to each measuring point in the tailwater pipe 6 for the two schemes under low flow conditions. The results show that after the installation of the groove 5, the pressure pulsation amplitude of the tailwater pipe 6 is significantly reduced, and the pressure pulsation reduction ratio can reach a maximum of 71.59%, indicating that the installation of the groove 5 has significantly improved the reduction of the overall pressure pulsation amplitude of the tailwater pipe 6.

[0044] Table 2 Pressure pulsation amplitude of vortex belt in tailwater pipe 6 under low flow condition

[0045]

[0046] The deflector 8 is fixed inside the horizontal diffusion section of the tailwater pipe 6 through the deflector plate 7. The deflector 8 is a trumpet-shaped structure, and the deflector 8 collects water flow and improves power generation efficiency.

[0047] The fixed shaft 11 has a hollow structure inside, and transmits the torque generated by the blades 9 of the energy recovery device to the external generator.

[0048] The energy recovery device has three blades 9, which are specifically axial flow blades. Water from the tailwater pipe 6 flows through the deflector 8, impacting the blades and outputting torque. The torque is transmitted upward through gears to an external generator, thereby generating electricity.

[0049] The central hub body 12 is a spindle-shaped structure, and the axis of the central hub body 12 coincides with the center line of the straight cone section of the draft tube 6. An air supply valve is provided inside the central hub body 12.

[0050] The guide gate blades 13 comprise an airfoil and a shaft section. One radial end of the guide gate blades 13 is connected to the central hub body 12 via a bearing, while the outer edge of the other end is connected to a fixed straight tapered tube 14 via a bearing. When not connected to the blade adjustment mechanism 15, the guide gate blades 13 can freely rotate along the centerline of their shaft section. The cross-section of the guide gate blades 13 conforms to the NACA series standard airfoil. The guide gate blades 13 effectively guide the water flow in the horizontal diffuser section of the draft tube 6, improving the flow pattern and providing timely air supply based on the pressure state in the horizontal diffuser section of the draft tube 6. This eliminates vortices at the runner outlet during turbine operation and pre-swirls the runner inlet water during pump operation, improving pump performance.

[0051] The specific airfoil equation of the guide grid blade 13 is as follows:

[0052] Taking the center point of the axis of the central hub body 12 as the origin, the inner diameter of the plane ring on the fixed straight tapered tube 14 as R, and the fitting curve equation of the cross-section profile 0.13R away from the origin is:

[0053] y1=-0.3189×x8+1.352×x7-2.364×x6+2.201×x5-1.176×x4+0.03649×x3-0.06496×x2+0.006606×x-0.01248;

[0054] y2=0.3189×x8-1.352×x7+2.364×x6-2.201×x5+1.176×x4-0.03649×x3+0.06496×x2-0.006606×x+0.01252;

[0055] Taking the center point of the axis of the central hub body 12 as the origin, the inner diameter of the plane ring on the fixed straight tapered tube 14 as R, and the fitting curve equation of the cross-section profile 0.5R from the origin is:

[0056] y1=-0.4345×x8+1.84×x7-3.209×x6+2.974×x5-1.579×x4+0.4853×x3-0.08634×x2+0.009392×x-0.009894;

[0057] y2=0.5984×x8-2.542×x7+4.46×x6-4.174×x5+2.25×x4-0.7062×x3+0.1259×x2-0.0118×x-0.01503;

[0058] Taking the center point of the axis of the central hub body 12 as the origin, the inner diameter of the plane ring on the fixed straight tapered tube 14 as R, and the fitting curve equation of the cross-section profile 0.95R from the origin is:

[0059] y1=-78.25×x8+329.6×x7-572.3×x6+528.5×x5-279.9×x4+85.99×x3-15.38×x2+1.704×x+0.01314;

[0060] y2=59.25×x8-251.7×x7+439.8×x6-410.8×x5+221.7×x4-70.08×x3+12.76×x2-1.244×x-0.003579.

[0061] The blade adjustment mechanism 15 includes an operating arm 151, a connecting rod 152, and a control ring 153. The control ring 153 is evenly distributed with a plurality of operating arms 151 that mate with the guide vanes 13. The operating arms 151 are connected to the control ring 153 via the connecting rod 152. The operating arms 151 and the guide vanes 13 are fixed together at the extended shaft section of the fixed straight tapered tube 14, and transmission is then achieved via the connecting rod 152 and the control ring 153 to adjust the opening of the guide vanes 13.

[0062] The control system includes several modules: real-time cavitation monitoring, air supply device on / off control, parameter trend analysis, intelligent predictive analysis, comprehensive multi-dimensional evaluation, and automatic report generation. Real-time cavitation monitoring includes two modules: cavitation coefficient monitoring and vibration and noise monitoring. The real-time monitoring module monitors and displays the unit's current cavitation status in real time, presenting various unit data to the user intuitively via corresponding monitoring pages in the form of charts, numerical values, and curves. Key functions include: real-time online monitoring of the cavitation status of the currently operating unit, observing the unit's operating status by state; and observing alarm and early warning event data as a basis for further analysis and diagnosis. The real-time cavitation coefficient calculation module calculates the real-time cavitation coefficient hourly and stores it in a database. Simultaneously, the database is stored and the current critical cavitation coefficient is queried to obtain an early warning indicator. The air supply device on / off control module activates the air supply device to replenish the unit when the real-time cavitation coefficient exceeds the critical cavitation coefficient. It deactivates the air supply device when the real-time cavitation coefficient decreases below the critical cavitation coefficient and then decreases to a fixed value. The cavitation noise analysis module performs time-frequency analysis on the monitored ultrasonic signal after FFT transformation, and displays the sound pressure change of the ultrasonic frequency when the cavitation coefficient of the power station reaches the critical cavitation coefficient.

[0063] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A tailwater pipe rectifying and energy collecting device for a low-load operating turbine, characterized by: The invention comprises a volute (1), wherein the interior of the volute (1) is respectively connected to a fixed guide vane (2), a movable guide vane (3) and a turbine blade (4); the rear end of the volute (1) is connected to a tailwater pipe (6), a plurality of grooves (5) are provided on the inner wall of the straight cone section of the tailwater pipe (6), a guide plate (7) is connected to the interior of the horizontal diffusion section of the tailwater pipe (6), and a guide cover (8) is provided on the guide plate (7). An air supply guide grid device is provided in the guide cover (8); the air supply guide grid device comprises a central hub body (12), guide grid blades (13), a fixed straight cone tube (14) and a blade adjustment mechanism (15); a plurality of guide grid blades (13) are evenly distributed on the outer periphery of the central hub body (12); the outer ring of the guide grid blades (13) is connected to the fixed straight cone tube (14); and the outer side of the fixed straight cone tube (14) is provided with a blade adjustment mechanism (15); an engine room (10) is provided inside the horizontal diffusion section of the tailwater pipe (6); the engine room (10) is provided with a plurality of guide grid blades (13) and a plurality of guide grid blades (13) are provided on the outer periphery of the tailwater pipe (6); and ... 0) is connected to the tailwater pipe (6) through a fixed shaft (11), and an energy recovery device blade (9) is connected to the engine room (10); the groove (5) is a groove of a rectangular parallelepiped structure, and the grooves (5) are evenly distributed on the inner wall surface of the straight cone section of the tailwater pipe (6); the relationship between the width a of the groove (5) and the depth h of the groove (5) is a=(1~2)h, and the length of the groove (5) is the same as the length of the straight cone section of the tailwater pipe (6); the circumferential ratio covered by the groove (5) is 50% of the entire circumference, and the angle between two adjacent grooves (5) is 7.2°.

2. The tailwater tube rectifying and energy collecting device for a low-load operating hydraulic turbine according to claim 1, characterized in that: The straight cone section at the inlet of the tailwater pipe (6) is provided with a pressure sensor, the movable guide vane (3) is provided with an angular displacement sensor, the main shaft (16) inside the horizontal diffusion section of the tailwater pipe (6) is provided with a speed sensor, the volute (1) is provided with a flow sensor, and the regulating air supply guide grid device is electrically connected to the control system.

3. The tailwater tube rectifying and energy collecting device for a low-load operating hydraulic turbine according to claim 1, characterized in that: The deflector (8) is fixed inside the horizontal diffusion section of the tailwater pipe (6) via a deflector plate (7), and the deflector (8) is a trumpet-shaped structure.

4. The tailwater tube rectifying and energy collecting device for a low-load operating hydraulic turbine according to claim 1, characterized in that: The fixed shaft (11) has a hollow structure inside, and the fixed shaft (11) transmits the torque generated by the blades (9) of the energy recovery device to an external generator.

5. The tailwater tube rectifying and energy collecting device for a low-load operating hydraulic turbine according to claim 4, characterized in that: The energy recovery device blades (9) comprise three blades in total, and the energy recovery device blades (9) are specifically axial flow blades.

6. The tailwater tube rectifying and energy collecting device for a low-load operating hydraulic turbine according to claim 1, characterized in that: The central hub body (12) has a spindle-shaped structure, and the axis of the central hub body (12) coincides with the center line of the straight cone section of the tailwater pipe (6).

7. The tailwater tube rectifying and energy collecting device for a low-load operating hydraulic turbine according to claim 1, characterized in that: The guide grating blade (13) comprises an airfoil and a shaft section. One end of the guide grating blade (13) is connected to the central hub body (12) via a bearing in the radial direction, and the outer edge of the other end is connected to the fixed straight tapered tube (14) via a bearing. The guide grating blade (13) can rotate freely along the center line of its shaft section when the blade adjustment mechanism (15) is not connected. The cross section of the guide grating blade (13) is a NACA series standard airfoil.

8. The tailwater tube rectifying and energy collecting device for a low-load operating hydraulic turbine according to claim 1, characterized in that: The blade adjustment mechanism (15) comprises an operating arm (151), a connecting rod (152) and a control ring (153). The control ring (153) is evenly distributed with a plurality of operating arms (151) adapted to the guide grid blades (13). The operating arms (151) are transmission-connected to the control ring (153) via the connecting rod (152).

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