An annular air supply device for reducing the vortex belt in the draft tube of an axial flow fixed-blade turbine

Abstract

The present invention relates to the field of hydroturbine equipment, and more particularly to an annular air supply device for reducing vortex bands in the draft tube of an axial-flow fixed-blade turbine. The device comprises an annular pipe, a connecting pipe, and an air supply main pipe. The annular pipe is disposed in the draft tube and is provided with a plurality of air supply holes. The air outlet of the connecting pipe communicates with the air inlet of the annular pipe, the air inlet of the connecting pipe communicates with the air supply main pipe, the outer wall of the connecting pipe is connected to the draft tube, and the air outlet of the connecting pipe is tilted upward. During natural air supply, the air vent valve is in an open state, and during forced air supply, the air vent valve is in a closed state. The present invention can uniformly supply air within the draft tube, thereby reducing the draft tube pressure pulsation phenomenon caused by the formation of vortex bands in the draft tube when the axial-flow fixed-blade turbine operates under abnormal working conditions, reducing the vibration of the turbine runner blades and the draft tube, preventing fatigue damage to turbine components, and ensuring the safe and stable operation of the turbine unit.

Description

Technical Field

[0001] The invention relates to the field of water turbine equipment, in particular to an annular air supply device for reducing the vortex belt of the draft tube of an axial flow fixed blade water turbine. Background Art

[0002] Electricity is crucial to the national economy and people's livelihoods. With the continuous expansion of hydropower, turbine development technology has matured, and efficiency is no longer the most critical factor restricting its operation. As turbines develop towards higher speeds, larger capacities, and higher water heads, the stability of hydro-generator sets is gaining increasing attention. Draft tube vibration, generated during turbine operation, has become a key factor affecting turbine stability.

[0003] Axial-flow fixed-pitch turbines are a type of reaction turbine. Their main components include a runner, a water guide, a water diversion component, and a water discharge component (draft tube). The tail tube, located below the turbine runner, is one of the main flow-through components, guiding the water flowing through the runner outward to recover some of the water's energy. The runner blades are fixed, meaning they are rigidly connected to the hub. While axial-flow fixed-pitch turbines have a simple structure and are inexpensive, they can only adjust their output using the water guide. When the head and output change, the turbine's efficiency decreases significantly.

[0004] In a turbine, the vortex formed at the runner outlet creates a central vortex band at the center of the draft tube. Violent pressure fluctuations occur near the central vortex band, generating significant vibration and noise within the draft tube. In axial-flow fixed-blade turbines, because the runner blades are rigidly attached to the hub, output can only be adjusted by adjusting the opening of the guide vanes when the water head changes. These turbines often operate under off-load conditions and are unable to adapt effectively to these conditions, resulting in reduced energy conversion efficiency and harmful effects such as hydraulic vibration, which compromises the unit's normal and stable operation. The primary cause of hydraulic vibration is the formation of a vortex band within the draft tube, which causes pressure pulsations that propagate upstream and subsequently cause vibration within the turbine unit. Furthermore, the formation of Karman vortices and labyrinth rings within the runner, as well as flow separation at the runner blade outlet, exacerbate hydraulic vibration. This vibration can cause fatigue fractures in flow-passing components such as the runner and loosen fasteners, compromising the unit's normal operation.

[0005] The existing vortex belt air supply device for the tailwater tube of the axial flow fixed blade turbine currently has uneven air supply under low flow conditions, and the effect of eliminating vortices is not obvious. The existing air supply device requires a high pressure at the pipeline inlet when supplying air, and the air supply flow rate is generally 1% to 4% of the rated flow rate of the turbine. Therefore, the existing device has high requirements for the air source and consumes a large amount of electricity. The existing device also has the disadvantage of being incompatible with natural air supply and forced air supply, and the two cannot be switched freely. The existing tailwater tube vortex belt air supply device also has the disadvantage of being complex in structure, and air supply under abnormal working conditions will cause the energy conversion efficiency of the turbine to decrease. Summary of the Invention

[0006] Aiming at the problems of uneven air supply, high energy consumption and complex structure in the air supply device in the prior art, the present invention provides an annular air supply device for reducing the vortex belt in the draft tube of an axial flow fixed-blade turbine.

[0007] The present invention is achieved through the following technical solutions:

[0008] The vent pipe is provided with a plurality of air supply holes, and the vent pipe is provided with a plurality of air supply holes. The vent pipe is arranged in the tailwater pipe, and the plurality of air supply holes are provided on the vent pipe. The plurality of air supply holes are evenly arranged on the outside of the vent pipe, and the air outlet of the vent pipe is connected with the air inlet of the vent pipe, and the air inlet of the vent pipe is connected with the air supply main pipe. The outer wall of the vent pipe is connected with the tailwater pipe, and the air outlet of the vent pipe is tilted upward. The air supply main pipe is located outside the tailwater pipe. The end of the vent pipe away from the connecting pipe is provided with a vent valve and a plurality of vent holes, and the vent valve is located below the vent holes. During natural air supply, the vent valve is in an open state, and during forced air supply, the vent valve is in a closed state.

[0009] Preferably, the annular pipe is located in the straight cone section of the tailwater pipe.

[0010] Preferably, the angle between the normal direction of the air supply hole and the annular plane of the annular tube is 10° to 25°.

[0011] Preferably, the air supply holes are evenly arranged on the inner wall of the annular tube.

[0012] Preferably, the cross-sectional area of ​​the air inlet of the annular tube is smaller than the cross-sectional area of ​​the air outlet of the connecting pipeline.

[0013] Preferably, the air supply hole and the air outlet of the connecting pipe are staggered.

[0014] Preferably, a plurality of connecting ribs are provided between the annular tube and the inner wall of the tailwater pipe, one end of the connecting rib is connected to the outer wall of the annular tube, and the other end is connected to the inner wall of the tailwater pipe.

[0015] Preferably, the sum of the cross-sectional areas of the plurality of vent holes is greater than the cross-sectional area of ​​the main air supply line.

[0016] Preferably, a drain port is provided at one end of the main air supply line away from the connecting line, and the drain port is located below the vent valve.

[0017] Preferably, the angle between the busbar of the connecting pipe and the annular cross-section of the tailwater pipe is 5° to 30°.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides an annular air supply device for reducing the vortex belt in the tailwater pipe of an axial flow fixed-blade turbine. The device can evenly supply air inside the tailwater pipe, thereby reducing the tailwater pipe pressure pulsation phenomenon caused by the formation of vortex belts in the tailwater pipe when the axial flow fixed-blade turbine is operating under an off-state condition, reducing the vibration of the turbine runner blades and the tailwater pipe, preventing fatigue damage to the turbine components, and ensuring the safe and stable operation of the turbine unit. At the same time, adding this component to the axial flow fixed-blade turbine will not affect the turbine's power generation efficiency. In addition, the present invention also aims to reduce the tailwater pipe air supply flow rate, thereby reducing the requirements for the air source and reducing the energy consumption cost of driving the air source.

[0020] When in use, the gas entering the annular tube through the connecting pipeline can enter the straight cone section of the tailwater pipe of the axial flow fixed-pitch turbine through the air supply hole, which is used to weaken or eliminate the hydraulic vibration caused by the vortex belt of the tailwater pipe.

[0021] Furthermore, the connecting ribs are used to enhance the structural stability of the connecting pipes.

[0022] Furthermore, the function of the vent hole is to connect the main air supply line with the atmosphere.

[0023] Furthermore, the drain port is used to prevent water in the tailwater pipe from flowing back into the vent valve and vent under abnormal operating conditions. In addition, the drain port can also serve as an air inlet when using an air compressor for forced air replenishment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a piping diagram of an annular air supply device for reducing vortex bands in the draft tube of an axial flow fixed-blade turbine according to the present invention;

[0025] Figure 2 This is a longitudinal section diagram of the annular air supply device and the straight cone section of the tailwater pipe;

[0026] Figure 3 This is a cross-sectional view of the assembly of the annular air supply device and the straight cone section of the tailwater pipe.

[0027] In the figure, 1, annular pipe; 2, connecting pipe; 3, connecting rib; 4, air supply main line; 5, drain port; 6, vent valve; 7, vent hole; 8, air supply hole. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0029] The present invention discloses an annular air supply device for reducing the vortex belt of the draft tube of an axial flow fixed blade turbine. Figure 1 、 2 The annular tube 1 comprises an annular tube 1, an air supply main line 4, and multiple connecting lines 2. The annular tube 1 is disposed within the straight tapered section of the tailwater pipe. A plurality of air supply holes 8 are evenly distributed on the inner wall of the annular tube 1. The angle between the normal direction of the air supply holes 8 and the annular plane of the annular tube 1 is 10° to 25°. In this embodiment, the inner diameter of the annular tube 1 is between 60mm and 200mm, the diameter of the circle formed by the axis of the annular tube 1 is between 1m and 4m, and the distance between the annular tube 1 and the center plane of the axial-flow fixed-blade turbine is between 1.5m and 3m. There are 8 to 10 air supply holes 8, and the angle between the normal direction of the air supply holes 8 and the annular plane of the annular tube 1 is 15°.

[0030] Multiple connecting pipes 2 are evenly arranged on the outside of the annular pipe 1, the air outlet of the connecting pipe 2 is connected to the air inlet of the annular pipe 1, the air inlet of the connecting pipe 2 is connected to the air supply main pipe 4, the outer wall of the connecting pipe 2 is connected to the tailwater pipe, the air outlet of the connecting pipe 2 is inclined upward, and the angle between the busbar of the connecting pipe and the annular cross-section of the tailwater pipe is 5° to 30°. In this embodiment, the angle between the busbar of the connecting pipe and the annular cross-section of the tailwater pipe is 10°.

[0031] The connecting pipe is both an important component for delivering gas into the annular pipe 1 and a structure that provides support for the annular pipe 1. The axis of the connecting pipe is tilted upward. On the one hand, this allows the direction of the airflow to be changed before entering the annular pipe 1, so that the airflow direction is directed towards the vortex. Therefore, the vortex can be weakened or eliminated with a smaller air supply flow rate, thereby reducing the requirements for the air source and saving energy for driving the air source. On the other hand, it allows the connecting pipe that affects the efficiency of the turbine to be as far away from the runner as possible, while the annular pipe 1 can be as close to the runner as possible, so as not to reduce the energy conversion efficiency of the turbine. Figure 3 In this embodiment, there are three connecting pipes 2, and the angle between each two is 120 degrees.

[0032] The cross-sectional area of ​​the air inlet of the annular tube 1 is smaller than the cross-sectional area of ​​the air outlet of the connecting pipe 2, that is, the air inlet of the annular tube 1 is located inside the connecting pipe 2, and a seal is provided between the annular tube 1 and the connecting pipe 2. In this embodiment, the filler at the seal is made of materials such as polytetrafluoroethylene raw tape or nylon sealing rope, and the sealing is achieved in conjunction with the thread. The seal can also be achieved by directly using sealant to fill the gap between the annular tube 1 and the connecting pipe 2.

[0033] Multiple connecting ribs 3 are provided between the annular tube 1 and the inner wall of the tailwater tube. One end of each connecting rib 3 is connected to the outer wall of the annular tube 1, and the other end is connected to the inner wall of the tailwater tube. In this embodiment, there are three connecting ribs 3, evenly spaced outside the annular tube 1, with each rib 3 forming a 120° angle.

[0034] In order to achieve the purpose of uniform air supply, the air supply hole 8 and the air outlet of the connecting pipe are staggered, that is, the air supply hole 8 cannot be directly opposite to the air outlet of the connecting pipe.

[0035] The main air supply line 4 is located outside the tailwater pipe. A vent valve 6 and multiple vent holes 7 are located at the end of the main air supply line 4 away from the connecting line 2. The vent valve 6 is located below the vent holes 7. During natural air supply, the vent valve 6 is open, while during forced air supply, the vent valve 6 is closed. In this embodiment, the number of vent holes 7 is 2 to 5. The combined cross-sectional area of ​​the multiple vent holes 7 is greater than the cross-sectional area of ​​the main air supply line 4.

[0036] A drain port 5 is provided at one end of the air supply main line 4 away from the connecting line 2. The drain port 5 is located below the vent valve 6. The drain port 5 is used to prevent the water in the tailwater pipe from flowing back under abnormal circumstances.

[0037] The air supply principle of the annular air supply device for reducing the vortex belt in the draft tube of an axial flow fixed-blade turbine of the present invention is as follows:

[0038] When the axial-flow fixed-pitch turbine unit operates within the restricted operating range and no significant low-frequency vibrations are generated within the draft tube, the natural air supply function of the annular air supply device can be activated. Opening the vent valve 6 allows air, under the influence of the low pressure within the draft tube, to enter the annular tube 1 through the air supply main line 4 and the connecting line 2, and then enter the straight tapered section of the draft tube of the axial-flow fixed-pitch turbine through the air supply hole 8, thereby expanding the operating range of the axial-flow fixed-pitch turbine unit. Experimental and simulation calculations have shown that the air supply volume flow rate range of natural air supply is between 0% and 0.5% of the rated flow rate of the turbine, which is lower than the air supply flow rate of existing air supply devices. Therefore, it can reduce the requirements for the air source and the energy consumption cost of the driving air source.

[0039] When the axial-flow fixed-blade turbine unit operates in a restricted operating area and obvious low-frequency hydraulic vibration occurs in the tailwater pipe, the natural air supply function cannot completely eliminate the vortex belt vibration in the tailwater pipe. At this time, it is necessary to switch the pipeline connected to the atmosphere to the air compressor pipeline to force the gas into the tailwater pipe. The forced-in gas enters the annular pipe 1 through the air supply main line 4 and the connecting pipe 2, and then enters the straight cone section of the tailwater pipe of the axial-flow fixed-blade turbine through the air supply hole 8. It is used to suppress the formation of vortex belts in the tailwater pipe and weaken or eliminate the hydraulic vibration caused by the vortex belts in the tailwater pipe. The air supply volume flow range of forced air supply is between 1.0% and 1.5% of the rated flow of the turbine. The flow rate during forced air supply is controlled by the pressure and flow provided by the air compressor.

[0040] The present invention offers the advantages of uniform air supply under all operating conditions, compatibility with both natural and forced air supply, operation at relatively low air supply flow rates, and energy conservation. Using relatively low air supply flow rates, the present invention can fully suppress the formation of vortex bands in the draft tube under both rated and biased operating conditions, reducing the draft tube pressure pulsation caused by vortex bands, alleviating vibrations in the turbine runner blades and draft tube, and preventing fatigue damage to turbine components, thereby ensuring safe and stable operation of the turbine unit without compromising the turbine's power generation efficiency.

[0041] The pipeline design of the present invention enables the annular air supply device to work in both natural air supply mode and air supply mode by forced air pumping using an air compressor. The air supply effect can be manually adjusted according to different working conditions, which has good adaptability.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and replacements, and these modifications and replacements are also within the scope of protection covered by the claims.

Claims

1. An annular air supply device for reducing the vortex belt in the draft tube of an axial flow fixed blade turbine, characterized in that: The invention comprises an annular pipe (1), an air supply main line (4) and a plurality of connecting pipes (2), wherein the annular pipe (1) is arranged in the tailwater pipe, and a plurality of air supply holes (8) are provided on the annular pipe (1); the plurality of connecting pipes (2) are evenly arranged outside the annular pipe (1), the air outlet of the connecting pipe (2) is communicated with the air inlet of the annular pipe (1), the air inlet of the connecting pipe (2) is communicated with the air supply main line (4), the outer wall of the connecting pipe (2) is connected to the tailwater pipe, and the air outlet of the connecting pipe (2) is tilted upward; the air supply main line (4) is located outside the tailwater pipe; a vent valve (6) and a plurality of vent holes (7) are provided at one end of the air supply main line (4) away from the connecting pipe (2), and the vent valve (6) is located below the vent hole (7); during natural air supply, the vent valve (6) is in an open state, and during forced air supply, the vent valve (6) is in a closed state; The sum of the cross-sectional areas of the plurality of vent holes (7) is greater than the cross-sectional area of ​​the main air supply line (4); The end of the main air supply line (4) away from the connecting line (2) is provided with a drain port (5), and the drain port (5) is located below the vent valve (6); The angle between the busbar of the connecting pipeline and the annular cross-section of the tailwater pipe is 5° to 30°.

2. The annular air supply device for reducing the vortex belt in the draft tube of an axial flow fixed-blade turbine according to claim 1 is characterized in that: The annular pipe (1) is located in the straight cone section of the tailwater pipe.

3. The annular air supply device for reducing the vortex belt in the draft tube of an axial flow fixed-blade turbine according to claim 1 is characterized in that: The angle between the normal direction of the air supply hole (8) and the annular plane of the annular tube (1) is 10° to 25°.

4. The annular air supply device for reducing the vortex belt in the draft tube of an axial flow fixed-blade turbine according to claim 1 is characterized in that: The air supply holes (8) are evenly arranged on the inner wall of the annular tube (1).

5. The annular air supply device for reducing the vortex belt in the draft tube of an axial flow fixed-blade turbine according to claim 1 is characterized in that: The cross-sectional area of ​​the air inlet of the annular tube (1) is smaller than the cross-sectional area of ​​the air outlet of the connecting pipeline (2).

6. The annular air supply device for reducing the vortex belt in the draft tube of an axial flow fixed-blade turbine according to claim 1 is characterized in that: The air supply hole (8) is arranged in a staggered manner with the air outlet of the connecting pipe.

7. The annular air supply device for reducing the vortex belt in the draft tube of an axial flow fixed-blade turbine according to claim 1 is characterized in that: A plurality of connecting ribs (3) are provided between the annular tube (1) and the inner wall of the tailwater tube, one end of the connecting rib (3) being connected to the outer wall of the annular tube (1) and the other end being connected to the inner wall of the tailwater tube.

Images