A draft tube with a hyperbolic central tube as vortex suppression device

Abstract

The present application belongs to the field of fluid machinery and hydroelectric power technology, and particularly relates to a draft tube with a hyperbolic center pipe as a vortex suppression device. The draft tube with a hyperbolic center pipe as a vortex suppression device comprises a hyperbolic center pipe, a support, a straight conical barrel, an elbow pipe and a diffusion pipe. The inner curved surface of the hyperbolic center pipe satisfies the equation and the hyperbolic center pipe is coaxially arranged with the straight conical barrel and fixed in the straight conical barrel through the support. The present application is suitable for the condition of a central spiral vortex band of the draft tube. When water flows out of the runner and enters the straight conical barrel, the central vortex band formed is destroyed due to the impact on the inner wall of the hyperbolic center pipe, the velocity circulation is reduced, the negative pressure at the center caused by the rotation of the water flow is reduced, thereby reducing the strength of the vortex band, weakening the pressure pulsation amplitude, separating the central vortex band from the main flow area outside the hyperbolic center pipe, and enhancing the hydraulic stability of the hydroelectric generating set under the condition of the central spiral vortex band of the draft tube.

Description

Technical Field

[0001] This invention belongs to the field of fluid machinery and hydroelectric power generation technology, specifically relating to a tailrace pipe that uses a hyperbolic central tube as a vortex suppression device. Background Technology

[0002] A water turbine is a power machine that converts the potential energy of water flow into mechanical energy. It uses water flow as power to drive other machinery and belongs to the category of turbine machinery within fluid machinery. Water turbines typically have a draft tube at their runner outlet. The draft tube utilizes the elevation difference between the downstream water surface and the runner outlet to create a static vacuum at the runner outlet and recover some of the kinetic energy there. However, the runner outlet has a certain circumferential velocity component, causing the water flow to rotate within the draft tube. Mixed-flow turbines are prone to developing a central vortex band within approximately 40% to 70% of their rated load. Due to the large-scale grid connection of renewable energy sources, mixed-flow turbines often operate outside their design operating points. Within the 40% to 70% rated load range, the central vortex band is relatively thick, exhibiting a spiral shape and periodic oscillation. This generates a periodically changing pressure at a fixed point on the draft tube wall, causing severe pressure pulsation, resulting in unit vibration and affecting the stable operation of the turbine.

[0003] Common methods for addressing these issues include installing an air supply device in the draft tube and improving the turbine runner outlet structure. While these methods effectively reduce pressure pulsations in the draft tube vortex and stabilize unit operation, air supply devices are costly and reduce draft tube vacuum, increasing flow resistance and thus lowering unit efficiency. Improving the turbine runner inlet and outlet also results in poor adaptability to changes in operating conditions. Therefore, suppressing vortex-induced pressure pulsations while maintaining economic efficiency remains a significant challenge.

[0004] Using a hyperbolic central tube as a vortex suppressor can limit the intensity of vortices in the draft tube, reduce pressure pulsation in the draft tube, increase the stability and safety of the turbine unit under low load conditions, and greatly reduce the maintenance cost of the turbine unit. Furthermore, the hyperbolic central tube has a simple structure, is easy to install, and is inexpensive, making it both practical and economical.

[0005] Therefore, how to suppress the tailrace vortex and reduce pressure pulsation in mixed-flow turbine units is a technical problem that the field is eager to solve. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention proposes a tailrace pipe that uses a hyperbolic central tube as a vortex suppressor to suppress the central vortex band. When the turbine is operating under low load conditions, the hyperbolic central tube is used as a vortex suppressor to disrupt the central vortex band, reduce its circumferential velocity, separate the mainstream area from the stagnant water area, and ensure the stable operation of the unit.

[0007] To achieve the above-mentioned objectives, this invention proposes a tailrace pipe utilizing a hyperbolic central tube as a vortex suppression device, characterized in that: the tailrace pipe utilizing a hyperbolic central tube as a vortex suppression device comprises a hyperbolic central tube, a support, a straight conical barrel, an elbow tube, and a diffuser tube; the inner curved surface of the hyperbolic central tube satisfies the equation Where A = B = (0.04~0.08)D1, C = (0.05~0.1)D1, 0.05L1>z>-0.1L1, D1 is the inner diameter of the straight cone barrel inlet, and L1 is the height of the straight cone barrel; the curved central tube is fixed inside the straight cone barrel by a bracket, and the central axis coincides with the axis of the straight cone barrel; it realizes the function of suppressing the formation of tailwater vortex and tailwater guidance, and reducing pressure pulsation at the impeller blades; the axial section of the straight cone barrel is conical, its upper end is the small end of the cone and is the open straight cone barrel inlet, and its lower end is the large end of the cone and is the open straight cone barrel outlet.

[0008] Preferably, the axial height L2 of the hyperbolic central tube (2) is (0.12~0.17)L1, the distance between the lower end face of the hyperbolic central tube (2) and the inlet (1) of the straight cone barrel is L3 = (1.2~1.4)L2, and L1 is the height of the straight cone barrel.

[0009] Preferably, the hyperbolic central tube (2) has an inner diameter D2 at the inlet of (0.08-0.14)D1, an inner diameter D3 at the outlet of (0.12-0.21)D1, an inner diameter of the minimum cross section of (0.04-0.06)D1, and a wall thickness t2 of (0.01-0.02)D1.

[0010] Preferably, the bracket (3) is composed of four long cylindrical solid bodies, which are evenly arranged along the circumference and have an included angle of 90° with each other. They are connected to the minimum cross section of the hyperbolic central tube (2) by welding. The diameter D5 of the bracket (3) is (0.1~0.2)L2, where L2 is the axial height of the hyperbolic central tube (2).

[0011] Compared with the prior art, the present invention has the following advantages: The present invention provides a novel tailrace pipe that utilizes a hyperbolic central tube as a vortex suppression device.

[0012] (1) The present invention sets a central tube with hyperbolic sidewalls in the tailrace pipe. Under the low load condition of the turbine, after the water flows out from the runner outlet and passes through the hyperbolic central tube, the vortex belt hits the inner and outer walls of the central tube, the velocity circulation decreases, the rotational motion of the water flow is destroyed, and the negative pressure at the center caused by the rotation of the water flow is reduced, thereby reducing the strength of the vortex belt and achieving the purpose of reducing pressure pulsation from the source.

[0013] (2) The hyperbolic central tube separates the main flow zone from the vortex, making the water flow more stable and reducing the possibility of resonance in the entire turbine unit. Furthermore, this invention has good adaptability to different operating conditions, enabling the entire turbine unit to operate stably and safely. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the tailrace pipe structure of a device using a hyperbolic central tube as a vortex suppressor according to the present invention.

[0015] Figure 2 This is a top view of the straight conical barrel of the present invention;

[0016] Figure 3 for Figure 2 AA view;

[0017] Figure 4 This is a top-view diagram of the vortex path in the hyperbolic central tube of the present invention.

[0018] Figure 5 This is a schematic diagram of the hyperbolic central tube structure of the present invention.

[0019] Among them: 1-straight cone barrel inlet, 2-hyperbolic center tube, 3-support, 4-straight cone barrel, 5-straight cone barrel outlet, 6-elbow tube, 7-diffuser tube. Detailed Implementation

[0020] like Figures 1-3 As shown, a tailrace pipe using a hyperbolic central tube as a vortex suppressor is characterized in that: the tailrace pipe using a hyperbolic central tube as a vortex suppressor includes a hyperbolic central tube 2, a support 3, a straight conical barrel 4, an elbow pipe 6, and a diffuser pipe 7; the inner curved surface of the hyperbolic central tube 2 satisfies the equation Where A = B = (0.04~0.08)D1, C = (0.05~0.1)D1, 0.05L1>z>-0.1L1, L1 is the height of the straight cone barrel, and D1 is the inner diameter of the straight cone barrel inlet; the curved central tube 2 is fixed inside the straight cone barrel 4 through the bracket 3, and the central axis coincides with the axis of the straight cone barrel 4; it realizes the function of suppressing the formation of tailwater vortex and tailwater guidance, and reducing pressure pulsation at the impeller blades; the axial section of the straight cone barrel 4 is conical, its upper end is the small end of the cone and is the open straight cone barrel inlet 1, and its lower end is the large end of the cone and is the open straight cone barrel outlet 5.

[0021] like Figure 2 As shown, in one embodiment, the inner diameter at the inlet of the hyperbolic central tube 2 is D2 = 0.08D1, the inner diameter at the outlet is D3 = 0.12D1, the inner diameter of the minimum cross section is D6 = 0.04D1, and the wall thickness is t2 = 0.01D1.

[0022] like Figure 3 As shown, in one embodiment, the axial height L2 of the hyperbolic central tube 2 is 0.13L1, the distance L3 between the lower end face of the hyperbolic central tube 2 and the inlet 1 of the straight conical barrel is 1.2L2, and L1 is the height of the straight conical barrel.

[0023] like Figure 3 As shown, in one embodiment, the support 3 is composed of four long cylindrical solid bodies, which are evenly arranged along the circumference and have an included angle of 90° with each other. They are connected to the minimum cross section of the hyperbolic central tube 2 by welding. The diameter D5 of the support 3 is 0.1L2, where L2 is the axial height of the hyperbolic central tube 2.

[0024] like Figure 4 and Figure 5 As shown, in one embodiment, when the turbine operates under low load conditions, the water flow entering the draft tube from the runner outlet often carries a certain velocity circulation, causing low pressure at the center and high pressure around the perimeter of the draft tube. This creates a dead water zone in the center, where the water flows upwards in reverse, easily generating spiral vortices. To ensure that the hyperbolic central tube 2 can divide the vortices and cause them to impact the wall, the inlet diameter of the hyperbolic central tube is designed to be 0.08D1. The central vortex impacts the inner wall of the hyperbolic central tube 2, breaking into many small vortices that flow out of the hyperbolic central tube 2. Furthermore, the velocity circulation of the vortices decreases, disrupting the rotational motion of the water flow. This reduces the negative pressure at the center caused by the water rotation, thereby reducing the intensity of the vortexes. This effectively weakens pressure pulsations at the source and separates the central vortex from the flow channel outside the hyperbolic central tube 2, ensuring the hydraulic stability and safety of the draft tube under low load conditions.

[0025] In one of the above embodiments, the invention objective of using a hyperbolic central tube as a vortex suppression device for the tailwater pipe can be achieved. Those skilled in the art can make selections based on the actual situation.

[0026] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A draft tube utilizing a hyperbolic center tube as a vortex suppression device, characterized by: The tailrace pipe with a hyperbolic center pipe as a vortex suppression device comprises a hyperbolic center pipe (2), a support (3), a straight cone barrel (4), an elbow pipe (6) and a diffusion pipe (7); the inner curved surface of the hyperbolic center pipe (2) satisfies the equation wherein A=B=(0.04-0.08)D1, C=(0.05-0.1)D1, 0.05L1>z>-0.1L1, D1 is the inner diameter size of the straight cone barrel inlet (1), and L1 is the height of the straight cone barrel; the curved center pipe (2) is fixed inside the straight cone barrel (4) through the support (3), and the center axis coincides with the axis of the straight cone barrel (4); the functions of suppressing the formation of a tailrace vortex zone and guiding the tailrace are realized, and the pressure pulsation at the runner blade is reduced; the axial section of the straight cone barrel (4) is conical, the upper end thereof is a conical small end and is an open straight cone barrel inlet (1), and the lower end thereof is a conical large end and is an open straight cone barrel outlet (5).

2. A draft tube utilizing a hyperbolic central tube as a vortex suppression device according to claim 1, characterized in that: The axial height L2 of the hyperbolic center tube (2) is (0.12-0.17)L1, and the distance L3 between the lower end surface of the hyperbolic center tube (2) and the straight conical barrel inlet (1) is (1.2-1.4)L2.

3. A draft tube utilizing a hyperbolic central tube as a vortex suppression device according to claim 1, characterized in that: The support (3) is composed of four long cylindrical solid bodies, which are uniformly arranged in the circumferential direction and have an included angle of 90° between each other, and is connected to the minimum section of the hyperbolic center tube (2) by welding. The diameter D5 of the support (3) is (0.1-0.2)L2, and L2 is the axial height of the hyperbolic center tube (2).

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