Tail water pipe using hyperbolic central pipe as vortex suppression device

Abstract

The invention belongs to the technical field of fluid machinery and hydroelectric generation, and particularly relates to a draft tube using a hyperbolic central tube as a vortex suppression device. The draft tube using the hyperbolic central tube as the vortex suppression device comprises the hyperbolic central tube, a support, a straight cone barrel, an elbow tube and a diffusion tube. The inner curved surface of the hyperbolic central pipe meets the equation # imgabs0 #, and the hyperbolic central pipe and the straight cone barrel are coaxially arranged, and the hyperbolic central pipe is fixed in the straight cone barrel through a support. The device is suitable for the central spiral vortex strip working condition of the draft tube, after water flow flows out of the rotating wheel and enters the straight cone barrel, the formed central vortex strip is damaged due to impact on the inner wall of the hyperbolic central tube, the speed circulation is reduced, and the negative pressure at the center is reduced due to water flow rotation, so that the strength of the vortex strip is reduced, and the pressure pulsation amplitude is weakened; and the central vortex strip is separated from a mainstream area outside the hyperbolic central pipe, so that the hydraulic stability of the hydroelectric generating set under the working condition of the central spiral vortex strip of the draft tube is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of fluid machinery and hydropower generation, and in particular relates to a tailwater pipe using a hyperbolic central pipe as a vortex suppression device. Background Art

[0002] A water turbine is a power machine that can convert the potential energy of water flow into mechanical energy. It uses water flow as power to drive other machines to work, and belongs to the turbine machine in fluid machinery. A water turbine will be equipped with a tailwater pipe at its runner outlet. The tailwater pipe can use the elevation difference from the downstream water surface to the runner outlet to form a static vacuum at the runner outlet and recover part of the kinetic energy at the runner outlet. However, the runner outlet has a certain circumferential component velocity, which makes the water flow rotate in the tailwater pipe. The central vortex belt is prone to appear in the range of about 40% to 70% of the rated load. Due to the large number of new energy sources connected to the grid, the Francis turbine often operates at non-designed working points. The central vortex belt in the range of 40% to 70% of the rated load is thicker, spiral-shaped and oscillating periodically, which will produce a periodically changing pressure at a fixed point on the tailwater pipe wall, thereby causing serious pressure pulsation, causing vibration of the unit, and affecting the smooth operation of the water turbine.

[0003] At present, common methods to solve the above problems include: installing an air supply device in the tailwater pipe, improving the runner outlet structure, etc. Although the above methods can effectively weaken the pressure pulsation of the tailwater pipe vortex and stabilize the operation of the unit, the air supply device has the problem of high cost, and will reduce the vacuum degree of the tailwater pipe, increase the water flow resistance and reduce the efficiency of the unit. Improvements to the runner inlet and outlet have poor adaptability to changes in operating conditions. Therefore, how to suppress the vortex belt to reduce pressure pulsation while taking into account economic benefits is a major challenge.

[0004] The use of a hyperbolic center tube as a vortex suppression device can limit the strength of the vortex belt in the tailwater pipe, reduce the pressure pulsation of the tailwater pipe, increase the stability and safety of the turbine unit under low load conditions, and greatly reduce the maintenance cost of the turbine unit. In addition, the hyperbolic center tube has a simple structure, is easy to install, and is low in cost, making it practical and economical.

[0005] Therefore, how to suppress the tailwater vortex of a mixed flow unit and reduce pressure pulsation is a technical problem that the field is eager to solve. Summary of the invention

[0006] In order to overcome the shortcomings of the prior art, the present invention proposes a tailwater pipe using a hyperbolic central tube as a vortex suppression device to suppress the central vortex belt. When the turbine is operating under low load conditions, the hyperbolic central tube is used as a vortex suppression device to destroy the central vortex belt, reduce the circumferential speed of the vortex belt, separate the mainstream area and the dead water area, and ensure the stable operation of the unit.

[0007] In order to achieve the above-mentioned invention object, the present invention proposes a tailwater pipe using a hyperbolic central tube as a vortex suppression device, characterized in that: the tailwater pipe using a hyperbolic central tube as a vortex suppression device comprises a hyperbolic central tube, a bracket, a straight cone barrel, an elbow pipe, and a diffuser; the inner surface of the hyperbolic central tube satisfies the equation (0.05L 1 >z>-0.1L 1 ), where A=B=(0.04~0.08)D 1 , C=(0.05~0.1)D 1 , D 1 is the inner diameter size of the inlet of the straight cone barrel; the curved center tube is fixed inside the straight cone barrel through a bracket, and the center axis coincides with the axis of the straight cone barrel; the function of suppressing the formation of tailwater vortex and diverting tailwater is realized, and the pressure pulsation at the runner blade is reduced; the axial section of the straight cone barrel is conical, the upper end of which is the small conical end and is the open inlet of the straight cone barrel, and the lower end is the large conical end and is the open outlet of the straight cone barrel.

[0008] Preferably, the axial height L of the hyperbolic central tube (2) is 2 =(0.12~0.17)L 1 , the distance L between the lower end surface of the hyperbolic center tube (2) and the inlet of the straight cone barrel (1) 3 =(1.2~1.4)L 2 , L 1 is the height of the straight cone barrel.

[0009] Preferably, the inner diameter D of the hyperbolic central tube (2) at the inlet is 2 =(0.08~0.14)D 1 、Inner diameter at outlet D 3 =(0.12~0.21)D 1 , minimum cross-sectional inner diameter D 6 =(0.04~0.06)D 1 , wall thickness t 2 =(0.01~0.02)D 1 .

[0010] Preferably, the support (3) is composed of four long cylindrical solid bodies, which are evenly arranged along the circumferential direction, with an angle of 90° between each other, and are connected to the minimum cross-section of the hyperbolic central tube (2) by welding. The diameter D of the support (3) is 5 =(0.1~0.2)L 2 , L 2 is the axial height of the hyperbolic central tube (2).

[0011] Compared with the prior art, the present invention has the following beneficial effects: the present invention provides a new tailwater pipe using a hyperbolic central tube as a vortex suppression device.

[0012] (1) The present invention provides a center tube with a hyperbolic side wall in the tail tube. Under low-load conditions of the turbine, after the water flows out from the runner outlet and passes through the hyperbolic center tube, the vortex belt hits the inner and outer wall surfaces of the center tube, the velocity circulation is reduced, and the rotational motion of the water flow is destroyed, so that the negative pressure at the center caused by the rotation of the water flow is reduced, thereby reducing the strength of the vortex belt, achieving the purpose of reducing pressure pulsation from the root;

[0013] (2) The hyperbolic central tube separates the main flow area from the vortex, making the water flow more stable and reducing the possibility of resonance of the entire turbine unit. In addition, the present invention has good adaptability to operation under different working conditions, so that the entire turbine unit can operate stably and safely. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of a tailwater pipe structure using a hyperbolic central tube as a vortex suppression device according to the present invention;

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

[0016] Figure 3 for Figure 2 AA view;

[0017] Figure 4 This is a vortex path diagram (viewed from top) in the hyperbolic central tube of the present invention;

[0018] Figure 5 It 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 pipe, 3-bracket, 4-straight cone barrel, 5-straight cone barrel outlet, 6-elbow pipe, 7-diffuser. DETAILED DESCRIPTION

[0020] like Figures 1 to 3 As shown, a tailwater pipe using a hyperbolic central tube as a vortex suppression device is characterized in that: the tailwater pipe using a hyperbolic central tube as a vortex suppression device comprises a hyperbolic central tube 2, a bracket 3, a straight cone barrel 4, an elbow 6, and a diffuser 7; the inner surface of the hyperbolic central tube 2 satisfies the equation Among them, A=B=(0.04~0.08)D1, C=(0.05~0.1)D1, D1 is the inner diameter size of the straight cone barrel inlet 1; the curved center tube 2 is fixed inside the straight cone barrel 4 through the bracket 3, and the center axis coincides with the axis of the straight cone barrel 4; the function of suppressing the formation of tail water vortex and diverting tail water is achieved, and the pressure pulsation at the runner blades is reduced; the axial section of the straight cone barrel 4 is conical, and its upper end is the small conical end and is the open straight cone barrel inlet 1, and its lower end is the large conical end and is the open straight cone barrel outlet 5.

[0021] like Figure 2 As shown, in one embodiment, the inner diameter D of the hyperbolic central tube 2 at the inlet is 2 =0.08D 1 、Inner diameter at outlet D 3 =0.12D 1 , minimum cross-sectional inner diameter D 6 =0.04D 1 , wall thickness t 2 =0.01D 1 .

[0022] like Figure 3 As shown, in one embodiment, the axial height L of the hyperbolic central tube 2 is 2 =0.13L 1 , the distance L between the lower end of the hyperbolic center tube 2 and the inlet 1 of the straight cone barrel 3 =1.2L 2 , L 1 is the height of the straight cone barrel.

[0023] like Figure 3 As shown, in one embodiment, the bracket 3 is composed of four long cylindrical solid bodies, which are evenly arranged along the circumferential direction, with an angle of 90° between each other, and are connected to the minimum cross-section of the hyperbolic central tube 2 by welding. The diameter D of the bracket 3 is 5 =0.1L 2 , where L 2 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 is running under low load conditions, the water flow entering the tailwater pipe from the runner outlet often has a certain velocity circulation, causing low pressure in the center of the tailwater pipe and high pressure around it, forming a dead water zone in the center. The water flow in the dead water zone flows upstream to form a reverse flow, which is easy to produce spiral vortex belts. In order to ensure that the hyperbolic center tube 2 can split the vortex belt and make the vortex belt hit the wall, the inlet diameter of the hyperbolic center tube is designed to be 0.08D 1The central vortex hits the inner wall of the hyperbolic center tube 2, breaks into many small vortices and flows out of the hyperbolic center tube 2, and the vortex speed circulation is reduced, the rotational motion of the water flow is destroyed, and the negative pressure caused by the rotation of the water flow at the center is reduced, thereby reducing the strength of the vortex, achieving the goal of weakening the pressure pulsation from the source, and separating the central vortex from the flow channel outside the hyperbolic center tube 2, ensuring the hydraulic stability and safety of the tailwater pipe under low load conditions.

[0025] In the above-mentioned embodiment, the invention purpose of a tailwater pipe using a hyperbolic central tube as a vortex suppression device can be achieved, and technicians in this field can make a selection according to actual conditions.

[0026] The above contents are merely examples and explanations of the structure of the present invention. The technical personnel in the relevant technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A draft tube using a hyperbolic central tube as a vortex suppression device, characterized in that: The tailwater pipe using a hyperbolic central tube as a vortex suppression device comprises a hyperbolic central tube (2), a bracket (3), a straight cone barrel (4), an elbow pipe (6), and a diffuser (7); the inner curved surface of the hyperbolic central tube (2) satisfies the equation (0.05L1>z>-0.1L1), wherein A=B=(0.04-0.08)D1, C=(0.05-0.1)D1, D1 is the inner diameter of the straight cone barrel inlet (1); the curved central tube (2) is fixed inside the straight cone barrel (4) through a bracket (3), and the central axis coincides with the axis of the straight cone barrel (4); the functions of suppressing the formation of tailwater vortex belts and diverting tailwater are achieved, and the pressure pulsation at the runner blades is reduced; the axial cross-section of the straight cone barrel (4) is conical, the upper end of which is a conical small end and an open straight cone barrel inlet (1), and the lower end of which is a conical large end and an open straight cone barrel outlet (5).

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

3. The tailwater pipe using a hyperbolic central tube as a vortex suppression device according to claim 1, characterized in that: The inner diameter D2 at the inlet of the hyperbolic central tube (2) is (0.08-0.14) D1, the inner diameter D3 at the outlet is (0.12-0.21) D1, the inner diameter D6 of the minimum cross section is (0.04-0.06) D1, and the wall thickness t2 is (0.01-0.02) D1.

4. The tailwater pipe using 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 evenly arranged along the circumferential direction, with an angle of 90° between each other, and are connected to the minimum cross-section of the hyperbolic central tube (2) by welding. The diameter D5 of the support (3) is (0.1-0.2)L2, where L2 is the axial height of the hyperbolic central tube (2).

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