A flow channel for suppressing vortex bands in the draft tube of an axial flow fixed-blade turbine

Abstract

The present invention belongs to the technical field of fluid machinery and engineering equipment, and specifically discloses a flow channel for suppressing vortex bands in the tailwater pipe of an axial flow fixed-blade turbine, comprising a volute, fixed guide vanes, movable guide vanes, a runner, and a tailwater pipe connected in sequence; water flows through the above components in sequence; the runner comprises a runner hub and runner blades; the runner blades are fixedly mounted on the outer side of the runner hub; the side of the runner blade connected to the runner hub is the runner inner edge; and the side of the runner blade away from the runner hub is the runner outer edge. The cross-sections of the runner outer edge and the runner inner edge of the runner blade provided in the present invention are both crescent-shaped, and the runner blades are airfoil-shaped with a thicker inlet edge. This widens the stable operating range of the fixed-blade turbine, reduces the maximum flow velocity, and suppresses pressure pulsations induced by the tailwater vortex bands. The present invention solves the problem that spiral vortex bands are easily formed in the tailwater pipe of axial flow fixed-blade turbines due to the inability to adjust the blades, thereby improving the operating stability and service life of the turbine.

Description

Technical Field

[0001] The invention belongs to the technical field of fluid machinery and engineering equipment, and in particular relates to a flow channel for suppressing vortex bands in a draft tube of an axial flow fixed-blade turbine. Background Art

[0002] Low-head small and medium-sized hydropower stations mostly use axial-flow turbines. Axial-flow fixed-blade turbines offer high flow capacity, high efficiency, and excellent cavitation performance. They are also inexpensive to manufacture and easy to install, operate, and maintain. However, they also suffer from a narrow stable operating range and a limited range of applicability.

[0003] Because of the immovable blade structure of an axial-flow fixed-blade turbine, when operating at optimal efficiency, the absolute velocity of the water flow at the runner outlet is axial, and the flow is relatively stable. However, when the turbine operates at low flow rates, the absolute velocity of the water flow at the runner outlet has a circumferential component in the same direction as the runner's rotation, forming a spiral vortex in the draft tube. The frequency of the vortex is only about 1 / 4 to 1 / 3 of the runner's rotational frequency. The presence of the vortex causes low-frequency pressure pulsations in the turbine draft tube under low flow conditions, which is a direct cause of unstable unit operation.

[0004] Furthermore, the automatic power generation control system continuously adjusts the unit's output based on power demand at different times, keeping it within a certain range to meet the power system's frequency and tie-line power control requirements. Therefore, increasing the stable operating range of axial-flow fixed-pitch turbines is crucial for maintaining the safe operation of the power grid and safeguarding national economy and people's livelihoods. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a flow channel for suppressing the vortex belt in the tailwater pipe of an axial flow fixed-blade turbine, so as to solve the problem that the blades of the axial flow fixed-blade turbine cannot be adjusted and spiral vortex belts are easily formed in the tailwater pipe.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a flow channel for suppressing vortex bands in the draft tube of an axial flow fixed-blade turbine, comprising a volute, a plurality of fixed guide vanes, a plurality of movable guide vanes, a runner and a draft tube connected in sequence; water flows through the above components in sequence;

[0008] The runner includes a runner hub and multiple runner blades; multiple runner blades are fixedly installed on the outer side of the runner hub; the side of the runner blades connected to the runner hub is the runner inner edge; the side of the runner blades away from the runner hub is the runner outer edge; the cross-sections of the runner outer edge and the runner inner edge are both crescent-shaped structures.

[0009] Furthermore, both sides of the runner blade in the longitudinal direction are the blade leading edge and the blade trailing edge, the side close to the movable guide vane is the blade leading edge, and the side away from the movable guide vane is the blade trailing edge.

[0010] Furthermore, the thickness of the runner blade close to the leading edge of the blade is greater than the thickness of the runner blade away from the leading edge of the blade.

[0011] Furthermore, the relationship between the cross-sectional blade angle β at the outer edge of the runner and the blade position M is:

[0012] β=-4.04994×10 -7 M 4 +0.000125265M 3 -0.012399393M 2 +0.57409207M

[0013] +50.59313709

[0014] The angle between the tangent line of the β blade airfoil bone line and the circumferential direction; M ranges from 0.00 to 0.88;

[0015] M is the ratio of the distance from the leading edge of the blade to the trailing edge of the blade to the total runner blade length.

[0016] Furthermore, the relationship between the cross-sectional blade thickness T at the outer edge of the runner and the blade position M is:

[0017] T = -1.69215 × 10 - 7M 4 +3.67245×10 - 5M 3 -3.48309×10 - 3M 2 +0.1485289M+1.5436704

[0018] T is the blade thickness, mm; M ranges from 0.00 to 0.88.

[0019] Furthermore, the relationship between the cross-sectional blade angle β at the inner edge of the runner and the blade position M is:

[0020] β=-1.57049×10 -7 M 4 -2.03391×10 -5 M 3 +0.00823027M 2 +0.031083424M

[0021] +6.805504481

[0022] The range of M is 0.00 to 1.12.

[0023] Furthermore, the relationship between the blade thickness T at the inner edge of the runner and the blade position M is: T = 5.00318 × 10 -7 M 4 -1.14035×10 -4 M 3 +4.88794×10 -3 M 2 +0.095141M+6.0817869

[0024] The range of M is 0.00 to 1.12.

[0025] Furthermore, the height of the movable guide vanes is 35%-45% of the runner diameter.

[0026] Furthermore, the radius of the cross section of the leading edge of the blade at the outer edge of the runner is 15mm-20mm, and the radius of the cross section of the trailing edge of the blade is 10mm-16mm.

[0027] Furthermore, the radius of the cross section of the leading edge of the blade at the inner edge of the runner is 70mm-80mm, and the radius of the cross section of the trailing edge of the blade is 15mm-20mm.

[0028] The present invention has at least the following beneficial effects:

[0029] 1. The cross-sections of the runner outer edge and the runner inner edge of the runner blades provided in the present invention are both crescent-shaped structures. The use of airfoil blades with a larger thickness at the water inlet edge of the runner blades widens the stable operating range of the fixed-blade turbine, reduces the value of the maximum flow velocity, and suppresses the pressure pulsation induced by the tailwater vortex. It solves the problem that spiral vortexes are easily formed in the tailwater pipe due to the inability to adjust the blades of axial-flow fixed-blade turbines, thereby improving the operating stability and safe operating life of the turbine.

[0030] 2. The outlet placement angle of the runner blades used in the present invention is smaller on the side close to the runner hub, while the placement angle on the side close to the outer edge of the runner is designed according to traditional design ideas. This is beneficial to reducing the circumferential component of the absolute velocity of the water flow at the runner outlet that is in the same direction as the runner rotation, and controlling the circumferential velocity circulation of the tailwater pipe vortex. Limiting the range of the guide vane height helps to suppress the vortex belt in the tailwater pipe flow channel by controlling the flow rate of the unit. At the same time, it helps to ensure the efficiency of the unit. The safe and stable operating range of the entire unit has been widened by more than 10%; the stable operating range of the turbine unit has been widened from 75%-100% to 60%-100%. The probability of abnormal vibration in the tailwater pipe is greatly reduced, and the operating stability and safe operating life of the turbine are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0032] Figure 1 Schematic diagram of the cross-section of the flow passage structure of the axial-flow fixed-pitch turbine of the present invention;

[0033] Figure 2 A three-dimensional diagram of the runner of the axial-flow fixed-blade turbine of the present invention;

[0034] Figure 3 Schematic diagram of a runner blade cross section P1 of an axial-flow fixed-pitch turbine according to the present invention;

[0035] Figure 4 Schematic diagram of a runner blade cross section P2 of an axial-flow fixed-pitch turbine according to the present invention;

[0036] Figure numerals: 1, volute; 2, fixed guide vane; 3, movable guide vane; 4, runner; 5, tailwater pipe; 6, runner hub; 7, runner blade; 8, runner outer edge; 9, runner inner edge; 10, blade leading edge; 11, blade trailing edge. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0038] The following detailed description is an exemplary description and is intended to provide further detailed description of the present invention. Unless otherwise indicated, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used in the present invention are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention.

[0039] Example 1

[0040] like Figure 1-2 As shown, a flow channel for suppressing vortex bands in the draft tube of an axial flow fixed-blade turbine comprises a volute 1, a plurality of fixed guide vanes 2, a plurality of movable guide vanes 3, a runner 4 and a draft tube 5 connected in sequence; water flows through the above components in sequence;

[0041] The runner 4 includes a runner hub 6 and a plurality of runner blades 7 ; the plurality of runner blades 7 are fixedly mounted on the outer side of the runner hub 6 .

[0042] The side of the runner blade 7 connected to the runner hub 6 is the runner inner edge 9; the side of the runner blade 7 away from the runner hub 6 is the runner outer edge 8. The cross-sections of the runner outer edge 8 and the runner inner edge 9 are both crescent-shaped. The two sides of the runner blade 7 in the longitudinal direction are the blade leading edge 10 and the blade trailing edge 11. The side close to the movable guide vane 3 is the blade leading edge 10, and the side away from the movable guide vane 3 is the blade trailing edge 11. The thickness of the runner blade 7 close to the blade leading edge 10 is greater than the thickness of the runner blade 7 away from the blade leading edge 10.

[0043] The cross section at the runner outer edge 8 of the runner blade 7 is cross section P1 ; the cross section at the runner inner edge 9 is cross section P2 .

[0044] Each point on the outer edge of the runner blade 7 is equidistant from the axis of the runner hub 6. A cylinder with a radius equal to the axis of the runner blade 7 to the runner hub 6 is tangent to the runner outer edge 8 to form an arc cross-section. The arc cross-section is unfolded to form a P1 cross-section. A cylinder with a radius equal to the radius of the runner hub 6 is tangent to the runner inner edge 9 to form an arc cross-section. The arc cross-section is unfolded to form a P2 cross-section.

[0045] like Figure 3 The figure shows a schematic diagram of the P1 section. The relationship between the blade angle β and the blade position M of the P1 section is:

[0046] β=-4.04994×10 -7 M 4 +0.000125265M 3 -0.012399393M 2 +0.57409207M

[0047] +50.59313709

[0048] β is the angle between the tangent line of the blade airfoil and the circumferential direction; M ranges from 0.00 to 0.88, and the reference line of the blade angle is perpendicular to the center axis of the runner hub 6;

[0049] M is the ratio of the distance from the leading edge 10 to the trailing edge 11 of the blade to the total length of the runner blade 7 .

[0050] The relationship between the blade thickness T and the blade position M at section P1 is:

[0051] T = -1.69215 × 10 - 7M 4 +3.67245×10 - 5M 3 -3.48309×10 - 3M 2 +0.001485289M+1.5436704

[0052] T is the blade thickness, mm; M ranges from 0.00 to 0.88.

[0053] like Figure 4 The figure shows a schematic diagram of the P2 section. The relationship between the blade angle β and the blade position M of the P2 section is:

[0054] β=-1.57049×10 -7 M 4 -2.03391×10 -5 M 3 +0.00823027M 2 +0.031083424M

[0055] +6.805504481

[0056] The range of M is 0.00 to 1.12.

[0057] The relationship between the blade thickness T and the blade position M at section P2 is:

[0058] T=5.00318×10 -7 M 4 -1.14035×10 -4 M 3 +4.88794×10 -3 M 2 +0.095141M+6.0817869

[0059] The range of M is 0.00 to 1.12.

[0060] The height H of the movable guide vane 3 is 35%-45% of the diameter of the runner 4. The purpose of limiting the range of the height of the movable guide vane 3 is to suppress the vortex belt in the tailwater pipe flow channel by controlling the flow rate of the unit.

[0061] The radius of the blade leading edge 10 section of the P1 section is 15mm-20mm, the radius of the blade trailing edge 11 section is 10-16mm, and the maximum thickness position of the P1 section is 35%-45% in the airfoil streamline direction.

[0062] The radius of the blade leading edge 10 section of the P2 section is 70mm-80mm, the radius of the blade trailing edge 11 section is 15mm-20mm, and the maximum thickness position of the P2 section is at 50-60% of the airfoil streamline direction.

[0063] The cross-sections of the runner outer edge 8 and the runner inner edge 9 of the runner blade 7 are both closed curves composed of two curves connected end to end: the position of the maximum thickness of the runner blade 7 is closer to the water inlet side, which is beneficial to controlling the maximum velocity value of the water flow, and thus beneficial to improving the cavitation performance of the entire runner; the runner blade 7 is an airfoil blade with a large leading edge radius, which makes the efficiency curve of the unit smooth and stable; the outlet placement angle of the runner blade 7 on the side close to the runner hub 6 is small, which is beneficial to reducing the absolute velocity of the water flow at the runner 4 outlet and the circumferential component in the same direction of rotation of the runner 4, thereby suppressing the generation of vortex belts in the tailwater pipe 5.

[0064] This helps eliminate the five vortex zones in the tailwater pipe, widening the stable operating range of the turbine unit from 75%-100% to 60%-100%, significantly extending the safe operating life of the turbine.

[0065] Example 2

[0066] A method for using a flow channel for suppressing vortex bands in a draft tube of an axial flow fixed-blade turbine comprises:

[0067] The runner blades 7 are designed and rigidly connected to the runner hub 6. The tailwater pipe 5 is connected to the axial-flow fixed-propeller turbine. The water flows through the volute 1, the fixed guide vanes 2 and the movable guide vanes 3 for pre-spin, drives the runner 4 to do work, and then flows into the tailwater pipe 5 and flows out through the tailwater pipe 5.

[0068] Numerical simulations and field tests were conducted on a prototype axial-flow fixed-blade turbine, analyzing the velocity and pressure pulsations in the runner and draft tube. The results demonstrate that the flow channel structure designed using this invention effectively suppresses pressure pulsations induced by tailwater vortices. In particular, under low-flow conditions, pressure pulsations induced by vortex rotation are significantly reduced, thereby improving the turbine's operational stability and safe operating life.

[0069] It is understood from common technical knowledge that the present invention may be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the embodiments disclosed above are, in all respects, merely illustrative and not exclusive. All modifications within the scope of the present invention or equivalent to the scope of the present invention are intended to be encompassed by the present invention.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A flow channel for suppressing vortex bands in the draft tube of an axial flow fixed-blade turbine, characterized in that: It comprises a volute (1), a plurality of fixed guide vanes (2), a plurality of movable guide vanes (3), a runner (4) and a tailwater pipe (5) connected in sequence; water flows through the above components in sequence; The runner (4) comprises a runner hub (6) and a plurality of runner blades (7); the plurality of runner blades (7) are fixedly mounted on the outer side of the runner hub (6); the side of the runner blades (7) connected to the runner hub (6) is the runner inner edge (9); the side of the runner blades (7) away from the runner hub (6) is the runner outer edge (8); the cross-sections of the runner outer edge (8) and the runner inner edge (9) are both crescent-shaped structures; The two sides of the runner blade (7) in the longitudinal direction are a blade leading edge (10) and a blade trailing edge (11), the side close to the movable guide vane (3) is the blade leading edge (10), and the side away from the movable guide vane (3) is the blade trailing edge (11); The thickness of the runner blade (7) close to the blade leading edge (10) is greater than the thickness of the runner blade (7) away from the blade leading edge (10); The relationship between the cross-sectional blade angle β at the outer edge (8) of the runner and the blade position M is: is the angle between the tangent line of the blade airfoil bone line and the circumferential direction; M is the ratio of the distance from the leading edge (10) to the trailing edge (11) of the blade to the total length of the runner blade (7); the range of M is 0.00~0.

88.

2. The flow channel for suppressing vortex bands in the draft tube of an axial flow fixed-blade turbine according to claim 1, characterized in that: The cross-sectional blade thickness at the outer edge (8) of the runner T and blade position M The relationship is: T=-1.69215× +3.67245× -3.48309× +0.1485289M+1.5436704 T is the blade thickness, mm; M ranges from 0.00 to 0.

88.

3. The flow channel for suppressing vortex bands in the draft tube of an axial flow fixed-blade turbine according to claim 1, characterized in that: The cross-sectional blade angle at the inner edge (9) of the runner β and blade position M The relationship is: The range of M is 0.00~1.

12.

4. The flow channel for suppressing vortex bands in the draft tube of an axial flow fixed-blade turbine according to claim 3, characterized in that: The cross-sectional blade thickness at the inner edge (9) of the runner T and blade position M The relationship is: The range of M is 0.00~1.

12.

5. The flow channel for suppressing vortex bands in the draft tube of an axial flow fixed-blade turbine according to claim 1, characterized in that: The height of the movable guide vane (3) is 35%-45% of the diameter of the runner (4).

6. The flow channel for suppressing vortex bands in the draft tube of an axial flow fixed-blade turbine according to claim 1, characterized in that: The radius of the cross section of the leading edge (10) of the blade at the outer edge (8) of the runner is 15 mm to 20 mm, and the radius of the cross section of the trailing edge (11) of the blade is 10 mm to 16 mm.

7. The flow channel for suppressing vortex bands in the draft tube of an axial flow fixed-blade turbine according to claim 1, characterized in that: The radius of the cross section of the leading edge (10) of the blade at the inner edge (9) of the runner is 70 mm to 80 mm, and the radius of the cross section of the trailing edge (11) of the blade is 15 mm to 20 mm.

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