A vortex suppression device for a draft tube of a spiral fin

Abstract

The present application belongs to the technical field of fluid machinery, water energy utilization and hydroelectric power generation, and particularly relates to a vortex suppression device for a spiral-ribbed draft tube. The draft tube comprises a straight conical pipe, an elbow pipe and a diffuser pipe, and the core component is the straight conical pipe. A conical center pipe with reverse spiral ribs is coaxially arranged inside the straight conical pipe, characterized in that the outer wall of the center pipe is attached with spiral ribs opposite to the rotation direction of the water flow, and the spiral ribs are fixed in the straight conical pipe by four streamline support rods. The present application is suitable for medium and low load conditions. When the water flow flows out of the runner and passes through the straight conical pipe, the center vortex belt formed is subjected to shear damage due to the flow through the reverse spiral ribs, thereby actively breaking the vortex belt structure, reducing the pressure pulsation amplitude in the draft tube, separating the center vortex belt from the flow passage outside the conical center pipe with reverse spiral ribs, and promoting the stability and safety of the draft tube under medium and low load conditions.

Description

Technical Field

[0001] This invention belongs to the fields of fluid machinery, water energy utilization and hydropower generation technology, and specifically relates to a tailwater pipe with a conical central tube with reverse spiral ribs as a vortex suppression device. Background Technology

[0002] With the transformation of the global energy structure, the complementary use of hydropower, wind power, and solar power has become the mainstream trend in clean energy development. Against this backdrop, the operational functions of hydropower units are shifting from traditional single-function power generation to grid peak shaving, frequency regulation, and emergency backup. This means that hydropower units must possess greater flexibility and be able to operate stably and frequently within a wide load range (0% to 100% load).

[0003] A water turbine is a power machine that converts the potential energy of water flow into mechanical energy. It uses water flow 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, when mixed-flow water turbines operate outside their optimal design conditions (especially at 40%–70% of rated load), the water flow at the runner outlet often retains a large residual circumferential velocity, causing the water to rotate in the draft tube and easily leading to a central vortex. With the requirement for extensive grid connection of new energy sources, mixed-flow water turbines frequently operate under non-design conditions. Within the 40%–70% rated load range, the central vortex is coarser, exhibiting a spiral shape and periodic oscillation, inducing periodic pressure pulsations. These pressure pulsations further induce vibrations in the hydroelectric generator unit, affecting its stability and even reducing its service life.

[0004] To address these issues, existing technologies primarily employ two types of flow control methods: First, the fluid control method (active), such as injecting air or water into the draft tube. While air injection can mitigate pressure pulsations to some extent, this method is complex, costly to operate, and excessive gas can reduce the draft tube vacuum, leading to decreased unit efficiency. Water injection, on the other hand, uses high-pressure jets to impact the vortex belt, but this consumes significant energy and is difficult to implement. Second, the geometric control method (passive), which optimizes the turbine structure, such as adding guide vanes to the inner wall of the draft tube. However, guide vanes generate substantial hydraulic losses under high-load conditions, and their roots are highly susceptible to cavitation damage. Furthermore, while some existing technologies utilize central tubes (such as cylindrical or hyperbolic central tubes) to occupy dead water zones, these central tubes typically have smooth curved surfaces, providing only passive volumetric occupancy and lacking an active shearing and disruptive mechanism against strongly rotating water flow. Therefore, their effectiveness in suppressing pressure pulsations under partial load conditions is limited. Therefore, how to suppress vortex bands, reduce pressure pulsation, and take into account economic benefits is a major challenge.

[0005] Therefore, how to design a tailrace vortex suppression device that is simple in structure, low in cost, and can both take advantage of the central pipe occupying the dead water zone and actively destroy the vortex rotation structure through structural features is a technical problem that this field is eager to solve. Summary of the Invention

[0006] To overcome the lack of an active mechanism for disrupting rotating water flow in existing technologies, this invention proposes a helical ribbed draft tube vortex suppression device. When the turbine is operating under low load conditions, the conical central tube occupies the central dead water zone, and the reverse helical ribs actively shear and break the central vortex band, thereby reducing pressure pulsation within the draft tube and promoting stable operation of the turbine unit under medium and low load conditions.

[0007] To achieve the above-mentioned objectives, this invention proposes a helical ribbed tailrace vortex suppression device, characterized in that the device comprises a conical central tube with reverse helical ribs, a streamlined support rod, a straight conical tube, an elbow tube, and a diffuser tube; the conical central tube with reverse helical ribs is coaxially disposed inside the straight conical tube and fixedly connected by the streamlined support rod; the conical central tube with reverse helical ribs comprises a conical tube body and helical ribs attached and fixed to its outer wall surface; the helical ribs extend in a helical shape along the axial direction, and their helical direction is opposite to the rated rotation direction of the turbine runner; the axial section of the straight conical tube is conical, with its upper end being a small conical end and an open straight conical tube inlet, and its lower end being a large conical end and an open straight conical tube outlet; the straight conical tube inlet is used to receive the water flow out of the turbine runner, the straight conical tube outlet is connected to the inlet of the elbow tube, and the elbow tube outlet is connected to the inlet of the diffuser tube.

[0008] Preferably, the conical central tube with reverse spiral ribs is shaped like an inverted frustum, with its upper end being the inlet and its lower end being the outlet; the inlet diameter D2 of the conical central tube with reverse spiral ribs is 0.08 to 0.12 times the inlet inner diameter D1 of the straight conical tube; the outlet diameter D3 of the conical central tube with reverse spiral ribs is 0.05 to 0.09 times the inlet inner diameter D1 of the straight conical tube; the axial height L2 of the conical central tube with reverse spiral ribs is 0.13 to 0.17 times the axial height L1 of the straight conical tube; the vertical distance L3 between the outlet end face of the conical central tube with reverse spiral ribs and the horizontal plane where the inlet of the straight conical tube is located is 0.45 to 0.5 times the axial height L1 of the straight conical tube; the conical central tube with reverse spiral ribs has a uniform wall thickness t1, which is 0.017 to 0.019 times the inlet inner diameter D1 of the straight conical tube.

[0009] Preferably, the cross-section of the spiral rib is circular or semi-circular, and its cross-sectional diameter d is 0.08 to 0.12 times the inlet diameter D2 of the conical central tube with reverse spiral ribs; the axial distance L4 from the upper starting point of the spiral rib to the inlet end of the conical central tube is 0.04 to 0.06 times the axial height L2 of the conical central tube with reverse spiral ribs; the axial height L5 of the spiral rib is 0.7 to 0.85 times the axial height L2 of the conical central tube with reverse spiral ribs; the number of spiral extensions of the spiral rib around the conical central tube is 0.3 to 0.5 turns; the number of spiral ribs is 6 to 8, and they are evenly spaced along the circumference of the conical central tube.

[0010] Preferably, the streamlined support rod has a streamlined cross-section, formed by a first semicircle on the water-facing side, a second semicircle on the back-water side, and two tangents connecting the first and second semicircles; the diameter D6 of the first semicircle (i.e., the diameter of the upper water-facing semicircle) is 0.08 to 0.12 times the inlet diameter D2 of the conical central tube with reverse spiral ribs; the diameter D7 of the second semicircle (i.e., the diameter of the lower back-water semicircle) is 0.02 to 0.03 times the inlet diameter D2 of the conical central tube with reverse spiral ribs. There are four streamlined support rods, evenly spaced along the circumference of the straight conical tube, with an included angle of 90° between them; the cross-sectional length D5 of the streamlined support rod along the water flow direction is 0.4 to 0.6 times the inlet diameter D2 of the conical central tube with reverse spiral ribs.

[0011] Compared with existing technologies, this invention has the following advantages: This invention provides a novel tailrace pipe that utilizes a conical central tube with reverse spiral ribs as a vortex suppression device. (1) The present invention sets a conical central tube with reverse spiral ribs in the tailrace, which changes the limitation of the traditional smooth central tube that can only passively occupy the space. Under the low load condition of the turbine, when the water flow containing a large number of circumferential velocity components enters the straight conical section of the tailrace from the runner outlet, the reverse spiral ribs generate a strong reverse shearing effect, which can actively cut off and break the high-strength spiral vortex structure, disperse the original vortex structure with strong periodicity, significantly reduce the pressure pulsation amplitude in the tailrace, and achieve the purpose of reducing pressure pulsation from the root. (2) The conical central tube of the present invention adopts an inverted frustum design, which conforms to the flow field distribution law in the tailwater pipe and can effectively occupy the low-pressure dead water area in the center; combined with the teardrop-shaped streamline structure support rod, while ensuring the structural stability, it minimizes the resistance interference and additional hydraulic loss to the mainstream area.

[0012] (3) This device has a simple structure, no complex moving parts, and no need for additional power supply. It is simple to manufacture and easy to install. It is suitable for both new power plants and old power plants, and has high engineering practicality and economic benefits. Attached Figure Description

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments; Figure 1 This is a schematic diagram of the tailwater pipe flow channel of the present invention; Figure 2 This is a top view of the straight tapered tube of the present invention; Figure 3 for Figure 2 A sectional view of a straight tapered tube at section AA (front view direction); Figure 4 Front view of a tapered central tube with reverse spiral ribs; Among them: 1-straight tapered tube inlet, 2-conical center tube with reverse spiral ribs, 3-streamlined support rod, 4-straight tapered tube, 5-straight tapered tube outlet, 6-elbow tube, 7-diffuser tube, 8-spiral ribs. Detailed Implementation

[0014] like Figure 1 As shown, a spiral ribbed tailpipe vortex suppression device is characterized in that: the spiral ribbed tailpipe vortex suppression device includes a conical central tube 2 with reverse spiral ribs, a streamlined support rod 3, a straight conical tube 4, an elbow tube 6, and a diffuser tube 7; the conical central tube with reverse spiral ribs is coaxially disposed inside the straight conical tube 4 and fixedly connected by the streamlined support rod 3; the conical central tube 2 with reverse spiral ribs includes a conical tube body and an outer wall surface attached to it. The spiral rib 8 extends spirally along the axial direction, and its spiral direction is opposite to the rated rotation direction of the turbine runner; the axial section of the straight tapered tube 4 is tapered, with its upper end being a small tapered end and an open straight tapered tube inlet 1, and its lower end being a large tapered end and an open straight tapered tube outlet 5; the straight tapered tube inlet 1 is used to receive the water flow out of the turbine runner, the straight tapered tube outlet 5 is connected to the inlet of the elbow tube 6, and the outlet of the elbow tube 6 is connected to the inlet of the diffuser tube 7.

[0015] like Figure 2 and Figure 3As shown, in one embodiment, the conical central tube 2 with reverse spiral ribs is shaped like an inverted frustum, with its upper end being the inlet end and its lower end being the outlet end. In this embodiment, the inner diameter of the straight conical tube inlet 1 is set to D1, the inner diameter of the straight conical tube outlet 5 is set to D4, and the axial height of the straight conical tube 4 is set to L1. The inlet diameter D2 of the conical central tube 2 with reverse spiral ribs is 0.08 to 0.12 times the inner diameter D1 of the straight conical tube inlet 1. The outlet diameter D3 of the conical central tube 2 with reverse spiral ribs is equal to the inner diameter of the straight conical tube inlet 1. The axial height L2 of the conical central tube 2 with reverse spiral ribs is 0.13 to 0.17 times the axial height L1 of the straight conical tube; the vertical distance L3 between the outlet end face of the conical central tube 2 with reverse spiral ribs and the horizontal plane where the inlet 1 of the straight conical tube is located is 0.45 to 0.5 times the axial height L1 of the straight conical tube; the conical central tube 2 with reverse spiral ribs has a uniform wall thickness t1, which is 0.017 to 0.019 times the inner diameter D1 of the inlet 1 of the straight conical tube.

[0016] like Figure 4 As shown, in one embodiment, the cross-section of the spiral rib 8 is circular or semi-circular, and its cross-sectional diameter d is 0.08 to 0.12 times the inlet diameter D2 of the conical central tube 2 with reverse spiral ribs; the axial distance L4 between the upper starting point of the spiral rib 8 and the inlet end of the conical central tube 2 is 0.04 to 0.06 times the axial height L2 of the conical central tube with reverse spiral ribs; the axial height L5 of the spiral rib 8 is 0.7 to 0.85 times the axial height L2 of the conical central tube with reverse spiral ribs; the number of spiral ribs 8 extending spirally around the conical central tube 2 is 0.3 to 0.5 turns; the number of spiral ribs 8 is 6 to 8, and they are evenly spaced along the circumference of the conical central tube 2.

[0017] like Figure 2As shown, in one embodiment, the streamlined support rod 3 has a streamlined cross-section, formed by a first semicircle on the water-facing side, a second semicircle on the back-water side, and two tangents connecting the first and second semicircles. The diameter D6 of the first semicircle (i.e., the diameter of the upper water-facing semicircle) is 0.08 to 0.12 times the inlet diameter D2 of the conical central tube 2 with reverse spiral ribs. The diameter D7 of the second semicircle (i.e., the diameter of the lower back-water semicircle) is 0.02 to 0.03 times the inlet diameter D2 of the conical central tube 2 with reverse spiral ribs. There are four streamlined support rods 3, evenly spaced along the circumference of the straight conical tube 4, with an included angle of 90° between them. The cross-sectional length D5 of the streamlined support rod 3 along the water flow direction is 0.4 to 0.6 times the inlet diameter D2 of the conical central tube 2 with reverse spiral ribs. When the turbine is under low load, the water flowing out of the runner outlet carries a strong circumferential velocity component, forming a spiral vortex within the straight conical tube 4 of the draft tube. At this time, the inverted frustum-shaped conical central tube 2 first occupies the low-pressure core area where the vortex is generated. Simultaneously, the reverse spiral ribs 8 attached to the surface of the central tube play a role, with their spiral direction opposite to the direction of water flow, thus generating a strong reverse shearing effect on the rotating water flow. This physical shearing effect actively cuts off and breaks up the originally continuous, high-intensity periodic spiral vortex structure, significantly reducing the amplitude of pressure pulsation within the draft tube, achieving the goal of reducing pressure pulsation at its source, and promoting the stable operation of the turbine unit under medium and low load conditions.

[0018] In one of the above embodiments, the invention objective of a spiral ribbed tailpipe vortex suppression device can be achieved, and those skilled in the art can make selections based on actual circumstances.

[0019] 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 tailrace vortex suppression device with spiral ribs, characterized in that: The aforementioned spiral ribbed tailrace vortex suppression device includes a conical central tube (2) with reverse spiral ribs, a streamlined support rod (3), a straight conical tube (4), an elbow tube (6), and a diffuser tube (7); the conical central tube (2) with reverse spiral ribs is coaxially disposed inside the straight conical tube (4) and fixedly connected by the streamlined support rod (3); the conical central tube (2) with reverse spiral ribs includes a conical tube body and spiral ribs (8) attached and fixed to its outer wall surface; the spiral ribs (8) extend spirally along the axial direction, and their spiral direction is opposite to the rated rotation direction of the turbine runner; the axial section of the straight conical tube (4) It is conical, with the upper end being a small conical end and an open straight conical pipe inlet (1), and the lower end being a large conical end and an open straight conical pipe outlet (5); the straight conical pipe inlet (1) is used to receive the water flow out of the turbine runner, the straight conical pipe outlet (5) is connected to the inlet of the elbow pipe (6), and the outlet of the elbow pipe (6) is connected to the inlet of the diffuser pipe (7); after the water flow flows out of the runner and enters the straight conical pipe (4), the central vortex is blocked by the conical central pipe (2) with reverse spiral ribs and destroyed by the reverse shearing action of the spiral ribs (8), thereby realizing the function of suppressing the formation of vortex in the tailrace pipe and guiding the tailrace, and reducing the pressure pulsation amplitude between the runner blades.

2. The tailrace vortex suppression device with spiral ribs according to claim 1, characterized in that: The conical central tube (2) with reverse spiral ribs is shaped like an inverted frustum, with its upper end being the inlet and its lower end being the outlet; the inlet diameter D2 of the conical central tube (2) with reverse spiral ribs is 0.08 to 0.12 times the inner diameter D1 of the straight conical tube inlet (1); the outlet diameter D3 of the conical central tube (2) with reverse spiral ribs is 0.05 to 0.09 times the inner diameter D1 of the straight conical tube inlet (1); the conical central tube (2) with reverse spiral ribs ( 2) The axial height L2 is 0.13 to 0.17 times the axial height L1 of the straight tapered tube; the vertical distance L3 between the outlet end face of the tapered central tube (2) with reverse spiral ribs and the horizontal plane where the inlet (1) of the straight tapered tube is located is 0.45 to 0.5 times the axial height L1 of the straight tapered tube; the tapered central tube (2) with reverse spiral ribs has a uniform wall thickness t1, which is 0.017 to 0.019 times the inner diameter D1 of the inlet (1) of the straight tapered tube.

3. The spiral ribbed tailpipe vortex suppression device according to claim 1, characterized in that: The cross-section of the spiral rib (8) is circular or semi-circular, and its cross-sectional diameter d is 0.08 to 0.12 times the inlet diameter D2 of the conical central tube (2) with reverse spiral ribs; the axial distance L4 between the upper starting point of the spiral rib (8) and the inlet of the conical central tube (2) is 0.04 to 0.06 times the axial height L2 of the conical central tube with reverse spiral ribs; the axial height L5 of the spiral rib (8) is 0.7 to 0.85 times the axial height L2 of the conical central tube with reverse spiral ribs; the spiral rib (8) extends spirally around the conical central tube (2) 0.3 to 0.5 times; the number of spiral ribs (8) is 6 to 8, and they are evenly spaced along the circumference of the conical central tube (2).

4. The spiral ribbed tailpipe vortex suppression device according to claim 1, characterized in that: The streamlined support rod (3) has a streamlined cross-section, which is formed by a first semicircle on the water-facing side, a second semicircle on the back water-facing side, and two tangents connecting the first and second semicircles. The diameter D6 of the first semicircle (i.e., the diameter of the upper water-facing semicircle) is 0.08 to 0.12 times the diameter D2 of the inlet end of the conical central tube (2) with reverse spiral ribs. The diameter D7 of the second semicircle (i.e., the diameter of the lower back water-facing semicircle) is 0.02 to 0.03 times the diameter D2 of the inlet end of the conical central tube (2) with reverse spiral ribs.

5. A spiral ribbed tailpipe vortex suppression device according to claim 1, characterized in that: The number of streamlined support rods (3) is 4, which are evenly spaced along the circumference of the straight conical tube (4) and the included angle between them is 90°; the cross-sectional length D5 of the streamlined support rod (3) along the water flow direction is 0.4 to 0.6 times the inlet diameter D2 of the conical central tube (2) with reverse spiral ribs.

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