Sealing segment for turbomachinery

Abstract

A sealing segment (1) for sealing a gap (16) between a rotating part (2) and a fixed part, centered on a rotating shaft (3), wherein the fluid medium flowing between the sealing segment (1) and the rotating part (2) during operation has axial and tangential fluid components with respect to the rotating shaft (3), the sealing segment (1) has a lower surface (6) opposite to the rotating part (2), the rotating part (2) has a seal tip (8, 8a), the seal tip (8, 8a) is formed opposite the lower surface (6), the lower surface (6) has a region located opposite the seal tip (8, 8a), and this region has a recess (15) in the circumferential direction (5) with respect to the rotating shaft (3).

Description

Technical Field

[0001] The present invention relates to a sealing segment for sealing a gap between a rotating part and a fixed part around a rotating shaft, wherein a fluid medium flowing between the sealing segment and the rotating part during operation has axial and tangential fluid components with respect to the rotating shaft, the sealing segment has a lower surface on the opposite side of the rotating part, the rotating part has a seal tip, and the seal tip is formed on the opposite side of the lower surface.

[0002] A turbomachine in the sense of this invention is, for example, a steam turbine, a gas turbine, or a compressor, and the present invention preferably relates to a steam turbine. A turbomachine is characterized by a fluid medium. The general term "turbomachine" encompasses hydraulic turbines, steam and gas turbines, wind turbines, centrifugal pumps, and centrifugal compressors, as well as propellers. All of these machines have in common the purpose of extracting energy from a fluid and thereby driving other machines or, conversely, supplying energy to a fluid to increase its pressure. In a turbomachine, the energy conversion is indirect and preferably takes a path through the kinetic energy of the fluid.

[0003] For example, in turbomachinery such as steam turbines, the fluid medium flows in the direction of the main flow during operation, which substantially corresponds to the direction of the rotation axis. Ideally, the fluid medium should flow only through so-called flow channels, which are equipped with so-called guide blades and movable blades. Typically, flow channels are formed by various guide blades and movable blades positioned forward and backward. The fluid medium flows through the flow channels and passes through the guide blades and movable blades, and its kinetic energy is converted into rotational energy, thereby causing the rotor to rotate. Since the rotor's motion occurs within the housing, a gap exists between the housing and the rotor, and this gap should be designed to be as small as possible. However, gaps cannot be avoided, and this results in unwanted flow through them. Unwanted flow originates from the main flow, with some branching off from this main flow and flowing through the gap. This gap flow is sometimes called secondary flow, and in any turbomachinery structure, the goal is to keep secondary flow as low as possible. Therefore, various approaches exist to minimize secondary flow. The first approach is to place so-called seal lips or seal tips between the rotating components and the stationary components. The seal lip or seal tip is positioned rotationally symmetrically and acts as a barrier to the secondary flow. Therefore, the secondary flow, which is effectively flowing towards the main flow, is slowed down.

[0004] However, in turbomachinery, secondary flow can introduce undesirable additional effects. Secondary flow passing through gaps can cause or dampen existing rotor vibrations during operation, depending on the dominant boundary conditions. In turbomachinery, this effect is called gap excitation (Spalterregung). In steam turbine engineering in particular, this effect is called steam stimulation (Dampfanfachung). Because the fluid medium portion branching into the gap has various directional components, in addition to the main directional component along the main flow channel, there is also a circumferentially oriented directional component. This circumferentially oriented secondary flow component is also called a vortex. Gap excitation or steam stimulation depends on the direction and size of this vortex in the secondary flow as it enters the gap. Generally, secondary flow in turbines has an effect that produces a stimulating rather than a damping effect.

[0005] This stimulating effect is detrimental, and efforts are being made to prevent this detriment. Here, it is known that vortex breakers (Drallbrechers) are used in various construction forms. Here, a vortex breaker is understood to be a component that forms a barrier against secondary flows that flow in the circumferential direction, called vortices.

[0006] Alternatively, or in addition, brake fluid can be injected into the secondary flow to minimize or prevent vortices.

[0007] The vortex fracturing section is formed from individual components and individually assembled within the housing in the circumferential direction using appropriate techniques. This increases manufacturing costs and, consequently, manufacturing time.

[0008] In a steam turbine, an embodiment of turbomachinery, steam is used as the fluid medium. The steam forms a mass flow and possesses thermal energy, which is ultimately converted into rotational energy in the steam turbine. This rotational energy causes a rotor, rotatably mounted around a rotating shaft, to rotate at any frequency. The majority of the mass flow flows along the so-called guide blades and movable blades, while a certain portion flows as a lost mass flow between the stationary and rotating parts. This mass flow flowing between the rotating and stationary parts is not used to do work between the guide blades and movable blades, thereby resulting in a loss of efficiency. It is necessary to reduce this lost mass flow.

[0009] A further problem with these loss mass flows is that the flow direction is both axial (pointing to the axis of rotation) and tangential (pointing to the circumferential direction). This causes the loss mass flow to induce rotation in the direction of rotational motion, which is called a vortex, as mentioned above. Excessive vortices are characterized by a relatively high tangential velocity of the loss mass flow, which can stimulate vibrations, thereby potentially having an undesirable effect on the rotor's dynamic stability.

[0010] Therefore, it is desirable to reduce vortices in the loss mass flow. For this purpose, the aforementioned vortex-breaking sections, formed as milled grooves within the housing, and flow guide plates that deflect the flow direction of the loss mass flow are used. Furthermore, it is known that so-called flow dam seals, also called axially extending seal tips, are used to alter the flow direction. Obstacles in the flow path are also suitable means of reducing the tangential flow component of the loss mass flow. For example, brush sealing can be such an obstacle.

[0011] The center of a turbine shaft does not typically remain stationary in a specific position, but rather undergoes orbital motion around a virtual center. Both circular and elliptical paths are possible. Under these conditions, in non-contact sealing of the turbine, for example, in the cover bands of the turbine stages, or in shaft sealing present at the shaft ends or the machine center, flow phenomena occur that impart forces to the shaft that move along with the orbital motion, depending on the rotational speed, orbital frequency, and peripheral velocity of the fluid in front of and inside the sealing and / or labyrinth sealing components. Consequently, a pressure field rotating around the rotating shaft emerges, which, in the worst-case scenario, may result in undesirable rotor excitation.

[0012] Therefore, the vortex at the inlet before the seal should be kept as small as possible when the fluid flow enters the seal, or forced in the opposite direction to the rotor rotation. As described above, vortex breakers are used for this purpose, which often consist of a number of small fins that direct the flow as needed.

[0013] It would be desirable to reduce the tangential component of the mass loss flow by simple means.

[0014] This is where the present invention comes in, and its objective is to reduce vortices in lossy mass flow.

[0015] This problem is solved by a sealing segment for sealing a gap between a rotating part and a stationary part around a rotation axis, wherein the fluid medium flowing between the sealing segment and the rotating part during operation has axial and tangential flow components with respect to the rotation axis, the sealing segment has a lower surface opposite to the rotating part, the rotating part has a seal tip, the seal tip is formed opposite the lower surface, and the lower surface has a region located opposite the seal tip, which has a recess in the circumferential direction when viewed with respect to the rotation axis.

[0016] In this way, a novel configuration for the vortex fracturing section is presented. The recesses create an effective possibility for forming the vortex fracturing section.

[0017] The advantageous development forms are described in the dependent claims.

[0018] In the first advantageous developmental form, the recesses are arranged at equal intervals in the circumferential direction.

[0019] This allows for a more targeted flow, potentially making it easier to manufacture recessed areas.

[0020] In the advantageous developmental form, multiple seal chips are arranged on the lower side, and the seal chips are positioned front to back along the axis of rotation.

[0021] In an advantageous developmental form, the rotating component also has multiple sealing tips on the opposite side of its lower surface, with the sealing tips arranged front to back along the axis of rotation.

[0022] In a particularly advantageous development, the recess is positioned opposite the last seal tip on the rotating part, when viewed along the axis of rotation and in the flow direction. Thus, the vortex breaking section is positioned opposite the last seal tip. This results in a particularly effective reduction of secondary flow.

[0023] In a favorable developmental form, the recess is formed in a circular, or more precisely, semicircular shape when viewed in the direction of rotation. This is particularly easy to manufacture. If the distance between the lower surface and the surface of the rotating part is L, the diameter D of the circle should be between 3 × L and 10 × L.

[0024] In a favorable developmental form, the recesses are spaced circumferentially such that a web with width d is formed between the recesses. A particularly favorable flow ratio can be achieved when the web is formed such that the following conditions hold: d=0 to d=5 × D.

[0025] In a further advantageous development, the recess is inclined radially at an angle β with respect to the axis of rotation. A particularly favorable flow ratio can be achieved if the recess is formed such that the following holds: 0 < |β| < 20°.

[0026] In a favorable developmental form, the recess is formed such that the tangent to the recess in the web is inclined at an angle α with respect to the radial direction. A particularly favorable flow ratio can be achieved if the recess is formed such that the following holds: 0 < |α| < 20°.

[0027] According to the present invention, the vortex breaking section consists of a recess located in the fixed part of the sealing, which is large in the axial direction or inclined up to 20° around the axial or circumferential axis, relative to the size of the labyrinth sealing chamber. The diameter is 3 to 10 times the distance from the rotor to the housing. The number of circumferential recesses must be measured so that a radial web exists. Thus, the web has a width of 0 to 5 times the diameter of the axial recesses. The recesses may also not be circular, but may be square, elliptical, or round. A seal tip positioned on the rotor side, which needs to be applied below the axial recesses, exerts a centrifugal force (schleudert) on the fluid radially outward into the large chambers within the stator. Within these chambers, the fluid is centrifuged against the sides of the axial recesses, causing the circumferential vortices to dissipate, and thus no circumferential mass flow is generated. In a further process, the fluid remaining in the circumferential direction flows back into the sealing and is dragged by the rotor.

[0028] The sealing segment according to the present invention can be manufactured quickly and cost-effectively. The vortex breaking section according to the present invention is efficient and can remove vortices from vortex flow almost completely. Furthermore, because of its small size, it can be used in large numbers within a sealing, thereby regulating the entire flow regime (Stroemungsregime) within the sealing.

[0029] The embodiments of the present invention will be described in more detail below with reference to the following figures.

[0030] The above characteristics, features, and advantages of the present invention, and the manner in which these are achieved, will be more clearly and distinctly understood in connection with the following description of embodiments, which will be described in more detail in connection with the accompanying drawings.

[0031] Here, the same reference numerals are used for the same parts or parts having the same function.

[0032] Hereinafter, embodiments of the present invention will be described based on the drawings. These are not intended to represent the embodiments to scale; rather, the drawings are shown in a schematic and / or slightly distorted form when used for explanation. For supplementary teachings that can be immediately recognized in the drawings, refer to the relevant prior art.

Brief Description of the Drawings

[0033] [Figure 1] It is a perspective view of a sealing segment. [Figure 2] It is a plan view of a sealing segment. [Figure 3] It is a side view of a sealing segment. [Figure 4] It is a side view of a sealing segment in an alternative embodiment.

[0034] The sealing segment 1 illustrated in Figure 1 is used, for example, in a steam turbine as an embodiment of turbomachinery. This type of sealing segment 1 is housed within a housing (not shown) which contains a component 2 that rotates around a rotating shaft 3 and can constitute a rotor. The rotor illustrated in Figure 1 rotates, for example, clockwise in a rotational direction 4 during operation. The sealing segment 1 is formed in a circumferential direction 5. This means that the sealing segment 1 is substantially aligned with the circumferential direction 5, i.e., it is designed to be curved. On the lower side surface 6, which is located opposite the upper side surface 7 of the rotating component 2 during operation, there is a groove formed to accommodate a seal tip 8.

[0035] The sealing segment 1 is formed to seal the gap 16 between the rotating part 2 and the fixed part (not shown).

[0036] Similarly, a groove formed to accommodate the seal tip 9 is also provided on the upper surface 7 of the rotating part 2.

[0037] As illustrated in Figure 1, this creates a kind of labyrinth sealing between the sealing segment 1 and the rotating part 2. The sealing segment 1 has an end face 10. During operation, the fluid medium flows in the flow direction 11 between the sealing segment 1 and the upper surface 7 of the rotating part 2 through the labyrinth sealing formed by the seal tips 8 and 9.

[0038] At the end portion 12 of the sealing segment 1, the flow is accompanied by vortices 13 in the circumferential direction 5. Viewed in the flow direction 11, opposite the last seal tip 8a, is a vortex-breaking section 14 in the shape of a recess 15. The vortex-breaking section 14 is formed by removing material from the lower surface 6 of the sealing segment 1, thereby creating the recess 15.

[0039] Here, it is desirable that the vortex-breaking section 14 acts as a barrier against the vortices 13 in the flow, and therefore against the flow in the circumferential direction 5.

[0040] Figures 2, 3, and 4 show embodiments of the vortex-breaking section 14 or recess 15, which are described below.

[0041] Figure 2 shows a schematic plan view of the end of the sealing segment 1. Multiple recesses 15 are arranged at equal intervals in the circumferential direction 5. This means that a web 17 is formed between two recesses 15. The web 17 acts as a ridge to resist the flow (not shown in Figure 2), thereby reducing the flow in the circumferential direction 5. Therefore, the recesses 15 are milled into the sealing segment 1 by removing material at an angle β using a suitable milling machine, where the value of angle β is between 0 and 20°. Since the milling is done substantially near the surface, a projection is formed. The milling machine forms a web 17 with a width d. If the recess 15 represents a circle or arc with a diameter D, the width d of the web is given by the formula: d = 0 to 5 × D. In Figure 2, for clarity, only the two webs 17 are labeled with the reference symbol d. As clearly shown in Figure 2, the recesses 15 are located above the seal tip 8a attached to the rotating part 2.

[0042] Therefore, the means for reducing the tangential flow component is implemented as a milling section.

[0043] Figure 3 shows a side view of the sealing segment 1. The shape of the recess 15 corresponds to a circle or arc with diameter D. D=2 *The equation R holds true. The distance between the rotating part 2 and the lower surface is L (not shown in Figure 3). For distance L and diameter D, the equation D = (3...10) × L holds true. In other words, the diameter D of the recess 15 is 3 to 10 times the distance L from the rotor 2 to the sealing segment 1. The number of circumferential directions 5 must be measured so that a radial web 17 is formed. Therefore, the web 17 has a width d of 0 to 5 times the diameter D of the recess 15 in the axial direction. Also, the recess 15 may have a shape other than circular, and may be square, elliptical, or round, which will be described in more detail in Figure 4. The recess 15 in Figure 4 is round, not circular, and therefore the tangent 18 can contact it at the transition point to the web 17. The tangent 18 and the radial direction 19 make an angle α with each other. For the value of angle α, the equation 0 < α < 20° holds true. In Figure 4, for clarity, the reference symbol d is attached to only one web 17, and the angle α is illustrated for only one recess 15.

[0044] Although the present invention has been illustrated and described in more detail by preferred embodiments, the present invention is not limited to the examples disclosed, and those skilled in the art can derive other modifications without departing from the scope of protection of the present invention. [Explanation of symbols]

[0045] 1...Sealing segment, 2...Rotating part, 3...Rotation axis, 4...Rotation direction, 5...Circumferential direction, 6...Lower side, 7...Upper side, 8...Seal tip, 8a...Seal tip, 9...Seal tip, 10...End face, 11...Flow direction, 12...End, 13...Vortex, 14...Vortex breaking section, 15...Recess, 16...Gap, 17...Web, 18...Tangential, 19...Radial direction, α...Angle, β...Angle, D...Diameter, L...Distance, d...Width

Claims

1. A sealing segment (1) for sealing the gap (16) between a rotating part (2) and a fixed part with respect to the rotating shaft (3), During operation, the fluid medium flowing between the sealing segment (1) and the rotating part (2) has flow components in the axial direction and tangential direction with respect to the rotating shaft (3). The sealing segment (1) has a lower surface (6) opposite to the rotating part (2), The rotating part (2) has seal tips (8, 8a), and the seal tips (8, 8a) are formed on the side opposite the lower surface (6). In the sealing segment (1), The lower surface (6) has a region located opposite the seal tip (8, 8a), The region has a plurality of recesses (15) in the circumferential direction (5) with respect to the rotation axis (3). A sealing segment (1) characterized by the above.

2. The sealing segment (1) according to claim 1, wherein the plurality of recesses (15) are arranged at equal intervals in the circumferential direction (5).

3. The sealing segment (1) according to claim 1 or 2, wherein the sealing segment has a plurality of sealing chips (9) on the lower surface (6).

4. The sealing segment (1) according to any one of claims 1 to 3, wherein the sealing tips (8, 8a, 9) are arranged along the rotating shaft (3).

5. The sealing segment (1) according to any one of claims 1 to 4, wherein the rotating part (2) has a plurality of seal tips (8, 8a) opposite the lower surface (6), and the seal tips (8, 8a) are arranged along the rotating shaft (3).

6. The sealing segment (1) according to any one of claims 1 to 5, wherein the rotating part (2) (viewed in the flow direction (11) along the rotation axis (3)) has a final seal tip (8a), and the plurality of recesses (15) are arranged to face the final seal tip (8a).

7. The sealing segment (1) according to any one of claims 1 to 6, wherein the plurality of recesses (15) are substantially circular when viewed from the direction of the rotation axis (3).

8. The sealing segment (1) according to claim 7, wherein the circular shape can be represented by a diameter D, the distance between the rotating part and the lower surface is L, and D = (3...10) × L.

9. The sealing segment (1) according to any one of claims 1 to 8, wherein the plurality of recesses (15) are arranged at intervals in the circumferential direction (5), and a web (17) having a width d is formed between the plurality of recesses (15).

10. The sealing segment (1) according to claim 9, wherein the width d is d = 0 to 5 × D.

11. The sealing segment (1) according to any one of claims 1 to 10, wherein the plurality of recesses (15) are inclined by an angle β with respect to the rotation axis (3) when viewed from the radial direction (19).

12. The sealing segment (1) according to claim 11, wherein the angle β is 0 < |β| < 20°.

13. The sealing segment (1) according to any one of claims 9 to 12, wherein the plurality of recesses (15) in the web (17) are formed such that the tangents (18) of the plurality of recesses (15) are inclined at an angle α with respect to the radial direction (19).

14. The sealing segment (1) according to claim 13, wherein the angle α is 0 < |α| < 20°.

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