Sealing segment for a turbomachine

Abstract

The invention relates to a sealing segment (1) for sealing a gap (16) between a component (2) which rotates about an axis of rotation (3) and a stationary component, wherein a flow medium which flows between the sealing segment (1) and the rotating component (2) during operation has, with respect to the axis of rotation (3), an axial flow component and a tangential flow component, wherein the sealing segment (1) has a lower side (6) facing the rotating component (2), wherein the rotating component (2) has a sealing tip (8, 8a), wherein the sealing tip (8, 8a) faces the lower side (6), wherein the lower side (6) has a region facing the sealing tip (8, 8a), wherein the region has recesses (15) in a circumferential direction (5) with respect to the axis of rotation (3).

Description

[0001] Description

[0002] Sealing segment for a turbomachine

[0003] The invention relates to a sealing segment for sealing a gap between a component rotating about a rotational axis and a stationary component, wherein a flow medium flowing between the sealing segment and the rotating component during operation has an axial and tangential flow component with respect to the rotational axis, wherein the sealing segment has a lower side opposite the rotating component, wherein the rotating component has a sealing tip, wherein the sealing tip is formed opposite the lower side.

[0004] Turbomachines within the meaning of this invention are, for example, steam turbines, gas turbines or compressors, whereby the invention preferably relates to steam turbines . Turbomachines are characterized by a flow medium . The collective term "turbinemachines" covers water turbines, steam and gas turbines, wind turbines, centrifugal pumps and centrifugal compressors as well as propellers . What all of these machines have in common is that they serve the purpose of extracting energy from a fluid in order to drive another machine or, conversely, of supplying energy to a fluid in order to increase its pressure . In turbomachines, the energy is converted indirectly and preferably via the kinetic energy of the fluid .

[0005] In turbomachines, such as steam turbines, a flow medium flows during operation in a main flow direction which essentially corresponds to the direction of the axis of rotation. Ideally, the flow medium should only flow through a so-called flow channel, which has so-called guide vanes and rotor blades. The flow channel is usually formed from various guide vanes and rotor blades arranged one behind the other. The flow medium flows through the flow channel past the guide vanes and rotor blades, with the kinetic energy being converted into rotational energy, which causes the rotor to rotate. Since the rotor moves in a housing, gaps exist between the housing and the rotor and should be kept as small as possible. However, gaps cannot be avoided, which leads to undesirable flow through the gaps.The unwanted flow arises from the main flow, with a portion branching off from the main flow and flowing through the gap. This gap flow can be referred to as secondary flow, and the aim of every turbomachine design is to keep the secondary flow as low as possible. There are therefore various approaches to minimizing the secondary flow. A first approach is to arrange so-called sealing lips or sealing tips between the rotating and the stationary components. The sealing lips or sealing tips are arranged rotationally symmetrically and act as a barrier to the secondary flow. This slows down a secondary flow that essentially flows towards the main flow.

[0006] However, in turbomachinery construction the secondary flow leads to a further effect which is undesirable. The secondary flow through the gaps can cause or dampen rotor vibrations that are present during operation, which becomes apparent depending on the prevailing boundary conditions. In turbomachinery construction this effect is known as gap excitation. In steam turbine construction in particular this effect is referred to as steam agitation. Since the portion of the flow medium branching off towards the gap has various directional components, in addition to the main directional component that runs along the main flow channel there are also directional components that are directed in the circumferential direction. This circumferentially directed secondary flow component is also referred to as swirl. The gap excitation or steam agitation depends on the direction and magnitude of this swirl of the secondary flow when it enters the gap.In general, the secondary flow in turbines has the effect of stimulating rather than dampening the flow.

[0007] This fanning effect is disruptive, and efforts are underway to prevent this disruption. For this purpose, it is known to use swirl breakers of various designs.

[0008] Swirl breakers are components that form a barrier for the secondary flow flowing in the circumferential direction, which is referred to as swirl.

[0009] Alternatively or additionally, a brake fluid can be injected into the secondary flow in such a way that the swirl is minimized or prevented.

[0010] The swirl breakers are constructed from individual components and are individually incorporated into the housing in a suitable manner along the circumferential direction. This results in high manufacturing costs, which in turn increases production times.

[0011] In a steam turbine as an embodiment of a turbomachine, steam is used as the flow medium. The steam forms a mass flow and has thermal energy which is ultimately converted into rotational energy in the steam turbine. This rotational energy causes a rotor mounted to rotate about a rotational axis to rotate at any frequency. The majority of the mass flow flows along so-called guide vanes and rotor blades, with a certain portion flowing as a lost mass flow between the stationary and rotating components. This mass flow flowing between the rotating and stationary components is not used to transfer work between the guide vanes and rotor blades, which results in a loss of efficiency. The aim is to reduce this lost mass flow.

[0012] A further problem with these lost mass flows is that the flow direction has both an axial direction pointing in the rotation axis and a tangential direction pointing in the circumferential direction. This leads to the lost mass flow in the direction of the rotational movement, which, as described above, is referred to as swirl. Excessively high swirl is characterized by the comparatively high tangential velocity of the lost mass flow, which could incite oscillation, which can adversely affect rotordynamic stability.

[0013] It is therefore desirable to reduce the swirl of the lost mass flow. For this purpose, the swirl breakers described above are used; these are designed as grooves milled into the housing, as well as flow guide vanes that divert the flow direction of the lost mass flow. Furthermore, it is known to use so-called flow dam seals, also known as axially extending sealing tips, to change the flow direction. Obstacles in the flow path are also suitable means of reducing the tangential flow component of the lost mass flow. Brush seals, for example, can represent such an obstacle.

[0014] The center of a turbine shaft does not usually remain static in a certain position, but rather moves in an orbit around an imaginary center. Both circular and elliptical paths are possible here. Under these conditions, flow phenomena occur in non-contact seals on turbines, such as on shrouds on turbine stages or shaft seals that exist at the shaft ends or in the middle of the machine, depending on factors such as the speed, orbit frequency, circumferential speed of the fluid in front of and inside the seal and / or labyrinth seal design. These flow phenomena generate forces on the shaft that move with the orbit. It is therefore possible for a pressure field to develop that rotates around the rotating shaft and, in the worst case, can lead to undesired rotor excitation.Therefore, the inlet swirl in front of the seal should be kept as small as possible or even imposed against the rotor rotation direction when the fluid flow enters the seal. As described above, swirl breakers are used for this purpose. These usually consist of a large number of small fins and direct the flow as desired.

[0015] It would be desirable to reduce the tangential component of the loss mass flow by simple means.

[0016] This is where the invention comes in, the purpose of which is to reduce the swirl of the loss mass flow.

[0017] This object is achieved by a sealing segment for sealing a gap between a component rotating about a rotational axis and a stationary component, wherein a flow medium flowing between the sealing segment and the rotating component during operation has an axial and tangential flow component with respect to the rotational axis, wherein the sealing segment has an underside opposite the rotating component, wherein the rotating component has a sealing tip, wherein the sealing tip is formed opposite the underside, wherein the underside has a region which is arranged opposite the sealing tip, wherein the region has recesses in a circumferential direction viewed with respect to the rotational axis.

[0018] A novel design for a swirl breaker is thus presented. The recesses provide an effective way to construct a swirl breaker.

[0019] Advantageous further developments are specified in the subclaims. In a first advantageous development, the recesses are arranged at equidistant intervals in the circumferential direction.

[0020] This leads to targeted flows and to the possibility of producing the recesses more easily.

[0021] In an advantageous further development, several sealing tips are arranged on the underside, wherein the sealing tips are arranged one behind the other along the axis of rotation.

[0022] In an advantageous further development, the rotating component also has a plurality of sealing tips opposite the underside, wherein the sealing tips are arranged one behind the other along the axis of rotation.

[0023] In a particularly advantageous development, the recesses are arranged opposite each other on the rotating component at the last sealing tip, viewed along the rotation axis in the direction of flow. Thus, the swirl breakers are arranged opposite the last sealing tip. This leads to a particularly effective reduction of the secondary flow.

[0024] In an advantageous further development, the recesses are circular, or more precisely semicircular, as seen in the direction of rotation. This is particularly easy to manufacture. If the distance between the underside and the surface of the rotating component is L, the diameter D of the circular recesses should be between 3xL and 10xL.

[0025] In an advantageous development, the recesses are spaced apart in the circumferential direction in such a way that a web with a width d is created between the recesses. Particularly advantageous flow conditions can be achieved if the web is designed such that the following applies: d = 0 to d = 5 x D . In a further advantageous development, the recesses are inclined by an angle ß with respect to the axis of rotation in the radial direction. Particularly advantageous flow conditions can be achieved if the recesses are designed such that the following applies: 0 < | | < 20 ° .

[0026] In an advantageous development, the recess is designed such that the tangent of the recess to the web is inclined by an angle a relative to the radial direction. Particularly advantageous flow conditions can be achieved if the recesses are designed such that the following applies: 0 < | a | < 20 ° .

[0027] According to the invention, the swirl breaker consists of large axial recesses in relation to the size of a labyrinth seal chamber or recesses inclined by up to 20° around the axial or circumferential axis in the stationary part of the seal. The diameter is three to ten times the distance from the rotor to the housing. The number of recesses in the circumferential direction is to be dimensioned such that radial webs are created. The webs therefore have a width of zero to five times the diameter of the axial recesses. The recess may also deviate from a circular shape and be square, oval or rounded. The sealing tip arranged on the rotor side, which must be applied below the axial recesses, throws the fluid radially outwards into the large chambers in the stator. The circumferential swirl dissipates in these chambers because the fluid is thrown against the flanks of the axial recesses, which do not permit any circumferential mass flow.As the process continues, the fluid, which is now stationary in the circumferential direction, flows back into the seal and is dragged along by the rotor.

[0028] The sealing segment according to the invention can be manufactured quickly and cost-effectively. The swirl breaker according to the invention is efficient and can remove the swirl almost completely from the swirling flow. Furthermore, it can be used multiple times within a seal – due to its small dimensions – allowing the entire flow regime within the seal to be trimmed.

[0029] In the following, an embodiment of the invention is explained in more detail with reference to the following figures.

[0030] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0031] Identical components or components with the same function are marked with the same reference symbols.

[0032] Exemplary embodiments of the invention are described below with reference to the drawings. These are not intended to represent the exemplary embodiments to scale; rather, where useful for explanation, the drawings are presented in a schematic and / or slightly distorted form. For supplements to the teachings immediately apparent in the drawings, reference is made to the relevant prior art.

[0033] It shows :

[0034] FIG 1 is a perspective view of a sealing segment;

[0035] FIG 2 a plan view of a sealing segment;

[0036] FIG 3 a side view of a sealing segment;

[0037] FIG 4 is a side view of a sealing segment in an alternative embodiment; the sealing segment 1 shown in FIG. 1 is used, for example, in a steam turbine as an embodiment of a turbomachine. Such a sealing segment 1 is arranged in a housing (not shown) which is arranged around a component 2 which rotates about an axis of rotation 3 and which can be designed as a rotor. The rotor shown in FIG. 1 rotates, for example, in the clockwise direction of rotation 4 during operation. The sealing segment 1 is formed in a circumferential direction 5. This means that the sealing segment 1 essentially follows the circumferential direction 5, i.e. is curved. Grooves which are designed to receive sealing tips 8 are arranged on an underside 6 which, during operation, is arranged opposite an upper side 7 of the rotating component 2.

[0038] The sealing segment 1 is designed to seal a gap 16 between the rotating component 2 and a stationary component (not shown).

[0039] Grooves are also arranged on the upper side 7 of the rotating component 2 and are designed to receive sealing tips 9.

[0040] As shown in Fig. 1, this creates a type of labyrinth seal between the sealing segment 1 and the rotating component 2. The sealing segment 1 has an end face 10. During operation, a flow medium flows in a flow direction 11 between the sealing segment 1 and the rotating component 2 at the top side 7 through the labyrinth seal formed by sealing tips 8 and 9.

[0041] At the end 12 of the sealing segment 1, the flow exhibits a swirl 13 in the circumferential direction 5. Swirl breakers 14 in the form of recesses 15 are arranged opposite a sealing tip 8a, which is the last one as seen in the flow direction 11. The swirl breakers 14 are created by removing material from the underside 6 of the sealing segment 1, thereby creating the recesses 15. The swirl breakers 14 are intended to counteract the swirl 13 in the flow and thus represent a barrier that counteracts a flow in the circumferential direction 5.

[0042] Figures 2, 3 and 4 show embodiments of the swirl breakers 14 and recesses 15 respectively and are described below.

[0043] Figure 2 shows a schematic plan view of the end of the sealing segment 1. The recesses 15 are arranged at equidistant intervals in the circumferential direction 5. This means that a web 17 is formed between two recesses 15. The web 17 acts as an elevation to counteract the flow (not shown in Figure 2) and thus reduces flow in the circumferential direction 5. The recesses 15 are therefore milled into the sealing segment 1 at an angle ß using suitable milling measures, removing material. The value of the angle ß has values ​​between 0 and 20°. Milling is essentially close to the surface, so that a bulge is created. The milling measure creates the webs 17, which have a width d. If the recess 15 is a circle or represents a circular section with a diameter D , the width d of the webs is determined by the following equation : d = 0 to 5 x D .For reasons of clarity, only two webs 17 are provided with the reference symbol d in Figure 2. As Figure 2 clearly shows, the recesses 15 are arranged above the sealing tip 8a mounted in the rotating component 2.

[0044] Thus, the means for reducing the tangential flow component are realized as milled recesses.

[0045] Figure 3 shows a side view of the sealing segment 1 . The shape of the recesses 15 corresponds to a circle or a circular section with a diameter D . The following applies: D = 2 * R . The distance between the rotating component 2 and the underside is L (not shown in Figure 3 ). The following applies to the distance L and the diameter D: D = ( 3 ... 10 ) x L . In other words: The diameter D of the recess 15 is three to ten times the distance L from the rotor 2 to the sealing segment 1 . The number 5 in the circumferential direction is to be dimensioned such that radial webs 17 are created. The webs 17 therefore have a width d of zero to five times the diameter D of the axial recesses 15 . The recess 15 may also deviate from the circular shape and be square, oval or rounded, which is described in more detail in Figure 4.The recesses 15 in Figure 4 deviate from the circular shape and are rounded so that a tangent 18 can be created at the point of transition to the web 17. The tangent 18 and the radial direction 19 are arranged at an angle a to one another. The following applies to the value of the angle a: 0 < a < 20 °. For reasons of clarity, only one web 17 is provided with the reference symbol d in Figure 4 and the angle a is only shown for one recess 15.

[0046] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variants can be derived by the person skilled in the art without departing from the scope of the invention.

Claims

Patent claims 1. Sealing segment (1) for sealing a gap (16) between a component (2) rotating about a rotational axis (3) and a stationary component, wherein a flow medium flowing between the sealing segment (1) and the rotating component (2) during operation has an axial and tangential flow component with respect to the rotational axis (3), wherein the sealing segment (1) has a (2) opposite underside (6), wherein the rotating component (2) has a sealing tip (8, 8a), wherein the sealing tip (8, 8a) is formed opposite the underside (6), characterized in that the underside (6) has a region which is arranged opposite the sealing tip (8, 8a), wherein the region has recesses (15) in a circumferential direction (5) viewed with respect to the axis of rotation (3).

2. Sealing segment (1) according to claim 1, wherein the recesses (15) are arranged at equidistant intervals in the circumferential direction (5).

3. Sealing segment (1) according to claim 1 or 2, wherein the sealing segment has a plurality of sealing tips (9) on the underside (6).

4. Sealing segment (1) according to one of the preceding claims, wherein the sealing tips (8, 8a, 9) are arranged one behind the other along the rotation axis (3).

5. Sealing segment (1) according to one of the preceding claims, wherein the rotating component (2) has a plurality of sealing tips (8, 8a) opposite the underside (6), wherein the sealing tips (8, 8a) are arranged one behind the other along the axis of rotation (3).

6. Sealing segment (1) according to one of the preceding claims, with a last sealing tip (8a) on the rotating component (2) viewed along the rotation axis (3) in the flow direction (11), wherein the recesses (15) are arranged opposite the last sealing tip (8a).

7. Sealing segment (1) according to one of the preceding claims, wherein the recesses (15) have a substantially circular shape when viewed in the direction of the rotation axis (3).

8. Sealing segment (1) according to claim 7, wherein the circular shape can be described by a diameter D, wherein a distance between the rotating component and the underside is L, where: D = (3...10) x L.

9. Sealing segment (1) according to one of the preceding claims, wherein the recesses (15) are spaced apart in the circumferential direction (5) such that a web (17) with a width d is formed between the recesses (15).

10. Sealing segment (1) according to claim 9, wherein: d = 0 to 5 x D.

11. Sealing segment (1) according to one of the preceding claims, wherein the recesses (15) are inclined by an angle ß relative to the rotation axis (3) as seen in the radial direction (19).

12. Sealing segment (1) according to claim 11, wherein: 0 < |ß| < 20°.

13. Sealing segment (1) according to one of claims 9 to 12, wherein the recesses are designed such that the Tangent (18) of the recess (15) on the web (17) is inclined by an angle a relative to the radial direction (19).

14. Sealing segment (1) according to claim 13, wherein: 0 < |a| < 20°.

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