BLEED AIR EXTRACTION DEVICE FOR A GAS TURBINE ENGINE

Abstract

The invention relates to a bleed air extraction device for a turbomachine, which has: an axial compressor, formed in a flow path and having at least one compressor stage, which comprises a rotor and a stator, and a bleed air duct, which is provided and designed to guide a bleed air flow branched off from the flow path of the axial compressor. In this case, the bleed air duct comprises an inlet opening, which is formed downstream of a stator of the axial compressor in the radially outer flow path boundary, an axially forward wall adjoining the inlet opening, and an axially rearward wall adjoining the inlet opening. Guide means are provided, which are provided and designed for the purpose of guiding at least a portion of the bleed air flow branched off from the flow path in the direction of the axially forward wall of the bleed air duct.

Claims

1. A bleed air extraction device for a turbomachine, which has: an axial compressor, formed in a flow path and having at least one compressor stage, which comprises a rotor and a stator, wherein the flow path is bounded radially on the inside by a radially inner flow path boundary and radially on the outside by a radially outer flow path boundary, a bleed air duct, which is provided and designed to guide a bleed air flow branched off from the flow path of the axial compressor, wherein the bleed air duct has: an inlet opening, which is formed downstream of a rotor or stator of the axial compressor in the radially outer flow path boundary, an axially forward wall adjoining the inlet opening, and an axially rearward wall adjoining the inlet opening, wherein guide means, which are provided and designed for the purpose of guiding at least a portion of the bleed air flow branched off from the flow path in the direction of the axially forward wall of the bleed air duct.

2. The device according to claim 1, wherein the guide means are provided and designed to guide a portion of the bleed air flow branched off from the flow path in the direction of the axially forward wall of the bleed air duct in such a way that a low-momentum zone which is formed adjoining the inlet opening at the axially forward wall is reduced or dispersed by said portion of the branched-off bleed air flow.

3. The device according to claim 1, wherein the guide means are provided and designed to guide a portion of the bleed air flow branched off from the flow path in the direction of the axially forward wall of the bleed air duct in such a way that a portion of the flow adjacent to the axially forward wall flows parallel to said wall.

4. The device according to claim 1, wherein the stator comprises a guide vane and a radially outer vane platform connected to the guide vane, wherein the vane platform has at least one slot extending in the circumferential direction, the vane platform, by means of the at least one slot, forms at least one flow-guiding profile extending in the circumferential direction, and the profile is designed in such a way that a portion of the flow in the flow path is deflected by the profile in the direction of the axially forward wall.

5. The device according to claim 4, wherein the at least one slot extends in the vane platform at a distance from the axially rearward end thereof.

6. The device according to claim 4, wherein the stator comprises a multiplicity of vane platforms, which adjoin one another in the circumferential direction and which each comprise at least one slot to form at least one profile.

7. The device according to claim 6, wherein each vane platform forms a plurality of slots, which are arranged one behind the other in the circumferential direction, and associated profiles.

8. The device according to claim 1, characterized by a flow-guiding profile which extends over 360° in the circumferential direction and is arranged in the region of the inlet opening of the bleed air duct, wherein the profile projects into the flow path and is designed in such a way that a portion of the flow in the flow path is deflected by the profile in the direction of the axially forward wall.

9. The device according to claim 8, wherein the 360° profile has a plurality of ribs, which are spaced apart in the circumferential direction and which each extend transversely in the bleed air duct and are used for securing the 360° profile in the bleed air duct.

10. The device according to claim 8, wherein the stator comprises vane platforms which are each connected to at least one guide vane and adjoin one another in the circumferential direction, wherein the 360° profile projects beyond the vane platform into the flow path counter to the radial direction.

11. The device according to claim 8, wherein the 360° profile is of integral design.

12. The device according to claim 1, wherein flow-guiding bodies in the form of ribs are formed on the axially rearward wall of the bleed air duct, said ribs being aligned in the longitudinal direction of the bleed air duct and deflecting the flow in the bleed air duct in the direction of the axially forward wall of the bleed air duct.

13. The device according to claim 12, wherein the ribs extend from the axially rearward wall into the bleed air duct and, at the same time, are profiled in such a way that the flow in the bleed air duct undergoes a greater deflection adjacent to the axially rearward wall than at the tip of the ribs.

14. The device according to claim 13, wherein the ribs are profiled in such a way that the flow in the bleed air duct undergoes no deflection or a relatively slight deflection at the tip of the ribs.

15. The device according to claim 1, wherein flow-guiding bodies in the form of ribs are formed on the axially forward wall of the bleed air duct, said ribs being aligned in the longitudinal direction of the bleed air duct, extending from the axially forward wall into the bleed air duct and, at the same time, being profiled in such a way that the flow in the bleed air duct undergoes a deflection in the direction of the axially forward wall.

16. The device according to claim 15, wherein the ribs are profiled in such a way that the flow in the bleed air duct undergoes a deflection toward the axially forward wall at the tip of the ribs, while there is no deflection or a relatively slight deflection of the flow adjacent to the axially forward wall.

17. The device according to claim 1, wherein the bleed air duct opens into a collecting volume of a secondary air system, which is fed with the bleed air, and an annular structure, which contains openings through which the bleed air flow can pass through the annular structure, is formed upstream of the collecting volume in the bleed air duct, wherein the openings are designed as deflecting profiles.

18. The device according to claim 17, wherein the deflecting profiles are formed by webs, which are formed in the circumferential direction between mutually adjoining openings and define said openings in the circumferential direction.

19. The device according to claim 1, wherein the bleed air duct opens into a collecting volume of a secondary air system, which is fed with the bleed air, and the bleed air duct is designed as a diffuser, at least in a section upstream of the collecting volume.

20. The device according to claim 20, wherein the bleed air duct is designed in such a way that the bleed air flow undergoes an acceleration in the region of the guide means which guide at least a portion of the bleed air flow branched off from the flow path in the direction of the axially forward wall of the bleed air duct.

21. The device according to claim 1, wherein the bleed air duct is designed as an annular gap.

Description

[0073] The invention will be explained in more detail below on the basis of a plurality of exemplary embodiments with reference to the figures of the drawing. In the drawing:

[0074] FIG. 1 shows a lateral sectional view of a gas turbine engine;

[0075] FIG. 2 shows, in plan view and in side view, an exemplary embodiment of a bleed air extraction device, in which a flow-guiding profile, which guides a portion of the bleed air flow branched off from the flow path in the direction of the axially forward wall of the bleed air duct, is formed in a vane platform;

[0076] FIG. 3 shows a plan view of a plurality of vane platforms corresponding to FIG. 2 arranged adjacent to one another in the circumferential direction;

[0077] FIG. 4 shows a variation of the exemplary embodiment in FIG. 2, wherein a plurality of flow-guiding profiles is formed one behind the other in the circumferential direction in a vane platform;

[0078] FIG. 5 shows, in plan view and in side view, an exemplary embodiment of a bleed air extraction device, in which a flow-guiding profile, which guides a portion of the bleed air flow branched off from the flow path in the direction of the axially forward wall of a bleed air duct, is formed by a ring extending over 360° in the circumferential direction;

[0079] FIG. 6 shows the arrangement according to FIG. 5 in a view from above;

[0080] FIG. 7 shows the arrangement according to FIG. 5 in a side view;

[0081] FIG. 8 shows the arrangement according to FIG. 5 in a view from the front;

[0082] FIG. 9 shows, in plan view and in side view, an exemplary embodiment of a bleed air extraction device, in which a flow-guiding profile, which guides a portion of the bleed air flow branched off from the flow path in the direction of the axially forward wall of a bleed air duct, is formed by ribs arranged on the axially rearward wall of the bleed air duct;

[0083] FIG. 10 shows a view along the line A-A in FIG. 9;

[0084] FIG. 11 shows, in plan view and in side view, an exemplary embodiment of a bleed air extraction device, in which a flow-guiding profile, which guides a portion of the bleed air flow branched off from the flow path in the direction of the axially forward wall of a bleed air duct, is formed by ribs arranged on the axially forward wall of the bleed air duct;

[0085] FIG. 12 shows a view along the line A-A in FIG. 11;

[0086] FIG. 13 shows, in plan view and in side view, an exemplary embodiment of a bleed air extraction device, in which the bleed air duct is passed through a casing flange, wherein the casing flange has a plurality of openings of different sizes arranged in a ring, through which the bleed air is guided into an adjoining collecting space;

[0087] FIG. 14 shows an illustration of a bleed air extraction device which, in addition to the components in FIG. 13, also shows a collecting space, into which the bleed air is guided, and bleed air extraction points starting from the collecting space;

[0088] FIG. 15 shows a view along the line A-A in FIG. 14, illustrating the openings of different sizes arranged in a ring in the casing flange;

[0089] FIG. 16 shows a development of the grid in FIG. 15 consisting of the openings arranged in a ring, along section B-B in FIG. 15;

[0090] FIG. 17 shows a view along the line A-A in FIG. 14 of an alternative embodiment of the casing flange, illustrating a reduced number of openings arranged in a ring as compared with the embodiment in FIG. 15; and

[0091] FIG. 18 shows a development of the grid in FIG. 17 consisting of the openings arranged in a ring, along section B-B in FIG. 17.

[0092] FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a thrust fan 23 that generates two air flows: a core air flow A and a bypass air flow B. The gas turbine engine 10 comprises a core 11 which receives the core air flow A. In the sequence of axial flow, the engine core 11 comprises a low-pressure compressor 14, a high-pressure compressor 15, a combustion device 16, a high-pressure turbine 17, a low-pressure turbine 19, and a core thrust nozzle 20. An engine nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass thrust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 by way of a shaft 26 and an epicyclic gear box 30.

[0093] During use, the core airflow A is accelerated and compressed by the low-pressure compressor 14 and directed into the high-pressure compressor 15, where further compression takes place. The compressed air expelled from the high-pressure compressor 15 is directed into the combustion device 16, where it is mixed with fuel and the mixture is combusted. The resulting hot combustion products then propagate through the high-pressure and the low-pressure turbines 17, 19 and thereby drive said turbines, before they are expelled through the nozzle 20 to provide a certain thrust. The high-pressure turbine 17 drives the high-pressure compressor 15 by means of a suitable connecting shaft 27. The fan 23 generally provides the major part of the thrust force. The epicyclic gear box 30 is a reduction gear box.

[0094] It is noted that the terms “low-pressure turbine” and “low-pressure compressor” as used herein can be taken to mean the lowest pressure turbine stage and the lowest pressure compressor stage (that is to say not including the fan 23) respectively and/or the turbine and compressor stages that are connected to one another by the connecting shaft 26 with the lowest rotational speed in the engine (that is to say not including the gear box output shaft that drives the fan 23). In some documents, the “low-pressure turbine” and the “low-pressure compressor” referred to herein may alternatively be known as the “intermediate-pressure turbine” and “intermediate-pressure compressor”. Where such alternative nomenclature is used, the fan 23 can be referred to as a first compression stage or lowest-pressure compression stage.

[0095] Other gas turbine engines in which the present disclosure can be used may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of connecting shafts. By way of a further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 20, 22, meaning that the flow through the bypass duct 22 has its own nozzle that is separate from and radially outside the core engine nozzle 20. However, this is not restrictive, and any aspect of the present disclosure can also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed or combined before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) can have a fixed or variable area. Although the example described relates to a turbofan engine, the disclosure can be applied, for example, to any type of gas turbine engine, such as, for example, an open rotor engine (in which the fan stage is not surrounded by an engine nacelle) or a turboprop engine. In some arrangements, the gas turbine engine 10 may not comprise a gear mechanism 30.

[0096] The geometry of the gas turbine engine 10, and components thereof, is/are defined by a conventional axis system, comprising an axial direction (which is aligned with the rotation axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the view in FIG. 1). The axial, radial and circumferential directions run so as to be mutually perpendicular.

[0097] In the context of the present invention, it is bleed air extraction via a bleed air duct which is of significance. Bleed air extraction takes place, for example, downstream of a stator of the low-pressure compressor or of the high-pressure compressor in FIG. 1.

[0098] In the upper part of the figure in a view from above and, in the lower part of the figure, in a side view, FIG. 2 shows a bleed air extraction device, which comprises an axial compressor, which is formed in a flow path 1 and comprises at least one compressor stage having a rotor and a stator, wherein a stator 2 of a compressor stage is illustrated. The flow path 1 is bounded radially on the outside by a radially outer flow path boundary 110. It is bounded radially on the inside by a radially inner flow path boundary (cf. flow path boundary 120 in FIG. 14).

[0099] The bleed air extraction device furthermore comprises a bleed air duct 3, via which a bleed air flow 4 is branched off from the flow path 1. The bleed air duct 3 comprises an inlet opening 31, which is formed downstream of the stator 2 in the radially outer flow path boundary 110. Moreover, the bleed air duct 3 comprises an axially forward wall 32 and an axially rearward wall 33, which adjoin the inlet opening 31. The bleed air duct 3 is of annular design and extends over an angular range of 360° in the circumferential direction. As an alternative, provision can be made for the bleed air duct 3 to be formed only in certain circumferential regions of the bleed air extraction device.

[0100] The stator 2 comprises a guide vane 210 and a radially outer vane platform 220, on which the guide vane 210 is secured. The stator 2 can furthermore have a radially inner vane platform (not illustrated). A slot 6 extending in the circumferential direction is formed in the vane platform 220. That region of the vane platform 220 which extends between the slot 6 and the downstream end of the vane platform 220 is designed as a flow-guiding profile 51, which likewise extends in the circumferential direction.

[0101] As illustrated in FIG. 2, this leads to a portion of the bleed air flow 4 branched off from the flow path 1 flowing through the slot 6 and, in the process, being deflected by the flow-guiding profile 51 in the direction of the axially forward wall 32 of the bleed air duct 3.

[0102] FIG. 3 illustrates that, in the circumferential direction, a plurality of vane platforms 220 with guide vanes 210 is formed adjacent to one another in the circumferential direction, wherein a flow-guiding profile 51 according to FIG. 2 is in each case formed by the slot 6. Bleed air flow 4 is thus guided in the direction of the axially forward wall 32 by slots 6 and profiles 51 over the entire circumference of the bleed air duct 3.

[0103] In this case, provision can be made for the bleed air flow 4 to be guided onto the axially forward wall 32 by the profile 51 in such a way that it is substantially parallel to the axially forward wall 32 adjacent to the latter. Flow losses due to deflection at the wall 32 are thereby avoided.

[0104] FIG. 4 shows a modification of the bleed air extraction device in FIG. 2. The modification consists in that, instead of a slot 6 extending in the vane platform 220, as provided in FIG. 2, a plurality of shorter slots 6a, 6b, 6c is provided, which each form correspondingly shorter flow-guiding profiles 51a, 51b, 51c. This illustrates that numerous variations are possible in the number and positioning of the slots and profiles.

[0105] In the case of the exemplary embodiments in FIGS. 2 to 4, the bleed air is guided by means of the slots 6, 6a, 6b, 6c and the profiles 51, 51a, 51b, 51c into low-momentum zones at the axially forward wall 32, with the result that backflow regions at the forward wall 32, which may occur especially in the case of low bleed air rates, are reduced or completely eliminated. This leads to a reduction in the total pressure loss of the flow guidance and maximization of the static pressure recovery.

[0106] FIG. 5 shows, in side view from above and in a side view, a further exemplary embodiment of a bleed air extraction device. Unlike the exemplary embodiment in FIGS. 2 to 4, no flow-guiding profile is formed in the vane platform 220 of the stator 2. Instead, an annular flow-guiding profile 52, which extends over 360° in the circumferential direction and is arranged in the region of the inlet opening of the bleed air duct 3, is provided.

[0107] At its radially inner edge, the 360° profile 52 projects over a radial region Δr relative to the inside of the vane platform 220. This ensures that the profile 52 can effectively deflect air from the flow of the flow path 1 into the bleed air duct 3. In this case, the required gas path area which is required to extract the minimum bleed air mass flow is not exceeded.

[0108] To secure the profile 52 in the bleed air duct 3, the profile 52 has a plurality of ribs 521 spaced apart in the circumferential direction, which each extend transversely in the bleed air duct 3. The ribs 521, which hold the profile 52 structurally, are oriented in a tangential direction relative to the flow and, for their part, likewise deflect the flow in a tangential direction. Through swirl reduction in the extraction mass flow they make an additional contribution to the static pressure increase in a downstream collecting volume, which is explained in greater detail with reference to FIG. 14.

[0109] In variant embodiments, the ribs 521 are connected only to the axially forward wall 32, only to the axially rearward wall 33 or to both walls 32, 33.

[0110] FIGS. 6 to 8 show, in a view from above, in a side view and in a view from the front, a section of the bleed air duct 3 with the axially forward wall 32, the axially rearward wall 33, the flow-guiding profile 52 and the ribs 521 of the flow-guiding profile.

[0111] In the exemplary embodiment in FIGS. 5 to 8 too, the momentum extracted is deflected into the dead zone, formed at the axially forward wall 32, of the bleed air extraction system, and ensures adequate flow through this zone, even at low mass flows. The total pressure loss is thereby reduced and the static pressure recovery is maximized.

[0112] Another exemplary embodiment is illustrated in FIGS. 9 and 10. In this exemplary embodiment, the guide means which deflect the bleed air in the direction of the axially forward wall 32 are in the form of ribs 53, which are formed on the axially rearward wall 33 of the bleed air duct 3. In this case, the ribs 53 are aligned in the longitudinal direction of the bleed air duct 3. Starting from the axially rearward wall, they extend into the bleed air duct 3, wherein the tip of the ribs 53 is situated in the bleed air duct 3. They are profiled in such a way that the flow in the bleed air duct 3 adjacent to the axially rearward wall 33 undergoes a greater deflection than at the tip of the ribs 53. In particular, the bleed air flow at the tip of the ribs 33 no longer undergoes a deflection. This increases successively from the tip of the ribs 53 in the direction of the axially rearward wall 33. The flow 4 in the bleed air duct 3 is thereby deflected in the direction of the axially forward wall 32 of the bleed air duct 3.

[0113] In this case, FIG. 10 illustrates that the flow 42 which is adjacent to the axially rearward wall 33 undergoes a deflection, while the flow 41 which flows in the region of the tip of the ribs 53 projecting into the bleed air duct undergoes no deflection or a relatively slight deflection.

[0114] In the exemplary embodiment in FIGS. 9 and 10, the ribs 53 introduce into the bleed air duct 3 profiles which bring about redistribution of the flow toward the axially forward duct wall 32. The high-loss zone present at low bleed air rates at the axially forward wall 32 is supplied with momentum by the ribs 53, and the separated flow is reduced. The deflection of the flow into this zone is accomplished by profiling which generates a large deflection at the axially rearward wall 33 and thus delivers a higher static pressure at the outlet and does not generate a deflection at the rib edge facing the axially forward wall 32. At the non-deflecting part of the ribs 53, the static backpressure is lower and allows the “healthy” flow to divert in this direction toward the axially forward wall 32.

[0115] In the exemplary embodiment in FIGS. 11 and 12, the guide means which deflect the bleed air in the direction of the axially forward wall 32 are likewise in the form of ribs 54. Unlike in the exemplary embodiment in FIGS. 9 and 10, however, the ribs 54 in the exemplary embodiment in FIGS. 11 and 12 are formed on the axially forward wall 32 of the bleed air duct 3. In this case, they are aligned in the longitudinal direction of the bleed air duct 3. Starting from the axially forward wall 32, the ribs 54 extend into the bleed air duct 3, wherein the tip of the ribs 54 is situated in the bleed air duct 3. The part of the bleed air flow 44 which passes through the ribs 54 is deflected in the direction of the axially forward wall 32. The part of the bleed air flow 43 which flows between the ribs 54 and the axially rearward wall 33 is not influenced by the ribs 54.

[0116] As can be seen especially from FIG. 12, the ribs 54 are profiled in such a way that the flow 442 in the bleed air duct 3 undergoes a deflection toward the axially forward wall 32 at the tip of the ribs 54, while the flow 441 which flows adjacent to the axially forward wall 32 undergoes no deflection or a relatively slight deflection. The deflection in the direction of the axially forward wall 32 decreases from the tip of the ribs 53 in the direction of the axially forward wall 32.

[0117] In the exemplary embodiment in FIGS. 11 and 12, the ribs 54 thus provide profiles positioned on the axially forward wall 32 which bring about redistribution of the flow toward the axially forward duct wall 32. A circumferential movement of the flow separation at low bleed air rates is thereby prevented. At the same time, high-momentum flow toward the axially forward wall 32 is redistributed by the different profile shapes of the ribs 54 on the axially forward wall 32 and the rib tip. In this case, the main flow swirl is assumed at all levels at the inlet of the ribs 54. At the axially forward wall 32, the swirl is not reduced by the ribs 54. On other hand, there is a deflection at the rib outer edge. The profile shape of the ribs 54 thus has the effect of redistributing the momentum to the axially forward wall 32, leading to more uniform separation with lower backflow components.

[0118] In all the abovementioned exemplary embodiments, the structures 51-54 for deflecting the bleed air at the axially forward wall 32 can be followed by controlled diffusion by the contouring of the side walls of the bleed air duct 3 in order to avoid flow separations and to maximize a static pressure recovery into a collecting volume.

[0119] FIG. 13 shows an exemplary embodiment in which the bleed air duct 3 is passed through an annular structure 7, which is provided in the exemplary embodiment illustrated by a region of a casing flange 70. Guide means 51-54 corresponding to FIGS. 2 to 11, which deflect a portion of the bleed air flow 4 in the direction of the axially forward wall 32, can be provided but are not separately illustrated. The fundamental construction of the bleed air extraction device corresponds to that in FIG. 2.

[0120] Here, FIG. 14 illustrates the overall arrangement. Thus, the bleed air duct 3 opens into a collecting volume 8, which is defined by a surrounding casing 80. The collecting volume 8 is part of a secondary air system for supplying various components of the gas turbine engine with bleed air. For this purpose, the collecting volume 8 has a plurality of bleed air extraction points 81. The volume flow of bleed air which is extracted can vary at the individual bleed air extraction points 81.

[0121] The bleed air enters the collecting volume 8 via the annular structure 7, which is formed upstream, directly ahead of the collecting volume 8. By virtue of the fact that the annular structure 7 is formed in the casing flange 70, the bleed air duct 3 can be oriented with a relatively small slope relative to the flow direction in the flow path 1 of the compressor. Thus, it is not necessary to route the bleed air duct 3 past the casing flange 70 that is inevitably present. The bleed air duct 3 extends at an angle of less than 90°, for example, in particular at an angle of less than 60°, to the flow direction in the flow path 1. By virtue of the slight slope of the bleed air duct 3, only slight deflections of the bleed air in the radial direction are required during the extraction of bleed air, and this reduces pressure losses during the extraction of bleed air, thus making it possible to achieve a higher static pressure in the collecting volume.

[0122] According to the sectional illustration in FIG. 15, which illustrates a section along the line A-A in FIG. 14, a multiplicity of openings 71 is formed in the annular structure 7, these being distributed over the circumference of the annular structure 7 and, at the same time, possibly being of different sizes, i.e. having different cross-sectional areas. In this case, the openings 71 are designed as deflecting profiles, as will be explained below.

[0123] In FIG. 15, it is possible to see a plurality of bleed air extraction points 81-84, which are formed on the collecting volume 8 in a manner spaced apart in the circumferential direction. The volume flow that can be extracted at the individual bleed air extraction points 81-84 can vary.

[0124] To achieve different sizes of the openings 71, it is envisaged that, although the inner radius R1 of the lower edge of the openings 71 is the same for all the openings 71, the outer radius R2 of the upper edge of the openings 71 varies in accordance with the hole size. In this case, the openings 71 are of substantially rectangular design.

[0125] The air in the bleed air duct 3 can pass through the annular structure 7 only through the openings 71 and therefore enters the collecting volume 8 only via said openings.

[0126] Webs or wall regions 72 which define the width of the openings are formed in the circumferential direction between the openings 71. As can be seen from the developed illustration in FIG. 16, the webs 72 are designed as deflecting profiles. By virtue of the shape of the webs 72, the openings 71 are designed as deflecting profiles. In this case, the webs 72 are shaped in such a way that adjacent groups of openings 71 guide the flow in the bleed air duct 3 to a particular one of the bleed air extraction points 81-84. In this case, the distribution of the sizes of the openings 71 is matched to the bleed air extraction points 81-84. As can also be seen from FIG. 15, the extraction openings 71 are of smaller design, for example, if the associated bleed air extraction points 82, 84 form a large pressure sink. The mass flow of the bleed air is thereby made more uniform overall.

[0127] FIGS. 17 and 18 show a modification of the exemplary embodiment in FIGS. 15 and 16, in which the openings 71 are of wider design and extend over a large angular range in the circumferential direction. In this case, the radial height of the openings 71 can vary within an opening 71. The webs 82, which extend in the circumferential direction between the openings 71, are also of correspondingly wider design. However, the principle of action is the same as in the exemplary embodiment in FIGS. 15 and 16, as can be seen from FIG. 18. The bleed air is fed selectively to individual bleed air extraction points 81-84 via the openings 71, wherein openings which are in a particular circumferential angular range feed the bleed air to an associated bleed air extraction opening. At the same time, the air fed to a particular bleed air extraction opening can be set by means of the size of the openings 71.

[0128] In the case of the exemplary embodiment in FIGS. 13 to 18, an annular structure 7 is thus arranged upstream of the collecting volume 8 in the bleed air duct 3, wherein the annular structure 7 uses nonuniform hole sizes over the circumference in order to achieve as uniform as possible extraction of bleed air from the main flow path 1 of the compressor across all extraction rates. In this case, webs 82, the number and circumferential position of which are matched to the bleed air extraction points 81-84, are used in the flange 70 for structural connection of the flange 70 and for flow deflection. The throttling of the flow toward the bleed air extraction points 81-84 is achieved by variation of the outer radius of the openings 71 or of the slot produced by said openings, for example.

[0129] The reduction of the through flow area depending on the circumferential position allows adaptation to the static pressure sinks caused by the bleed air extraction points 81-84 and ensures uniform mass flow extraction from the flow path 1 of the compressor. The webs 82 required for the structural task are used in a way which matches the static pressure sinks for additional throttling of the bleed air extraction points 82, 84 with a powerful extraction effect. The transitions are rounded in order to minimize separations of the flow and to reduce buildup effects for the compressor gas path.

[0130] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. In particular, the configurations of the various exemplary embodiments can also be implemented in combination. The provision of an annular structure with openings as shown in FIGS. 13-18 can additionally be implemented in each of the other exemplary embodiments, for example. It is also possible, for example, to provide for a flow-guiding profile as per FIGS. 2-4 which is implemented in the vane platform to be combined with flow-guiding profiles as per FIGS. 5-12. Attention is furthermore drawn to the fact that—apart from the configurations according to claims 4 to 7—the embodiments of the bleed air extraction system are not restricted to use behind the stator, but can also be used behind the rotor if the bleed air is to be extracted behind the rotor.

[0131] Furthermore, except where mutually exclusive, any of the features may be used separately or in combination with any other features, and the disclosure extends to and includes all combinations and sub-combinations of one or more features that are described herein. If ranges are defined, said ranges thus comprise all of the values within said ranges as well as all of the partial ranges that lie in a range.