Wheel of a fluid flow machine

Abstract

A blade wheel of a turbomachine, which blade wheel has a multiplicity of blades which are suitable and provided for extending radially in a flow path of the turbomachine, wherein the blades form a blade entry angle and a blade exit angle. Provision is made whereby the blade wheel forms N blocks of blades, where N≥2, wherein the blades of a block have in each case the same blade entry angle and the same blade exit angle, and the blades of at least two mutually adjacent blocks have a different blade entry angle and/or a different blade exit angle. According to a further aspect of the invention, partial gaps that the blades form in relation to an adjacent flow path boundary are varied in mutually adjacent blocks.

Claims

1. A blade wheel of a turbomachine, which blade wheel has: a multiplicity of guide blades which are suitable and provided for extending in a flow path of the turbomachine, which flow path is delimited radially at the outside by an outer flow path boundary and radially at the inside by an inner flow path boundary, wherein the guide blades are designed to be adjustable in terms of their stagger angle, wherein the guide blades have first partial gaps with respect to the outer flow path boundary and/or second partial gaps with respect to the inner flow path boundary, wherein the first partial gaps and the second partial gaps in each case extend not over the entire axial length of the guide blades but only over a partial length, wherein the blade wheel forms N blocks of blades, where N≥2, wherein the guide blades of a block have in each case identically formed partial gaps, and the guide blades of at least two mutually adjacent blocks have differently formed partial gaps.

2. The blade wheel according to claim 1, wherein the guide blades of at least two mutually adjacent blocks have partial gaps which have a different axial length.

3. The blade wheel according to claim 1, wherein the guide blades of at least two mutually adjacent blocks have partial gaps which have a different radial height.

4. The blade wheel according to claim 1, wherein the guide blades of at least two mutually adjacent blocks have partial gaps which have a different axial length and a different radial height.

5. The blade wheel according to claim 1, wherein the partial gaps are formed by cut-backs that the guide blades form in relation to the adjacent flow path boundary.

6. A blade wheel arrangement for a compressor of a turbomachine, which blade wheel arrangement has: a first blade wheel, which is formed as a rotor, a second blade wheel, which is arranged upstream of the first blade wheel and which is formed as a stator, and a third blade wheel, which is arranged downstream of the first blade wheel and which is formed as a stator, wherein the second blade wheel and/or the third blade wheel is formed as a blade wheel according to claim 1.

7. The blade wheel arrangement according to claim 6, wherein the second blade wheel and the third blade wheel are formed as blade wheels, wherein the two blade wheels form the same number of N blocks of blades, where N≥2.

8. The blade wheel arrangement according to claim 7, wherein the second blade wheel is formed as an inlet stator, and a block of the second blade wheel, in which the gap volume of the partial gaps is relatively large, is assigned a block of the third blade wheel, in which the gap volume of the partial gaps is relatively small, and vice versa.

9. The blade wheel arrangement according to claim 7, wherein the second blade wheel is formed as a stator embedded into a compressor, and a block of the second blade wheel, in which the gap volume of the partial gaps is relatively small, is assigned a block of the third blade wheel, in which the gap volume of the partial gaps is likewise relatively small, and a block of the second blade wheel, in which the gap volume of the partial gaps is relatively large, is assigned a block of the third blade wheel, in which the gap volume of the partial gaps is likewise relatively large.

Description

(1) The invention will be explained in more detail hereunder by means of a plurality of exemplary embodiments with reference to the figures of the drawing. In the drawing:

(2) FIG. 1 shows a sectional lateral view of a gas turbine engine;

(3) FIG. 2 shows a close-up sectional lateral view of an upstream portion of a gas turbine engine;

(4) FIG. 3 shows a partially cut-away view of a gearbox for a gas turbine engine;

(5) FIG. 4 shows the basic geometrical construction and the basic designations in a compressor cascade;

(6) FIG. 5 schematically shows, in an axial sectional illustration, a blade arrangement of a compressor of a gas turbine engine having upstream stator, a rotor and a downstream stator;

(7) FIG. 6 schematically shows a section through the blade wheel of a rotor or of a stator according to FIG. 5 in a plane perpendicular to the machine axis, wherein the blade wheel comprises two regions which have a different blade entry angle and/or blade exit angle;

(8) FIG. 7 shows a blade wheel arrangement according to FIG. 5, wherein the blades of the individual blade wheels are each formed as nominal blades;

(9) FIG. 8 shows a blade wheel arrangement according to FIG. 5, in which the blades of all three blade wheels form blocks which form a different blade stagger angle;

(10) FIG. 9 shows a blade wheel arrangement according to FIG. 5, in which the blades of all three blade wheels form blocks which have a different blade entry angle or blade exit angle; and

(11) FIG. 10 shows a schematic illustration of the advantages attained with the invention, illustrating the aerodynamic damping in a manner depending on the nodal diameter, wherein, in the case of a blade wheel arrangement according to the invention, the blades are excited so as to perform oscillations, which are subjected to relatively intense damping;

(12) FIG. 11 schematically shows a structural subassembly which has an inlet stator with adjustable stagger angle and partial gaps to the adjacent flow path boundaries;

(13) FIG. 12 shows an inlet stator according to FIG. 11 with partial gaps formed thereon;

(14) FIG. 13 shows, in a cascade illustration, an exemplary embodiment of a blade wheel arrangement having an upstream inlet stator, a rotor and a downstream stator, wherein the blades of the inlet stator and of the stator are arranged in each case in blocks which have differently formed partial gaps; and

(15) FIG. 14 shows, in a cascade illustration, an exemplary embodiment of a blade wheel arrangement embedded into a compressor, having an upstream stator, a rotor and a downstream stator, wherein the blades of the two stators are arranged in each case in blocks which have differently formed partial gaps.

(16) FIG. 1 illustrates a gas turbine engine 10 having a main axis of rotation 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 air flow 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 gearbox 30.

(17) During use, the core air flow 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 resultant hot combustion products then expand through, and thereby drive, the high-pressure and low-pressure turbines 17, 19 before being expelled through the nozzle 20 to provide some propulsive 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 gearbox 30 is a reduction gearbox.

(18) An exemplary arrangement for a gearbox fan gas turbine engine 10 is shown in FIG. 2. The low-pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun gear 28 of the epicyclic gearbox assembly 30. Radially to the outside of the sun gear 28 and meshing therewith are a plurality of planet gears 32 that are coupled to one another by a planet carrier 34. The planet carrier 34 limits the planet gears 32 to orbiting around the sun gear 28 in a synchronous manner whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled by way of linkages 36 to the fan 23 so as to drive the rotation of the latter about the engine axis 9. Radially to the outside of the planet gears 32 and meshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

(19) 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 gearbox output shaft that drives the fan 23). In some literature, the “low-pressure turbine” and “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.

(20) The epicyclic gearbox 30 is shown in an exemplary manner in greater detail in FIG. 3. Each of the sun gear 28, the planet gears 32 and the ring gear 38 comprise teeth about their periphery to mesh with the other gears. However, for clarity, only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the person skilled in the art that more or fewer planet gears 32 may be provided within the scope of protection of the claimed invention. Practical applications of an epicyclic gearbox 30 generally comprise at least three planet gears 32.

(21) The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, wherein the ring gear 38 is fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held so as to be fixed, wherein the ring gear (or annulus) 38 is allowed to rotate. In the case of such an arrangement, the fan 23 is driven by the ring gear 38. By way of a further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

(22) It is self-evident that the arrangement shown in FIGS. 2 and 3 is merely an example, and various alternatives fall within the scope of protection of the present disclosure. Purely by way of example, any suitable arrangement may be used for positioning the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the example of FIG. 2) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have a certain degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts of the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the person skilled in the art would readily understand that the arrangement of output and support linkages and bearing positions would typically be different to that shown by way of example in FIG. 2.

(23) Accordingly, the present disclosure extends to a gas turbine engine having an arbitrary arrangement of gearbox types (for example star-shaped or planetary), support structures, input and output shaft arrangement, and bearing positions.

(24) Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate-pressure compressor and/or a booster compressor).

(25) Other gas turbine engines to which the present disclosure can be applied may have alternative configurations. For example, engines of this type 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, which means 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 limiting, and any aspect of the present disclosure may 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-flow or split flow) may have a fixed or variable area. Whilst the example described relates to a turbofan engine, the disclosure may 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 gearbox 30.

(26) 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 axis of rotation 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 are mutually perpendicular.

(27) In the context of the present invention, the design of the blade wheels in the compressor is of importance. Here, the invention may basically be used in a low-pressure compressor, an intermediate-pressure compressor (where present) and/or a high-pressure compressor.

(28) The basic construction of a compressor cascade will firstly be described on the basis of FIG. 4. The compressor cascade is illustrated in a conventional illustration in meridional section and in a developed view. Said compressor cascade comprises a multiplicity of blades S, which each have a leading edge S.sub.VK and a trailing edge S.sub.HK. The leading edges S.sub.VK lie on an imaginary line L.sub.1, and the trailing edges S.sub.HK lie on an imaginary line L.sub.2. The lines L.sub.1 and L.sub.2 run parallel. The blades S furthermore each comprise a suction side SS and a pressure side DS. Their maximum profile thickness is denoted by d.

(29) The compressor cascade has a cascade pitch t and a profile chord s with a profile chord length s.sub.k. The profile chord s is the connecting line between the leading edge S.sub.VK and the trailing edge S.sub.HK of the profile. The blade stagger angle (hereinafter referred to as stagger angle) α.sub.s is formed between the profile chord s and the perpendicular to the line L.sub.1 (wherein the perpendicular at least approximately corresponds to the direction defined by the machine axis). The stagger angle α.sub.s indicates the inclination of the blades S.

(30) The blades S have a camber line SL, which is also referred to as profile centreline. This is defined by the connecting line of the circle centre points inscribed into the profile. The tangent to the camber line SL at the leading edge is denoted by T.sub.1. The tangent to the camber line SL at the trailing edge is denoted by T.sub.2. The angle at which the two tangents T.sub.1, T.sub.2 intersect is the blade camber angle λ. The inflow direction, at which the gas flows into the cascade, is denoted by Z, and the outflow direction, at which the gas flows away from the cascade, is denoted by D. The angle of incidence β.sub.1 is defined as the angle between the tangent T.sub.1 and the inflow direction Z. The deviation angle β.sub.2 is defined as the angle between the tangent T.sub.2 and the outflow direction A.

(31) Of particular importance in the context of the present invention are the blade entry angle γ.sub.1 and the blade exit angle γ.sub.2. The blade exit angle γ.sub.1 is defined as the angle between the tangent T.sub.1 to the camber line SL and the perpendicular to the line L.sub.1. The blade exit angle γ.sub.2 is defined as the angle between the tangent T.sub.2 to the camber line SL and the perpendicular to the line L.sub.2. The blade entry angle γ.sub.1 is also referred to as airfoil entry angle or as inflow metal angle and the blade exit angle γ.sub.2 is also referred to as airfoil exit angle or as outflow metal angle.

(32) The blade entry angle γ.sub.1 and the blade exit angle γ.sub.2 both change if the stagger angle α.sub.s is changed in the case of an unchanged shape of the blades, because a change in the stagger angle α.sub.s in such a situation, owing to the associated adjustment of the inclination of the blades, changes the orientation of the tangents T.sub.1, T.sub.2. By changing the camber of the blades S, it is however also possible for the blade entry angle γ.sub.1 and/or the blade exit angle γ.sub.2 to be changed without changing the stagger angle α.sub.s. Provision may also be made whereby, through corresponding shaping of the blades S, only the blade entry angle γ.sub.1 or the blade exit angle γ.sub.2 is changed, wherein this also leads to a change in the stagger angle α.sub.s.

(33) FIG. 5 shows a blade wheel arrangement for a compressor, which has a first blade wheel 6 formed as a rotor. Upstream of the rotor 6, there is arranged a second blade wheel 5, which is formed as a stator. Furthermore, downstream of the rotor 6, there is arranged a third blade wheel 7, which is formed as a further stator. The stator 5 arranged upstream may be formed as an inlet stator (IGV). However, this is not necessarily the case. It may also be a normal compressor stator of a stage embedded into the compressor. A flow path 8 of the compressor or of the core engine extends through the blade wheel arrangement.

(34) Each of these blade wheels 5, 6, 7 comprises a multiplicity of blades which extend radially in the flow path 8 of the turbomachine. Provision is made here whereby, on at least one of the blade wheels 5, 6, 7, the blades are divided into blocks, for which it is the case that the blades within a block have in each case the same blade entry angle and the same blade exit angle. By contrast, the blades of at least two mutually adjacent blocks have a different blade entry angle and/or a different blade exit angle.

(35) This is illustrated by way of example and schematically in FIG. 6. FIG. 6 shows, in a cross section transversely with respect to the machine axis, with the polar coordinates r, φ being illustrated, a blade wheel which may be one of the blade wheels 5, 6, 7 of FIG. 5. The individual blades are not separately illustrated. The blade wheel is divided into two blocks B1, B2. Each of the blocks extends in a circumferential direction φ over an extent angle δ of 180°. Alternatively, the blade wheel may be divided into a greater number of blocks, wherein, for the extent angle δ, the following applies:
δ=360°/N
where N denotes the number of blocks and is a natural number greater than or equal to 2. In FIG. 6, N is equal to 2.

(36) The blades of the blocks B1, B2 have a different blade entry angle and/or a different blade exit angle.

(37) FIG. 6 additionally shows an alternative exemplary embodiment, in which the individual blocks B1, B2 have a different extent angle in the circumferential direction. Accordingly, one block B1 has an extent angle δ1 of less than 180°, and the block B2 has an extent angle which is correspondingly greater than 180°. In further variants, the blade wheel is divided into a greater number of blocks, wherein the individual blocks each have a different extent angle and accordingly a different number of blades.

(38) On the basis of FIGS. 7 to 9, two exemplary embodiments will be discussed, in the case of which the blade wheels form blocks with different blade entry angle and/or different blade exit angle. Here, FIG. 7 firstly shows a nominal setting of the blades, wherein all of the blades have the same blade entry angle and the same blade exit angle. Here, the illustrated blade wheel arrangement comprises a rotor 6, which has a multiplicity of rotor blades 60 which rotate in a direction F. The blades 60 of the rotor 6 form a blade row.

(39) Upstream of the rotor 6, there is arranged a stator 5 which has a multiplicity of guide blades 50. Furthermore, downstream of the rotor 6, there is arranged a stator 7 which has a multiplicity of guide blades 70. The flow direction in which the gas flows in onto the stator 5 is denoted by the arrow E. All of the blades of the blade wheels 5, 6, 7 are formed and oriented identically in FIG. 7.

(40) FIG. 8 shows a first exemplary embodiment of a blade wheel arrangement which differs from this. The stator 5 will firstly be considered. This has N blocks of blades, wherein blades of two blocks, specifically the blocks B.sub.j and B.sub.k, are illustrated. In the illustration of FIG. 8, the individual blocks have in each case two blades. This is to be understood merely as an example. The individual blocks B.sub.j and B.sub.k may also have a greater number of blades, wherein the blades are, overall, divided into at least N=2 blocks. FIG. 8 may also be regarded as not illustrating all blades of a block, that is to say further blades of the block B.sub.j are situated adjacent above the uppermost blade in the drawing, and further blades of the block B.sub.k are situated adjacent below the lowermost blade in the drawing, wherein FIG. 8 illustrates only the transition between the two blocks B.sub.j and B.sub.k.

(41) FIG. 8 shows both the blades 50 in the nominal setting corresponding to FIG. 7 and also the blades in a setting changed in relation thereto. The blades in the changed setting are denoted by 51 in the block B.sub.j and by 52 in the block B.sub.k. It is the case that the blades 51, 52 of the two blocks B.sub.j and B.sub.k have a different stagger angle. In the case of the stator 5 (the second blade wheel S2 of FIG. 5), the stagger angle is defined as follows:
α.sub.S2,i=αS.sub.2,0+(−1).sup.iΔα.sub.S2

(42) Here, α.sub.S2,0 is a constant which denotes the nominal stagger angle as per FIG. 7. For i, the following applies: 1≤i≤N. From the nominal setting, the stagger angle is adjusted in one direction or in the other direction by the degree of change Δα.sub.S2. Here, in the case of the blades of mutually adjacent blocks B.sub.j and B.sub.k, the stagger angle is changed with a different sign. Thus, there a change of the stagger angle between the blades 50 and the blades 51 of the block B.sub.j by the degree of change −Δα.sub.S2, as indicated in FIG. 5. Between the blades 50 and the blades 52 of the block B.sub.k, there is a change of the stagger angle by the degree of change +Δα.sub.S2. Here, the stagger angle is defined as discussed with regard to FIG. 4.

(43) The change of the stagger angle in the individual blocks is associated with the stator blades being closed to a greater degree in the block B.sub.j, and being opened to a greater degree in the block B.sub.k, in relation to the nominal setting.

(44) In the exemplary embodiment illustrated, modifications have also been made in the stagger angle in the case of the rotor 6 and in the case of the stator 7, though this is not imperative. Here, the further stator 7 will firstly be considered. This has been divided into the same number N of blocks in each case with a different stagger angle.

(45) FIG. 8 shows both the blades 70 in the nominal setting corresponding to FIG. 7 and also the blades in a modified setting. The blades in the modified setting are denoted by 71 in the block B.sub.j and by 72 in the block B.sub.k. It is the case that the blades 71, 72 of the two blocks B.sub.j and B.sub.k have a different stagger angle. In the case of the stator 7 (the third blade wheel S3 of FIG. 5), the stagger angle is defined as follows:
α.sub.S3,i=α.sub.S3,0−(−1).sup.iΔα.sub.S3

(46) Here, α.sub.S3,0 is a constant which denotes the nominal stagger angle as per FIG. 7. For i, the following applies: 1≤i≤N. The explanations relating to the stator 5 apply here correspondingly. Thus, there a change of the stagger angle between the blades 70 and the blades 71 of the block B.sub.j by the degree of change +Δα.sub.S3, as indicated in FIG. 5. Between the blades 70 and the blades 72 of the block B.sub.k, there is a change of the stagger angle by the degree of change −Δα.sub.S3.

(47) The change of sign in the individual blocks of the stator 7 is in this case in the opposite direction than in the case of the blocks of the stator 5. Thus, if the stator blades 51 are closed to a greater degree in the block B.sub.j of the stator 5, then the stator blades 71 are opened to a greater degree in the block B.sub.j of the stator 7. It is likewise the case that, if the stator blades 52 are opened to a greater degree in the block B.sub.k of the stator 5, the stator blades 71 in the block B.sub.k of the stator 7 are closed to a greater degree.

(48) The degree of change Δα.sub.S3 may be equal to the degree of change Δα.sub.S2. However, this is not necessarily the case.

(49) In FIG. 8, the blades of the rotor 6 are also divided into groups with different stagger angle. However, this is not necessarily the case. In exemplary embodiments of the invention, only the blades of the stator 5 and/or the blades of the stator 7 are divided into groups with different stagger angle. In further exemplary embodiments, provision may be made whereby only the blades of the rotor 6 are divided into groups with different stagger angle.

(50) FIG. 8 shows both the blades 60 in the nominal setting corresponding to FIG. 7 and also the blades in a modified setting. Here, the rotor 6 is divided into the same number N of blocks of in each case different stagger angle as the stators 5, 7. The blades in the modified setting are denoted by 61 in the block B.sub.j and by 62 in the block B.sub.k. It is the case that the blades 61, 62 of the two blocks B.sub.j and B.sub.k have a different stagger angle. In the case of the rotor 6 (the first blade wheel S1 of FIG. 5), the stagger angle is defined as follows:
α.sub.S1,i=α.sub.S1,0−(−1).sup.iΔα.sub.S1

(51) Here, α.sub.S1,0 is a constant which denotes the nominal stagger angle as per FIG. 7. For i, the following applies: 1≤i≤N. The explanations relating to the stator 5 apply correspondingly. Thus, there a change of the stagger angle between the blades 60 and the blades 61 of the block B; by the degree of change +Δα.sub.S1, as indicated in FIG. 5. Between the blades 60 and the blades 62 of the block B.sub.k, there is a change of the stagger angle by the degree of change −Δα.sub.S1.

(52) It is pointed out that, as discussed with regard to FIG. 4, a change in the stagger angle α.sub.s in the case of identical shaping of the blades automatically also leads to a change in the blade entry angle and in the blade exit angle of the blades.

(53) FIG. 9 shows a second exemplary embodiment of a blade wheel arrangement which differs from the arrangement of FIG. 7. The main difference in relation to the exemplary embodiment of FIG. 8 consists in that, in the exemplary embodiment of FIG. 9, the stagger angle (and thus, in the case of identical shaping of the individual blades, the blade entry angle and the blade exit angle) has not been changed, but rather, with different shaping of the blades of the different blocks being provided, only the blade entry angle or the blade exit angle has been changed.

(54) The stator 5 will firstly be considered. This has N blocks of blades, wherein blades of two blocks, specifically the blocks B.sub.j and B.sub.k, are illustrated. The statements relating to the size and number of the blocks with regard to FIG. 8 also apply correspondingly to FIG. 9.

(55) FIG. 9 shows both the blades 50 in the nominal setting corresponding to FIG. 7 and also the blades in a setting changed in relation thereto. The blades with modified shaping are denoted by 53 in the block B.sub.j and by 54 in the block B.sub.k. It is the case that the blades 53, 54 of the two blocks B.sub.j and B.sub.k, whilst having an identical blade entry angle, have a different blade entry angle. In the case of the stator 5 (the second blade wheel S2 of FIG. 5), the blade exit angle γ2 of the i-th block is defined as follows:
γ.sub.2,S2,i=γ.sub.2,S2,0+(−1).sup.iΔγ.sub.2,S2

(56) Here, γ.sub.2,S2,0 is a constant which denotes the nominal blade exit angle as per FIG. 7. For i, the following applies: 1≤i≤N. From the nominal setting, the blade exit angle is adjusted in one direction or in the other direction by the degree of change Δγ.sub.2,S2. Here, in the case of the blades of mutually adjacent blocks B.sub.j and B.sub.k, the blade exit angle is changed with a different sign. Thus, there a change of the blade exit angle between the blades 50 and the blades 53 of the block B.sub.j by the degree of change −Δγ.sub.2,S2, as indicated in FIG. 5. Between the blades 50 and the blades 54 of the block B.sub.k, there is a change of the blade exit angle by the degree of change +Δγ.sub.2,S2. Here, the blade exit angle is defined as discussed with regard to FIG. 4.

(57) The change of the blade exit angle in the individual blocks is associated with the stator blades being closed to a greater degree in the block B.sub.j and being opened to a greater degree in the block B.sub.k.

(58) In the exemplary embodiment illustrated, modifications have also been made in the stagger angle in the case of the rotor 6 and in the case of the stator 7, though this is not imperative. Here, the further stator 7 will firstly be considered. This has been divided into the same number N of blocks in each case with a different stagger angle.

(59) FIG. 9 shows both the blades 70 in the nominal setting corresponding to FIG. 7 and also the blades in a modified setting. The blades with modified shaping are denoted by 73 in the block B.sub.j and by 74 in the block B.sub.k. It is the case that the blades 73, 74 of the two blocks B; and B.sub.k, whilst having an identical blade entry angle, have a different blade exit angle. In the case of the stator 7 (the third blade wheel S3 of FIG. 5), the blade exit angle γ.sub.2 of the i-th block is defined as follows:
γ.sub.2,S3,i=γ.sub.2,S3,0+(−1).sup.iΔγ.sub.2,S3

(60) Here, γ.sub.2,S3,0 is a constant which denotes the nominal blade exit angle as per FIG. 7. For i, the following applies: 1≤i≤N. From the nominal setting, the blade exit angle is adjusted in one direction or in the other direction by the degree of change Δγ.sub.2,S3. Here, in the case of the blades of mutually adjacent blocks B.sub.j and B.sub.k, the blade exit angle is changed with a different sign. Thus, there a change of the blade exit angle between the blades 70 and the blades 73 of the block B.sub.j by the degree of change +Δγ.sub.2,S3. Between the blades 70 and the blades 74 of the block B.sub.k, there is a change of the blade exit angle by the degree of change −Δγ.sub.2,S3.

(61) The change of sign in the individual blocks of the stator 7 is in this case in the opposite direction than in the case of the blocks of the stator 5. Thus, if the stator blades 51 are closed to a greater degree in the block B.sub.j of the stator 5, then the stator blades 71 are opened to a greater degree in the block B.sub.j of the stator 7. It is likewise the case that, if the stator blades 52 are opened to a greater degree in the block B.sub.k of the stator 5, the stator blades 71 in the block B.sub.k of the stator 7 are closed to a greater degree.

(62) In FIG. 9, the blades of the rotor 6 are also divided into groups with different blade entry angle, wherein this is not necessarily the case. In a further design variant, too, provision may be made whereby only the blades of the rotor 6 are divided into groups with different blade entry angle.

(63) FIG. 9 shows both the blades 60 in the nominal setting corresponding to FIG. 7 and also the blades with modified shaping. Here, the rotor 6 is divided into the same number N of blocks as the other blade wheels 5, 7. The blades with the modified shaping are denoted by 61 in the block B.sub.j and by 62 in the block B.sub.k. It is the case that the blades 61, 62 of the two blocks B.sub.j and B.sub.k, whilst having an identical blade exit angle, have a different blade entry angle. In the case of the rotor 6 (the first blade wheel S1 of FIG. 5), the blade entry angle γ.sub.1 of the i-th block is defined as follows:
γ.sub.1,S1,i=γ.sub.1,S1,0+(−1).sup.iΔγ.sub.1,S1

(64) Here, γ.sub.1,S1,0 is a constant which denotes the nominal blade entry angle as per FIG. 7. For i, the following applies: 1≤i≤N. From the nominal setting, the blade exit angle is adjusted in one direction or in the other direction by the degree of change Δγ.sub.1,S1. Here, in the case of the blades of mutually adjacent blocks B.sub.j and B.sub.k, the blade entry angle is changed with a different sign. Thus, there a change of the blade entry angle between the blades 60 and the blades 63 of the block B.sub.j by the degree of change +Δγ.sub.1,S1. Between the blades 60 and the blades 64 of the block B.sub.k, there is a change of the blade exit angle by the degree of change −Δγ.sub.1,S1.

(65) On the basis of FIGS. 11-14, a further exemplary embodiment of the invention will be described, in which the blades of a blade wheel are likewise divided into a multiplicity of blocks, wherein the blades are of identical form within a block. By contrast to the exemplary embodiments of FIGS. 4-9, however, the characteristic by which the individual blocks differ is however not the blade entry angle and/or the blade exit angle, but lies in the design of partial gaps that the blades form to the respectively adjacent flow path boundary. Here, the statements relating to FIGS. 4-9 apply correspondingly with regard to the division of the blade wheel into individual blocks.

(66) FIG. 11 shows, in a sectional view, a structural subassembly, which defines a flow path 8 and which comprises a stator 5, a rotor 6 of a compressor stage of a compressor and flow path boundaries. The stator 5 is formed as an inlet stator, wherein this is not necessarily the case. The flow path 8 guides the core air flow A as per FIG. 1 through the core engine.

(67) Radially on the inside, the flow path 8 is delimited by a hub 95, which forms an inner flow path boundary 950. Radially on the outside, the flow path 8 is delimited by a compressor casing 4, which forms a radially outer flow path boundary 410. The flow path 8 is formed as an annular space. The inlet stator 5 has stator blades or guide blades 55 which adjustable in terms of stagger angle and which are arranged in the flow path 8 so as to be distributed in the circumferential direction. The guide blades 55 each have a leading edge 551 and a trailing edge 552.

(68) The swirl in the flow is increased by the inlet stator 5 and, as a result, the downstream rotor 6 is driven more effectively. The rotor 6 comprises a row of rotor blades 60, which extend radially in the flow path 8.

(69) For adjustability of the stagger angle, the guide blades 55 are mounted so as to be rotatable. For this purpose, said guide blades are each connected rotationally conjointly to, or formed integrally with, a spindle 25. The spindle 25 has an axis of rotation, which is identical to the axis of rotation of the guide blades 55. Here, the spindle 25 is accessible and adjustable from outside the flow path 8.

(70) Specifically, provision is made for the guide blade 55 to be connected at its radially outer end to an outer circular platform 75, which forms a rotary plate and which is connected to a radially outer spindle portion 251 of the spindle 25. The platform 75 and the spindle portion 251 are in this case mounted in a casing shroud 420, which is part of the compressor casing 4. Correspondingly, the guide blade 55 is connected at its radially inner end to an inner circular platform 78, which forms a rotary plate and which is connected to a radially inner spindle portion 252 of the spindle 25. The platform 78 and the spindle portion 252 are in this case mounted in an inner shroud 910, which locally forms the inner flow path boundary 950.

(71) To permit rotatability the of the guide blades 55 or adjustability of the stagger angle, it is necessary for the guide blades 55 to form, in the region of their trailing edge 552 and radially adjacent to the outer flow path boundary 410 and radially adjacent to the inner flow path boundary 950, cut-backs 553, 554 which ensure that the guide blades 55, in their axially rear region, form in each case one partial gap 81 to the radially outer flow path boundary 410 and one partial gap 82 to the radially inner flow path boundary 950. This prevents, during an adjustment of the guide blade 55 by rotation about the axis of rotation, said guide blade colliding with the outer flow path boundary 410 and/or with the inner flow path boundary 950.

(72) The gaps 81, 82 are referred to here as partial gaps because they do not extend over the entire axial length of the guide blades 55.

(73) Provision may alternatively be made whereby the guide blades 55 are formed without a shroud at their radially inner end, for which case they end in freely floating fashion, forming a continuous gap, in a manner radially spaced apart from the inner flow path boundary 95. It may also alternatively be provided that partial gaps are formed in the region of the leading edge 51 or both in the region of the leading edge 51 and in the region of the trailing edge 52.

(74) FIG. 12 shows the arrangement of guide blades 55, outer and inner platform 75, 78 and spindle 25 of FIG. 11 in an enlarged illustration. The cut-backs 553, 554 give rise to the partial gaps 81, 82 to the outer and inner flow path boundary respectively. Here, the partial gaps 81, 82 have a gap volume which is defined by the axial length and the radial height of the partial gaps 81, 82 or of the cut-backs 553, 554 which form said partial gaps.

(75) For the variation of the partial gap 81 and/or of the partial gap 82 in different blocks which form the guide blades 55 of the stator 5, the radial height r of the partial gap and/or the axial length x of the partial gap may be varied. Two variations V1, V2 of the partial gaps 81, 82 are shown in FIG. 12. The first variation V1 has been implemented at the upper partial gap 81, wherein it may alternatively or simultaneously also be implemented at the lower partial gap 82. Accordingly, the radial height of the partial gap 81 has been increased by virtue of the cut-back 553′ being made deeper. The second variation V2 has been implemented at the lower partial gap 82, wherein it may alternatively or simultaneously also be implemented at the upper partial gap 81. Accordingly, the axial length of the partial gap 81 has been increased by virtue of the diameter of the lower platform 78 being reduced and, at the same time, the cut-back 554 having a greater axial length.

(76) It is also possible for the illustrated variations to be combined, that is to say the upper partial gap 81 and/or the lower partial gap 82 are varied by means of a changed axial length and a changed radial height.

(77) Below, on the basis of FIGS. 13 and 14, two exemplary embodiments will be discussed, in the case of which the blade wheels form blocks with differently designed partial gaps. The basic arrangement corresponds here to that of FIG. 5, wherein a blade wheel arrangement for a compressor has a rotor 6, a variable stator 5 arranged upstream of the rotor 6, and a variable stator 7 arranged downstream of the rotor 6. In FIG. 13, the stator 5 arranged upstream is an inlet stator. FIG. 14 illustrates a sequence, embedded into a compressor, of stator 5, rotor 6 and stator 7.

(78) The inlet stator 5 will firstly be considered with reference to FIG. 13. This has N blocks of blades, wherein blades of two blocks, specifically the blocks B.sub.j and B.sub.k, are illustrated. In the illustration of FIG. 13, the individual blocks have in each case two blades 56, 57. This is to be understood merely as an example. The individual blocks B.sub.j and B.sub.k may also have a greater number of blades, wherein the blades are, overall, divided into at least N=2 blocks. FIG. 13 may also be regarded as not illustrating all blades of a block, that is to say further blades of the block B.sub.j are situated adjacent above the uppermost blade in the drawing, and further blades of the block B.sub.k are situated adjacent below the lowermost blade in the drawing, wherein FIG. 13 illustrates only the transition between the two blocks B.sub.j and B.sub.k.

(79) The blocks B.sub.j and B.sub.k differ by the partial gaps that the blades 56, 57 form in relation to the adjacent flow path boundary. Accordingly, the partial gaps 811 of the blades 56 of the block B; of the inlet stator 5 have greater axial extent than the partial gaps 812 of the blades 57 of the block B.sub.k. The gap area covered by the partial gaps 811 is accordingly larger than the gap area covered by the partial gaps 812.

(80) In the exemplary embodiment illustrated, modifications have also been made in the partial gaps in the case of the stator 7, though this is not imperative. Said stator has been divided into the same number N of blocks B.sub.j and B.sub.k with in each case differently formed partial gaps to the outer flow path boundary and/or to the inner flow path boundary. Alternatively, modifications are realized in the partial gaps only in the case of the stator 7.

(81) The partial gaps 813 of the blades 76 of the block B.sub.j of the stator 7 have smaller axial extent than the partial gaps 814 of the blades 77 of the block B.sub.k. The gap area covered by the partial gaps 813 is accordingly smaller than the gap area covered by the partial gaps 814. The assignment of the partial gaps between the blocks of the inlet stator 5 and the blocks of the stator 7 is in this case offset, that is to say blocks with relatively large partial gaps 811 of the inlet stator 5 are assigned blocks 813 with relatively small partial gaps 813 of the stator 7, and vice versa.

(82) Here, in FIG. 13 and in FIG. 14, the section of the illustration lies directly adjacent to the radially outer flow path boundary 410. Partial gaps are thus formed in the regions 811, 812, 813, 814. Correspondingly, partial gaps may additionally be formed adjacent to the radially inner flow path boundary 950 or only adjacent to the radially inner flow path boundary 950, see FIG. 11.

(83) It is furthermore pointed out that the partial gaps 811, 812, 813, 814 may additionally also have a radial variation, as illustrated schematically in FIG. 12. Such a radial variation cannot be seen in the sectional illustration of FIGS. 13 and 14.

(84) A further variation may consist in the partial gaps being realized not in the region of the trailing edge of the blades but in the region of the leading edge of the blades, or both in the region of the trailing edge and in the region of the leading edge of the blades.

(85) FIG. 14 shows, in the blade profile, a blade wheel arrangement which comprises two variable stators 5, 7, and a rotor 6 arranged in between, embedded into a compressor.

(86) The inlet stator 5 has N blocks of blades, wherein blades of two blocks, specifically the blocks B.sub.j and B.sub.k, are illustrated. In the illustration of FIG. 14, the individual blocks have in each case two blades 58, 59. With regard to the size of the individual blocks B.sub.j and B.sub.k, the statements relating to FIG. 13 apply correspondingly. The blocks B.sub.j and B.sub.k differ by the partial gaps that the blades 58, 59 form in relation to the adjacent flow path boundary. Accordingly, the partial gaps 815 of the blades 58 of the block B.sub.j of the stator 5 have smaller axial extent than the partial gaps 816 of the blades 59 of the adjacent block B.sub.k. The gap area covered by the partial gaps 815 is accordingly smaller than the gap area covered by the partial gaps 816.

(87) In the exemplary embodiment illustrated, modifications have also been made in the partial gaps in the case of the stator 7, though this is not imperative. Said stator has been divided into the same number N of blocks B.sub.j and B.sub.k with in each case differently formed partial gaps to the outer flow path boundary and/or to the inner flow path boundary. Alternatively, modifications are realized in the partial gaps only in the case of the stator 7.

(88) Here, the stator 7 is formed in the same way as the stator 7 of FIG. 13. The partial gaps 813 of the blades 76 of the block B.sub.j of the stator 7 have smaller axial extent than the partial gaps 814 of the blades 77 of the block B.sub.k. The gap area covered by the partial gaps 813 is accordingly smaller than the gap area covered by the partial gaps 814. The assignment of the partial gaps between the blocks of the inlet stator 5 and the blocks of the stator 7 is in this case such that blocks with relatively small partial gaps 815 of the stator 5 are assigned blocks 813 with relatively small partial gaps 813 of the stator 7, and blocks with relatively large partial gaps 816 of the stator 5 are assigned blocks with relatively large partial gaps 814 of the stator 7.

(89) The variants discussed with regard to the exemplary embodiment of FIG. 13 also apply correspondingly to the exemplary embodiment of FIG. 14.

(90) It is also pointed out that the design embodiments of FIGS. 11-14 may be combined with the design embodiments of FIGS. 3-9. The individual blocks of blades that form a blade wheel may thus differ both with regard to the blade entry angle and/or blade exit angle and/or the stagger angle and with regard to the design embodiment of the partial gaps.

(91) FIG. 10 schematically shows the advantages attained by means of the present invention. The aerodynamic damping is plotted versus the nodal diameter. Here, it is firstly to be noted that the blade rows form cyclic overall modes of oscillation which are characterized by nodal lines. Here, the maximum number of nodal lines is equal to half of the blades in the case of an even number of blades, and is equal to half of the blades minus one in the case of an odd number of blades. In a nodal line, the deflection is equal to zero.

(92) The nodal diameter is defined by the nodal pattern. In FIG. 10, the bar X1 shows oscillation excitations without implementation of the invention, and the bar X2 shows oscillation excitations with implementation of the invention. By means of the invention, a different nodal pattern has been generated, in the case of which the aerodynamic damping is increased, such that the build-up of rotating separation is prevented in an effective manner.

(93) It is self-evident that the invention is not limited to the embodiments described above and that various modifications and improvements may be made without departing from the concepts described herein. For example, provision may be made whereby the individual blocks realize more than two different blade entry angles and/or blade exit angles, that is to say for example a total of 6 blocks are provided, of which two have a first blade entry angle and/or blade exit angle, two further have a second blade entry angle and/or blade exit angle, and two further have a third blade entry angle and/or blade exit angle. Here, in further exemplary embodiments, provision may be made whereby the blade entry angle and/or blade exit angle changes not in discrete fashion but in continuous fashion between adjacent blocks, for example in accordance with the shape of a sinusoidal curve.

(94) It is also pointed out that, in the case of a discrete change, an identical deviation, which differs only in terms of the sign, of the respectively considered angle from the nominal setting is to be understood merely as an example. Provision may alternatively be made whereby the change in angle in one direction does not imperatively correspond to the change in angle in the other direction.

(95) It is pointed out that any of the features described may be used separately or in combination with any other features, unless they are mutually exclusive. The disclosure also extends to and comprises all combinations and sub-combinations of one or a plurality of features which are described here. 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.