Stator assembly for a gas turbine and gas turbine including said stator assembly

Abstract

The stator assembly for a gas turbine is provided with a stator ring that extends around a longitudinal axis and includes an outer edge having an annular groove; the annular groove defines a front wall and a rear wall; the front wall has an annular front radial face and an annular front axial face; and there are provided a plurality of stator vanes that are arranged radially and are connected to the outer edge of the stator ring side by side with each other so as to enclose the annular groove and define an annular cooling passage; each stator vane includes an airfoil, an outer shroud, and an inner shroud connected to the stator ring; the inner shroud includes a platform, a front flange and a rear flange that extend radially inward from the platform; the front flange is connected to the front wall and the rear flange is connected to the rear wall; the front flange is connected to the front wall so as to leave a primary radial gap between the front wall and the platform and define a front surface of the front flange; the platform has a front boundary and a rear boundary that extend circumferentially; the front boundary includes at least one first surface facing the primary radial gap; the first surface is curved.

Description

[0001] Cross-reference to related applications

[0002] This patent application claims priority from European patent application No. 19425078.3, filed on November 4, 2019, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to a stator assembly for a gas turbine and to a gas turbine comprising said stator assembly. In particular, the gas turbine of the present invention is part of a device for generating electrical energy. Background art

[0004] As is known, a gas turbine for a power plant comprises a compressor, a combustor and a turbine.

[0005] In particular, the compressor comprises an inlet supplied with air and a plurality of rotating blades for compressing the air passing therethrough. The compressed air leaving the compressor flows into a plenum chamber (i.e., an enclosed volume defined by a casing) and from there into the combustor. Inside the combustor, the compressed air is mixed with and burned with at least one fuel. The hot gases produced leave the combustion chamber and expand in the turbine. In the turbine, the expansion of the hot gases causes the rotating blades connected to the rotor to move to do work.

[0006] Both the compressor and the turbine comprise a plurality of stator assemblies axially disposed between rotor assemblies.

[0007] Each rotor assembly comprises a rotor disk rotating about a main axis and a plurality of blades supported by the rotor disk.

[0008] Each stator assembly comprises a plurality of stator vanes supported by a respective vane carrier and a stator ring arranged around the rotor.

[0009] A plurality of cavities between the components are defined between the stator assembly and the rotor assembly.

[0010] In the turbine, sealing air is typically bled from the compressor and introduced into the cavities between the components in order to avoid or limit the ingestion of hot gases from the hot gas path in the cavities between the components.

[0011] Minimizing the amount of air used to seal and cool the cavities between the components is beneficial to the performance of the power plant. However, said minimization implies the use of expensive advanced materials and / or the adoption of arrangements with very complex geometries. Summary of the invention

[0012] Therefore, an object of the present invention is to provide a stator assembly for a gas turbine which makes it possible to avoid or at least mitigate the described drawbacks.

[0013] In particular, the object of the present invention is to provide a stator assembly with an improved structure, which can minimize the amount of sealing air and at the same time ensure sufficient protection against thermal damage.

[0014] According to said object, the present invention relates to a stator assembly for a gas turbine, the stator assembly comprising:

[0015] A stator ring that extends around a longitudinal axis and includes an outer edge provided with an annular groove; the annular groove defines a front wall and a rear wall; the front wall is provided with an annular front radial surface and an annular front axial surface;

[0016] A plurality of stator vanes that are arranged radially and are connected side by side to the outer edge of the stator ring so as to enclose the annular groove and define an annular cooling channel; each stator vane includes an airfoil, an outer shroud, and an inner shroud connected to the stator ring; the inner shroud includes a platform, a front flange and a rear flange that extend radially inwards from the platform; the front flange is connected to the front wall and the rear flange is connected to the rear wall; the front flange is connected to the front wall so as to leave a primary radial gap between the front wall and the platform and define a front surface of the front flange; the platform has a front boundary and a rear boundary, both of which extend circumferentially; the front boundary includes at least one first surface facing the primary radial gap; the first surface is curved.

[0017] Advantageously, the curved shape of the surface of the front boundary facing the primary radial gap deflects the hot gas intake flow into a restricted area: the primary radial gap, where the gas intake flow can be cooled, controlled and flushed again.

[0018] In contrast, a conventional thin platform front boundary generates flow separation on the intake flow, which guides the hot gas radially downwards to the bottom of the cavity between the front components, bringing dangerous consequences to the stator and rotor sides.

[0019] Therefore, the intake of hot gas can be accepted, purged and deflected. This results in a smaller total consumption of sealing air, thus improving the overall performance of the engine as well as the thermal state and integrity of the components of the stator assembly.

[0020] In other words, the present invention allows the hot gas inlet to be restricted to the upper part of the cavity between the components, rather than completely avoiding the intake of hot gas by using a high flow rate of sealing air.

[0021] According to an embodiment of the present invention, the first surface is convex and curved with a first radius of curvature.

[0022] According to an embodiment of the present invention, the radius of curvature of the surface includes between 10% and 50% of the distance between the outer axial surface of the platform and the lower point of the annular front axial surface.

[0023] According to an embodiment of the present invention, the front boundary includes a second surface facing the airfoil, which is curved.

[0024] According to an embodiment of the invention, the second surface is convex and curved with a second radius of curvature.

[0025] According to an embodiment of the invention, the stator assembly includes a connection surface that connects the platform and the front surface; the connection surface is recessed with a third radius of curvature.

[0026] In this way, the ingested hot gas is forced to recirculate inside the primary radial gap, generating a vortex.

[0027] According to an embodiment of the invention, the annular front axial surface of the front wall is recessed with a fourth radius of curvature.

[0028] According to an embodiment of the invention, the front flange is provided with at least one primary cooling hole on the front surface that is in fluid communication with the annular cooling channel.

[0029] The presence of at least the primary cooling holes in the front flange improves the thermal state of the upper part of the front cavity between the components. In particular, the primary cooling holes improve the thermal state of the annular front axial surface of the front wall, which is typically made of a material with poorer properties compared to the guide vanes.

[0030] The cooling air is provided where it is more needed, rather than providing a large amount of air as is typically done in prior art solutions.

[0031] According to an embodiment of the invention, the front flange is provided with a plurality of circumferentially aligned primary cooling holes, which are preferably evenly distributed.

[0032] According to an embodiment of the invention, the primary cooling holes extend along a primary extension axis; in a longitudinal axial plane defined by the longitudinal axis and a radial direction that is orthogonal to the longitudinal axis and intersects the primary extension axis, a first angle defined by the projection of the primary extension axis on the longitudinal axial plane and the radial direction is included between 70° and 110°.

[0033] According to an embodiment of the invention, the primary cooling holes extend along a primary extension axis; in a circumferential plane defined by the longitudinal axis and a circumferential direction, a second angle defined by the projection of the primary extension axis on the circumferential plane and the axial direction is included between 100° and 200°, the circumferential direction being orthogonal to the longitudinal axis and orthogonal to the radial direction, and the radial direction being orthogonal to the longitudinal axis.

[0034] An object of the present invention is also to provide a reliable gas turbine in which the consumption of sealing air is reduced. According to this object, the present invention relates to a gas turbine that extends along a longitudinal axis and includes:

[0035] A plurality of rotor assemblies, each of the plurality of rotor assemblies including a rotor disk and a plurality of rotor blades arranged radially and coupled to the rotor disk;

[0036] A plurality of stator assemblies; the stator assemblies and the rotor assemblies are alternating in the axial direction;

[0037] At least one of the stator assemblies is described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will now be described with reference to the accompanying drawings, which show some non-limiting embodiments, in which:

[0039] Figure 1 is a schematic cross-sectional front view of a gas turbine electric power device according to the present invention, with parts removed for clarity;

[0040] Figure 2 is Figure 1 a schematic cross-sectional front view of a first detail of

[0041] Figure 3 is Figure 1 a schematic perspective view of a second detail of

[0042] Figure 4 is Figure 1 a schematic cross-sectional side view of a third detail of

[0043] Figure 5 is Figure 4 a schematic up view of a detail of

[0044] Figure 6 is Figure 4 a schematic cross-sectional side view of a detail of DETAILED DESCRIPTION

[0045] Figure 1 in which reference numeral 1 indicates a gas turbine electric power device (schematically shown in Figure 1 )

[0046] The device 1 includes a compressor 3, a combustion chamber 4, a gas turbine 5, and a generator (not shown in the drawings for simplicity).

[0047] The compressor 3, the turbine 5, and the generator (not shown) are mounted on the same shaft to form a rotor 8, which is received in a stator housing 9 and extends along an axis A.

[0048] More specifically, the rotor 8 includes a front shaft 10, a plurality of rotor assemblies 11, and a rear shaft 13.

[0049] Each rotor assembly 11 includes a rotor disk 15 and a plurality of rotor blades 16 that are coupled to the rotor disk 15 and arranged radially.

[0050] The plurality of rotor disks 15 are arranged continuously between the front shaft 10 and the rear shaft 13 and are preferably clamped in groups by a central tie rod 14. Alternatively, the rotor disks can be welded together.

[0051] The central shaft 17 separates the rotor disks 15 of the compressor 3 from the rotor disks 15 of the turbine 5 and extends through the combustion chamber 4.

[0052] In addition, the stator assemblies 22 are alternated with the compressor rotor assemblies 11.

[0053] Each stator assembly 22 includes a stator ring 24 and a plurality of stator guide vanes 25 that are arranged radially and coupled to the stator ring 24 and the corresponding stator housing 9.

[0054] Figure 2 In, an enlarged view of the stator assembly 22 between two rotor assemblies 11 in the turbine 5 is shown.

[0055] Arrow D indicates the direction of the hot gas flow in the hot gas passage 18 of the turbine 5.

[0056] The cavity 27 between the components is arranged between the rotor assembly 11 and the stator assembly 22.

[0057] Specifically, each stator assembly 22 defines a front inter-component cavity 27a and a rear inter-component cavity 27b, where the front inter-component cavity 27a is upstream of the rear inter-component cavity 27b in the direction D of the hot gas flow.

[0058] Referring to Figure 3 and Figure 4 , the stator ring 24 (only a part of which is visible in Figure 3 and Figure 4 ) extends around the longitudinal axis A and includes an inner edge 28 and an outer edge 29, and the outer edge 29 is provided with an annular groove 30.

[0059] The plurality of stator guide vanes 25 are coupled to the outer edge 29 of the stator ring 24 side by side with each other so as to enclose the annular groove 30 and define an annular cooling channel 32.

[0060] The annular cooling channel 32 is supplied with air, which is preferably from the compressor 3.

[0061] The annular groove 30 defines a front wall 34 and a rear wall 35. The front wall 34 is upstream of the rear wall 35 in the direction D of the hot gas flow.

[0062] Preferably, the front wall 34 is provided with a plurality of cooling openings 36 that are in fluid communication with the annular cooling channel 32.

[0063] Preferably, the cooling openings 36 are arranged near the inner edge 28.

[0064] In the non - limiting example disclosed and shown herein, the cooling openings 36 are circumferentially aligned and evenly distributed.

[0065] According to a variant (not shown), the rear wall is also provided with cooling openings that are in fluid communication with the annular cooling channel.

[0066] Each stator vane 25 includes an airfoil 38, an outer shroud 39, and an inner shroud 40 connected to the stator ring 24.

[0067] The airfoil 38 is provided with a cooling air duct 41a that is supplied by a dedicated opening 41b in the outer shroud 39.

[0068] The outer shroud 39 is connected to the corresponding stator housing 9.

[0069] The inner shroud 40 includes a platform 42, a front flange 43 that extends radially inwards from the platform 42, and a rear flange 44. The front flange 43 is upstream of the rear flange 44 in the direction D of the hot gas flow.

[0070] The front flange 43 is connected to the front wall 34, and the rear flange 44 is connected to the rear wall 35. In the non - limiting example disclosed and shown herein, the front flange 43 engages a corresponding annular seat 46 of the front wall 34, and the rear flange 44 engages a corresponding annular seat 47 of the rear wall 35.

[0071] In particular, the front flange 43 is connected to the front wall 34 so as to leave a primary radial clearance 48 between the front wall 34 and the platform 42 and to define a front surface 50 of the front flange 43 facing the primary radial clearance 48.

[0072] Preferably, the rear flange 44 is also connected to the rear wall 35 so as to leave a secondary radial clearance 52 between the rear wall 35 and the platform 42 and to define a rear surface 53 of the rear flange 44 facing the secondary radial clearance 52.

[0073] The platform 42 includes a circumferentially extending front boundary 54a and a rear boundary 54b. The front boundary 54a is upstream of the rear boundary 54b in the direction D of the hot gas flow.

[0074] The front flange 43 is provided with at least one primary cooling hole 55 on the front surface 50 that is in fluid communication with the annular cooling channel 32.

[0075] Preferably, the front flange 43 is provided with a plurality of circumferentially aligned primary cooling holes 55 on the front surface 50.

[0076] In the non-limiting examples disclosed and illustrated herein, the primary cooling holes 55 are evenly distributed.

[0077] Referring to Figure 5 and Figure 6 , each primary cooling hole 55 extends along a primary extension axis O P extends.

[0078] Referring to Figure 6 , in the longitudinal axial plane defined by the longitudinal axis A and the radial direction that is orthogonal to the longitudinal axis A and intersects the primary extension axis O P , the angle α is defined by the projection of the primary extension axis O P on the longitudinal axial plane A-R and the radial direction R. The angle α is measured from the radial direction R to the projection of the primary extension axis O P in the direction of the hot gas flow D. Preferably, the angle α of the primary cooling holes 55 is included between 70° and 110°.

[0079] Referring to Figure 5 , in the tangential plane defined by the longitudinal axis A and the circumferential direction C, the angle θ is defined by the projection of the primary extension axis O P on the circumferential plane A-C and the axial direction A, the circumferential direction C being orthogonal to the longitudinal axis A and orthogonal to the radial direction R (which is in turn orthogonal to the longitudinal axis A).

[0080] The angle θ is measured in the clockwise direction looking radially inwards from the axial direction A to the projection of the primary extension axis O P on the tangential plane A-C. Preferably, the angle θ is included between 100° and 200°.

[0081] Preferably, the primary cooling holes 55 have different angles α and / or different angles θ.

[0082] According to a variant, the primary cooling holes can be substantially identical to each other.

[0083] Referring to Figure 3 , Figure 4 and Figure 6 , the front wall 34 is provided with an annular front radial face 56 and an annular front axial face 57.

[0084] Preferably, the annular front axial face 57 of the front wall 34 is recessed with a radius of curvature r4.

[0085] Particularly referring to Figure 6 , the front boundary 54a includes at least one surface 61 facing the primary radial gap 48 and at least one surface 60 facing the airfoil 38. In other words, in use, the surface 61 faces the cavity 27a between the front components, and the surface 60 faces the hot gas passage 18.

[0086] Preferably, surfaces 60 and 61 are curved.

[0087] Preferably, surfaces 60 and 61 are continuous.

[0088] Preferably, surface 60 has a radius of curvature r1 and is convex.

[0089] Preferably, surface 61 has a radius of curvature r2 and is also convex.

[0090] The stator assembly 22 further includes a connecting surface 65 that connects the platform 42 and the front surface 50. Preferably, the connecting surface 65 is concave with a third radius of curvature r3.

[0091] According to a variant not shown, the connecting surface is not circular and has a triangular cross-section in the longitudinal axial plane.

[0092] Preferably, the radius of curvature r1 of surface 60 is between 5% and 40% of the distance h between the outer axial surface 59 of the platform and the lower point T of the annular front axial face 57.

[0093] Preferably, the radius of curvature r2 of surface 61 is between 10% and 50% of the distance h between the outer axial surface 59 of the platform and the lower point T of the annular front axial face 57.

[0094] Preferably, the radius of curvature r3 of the connecting surface 65 is between 20% and 40% of the distance h between the outer axial surface 59 of the platform and the lower point T of the annular front axial face 57.

[0095] Preferably, the radius of curvature r4 of the annular front axial face 57 is between 45% and 60% of the distance h between the outer axial surface 59 of the platform and the lower point T of the annular front axial face 57.

[0096] Preferably, the axial distance s between the outermost point P of the front boundary 54a and the outermost point Q of the annular front axial face 57 is between -50% and +50% of the axial length L of the cavity 27a between the front components ( Figure 2 ).

[0097] Preferably, the front surface 50 has a planar and radially arranged portion arranged radially inwards. At the same time, the portion of the front surface 50 arranged radially outside the primary cooling holes 55 and connected to the connecting surface 65 is tangent to the connecting surface 65.

[0098] In use, the hot gas flowing in the hot gas passage 18 is ingested at the front and flows into the primary radial gap 48. In particular, the hot gas ingestion flow is first deflected by the front boundary 54a and then forced to recirculate inside the primary radial gap 48, generating a vortex.

[0099] By exciting the eddy current recirculation and utilizing the pumping effect on the rotor side, the primary cooling holes 55 cool the hot gas ingestion flow and push it back outside the cavity 27a between the components. The secondary cooling openings 36 in the front wall 34 also provide a film cooling effect on the upper edge of the stator ring 24.

[0100] Finally, it is obvious that modifications and variations can be made to the stator assembly and the gas turbine described herein without departing from the scope of the invention as defined in the appended claims.

Claims

1. A stator assembly (22) for a gas turbine, said stator assembly (22) comprising: a stator ring (24) extending around a longitudinal axis (A) and including an outer edge (29) provided with an annular groove (30); said annular groove (30) defining a front wall (34) and a rear wall (35); said front wall (34) being provided with an annular front radial surface (56) and an annular front axial surface (57); a plurality of stator vanes (25) radially arranged and connected side by side to the outer edge (29) of said stator ring (24) so as to enclose said annular groove (30) and define an annular cooling channel (32); each stator vane (25) including an airfoil (38), an outer shroud (39) and an inner shroud (40) connected to said stator ring (24); said inner shroud (40) including a platform (42), a front flange (43) and a rear flange (44) extending radially inwards from said platform (42); said front flange (43) being connected to said front wall (34) and said rear flange (44) being connected to said rear wall (35); said front flange (43) being connected to said front wall (34) so as to leave a primary radial gap (48) between said front wall (34) and said platform (42) and define a front surface (50) of said front flange (43); said platform (42) having a front boundary (54a) and a rear boundary (54b), both extending circumferentially; said front boundary (54a) including at least one first surface (61) facing said primary radial gap (48); said first surface (61) being curved; wherein said front flange (43) is provided with at least one primary cooling hole (55) in said front surface (50) in fluid communication with said annular cooling channel (32).

2. The stator assembly according to claim 1, wherein, said first surface (61) is convex.

3. The stator assembly according to claim 2, wherein, said first surface (61) is curved with a first radius of curvature (r2).

4. The stator assembly according to claim 3, wherein, the radius of curvature (r2) of said first surface (61) is between 10% and 50% of the distance (h) between the outer axial surface (59) of said platform (42) and the lower point (T) of said annular front axial surface (57).

5. The stator assembly according to claim 1, wherein, said front boundary (54a) includes a second surface (60) facing said airfoil (38), which is curved.

6. The stator assembly according to claim 5, wherein, said second surface (60) is convex.

7. The stator assembly according to claim 6, wherein, said second surface (60) is curved with a second radius of curvature (r1).

8. The stator assembly according to claim 1, wherein, The stator assembly includes a connection surface (65) that connects the platform (42) and the front surface (50); the connection surface (65) is recessed with a third radius of curvature (r3).

9. The stator assembly according to claim 1, wherein, the annular front axial surface (57) of the front wall (34) is recessed with a fourth radius of curvature (r4).

10. The stator assembly according to claim 1, wherein, the front flange (43) is provided with a plurality of primary cooling holes (55) that are circumferentially aligned on the front surface (50).

11. The stator assembly according to claim 10, wherein, the primary cooling holes (55) are evenly distributed.

12. The stator assembly according to claim 9, wherein, The primary cooling holes (55) extend along a primary extension axis (O P ) ; in a longitudinal axial plane (A-R) defined by the longitudinal axis (A) and a radial direction (R) orthogonal to the longitudinal axis (A) and intersecting the primary extension axis (O P ), a first angle (α) defined by the projection of the primary extension axis (O P ) on the longitudinal axial plane (A-R) and the radial direction (R) is between 70° and 110°.

13. The stator assembly according to claim 9, wherein, The primary cooling holes (55) extend along a primary extension axis (O P );in the circumferential plane defined by the longitudinal axis (A) and the circumferential direction (C), a second angle (θ) defined by the projection of the primary extension axis (O P ) in the circumferential plane and the axial direction is between 100° and 200°, the circumferential direction (C) is orthogonal to the longitudinal axis (A) and orthogonal to the radial direction (R), and the radial direction (R) is in turn orthogonal to the longitudinal axis (A).

14. A gas turbine that extends along a longitudinal axis (A) and comprises: a plurality of rotor assemblies (11), each of the plurality of rotor assemblies (11) includes a rotor disk (15) and a plurality of rotor blades (16) that are radially arranged and connected to the rotor disk (15); a plurality of stator assemblies (22); the stator assemblies (22) and the rotor assemblies (11) are alternately arranged in the axial direction; at least one of the stator assemblies (22) is the stator assembly according to claim 1.

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