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

Abstract

A stator assembly (22) for a gas turbine comprising and provided with: • a stator ring (24) extending around a longitudinal axis (A) and comprising an inner edge and an outer edge (29); the outer edge is provided with an annular recess (30); the annular recess (30) defines a front wall (34) and a rear wall (35); the rear wall (34) is provided with an annular rear radial face (36a) and an annular rear axial face (36b); • a plurality of stator vanes (25) radially arranged and coupled side by side to the outer edge (29) of the stator ring (24) so as to close the annular recess (30) and define an annular cooling channel (32); the stator ring (24) is provided with at least one rear cooling hole (39) having an inlet (40) facing the annular cooling channel (32) and an outlet (41) arranged on the annular rear radial face (36b).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority from European patent application number 19425077.5 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 invention is part of an apparatus for generating electrical energy. Background Art

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

[0005] Specifically, a compressor includes an inlet supplied with air and a plurality of rotating blades that compress the passing air. The compressed air exiting the compressor flows into a plenum (i.e., an enclosed volume defined by a casing), and from there into a combustor. Inside the combustor, the compressed air is mixed with at least one fuel and combusted. The resulting hot gases exit the combustion chamber and expand in a turbine. In the turbine, the hot gas expansion moves rotating blades connected to a rotor, producing work.

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

[0007] Each rotor assembly includes a rotor disk that rotates about a main axis and a plurality of blades supported by the rotor disk.

[0008] Each stator assembly includes a plurality of stator vanes supported by corresponding vane carriers and a stator ring disposed around the rotor.

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

[0010] In turbines, seal air is typically bled from the compressor and introduced into the inter-component cavity in order to avoid or limit the ingestion of hot gases from the hot gas path in the inter-component cavity.

[0011] Minimizing the amount of air used to seal and cool the cavity between components is beneficial to the performance of the power device. However, such minimization means using expensive advanced materials and / or employing arrangements with very complex geometries. Summary of the Invention

[0012] It is therefore an object of the present invention to provide a stator assembly for a gas turbine which makes it possible to avoid or at least alleviate the described disadvantages.

[0013] In particular, the present invention aims to provide a stator assembly with an improved structure that can minimize the amount of sealing air while maintaining the thermal conditions of the stator and rotor parts.

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

[0015] • a stator ring extending about a longitudinal axis and comprising an inner edge and an outer edge; the outer edge being provided with an annular groove; the annular groove defining a front wall and a rear wall; the rear wall being provided with an annular rear radial face and an annular rear axial face;

[0016] • a plurality of stator guide vanes arranged radially and coupled to the outer edge of the stator ring alongside one another so as to close the annular groove and define an annular cooling channel;

[0017] • The stator ring is provided with at least one rear cooling hole having an inlet facing the annular cooling channel and an outlet arranged on the annular rear radial face.

[0018] Advantageously, the presence of the aft cooling holes creates a sealing flow in the cavity between the aft components that interacts with the hot air flow originating from the intake.

[0019] According to a variant of the invention, each stator vane comprises an inner shroud coupled to a stator ring, an outer shroud and an airfoil; the inner shroud comprising a platform.

[0020] Preferably, the radial distance between the center of the outlet of the aftercooling hole and the inner edge of the stator ring is included in the range of 0.45·DP to 0.75·DP, where DP is the radial distance between the outer face of the platform and the inner edge of the stator ring.

[0021] According to a variant of the invention, the rear cooling hole extends along the extension axis; on a longitudinal axial plane defined by the longitudinal axis and a radial direction orthogonal to the longitudinal axis and intersecting the extension axis, a first angle defined by the projection of the extension axis on the longitudinal axial plane (AR) and the radial direction is included between 0° and 50°.

[0022] According to a variant of the invention, the rear cooling hole extends along the extension axis; on a tangential plane defined by the longitudinal axis and a circumferential direction, a second angle defined by the projection of the extension axis on the tangential plane and the axial direction is included between 20° and 70°, the circumferential direction being orthogonal to the longitudinal axis and to a radial direction which in turn is orthogonal to the longitudinal axis.

[0023] Due to the radial position and inclination of the aft cooling holes, the seal cooling air from the aft cooling holes is directed towards the inlet of the aft inter-assembly cavity.

[0024] In this manner, the heat flux ingested by the seal cooling air penetration from the rear cooling holes facilitates more adequate sealing / cooling of the rear inter-component cavity.

[0025] According to a variant of the invention, the inlet of the aftercooling hole has a diameter comprised between 1 mm and 5 mm.

[0026] According to a variant of the invention, the aftercooling holes have a constant cross section.

[0027] According to a variant of the invention, the stator ring is provided with a plurality of aftercooling holes.

[0028] According to a variant of the present invention, the outlets of the plurality of rear cooling holes are evenly distributed along the annular rear radial surface.

[0029] According to a variant of the invention, the number of aftercooling holes is comprised in the range of 0.5·NV-2·NV; wherein NV is the number of stator vanes of the stator assembly.

[0030] According to a variation of the present invention, the inner shroud includes a front flange and a rear flange, both extending 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 rear flange is connected to the rear wall so as to leave a rear radial gap between the rear wall and the platform and define a rear surface of the rear flange facing the rear radial gap.

[0031] According to a variant of the invention, the rear flange is provided on the rear surface with at least one secondary cooling hole in fluid communication with the annular cooling channel.

[0032] According to a variant of the invention, the rear flange is provided on the rear surface with a plurality of secondary cooling holes aligned in the circumferential direction.

[0033] According to a variant of the invention, the secondary cooling holes are evenly distributed.

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

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

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

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

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

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

[0040] Figure 2 yes Figure 1 a schematic cross-sectional front view of a first detail of , with parts removed for clarity;

[0041] Figure 3 yes Figure 1 a schematic perspective view of a second detail of , with parts cut away and parts removed for clarity;

[0042] Figure 4 yes Figure 3 different schematic perspective views of a second detail of;

[0043] Figure 5 yes Figure 1 a schematic cross-sectional side view of a third detail of FIG, with parts removed for clarity;

[0044] Figure 6 yes Figure 4 Schematic perspective view of a fourth detail of FIG, with parts cut away and parts removed for the sake of clarity. DETAILED DESCRIPTION

[0045] Figure 1 In the figure, reference numeral 1 indicates a gas turbine electric power plant (in Figure 1 Schematically shown in FIG).

[0046] The plant 1 comprises a compressor 3, a combustion chamber 4, a gas turbine 5 and a generator (not shown in the drawings for the sake of 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 housed in a stator housing 9 and extends along an axis A.

[0048] In more detail, 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 coupled to the rotor disk 15 and arranged in the radial direction.

[0050] A plurality of rotor discs 15 are arranged in series between the front axle 10 and the rear axle 13 and are preferably clamped in groups by a central tie rod 14. Alternatively, the rotor discs may be welded together.

[0051] A 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] Furthermore, stator assemblies 22 alternate with compressor rotor assemblies 11 .

[0053] Each stator assembly 22 includes a stator ring 24 and a plurality of stator vanes 25 arranged in a radial direction and coupled to the stator ring 24 and the corresponding stator case 9 .

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

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

[0056] An inter-assembly cavity 27 is disposed between the rotor assembly 11 and the stator assembly 22 .

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

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

[0059] A plurality of stator vanes 25 are coupled to an outer edge 29 of the stator ring 24 alongside one another so as to close an annular groove 30 and define an annular cooling channel 32 .

[0060] The annular cooling channel 32 is supplied with air, which preferably comes 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] The rear wall 35 is further provided with an annular rear radial face 36a and an annular rear axial face 36b.

[0063] Preferably, the front wall 34 is provided with a plurality of front cooling holes 37 in fluid communication with the annular cooling passage 32 .

[0064] Preferably, the cooling openings 37 are arranged near the inner edge 28 .

[0065] In the non-limiting example disclosed and illustrated herein, the cooling openings 37 are circumferentially aligned and evenly distributed.

[0066] The rear wall 35 is provided with at least one rear cooling hole 39 , which is in fluid communication with the annular cooling passage 32 .

[0067] In more detail, each aft cooling hole 39 passes through the aft wall 35 and has an inlet 40 facing the annular cooling channel 32 and an outlet 41 arranged on the annular aft radial face 36a and, in use, facing the aft inter-assembly cavity 27b.

[0068] Each stator vane 25 includes an inner shroud 44 , an outer shroud 43 , and an airfoil 42 coupled to the stator ring 24 .

[0069] The airfoils 42 are provided with cooling air ducts 45 a which are fed by dedicated openings 45 b in the outer shroud 43 .

[0070] The outer shrouds 43 are coupled to the corresponding stator cases 9 .

[0071] The inner shroud 44 includes a platform 46, an aft flange 49 extending radially inward from the platform 46, and a forward flange 48. The forward flange 48 is upstream of the aft flange 49 in the direction D of hot gas flow.

[0072] Front flange 48 is coupled to front wall 34 , while rear flange 49 is coupled to rear wall 35 .

[0073] In the non-limiting example disclosed and illustrated herein, the front flange 48 engages a corresponding annular seat 50 of the front wall 34 , while the rear flange 49 engages a corresponding annular seat 51 of the rear wall 35 .

[0074] Reference Figure 5 The front flange 48 is coupled to the front wall 34 so as to leave a front radial gap 53 between the front wall 34 and the platform 46 and to define a front surface 54 of the front flange 48 facing the front radial gap 53 .

[0075] The rear flange 49 is coupled to the rear wall 35 so as to leave a rear radial gap 55 between the rear wall 35 and the platform 46 and to define a rear surface 56 of the rear flange 49 facing the rear radial gap 55 .

[0076] The forward flange 48 defines at least one primary cooling hole 60 on the forward surface 54 in fluid communication with the annular cooling passage 32 .

[0077] Preferably, the forward flange 48 is provided with a plurality of primary cooling holes 60 aligned circumferentially on the forward surface 54 .

[0078] The aft flange 49 defines at least one secondary cooling hole 61 on the aft surface 56 in fluid communication with the annular cooling passage 32 .

[0079] Preferably, the aft flange 49 is provided with a plurality of secondary cooling holes 61 aligned along the circumferential direction on the aft surface 56 .

[0080] In the non-limiting example disclosed and illustrated herein, the secondary cooling holes 61 are evenly distributed.

[0081] According to the non-limiting embodiment disclosed and illustrated herein, the secondary cooling holes 61 have a smaller passage cross-section than the passage cross-section of the primary cooling holes 60 .

[0082] Reference Figure 3 and Figure 4 The stator assembly 22 preferably includes a plurality of rear cooling holes 39 that are evenly distributed and preferably circumferentially aligned on the annular rear radial face 36a.

[0083] Preferably, the number of the aftercooling holes 39 is comprised in the range of 0.5·NV−2·NV; where NV is the number of stator vanes 25 of the stator assembly 22 .

[0084] In particular, a distance DH between the center of the outlet 41 of the cooling hole 39 and the inner edge 28 of the stator ring 24 is included in the range of 0.45*(DP) to 0.75*(DP), where DP is the radial distance between the outer face 46 a of the platform 46 and the inner edge 28 of the stator ring 24 .

[0085] Reference Figure 6 , the inlet 40 of the aftercooling hole 39 preferably has a diameter d comprised between 1 mm and 5 mm.

[0086] Preferably, the aftercooling holes 39 have a constant cross-section.

[0087] The aftercooling holes 39 extend along an extension axis O; on a tangential plane defined by the longitudinal axis A and a circumferential direction C, which is orthogonal to the longitudinal axis A and to a radial direction R which in turn is orthogonal to the longitudinal axis A, a first angle α defined by the projection of the extension axis O on the tangential plane AC and the axial direction is comprised between 0° and 50°. The angle α is measured in the counterclockwise direction (seen in the tangential direction with the compressor side on the left) from the projection of the extension axis O in the axial direction A.

[0088] On a longitudinal axial plane AR defined by the longitudinal axis A and a radial direction R perpendicular to the longitudinal axis A and intersecting the extension axis O, a second angle β is defined by a projection of the extension axis on the longitudinal axial plane AR and the axial direction A.

[0089] Preferably, the aftercooling holes 39 have a tangential inclination (defined by an angle β) that coincides with the direction of rotation of the machine W (counterclockwise about the axis A, viewed from the compressor side).

[0090] Said second angle β is preferably comprised between 20° and 70°.

[0091] The angle β is measured from the projection of the axial direction A to the axis of extension O in the counterclockwise direction (seen in the tangential direction with the compressor side on the left).

[0092] In use, hot gas flowing in the hot gas path 18 is taken into the aft inter-assembly cavity 27b. However, due to the radial position and inclination of the aft cooling holes 39, the seal cooling air from the aft cooling holes 39 is directed towards the inlet of the aft inter-assembly cavity 27b.

[0093] In this manner, the heat flux ingested by the seal cooling air penetration from the rear cooling holes 39 facilitates more adequate sealing / cooling of the rear inter-assembly cavity 27b.

[0094] In particular, as the seal cooling air from the aft cooling holes 39 swirls in the rotational direction, the tangential velocity difference between the inlet hot gas and the seal cooling air flow decreases; this results in reduced shear stress between the two interacting flows and promotes penetration of the seal cooling air into the hot gas.

[0095] In this way, in the rear inter-assembly cavity 27b, the flow resulting from the interaction between the hot gas intake flow and the seal cooling air flow exhibits a more uniform swirl number distribution, which ensures significantly improved sealing / cooling capabilities.

[0096] In this way, the claimed solution allows improving the sealing efficiency and thermal conditions of the rear inter-assembly cavity 27b and thus significantly reducing the total amount of sealing air used to seal the rear inter-assembly cavity 27b, with a consequent improvement in engine performance.

[0097] Finally, it is evident that modifications and variations may be made to the stator assembly and to the gas turbine described herein without departing from the scope of the present invention as defined in the appended claims.

Claims

1. A stator assembly (22) for a gas turbine, the stator assembly (22) comprising: a stator ring (24) extending about a longitudinal axis and comprising an inner edge and an outer edge (29); the outer edge being provided with an annular groove (30); the annular groove (30) defining a front wall (34) and a rear wall (35); the rear wall (35) being provided with an annular rear radial face (36a) and an annular rear axial face (36b); a plurality of stator guide vanes (25) arranged radially and coupled to the outer edge (29) of the stator ring (24) side by side so as to close the annular groove (30) and define an annular cooling channel (32); The stator ring (24) is provided with at least one rear cooling hole (39), the at least one rear cooling hole (39) having an inlet (40) facing the annular cooling channel (32) and an outlet (41) arranged on the annular rear radial face (36a); wherein each stator vane (25) includes an inner shroud (44), an outer shroud (43), and an airfoil (38) coupled to the stator ring (24); the inner shroud (44) includes a platform (46); wherein the inner shroud (44) includes a front flange (48) and a rear flange (49), both extending radially inward from the platform (46); the front flange (48) is coupled to the front wall (34) and the rear flange (49) is coupled to the rear wall (35); the rear flange (49) is coupled to the rear wall (35) so as to leave a rear radial gap (55) between the rear wall (35) and the platform (46) and define a rear surface (56) of the rear flange (49) facing the rear radial gap (55); The rear flange (49) is provided with at least one secondary cooling hole (61) on the rear surface (56) in fluid communication with the annular cooling channel (32).

2. The stator assembly according to claim 1, characterized in that A radial distance (DH) between the center of the outlet (41) of the aftercooling hole (39) and the inner edge (28) of the stator ring (24) is in the range of 0.45·DP to 0.75·DP, where DP is the radial distance between the outer surface (46a) of the platform (46) and the inner edge (28) of the stator ring (24).

3. The stator assembly according to claim 1, characterized in that The rear cooling hole (39) extends along an extension axis (O); on a tangential plane (AC) defined by the longitudinal axis and a circumferential direction (C), a first angle (α) is defined by a projection of the extension axis (O) on the tangential plane (AC) and the axial direction (A) and is between 0° and 50°, the circumferential direction (C) being orthogonal to the longitudinal axis and to a radial direction (R), which in turn is orthogonal to the longitudinal axis.

4. The stator assembly according to claim 1, characterized in that The rear cooling hole (39) extends along an extension axis (O); on a longitudinal axial plane (AR) defined by the longitudinal axis and a radial direction (R) orthogonal to the longitudinal axis and intersecting the extension axis (O), a second angle (β) is defined by a projection of the extension axis (O) on the longitudinal axial plane (AR) and the axial direction (A) and is between 20° and 70°.

5. The stator assembly according to claim 1, characterized in that The inlet (40) of the aftercooling hole (39) has a diameter (d) between 1 mm and 5 mm.

6. The stator assembly according to claim 1, characterized in that The aftercooling hole (39) has a constant cross section.

7. The stator assembly according to claim 1, characterized in that The stator ring (24) is provided with a plurality of after-cooling holes (39).

8. The stator assembly according to claim 4, characterized in that The outlets of the plurality of rear cooling holes (39) are evenly distributed along the annular rear radial surface (36a).

9. The stator assembly according to claim 7, characterized in that The number of the aftercooling holes (39) is in the range of 0.5·NV-2·NV; wherein NV is the number of stator guide vanes of the stator assembly (22).

10. The stator assembly according to claim 1, wherein: The rear flange (49) is provided with a plurality of secondary cooling holes (61) aligned in a circumferential direction on the rear surface (56).

11. The stator assembly according to claim 10, characterized in that The secondary cooling holes (61) are evenly distributed.

12. A gas turbine extending along a longitudinal axis and comprising: a plurality of rotor assemblies (11), each of the plurality of rotor assemblies (11) including a rotor disk (15) and a plurality of rotor blades (16) arranged radially and coupled to the rotor disk (15); A plurality of stator assemblies (22); the stator assemblies (22) and the rotor assemblies (11) are alternated along an axial direction (A); At least one of the stator assemblies (22) includes: a stator ring (24) extending about a longitudinal axis and comprising an inner edge and an outer edge (29); the outer edge being provided with an annular groove (30); the annular groove (30) defining a front wall (34) and a rear wall (35); the rear wall (35) being provided with an annular rear radial face (36a) and an annular rear axial face (36b); a plurality of stator guide vanes (25) arranged radially and coupled to the outer edge (29) of the stator ring (24) side by side so as to close the annular groove (30) and define an annular cooling channel (32); The stator ring (24) is provided with at least one rear cooling hole (39), the at least one rear cooling hole (39) having an inlet (40) facing the annular cooling channel (32) and an outlet (41) arranged on the annular rear radial face (36a); wherein each stator vane (25) includes an inner shroud (44), an outer shroud (43), and an airfoil (38) coupled to the stator ring (24); the inner shroud (44) includes a platform (46); wherein the inner shroud (44) includes a front flange (48) and a rear flange (49), both extending radially inward from the platform (46); the front flange (48) is coupled to the front wall (34) and the rear flange (49) is coupled to the rear wall (35); the rear flange (49) is coupled to the rear wall (35) so as to leave a rear radial gap (55) between the rear wall (35) and the platform (46) and define a rear surface (56) of the rear flange (49) facing the rear radial gap (55); The rear flange (49) is provided with at least one secondary cooling hole (61) on the rear surface (56) in fluid communication with the annular cooling channel (32).

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