FLOW BODY FOR A GAS TURBINE, GAS TURBINE, METHOD FOR MANUFACTURING A FLOW BODY FOR A GAS TURBINE, AND METHOD FOR REPAIRING A FLOW BODY OF A GAS TURBINE

Abstract

A flow body for a gas turbine includes an airfoil extending along a radial direction between a platform end and a tip which has a tip surface. The airfoil is formed of a first metal material and comprises an inner cavity for receiving a gaseous cooling fluid. The flow body further includes a squealer tip protruding from the tip surface. The squealer tip is formed from a second metal material and includes an internal cooling structure which is in fluid communication with the inner cavity. The squealer tip is joined to a contact surface of the tip by a transition layer that connects the contact surface and a remaining portion of the squealer tip. The transition layer, compared to at least one of the remaining portion of the squealer tip and the airfoil, has one of a reduced stiffness and an increased ductility in combination with reduced yield strength.

Claims

1. A flow body for a gas turbine, comprising: an airfoil extending along a radial direction between a platform end and a tip which has a tip surface, the airfoil being formed of a first metal material and comprising an inner cavity for receiving a gaseous cooling fluid; and a squealer tip protruding from the tip surface of the tip and extending along a circumference of the tip so that the squealer tip at least partially surrounds the tip surface, wherein the squealer tip is formed from a second metal material and includes an internal cooling structure which is in fluid communication with the inner cavity via one or more fluid passages; wherein the squealer tip is material bonded to a contact surface of the tip of the airfoil by a transition layer that connects the contact surface and a main portion of the squealer tip, the contact surface at least partially surrounding the tip surface of the tip, and wherein the transition layer, compared to at least one of the main portion of the squealer tip and the airfoil, has at least one of a reduced stiffness and an increased ductility in combination with reduced yield strength.

2. The flow body of claim 1, wherein the first metal material is a cast metal material.

3. The flow body of claim 1, wherein the second metal material is a metal material deposited in an additive manufacturing process.

4. The flow body of claim 1, wherein the transition layer is made of the second metal material, wherein a porosity of the second metal material is increased within the transition layer compared to the main portion of the squealier tip.

5. The flow body of claim 4, wherein the porosity varies within the transition layer between the contact surface of the tip of the airfoil and the main portion of the squealer tip.

6. The flow body of claim 5, wherein the transition layer is made of a third metal material comprising an increased ductility and reduced yield strength compared to the first and the second metal material.

7. The flow body of claim 6, wherein the internal cooling structure of the squealer tip includes a plurality of internal cooling cavities that are separated from each other within the squealer tip, wherein each of the internal cooling cavities is fluid communication with the inner cavity of the airfoil via the one or more fluid passages.

8. The flow body of claim 7, wherein the internal cooling cavities of the squealer tip are spaced from each other along the circumference of the tip.

9. The flow body of claim 8, wherein the one or more fluid passages connecting at least some of the internal cooling cavities of the squealer tip to the inner cavity of the airfoil are formed as cooling holes that are inclined such that a central axis of the respective cooling hole intersects a lateral inner surface of the respective internal cooling cavity.

10. A gas turbine comprising a flow body of claim 1.

11. The gas turbine of claim 10, wherein the flow body forms a rotating blade or a stator vane.

12. A method for manufacturing a flow body for a gas turbine according to claim 1, the method comprising: casting the airfoil from the first metal material with the inner cavity, the tip surface and the contact surface; forming a plurality of fluid passages between the inner cavity and the contact surface of the tip; and building the squealer tip from the second metal material and the transition layer on the contact surface of the tip by means of an additive manufacturing process, such that the internal cooling structure is formed and is in fluid communication with the inner cavity via the one or more of the plurality of fluid passages and such that the transition layer material bonds the main portion of the squealer tip to the tip of the airfoil.

13. The method of claim 12, wherein the contact surface extends inclined relative to the tip surface.

14. The method of claim 12, wherein the additive manufacturing process of building the squealer tip includes selective laser melting, direct metal deposition, or electron beam welding.

15. A method for repairing a flow body of a gas turbine, the flow body comprising an airfoil extending along a radial direction between a platform end and a tip which has a tip surface, and a squealer tip protruding from the tip surface and extending along a circumference of the tip so that the squealer tip at least partially surrounds the tip surface, wherein the airfoil includes an inner cavity for receiving a gaseous cooling fluid, and wherein the squealer tip includes a cooling system in fluid communication with the inner cavity of the airfoil via a plurality of fluid passages, the method comprising: removing the squealer tip from the airfoil in a subtractive process, forming a contact surface that at least partially surrounds the tip surface of the tip of the airfoil; and building a new squealer tip and a transition layer on the contact surface of the tip by means of an additive manufacturing process, such that the new squealer tip includes an internal cooling structure in fluid communication with the inner cavity via the one or more of the plurality of fluid passages and such that the transition layer material bonds a main portion of the squealer tip to the tip of the airfoil, wherein the transition layer, compared to at least one of the main portion of the squealer tip and the airfoil, has at least one of a reduced stiffness and an increased ductility in combination with reduced yield strength.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings. The invention is explained in more detail below using exemplary embodiments, which are specified in the schematic figures of the drawings, in which:

[0041] FIG. 1 schematically illustrates a cross-sectional view of a gas turbine according to an embodiment of the invention.

[0042] FIG. 2 schematically illustrates a side view of a flow body according to an embodiment of the invention.

[0043] FIG. 3 schematically illustrates a front view towards a leading edge of the flow body of FIG. 2.

[0044] FIG. 4 schematically illustrates a partial cross-sectional view of the flow body of FIG. 2 taken along line X2-X2 shown in FIG. 2.

[0045] FIG. 5 schematically illustrates a partial cross-sectional view of the flow body of FIG. 2 taken along line X3-X3 shown in FIG. 3.

[0046] FIG. 6 schematically illustrates a partial cross-sectional view of a flow body in the region of the tip of an airfoil and a squealer tip according to an embodiment of the invention.

[0047] FIG. 7 schematically illustrates a partial cross-sectional view of a flow body in the region of the tip of an airfoil and a squealer tip according to a further embodiment of the invention.

[0048] FIG. 8 shows a schematic cross-sectional view of the squealer tip of the flow body of FIG. 7 taken along line X7-X7 in FIG. 7.

[0049] FIG. 9 schematically illustrates a partial cross-sectional view of an internal cooling cavity of a squealer tip of a flow body according to an embodiment of the invention.

[0050] FIG. 10 illustrates a perspective view of a partial cross-sectional representation of a flow body according to a further embodiment of the invention.

[0051] FIG. 11 schematically illustrates a partial cross-sectional view of a flow body in the region of the tip of an airfoil and a squealer tip according to an embodiment of the invention.

[0052] FIG. 12 illustrates a flowchart of a method for manufacturing a flow body of a turbine according to an embodiment of the invention.

[0053] FIG. 13 illustrates a flowchart of a method for repairing a flow body of a turbine according to an embodiment of the invention.

[0054] In the figures like reference signs denote like elements unless stated otherwise.

DETAILED DESCRIPTION

[0055] FIG. 1 schematically shows a gas turbine 300. The gas turbine 300 includes a compressor 310, a burner or combustor 320, and a turbine 330. The turbine 330 and the compressor 310 may be mechanically integrated to form a rotor 350 which is rotatable about a common rotational axis A350.

[0056] The compressor 310 of the gas turbine 300 may draw air as a working fluid from the environment and compress the drawn air. The compressor 310 may be realized as centrifugal compressor or an axial compressor. FIG. 1 exemplarily shows a multistage axial compressor which is configured for high mass flows of air. The axial compressor may include multiple rotor disks, each carrying a plurality of blades. The rotor disks (not shown) are coupled to each other so as to be rotatable together about the rotational axis A350. Compressor vanes 313 are arranged downstream of the blades 312. The blades 312 compress the introduced air and deliver the compressed air to the compressor vanes 313 disposed adjacently downstream. The plurality of compressor vanes 313 guide the compressed air flowing from compressor blades 312 disposed upstream to compressor blades 312 disposed at a following, downstream stage. The air is compressed gradually to a high pressure while passing through the stages of compressor blades 312 and vanes 313.

[0057] The compressed air is supplied to the combustor 320 for combustion of a fuel, such as natural gas, hydrogen, diesel, kerosene, ethanol or similar. Further, a part of the compressed air is supplied as a gaseous cooling fluid to high-temperature regions of the gas turbine 300 for cooling purposes. The burner or combustor 320, by use of the compressed air, burns fuel to heat the compressed air.

[0058] As schematically shown in FIG. 1, the turbine 330 includes a plurality of blade assemblies, each comprising a rotor disk to which a plurality of turbine blades 336 are coupled. The turbine 330 further includes a plurality of turbine vanes 335. Generally, the rotor disks are coupled to each other so as to be rotatable together about the rotational axis A350. For example, the rotor disks of the turbine and the rotor disks of the compressor may be fastened together by means of a central element such as a bolt to form the rotor 350. The turbine blades 336 are coupled to the respective rotor disk and extend radially therefrom. The turbine vanes 335 are positioned upstream of the blades 336 of the respective rotor disks 210. The turbine vanes 335 are fixed in a stator frame so that they do not rotate about the rotational axis and guide the flow of combustion gas coming from the burner 320 passing through the turbine blades 336. The combustion gas is expanded in the turbine 330 and gas applies a force to the turbine blades 336 which causes the rotor 350 to rotate about the rotational axis A350. The compressor 310 may be driven by a portion of the power output from the turbine 330.

[0059] Generally, a blade 312 or 336 and a vane 313, 335 of the gas turbine 300 are referred to in the following as flow body 100.

[0060] FIG. 2 exemplarily and schematically shows a flow body 100 in the form of a turbine blade 336. However, the invention is not limited to a blade 336 of a turbine part 330 but may also be employed in a vane of the turbine part 330, or a blade 312 or a vane 313 of the compressor part 313. FIG. 3 shows a front view of the flow body of FIG. 2. FIGS. 4 and 5 show partial sectional views of the flow body 100.

[0061] As shown in FIGS. 2 and 3, the flow body 100 includes an airfoil 1 and a squealer tip 2, and, optionally, may further include a platform 4 and a root 5.

[0062] The airfoil 1 extends along radial or span direction R between a platform end 11 and a tip 12. With regard to an axial or chord direction A, that extends transverse to the radial direction, the airfoil 1 may extend between a leading edge 13 and a trailing edge 14. An outer surface of the airfoil 1, between the leading edge 13 and the trailing edge 14, may define a pressure side surface 1p and a suction side surface 1s being oriented opposite to the pressure side surface 1p. The pressure side surface 1p and the suction side surface 1s meet at the leading edge 13 and at the trailing edge 14.

[0063] As schematically shown in FIGS. 2 and 3, the platform 4 may be a substantially plate shaped structure having an expanse with respect to the axial direction A and with respect to a circumferential direction C. The circumferential direction C extends transverse to the axial direction A and to the radial direction R. The platform 4 is coupled to the platform end 11 of the airfoil 1 and may protrude from the airfoil 1 with respect to the circumferential direction C.

[0064] The outer surface 1a of the airfoil 1, in particular, the pressure side surface 1p and the suction side surface 1s, each may be connected to an upper surface of the platform 4 via a transition surface 4t. As exemplarily shown in FIG. 3, the transition surface 4t may be a concave curved surface.

[0065] The root 5 is connected to the platform 4, in particular, to a lower surface of the platform 4 and protrudes from the lower surface of the platform 4 along the radial direction R. As exemplarily shown in FIG. 3, the root 5 may include a firtree shaped cross-section. Generally, coupling interfaces of the rotor disk or coupling interfaces of the stator frame of the gas turbine 300 and the roots 5 of the flow bodies 100 may have complementary cross-sections.

[0066] As shown in FIGS. 2 and 3 in dashed lines and as further visible in the cross-sectional views of FIGS. 4 and 5, the flow body 100, in particular, the airfoil 1, comprises an inner cavity or void 10. The inner cavity 10 is limited by an inner surface 10i of flow body 100 and serves as a reservoir for receiving a gaseous cooling fluid, e.g., compressed air bleed from the compressor 310. As shown in FIGS. 2 and 3, the inner cavity 10 may extend within the airfoil 1 from the platform end 11 towards the tip 12 and, optionally, may also extend through the root 5 of the flow body 100.

[0067] As visible best in FIGS. 4 and 5, the tip 12 of the airfoil 1 has a tip surface 12a. The tip surface 12a extends transverse to the radial direction R and forms part of an outer surface of the airfoil 1. As shown in FIGS. 4 and 5, the tip surface 12a may be planar or substantially planar. However, the tip surface 12a may also be curved, e.g., with a concave or convex curvature. The tip surface 12a is surrounded along its circumference, at least partially, by a contact surface 12b. The contact surface 12b may be planar or substantially planar, as exemplarily shown in FIGS. 4 and 5. However, the contact surface 12b may also be curved, e.g., with a concave or convex curvature. The contact surface 12b may extend inclined relative to the tip surface 12a and, optionally, also with respect to the pressure side surface 1p and the suction side surface 1s. Generally, the contact surface 12b may be inclined relative to the radial direction, e.g., by an angle within a range between 30 degrees and 120 degrees, in particular, between 60 degrees and 95 degrees. As schematically shown in FIG. 4, a first surface angle between the contact surface 12b on the side of the suction side surface 1s and a center line LR of the airfoil 1 parallel to the radial direction R may be in a range between 60 degrees and 95 degrees. As further shown in FIG. 4, a second surface angle between the contact surface 12b on the side of the pressure side surface 1p and the line LR parallel to the radial direction R may be in a range between 60 degrees and 95 degrees. The first and second surface angles , may be equal to each other but they may also be different from each other. Further, it should be noted that the first and second surface angles , may vary along the circumference of the tip surface 12a.

[0068] As further shown in FIG. 4, a fluid passage 15, which may, for example, be formed as a drilled hole or a cast passage, extends between the inner cavity 10 of the airfoil 1 and the contact surface 12b of the tip 12 so that a gaseous fluid, such as compressed air, can be discharged from the inner cavity 10 through the fluid passage 15. Although FIG. 4 only shows one fluid passage 15, a plurality of fluid passages 15 may be distributed along the circumference of the tip surface 12a and extend between the contact surface 12b and the inner cavity 10.

[0069] The airfoil 1, the platform 4, and the root 5 may be integrally formed from a first metal material. In particular, the first metal material may be a cast metal material. For example, the first metal material may be a Nickel or Cobalt based high temperature alloy such as, for example, IN792SX, CM247LC, or similar.

[0070] The squealer tip 2 is material joined to the tip 12 of the airfoil 1, in particular, to the contact surface 12b of the tip 12 by a transition layer 3 (not shown in FIGS. 4 to 8 and 10 for reasons of simplifying the illustration), as will be explained in more detail below. As visible, for example, in FIGS. 4 and 5, the squealer tip 2 extends between a first end 21 and a second end 22 opposite to the first end 21. The first end 21 is joined to the contact surface 12b of the tip 12 of the airfoil 1. The second end 22 may comprise an end face 22a, facing away from the tip 12 of the airfoil 1. Between the first 21 and the second end 22, the squealer tip 2 may extend at least partially along the radial direction R. Generally, the squealer tip 2 protrudes from the tip surface 12a with respect to the radial direction. The squealer tip 2 may have a first lateral surface 2a facing towards the tip surface 12a of the tip 12, and a second lateral surface 2b being oriented opposite to the first lateral surface 12a. As shown in FIG. 4, the second lateral surface 2b may form a continuous surface with the outer surface of the airfoil 1, in particular, with the suction side surface 1s and the pressure side surface 1p.

[0071] Optionally, the squealer tip 2 may protrude over at least one of the suction side surface 1s and a pressure side surface 1p, in particular, with respect to the circumferential direction C, as exemplarily shown in FIGS. 4, 6, 7, 10, and 11. In this case, the second end 22 of the squealer tip 2 is spaced to the first end 21 of the squealer tip 2 in the circumferential direction C.

[0072] Further optionally, as schematically shown in FIGS. 4, 6, 7, 10, and 11, the second lateral surface 2b and the respective pressure side surface 1p or suction side surface 1s may be concave curved in a transition region from the second lateral surface 2b to the respective pressure side surface 1p or suction side surface 1s.

[0073] Generally, the first lateral surface 2a may extend substantially parallel to the second lateral surface 2b of the squealer tip 2, as exemplarily shown in FIGS. 6, 10, and 11. However, the invention is not limited thereto. For example, a distance between the first and second lateral surfaces 2a, 2b of the squealer tip 2 may also decrease towards the second end 22 of the squealer tip 2, so that a wedge shaped or narrowing cross-section may be realized, as exemplarily and schematically shown in FIG. 7.

[0074] The squealer tip 2 may be formed along the total circumference of the airfoil 1, i.e., on both the pressure side and the suction side over the total length between the leading edge 13 and the trailing edge 14, or only about a part of the circumference. Generally, the squealer tip 2 extends along a circumference of the tip 12 so that the squealer tip 2 at least partially surrounds the tip surface 12a.

[0075] As schematically illustrated in FIG. 4, the squealer tip 2 may have a predefined squealer tip height d, measured perpendicular to the contact surface 12b. The airfoil 1 and the squealer tip 2 may have a total height h, wherein the total height h is measured from the platform end 11 of the airfoil 1 to the second end 22 of the squealer tip 2 in the radial direction R, as schematically illustrated in FIG. 2. The squealer tip height d may be smaller than or equal to 15% of the total height h.

[0076] An axial squealer tip width W which is a shortest distance measured in the axial direction A through the center line LR between opposite portions of the second end 22 of the squealer tip 2 is further depicted in FIG. 5. The airfoil 1, at a radial position corresponding to the half distance between the platform end 11 and the second end 22 of the squealer tip 2 has an axial airfoil width V measured in the axial direction A between the leading edge 13 and the trailing edge 14. The axial squealer tip width W may be in a range between 50% and 130% of the axial airfoil width V. An angle between the center line LR of the airfoil 1 and the first lateral surface 2a of the squealer tip 2 may be in a range between 0 degrees and 90 degrees. For example, a first inner angle between the first lateral surface 2a and the center line LR, at a position corresponding to the leading edge 13 may be in a range between 0 degrees and 90 degrees. A second inner angle between the first lateral surface 2a and the center line LR, at a position corresponding to the trailing edge 13 may be in a range between 0 degrees and 90 degrees, as depicted schematically in FIG. 5. The first and the second inner angle , may be equal to each other or different from each other.

[0077] The squealer tip 2 includes an internal cooling structure. As shown schematically in FIG. 4, the internal cooling structure may include at least one internal cooling cavity. Generally, an internal cooling cavity 20 of the squealer tip is limited by an inner surface 20i of the squealer tip 2. A distance between the inner surface 20i and an adjacent one of the lateral surfaces 2a, 2b of the squealer tip 2 or between end face 22a and the adjacent portion of the inner surface 20i defines a wall thickness of a squealer tip wall separating the internal cooling cavity 20 from the environment or outside. FIG. 4, for the purpose of explanation, only shows one cooling cavity 20. However, the internal cooling structure of the squealer tip 2 may include a plurality of internal cooling cavities 20 that are separated from each other. For example, the cooling cavities 20 may be separated and spaced from each other along the circumference of the tip surface 12a as exemplarily shown in FIG. 10. Additionally or alternatively, the internal cooling cavities 20 may be separated and spaced along the radial direction R or, more specifically, in a direction from the first to the second end 21, 22 of the squealer tip 2, as exemplarily shown in FIGS. 6 and 10. It should be noted that separate internal cooling cavities 20, optionally, may be in fluid communication via one or more cooling passages, wherein a hydraulic diameter of those fluid passages is small compared to the hydraulic diameter of the cavities 20 connected by those passages. For example, the hydraulic diameter of a passage connecting two separate internal cavities 20 may be in a range of 1% to 25%, in particular, between 1% and 10% of the hydraulic diameter of the smaller one of the two separate internal cavities 20.

[0078] As schematically shown in FIGS. 4, 6, 7, and 11 each of the separated internal cooling cavities 20 is in fluid communication with the inner cavity 10 via one or more of the plurality of fluid passages 15. To this end, the cooling passage 15 formed in the tip 12 of the airfoil 1 may directly open into the internal cooling cavity 20 of the squealer tip 2, or the squealer tip 2 itself may include a cooling passage 25 opening into the internal cooling cavity 20 and being connected to the cooling passage 15 of the tip 2 so that they form a continuous fluid passage connecting the internal cooling cavity 20 to the inner cavity 10 of the airfoil 1. Thus, a gaseous cooling fluid such as compressed air can be supplied from the inner cavity 10 of the airfoil 1 to a plurality of separate internal cooling cavities 20 in the squealer tip 2 via separate cooling passages 15, 25. Therefore, the squealer tip 2 can be cooled more efficiently and the cooling capacity can be adapted more precisely to the local heat loads applied to the squealer tip 2.

[0079] Referring to FIG. 6, and as already mentioned above, it may be provided that multiple internal cooling cavities 20 are spaced to one another within the squealer tip 2 with respect to the radial direction R or, generally, with respect to the direction from the first to the second end 21, 22 of the squealer tip 2. FIG. 6 exemplarily shows a configuration with a first internal cooling cavity 20 positioned adjacent to the first end 21 of the squealer tip 2 and connected to the inner cavity 10 of the airfoil 1 via a first cooling passage 15A, 25A, and with a second internal cooling cavity 20 positioned spaced to the first internal cooling cavity 20 towards the second end 22 of the squealer tip 2 and connected to the first internal cooling cavity 20 of the squealer tip 2 via a second cooling passage 25B. Optionally, the second internal cooling cavity 20 may be connected to the environment, e.g., to a main gas flow around the flow body 100, via an exhaust passage (not shown in FIG. 6) that may, for example, open to the second lateral surface 2b of the squealer tip 2. FIG. 6 exemplarily shows a first and a second internal cooling cavity adjacent to each other with respect to the radial direction R. It should be noted that there might be more than two internal cooling cavities spaced to each other in the radial direction R within the squealer tip 2. Additionally, or alternatively, multiple first and second internal cooling cavities 20 spaced in the radial direction R may be distributed along the circumference of the tip 12, as schematically shown in FIG. 10. Generally, the plurality of internal cooling cavities 20 may include a first set 20A of the cavities 20 and a second set 20B of cavities 20 that are spaced in the radial direction R and/or along the circumference of the tip surface 12a, wherein each cavity of the first set 20A of cavities 20 is in fluid communication with the inner cavity 10 of the airfoil 1 via at least one first fluid passage 15A and with one cavity 20 of the second set 20B of cavities 20 being adjacent in the radial direction R or along the circumference of the tip surface 12a via at least one second fluid passage 25B.

[0080] As is further illustrated in FIG. 6, the fluid passage 15A, 25A connecting the internal cavity 20 of the first set 20A to the inner cavity 10 of the airfoil 10 may be formed as a cooling hole that is inclined such that a central axis A15 of the respective cooling hole intersects the inner surface 20i adjacent to the second lateral surface 2b of the squealer tip 2. Thereby, the cooling fluid discharged from the inner cavity 10 of the airfoil 1 to the cooling cavity 20 of the squealer tip 2 impinges onto the inner surface 20i which further promotes heat transfer. As visible in FIG. 6, also the second fluid passage 25B can be realized inclined such that its central axis (not depicted in FIG. 6) intersects the inner surface 20i adjacent to the second lateral surface 2b of the squealer tip 2. It should be noted that this configuration of the cooling passages 15A, 25A is not limited to a squealer tip 2 with a first and a second cooling cavity 20 spaced in the radial direction R. Rather, it may generally be provided that at least some of the cooling passages 15, 25 that connect at least some of the internal cooling cavities 20 of the squealer tip 2 to the inner cavity 10 of the airfoil 1 are formed as cooling holes that are inclined such that the central axis A15 of the respective cooling hole intersects a lateral inner surface 20i of the respective internal cooling cavity 20.

[0081] FIG. 7 exemplarily shows a squealer tip 2 in which an inner diameter of at least some of the internal cooling cavities 20 of the squealer tip 2 decreases with increasing distance from the tip 12 of the airfoil 1. In the example of FIG. 7, the internal cooling cavity 20 extends as a continuous channel from a region adjacent to the first end 21 to a region adjacent to the second end 22 of the squealer tip 2, wherein an effective flow area of the channel decreases towards the second end 22. As is further exemplarily shown in FIG. 7, the fluid passage 15, 25 that connects the internal cooling cavity 20 to the inner cavity 10 of the airfoil 1 may extend along, i.e., parallel, to a longitudinal axis of the internal cooling cavity 20. However, the invention is not limited to this configuration. For example, the fluid passage 15, 25 may also extend inclined relative to the inner surface 20i of the internal cooling cavity 2 as described above with reference to FIG. 6. FIG. 7, by way of example, shows an exhaust passage 26 that extends between the second lateral surface 2b of the squealer tip 2 and the internal cooling cavity 20 so that the cooling fluid can be exhaust or discharge from cooling cavity 20 through the exhaust passage 26. Not only in the example of FIG. 7 but generally, the exhaust passage 26 may be positioned adjacent to the second end 22 of the squealer tip 2. As visible in FIG. 8, which is a cross-sectional view of the squealer tip 2 of FIG. 2, multiple internal cooling cavities 20, in this example in the form of continuous channels, may be arranged separated and spaced from one another along the circumference of the tip 12.

[0082] In the schematical FIGS. 4 and 6 to 8, the inner surface 20i of the internal cooling cavities 2 have been shown as smooth surface. Optionally, at least some of the internal cooling cavities 20 of the squealer tip 2 may include at least one of projections 28, e.g., in the form of ribs, and recesses 29, e.g., in the form of grooves, formed on the inner surface 20i, as exemplarily and schematically shown in FIG. 9.

[0083] The squealer tip 2 is made of a second metal material, in particular, by a metal material deposited in an additive manufacturing process. For example, the second metal material may be a Nickel or Cobalt based high temperature alloy suitable for additive manufacturing, such as Haynes 230, Hastelloy-X, IN625, or CM247. As will be explained in more detail below with reference to FIG. 12, the squealer tip 2 is built in an additive manufacturing process directly onto the contact surface 12b of the tip 12 of the airfoil 1. Thereby, the squealer tip 2 is material joined to the tip 12. One advantage of this configuration is that additive manufacturing technology allows for realizing complex geometries of the squealer tip 2, including aerodynamically advantageous outer shapes defined by the first and second lateral surface 2a, 2b and the end face 22a of the squealer tip 2. On the other hand, additive manufacturing the squealer tip 2 allows forming internal cooling cavities 20 even in a complex shaped squealer tip 2. In particular, multiple separated internal cooling cavities 20, as described above, can efficiently be manufactured to improve cooling performance within the squealer tip 2.

[0084] FIG. 11 schematically shows a cross-sectional view of the flow body 100 in the region of the tip 12 of the airfoil 1. As schematically shown, the squealer tip 2 is material bonded to the contact surface 12b of the tip 12 of the airfoil 12 by an additively manufactured transition layer 3. The transition layer 3 forms part of the squealer tip 2 as it is additively manufactured, optionally, in the same process of building the squealer tip 2. The main portion of the squealer tip 2 may be defined as a portion of the squealer tip 2 which extends between the transition layer 3 and the second end 22 and in which the physical properties of the second metal material are substantially constant. Thus, the squealer tip 2, generally, includes the transition layer 3 and the main portion, which is made from the second metal material. Since the airfoil 1 and the squealer tip 2 are made from different materials and are manufactured in different processes, physical properties of the materials of the airfoil 1 and the squealer tip 2 are different on either side of an interface, e.g., the contact surface 12b, between the airfoil 1 and the squealer tip 2. The transition layer 3 serves for reducing mechanical stress in the transition region of the airfoil 1 and the squealer tip 2 by lowering stress within the transition layer 3. Therefore, the transition layer 3, compared to at least one of the main portion of the squealer tip 2 and the airfoil 1, has a reduced stiffness and/or an increased ductility combined with reduced yield strength.

[0085] The transition layer 3, for example, may also be made of the second metal material from which the main portion of the squealer tip 2 is made. In this case, the second metal material has a greater porosity in the transition layer 3 than in the main portion of the squealer tip 2. In other words, a porosity of the second metal material is increased within the transition layer 3 compared to the main portion of the squealer tip 2. Thereby, the stiffness of the transition layer 3 is reduced compared to the main portion of the squealer tip 2 which helps in lowering mechanical stress within the transition layer 3.

[0086] The porosity P.sub.3 of the transition layer 3 may be quantified by equation (1) below:

[00001]$\begin{array}{cc}{P}_3=1-\frac{{}_3}{{}_2}& \left(1\right)\end{array}$ [0087] in which .sub.3 is an average volume density of the second metal material within the transition layer 3 and .sub.2 is an average volume density of the second metal material within the main portion of the squealer tip 2. P.sub.3, for example, may be smaller or equal than 0.5, in particular, smaller or equal than 0.2. For example, P.sub.3 may be in a range between 0.02 to 0.05.

[0088] Alternatively, the transition layer 3 may be made of a third metal material comprising an increased ductility and reduced yield strength compared to the first and the second metal material. For example, the third metal material may be deposited on the contact surface 12b in a first step of additively manufacturing the squealer tip 2 to form the transition layer 3, and the second material may be deposited onto the transition layer 3 in a further step of the additive manufacturing process. For example, the third metal material may be Haynes230, Hastelloy-X, IN617, or similar.

[0089] Irrespective of whether porosity is increased in the transition layer 3 or whether the transition layer 3 is made of a third metal material, it may have a thickness t3, measured perpendicular to the contact surface 12b, in a range between 0.1 mm and 5.0 mm, in particular, between 0.5 mm and 2.0 mm. Generally, the thickness t3 of the transition layer 3 may be smaller or equal than 35% of the squealer tip height d.

[0090] FIG. 12 shows a flowchart of a method M for manufacturing a flow body 100 for a gas turbine 300. The method M will be explained below by reference to the flow bodies 100 described above.

[0091] In a first step M1, the airfoil 1 is cast from the first metal material. This may, for example, include a conventionally cast (CC), a directionally solidified (DS), or a single crystal (SX) cast process. In the casting step M1, the inner cavity 10, the tip surface 12a and the contact surface 12b are formed as well as the pressure and suction side surfaces 1p, 1s. Optionally, also the platform 4 and the root 5 are formed in the casting step M1.

[0092] In step M2, the plurality of fluid passages 15 is formed between the inner cavity 10 and the contact surface 12b of the tip 12. This step M2 may include drilling, electrical discharge machining, or similar subtractive processes. Alternatively, step M2 may form part of step M1, in that the passages 15 are formed in the casting process.

[0093] Step M3 includes building the squealer tip 2 from the second metal material on the contact surface 12b of the tip 12 by means of an additive manufacturing process. The additive manufacturing process may include, for example, selective laser melting (SLM), direct metal deposition (DMD), or electron beam welding (EBW). In step M3, the outer shape of the squealer tip 2 defined by the first and second lateral surfaces 2a, 2b and the end face 22a is built as well as the internal cooling cavities 20. In particular, the squealer tip 2 is built such that the internal cooling cavities 20 are separately formed and such that each of the internal cooling cavities 20 is in fluid communication with the inner cavity 10 via the one or more of the plurality of fluid passages 15, 25.

[0094] Step M3 also includes building the transition layer 3 by an additive manufacturing process. The additive manufacturing process for building the transition layer 3 may be the same as the one for building the remaining squealer tip 2, e.g., SLM, DMD, or EBW. The transition layer 3, as explained above, may be formed from the same second metal material as the main portion of the squealer tip 2 and may have an increased porosity compared to the main portion. In the additive manufacturing process, an increased porosity may be achieved, for example, by depositing and melting the second metal material spot wise with wider pitches between the individual spots than in the main portion. For example, in an SLM process, in a layer of metal powder, not all of the metal powder may be melted and subsequently solidified. Thereby, spots with non-melted powder remain within the layer that form pores. Alternatively, the third metal material may be deposited on the contact surface 12b in step M3 to build the transition layer 3, and the main portion of the squealer tip 2 is built on the transition layer in the second metal material.

[0095] Optionally, the contact surface 12b may be subject to a surface treatment step (not shown in the flowchart of FIG. 12), in which the contact surface 12b is prepared for depositing the second or third metal material thereon in the subsequent step M3 of building the squealer tip 2. The surface treatment step may, for example, include a subtractive process such as grinding to vary or adapt the surface roughness and/or to orientation of the contact surface 12b.

[0096] As already discussed above, the additive manufacturing of the squealer tip 2 directly onto the tip 12 provides various benefits. For example, the thickness of the walls of the squealer tip 2 that limit the internal cooling structure may be reduced. Consequently, a temperature difference across the wall is reduced which, in turn, reduces mechanical stress in the wall. Thereby, lifetime of the squealer tip can be increased. Further, less cooling fluid is required which helps to increase the efficiency of the gas turbine 300. Moreover, additive manufacturing is less sensitive to manufacturing tolerances and provides a high freedom of design for the squealer tip 2. For example, the mass of the squealer tip 2 can be easily adapted to engine frequencies and mode shapes. The high freedom of design achieved by the additive manufacturing process finally allows to realize greater aerodynamic improvements than it would be possible with conventional methods, since any shape, that can be made by additive methods, can be also cooled efficiently.

[0097] The transition layer 3 provides the advantage that mechanical stress is remarkably reduced in the transition region between the tip 12 of the airfoil 1 and the squealer tip 2, even though the squealer tip 2 is made from a different material than the airfoil 1. This helps to further increase lifetime of the flow body 100.

[0098] Moreover, the present invention provides an improved solution for repairing a flow body 100 of a gas turbine 300, e.g., a blade or a vane. FIG. 13 schematically shows a flowchart of a method S for repairing a flow body 100 of a gas turbine 300. The method M may be applied to the flow body 100 described above. However, the method is not limited thereto. Generally, the method S may be applied to any flow body 100 comprising an airfoil 1 extending along a radial direction R between a platform end 11 and a tip 12 which has a tip surface 12a, a squealer tip 2 that protrudes from the tip surface 12a and extends along a circumference of the tip 12 so that the squealer tip 2 at least partially surrounds the tip surface 12a, and an inner cavity 10 for receiving a gaseous cooling fluid. The squealer tip 2 of the flow body 100 to be repaired further includes a cooling system in fluid communication with the inner cavity 10 of the airfoil (1) via a plurality of fluid passages 15. The cooling system, generally, may include one or more cooling channels that are in fluid communication with the inner cavity 10 of the airfoil 1 via the fluid passages 15.

[0099] As shown in FIG. 13, the method S a step S1, in which the squealer tip 2 is removed from the airfoil 1 in a subtractive process such as grinding, milling or similar.

[0100] In step S2, a contact surface 12b that at least partially surrounds the tip surface 12a of the tip 12 of the airfoil 1 is formed. Step S2 may form part of step S1 insofar as the subtractive process of step S1 may also be used to form the contact surface 12b. The contact surface 12b may, in particular, be formed in one of the configurations described above, e.g., by reference to FIG. 4.

[0101] In an optional step S3, additional fluid passages 15 may be formed between the contact surface 12b and the inner cavity 10 of the airfoil 1, e.g., by drilling or another subtractive process. Additionally, or alternatively, the existing fluid passages 15 may be cleaned or widened in step S3.

[0102] In step S4, a new squealer tip 2 is built on the contact surface 12b of the tip 12 by means of an additive manufacturing process such as SLM, DMD, EBW, or similar. The new squealer tip 2 may, for example, be built from the second metal material as described above. Generally, the new squealer tip 2 may be built in step S3 in the same process as in step M3 of method M described by reference to FIG. 12.

[0103] The repair method S, hence, provides an efficient process for improving the cooling efficiency of a squealer tip 2 and reducing susceptibility to mechanical stress at the interface of squealer tip 2 and tip 12 of existing flow bodies 100 in an overhaul process.

[0104] In both, the repair method S and the manufacturing method M, a further optional step may be performed after step M3 and S4, respectively. In this further optional step, one or more coating layers (not shown) may be applied to the outer surface of the flow body 100, e.g., to the pressure and suction side surfaces 1p, 1s and the tip surface 12a of the airfoil 1, and the outer surfaces 2a, 2b, 22a of the squealer tip 2. For example, a MCrAlY material or other suitable material as bond coat may be applied by a low pressure plasma spray (LPPS), an air plasma spray (APS), a vacuum plasma spray (VPS), or high velocity oxy fuel (HVOF) process. The letter M in McrAlY is a placeholder for Co, Ni, or NiCo. Additionally, a topcoat may be applied to the coating. For example, a single or multi-layered ceramic, e.g., Yttrium stabilized zirconium (YSZ), may be applied by LPPS or APS.

[0105] Further optionally, in both, the repair method S and the manufacturing method M, an additional step (not shown in the flowcharts of FIGS. 12 and 13) may be carried out after building the squealer tip 2. In this additional step, the outer surface of the airfoil 1, e.g., the pressure and the suction side surface 1p, 1s, and the outer surface of the squealer tip 2, e.g., the second lateral surface 2b of the squealer tip 2 may be treated to remove steps between their outer surfaces. E.g., a transition area between the second lateral surface 2b of the squealer tip 2 and the respective pressure and the suction side surface 1p, 1s may be subject to a subtractive process, such as grinding or similar, to remove possible level differences and form a continuous surface.

[0106] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of at least ordinary skill in the art that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

LIST OF REFERENCE SIGNS

[0107] 1 airfoil [0108] 1p pressure side surface [0109] 1s suction side surface [0110] 2 squealer tip [0111] 2a first lateral surface of squealer tip [0112] 2b second lateral surface of squealer tip [0113] 3 transition layer [0114] 4 platform [0115] 4t transition surface [0116] 5 root [0117] 10 inner cavity of airfoil [0118] 11 platform end of airfoil [0119] 12 tip end of airfoil [0120] 12a tip surface [0121] 12b contact surface [0122] 13 leading edge of airfoil [0123] 14 trailing edge of airfoil [0124] 15, 25 fluid passage [0125] 15A, 25A first fluid passage [0126] 20 internal cooling cavity of squealer tip [0127] 20A first set of internal cooling cavities [0128] 20B second set of internal cooling cavities [0129] 20i inner surface of internal cooling cavity [0130] 21 first end of squealer tip [0131] 22 second end of squealer tip [0132] 22a end face of squealer tip [0133] 25B second fluid passage [0134] 26 exhaust passage [0135] 28 projection [0136] 29 recess [0137] 100 flow body [0138] 300 gas turbine [0139] 310 compressor [0140] 312 compressor blade [0141] 313 compressor vane [0142] 320 burner [0143] 330 turbine [0144] 335 turbine vane [0145] 336 turbine blade [0146] 350 rotor [0147] A axial direction [0148] C circumferential direction [0149] d squealer tip height [0150] h total height of airfoil and squealer tip [0151] M manufacturing method [0152] M1-M3 method steps of the manufacturing method [0153] LR center line [0154] S repair method [0155] S1-S4 method steps of the repair method [0156] R radial direction [0157] V axial airfoil width [0158] W axial squealer tip width [0159] Z radial height [0160] first inner angle [0161] second inner angle [0162] first surface angle [0163] second surface angle