HOLES

BACKGROUND 1. Field

[0001] The present invention relates generally to a gas turbine engine, and more specifically to a turbine stator vane with an endwall mate face seal and cooling design.

2. Description of the Related Art

[0002] In a turbomachine, such as a gas turbine engine, air is pressurized in a compressor section and then mixed with fuel and burned in a combustor section to generate hot combustion gases. The hot combustion gases are expanded within a turbine section of the engine where energy is extracted to power the compressor section and to produce useful work, such as turning a generator to produce electricity. The hot combustion gases travel through a series of turbine stages within the turbine section. A turbine stage may include a row of stationary airfoils, i.e., stator vanes, followed by a row of rotating airfoils, i.e., rotor blades, where the rotor blades extract energy from the hot combustion gases for providing output power. Since stator vanes and rotor blades are directly exposed to the hot combustion gases, they are typically provided with internal cooling channels, whereby coolant is discharged into the hot gas path via exhaust orifices, such as film cooling holes formed on hot gas exposed surfaces of these components.

[0003] Stator vanes are typically made up of segments with one or more airfoils extending between an outer endwall and an inner endwall. As shown in FIG 1, film cooling holes 50 may be formed on the airfoil 4. Film cooling holes 60 may be also formed on the inner endwall 6 and the outer endwall 8, including film cooling holes 60a on an endwall edge 26 adjacent to a mate face 22 of an endwall segment. Drilling such film cooling holes is expensive and time consuming. Furthermore, film cooling holes at the endwall edges often develop cracks due to stress concentration, which are difficult to repair. It is desirable to have a more simplified manufacturing process while still achieving the equivalent cooling effectiveness.

SUMMARY

[0004] Briefly, aspects of the present invention provide a stator vane assembly having a mate face seal with cooling holes.

[0005] According to a first aspect of the present invention, a stator vane assembly for a gas turbine engine comprises a first endwall segment and a second endwall segment arranged circumferentially spaced from each other, whereby a mate face gap is defined between a first mate face of the first endwall segment and a second mate face of the second endwall segment. A mate face seal extends between the first and second mate faces to seal said mate face gap. The mate face seal comprises through-holes forming film cooling holes connecting a first surface of the mate face seal facing a hot gas path to a second surface of the seal strip facing a coolant plenum.

[0006] According to a second aspect of the present invention, stator vane assembly for a gas turbine engine comprises an airfoil extending span-wise between an inner endwall and an outer endwall. Each of the inner and outer endwalls is made up multiple endwall segments arranged circumferentially next to each other. Each of the inner endwall and the outer endwall respectively comprises a first endwall segment and a second endwall segment arranged circumferentially spaced from each other, whereby a mate face gap is defined between a first mate face of the first endwall segment and a second mate face of the second endwall segment. A mate face seal extends between the first and second mate faces to seal said mate face gap. A plurality endwall film cooling holes are distributed on hot gas exposed surfaces of the first and second endwall segments so as to be spaced from endwall edges that are adjacent to the first and second mate faces. A plurality of mate face seal film cooling holes are formed on a hot gas path facing surface of the mate face seal, to effect convective cooling along the mate faces and the endwall edges.

BRIEF DESCRIPTION OF THE DRAWINGS [0007] The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention.

[0008] FIG 1 is a perspective view of a typical stator vane segment;

[0009] FIG 2 is a perspective view of a stator vane assembly comprising a mate face seal for sealing a gap between adjacent endwall segments;

[0010] FIG 3 is a partial cross-sectional view along the section III-III in FIG 2;

[0011] FIG 4 is a perspective view of a portion of a stator vane assembly illustrating a mate face seal with cooling holes according to one embodiment of the present invention;

[0012] FIG 5 is a cross-sectional view along the section V-V in FIG 4;

[0013] FIG 6 is a perspective top view of a stator vane assembly according to one embodiment of the present invention, and

[0014] FIG 7-9 represent schematic plan views of a mate face seal showing varying configurations of film cooling holes in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

[0001] In the following detailed description, across different embodiments, like reference characters have been used to designate like or corresponding elements for the sake of simplicity.

[0002] In this description, various specific details are set forth in order to provide a thorough understanding of such embodiments. However, those skilled in the art will understand that disclosed embodiments may be practiced without these specific details, that the present invention is not limited to the depicted embodiments, and that the present invention may be practiced in a variety of alternative embodiments. In other instances, methods, procedures, and components, which would be well-understood by one skilled in the art have not been described in detail to avoid unnecessary and burdensome explanation.

[0003] Furthermore, usage of the phrase "in one embodiment" does not necessarily refer to the same embodiment, although it may. It is noted that disclosed embodiments need not be construed as mutually exclusive embodiments, since aspects of such disclosed embodiments may be appropriately combined by one skilled in the art depending on the needs of a given application.

[0015] The terms "comprising", "including", "having", and the like, as used in the present application, are intended to be synonymous unless otherwise indicated. Also, unless otherwise specified, the connector "or", as used herein, implies an inclusive "or", which is to say that the phrase "A or B" implies: A; or B; or both A and B. Lastly, as used herein, the phrases "configured to" or "arranged to" embrace the concept that the feature preceding the phrases "configured to" or "arranged to" is intentionally and specifically designed or made to act or function in a specific way and should not be construed to mean that the feature just has a capability or suitability to act or function in the specified way, unless so indicated.

[0016] A portion of a stator vane assembly 10 is now illustrated referring to FIGS 2 and 3, which depict a pair adjacent stator vane segments 92, 94 that are positioned circumferentially next to each other in a row of stator vanes. Each of the stator vane segments 92, 94 includes one or more airfoils 4, extending span-wise between a segment of an inner endwall 6 and a segment of an outer endwall 8. The inner 6 and outer 8 endwalls are coupled to the radial or span-wise ends of each airfoil 4. In the illustrated example, each stator vane segment 92, 94 comprises a single airfoil 4. As shown, the inner endwall 6 comprises a first endwall segment 12 and a second endwall segment 14 arranged circumferentially spaced from each other. In this example as shown in FIG 3, the first endwall segment 12 forms a pressure side endwall segment while the second endwall segment 14 forms a suction side endwall segment. The endwall segments 12, 14 have respective radially extending surfaces 22, 24, referred to as mate faces, which are spaced from each other to define a mate face gap 20 therebetween. A mate face seal 30 extends between the first 22 and second 24 mate faces to seal the mate face gap 20. It is understood that a similar arrangement may be provided between adjacent endwall segments of the outer endwall 8.

[0017] Referring to FIG 3, the mate face seal 30 includes a first surface 30a facing a hot gas path H and a second surface 30b opposite to the first surface 30a, facing a coolant plenum C, which in this case is located radially inward to the inner diameter of the vane segment. In the illustrated configuration, each mate face 22, 24, has a respective axial slot 52, 54 extending generally along the engine axis, i.e., in a direction from an endwall leading edge 56 toward an endwall trailing edge 58. The mate face seal 30 may be placed inside the slots 52, 54 on both pressure and suction side endwall segments 12, 14 to prevent the hot gas ingesting into the cavity C under the inner endwall 6. The first surface 30a of the mate face seal 30 may be positioned further away from the hot gas path H than hot gas exposed surfaces 12a, 14a respectively of the endwall segments 12, 14, such that the mate face seal 30 and the mate faces 22, 24 define an open trench 33 facing the hot gas path H.

[0018] As shown, film cooling holes 50 may be formed on the airfoil 4 at various locations on the outer surface of the airfoil 4 exposed to the hot gas path H. Film cooling holes 60 may also be formed on surfaces of the endwall segments 12 and 14 of the inner endwall 6 that are exposed to the hot gas path H. The film cooling holes 50, 60 fluidically connect the hot gas exposed surfaces of the airfoil 4 and the end wall segments 12, 14 to the coolant plenum C located radially inward from the inner diameter of the vane segment. Since the corners or circumferential edges 26, 28 of the endwall segments 12, 14 tend to get especially heated because further away from the cooling plemum, it has been expedient to provide film cooling holes 60a at the circumferential endwall edges 26, 28 respectively of the first endwall segment 12 and the second endwall segment 14. The film cooling holes 50, 60, 60a may be typically formed by drilling, for example, via an electrical discharge machining (EDM) operation. Although not visible in the drawings, an additional row of film cooling holes may be likewise drilled from the pressure side mate face 22 toward the coolant plenum C under the inner endwall 6. [0019] During engine operation, the pressure gradient between adjacent airfoils causes the boundary layer hot gases on the inner endwall surface to flow from the pressure side endwall surface 12a toward the suction side endwall surface 14a. This cross-flow boundary layer hot gas carries the surface film cooling air on the pressure side endwall surface 12a across the mate face open trench 33 toward the suction side endwall surface 14a to provide film cooling protection for the entire inner endwall. A similar film cooling arrangement may be provided at the outer endwall 8 via a further coolant plenum located radially outward from an outer diameter of the vane segment. In the current design, film cooling holes especially at the endwall edges often develop cracks due to stress concentration, which are difficult to repair. Furthermore, drilling film cooling holes, especially at the endwall edges and the radial mate faces is expensive and time consuming from a manufacturing standpoint.

[0020] An exemplary embodiment of the present invention is now described referring to FIGS 4-6. Similar to the configuration shown in FIGS 2-3, mate face seal 30 of the illustrated embodiment includes a first surface 30a facing a hot gas path H and a second surface 30b opposite to the first surface 30a, facing a coolant plenum C, which in this case is located radially inward to the inner diameter of the vane segment. As shown, the mate face seal 30 may be formed as a seal strip elongated in an axial direction of the gas turbine engine. In the shown embodiment, the seal strip 30 has a rectangular cross-section and is placed within respective axial slots 52, 54 formed on the first mate face 22 and on the second mate face 24. The first surface 30a of the mate face seal 30 may be positioned further away from the hot gas path H than the hot gas exposed surfaces 12a, 14a respectively of the endwall segments 12, 14, such that the mate face seal 30 and the mate faces 22, 24 define an open trench 33 facing the hot gas path H. The present embodiment differs from the configuration shown in FIGS 2-3 in that in the present embodiment, the mate face seal 30 is perforated, comprising a row of film cooling holes 40. The mate face seal film cooling holes 40 are essentially through-holes connecting the first surface 30a of the mate face seal 30 facing a hot gas path H to a second surface 30b of the mate face seal 30 facing a coolant plenum C, which in this case is located radially inward of the inner diameter of the vane segment. The mate face seal film cooling holes 40 may be arranged spaced apart along an axial length of the mate face seal 30.

[0021] As per aspects of the present invention, the mate face seal film cooling holes 40 may replace the film cooling holes 70a at the endwall edges 26, 28 adjacent to the mate faces 22, 24, as well as film cooling holes on the radial mate faces 22, 24. The perforated seal strip 30 in combination with the mate faces 22, 24 forms an open trench 33 with active film cooling for the mate faces 22, 24 and the downstream suction side endwall surface 14a via the mate face seal film cooling holes 40. The open trench 33 provides a transition zone to convert the discrete film cooling jets into a continuous film cooling slot for a broader coolant coverage and better cooling. The mate face seal film cooling holes 40 may be formed by drilling, for example laser drilling. Because of the geometry of the flat seal strip 30, the holes 40 are simpler to form than drilling holes in the endwall edges. Furthermore, since the holes 40 are not located at edges or areas of high stress concentration, risk of crack propagation is minimized. Still further, since the mate face seal 30 is easily replaceable, repair costs are minimized.

[0022] The mate face seal film cooling holes 40 can be either radial or inclined with respect to the radial direction. As shown in FIG 5, the mate face seal 30 has axially opposite leading 32 and trailing 34 edges. In the illustrated embodiment, the mate face seal film cooling holes 40 have a respective flow axis 40a which is non-parallel to the radial direction R, and inclined toward the trailing edge 34 of the mate face seal 30. By angling the flow axes 40a toward the trailing edge 34 in the direction of the hot gas flow, it is ensured that the film will accumulate in the trench, providing improved film attachment

[0023] The mate face seal film cooling holes 40 essentially eliminate the need for providing film cooling holes at the endwall edges 26, 28. As shown in FIG 6, in the exemplary embodiment, the endwall film cooling holes 60 may be distributed on the hot gas exposed surfaces 12a, 14a of the first 12 and second 14 endwall segments so as to be spaced from endwall edges 26, 28 that are adjacent to the first 22 and second 24 mate faces. The spacing between the endwall edge 26, 28 and the nearest endwall film cooling hole 60 may, for example be at least 5% of the circumferential (arc) length L of each endwall segment 12, 14.

[0024] In the illustrated example, the mate face seal film cooling holes have a circular cross-section. However, other cross-sectional shapes may be used, depending on the ease of manufacturing and/or the distribution of film cooling required. In alternate embodiments, one or more of the mate face seal film cooling holes 40 may have, for example, a rectangular or an oval cross-section as shown in FIGS 7-8 respectively. In a still further embodiment, the axial spacing of mate face seal film cooling holes 40 may be varied as shown in FIG 9. The variation in axial spacing of the mate face seal film cooling holes 40 may be designed, for example, as a function of film cooling hole distribution on the endwall surfaces 12a and 14a.

[0025] Embodiments of the present invention have been described in relation to an inner endwall of a vane assembly. It should however be understood that the inventive concepts may be applied to additionally to an outer endwall of a vane assembly.

[0026] While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.