Segmented component seal

Abstract

A seal for restricting leakage of a fluid from a first chamber, through a gap between two components, to a second chamber, is provided. A slot is formed in each of the two components. The slots face one another and are open to the gap. Each slot contains a longitudinal axis, an upstream surface proximate the first chamber and a downstream surface proximate the second chamber. Disposed in the slots and spanning the gap is a bridging element. The bridging element contains a sectional profile, transverse to the longitudinal slot axis, that includes a flat central portion disposed between two approximately wave shaped end portions. The bridging element spans the gap between the two components with the end portions disposed in the slots, and the central portion disposed in the gap.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to gas turbine engine components in general, and specifically to a seal for preventing leakage of high pressure air or other fluids between segmented components found in such engines.

2. Description of the Related Art

As illustrated in FIG. 1, a gas turbine engine 10 comprises one or more forward compressor sections 12, a central combustor section 14 and one or more rearward turbine sections 16. The engine 10 operates by compressing ambient air 18 with the compressors 12, adding fuel upstream of the combustor 14 and burning a fuel-air mixture 20 in the combustor 14. High temperature combustion gases 22 are directed axially rearward from the combustor 14, through an annular duct 24 disposed in the turbines 16. The combustion gases 22 interact with one or more turbine rotors 26 disposed in the duct 24. The turbine rotors 26 are coupled to compressor rotors 28 via concentric shafts 30 rotating about a central longitudinal axis 32 of the engine 10. Gas turbine engines are known to power aircraft, ships and electrical generators.

Extending into the annular gas duct 24 are alternating circumferential stages of rotating blades 34 and stationary vanes 36. The stationary vanes 36 extend radially inwardly from a casing structure 38 surrounding the turbines 16. To prevent oxidation of the vanes 36 and other stationary components due to the hot combustion gases 22, low temperature compressor air 40 is directed radially inboard and outboard of the duct 24 to the components. The compressor air 40 is maintained at a higher pressure than the combustion gas 22 pressure, to ensure a continuous supply of compressor air 40 reaches the components.

Because stationary components such as vanes, shrouds, supports and the like are subject to extreme temperature gradients, they can develop cracks due to thermal mechanical fatigue (TMF). To reduce the occurrence of TMF induced cracking, these components are typically installed in semi annular segments distributed circumferentially about the engine's longitudinal axis. The segmented components are uncoupled from one another, thus allowing them to expand and contract independently. In addition to their improved resistance to TMF, segmented components are also less expensive to repair and/or replace after extended use.

Despite the aforementioned benefits, axial and radial gaps must be included between adjacent components to allow for thermal expansion. These gaps require sealing to ensure an adequate pressure differential exists between the compressor air and the combustion gas. Maintaining a compressor air pressure that is greater than the combustion gas pressure ensures a continuous flow of compressor air and prevents backflow of the combustion gas. Excessive leakage of the compressor air may cause premature oxidation of the components and can increase the engine's fuel burn. With jet fuel accounting for up to sixty five percent of the operating expense of a commercial airliner, any reduction in fuel burn is beneficial.

Various seal configurations are known to restrict leakage of a pressurized fluid through a gap between two components. Feather seals are the type most commonly used between segmented components in gas turbine engines. Feather seals comprise a slot in the adjacent components that are open to the gap, and a bridging element disposed in the slots, spanning across the gap.

Flat bridging elements, such as those disclosed in U.S. Pat. No. 5,154,577 to Kellock, et al, are fit into the adjoining slots. They depend on the higher-pressure compressor air to seat the bridging elements against the slots to form the seal. Assembly damage, misaligned slots, slot surface finish and low compressor air pressure may negatively affect the performance of flat bridging elements.

Resilient bridging elements, such as those disclosed in U.S. Pat. No. 4,537,024 to Grosjean, are press fit into the adjoining slots. They rely on the contact pressure between the bridging element and the slot being greater than the compressor air pressure to form the seal. However, the single loop ends of the Grosjean bridging element offer limited contact pressure with the slot and are subject to compression about their minor axis.

Although misaligned slots, slot surface finish and low compressor air pressure have a less negative impact on resilient bridging elements, feather seal improvement is still needed.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a seal for restricting leakage of a high-pressure fluid from a first chamber, through a gap between two adjoining components, to a second chamber.

According to an embodiment of the seal, a slot is formed in each of the two components. The slots face one another and are open to the gap. Each slot contains a longitudinal axis, an upstream surface proximate the first chamber and a downstream surface proximate the second chamber. Disposed in the slots and spanning the gap is a bridging element. The bridging element contains a sectional profile, transverse to the longitudinal slot axis, that includes a flat central portion disposed between two approximately wave shaped end portions. The bridging element spans the gap between the two components with the end portions disposed in the slots, and the central portion disposed against a slot surface.

A primary feature of the seal is the approximately wave shaped profile of the end portions. The approximate wave shape increases the contact force between the ends of the bridging element and the slot surfaces. Also, the approximately wave shaped ends force the flat center portion against a slot surface.

A primary advantage of the seal is an increased leakage restriction over conventional seals with minimum increase in weight and cost.

Other details of the seal according to the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a simplified sectional view of an axial flow gas turbine engine.

FIG. 2 is a partial sectional view of a high pressure turbine of the type used in the gas turbine engine of FIG. 1.

FIG. 3 is a partial isometric view of a segmented vane assembly of the type used in the high pressure turbine of FIG. 2.

FIG. 4a is a simplified sectional view, taken perpendicular to the longitudinal axis of the slots, of a seal in accordance with an embodiment of the invention disposed between segmented components with aligned slots.

FIG. 4b is a simplified sectional view, taken perpendicular to the longitudinal axis of the slots, of a seal in accordance with an embodiment of the invention disposed between segmented components with misaligned slots.

FIG. 4c is a simplified sectional view of a gap bridging element of FIGS. 4a and 4b prior to installation.

DETAILED DESCRIPTION OF THE INVENTION

An exemplary turbine 16 of a gas turbine engine 10 is illustrated in FIG. 2. The high temperature combustion gases 22 discharge rearward from the combustor 14, at a pressure (P1), to an annular duct 24 defined by an inner periphery 42 and an outer periphery 44. Stationary vanes 36 guide the combustion gases 22 to rotating blades 34, extending radially outwardly from rotor disks 46. The vanes 36 span radially between inner 48 and outer 50 shrouds, which are suspended from an inner support 52 and/or outer casing 38 structures. Inner seals 54 restrict leakage of the combustion gases 22 from beneath the vanes 36 at the inner periphery 42. Outer seals 56 restrict leakage of the combustion gases 22 from above tips 58 of the blades 34 at the outer periphery 44.

Those skilled in the art will appreciate that each of the above-described turbine 16 components must be actively cooled, because the combustion gas 22 temperature typically exceeds the melting temperatures of the components' base alloy. For cooling purposes, relatively low temperature compressor air 40 is distributed from the compressor 12 (FIG. 1), at a pressure (P2), to the inner 42 and outer 44 duct peripheries and away from the annular duct 24. The compressor air 40 pressure (P2) is maintained at a higher level than the combustion gas 22 pressure (P1) in order to allow compressor air to flow through turbine 16 components for cooling and thus preventing overheating and premature oxidation of the components. Seals ensure a typical pressure ratio (P2:P1) of approximately 1.03, but certainly greater than 1.0, exists during all engine operating conditions.

Circumferentially segmented components such as the vanes 36, inner seals 54, outer seals 56 and the like, include a seal 60 between adjacent segments. As best illustrated in FIG. 3, a seal 60 in accordance with an embodiment of the invention contains a bridging element 62 that fits into axial and/or radial slots 64 machined into a mate face 66 of the vanes 36. With the vanes 36 installed, a gap 38 between the vanes 36 typically between 0:010 inch (0.254 mm) and 0.030 inch (0.762 mm) depending on the size of the components accounts for thermal growth and reduces TMF. The slots 64 face one another and are open to the gap 68. The bridging element 62 fits into the slots 64, while spanning across the gap 68. Although segmented vanes 36 are illustrated in the figure, other segmented components are similarly sealed.

Further details of a segmented component seal 60 according to an embodiment of the invention are generally illustrated in FIGS. 4a-4c. Opposed slots 64 are open to a gap 68 and each contain a longitudinal axis 70, an upstream surface 72 proximate a first chamber 74 and a downstream surface 76 proximate a second chamber 78. Although the upstream 72 and downstream 76 surfaces are shown parallel in the illustration, they could also converge or diverge away from the gap 68. Typically, the slots 64 have an opening width (W) of between about 0.030 inch (0.762 mm) and 0.060 inch (1.524 mm). The slots 64 are preferably aligned as illustrated in FIG. 4a, but in some instances they may be slightly misaligned due to manufacturing tolerances as illustrated in FIG. 4b. Preferably, the slot axis 70 is linear, but a curvilinear slot axis 70 may also be used. The slots are produced by casting, abrasive machining, electrodischarge machining, or other suitable means.

The bridging element 62 contains a sectional profile, transverse to the longitudinal slot axis 64 that includes a flat shaped central portion 84 disposed between two, approximately wave shaped, end portions 86.

The central portion 84 spans across the gap 68 and the end portions 86 seat against surfaces 72, 76 of each slot 64. For lower (P2:P1) pressure ratio installations, the bridging element 62 may be installed with the central portion 84 positioned adjacent the upstream surface 72. Preferably, the bridging element 62 is installed with the central portion 84 positioned adjacent the downstream surface 76. When installed in the latter configuration, the higher fluid pressure P2 in the first chamber 74 and in the gap 68 aids in seating the bridging element 62 against the downstream surface 76.

The end portions 86 are resiliently sprung into the slots 64, and are in direct contact with each of the upstream 72 and downstream 76 surfaces. The end portions 86 alternate in direction, first away from and then back toward the central portion 84 and the gap 68, thus approximating a waveform. Although the examples in the figures illustrate approximately one wave cycle, more or less wave cycles may be used. The number of wave cycles depends on the slot width (W) and the amount of resilient spring force necessary to positively seat the end portions 86 against the upstream 72 and downstream 76 surfaces.

As may best be seen in FIG. 4C, a free height (H) of the uninstalled bridging element 62 is slightly larger than the opening width (W) of the slot 64. Preferably, the free height (H) is between 0.005 inch (0.127 mm) and 0.020 inch (0.508 mm) larger than the opening width (W). These dimensions are exemplary only and the actual sizes may vary for a specific application. The bridging element 62 is made of a material with suitable low temperature ductility and high temperature strength. Preferably, a Nickel or Cobalt based alloy strip approximately 0.010 inch (0.254 mm) thick is used. Stamping, progressive rolling or other suitable forming process may be used to form the profile of the strip.

Since the free height (H) is greater than the opening width (W), the end portions 86 are compressed together and resiliently sprung into the slots 64 during assembly. The interference fit between the end portions 86 and the upstream 80 and downstream 82 surfaces creates four independent leakage restrictions 90. The multiple restrictions 90 significantly reduce leakage from the first chamber 74 to the second chamber 78. As may also be seen in FIG. 4B, the multiple restrictions 90 remain intact, even if the slots 64 are slightly misaligned.

While the present invention has been described in the context of specific embodiments thereof, other alternatives, modifications and variations will become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications and variations as fall within the broad scope of the appended claims.

Claims

1. A seal for restricting leakage of a fluid from a first chamber, through a gap between two spaced components, to a second chamber, comprising:

a slot in each of the components, wherein the slots are open to the gap and each slot contains a longitudinal axis;

a bridging element, wherein said bridging element contains a sectional profile, transverse to the longitudinal slot axis, that includes a flat central portion disposed between two approximately waveform shaped end portions; and

wherein the bridging element spans between the two components with the end portions being disposed in the slots and the central portion being disposed in the gap.

2. The seal of claim 1 wherein the slots each contain an upstream surface proximate the first chamber and a downstream surface proximate the second chamber, and the end portions are resiliently sprung into the slots, forming an interference fit between the end portions and the upstream and downstream surfaces.

3. The seal of claim 2 wherein the central portion is adjacent the downstream surfaces.

4. The seal of claim 3 wherein the end portions alternate in direction, first away from and then back towards the gap.

5. The seal of claim 4 wherein the end portions alternate for approximately one wave cycle.

6. The seal of claim 1 wherein the bridging element is made of a nickel based alloy strip.

7. The seal of claim 1 wherein the longitudinal axis of each slot is linear.

8. The seal of claim 1 wherein the two components are turbine vanes.

9. The seal of claim 1 wherein the fluid is compressor air.

10. A gap bridging element comprising:

a sectional profile, transverse to a longitudinal axis, said profile including a flat, central portion disposed between two approximately waveform shaped, end portions.

11. The gap bridging element of claim 10 wherein the end portions alternate in direction, away from and towards the central portion.

12. The gap bridging element of claim 11 wherein the end portions alternate for approximately one wave cycle.

13. The gap bridging element of claim 10 wherein the bridging element is made of a nickel based alloy strip.

14. The gap bridging element of claim 10 wherein the longitudinal axis is linear.