Patent Application
20070212214
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
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.
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.
a 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.
b 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.
c is a simplified sectional view of a gap bridging element of
An exemplary turbine 16 of a gas turbine engine 10 is illustrated in
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 (
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
Further details of a segmented component seal 60 according to an embodiment of the invention are generally illustrated in
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
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
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.
