US20080025838A1

US20080025838A1 - Ring seal for a turbine engine

Info

Publication number: US20080025838A1
Application number: US11/492,589
Authority: US
Inventors: Bonnie D. Marini; Douglas A. Keller; David C. Radonovich; Gary B. Merrill; Steven J. Vance; Anthony L. Schiavo
Original assignee: Siemens Power Generations Inc
Current assignee: Siemens Energy Inc
Priority date: 2006-07-25
Filing date: 2006-07-25
Publication date: 2008-01-31

Abstract

Aspects of the invention are directed to a ceramic matrix composite ring seal segment. The ring seal segment according to aspects of the invention includes a relatively simple body that is circumferentially curved. At least a portion of the hot gas path surface of the ring seal segment can be coated with a thermal insulating. material. In one embodiment, each ring seal segment can be operatively connected to a stationary support structure, such as by way of isolation rings. The ring seal segments and/or the isolation rings can be configured so as to restrain the ring seal segments in the axial, radial and/or circumferential directions. The ring seal segments can be attached to the isolation rings so that the support points act opposite the operating pressure loads. Thus, the ring seal segments carry these loads in compression, a strong direction of the CMC fibers.

Description

FIELD OF THE INVENTION

Aspects of the invention relate in general to turbine engines and, more particularly, to ring seals in the turbine section of a turbine engine.

BACKGROUND OF THE INVENTION

FIG. 1 shows an example of one known turbine engine 10 having a compressor section 12, a combustor section 14 and a turbine section 16. In the turbine section 16 of a turbine engine, there are alternating rows of stationary airfoils 18 (commonly referred to as vanes) and rotating airfoils 20 (commonly referred to as blades). Each row of blades 20 is formed by a plurality of rotating airfoils 20 attached to a disc 22 provided on a rotor 24. The blades 20 can extend radially outward from the discs 22 and terminate in a region known as the blade tip 26. Each row of vanes 18 is formed by attaching a plurality of vanes 18 to a vane carrier 28. The vanes 18 can extend radially inward from the inner peripheral surface 30 of the vane carrier 28. The vane carrier 28 is attached to an outer casing 32, which encloses the turbine section 16 of the engine 10.
Between the rows of vanes 18, a ring seal 34 can be attached to the inner peripheral surface 30 of the vane carrier 28. The ring seal 34 is a stationary component that acts as a hot gas path guide between the rows of vanes 18 at the locations of the rotating blades 20. The ring seal 34 is commonly formed by a plurality of metal ring segments. The ring segments can be attached either directly to the vane carrier 28 or indirectly such as by attaching to metal isolation rings (not shown) that attach to the vane carrier 28. Each ring seal 34 can substantially surround a row of blades 20 such that the tips 26 of the rotating blades 20 are in close proximity to the ring seal 34.
During engine operation, high temperature, high velocity gases flow through the rows of vanes 18 and blades 20 in the turbine section 16. The ring seals 34 are exposed to these gases as well. Some metal ring seals 34 must be cooled in order to withstand the high temperature. In many engine designs, demands to improve engine performance have been met in part by increasing engine firing temperatures. Consequently, the ring seals 34 require greater cooling to keep the temperature of the ring seals 34 within the critical metal temperature limit. In the past, the ring seals 34 have been coated with thermal barrier coatings to minimize the amount of cooling required. However, even with a thermal barrier coating, the ring seal 34 must still be actively cooled to prevent the ring seal 34 from overheating and burning up. Such active cooling systems are usually complicated and costly. Further, the use of greater amounts of air to cool the ring seals 34 detracts from the use of air for other purposes in the engine.
As an alternative, the ring seals 34 could be made of ceramic matrix composites (CMC), which have higher temperature capabilities than metal alloys. By utilizing such materials, cooling air can be reduced, which has a direct impact on engine performance, emissions control and operating economics. However, there are a number of natural limitations and manufacturing constraints associated with CMC materials. For instance, CMC materials (oxide and non-oxide based) can have anisotropic strength properties. The interlaminar tensile strength (the “through thickness” tensile strength) can be substantially less than the in-plane strength. Many prior ring seal designs include small radius corners and tightly-curved sections. Such areas are difficult to form in a CMC component using known fabrication techniques. Further, anisotropic shrinkage during processing can lead to result in de-lamination defects in such areas, which can further reduce the interlaminar tensile strength of the CMC material.
Thus, there is a need for a ring seal construction that can minimize the effects of the anisotropic characteristics of CMC materials.

SUMMARY OF THE INVENTION

Aspects of the invention are directed to a turbine engine ring seal system. The system includes a ring seal segment that has a first circumferential end and a second circumferential end. The ring seal segment is circumferentially curved as it extends between the first and second circumferential ends. The ring seal segment also has an axial forward end, an axial aft end, a radially outer surface and a radially inner surface. The radially inner surface is radially inwardly concave.
The ring seal segment is made of ceramic matrix composite, such as, for example, an oxide-oxide ceramic matrix composite. Thus, the ring seal segment can include a ceramic matrix in which there are a plurality of fibers. At least a substantial majority of the fibers can be oriented parallel to an axis about which the ring seal segment is circumferentially curved.
A thermal insulating material can be attached to the radially inner surface of the ring seal segment. The thermal insulating material can be a friable graded insulation. The thermal insulating material can be recessed from the axial forward end of the ring seal segment so that a forward shelf is formed. Likewise, the thermal insulating material can be recessed from the axial aft end of the ring seal segment so that an aft shelf is formed.
The system further includes a stationary support structure. The ring seal segment is operatively connected to the stationary support structure at the axial forward end and at the axial aft end of the ring seal segment. In one embodiment, a forward isolation ring and an aft isolation ring can be attached to the stationary support structure. In such case, the forward shelf can engage the forward isolation ring, and the aft shelf can engage the aft isolation ring. As a result, the ring seal segment can be indirectly connected to the stationary support structure by the isolation rings.
Each of the forward and aft isolation rings can include a radially extending body and a ledge that extends substantially axially. The ledge can include a radially inner surface and a radially outer surface. The forward shelf can engage the ledge of the forward isolation ring, and the aft shelf can engage the ledge of the aft isolation ring. When such engagement occurs, the thermal insulating material can be substantially flush with the radially inner surface of each of the ledges.
In one embodiment, the ring seal segment can operatively engage the stationary support structure so that the ring seal segment is restrained in the radially outward direction. To that end, each of the isolation rings can have an elongated channel. A portion of the ring seal segment including the axial forward end can be received within the channel in the forward isolation ring. Similarly, a portion of the ring seal segment including the axial aft end can be received in the channel in the aft isolation ring. Thus, the ring seal segment can be restrained in at least the radially outward direction.
Alternatively or in addition, the ring seal segment can operatively engage the stationary support structure such that the ring seal segment is substantially circumferentially restrained. To that end, each of the isolation rings can provide an axially extending protrusion, and each of the axial forward and aft ends of the ring seal segment can include a notch. The protrusion of the forward isolation ring can be received in the notch in the forward end of the ring seal segment. The protrusion of the aft isolation ring can be received in the notch in the aft ring seal segment. As a result, the ring seal segment can be restrained in the circumferential direction.
Another turbine engine ring seal system according to aspects of the invention includes a stationary support structure, a forward isolation ring and an aft isolation ring opposite the forward isolation ring. The forward and aft isolation rings are attached to the stationary support structure and extend substantially radially inward from it. Each of the isolation rings can have a radially inner surface.
The system further includes a ring seal segment that has a first circumferential end and a second circumferential end. The ring seal segment is circumferentially curved as it extends between the first and second circumferential ends. The ring seal segment can be circumferentially curved relative to an axis. The ring seal segment further has an axial forward end, an axially aft end, a radially outer surface and a radially inner surface. The radially inner surface is radially inwardly concave.
The ring seal segment is made of ceramic matrix composite, such as an oxide-oxide ceramic matrix composite. Thus, the ring seal segment includes a ceramic matrix with a plurality of fibers. At a minimum, a substantial majority of the fibers can be oriented parallel to the axis.
At least a portion of the radially inner surface of the ring seal segment is coated with a thermal insulating material, which can be, for example, a friable graded insulation. The thermal insulating material can be recessed from the axial forward end of the ring seal segment so that a forward shelf is formed. Further, the thermal insulating material can be recessed from the axial aft end of the ring seal segment so that an aft shelf is formed.
The axial forward end of the ring seal segment is operatively attached to the forward isolation ring. The axial aft end of the ring seal segment is operatively attached to the aft isolation ring. In one embodiment, the forward shelf of the ring seal segment can operatively engage the forward isolation ring, and the aft shelf of the ring seal segment can operatively engage the aft isolation ring. The thermal insulating material can be substantially flush with the radially inner surface of each of the isolation rings.
Each of the isolation rings can have an elongated channel therein. A portion of the ring seal segment that includes the axial forward end can be received within the channel in the forward isolation ring. Similarly, a portion of the ring seal segment that includes the axial aft end can be received in the channel in the aft isolation ring. Thus, the ring seal segment can be restrained in at least the radially outward direction.
In one embodiment, each of the isolation rings can also provide an axially extending protrusion, which can be located within the channel. Each of the axial forward and aft ends of the ring seal segment can include a notch. The protrusion of the forward isolation ring can be received in the notch in the forward end of the ring seal segment. The protrusion of the aft isolation ring can be received in the notch in the aft ring seal segment. As a result, the ring seal segment can be restrained in the circumferential direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the turbine section of a known turbine engine.

FIG. 2 is an isometric view of a ring seal segment according to aspects of the invention.

FIG. 3 is an exploded isometric view of a ring seal segment attachment system according to aspects of the invention.

FIG. 4 is an isometric bottom view of a ring seal segment attachment system according to aspects of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention are directed to a ceramic matrix composite (CMC) ring seal construction and attachment system that can minimize the manufacturing limitations and natural anisotropic effects of CMC materials. Aspects of the invention will be explained in connection with one possible ring seal segment for a turbine engine, but the detailed description is intended only as exemplary. An embodiment of the invention is shown in FIGS. 2-4, but the present invention is not limited to the illustrated structure or application.
FIG. 2 shows a ring seal body according to aspects of the invention. The ring seal body can be, for example, a ring seal segment 50. The ring seal segment 50 can have an axial forward end 52 and an axial aft end 54. The terms “forward” and “aft” are intended to mean relative to the direction of the gas flow 56 through the turbine section when the ring seal segment 50 is installed in its operational position. The ring seal segment 50 can also have a radially inner surface 58 and a radially outer surface 60. The ring seal segment 50 can have a first circumferential end 62 and a second circumferential end 64. The ring seal segment 50 can be curved circumferentially as it extends from the first circumferential end 62 to the second circumferential end 64. The radially inner surface 58 can be radially inwardly concave. The terms “axial,” “radial” and “circumferential” and variations thereof are intended to mean relative to the turbine axis 66 when the ring seal segment 50 is installed in its operational position.
The ring seal segment 50 can be made of ceramic matrix composite (CMC). For example, the ring seal segment 50 can be made of an oxide-oxide CMC, such as AN-720, which is available from COI Ceramics, Inc., San Diego, Calif. In one embodiment, the ring seal segment 50 can be made of a hybrid oxide CMC material, an example of which is disclosed in U.S. Pat. No. 6,733,907, which is incorporated herein by reference. The thickness of the ring seal segment 50 can be substantially uniform throughout. The ring seal segment 50 can be formed by any suitable fabrication technique, such as winding, weaving, and lay-up. The manufacture of a ring seal segment 50 according to aspects of the invention is facilitated by the relatively simple arc-like shape. It will be appreciated that the absence of areas with a small radius of curvature can avoid the prior difficulties that could arise in such areas due to the anisotropic characteristics of CMC materials.
The CMC material of the ring seal segment 50 includes a ceramic matrix 68 and a plurality of fibers 70 within the matrix 68. The fibers 70 of the CMC can be oriented to provide the desired strength properties. For instance, the fibers 70 can be oriented to provide anisotropic, orthotropic, or in-plane isotropic properties. In one embodiment, a substantial majority of the fibers 70 can extend substantially parallel to the flow path 56 of the turbine. For instance, at least some of the fibers 70 can extend from the axial forward end 52 toward the axially aft end 54. Alternatively or in addition, at least some of the fibers 70 can extend from the first circumferential end 62 toward the second circumferential end 64. In one embodiment, the fibers 70 can be arranged at substantially 90 degrees relative to each other, such as a 0-90 degree orientation or a ±45 degree orientation. Again, these are merely examples as the fibers 70 of the CMC can be arranged as needed.
Because the ring seal segment 50 is exposed to the hot combustion gases 56, at least a portion of the radially inner surface 58 of the ring seal segment 50 can be coated with a thermal insulating material 72. The thermal insulating material 72 can be, for example, a friable graded insulation (FGI). Various examples of FGI are disclosed in U.S. Pat. Nos. 6,676,783; 6,670,046; 6,641,907; 6,287,511; 6,235,370; and 6,013,592, which are incorporated herein by reference. A layer of adhesive or other bond-enhancing material (not shown) can be used between the CMC ring seal segment 50 and the thermal insulating material 72 to facilitate attachment.
In one embodiment, the thermal insulating material 72 can cover a portion of the radially inner surface 58. As shown in FIG. 2, the thermal insulating material 72 can be recessed from at least the axial forward end 52 and the axially aft end 54 of the ring seal segment 50. As a result, a forward shelf 74 can be formed by the uncoated portion of the radially inner surface 58 proximate the axial forward end 52, and an aft shelf 76 can be formed by the uncoated portion of the radially inner surface 58 proximate the axial aft end 54. Similarly, the thermal insulating material 72 can be recessed from the first and second circumferential ends 62, 64. In such case, additional shelves 78 can be formed by the uncoated portions of the radially inner surface 58 proximate each of the circumferential ends 62, 64.
A plurality of the ring seal segments 50 configured in accordance with aspects of the invention can be installed so that each of the circumferential end 62, 64 of a ring seal segment 50 is substantially adjacent to one of the circumferential ends 62, 64 of a neighboring ring seal segment. The plurality of ring seal segments 50 can collectively form an annular ring seal.
The ring seal segments 50 can be operatively connected to a stationary support structure 80 in the turbine section. The stationary support structure 80 can be, for example, a turbine casing or a vane carrier. Preferably, most, if not all, of the features directed to facilitating the operative connection of the ring seal segments 50 are provided in the stationary support structure 80 or other associated structures so as to retain the relatively simple geometry of the ring seal segments 50.
In one embodiment, the operative connection between each ring seal segment 50 and the stationary support structure 80 can be indirect. For instance, each ring seal segment 50 can be operatively connected to the stationary support structure 80 by way of a forward isolation ring 82 and an aft isolation ring 84. The isolation rings 82, 84 can be attached to the stationary support structure 80 in any of a number of known ways. For instance, a portion of each isolation ring 82, 84 can be configured as a hook to be received in a respective slot (not shown) provided in the stationary support structure 80. The isolation rings 82, 84 can extend radially inwardly from the stationary support structure 80. Each of the isolation rings 82, 84 can form a substantially 360 degree ring.
The isolation rings 82, 84 can have various configurations. In one embodiment, each of the isolation rings 82, 84 can be a single piece or can be made of a plurality of pieces. The forward and aft isolation rings 82, 84 may or may not be substantially identical to each other. The isolation rings 82, 84 can have any suitable configuration. In one embodiment, the isolation rings 82, 84 can be generally L-shaped having a body 86 and an axially extending ledge 88. The ledge 88 can have a radially inner surface 90 and a radially outer surface 92.
The ring seal segments 50 can be installed so that the forward and aft shelves 74, 76 of each ring seal segment engage a respective ledge 88 of the forward and aft isolation rings 82, 84. For instance, the forward shelf 74 can engage the radially outer surface 92 of the ledge 88 of the forward isolation ring 82. Likewise, the aft shelf 88 can engage the radially outer surface 88 of the ledge 88 of the aft isolation ring 84. In such case, it is preferred if the thermal insulating material 72 is substantially flush with the radially inner surface 90 of each ledge 88, as shown in FIG. 4. As a result of such an arrangement, neither the isolation rings 82, 84 nor the thermal insulating material 72 protrude into the hot gas path 56. Thus, flow interruptions in the hot gas path 56 and consequent aerodynamic losses are minimized. It will be appreciated that the engagement between the shelves 74, 76 and ledges 88 can restrain the ring seal segments 50 in the radially inward direction. Further, the forward and aft isolation rings 82, 84 can restrain axial movement of the ring seal segments 50.
The ring seal segments 50 can be restrained in other directions as well. The ring seal segments 50 and/or the isolation rings 82, 84 can be adapted to provide the desired restraint. For instance, the forward isolation ring 82 can provide a channel 94 for receiving a portion of the ring seal segment 50 including the axial forward end 52. Likewise, the aft isolation ring 84 can provide a channel 94 for receiving a portion of the ring seal segment 50 including the axial aft end 54. In such case, the ring seal segments 50 can be restrained in at least the radially outward direction by the channels 94.
Alternatively or in addition, the isolation rings 82, 84 and/or the ring seal segments 50 can be adapted to provide circumferential restraint. In one embodiment, the axial forward end 52 of the ring seal segment 50 can provide at least one notch 96. Likewise, the axial aft end 54 of the ring seal segment 50 can include at least one notch 96. The notches 96 can be centrally located on each end 52, 54 of the ring seal segment 50. The notches 96 can be formed in the ring seal segment 50 by any suitable process. Each of the isolation rings 82, 84 can provide one or more protrusions 98 to be received in a respective notch 96 in the forward and aft ends 52, 54 of the ring seal segments 50. The protrusions 98 can be located within the channels 94. It will be appreciated that the engagement between the protrusions 98 and the notches 96 can restrain circumferential movement of the ring seal segments 50. Significantly, in any of the above schemes, the ring seal segment 50 can be retained by the isolation rings 82, 84 without the use of additional fasteners or other mounting hardware.
The isolation rings 82, 84 can be made of metal. Because of the high temperature environment of the turbine, the isolation rings 82, 84 must be cooled. The isolation rings 82, 84 can be cooled in any of a number of ways. In one embodiment, the isolation rings 82, 84 can include one or more internal-cooling passages (not shown). A coolant, such as compressed air, can be supplied to the passages. The coolant can exit the isolation rings 82, 84 through outlet passages 100 and enter the hot gas path 56 of the turbine.
Like the isolation rings 82, 84, the ring seal segment 50 according to aspects of the invention can be cooled during engine operation. A coolant, such as air, can be supplied to the radially outer surface 60 of the ring seal segment 50. However, there is a potential for such coolant, which is at a relatively high pressure, to leak through the interfaces between adjacent circumferential ends 62, 64 of neighboring ring seal segments 50. Another leakage path is between the engaging portions of the isolation rings 82, 84 and the ring seal segments 50. Seals (not shown) can be operatively positioned to minimize these leakage paths. The ring seal segment 50 and/or isolation rings 82, 84 can be adapted as necessary to facilitate sealing.
During engine operation, the ring seal segment 50 can be subjected to a variety of loads. The ring seal segment 50 according to aspects of the invention is well suited to withstand the expected operational loads. The ring seal segments 50 and their associated attachment system are configured so that the support points act opposite the operating pressure loads. Thus, the loads are carried by the ring seal segments 50 in compression, which is one of the strongest strength directions of the CMC fibers. Further, the ring seal segment attachment system allows thermal growth and contraction of the ring seal segment without undue constraint, thereby minimizing thermally induced stresses.
The foregoing description is provided in the context of one possible ring seal segment for use in a turbine engine. Thus, it will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention as defined in the following claims.

Claims

1. A turbine engine ring seal system comprising:

a ceramic matrix composite ring seal segment having a first circumferential end and a second circumferential end, the ring seal segment being circumferentially curved as it extends between the first and second circumferential ends, the ring seal segment further having an axial forward end, an axial aft end, a radially outer surface and a radially inner surface, the radially inner surface being radially inwardly concave; and

a stationary support structure, wherein the ring seal segment is operatively connected to the stationary support structure at the axial forward end and at the axial aft end.

2. The system of claim 1 wherein the ceramic matrix composite is an oxide-oxide ceramic matrix composite.

3. The system of claim 1 further including a thermal insulating material attached to the radially inner surface of the ring seal segment.

4. The system of claim 3 wherein the thermal insulating material is a friable graded insulation.

5. The system of claim 3 further including a forward isolation ring and an aft isolation ring attached to the stationary support structure, wherein the thermal insulating material is recessed from the axial forward end of the ring seal segment so that a forward shelf is formed, and wherein the thermal insulating material is recessed from the axial aft end of the ring seal segment so that an aft shelf is formed, and wherein the forward shelf engages the forward isolation ring and the aft shelf engages the aft isolation ring, whereby the ring seal segment is indirectly connected to the stationary support structure by the isolation rings.

6. The system of claim 5 wherein each of the forward and aft isolation rings includes a radially extending body and a ledge that extends substantially axially, wherein the ledge includes a radially inner surface and a radially outer surface, wherein the forward shelf engages the ledge of the forward isolation ring and the aft shelf engages the ledge of the aft isolation ring, and wherein the thermal insulating material is substantially flush with the radially inner surface of each of the ledges.

7. The system of claim 1 wherein the ring seal segment operatively engages the stationary support structure so as to be restrained in the radially outward direction.

8. The system of claim 7 further including a forward isolation ring and an aft isolation ring attached to the stationary support structure, wherein each of the isolation rings has an elongated channel therein, wherein a portion of the ring seal segment including the axial forward end is received within the channel in the forward isolation ring, and wherein a portion of the ring seal segment including the axial aft end is received in the channel in the aft isolation ring, whereby the ring seal segment is restrained in at least the radially outward direction.

9. The system of claim 1 wherein the ring seal segment operatively engages the stationary support structure so as to be substantially circumferentially restrained.

10. The system of claim 9 further including a forward isolation ring and an aft isolation ring attached to the stationary support structure, each of the isolation rings providing an axially extending protrusion, wherein each of the axial forward and aft ends of the ring seal segment include a notch, wherein the protrusion of the forward isolation ring is received in the notch in the forward end of the ring seal segment, and wherein the protrusion of the aft isolation ring is received in the notch in the aft end of the ring seal segment, whereby the ring seal segment is restrained in the circumferential direction.

11. The system of claim 1 wherein the ring seal segment is circumferentially curved relative to an axis, wherein the ceramic matrix composite of the ring seal segment includes a ceramic matrix with a plurality of fibers therein, wherein at least a substantial majority of the fibers are oriented parallel to the axis.

12. A turbine engine ring seal system comprising:

a stationary support structure;

a forward isolation ring;

an aft isolation ring opposite the forward isolation ring, the forward and aft isolation rings attached to the stationary support structure and extending substantially radially inward therefrom; and

a ceramic matrix composite ring seal segment having a first circumferential end and a second circumferential end, the ring seal segment being circumferentially curved as it extends between the first and second circumferential ends, the ring seal segment further having an axial forward end, an axially aft end, a radially outer surface and a radially inner surface, the radially inner surface being radially inwardly concave, wherein at least a portion of the radially inner surface of the ring seal segment is coated with a thermal insulating material,

wherein the axial forward end of the ring seal segment is operatively attached to the forward isolation ring and the axial aft end of the ring seal segment is operatively attached to the aft isolation ring.

13. The system of claim 12 wherein the ceramic matrix composite is an oxide-oxide ceramic matrix composite.

14. The system of claim 12 wherein the thermal insulating material is a friable graded insulation.

15. The system of claim 12 wherein the thermal insulating material is recessed from the axial forward end of the ring seal segment so that a forward shelf is formed, and wherein the thermal insulating material is recessed from the axial aft end of the ring seal segment so that an aft shelf is formed, and wherein the forward shelf operatively engages the forward isolation ring and the aft shelf operatively engages the aft isolation ring.

16. The system of claim 12 wherein each of the isolation rings has a radially inner surface, wherein the thermal insulating material is substantially flush with the radially inner surface of each of the isolation rings.

17. The system of claim 12 wherein each of the isolation rings has an elongated channel therein, wherein a portion of the ring seal segment including the axial forward end is received within the channel in the forward isolation ring, and wherein a portion of the ring seal segment including the axial aft end is received in the channel in the aft isolation ring, whereby the ring seal segment is restrained in at least the radially outward direction.

18. The system of claim 17 wherein each of the isolation rings providing an axially extending protrusion, wherein each of the axial forward and aft ends of the ring seal segment includes a notch, wherein the protrusion of the forward isolation ring is received in the notch in the forward end of the ring seal segment, and wherein the, protrusion of the aft isolation ring is received in the notch in the aft ring seal segment, whereby the ring seal segment is restrained in the circumferential direction.

19. The system of claim 18 wherein the protrusion is located within the channel.

20. The system of claim 12 wherein the ring seal segment is circumferentially curved relative to an axis, wherein the ceramic matrix composite of the ring seal segment includes a ceramic matrix with a plurality of fibers therein, wherein at least a substantial majority of the fibers are oriented parallel to the axis.