Patent Application
20080025838
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
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
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
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.
