Patent Application
20080087021
Embodiments of the invention are directed to a construction for a ceramic matrix composite turbine engine component. Aspects of the invention will be explained in connection with a ring seal segment, but the detailed description is intended only as exemplary. An embodiment of the invention is shown in
The base portion 52 can have a radially inner surface 56 and a radially outer surface 58. The ring seal segment 50 can have an axial forward side 60 and an axial aft side 62. Further, the ring seal segment 50 can have a first circumferential side 64 and a second circumferential side 66. The terms “axial,” “radial” and “circumferential” and variations thereof are intended to mean relative to the turbine axis 59 when the ring seal segment 50 is installed in its operational position.
The base portion 52 can have any of a number of suitable configurations. In one embodiment, the base portion 52 can be substantially flat. In another embodiment, the base portion 52 can be curved circumferentially as it extends from the first circumferential side 64 to the second circumferential side 66. The entire base portion 52 can be arcuate or otherwise curved. Alternatively, a portion of the base portion 52 can be curved. For example, in one embodiment, only the radially inner surface 56 of the base portion 52 may be radially inwardly concave. In such case, the radially outer surface 58 of the base portion 52 can be substantially flat. The term “radially inwardly concave” means that the radially inner surface 56 of the base portion 52 is curved so that it opens to the turbine axis 59. Further, the term “radially inwardly concave” can include embodiments in which the radially inner surface 56 is substantially cylindrical, such that each point on the radially inner surface 56 can be at a substantially uniform radial distance from the turbine axis 59. In addition, “radially inwardly concave” can include a radially inner surface that is conical. Depending on its circumferential length and its radius of curvature, the base portion 52 may have negligible curvature such that it is substantially flat. For example, if the circumferential length of the base portion 52 is sufficiently short and/or when the radius of curvature of the base portion 52 is sufficiently large, the base portion 52 can be substantially flat.
The frame portion 54 can be made of at least three side walls, so as to enclose a space 55 therein. In one embodiment, the frame portion 54 can have four side walls: a forward side wall 68, an aft side wall 70, a first transverse side wall 72 and a second transverse side wall 74. The terms “forward” and “aft” are intended to mean relative to the direction of the gas flow 71 through the turbine section when the ring seal segment 50 is installed in its operational position. The forward and aft side walls 68, 70 can be axially spaced from each other. Further, the forward and aft side walls 68, 70 can be substantially parallel to each other. Each of the transverse side walls 72, 74 is angled relative to the forward and aft side walls 68, 70. In one embodiment, the transverse side walls 72, 74 extend at substantially 90 degrees relative to both the forward and aft side walls 68, 70. The first and second transverse side walls 72, 74 can be substantially parallel to each other. In some instances, first and second transverse side walls 72, 74 can be non-parallel. Depending on their relationships to each other, the four side walls 68, 70, 72, 74 can collectively have various general conformations, including, for example, substantially rectangular, parallelogrammatic or trapezoidal in conformation.
It should be noted that the frame portion 52 can include other walls in addition to the side walls. For example, as shown in
While the foregoing and subsequent description is directed to an embodiment in which the frame portion has four side walls, it should be noted that a ring seal segment according to aspects of the invention is not limited to a frame portion with four side walls. As noted earlier, the frame portion 52 can have three or more side walls. For example, in one embodiment, the frame portion 52 can have three side walls 110, 112, 114, as shown in
Referring to
The first and second transverse side walls 72, 74 can have an associated axial length A and radial length R, which can be sized as desired depending on the application at hand. The first and second transverse side walls 72, 74 can have any suitable axial length A and radial length R. In one embodiment, the first and second transverse side walls 72, 74 can have substantially the same axial and radial lengths A, R. However, the first and second transverse side walls 68, 70 can have different circumferential and/or radial lengths C, R.
In one embodiment, the forward and aft side walls 68, 70 can have substantially the same radial length as the first and second transverse side walls 72, 74. Further, the circumferential length C of the forward and aft side walls 68, 70 can be substantially equal to the axial length A of the first and second transverse side walls 72, 74. However, the first and second transverse side walls 72, 74 may be shorter or longer than the forward and aft side walls 72, 74 in one or more of the axial, circumferential and radial directions A, C, R.
The thickness of the ring seal segment 50 can be substantially uniform throughout; that is, the thickness of the side walls 68, 70, 72, 74 can be substantially identical to each other and to the thickness of the base portion 52. However, the thickness of at least one of the walls 68, 70, 72, 74 and/or the base 52 can be different. The variation in thickness can be gradual across one or more of the associated lengths of a side wall, or the thickness can be varied in local areas. The thickness of one or more of the side walls 68, 70, 72, 74 can vary, as may be needed to facilitate installation into the engine, hardware attachment and dimensional control. Further, variation in the thickness of one of more of the side walls 68, 70, 72, 74 can be helpful to in the management of mechanical loading of the ring seal segment 50 as well as vibratory wear and subsequent material loss.
The transition region 76 between two of the side walls can have any suitable form. For example, as shown in
The four side walls 68, 70, 72, 74 can extend from the base portion 52 at any suitable angle. In one embodiment, each of the side walls 68, 70, 72, 74 can extend at substantially 90 degrees from the base portion 52. Thus, when the ring seal segment 50 is installed in its operational position, the side walls 68, 70, 72, 74 can extend substantially radially outward relative to the turbine axis 59. One or more of the side walls 68, 70, 72, 74 can extend at angles greater than or less than 90 degrees so as to form an acute or obtuse angle relative to the base portion 52. Ideally, the side walls 68, 70, 72, 74 extend at the same angle relative to the base portion 52; however, one or more of the side walls 68, 70, 72, 74 can extend from the base portion 52 at a different angle.
The frame portion 52 can have an outer surface 81, which can be collectively defined by the side walls 68, 70, 72, 74 and the transition regions 76 therebetween. The outer surface 81 can have any suitable conformation. For instance, the outer surface 81 can be substantially flat. Alternatively, the outer surface 81 can be substantially conical or a substantially cylindrical. It will be understood that the outer surface 81 can have any suitable surface contour.
The ring seal segment 50 can be made of ceramic matrix composite (CMC). The CMC can be an oxide based 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 CMC material of the ring seal segment 50 includes a ceramic matrix 77 and a plurality of reinforcing fibers 75 (only a few fibers are shown in
Between each of the side walls 68, 70, 72, 74 and the base portion 52, at least some of the reinforcing fibers 75 and/or laminate plies 79 span continuously across the transition region 80; that is, at least some of the fibers 75 and/or laminate plies 79 extend unbroken across the transition region 80 and into the base portion 52 and each of the respective side walls 68, 70, 72, 74. An example of such an arrangement between the forward side wall 68 and the base portion 52 is shown in
In addition, at least some of the reinforcing fibers 75 and/or laminate plies 79 span continuously across the transition region 76 between a connected pair of the side walls 68, 70, 72, 74. In other words, at least some of the fibers 75 and/or laminate plies 79 extend unbroken across the transition region 76 and into the respective pair of the side walls 68, 70, 72, 74.
Again, the above fibers arrangements in the CMC described above are merely examples. It will be understood that the fibers of the CMC can be arranged as needed.
The ring seal segment 50 can be formed by any suitable fabrication technique, such as winding, weaving, and fabric or unidirectional tape lay-ups. In one embodiment, ceramic fabric can be preimpregnated with matrix slurry and can be formed into or onto a mold. Each fabric ply 79 can be cut with a unique pattern such that during lay-up, any fabric splices are not aligned between adjacent plies or occur within a minimum specified distance from splices in other superimposed plies. In addition, the individual plies 79 can be formed to have most or all of the fibers 75 in the base portion 52 that extend continuously into each of the four side walls 68, 70, 72, 74 with minimal splices. Also, the necessary darts cut to allow formation of the transition regions 76, 80 and the sidewalls 68, 70, 72, 74 are designed to account for displacement that can occur from compaction of the laminae such that, in the compacted state, the splices can form butt-joints with minimal gap. Compaction can be by any of various forms, including hard tooling, pressure, vacuum, or combinations thereof. In the final state, the spliced joints can be distributed uniformly across either side of the transition regions 76, 80, thus retaining most of the reinforcing fibers 75 intact across the transition regions 76, 80.
It can be seen that various embodiments can alter the amount and method of reinforcing fiber 75 joining the base portion 52 and the sidewalls 68, 70, 72, 74 as well as the mating sidewalls 68, 70, 72, 74 to each other.
Because the ring seal segment 50 is exposed to the hot combustion gases during engine operation, at least a portion of the radially inner surface 56 of the ring seal segment 50 can be coated with a thermal insulating material 84. The thermal insulating material 84 can be, for example, a friable graded insulation (FGI) 86. 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 84 to facilitate attachment.
The thermal insulating material 84 can be applied over at least a portion of the radially inner surface 56 of the base portion 52. In one embodiment, the thermal insulating material 84 can completely cover the radially inner surface 56 of the base portion 52. The thickness of the thermal insulating material 84 can be substantially uniform, but, in some cases, it may be preferred if the thickness of the thermal insulating material 84 is non-uniform. The variation in thickness of the thermal insulating material 84 can occur in one or more directions, or it may vary in localized regions.
The thermal insulating material 84 can have a radially inner surface 87 that can form a gas path sealing surface during engine operation. The radially inner surface 87 can be substantially flat. Alternatively, as is shown in
The thermal insulating material 84 can terminate substantially at each side 60, 62, 64, 66 of the ring seal segment 50.
A ring seal segment 50 according to aspects of the invention can be installed in the turbine section of the engine in any suitable way. For instance, the ring seal segment 50 can be operatively connected to one or more stationary support structures in the turbine section of the engine including, for example, the turbine casing (not shown), a vane carrier 92 (see
The ring seal segment 50 can be operatively connected to the stationary support structure in any of a number of ways. Preferably, at least two of the side walls 68, 70, 72, 74 of the ring seal segment 50 are operatively connected to the stationary support structure. In one embodiment, one or more fasteners can be used to operatively connect the ring seal segment 50 and the stationary support structure. For example, the ring seal segment 50 can be operatively connected to the stationary support structure using pins. A first plurality of pins 98 can operatively connect the forward isolation ring 94 to the forward side wall 68 of the ring seal segment 50, and a second plurality of pins 100 can operatively connect the aft isolation ring 96 to the aft side wall 70 of the ring seal segment 50.
The pins 98, 100 can be made of any suitable material, such as metal. The pins 98, 100 can have any cross-sectional shape, such as circular, polygonal or rectangular. The first and second plurality of pins 98, 100 may or may not be substantially identical to each other. At least some of the pins 98, 100 can be removable. It will be understood that such an arrangement is provided to facilitate discussion, and aspects of the invention are not limited to such an arrangement.
Any quantity of pins 98, 100 can be used to operatively connect the forward side wall 68 and the forward isolation ring 94. In one embodiment, each of the first plurality of pins 98 and the second plurality of pins 100 can include three pins. The number and arrangement of the pins 98, 100 can be optimized for the load conditions and specific geometric allowances. In one embodiment, the quantity and/or the arrangement of the first plurality of pins 98 can be substantially identical to the quantity and the arrangement of the second plurality pins 100. However, the quantity and/or arrangement of the first plurality of pins 98 can be different from the quantity and arrangement of second plurality of pins 100. At least some of the pins 98, 100 can be threaded.
The ring seal segment 50 can be adapted to facilitate operative connection to the stationary support structure. In one embodiment, the forward and aft side walls 68, 70 can include one or more passages 102a, 102b to receive the pins 98, 100 so as to operatively connect the ring seal segment 50 and the isolation rings 94, 96.
Naturally, the passages 102a, 102b can be sized and arranged to correspond to receive the first and second plurality of pins 98 and 100, respectively. The passages 102a, 102b in the ring seal segment 50 can be oversized or slotted to allow for differential thermal expansion between the ring seal segment 50, the isolation rings 94, 96, and the pins 98, 100. Preferably, at least one of the passages 102a in the forward side wall 68 and at least one of the passages 102b in the aft side wall 70 can be substantially circular or otherwise shaped to substantially correspond to the cross-sectional shape of the pins 98, 100 received therein. The passages 102a, 102b can be formed in the spans 58, 60 by any suitable process.
Additional ring seal segments 50 can be attached to the stationary support structure in a similar manner to that described above. The plurality of the ring seal segments 50 can be installed so that each circumferential side 64, 66 of one ring seal segment 50 substantially abuts one of the circumferential side 64, 66 of a neighboring ring seal segment 50 so as to collectively form an annular ring seal. The ring seal substantially surrounds a row of blades such that the tips of the rotating blades are in close proximity to the ring seal. In cases where the thermal insulating material 84 extends beyond the circumferential sides 64, 66 of the ring seal segment 60, the ledge 88 of one ring seal segment 50 can substantially abut the ledge 88 of a neighboring ring seal segment 50.
During engine operation, the ring seal segment 50 will be exposed to the high temperature combustion gases 71. Because the ring seal segment 50 is made of a ceramic material, it can withstand the exposure to the hot gases 71 in the turbine section. Nonetheless, some cooling should be provided to the ring seal segment 71, though it will be appreciated that the amount of coolant needed will be less than that required for a metal ring seal. In one embodiment, a coolant 106, such as air or other suitable fluid, can be supplied in the space 101. The source of the coolant can be internal or external to the engine. Sealing can be provided as appropriate to minimize the escape of coolant 106 into the hot gas path 71.
During engine operation, the ring seal segments 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. For instance, the base portion 52 can be subjected to bending forces due to, among other things, the pressure differential across it. The side walls 68, 70, 72, 74 stiffen the base portion 52, and they provide bending strength to the base portion 52. Further, the first and second transverse side walls 72, 74 can strengthen the forward and aft side walls 68, 70 by acting as braces. The benefit is most pronounced for CMC materials with a low elastic modulus, such as oxide-oxide CMC materials, in which the material compliance assists in load redistribution from peak locations to neighboring side walls. In addition, the ability of oxide-based CMCs to operate in a nonlinear stress-strain regime also adds to the potential load sharing of such redundant load-bearing structures. Load (e.g., pressure or other mechanical load) can be reacted by the fasteners attaching the respective side walls to the stationary support structure, and can be transmitted through the CMC material in an in-plane orientation.
The ring seal segment 50 according to aspects of the invention can have relatively small radii of curvature in the transition region 80 between each side wall 68, 70, 72, 74 and the base portion 52, despite past problems with forming CMC structures such geometry. The ring seal segment 50 according to aspects of the invention can minimize these prior issues because the ring seal segment 50 is strengthened by three substantially perpendicular planes (defined by the base portion 52 and two of the side walls) that cooperate to provide structural strength to the ring seal segment 50. Because the unitary construction strengthens the ring seal segment 50, thinner CMC sections can be used compared to a ring seal segment design with separately formed and subsequently joined sidewalls. Such relatively thinner sections can appreciably reduce thermal stresses during operation.
The foregoing description is provided in the context of one possible ring seal segment for use in a turbine engine. However, aspects of the invention are not limited to ring seal segments. A CMC structure, as described herein, can be used in other areas of a turbine engine. For instance, the CMC structure can also be used as a heat shield 132 in the combustor section 134 of a turbine engine, as shown in
It will 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.
