Feather seal for CMC BOAS

A blade outer air seal assembly includes a support structure. A blade outer air seal has a plurality of segments that extends circumferentially about an axis and is mounted in the support structure. At least two of the segments have a base portion that extends from a first circumferential side to a second circumferential side. A first protrusion extends from the first circumferential side and has a first radially extending slot. A second protrusion extends from a second circumferential side and has a second radially extending slot. A feather seal is arranged in the first radially extending slot and the second radially extending slot between at least two segments.

BACKGROUND

This application relates to a ceramic matrix composite component assembly, such as a blade outer air seal assembly.

Gas turbine engines are known and typically include a compressor compressing air and delivering it into a combustor. The air is mixed with fuel in the combustor and ignited. Products of the combustion pass downstream over turbine rotors, driving them to rotate.

It is desirable to ensure that the bulk of the products of combustion pass over turbine blades on the turbine rotor. As such, it is known to provide blade outer air seals radially outwardly of the blades. Blade outer air seals have been proposed made of ceramic matrix composite fiber layers.

SUMMARY

In one exemplary embodiment, a blade outer air seal assembly includes a support structure. A blade outer air seal has a plurality of segments that extends circumferentially about an axis and is mounted in the support structure. At least two of the segments have a base portion that extends from a first circumferential side to a second circumferential side. A first protrusion extends from the first circumferential side and has a first radially extending slot. A second protrusion extends from a second circumferential side and has a second radially extending slot. A feather seal is arranged in the first radially extending slot and the second radially extending slot between at least two segments.

In a further embodiment of the above, at least one segment has at least one hook extending radially outward from the base portion. The first and second radially extending slots are circumferentially outward of at least one hook.

In a further embodiment of any of the above, the feather seal has a thickness that is less than a circumferential width of the first and second radially extending slots.

In a further embodiment of any of the above, a ratio of the circumferential width of the first and second radially extending slots to the thickness of the feather seal is between about 1.5 and 2.5.

In a further embodiment of any of the above, the feather seal has a thickness and a rounded end that has a greater thickness at a radially inner end.

In a further embodiment of any of the above, the feather seal is configured to rotate about the rounded end.

In a further embodiment of any of the above, the feather seal is configured to rotate less than about 10°.

In a further embodiment of any of the above, the thickness is about 0.010 to 0.030 inches (0.254-0.762 mm).

In a further embodiment of any of the above, the base portion extends from a first axial side to a second axial side to define a seal segment axial length. The feather seal extends in an axial direction for most of the seal segment axial length.

In a further embodiment of any of the above, the feather seal extends in the axial direction for at least about 80% of the seal segment axial length.

In a further embodiment of any of the above, he first and second protrusions are offset in a radial direction and overlap one another in a circumferential direction.

In a further embodiment of any of the above, a gap is arranged between each of the plurality of seal segments to accommodate thermal expansion. The gap is less than about 0.040 inches (0.254-1.016 mm).

In a further embodiment of any of the above, at least two seal segments are a ceramic matrix composite material.

In a further embodiment of any of the above, at least two seal segments are a monolithic ceramic material.

In a further embodiment of any of the above, the feather seal is a ceramic matrix composite material.

In a further embodiment of any of the above, the feather seal is a metallic material.

In another exemplary embodiment, a gas turbine engine includes a compressor section, a combustor section, and a turbine section arranged about an axis of rotation. An assembly has a plurality of segments arranged circumferentially about the axis of rotation. At least two of the segments have a base portion extending from a first circumferential side to a second circumferential side. A first protrusion extends from the first circumferential side and has a first radially extending slot. A second protrusion extends from a second circumferential side and has a second radially extending slot. A feather seal is arranged in the first radially extending slot and the second radially extending slot between the at least two segments.

In a further embodiment of any of the above, at least two segments are a ceramic material.

In a further embodiment of any of the above, the feather seal is ceramic material.

In a further embodiment of any of the above, the feather seal is a metallic material.

DETAILED DESCRIPTION

FIG. 2shows a portion of an example turbine section28, which may be incorporated into a gas turbine engine such as the one shown inFIG. 1. However, it should be understood that other sections of the gas turbine engine20or other gas turbine engines, and even gas turbine engines not having a fan section at all, could benefit from this disclosure. The turbine section28includes a plurality of alternating turbine blades102and turbine vanes97.

A turbine blade102has a radially outer tip103that is spaced from a blade outer air seal assembly104with a blade outer air seal (“BOAS”)106. The BOAS106may be made up of a plurality of seal segments105that are circumferentially arranged in an annulus about the central axis A of the engine20. The BOAS segments105may be monolithic bodies that are formed of a high thermal-resistance, low-toughness material, such as a ceramic matrix composite (“CMC”).

The BOAS106may be mounted to an engine case or structure, such as engine static structure36via a control ring or support structure110and a carrier112. The engine structure36may extend for a full 360° about the engine axis A. The engine structure36may support the support structure110via a hook or other attachment means. The engine case or support structure holds the BOAS106radially outward of the turbine blades102. Although a BOAS106is described, this disclosure may apply to other components, such as a combustor, inlet, exhaust nozzle, transition duct, or turbine vane, for example.

FIG. 3shows a portion of an example BOAS assembly104. The assembly104includes seal segments105mounted on a carrier112. Each seal segment105is a body that defines radially inner and outer sides R1, R2, respectively, first and second axial sides A1, A2, respectively, and first and second circumferential sides C1, C2, respectively. The radially inner side R1faces in a direction toward the engine central axis A. The radially inner side R1is thus the gas path side of the seal segment105that bounds a portion of the core flow path C. The first axial side A1faces in a forward direction toward the front of the engine20(i.e., toward the fan42), and the second axial side A2faces in an aft direction toward the rear of the engine20(i.e., toward the exhaust end).

In the illustrated example, each BOAS segment105includes a first wall120and a second wall122that extend radially outward from a base portion124. The first and second walls120,122extend along the base portion124in a generally axial direction, and are circumferentially spaced from one another. The base portion124extends between the first and second axial sides A1, A2and defines a gas path on a radially inner side and a non-gas path on a radially outer side. In this disclosure, forward, aft, upstream, downstream, axial, radial, or circumferential is in relation to the engine axis A unless stated otherwise. The base portion124may extend axially forward and/or aft of the first and second walls120,122to provide a surface for sealing of the BOAS first and second axial sides A1, A2. That is, the walls120,122may extend less than the full length of the seal segment105in the axial direction.

The walls120,122include hooks126,127, respectively at a radially outermost portion. The hooks126,127extend circumferentially inward towards one another. The hooks126,127are configured to secure the seal segment105to the carrier112. The hooks126,127extend towards the matefaces, or first and second circumferential sides C1, C2.

The carrier112has a platform118with axially extending hooks114,116. The hooks114,116extend radially outward from the platform118for attaching the carrier112and seal segment105to the support structure110. A portion of the platform118engages with the hooks126,127. The platform118is generally parallel to the base portion124of the seal segment105. In the illustrated example, the hooks126,127extend in a direction perpendicular to the walls120,122. In other examples, the hooks126,127may extend at an angle relative to the walls120,122. The axially extending hooks126,127provide engagement with the carrier112along all or most of the axial length of the carrier112. The carrier hooks114,116extend generally perpendicular to the seal segment hooks126,127. That is, the carrier hooks114,116extend generally circumferentially, while the seal segment hooks126,127extend generally axially.

The first and second circumferential sides C1, C2are configured to mate with adjacent seal segments105. In the illustrated example, the first circumferential side C1of each seal segment105has a protrusion130extending circumferentially outward from the seal segment105. The second circumferential side C2of each seal segment105has a second protrusion132extending circumferentially outward from the seal segment105. The protrusions130,132have different positions in the radial direction from one another. The protrusion130of a seal segment105is configured to engage with the second protrusion132of an adjacent seal segment. The protrusions130,132may extend along an axial length of the first and second walls120,122. The protrusions130,132provide sealing between the first and second circumferential sides C1, C2of each seal segment105.

The BOAS106may be formed of a ceramic matrix composite (“CMC”) material. Each seal segment105is formed of a plurality of CMC laminates. The laminates may be silicon carbide fibers, formed into a braided or woven fabric in each layer. In other examples, the BOAS106may be made of a monolithic ceramic.

CMC components such as BOAS segments105are formed by laying fiber material, such as laminate sheets or braids, in tooling, injecting a gaseous infiltrant into the tooling, and reacting to form a solid composite component. The component may be further densified by adding additional material to coat the laminates.

In an embodiment, the BOAS segment105is formed from fiber material such as silicon carbide (SiC). In one example, the protrusions130,132are integrally formed from the construction. The protrusions130,132may be formed by wrapping braided plies about a mandrel, then pressing the laminates in the axial direction to form the protrusions130,132in one example. In another example, the protrusions130,132may be ply dropped into preforms using inner and outer molds that form the protrusions130,132.

In some examples, the radially inner side R1may have a coating160. In the illustrated example, the BOAS segment105has an environmental barrier coating (EBC)162in addition to an abradable coating160. In other examples, the BOAS segment105may have one of the coatings160,162. The BOAS segment105may have no coating, or a different coating, in some examples.

A slot142is formed in the protrusion132. The slot142extends radially inward towards the first radial side R1. A slot144is formed in the protrusion130. The slot144extends radially outward. The slots142,144are substantially aligned with one another when two seal segments105are arranged adjacent one another. The slots142,144may extend less than the entire radial height of the protrusions132,130. The slots142,144extend most of an axial length of the protrusions132,130. For example, the slots142,144may extend at least about 80% of the axial length of the protrusions132,130. The slots142,144may extend less than about 95% of the axial length of the protrusions132,130, and ending at a wall near the second axial side A2. The wall near the second axial side A2may help prevent axial leakage.

An intersegment seal is arranged in the slots142,144. The intersegment seal may be a feather seal140, for example. The feather seal140extends in a generally radial direction. The feather seal140may have a length in the axial direction between about 1.5 and 2.5 inches (38.1-63.5 mm). In a further embodiment, the feather seal140may have a length in the axial direction of about 2 inches (50.8 mm). The feather seal140provides a seal between first and second circumferential sides C1, C2of adjacent BOAS segments105.

The feather seal140may be a metallic material or ceramic material. The feather seal140may be a cobalt-based alloy, for example. In another example, the feather seal140may be formed from CMC laminates, such as a woven architecture. The slots142,144may be machined into the BOAS segments105. The slots142,144may be machined via ultrasonic machining or conventional grinding, for example. The slots142,144provide forward line of sight access for the feather seal140to be inserted in the axial direction.

FIG. 4is a portion of the BOAS assembly104in a cold assembly state. In the cold assembly state, the slots142,144are circumferentially offset. A gap GCis formed between two adjacent seal segments105A,105B. The feather seal140and slot142,144arrangement permits this gap to change as the temperature of the assembly104changes during engine operation.

The slots have a width WSthat is greater than a thickness T of the feather seal140. The thickness T may be between about 0.01 and 0.03 inches (0.254-0.762 mm). In a further embodiment, the thickness T may be about 0.02 inches (0.508 mm). The slot width WSmay be about 1.5-2.5 times the thickness T. The feather seal140has a length L that extends generally in the radial direction. The length L is slightly less than a radial length of the two slots142,144, combined. The length L may be between about 0.25 and 0.35 inches (6.35-8.89 mm), for example. In a further example, the length L may be about 0.3 inches (7.62 mm). In the cold assembly state, the feather seal140contacts the slot144at a point150and contacts the slot144at a point152. The point150is near a radially innermost portion of the protrusion130and the point152is near a radially outermost portion of the protrusion132.

The feather seal140may have a bull-nosed end146. The end146has a larger width than the thickness T, in some examples. The feather seal140is configured to rotate about the end146. In this example, the feather seal140is arranged at an angle158with respect to the radial direction R. The angle158may be about 10° or less. In the illustrated example, the bull-nosed end146is at the radially inner end of the feather seal140. In other examples, the bull-nosed end146may be at the radially outer end of the feather seal140, or the feather seal140may rotate about an end that does not have a bull-nosed portion.

FIG. 5is a portion of the BOAS assembly104in a hot operation state. In a hot operation state, the gap GHbetween adjacent seal segments105A,105B may be larger than the gap GCin the cold state. In a hot operation state, the gap GHbetween adjacent seal segments105A,105B may likewise be transiently smaller than the gap GCin the cold state. The gap GHmay grow to between about 0 and about 0.040 inches (0.254-1.016 mm), for example. The larger gap GHshifts the slots142,144with respect to one another. The radial feather seal140rotates about the end146to remain in the slots142,144. In the hot state, the intersegment seal150contacts the seal segments at points154,156. In one example, the point154is near a radially outer portion of the slot144and the point156is at a radially outer portion of the slot142. In this position, the feather seal140is arranged at a second angle159relative to the radial direction R. In some examples, the second angle159is smaller than the angle158.

The disclosed radially extending slots and feather seal accommodate large mateface gap excursions from thermal growth mismatch within the BOAS assembly. This may be particularly helpful for CMC BOAS segments mounted to a metallic segmented carrier or full ring case. The feather seal slots are arranged away from highly stressed ply regions within the seal segment hooks. The featherseal itself is shielded from direct line of sight exposure to hot turbine flowpath gases. The design provides robust mateface sealing with the feather seal and with the shiplap protrusions on the circumferential sides of each seal segment. This arrangement may also permit a smaller feather seal than known circumferentially extending feather seals, which typically must be large enough to accommodate the changing gap between seal segments105.

In this disclosure, “generally axially” means a direction having a vector component in the axial direction that is greater than a vector component in the circumferential direction, “generally radially” means a direction having a vector component in the radial direction that is greater than a vector component in the axial direction and “generally circumferentially” means a direction having a vector component in the circumferential direction that is greater than a vector component in the axial direction.