Intersegment seal for CMC boas assembly

A blade outer air seal assembly includes a blade outer air seal that has a plurality of segments that extend circumferentially about an axis and are mounted in a carrier. At least two of the plurality of segments have a first wall and a second wall circumferentially spaced from one another and a base portion that extends from the first wall to the second wall. The base portion extends circumferentially outward past the first and second walls to form first and second sealing surfaces. An intersegment seal has a curved surface. The curved surface is engaged with the first and second sealing surfaces between the at least two segments.

BACKGROUND

This application relates to an intersegment seal for a blade outer air seal assembly and method of manufacturing an intersegment seal.

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 OF THE INVENTION

In one exemplary embodiment, a blade outer air seal assembly includes a blade outer air seal that has a plurality of segments that extend circumferentially about an axis and are mounted in a carrier. At least two of the plurality of segments have a first wall and a second wall circumferentially spaced from one another and a base portion that extends from the first wall to the second wall. The base portion extends circumferentially outward past the first and second walls to form first and second sealing surfaces. An intersegment seal has a curved surface. The curved surface is engaged with the first and second sealing surfaces between the at least two segments.

In a further embodiment of any of the above, the curved surface has a radius of curvature between about 0.050 and 0.300 inches (1.27-7.62 mm).

In a further embodiment of any of the above, the curved surface is on a radially inner side of the intersegment seal. A second curved surface is on a radially outer side of the intersegment seal.

In a further embodiment of any of the above, the second curved surface has a radius of curvature between about 0.020 and 0.150 inches (0.508-3.81 mm).

In a further embodiment of any of the above, the curved surface is on a radially inner side of the intersegment seal and a radially outer side has a flat surface.

In a further embodiment of any of the above, the first and second sealing surfaces taper radially inward.

In a further embodiment of any of the above, a clip secures the intersegment seal between the at least two segments.

In a further embodiment of any of the above, the clip has first and second wings that engage with the first and second walls of the at least two seal segments.

In a further embodiment of any of the above, the clip includes a tab at an axial side for axial retention of the intersegment seal.

In a further embodiment of any of the above, the clip includes a radial tab configured to bias the intersegment seal radially inward.

In a further embodiment of any of the above, the radial tab is a spring loaded tab.

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

In a further embodiment of any of the above, the intersegment seal is formed from a ceramic material.

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

In another exemplary embodiment, a method of manufacturing a blade outer air seal assembly includes laying a plurality of laminates to form a seal body. Excess material is machined off the seal body to form a seal segment that has first and second walls and a base portion. The excess material is machined to form an intersegment seal.

In a further embodiment of any of the above, the seal body is densified before the machining steps.

In a further embodiment of any of the above, the intersegment seal is densified after the machining steps.

In a further embodiment of any of the above, the seal body is formed about a mandrel.

In a further embodiment of any of the above, the mandrel has a generally triangular cross section.

In a further embodiment of any of the above, a flat top surface of the intersegment seal is machined.

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 ceramic material, such as a ceramic matrix composite (“CMC”) or monolithic ceramic.

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.

FIG. 3illustrates an example BOAS segment105. 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 wall120circumferentially spaced from a second wall122. The first and second walls120,122extend generally radially outward from a base portion124. The first and second walls120,122extend along an axial length of the seal segment105. The first and second walls120,122may be angled toward one another, in one example. The first and second walls120,122are arranged near the first and second circumferential sides C1, C2, respectively. 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. The base portion124extends circumferentially beyond the first and second walls120,122to form seal surfaces125,127, respectively. The sealing surfaces125,127may taper radially inward, for example. 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.

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 some examples, the base portion124and first and second walls120,122may be formed from the same number of laminate plies, and thus have substantially the same thickness. The simple arrangement of the base portion124and first and second walls120,122allows for a simple ply layup.

FIG. 4illustrates a portion of an example BOAS assembly104. The BOAS segment105is mounted in a carrier112. The carrier112fits between the walls120,122. The carrier112has hooks114,116for securing the carrier112and BOAS segment105to the support structure110. The carrier112has a aft portion118that secures the BOAS segment105in the axial direction. The aft portion118extends in the circumferential direction and engages the second axial side A2of the BOAS segment105. In other embodiments, the carrier112may have a front portion that engages the first axial side A1of the BOAS segment105.

An intersegment seal150is arranged between adjacent seal segments105. The intersegment seal150is in engagement with the sealing surface125. The intersegment seal150extends along most of the axial length of the BOAS segment105. The intersegment seal150is held in place by a clip160. The clip160may be spring loaded to bias the intersegment seal150radially inward, for example. The clip160generally includes first and second wings162,166that extend radially outward and circumferentially outward. An end portion164,168of each of the wings162,166engages with the carrier112. A slot126may be formed in the carrier112radially inward of the hooks114,116. The slot126receives the clip160. The clip160may include a forward tab169to axially retain the clip160in place. An L-seal140may be arranged at a forward portion of the assembly104. The L-seal140may engage the first axial side A1of the BOAS segment105and the clip160.

FIG. 5illustrates a portion of the BOAS assembly104. The intersegment seal150is arranged between two adjacent BOAS segments105. A gap G is formed between the BOAS segments105. The intersegment seal150is in engagement with the sealing surfaces125,127of the BOAS segments105, spanning across the gap G. The intersegment seal150has a radially inner curved surface152. An outer surface154is opposite the inner curved surface152. The outer surface154may also be curved, or may be flat. Side surfaces156,158extend between the inner curved surface152and the outer surface154. The side surfaces156,158extend generally parallel to the first and second walls120,122, respectively. In some examples, a chamfer is formed between the outer surface154and the side surfaces156,158.

The inner curved surface152has a radius of curvature R. In some examples, the radius of curvature R may be between about 0.050 and 0.300 inches (1.27-7.62 mm). In a further embodiment, the radius of curvature R may be about 0.150 inches (3.81 mm). In some examples, the outer surface154has a smaller radius of curvature than the inner curved surface152. In some examples, the outer surface has a radius of curvature between about 0.020 and 0.150 inches (0.508-3.81 mm). In a further example, the outer surface154may have a radius of curvature of about 0.050 inches (1.27 mm), for example. The gap G may change size with thermal changes in the components. The inner curved surface152self-centers over the gap G as the gap G changes size.

FIG. 6illustrates an example method step of manufacturing a BOAS segment105and intersegment seal150. The BOAS segment105is formed by laying a plurality of laminate plies in tooling to form a seal body. The laminates may be wrapped around a mandrel170, for example. Excess material172is machined away from the seal body to form the first and second walls120,122and base portion124. The seal body may be densified before the machining of the excess material172. Some of the excess material172is used to form the intersegment seal150. Thus, the intersegment seal150is made from already densified material that may otherwise have been discarded. The intersegment seal may also be formed and densified independently from the BOAS in its own fixture. The intersegment seal150is then machined to its final shape. For example, the radially outer surface, side surfaces, and chamfers may be machined into the intersegment seal150.

In one embodiment, the mandrel170has a generally triangular cross section. The mandrel170may be an isosceles triangle, for example. The first and second walls120,122extend circumferentially inward at the same angle relative to the circumferential direction. This forms a third angle at the intersegment seal150. Although an example method is shown, the intersegment seal150may be formed with different methods and/or different materials. For example, the intersegment seal150may be a metallic material, in some examples.

FIG. 7Aillustrates a first example intersegment seal150. The intersegment seal150is formed from a plurality of CMC laminate plies148. The plies148form the radially inner curved surface152and the outer surface154. The plie arrangement ensures forces on the intersegment seal150are primarily directed through the plies148, rather than along them, improving stresses in the seal150. The intersegment seal150has a length Ls in the axial direction. The length Ls extends at least most of an axial length of the BOAS segment105.

FIG. 7Billustrates another example intersegment seal250. The intersegment seal250is also formed from a plurality of CMC laminate plies248. The inner surface152is curved, while the outer surface254is flat. That is, the outer surface254is substantially parallel to the base portion124of the BOAS segment105. In this example, the flat outer surface254may be machined into the plies248.

FIG. 8Aillustrates the BOAS assembly104with an example clip160. The clip160generally includes first and second wings162,166that extend radially outward and circumferentially outward. An end portion164,168of each of the wings162,166engages with the carrier112. A window165in a center of the clip160forms tabs167. The tabs167extend radially inward and contact the outer surface154of the intersegment seal150. In this example, the tabs167extend in an axial direction. The tabs167are spring loaded to bias the intersegment seal150radially inward. Although two tabs167are illustrated, one or more tabs167may be used. An aft tab169may be arranged at an aft end of the clip160. The aft tab169engages with the BOAS segments105to retain the clip160axially. The clip160has a length Lc in the axial direction. The length Lc may be the same as the length Ls, in some examples. In other embodiments, the length Lc may be smaller than the length Ls.

FIG. 8Billustrates another example clip260. This example clip260may be used with the intersegment seal250having a flat outer surface254. The clip260also has first and second wings262,266that extend radially outward and end portions264,268of the wings262,266engage with the first and second walls120,122of the BOAS segments105. The example clip260includes two windows265forming two tabs167. In this example, the tabs167extend generally circumferentially across the flat outer surface254. Although two tabs167are illustrated, one or more tabs167may be used.

The disclosed CMC BOAS assembly with a CMC intersegment seal provides a simple, lightweight, cost efficient way to seal intersegment gaps. The intersegment seal reuses densified CMC material, which may reduce costs. The CMC intersegment seal geometry ensures loading is perpendicular to the plies, which provides structural rigidity. The intersegment seal geometry further provides a self-centering seal. The arrangement eliminates the need for feather seal slots and reduces the risk of delamination on the BOAS segment. The CMC intersegment seal provides high temperature capability and reduces weight compared to known metallic seals.

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.