Patent Description:
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. Some gas turbine engine components are formed from ceramic materials.

<CIT> discloses an air seal assembly including a feather seal engaged between adjacent turbine engine components to close a gap therebetween.

<CIT> discloses a blade outer air seal (BOAS) segment having a first and a second mounting ears extending outward from the main body portion and cooperating with a first and a second respective end portion of the main body portion to define a first and a second respective circumferentially outwardly open mounting recesses.

According to an aspect of the present invention, there is provided a blade outer air seal assembly as recited in claim <NUM>.

In a further embodiment of any of the above, the first hook extends generally in a first circumferential direction. The second hook extends generally in a second circumferential direction opposite the first circumferential direction.

In a further embodiment of any of the above, the first and second hooks form a dovetail shape for engagement with the support structure.

In a further embodiment of any of the above, the third and fourth hooks form the dovetail shape for engagement with the support structure.

In a further embodiment of any of the above, the carrier has a first angled surface circumferentially spaced from a second angled surface. The first angled surface is in engagement with the first and third hooks and the second angled surface is in engagement with the third and fourth hooks.

In a further embodiment of any of the above, the base portion extends axially forward of the first wall and axially aft of the second wall.

In a further embodiment of any of the above, a tab extends from one of the first and second walls in a generally radial direction and engages a portion of the support structure.

In a further embodiment of any of the above, a slot is formed in the support structure for receiving the tab.

In a further embodiment of any of the above, a liner is arranged between the first, second, third, and fourth hooks and the carrier.

According to a further aspect of the present invention, there is provided a turbine section for a gas turbine engine as recited in claim <NUM>.

In a further embodiment of any of the above, the first and second hooks form a dovetail shape for engagement with the support structure. The third and fourth hooks form the dovetail shape for engagement with the support structure.

In a further embodiment of any of the above, a tab extends from one of the first and second walls in a generally radial direction and engages a portion of the support structure. A slot is formed in the support structure for receiving the tab.

In a further embodiment of any of the above, a metallic liner is arranged between the first, second, third, and fourth hooks and the carrier.

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

The inner shaft <NUM> is connected to the fan <NUM> through a speed change mechanism, which in the exemplary gas turbine engine <NUM> is illustrated as a geared architecture <NUM> to drive a fan <NUM> at a lower speed than the low speed spool <NUM>. A combustor <NUM> is arranged in the exemplary gas turbine engine <NUM> between the high pressure compressor <NUM> and the high pressure turbine <NUM>.

In one disclosed embodiment, the engine <NUM> bypass ratio is greater than about ten (<NUM>:<NUM>), the fan diameter is significantly larger than that of the low pressure compressor <NUM>, and the low pressure turbine <NUM> has a pressure ratio that is greater than about five (<NUM>:<NUM>).

<FIG> shows a portion of an example turbine section <NUM>, which may be incorporated into a gas turbine engine such as the one shown in <FIG>. However, it should be understood that other sections of the gas turbine engine <NUM> or other gas turbine engines, and even gas turbine engines not having a fan section at all, could benefit from this disclosure. The turbine section <NUM> includes a plurality of alternating turbine blades <NUM> and turbine vanes <NUM>.

A turbine blade <NUM> has a radially outer tip <NUM> that is spaced from a blade outer air seal assembly <NUM> with a blade outer air seal ("BOAS") <NUM>. The BOAS <NUM> may be made up of a plurality of seal segments <NUM> that are circumferentially arranged in an annulus about the central axis A of the engine <NUM>.

The BOAS <NUM> may be mounted to an engine case or structure, such as engine static structure <NUM> via a control ring or support structure <NUM> and a carrier <NUM>. The carrier <NUM> may or may not be integral to the support structure <NUM>. The support structure <NUM> may extend for a full <NUM>° about the engine axis A. The engine case or support structure holds the BOAS <NUM> radially outward of the turbine blades <NUM>. Although a BOAS <NUM> is described, this disclosure may apply to other components, and particularly flow path components. For example, this disclosure may apply to combustor liner panels, shroud, transition ducts, exhaust nozzle liners, or other CMC components.

<FIG> illustrates an example BOAS seal segment <NUM>. Each seal segment <NUM> is 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 R1 faces in a direction toward the engine central axis A. The radially inner side R1 is thus the gas path side of the seal segment <NUM> that bounds a portion of the core flow path C. The first axial side A1 faces in a forward direction toward the front of the engine <NUM> (i.e., toward the fan <NUM>), and the second axial side A2 faces in an aft direction toward the rear of the engine <NUM> (i.e., toward the exhaust end).

In the illustrated example, each BOAS segment <NUM> includes a first wall <NUM> axially spaced from a second wall <NUM>. The first and second walls <NUM>, <NUM> extend generally radially outward from a base portion <NUM>. The first and second walls <NUM>, <NUM> may extend along an entire circumferential length of the seal segment <NUM>, or may terminate circumferentially inward of the base portion <NUM>. In this example, the first and second walls <NUM>, <NUM> are generally parallel to one another and perpendicular to the base portion <NUM>. In other examples, the first and second walls <NUM>, <NUM> may be angled.

The base portion <NUM> extends between the first and second axial sides A1, A2 and defines a gas path on a radially inner side and a non-gas path on a radially outer side. The first wall <NUM> is spaced from the first axial side A1 to form a forward portion <NUM>, and the second wall <NUM> is spaced from the second axial side A2 to form an aft portion <NUM>. In this disclosure, forward, aft, upstream, downstream, axial, radial, or circumferential is in relation to the engine axis A unless stated otherwise.

Each of the first and second walls <NUM>, <NUM> includes two hooks. The first wall <NUM> has a first hook <NUM> near the first circumferential side C1, and a second hook <NUM> near the second circumferential side C2. The first and second hooks <NUM>, <NUM> form a dovetail shape. The second wall <NUM> has a third hook <NUM> near the first circumferential side C1, and a fourth hook <NUM> near the second circumferential side C2. The third and fourth hooks <NUM>, <NUM> form a dovetail shape. The first and third hooks <NUM>, <NUM> extend at an angle towards the first circumferential side C1. The first and third hooks <NUM>, <NUM> may have generally the same size and shape as one another. The second and fourth hooks <NUM>, <NUM> extend at an angle towards the second circumferential side C2. The second and fourth hooks <NUM>, <NUM> may have generally the same size and shape as one another. The shape of the hooks <NUM>, <NUM>, <NUM>, <NUM> may be selected to manage stiffness and stresses in the BOAS segment <NUM>. The hooks <NUM>, <NUM>, <NUM>, <NUM> may be machined into the first and second walls <NUM>, <NUM>, for example. The hooks <NUM>, <NUM>, <NUM>, <NUM> provide angled surfaces for engaging with the carrier <NUM>.

<FIG> illustrates a cross-sectional view of the example BOAS segment <NUM>. The BOAS <NUM> may be formed of a ceramic matrix composite ("CMC") material. Each seal segment <NUM> is formed of a plurality of CMC laminate sheets <NUM>. The laminate sheets <NUM> may be silicon carbide fibers, formed into a braided or woven fabric in each layer. In other examples, the BOAS <NUM> may be made of a monolithic ceramic.

CMC components such as BOAS segments <NUM> are 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 processed by adding additional material to coat the laminate sheets. The simple arrangement of the base portion <NUM> and first and second walls <NUM>, <NUM> allows for a simple ply layup.

In some examples, the base portion <NUM> and first and second walls <NUM>, <NUM> may be formed from the same number of laminate plies, and thus have substantially the same thickness. A plurality of plies <NUM> are layered to form the BOAS segment <NUM>. The plies <NUM> may be a braided or woven CMC material, such as <NUM>-Harness Satin weave, for example. In this example, wraparound plies <NUM> form the outermost layers of the BOAS segment <NUM>. The wraparound plies <NUM> extend about the base portion <NUM> and up the first and second walls <NUM>, <NUM>. The wraparound plies <NUM> may cover ends of some of the plies <NUM> in the base portion <NUM>. Covering the exposed ends prevents the ends from being exposed to the gas path flow, which may cause delamination. According to the invention, an overwrap ply <NUM> is arranged on an outer portion of the BOAS segment <NUM>. The overwrap ply <NUM> is arranged about the first and second walls <NUM>, <NUM>. The overwrap ply <NUM> thus covers ends of some of the laminate plies <NUM> that terminate at the first and second walls <NUM>, <NUM>. The overwrap ply <NUM> may prevent plies from separating due to pressure loading. The disclosed ply configuration may mitigate delamination stresses. The overwrap ply <NUM> may be applied before machining features into the BOAS segment <NUM>, in some examples. Although a particular ply layup is illustrated, this disclosure may extend to BOAS segments having different ply arrangements.

<FIG> illustrates an example BOAS assembly <NUM>. The BOAS segment <NUM> is mounted in a carrier <NUM>. The carrier <NUM> has a first radial portion <NUM> and a second radial portion <NUM>. The first and second radial portions <NUM>, <NUM> extend radially inwardly. The first radial portion <NUM> forms a first sloped surface <NUM>, and the second radial portion <NUM> forms a second sloped surface <NUM>. The first and third hooks <NUM>, <NUM> abut the first sloped surface <NUM>. The second and fourth hooks <NUM>, <NUM> abut the second sloped surface <NUM>. The carrier <NUM> may have a radially inwardly extending portion <NUM>. In some examples, the radially inwardly extending portion <NUM> may contact the BOAS segment <NUM>. In the illustrated example, the radially inwardly extending portion <NUM> contacts the second wall <NUM> and maintains an axial position of the BOAS segment <NUM>.

<FIG> illustrates another view of the example BOAS assembly <NUM>. The second sloped surface <NUM> extends at an angle <NUM> relative to the circumferential direction C. The angle <NUM> may be between about <NUM> and <NUM>°, for example. The first and second sloped surfaces <NUM>, <NUM> may have the same angle. The hooks <NUM>, <NUM>, <NUM>, <NUM> also extend at the angle <NUM> for retaining the BOAS segment <NUM> in place. The first and second sloped portions <NUM>, <NUM> extend radially and circumferentially beyond the hooks <NUM>, <NUM>, <NUM>, <NUM>, which permits expansion of the BOAS segment <NUM> relative to the carrier <NUM>.

In some examples, a liner <NUM> is arranged along the first and second sloped surfaces <NUM>, <NUM> between the carrier <NUM> and the BOAS segment <NUM>. The liner <NUM> may be sheet metal, for example. In other examples, the liner <NUM> may be a coating. The liner <NUM> eliminates contact between the BOAS segment <NUM> and the carrier <NUM>.

In some examples, a tab <NUM> is arranged on the BOAS segment <NUM>. The tab <NUM> may be on the first or second wall <NUM>, <NUM>, for example. A slot <NUM> is formed in the carrier <NUM> for receiving the tab <NUM>. The tab <NUM> and slot <NUM> help maintain a circumferential position of the BOAS segment <NUM>. In other examples, the tab <NUM> may be formed on the carrier <NUM>, and a slot <NUM> may be formed on the BOAS segment <NUM>.

<FIG> illustrates another view of the example BOAS assembly <NUM>. A resilient element <NUM> may be arranged between the carrier <NUM> and the BOAS segment <NUM> to bias the BOAS segment <NUM> radially inward. The element <NUM> helps prevent the BOAS segment <NUM> from shifting up one sloped surface <NUM>, <NUM>, and thus being angled with respect to the circumferential direction C. The element <NUM> may be a spring, for example. Some examples may include a resilient element <NUM> without a tab <NUM> and slot <NUM>, and other examples may include a tab <NUM> and slot <NUM> without a resilient element <NUM>. Although a particular resilient element <NUM> is shown, other example resilient elements <NUM> may be used. The resilient element <NUM> may be arranged within the slot <NUM>, for example.

The disclosed BOAS assembly arrangement includes four sloped surfaces on the BOAS segment for attaching to the carrier <NUM>. These four surfaces create independent regions on the part, which may limit thermal fight within the component. This arrangement constrains the BOAS segment in multiple directions, yet allows for uninhibited thermal growth between the CMC BOAS segment and support components. Features on the BOAS segment and support structure may be configured to optimize structural and bearing pressure capability to mitigate stresses due to mechanical loading.

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.

Claim 1:
A blade outer air seal assembly (<NUM>) for a gas turbine engine, comprising:
a support structure (<NUM>);
a blade outer air seal (<NUM>) having a plurality of segments (<NUM>) arranged circumferentially about an axis and mounted in the support structure (<NUM>) by a carrier (<NUM>); and
at least one of the segments (<NUM>) having a first wall (<NUM>) axially spaced from a second wall (<NUM>), the first wall (<NUM>) having first and second hooks (<NUM>, <NUM>) spaced apart from one another in a circumferential direction, the second wall (<NUM>) having third and fourth hooks (<NUM>, <NUM>) spaced apart from one another in the circumferential direction, wherein the first, second, third, and fourth hooks (<NUM>, <NUM>, <NUM>, <NUM>) are in engagement with the carrier (<NUM>);
wherein the blade outer air seal (<NUM>) is a ceramic material,
wherein the blade outer air seal (<NUM>) is formed from a plurality of ceramic matrix composite plies (<NUM>), and characterized in that, an overwrap ply (<NUM>) extends over and about the first and second walls (<NUM>, <NUM>);
wherein a portion of the plurality of ceramic matrix composite plies (<NUM>) have ends that terminate at the first or second wall (<NUM>; <NUM>) and the overwrap ply (<NUM>) covers the ends; and
wherein the first wall (<NUM>) and the second wall (<NUM>) extend radially outward from a base portion (<NUM>), the base portion (<NUM>) defining a gas path on a radially inner side and a non-gas path on a radially outer side.