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 a turbine shroud assembly or blade track assembly adapted to extend around a turbine wheel assembly.

<CIT> discloses a turbine ring assembly with axial retention.

<CIT> relates generally to a sliding seal between two components.

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

In a further embodiment of any of the above, the coating is a silicon metal coating.

In a further embodiment of any of the above, the coating extends to at least part of the base portion.

In a further embodiment of any of the above, the feature contacts the second wall.

In a further embodiment of any of the above, the w-seal contacts the coating on the first wall.

In a further embodiment of any of the above, a seal plate contacts the coating. A w-seal is arranged between the support structure and the seal plate.

In a further embodiment of any of the above, the coating is machined to provide dimensional control.

In a further embodiment of any of the above, the at least one segment has a first aperture and the support structure has a second aperture. A pin extends through the first and second apertures.

According to an aspect, there is provided a method of assembling a blade outer air seal assembly as recited in claim <NUM>. In a further embodiment of any of the above, the coating is a silicon metal coating.

In a further embodiment of any of the above, the coating is machined on the second wall to form the smooth contact surface. The coating on the first wall is machined to form a second smooth contact surface.

In a further embodiment of any of the above, a w-seal is arranged in contact with the second smooth contact surface.

In a further embodiment of any of the above, the mounting the segment to the support structure comprises inserting a pin through a first aperture on the segment and a second aperture on the support structure.

<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 ("BOAS") assembly <NUM>. The BOAS assembly <NUM> may include a plurality of seal segments <NUM> that are circumferentially arranged in an annulus about the central axis A of the engine <NUM>.

The BOAS segments <NUM> may be mounted to an engine case or structure, such as engine static structure <NUM> via a control ring or 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 segments <NUM> radially outward of the turbine blades <NUM>. Although a BOAS assembly <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.

Each seal segment <NUM> is a body that defines radially inner and outer sides R1, R2, respectively, and first and second axial sides A1, A2, 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. An aperture <NUM> extends through the first and second walls <NUM>, <NUM>, and receives a pin <NUM> for securing the seal segment <NUM> to a support structure <NUM>. In some examples, multiple apertures <NUM> circumferentially spaced apart extend through the first and second walls <NUM>, <NUM>.

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.

The BOAS segments <NUM> may be formed of a ceramic matrix composite ("CMC") material. Each seal segment <NUM> is formed of a plurality of CMC laminate sheets. The laminate sheets may be silicon carbide fibers, formed into a braided or woven fabric in each layer. In other examples, the BOAS segments <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. 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. The simple arrangement of the base portion <NUM> and first and second walls <NUM>, <NUM> allows for a simple ply layup.

The seal segment <NUM> is received radially within the support structure <NUM>, and secured in position by a pin <NUM> that extends through the support structure <NUM> and through the first and second walls <NUM>, <NUM>. The pin <NUM> extends through the aperture <NUM> on the BOAS segment <NUM> and through an aperture <NUM> on the support structure <NUM>. The pin <NUM> retains the BOAS segment <NUM> in the circumferential and radial directions. A seal plate <NUM> may secure the pin <NUM> in place. The seal plate <NUM> may secure to the support structure <NUM> or other engine structure via a snap fit, for example.

The seal segment <NUM> has a coating at a first portion <NUM> and a second portion <NUM>. The coating may be a silicon metal coating. In one example, the coating may be an Air Plasma Spray (APS) silicon metal coating. The coating bonds well to the CMC material, and behaves similarly to CMC under varying temperatures. The first portion <NUM> is on the first wall <NUM>, and the second portion <NUM> is on the second wall <NUM>. In some examples, the first portion <NUM> and/or the second portion <NUM> may extend onto the base portion <NUM>. The coating is machined to provide a smooth sealing area. The machined silicon metal coating may provide a smoother surface than CMC for sealing. The coating may also be machined to tightly controlled dimensions and mitigate surface tolerance variation.

The support structure <NUM> has a rounded feature <NUM> that protrudes axially toward the BOAS segment <NUM>. The feature <NUM> may be machined into the support structure <NUM>, for example. The feature <NUM> contacts the coating. In the illustrated example, the feature <NUM> contacts the coating at the second portion <NUM> on the second wall <NUM>. The rounded shape of the feature <NUM> may provide line contact between the support structure <NUM> and the BOAS segment <NUM>, which may minimize heat transfer between the support structure <NUM> and the BOAS segment <NUM>. Case feature <NUM> could be omitted in another embodiment where a local case surface could be flat or have another shape.

A W-seal <NUM> may be arranged between the BOAS segment <NUM> and the seal plate <NUM>. The W-seal <NUM> contacts the seal plate <NUM> at a point <NUM>, which may be radially inward of the support structure <NUM>. In the illustrated example, the W-seal <NUM> contacts the coating at the first portion <NUM> on the first wall <NUM>. The W-seal <NUM> biases the BOAS segment <NUM> axially to keep the BOAS segment <NUM> seated against the feature <NUM>.

The assembly <NUM> forms several cavities having air at different pressures. For example, high pressure air may be at locations <NUM> and <NUM>, while lower pressure air is present at locations <NUM> and <NUM>. The sealing provided by the feature <NUM> and the w-seal <NUM> in contact with the coating at portions <NUM>, <NUM> prevents leakage between these high and low pressure locations.

<FIG> illustrates another example BOAS assembly <NUM>. In this example, the seal plate <NUM> has a radial inner portion <NUM> that forms a rounded feature <NUM>. The seal plate <NUM> may provide a land <NUM> that positions a W-seal <NUM> radially. The seal plate <NUM> is positioned by a land <NUM>, which is tightly clearance to land <NUM> on the support structure <NUM>. The rounded features <NUM> contacts the coating at the first portion <NUM>, while the rounded feature <NUM> on the support structure <NUM> contacts the coating at the second portion <NUM>. The W-seal <NUM> is arranged between the seal plate <NUM> and a portion <NUM> of an engine structure, such as engine structure <NUM>. In this example, the seal plate <NUM> is not snapped into a supporting structure, and is instead biased axially by the W-seal <NUM>. The W-seal <NUM> biases the seal plate <NUM> into contact with the BOAS segment <NUM>, which biases the BOAS segment <NUM> into contact with the feature <NUM>. In some examples, a second W-seal <NUM> may be used aft of the feature <NUM>. The second W-seal <NUM> may be arranged between the support structure <NUM> and a structure <NUM> of a vane assembly <NUM>, for example.

<FIG> illustrates a side view of an example BOAS assembly <NUM>. The blade outer air seal assembly <NUM> includes a feather seal slot <NUM>. The feather seal slot <NUM> may be about halfway between the radially inner and outer sides R1, R2 of each BOAS segment <NUM>, for example. The slot <NUM> may include an axial portion <NUM> and a radial portion <NUM>. The radial portion <NUM> may extend up one or both of the walls <NUM>, <NUM>. The axial portion <NUM> may extend into the base portion <NUM> forward and aft of the walls <NUM>, <NUM>, for example. A feather seal <NUM> may be arranged in the slot <NUM>. The feather seal <NUM> may include an axial portion <NUM> and a radial portion <NUM> to engage with the axial and radial portions <NUM>, <NUM> of the slot <NUM>, for example. The axial portion <NUM> and radial portions <NUM> may be a single unitary piece, or may separate pieces. Although a particular feather seal <NUM> is shown, other intersegment seal configurations may be utilized. The feather seal <NUM> may be a metallic component, for example. An intersegment seal, such as the feather seal <NUM> may be used in combination with the forward and aft sealing embodiments described above.

BOAS require sealing between secondary flow paths and the gas path in order to maintain BOAS supply pressure and to minimize leakage. The disclosed arrangement provides axial sealing on both the front and rear sides of the BOAS, and may be used with intersegment seals between adjacent BOAS segments. The machinable coating provides a high surface finish which may improve sealing performance at front and rear sealing points. Machining the coating also allows for tighter tolerance control of the axial width of the BOAS, which may improve the distribution of contact between the W-seal and the BOAS segments for proper sealing. The W-seal provides a preload that maintains the BOAS segment in contact with the rounded support structure feature. The W-seal and rounded feature provide minimized surface area of the BOAS exposed to high velocity cooling air, which may impart high thermal stress on the BOAS segment. The disclosed arrangement provides a low-complexity sealing solution for a CMC BOAS.

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>; <NUM>), comprising:
a blade outer air seal having a plurality of segments (<NUM>; <NUM>) extending circumferentially about an axis and mounted in a support structure (<NUM>; <NUM>);
at least one of the plurality of segments (<NUM>; <NUM>) having a first wall (<NUM>; <NUM>) and a second wall (<NUM>; <NUM>) extending radially outward from a base portion (<NUM>; <NUM>), the first wall (<NUM>; <NUM>) axially spaced from the second wall (<NUM>; <NUM>), wherein the at least one of the plurality of segments (<NUM>; <NUM>) is formed from a ceramic material;
the blade outer air assembly characterised by:
a coating on a portion of the first wall (<NUM>; <NUM>) and a portion of the second wall (<NUM>; <NUM>), wherein the coating is in contact with a feature (<NUM>; <NUM>) on the support structure (<NUM>; <NUM>),
wherein the coating is machined to provide a smooth contact area,
wherein the feature (<NUM>; <NUM>) is a rounded protrusion that extends in an axial direction, and
wherein the feature (<NUM>; <NUM>) provides axial sealing between secondary flow paths and a gas path of the blade outer air seal assembly (<NUM>; <NUM>);
a w-seal (<NUM>; <NUM>) contacting the coating, wherein the w-seal (<NUM>; <NUM>) biases the at least one of the plurality of segments (<NUM>; <NUM>) axially to keep the at least one of the plurality of segments (<NUM>; <NUM>) seated against the feature (<NUM>: <NUM>); and
a seal plate (<NUM>; <NUM>) abutting the support structure (<NUM>; <NUM>) and contacting the w-seal (<NUM>; <NUM>).