Patent Description:
Lightweight CMC is a highly desirable material for gas turbine engine applications. CMCs exhibit excellent physical, chemical, and mechanical properties at high temperatures, making CMCs particularly desirable for producing hot section components, including blade outer air seals (BOAS). Designing a CMC BOAS capable of meeting a sufficient balance of strength and thermal gradient targets has been challenging in regions where both the maximum CMC interface temperature and bulk proportional stress targets are violated.

A need exists to produce a CMC BOAS with a relatively low through-wall thermal gradient while providing large cross-sectional moments of inertia to react to high pressure loads.

<CIT> and <CIT> disclose examples of CMC articles including BOAS and shrouds.

<CIT> discloses a prior art composite airfoil for a gas turbine engine.

In accordance with a first aspect of the invention, there is provided a fiber-reinforced blade outer air seal (BOAS) for use in a gas turbine engine as recited in claim <NUM>.

In accordance with a second aspect of the invention, there is provided a method for manufacturing a fiber-reinforced blade outer air seal (BOAS) with integral fiber-formed cooling channels for use in a gas turbine engine as recited in claim <NUM>.

The present summary is provided only by way of example, and not limitation. Other aspects of the present invention will be appreciated in view of the entirety of the present disclosure, including the entire text, claims and accompanying figures.

While the above-identified figures set forth embodiments of the present invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the invention as defined in the appended claims. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features, steps and/or components not specifically shown in the drawings.

The present invention concerns a CMC BOAS, with integral cooling channels constructed of CMC braided sleeves. The channels enable large film cooling access across the gas path face of the BOAS and reduce through-wall thermal gradients along the BOAS inner diameter wall. The use of CMC braided sleeves provides for seamless channel construction and can increase the specific stiffness of the BOAS, provide an efficient distribution of load, and provide resistance to crack propagation. Although the present disclosure is directed to cooling channels formed from braided fiber sleeves, woven and knit fiber tubes are also contemplated and it should be understood by one of ordinary skill in the art that woven and knit fiber tubes can replace the braided fiber sleeves in embodiments outside the subject-matter of the claims.

<FIG> is a quarter-sectional view of a gas turbine engine <NUM> that includes fan section <NUM>, compressor section <NUM>, combustor section <NUM> and turbine section <NUM>. Fan section <NUM> drives air along bypass flow path B while compressor section <NUM> draws air in along core flow path C where air is compressed and communicated to combustor section <NUM>. In combustor section <NUM>, air is mixed with fuel and ignited to generate a high pressure exhaust gas stream that expands through turbine section <NUM> where energy is extracted and utilized to drive fan section <NUM> and compressor section <NUM>.

Although the disclosed non-limiting embodiment depicts a turbofan gas turbine engine, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines; for example a low-bypass turbine engine, or a turbine engine including a three-spool architecture in which three spools concentrically rotate about a common axis and where a low spool enables a low pressure turbine to drive a fan via a gearbox, an intermediate spool that enables an intermediate pressure turbine to drive a first compressor of the compressor section, and a high spool that enables a high pressure turbine to drive a high pressure compressor of the compressor section.

The example engine <NUM> generally includes low speed spool <NUM> and high speed spool <NUM> mounted for rotation about an engine central longitudinal axis A relative to an engine static structure <NUM> via several bearing systems <NUM>. It should be understood that various bearing systems <NUM> at various locations may alternatively or additionally be provided.

Low speed spool <NUM> generally includes inner shaft <NUM> that connects fan <NUM> and low pressure (or first) compressor section <NUM> to low pressure (or first) turbine section <NUM>. Inner shaft <NUM> drives fan <NUM> through a speed change device, such as geared architecture <NUM>, to drive fan <NUM> at a lower speed than low speed spool <NUM>. High-speed spool <NUM> includes outer shaft <NUM> that interconnects high pressure (or second) compressor section <NUM> and high pressure (or second) turbine section <NUM>. Inner shaft <NUM> and outer shaft <NUM> are concentric and rotate via bearing systems <NUM> about engine central longitudinal axis A.

Combustor <NUM> is arranged between high pressure compressor <NUM> and high pressure turbine <NUM>. In one example, high pressure turbine <NUM> includes at least two stages to provide a double stage high pressure turbine <NUM>. In another example, high pressure turbine <NUM> includes only a single stage. As used herein, a "high pressure" compressor or turbine experiences a higher pressure than a corresponding "low pressure" compressor or turbine.

The example low pressure turbine <NUM> has a pressure ratio that is greater than about <NUM>. The pressure ratio of the example low pressure turbine <NUM> is measured prior to an inlet of low pressure turbine <NUM> as related to the pressure measured at the outlet of low pressure turbine <NUM> prior to an exhaust nozzle.

Mid-turbine frame <NUM> of engine static structure <NUM> is arranged generally between high pressure turbine <NUM> and low pressure turbine <NUM>. Mid-turbine frame <NUM> further supports bearing systems <NUM> in turbine section <NUM> as well as setting airflow entering low pressure turbine <NUM>.

The core airflow C is compressed by low pressure compressor <NUM> then by high pressure compressor <NUM> mixed with fuel and ignited in combustor <NUM> to produce high speed exhaust gases that are then expanded through high pressure turbine <NUM> and low pressure turbine <NUM>. Mid-turbine frame <NUM> includes airfoils/vanes <NUM>, which are in the core airflow path and function as an inlet guide vane for low pressure turbine <NUM>. Utilizing vanes <NUM> of mid-turbine frame <NUM> as inlet guide vanes for low pressure turbine <NUM> decreases the length of low pressure turbine <NUM> without increasing the axial length of mid-turbine frame <NUM>. Reducing or eliminating the number of vanes in low pressure turbine <NUM> shortens the axial length of turbine section <NUM>. Thus, the compactness of gas turbine engine <NUM> is increased and a higher power density may be achieved.

Each of the compressor section <NUM> and the turbine section <NUM> can include alternating rows of rotor assemblies and vane assemblies (shown schematically) that carry airfoils that extend into the core flow path C. To improve efficiency, static outer shroud seals (not shown), such as a BOAS, can be located radially outward from rotor airfoils to reduce tip clearance and losses due to tip leakage.

<FIG> illustrates a portion of a gas turbine engine, such as, but not limited to, gas turbine engine <NUM> of <FIG>, having BOAS <NUM>. The portion of the gas turbine engine illustrated in <FIG> is intended to be non-limiting. The portion of the gas turbine engine illustrated in <FIG> has stator assemblies <NUM> and <NUM>, and rotor <NUM>. Stator assemblies <NUM> and <NUM> can each have a plurality of airfoils <NUM> and <NUM>, respectively, to direct core airflow C. Rotor <NUM> can have a plurality of airfoils <NUM> to create or extract energy from core airflow. BOAS <NUM> can be configured to reduce core airflow leakage across rotor tip <NUM>. BOAS <NUM> can be located radially inward of an annular case (not shown) and radially outward of rotor tip <NUM>. Conventionally, a plurality of segmented BOAS <NUM> can be used, collectively forming a ring around rotor <NUM> to seal multiple airfoils <NUM>. BOAS <NUM> can be mounted to an annular ring or segmented seal carrier (not shown) or directly to the case as known in the art.

<FIG> and <FIG> provide schematicized sectional views of alternative embodiments of a fiber preform <NUM> and <NUM>' used for the manufacture of BOAS <NUM>. Preforms <NUM> and <NUM>' are intended to provide non-limiting examples of a geometry of BOAS <NUM>. It will be understood by those of ordinary skill in the art that the geometry of BOAS <NUM>, including the number and orientation of cooling channels can be varied as needed to meet thermal and mechanical stress requirements. Some of the possible alternative configurations are described herein.

A thermal barrier coating, environmental barrier coating, and/or abradable coating can be provided on a surface of BOAS <NUM>. Thermal barrier coatings and environmental barrier coatings can protect the CMC component from degradation. Abradable coatings can be applied in a blade rub zone to maintain close clearances thereby improving turbine efficiency.

<FIG> illustrates fiber preform <NUM>, which includes cooling channels 90a-90c fed by a source of cooling fluid through inlet apertures 92a-92c. As illustrated, cooling channels 90a-90c can extend in a circumferential direction relative to engine axis A. Preform <NUM> has three cooling channels 90a, 90b, 90c located adjacent one another and configured to cover an axial extent of BOAS <NUM>, extending from a leading edge LE to a trailing edge TE. While positioning cooling channels along a full axial extend of BOAS <NUM> can provide cooling fully along a radially inner wall positioned in the gas path, alternative configurations, which do not provide cooling along the full axial extent of BOAS <NUM>, are also contemplated.

As illustrated in <FIG>, a cooling fluid flow Cε can be fed to leading edge cooling channel 90a through a pair of apertures 92a. Cooling channel 90a can be substantially closed at an intersegment side <NUM> of BOAS <NUM> adjacent to apertures 92a to direct cooling fluid flow Cε through cooling channel 90a as indicated by the Cε arrow. In some embodiments, an adjacent BOAS <NUM> can be configured to allow flow exiting cooling channel 90a from an outlet at an opposite intersegment side <NUM> to enter a cooling fluid channel in the adjacent BOAS. In other embodiments, cooling channel 90a can be substantially closed at intersegment outlet <NUM> and cooling fluid flow Cε can be forced to exit through a plurality of intersegment gas path-facing film cooling apertures (not shown) as known in the art. Cooling fluid Cε can enter cooling channel 90b through a pair of apertures 92b. Cooling channel 92b can be substantially closed (not shown) at intersegment side <NUM> to direct cooling fluid flow Cε in a circumferential direction as illustrated by the Cε arrow. In some embodiments, cooling channel 90b can be fluidly connected to cooling channel 90c to allow cooling fluid flow Cε exiting cooling channel 90b at intersegment side <NUM> to enter cooling channel 90b at intersegment side <NUM> and flow back toward intersegment side <NUM> as illustrated by the Cε arrow. Cooling channels 90b and 90c can be substantially closed (not shown) at intersegment side <NUM> to limit cooling fluid flow Cε exiting BOAS <NUM> at intersegment side <NUM>, while allowing cooling fluid Cε to pass from cooling channel 90b to cooling channel 90c. In alternative embodiments, cooling channel 90c can be fluidly separated from cooling fluid channel 90b and cooling fluid can be fed to cooling channel 90c through optional apertures 92c (shown in phantom). Intersegment side or wall members (not shown) used to close or restrict cooling channels 90a-90c can be formed separately and joined to preform <NUM> following densification of fiber preform <NUM> via brazing or other suitable methods known in the art. Cooling fluid Cε can exit cooling fluid channels 90b and 90c through intersegment or gas path-facing film cooling apertures. In some embodiments, one or both cooling channels 90b, 90c can be open at intersegment sides <NUM> or <NUM> to allow cooling fluid Cf to enter cooling channels of adjacent BOAS as described with respect to cooling channel 90a. The internal cooling channels can function to actively cool BOAS <NUM> during operation to reduce bulk temperature, or to passively cool BOAS <NUM> to reduce through wall thermal gradients. Internal cooling channels can enable intersegment cooling via cooling holes directed between adjacent BOAS segments, as well as film cooling along a radially inner face of BOAS <NUM> exposed to the hot gas path. Although <FIG> illustrates three cooling channels 90a-90c, it should be appreciated that the number of cooling channels and fluid interconnection of cooling channels can be varied based on cooling needs, and that any number of cooling channels can be contemplated. In the disclosed BOAS, cooling channels configured to extend circumferentially (as illustrated) can generally range in number from two to six. The number of cooling fluid feed apertures 92a-92c can vary accordingly. Additionally, the location and number of feed apertures for each cooling channel can be varied as needed to maintain pressure requirements. In alternative embodiments, a single serpentine cooling channel may be used or walls of a braided sleeve may be compressed together to form multiple cooling channels. In some embodiments, a component could have spiral cooling channels originating at one or more center points and exiting at a rear of the component. Braided fiber sleeves can have a constant or variable cross-section to form cooling channels that are tapered in thickness and/or width. By varying the cross-section of fiber bundles within the braid (and weave or knit), cooling channels can be created with internal roughness that enhances heat transfer, which can provide significant advantage. Additionally, in braided fiber sleeves, it is possible to also introduce fibers only in one rotating direction to create swirling of air.

BOAS fiber preform <NUM> is formed from a plurality of braided fiber sleeves <NUM> (i.e., tubular braid with seamless fiber continuity from end to end), which are enclosed or wrapped in one or more layered woven or braided fiber plies <NUM>. Suitable materials used to make braided fiber sleeves <NUM> and fiber plies <NUM> can include, but are not limited to carbon, silicon carbide (SiC), alloyed and/or zirconium carbide, hafnium carbide, aluminum silicate, alumina, and other materials known in the art for use in various environmental conditions, including varying operational temperatures. Fibers can be impregnated with a SiC matrix and various binders. Interface coatings, such as boron nitride, can be applied to the fibers before or after a layup process to protect fibers from oxidation during operation.

Cooling channels 90a-90c of fiber preform <NUM> are formed from braided fiber sleeves <NUM>. Braided fiber sleeves offer multiple advantages over woven or unidirectional fiber plies. Braided fiber sleeves <NUM> have continuous fibers that are mechanically interlocked with one another providing for an efficient distribution of load and resistance to impact and crack propagation. Interlaminar shear properties are improved when braided fiber sleeves are nested together, which can further limit crack propagation. Braided fiber sleeves can expand to accommodate irregular cross-sections and can form irregular shapes. Because fibers are braided on the bias, there is a reduced tendency for fiber breakage when forced to accommodate a small radius. Braided fiber sleeves <NUM> can be formed from a biaxial braid or a triaxial braid, which provides reinforcement in the axial direction. The angles of the fibers of the braid can be tailored to balance the stresses better than is possible with a <NUM>/<NUM> woven fabric, which makes the braid structurally more efficient than a woven fabric for cooling channels that are required to hold cooling fluid at a higher pressure than the working fluid in the engine core gas path.

Each of cooling channels 90a-90c is defined by a braided fiber sleeve comprising nested fiber braids aligned concurrently to form inner wall <NUM> and outer wall <NUM>. As illustrated in <FIG>, braided fiber sleeves <NUM> can be consolidated to form an oblong shape with radiused ends <NUM> separated by elongated sides <NUM>. A length of elongated sides <NUM> can vary depending on the number cooling channels present. In the embodiment disclosed in <FIG>, a cross-section of cooling channels 90a-90c has an aspect ratio of approximately <NUM>:<NUM>. In alternative embodiments, cooling channels 90a-90c can be substantially cylindrical, having a circular cross-section. Bending constraints of braided fiber sleeves <NUM> generally limit radiused ends to a minimum radius around <NUM> millimeters, providing a cooling channel height h of <NUM> millimeters. In the embodiment disclosed in <FIG>, cooling channels 90a-90c can have a channel height ranging from <NUM> to <NUM> millimeters, and radii of radiused ends <NUM> ranging from <NUM> to <NUM> millimeters.

Fiber plies <NUM> can encase cooling channels 90a-90c thereby forming inner radial wall <NUM> facing the engine gas path and outer radial wall <NUM>. Plies can generally have a thickness ranging from <NUM>" to <NUM>". It should be appreciated that the number of plies or layers forming each of walls <NUM> and <NUM> can vary depending on ply thickness and structural requirements. Fiber plies <NUM> can be formed from separate fiber sheets, which can be a woven or braided fabric. Fiber plies <NUM> can be wrapped to extend from attachment mechanisms <NUM> and <NUM> underneath cooling channels 90a-90c to provide additional support. It should be appreciated that alternative fiber ply layup configurations are contemplated and that the design can be modified accordingly to accommodate varying structural requirements. Gaps between plies or locations where plies are absent can be filled with small braids or chopped fibers.

<FIG> is a schematicized sectional view of an alternative fiber preform <NUM>' for the manufacture of BOAS <NUM>. Preform <NUM>' is similar to preform <NUM> but includes a braided fiber overwrap <NUM>. Braided fiber overwrap <NUM> can replace a portion or all of fiber plies <NUM> and can be formed from one or more braided fibers sleeves. Braided fiber overwrap <NUM> can fully wrap around braided fiber sleeves <NUM> to form BOAS walls <NUM> and <NUM>. Braided fiber overwrap <NUM> can be shaped to provide attachment mechanisms <NUM>' and <NUM>'. The use of braided fiber overwrap <NUM> provides a seamless fiber preform structure, providing added strength and resistance to crack formation.

<FIG> is a schematicized sectional view of cooling channel 90a at different stages in the manufacturing process. Cooling channel 90a (as well as all other cooling channels disclosed) can be formed by braiding fiber sleeve <NUM> on a mandrel to produce a cylindrical tube as illustrated by step <NUM> in the process. In step <NUM>, braided fiber sleeve <NUM> can be consolidated to a desired aspect ratio or to provide a desired cooling channel height. In alternative embodiments, cooling channel 90a can be formed by braided fiber sleeve <NUM> on a mandrel more closely matched to the desired shape of cooling channel 90a, such that limited or no compression of braided sleeve <NUM> is necessary. This can limit an amount of buckling of inner wall <NUM> that can occur during shaping.

Plies <NUM> or braided sleeves <NUM> can be laid up around multiple consolidated braided fiber sleeves <NUM> to form preform <NUM> or <NUM>' with cooling channels 90a-90c. In some embodiments, braided fiber sleeves <NUM> can be placed on mandrels capable of maintaining cooling channels 90a-90c during CVI or other densification process and capable of being extracted in post processing. In alternative embodiments, braided fiber sleeves <NUM> can be separately densified-partially or fully-before layup with fiber plies <NUM> or braided fiber sleeves <NUM>. As such, use of additional tooling to maintain cooling channels 90a-90c can be avoided during densification of fiber preform <NUM> or <NUM>'. This may allow for the addition of intersegment walls or other structures that could have limited extraction of tooling post densification. Hoop oriented fibers (low braid angle or woven <NUM>/<NUM> tubes) can provide reasonable resistance to compression and, therefore, support for subsequent processing without internal tooling. This results in significant additional design space for optimization of cooling channels without the constraint of mandrel removal.

<FIG> is a flow chart of method <NUM> of manufacture of BOAS <NUM> using preforms <NUM> and <NUM>' of <FIG> and <FIG>. A plurality of braided fiber sleeves <NUM> can be formed on a graphite mandrel or other removable tooling (e.g., dissolvable or removed via vaporization/sublimation) in step <NUM> and consolidated in step <NUM> to provide a desired shape of cooling channels 90a-90c. Alternatively, cooling channels 90a-90c can be tapered slightly from intersegment ends <NUM> to <NUM> to allow for mechanical extraction of a graphite mandrel following densification. In some embodiments, braided fiber sleeves <NUM> can be densified via CVI or other process in step <NUM> to produce rigid structures that can be maintained during densification of preform <NUM> or <NUM>' without the need for a temporary mandrel. In step <NUM>, the plurality of braided fiber sleeves <NUM> can be enclosed in a plurality of fiber plies <NUM> or braided fiber sleeves <NUM> to produce preform <NUM> or <NUM>', respectively. Fiber preform <NUM> or <NUM>' can be densified with a ceramic matrix in step <NUM> using CVI, precursor infiltration and pyrolysis, slurry infiltration, melt infiltration, and combinations thereof as known in the art. Any tooling used to maintain cooling channels 90a-90c during densification can be removed in step <NUM>. Additional processing or finishing procedures as known in the art can be performed, including deposition of a thermal barrier or environmental barrier coating. Apertures 92a and 92b can be ultrasonically machined through wall <NUM> of BOAS <NUM> to provide a conduit for cooling fluid Cf into cooling channels 90a-90c.

The integral cooling channels constructed of CMC braided sleeves enable large film cooling access across the gas path face of the BOAS and reduce through-wall thermal gradients along the BOAS inner diameter wall. The use of CMC braided sleeves provides for seamless channel construction and can increase the specific stiffness of the BOAS, provide an efficient distribution of load, and provide resistance to crack propagation.

Any relative terms or terms of degree used herein, such as "substantially", "essentially", "generally", "approximately" and the like, should be interpreted in accordance with and subject to any applicable definitions or limits expressly stated herein. In all instances, any relative terms or terms of degree used herein should be interpreted to broadly encompass any relevant disclosed embodiments as well as such ranges or variations as would be understood by a person of ordinary skill in the art in view of the entirety of the present disclosure, such as to encompass ordinary manufacturing tolerance variations, incidental alignment variations, transient alignment or shape variations induced by thermal, rotational or vibrational operational conditions, and the like. Moreover, any relative terms or terms of degree used herein should be interpreted to encompass a range that expressly includes the designated quality, characteristic, parameter or value, without variation, as if no qualifying relative term or term of degree were utilized in the given disclosure or recitation.

Claim 1:
A fiber-reinforced CMC blade outer air seal (BOAS) (<NUM>) for use in a gas turbine engine (<NUM>), the fiber-reinforced blade outer air seal (BOAS) (<NUM>) comprising:
a plurality of cooling channels (90a-90c), each formed from a CMC braided fiber sleeve (<NUM>);
a plurality of fiber plies (<NUM>) enclosing each braided fiber sleeve (<NUM>), the plurality of fiber plies (<NUM>) forming first and second walls (<NUM>, <NUM>) separated by the braided fiber sleeves (<NUM>); and
a matrix material between fibers of each of the braided fiber sleeves (<NUM>) and the plurality of fiber plies (<NUM>)
wherein one of the cooling channels (90c) is either:
(a) fluidly connected to an adjacent cooling channel (90b) to receive cooling fluid from the adjacent cooling channel (90b); or
(b) fluidly separated from the adjacent cooling channel (90b) and is fluidly connected to apertures (92c) extending through the first wall (<NUM>) into the one of the cooling channels (90c);
wherein the plurality of cooling channels (90a-90c) extend in a circumferential direction relative to an engine axis (A).