Gas turbine engine features for tip clearance inspection

Turbine assemblies for a turbine of a gas turbine engine are disclosed herein. The turbine assembly includes a turbine wheel assembly and a turbine shroud. The turbine wheel assembly includes a disk and a plurality of blades that extend outwardly from the disk in a radial direction away from an axis. The turbine shroud extends around the blades of the turbine wheel assembly to block gasses from passing over the blades during operation of the turbine assembly. The turbine shroud includes a plurality of blade track segments arranged circumferentially adjacent to one another about the axis to form a ring. Each blade track segment has a runner that forms a primary track surface facing the axis and spaced from the axis in the radial direction.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to gas turbine engines, and more specifically to turbine shrouds included in gas turbine engines.

BACKGROUND

Gas turbine engines typically include a compressor, a combustor, and a turbine. The compressor compresses air drawn into the engine and delivers high pressure air to the combustor. In the combustor, fuel is mixed with the high pressure air and the air/fuel mixture is ignited. Products of the combustion reaction in the combustor are directed into the turbine where work is extracted to drive various components of the gas turbine engine.

Turbines typically include alternating stages of static vane assemblies and rotatable wheel assemblies. The rotatable wheel assemblies include disks carrying blades that are coupled to the disks. When the rotatable wheel assemblies turn in response to receiving the combustion reaction products, tips of the blades move along ceramic blade tracks included in static turbine shrouds surrounding the rotating wheel assemblies. Consequently, work is extracted in the form of mechanical energy.

Clearance between the tips of the blades and the static turbine shrouds affects gas turbine engine operating efficiency. Optimizing the clearance between the tips of the blades and the static shrouds to maximize gas turbine engine operating efficiency, however, can present challenges. For example, to determine the clearance between the blade tips and the static shrouds, disassembly of the gas turbine engine is often required to inspect those components, thereby resulting in increased downtime during the repair and/or testing of gas turbine engines.

SUMMARY

According to the present disclosure, a turbine assembly may include a turbine wheel assembly and a turbine shroud. The turbine wheel assembly includes a disk and a plurality of blades that extend outwardly from the disk in a radial direction away from an axis. The turbine shroud extends around the blades of the turbine wheel assembly to block gasses from passing over the blades during operation of the turbine assembly.

In illustrative embodiments, the turbine shroud may be a full hoop or may include a plurality of blade track segments arranged circumferentially adjacent to one another about the axis to form a ring. Each blade track segment may have a runner that forms a primary track surface facing the axis that is spaced from the axis in the radial direction. At least one of the plurality of blade track segments may include a first set of rub depth indicators spaced from one another and each having a first depth measured from the primary track surface and a second set of rub depth indicators spaced from one another and each having a second depth measured from the primary track surface. The first set of rub depth indicators and the second set of rub depth indicators are configured such that approximate rub depths of the turbine wheel assembly into the turbine shroud caused by turbine wheel assembly rotation within the turbine shroud during operation of the turbine assembly may be determined based on visual observation of the first set of rub depth indicators and the second set of rub depth indicators.

In illustrative embodiments, the first set of rub depth indicators may be arranged along a first pathway in a first direction such that the first depths successively increase as the first set of rub depth indicators are located adjacent to one another in the first direction. The second set of rub depth indicators may be arranged in the first direction along a second pathway such that the second depths successively decrease as the second set of rub depth indicators are located adjacent to one another in the first direction

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now toFIG. 1, an illustrative gas turbine engine10includes a fan12, a compressor14, a combustor16, and a turbine18, each of which is surrounded and supported by a metallic case20. The compressor14compresses and delivers air to the combustor16. The combustor16mixes the compressed air with fuel, ignites the air/fuel mixture, and delivers the combustion products (i.e., hot, high-pressure gases) to the turbine18. The turbine18converts the combustion products to mechanical energy (i.e., rotational power) that drives, among other things, the fan12and the compressor14.

Referring now toFIG. 2, the illustrative turbine18(also referred to herein as the turbine assembly18) includes a turbine wheel assembly22and a turbine shroud24surrounding the turbine wheel assembly22. The turbine shroud24blocks gasses from passing over the turbine wheel assembly22without causing the turbine wheel assembly22to rotate about an axis26as indicated by arrow22CW, thereby contributing to lost performance within the gas turbine engine10.

The illustrative turbine wheel assembly22includes a disk28and blades30extending outwardly from the disk28in a radial direction indicated by arrow R away from the axis26as shown inFIG. 2. The illustrative turbine shroud24includes a metallic carrier32and a blade track34having arcuate blade track segments36. The blade track segments36are arranged circumferentially adjacent to one another about the axis26to form the annular blade track34around the axis26. The metallic carrier32is coupled to the blade track34around the axis26. In operation, the metallic carrier32is coupled to the metallic case20so that the carrier32supports the blade track34relative to the metallic case20.

Each of the illustrative blade track segments36includes an arcuate runner38and an attachment feature40extending outward from the runner38in the radial direction as shown inFIG. 3. The runner38forms a primary track surface42facing the axis26and spaced a distance D from the axis26in the radial direction. The attachment feature40is configured to couple to the carrier32.

The illustrative blade track segment36A includes one set of rub depth indicators44and another set of rub depth indicators46formed in the primary track surface42as shown inFIGS. 2 and 3. Specifically, the sets of rub depth indicators44,46are embodied as, or otherwise include, features that are machined into, and thus located internally of, the primary track surface42.

The rub depth indicators44are spaced from one another and each have a depth44D measured from the primary track surface42and the rub depth indicators46are spaced from one another and each have a depth46D measured from the primary track surface42as shown inFIG. 3. The indicators44,46are configured such that approximate rub depths of the turbine wheel assembly22into the turbine shroud24caused by rotation of the assembly22within the shroud24during operation of the turbine assembly18may be determined based on visual observation of the indicators44,46. As such, the indicators44,46provide inspection features that may be used to determine rub (or a lack thereof) between the blades30and the blade track34. Because the indicators44,46may be visually observed using an optical device such as a borescope, interference between the blades30and the blade track34may be determined without disassembling the gas turbine engine10to examine the blades30and the blade track34.

The illustrative set of rub depth indicators44are arranged along a linear pathway, illustratively an arc A1in a direction indicated by arrow D1as shown inFIG. 3. Specifically, as discussed in greater detail below, the rub depth indicators44are arranged along the arc A1in the direction D1such that the depths44D of the indicators44successively increase as the indicators44are located adjacent to one another in the direction D1. The rub depth indicators44are circumferentially spaced from one another about the axis26.

The illustrative set of rub depth indicators46are arranged along a linear pathway, illustratively an arc A2in the direction D1as shown inFIG. 3. Specifically, as discussed in greater detail below, the rub depth indicators46are arranged along the arc A2in the direction D1such that the depths46D of the indicators46successively decrease as the indicators46are located adjacent to one another in the direction D1. The rub depth indicators46are circumferentially spaced from one another about the axis26.

The blade track34is illustratively constructed of a ceramic matrix composite material. In one example, the ceramic matrix composite material may include silicon-carbide fibers formed into fabric sheets and a silicon-carbide matrix. In another example, the ceramic matrix composite material may include another ceramic-based material that including reinforcing fibers and a matrix material.

The runner38of the illustrative blade track segment36A includes a base portion38B and a coating38C applied to the base portion38B as shown inFIG. 3. In some embodiments, the coating38C may be applied directly to an environmental barrier coating (not shown), and the environmental barrier coating may be applied directly to a bond coating (not shown) that is applied directly to the base portion38C. In any case, the base portion38B is formed from a ceramic matrix composite material and the coating38C is formed from a ceramic-containing material.

The primary track surface42and the sets of rub depth indicators44,46are illustratively formed by the coating38C as shown inFIG. 3. The illustrative coating38C is abradable and adapted to wear when the blades30rub into the coating38C such that interference between the blades30and the blade track34can be determined as indicated above. The coating38C is also adapted to withstand the high temperature gasses provided to the turbine assembly18during operation thereof. As such, in some embodiments, the coating38C may be a protective coating such as an environmental barrier coating adapted to resist degradation and protect the base portion38B during operation of the gas turbine engine10.

Referring now toFIG. 4, the set of rub depth indicators44illustratively includes four rub depth indicators44a,44b,44c,44darranged along the arc A1in the direction D1. The number of rub depth indicators44is dependent upon the operational application of the turbine assembly18. In some embodiments, another suitable number of rub depth indicators44may be provided. In any case, the direction D1is a clockwise circumferential direction about the axis26. In other embodiments, the direction D1may be a counterclockwise circumferential direction about the axis26.

The illustrative rub depth indicators44a,44b,44c,44dhave respective depths44D1,44D2,44D3,44D4measured from the primary track surface42that are indicated by respective patterns44ad,44bd,44cd,44ddas shown inFIG. 4. The depth44D2indicated by the pattern44bdis greater than the depth44D1indicated by the pattern44ad. The depth44D3indicated by the pattern44cdis greater than the depth44D2indicated by the pattern44bd. The depth44D4indicated by the pattern44ddis greater than the depth44D3indicated by the pattern44cd.

The set of rub depth indicators46illustratively includes four rub depth indicators46a,46b,46c,46darranged along the arc A2in the direction D1as shown inFIG. 4. The number of rub depth indicators46is dependent upon the operational application of the turbine assembly18. In some embodiments, another suitable number of rub depth indicators46may be provided. In any case, the arc A1and the arc A2are spaced from one another along the axis26.

The illustrative rub depth indicators46a,46b,46c,46dhave respective depths46D1,46D2,46D3,46D4measured from the primary track surface42that are indicated by respective patterns46ad,46bd,46cd,46ddas shown inFIG. 4. The depth46D1indicated by the pattern46adis greater than the depth46D2indicated by the pattern46bd. The depth46D2indicated by the pattern46bdis greater than the depth46D3indicated by the pattern46cd. The depth46D3indicated by the pattern46cdis greater than the depth46D4indicated by the pattern46dd.

The illustrative rub depth indicators44a,44b,44c,44dform respective rub indication surfaces44as,44bs,44cs,44dsas shown inFIG. 4. The rub depth indication surfaces44as,44bs,44cs,44dsare located internally of the primary track surface42. The rub depth indicators44a,44b,44c,44dare arranged in the direction D1such that the surfaces44as,44bs,44cs,44dsare spaced successively farther from the axis26in the radial direction than the primary track surface42as the indicators44a,44b,44c,44dare located adjacent to one another in the direction D1. As such, the surface44asis closer to the axis26than the surface44bs, the surface44bsis closer to the axis26that the surface44cs, and the surface44csis closer to the axis than the surface44ds.

The illustrative rub depth indicators46a,46b,46c,46dform respective rub indication surfaces46as,46bs,46cs,46dsas shown inFIG. 4. The rub depth indication surfaces46as,46bs,46cs,46dsare located internally of the primary track surface42. The rub depth indicators46a,46b,46c,46dare arranged in a direction D2generally opposite the direction D1such that the surfaces46as,46bs,46cs,46dsare spaced successively farther from the axis26in the radial direction than the primary track surface42as the indicators46a,46b,46c,46dare located adjacent to one another in the direction D2. As such, the surface46asis farther from the axis26that the surface46bs, the surface46bsis farther from the axis26than the surface46cs, and the surface46csis farther from the axis26that the surface46ds.

Referring now toFIG. 6, the rub depth indicator44aand the rub indication surface44asare shown in greater detail. The rub depth indicator44aillustratively has a generally circular cross-sectional shape as best seen inFIG. 4. In other embodiments, however, the rub depth indicator44amay take the shape of another suitable geometric form. The rub indication surface44asis illustratively a generally planar surface (also referred to herein as a flat-bottomed surface) defined by an aperture48formed in the coating38C that has a generally circular cross-sectional shape.

In the illustrative embodiment, the rub depth indicators44b,44c,44d,46a,46b,46c,46dhave cross-sectional shapes substantially identical to the cross-sectional shape of the indicator44aas shown inFIGS. 4 and 6. Additionally, in the illustrative embodiment, the rub indication surfaces44bs,44cs,44ds,46as,46bs,46cs,46dsare generally planar surfaces defined by respective apertures50,52,54,56,58,60,62formed in the coating38C that have cross-sectional shapes substantially identical to the aperture48.

Referring now toFIG. 5, an illustrative blade track segment136A adapted for use in a blade track134is shown. The blade track segment136A may be used in place of the segment36A described above with reference toFIGS. 2-4.

The illustrative blade track segment136A includes a set of rub depth indicators144, a set of rub depth indicators146, and a set of rub indicators148formed in a primary track surface142of the segment136A as shown inFIG. 5. Specifically, the sets of rub depth indicators144,146,148are embodied as, or otherwise include, features that are machined into, and thus located internally of, the primary track surface142.

The rub depth indicators144are spaced from one another and each have a depth144D measured from the primary track surface142as shown inFIG. 5. The rub depth indicators146are spaced from one another and each have a depth146D measured from the primary track surface142. The rub depth indicators148are spaced from one another and each have a depth148D measured from the primary track surface142. Similar to the rub depth indicators44,46, the rub depth indicators144,146,148provide inspection features that may be used to determine rub (or a lack thereof) between blades of a turbine wheel assembly (e.g., the blades30of the turbine wheel assembly22) and the blade track134.

The illustrative set of rub depth indicators144are arranged along a linear pathway A1′ in a direction indicated by arrow D1′ as shown inFIG. 5. Specifically, as discussed in greater detail below, the rub depth indicators144are arranged along the pathway A1′ in the direction D1′ (axially-forward) such that the depths144D of the indicators144successively increase as the indicators144are located adjacent to one another in the direction D1′. The rub depth indicators144are spaced from one another along an axis126oriented similar to the axis26.

The illustrative set of rub depth indicators146are arranged along a linear pathway A2′ in the direction D1′ as shown inFIG. 5. Specifically, as discussed in greater detail below, the rub depth indicators146are arranged along the pathway A2′ in the direction D1′ (axially-aft) such that the depths146D of the indicators146successively decrease as the indicators146are located adjacent to one another in the direction D1′. The rub depth indicators146are spaced from one another along the axis126.

The illustrative set of rub depth indicators148are arranged along a linear pathway A3′ in the direction D1′ as shown inFIG. 5. Specifically, as discussed in greater detail below, the rub depth indicators148are arranged along the pathway A3′ in the direction D1′ (axially-forward) such that the depths148D of the indicators148successively increase as the indicators148are located adjacent to one another in the direction D1′. The rub depth indicators148are spaced from one another along the axis126.

The blade track134is illustratively constructed of a ceramic matrix composite material. In one example, the ceramic matrix composite material may include silicon-carbide fibers formed into fabric sheets and a silicon-carbide matrix. In another example, the ceramic matrix composite material may include another ceramic-based material that including reinforcing fibers and a matrix material.

The illustrative blade track segment136A includes a base portion (not shown) similar to the base portion38B and a coating138C similar to the coating38C applied thereto as shown inFIG. 5. The base portion is formed from a ceramic matrix composite material and the coating138C is formed from a ceramic-containing material.

The primary track surface142and the sets of rub depth indicators144,146,148are illustratively formed by the coating138C as shown inFIG. 5. The illustrative coating138C is abradable and adapted to wear when blades (e.g., the blades30) rub into the coating138C such that interference between the blades and the blade track134can be determined. The coating138C is also adapted to withstand the high temperature gasses provided to a turbine assembly (e.g., the turbine assembly18) during operation thereof. As such, in some embodiments, the coating138C may be a protective coating such as an environmental barrier coating adapted to resist degradation and protect the base portion during operation of a gas turbine engine (e.g., the engine10).

The set of rub depth indicators144illustratively includes three rub depth indicators144a,144b,144carranged along the arc A1′ in the direction D1′ as shown inFIG. 5. The number of rub depth indicators144is dependent upon the operational application of the turbine assembly. In some embodiments, another suitable number of rub depth indicators144may be provided. In any case, the direction D1′ is an axially-forward direction along the axis126from an aft portion138A of a runner138defining the primary track surface142toward a forward portion138F of the runner138. In other embodiments, the direction D1′ may be an aftward direction along the axis126from the forward portion138F toward the aft portion138A.

The illustrative rub depth indicators144a,144b,144chave respective depths144D1,144D2,144D3measured from the primary track surface142that are indicated by respective patterns144ad,144bd,144cdas shown inFIG. 5. The depth144D2indicated by the pattern144bdis greater than the depth144D1indicated by the pattern144ad. The depth144D3indicated by the pattern144cdis greater than the depth144D2indicated by the pattern144bd.

The set of rub depth indicators146illustratively includes three rub depth indicators146a,146b,146carranged along the pathway A2′ in the direction D1′ as shown inFIG. 5. The number of rub depth indicators146is dependent upon the operational application of the turbine assembly. In some embodiments, another suitable number of rub depth indicators146may be provided. In any case, the pathway A1′ and the pathway A2′ are circumferentially spaced from one another about the axis126.

The illustrative rub depth indicators146a,146b,146chave respective depths146D1,146D2,146D3measured from the primary track surface142that are indicated by respective patterns146ad,146bd,146cdas shown inFIG. 5. The depth146D1indicated by the pattern146adis greater than the depth146D2indicated by the pattern146bd. The depth146D2indicated by the pattern146bdis greater than the depth146D3indicated by the pattern146cd.

The set of rub depth indicators148illustratively includes three rub depth indicators148a,148b,148carranged along the pathway A3′ in the direction D1′ as shown inFIG. 5. The number of rub depth indicators148is dependent upon the operational application of the turbine assembly. In some embodiments, another suitable number of rub depth indicators148may be provided. In any case, the pathway A1′, the pathway A2′, and the pathway A3are circumferentially spaced from one another about the axis126.

The illustrative rub depth indicators148a,148b,148chave respective depths148D1,148D2,148D3measured from the primary track surface142that are indicated by respective patterns148ad,148bd,148cdas shown inFIG. 5. The depth148D2indicated by the pattern148bdis greater than the depth148D1indicated by the pattern148ad. The depth148D3indicated by the pattern148cdis greater than the depth148D2indicated by the pattern148bd.

The illustrative rub depth indicators144a,144b,144cform respective rub indication surfaces144as,144bs,144csas shown inFIG. 5. The rub depth indication surfaces144as,144bs,144csare located internally of the primary track surface142. The rub depth indicators144a,144b,144care arranged in the direction D1′ such that the surfaces144as,144bs,144csare spaced successively farther from the axis126in a radial direction than the primary track surface142as the indicators144a,144b,144care located adjacent to one another in the direction D1′. As such, the surface144asis closer to the axis126than the surface144bsand the surface144bsis closer to the axis126that the surface144cs.

The illustrative rub depth indicators146a,146b,146cform respective rub indication surfaces146as,146bs,146csas shown inFIG. 5. The rub depth indication surfaces146as,146bs,146csare located internally of the primary track surface142. The rub depth indicators146a,146b,146care arranged in a direction D2′ generally opposite the direction D1′ such that the surfaces146as,146bs,146csare spaced successively farther from the axis126in the radial direction than the primary track surface142as the indicators146a,146b,146care located adjacent to one another in the direction D2′. As such, the surface146asis farther from the axis26that the surface146bsand the surface146bsis farther from the axis126than the surface146cs.

The illustrative rub depth indicators148a,148b,148cform respective rub indication surfaces148as,148bs,148csas shown inFIG. 5. The rub depth indication surfaces148as,148bs,148csare located internally of the primary track surface142. The rub depth indicators148a,148b,148care arranged in the direction D1′ such that the surfaces148as,148bs,148csare spaced successively farther from the axis126in a radial direction than the primary track surface142as the indicators148a,148b,148care located adjacent to one another in the direction D1′. As such, the surface148asis closer to the axis126than the surface148bsand the surface148bsis closer to the axis126that the surface148cs.

Referring now toFIG. 6, the rub depth indicator144aand the rub indication surface144asare shown in greater detail. The rub depth indicator144aillustratively has a generally circular cross-sectional shape as best seen inFIG. 5. In other embodiments, however, the rub depth indicator144amay take the shape of another suitable geometric form. The rub indication surface144asis illustratively a generally planar surface (also referred to herein as a flat-bottomed surface) defined by an aperture150formed in the coating138C that has a generally circular cross-sectional shape.

In the illustrative embodiment, the rub depth indicators144b,144c,146a,146b,146c,148a,148b,148chave cross-sectional shapes substantially identical to the cross-sectional shape of the indicator144aas shown inFIGS. 5 and 6. Additionally, in the illustrative embodiment, the rub indication surfaces144bs,144cs,146as,146bs,146cs,148as,148bs,148csare generally planar surfaces defined by respective apertures152,154,156,158,160,162,164,166formed in the coating138C that have cross-sectional shapes substantially identical to the aperture150.

Referring now toFIG. 7, an illustrative rub depth indicator244formed in a primary track surface242of a blade track segment236A of a blade track234is shown. The blade track segment236A may be used in place of the segment36A described above with reference toFIGS. 2-4or the segment136A described above with reference toFIG. 5. The blade track segment236A may include one or more substantially identical rub depth indicators244. In embodiments where the segment236A includes more than one rub depth indicator244, the indicators244may be arranged in similar fashion to the indicators44,46on the segment36A or the indicators144,146,148on the segment136A.

In the illustrative embodiment, the rub depth indicator244forms three rub indication surfaces244S1,244S2,244S3as shown inFIG. 7. The rub indication surfaces244S1,244S2,244S3are spaced different radial distances from an axis (not shown) defining the centerline of a turbine assembly (e.g., like the axis26) including the blade track segment236A. More specifically, the surfaces244S1,244S2,244S3are spaced successively farther from the axis in a radial direction indicated by arrow R1. In addition, the surfaces244S1,244S2,244S3are arranged such that midpoints MP1, MP2, MP3of the respective surfaces244S1,244S2,244S3are aligned along an axis254extending in the radial direction R1through the segment236A.

In the illustrative embodiment, because the midpoints MP1, MP2, MP3of the respective rub indication surfaces244S1,244S2,244S3are aligned along the axis254, the surfaces244S1,244S2,244S3are centered about a location L on the axis254as shown inFIG. 7. As such, different rub depths of a turbine wheel assembly (e.g., the assembly22) into the blade track234at and adjacent to the location L caused by turbine wheel assembly rotation within a turbine shroud (e.g., the shroud24) during operation of the turbine wheel assembly may be determined based on visual observation of the surfaces244S1,244S2,244S3.

In the illustrative embodiment, the rub indication surfaces244S1is spaced a radial distance244D1from the axis as shown inFIG. 7. The rub indication surface244S2is spaced a radial distance244D2from the axis greater than the radial distance244D1. The rub indication surface244S3is spaced a radial distance244D3from the axis greater than the radial distance244D2.

In the illustrative embodiment, each of the rub indication surfaces244S1,244S2, and244S3is a generally planar surface (also referred to herein as a flat-bottomed surface) formed by an abradable, ceramic-containing coating238C as shown inFIG. 7. The surface244S1is defined by an aperture256formed in the coating238C that has a diameter256D. The surface244S2is defined by an aperture258formed in the coating238C that has a diameter258D less than the diameter256D. The surface244S3is defined by an aperture260formed in the coating238C that has a diameter260D less than the diameter258D.

The rub depth indicator244may be produced by a series of operations with multiple tool sizes as suggested inFIG. 7. In some embodiments, the rub depth indicator244may be produced in one operation by a tool whose profile matches the stepped profile of the feature.

Referring now toFIG. 8, an illustrative rub depth indicator344formed in a primary track surface342of a blade track segment336A of a blade track334is shown. The blade track segment336A may be used in place of the segment36A described above with reference toFIGS. 2-4or the segment136A described above with reference toFIG. 5. The blade track segment336A may include one or more substantially identical rub depth indicators344. In embodiments where the segment336A includes more than one rub depth indicator344, the indicators344may be arranged in similar fashion to the indicators44,46on the segment36A or the indicators144,146,148on the segment136A.

In the illustrative embodiment, the rub depth indicator344forms a single rub indication surface344S as shown inFIG. 8. The rub indication surface344S includes points344P spaced at different radial distances from an axis (not shown) defining the centerline of a turbine assembly (e.g., like the axis26) than the primary track surface342. Each of the points344P is illustratively spaced farther from the axis than the surface342in a radial direction indicated by arrow R2. An axis354bisecting the surface344S passes through a location L2as shown inFIG. 8.

In the illustrative embodiment, because the rub indication surface344S is bisected by the axis354passing through the location L2, the surface344S is centered about the location L2as shown inFIG. 8. As such, different rub depths of a turbine wheel assembly (e.g., the assembly22) into the blade track334at and adjacent to the location L2caused by turbine wheel assembly rotation within a turbine shroud (e.g., the shroud24) during operation of the turbine wheel assembly may be determined based on visual observation of the surface344S.

In the illustrative embodiment, the rub indication surface344S includes a surface segment344S1and a surface segment344S2interconnected with the surface segment344S1as shown inFIG. 8. The segment344S1extends at an obtuse angle A1to a portion342A of the primary track surface342. The segment344S2extends at an obtuse angle A2to a portion342B of the primary track surface342.

In the illustrative embodiment, the rub indication surface344S is a generally planar surface formed by an abradable, ceramic-containing coating338C as shown inFIG. 8. The surface344S is defined by an aperture356formed in the coating338C that has a generally conical cross-sectional shape.

Referring now toFIG. 9, an illustrative rub depth indicator444formed in a primary track surface442of a blade track segment436A of a blade track434is shown. The blade track segment436A may be used in place of the segment36A described above with reference toFIGS. 2-4or the segment136A described above with reference toFIG. 5. The blade track segment436A may include one or more substantially identical rub depth indicators444. In embodiments where the segment436A includes more than one rub depth indicator444, the indicators444may be arranged in similar fashion to the indicators44,46on the segment36A or the indicators144,146,148on the segment136A.

In the illustrative embodiment, the rub depth indicator444forms a single rub indication surface444S as shown inFIG. 9. The rub indication surface444S includes points444P spaced at different radial distances from an axis (not shown) defining the centerline of a turbine assembly (e.g., like the axis26) than the primary track surface442. Each of the points444P is illustratively spaced farther from the axis than the surface442in a radial direction indicated by arrow R3. An axis454bisecting the surface444S passes through a location L3as shown inFIG. 9.

In the illustrative embodiment, because the rub indication surface444S is bisected by the axis454passing through the location L3, the surface444S is centered about the location L3as shown inFIG. 9. As such, different rub depths of a turbine wheel assembly (e.g., the assembly22) into the blade track434at and adjacent to the location L3caused by turbine wheel assembly rotation within a turbine shroud (e.g., the shroud24) during operation of the turbine wheel assembly may be determined based on visual observation of the surface444S.

In the illustrative embodiment, the rub indication surface444S is illustratively embodied as, or otherwise includes, an arcuate surface as shown inFIG. 9. The rub indication surface444S is formed by an abradable, ceramic-containing coating438C. The surface444S is defined by an aperture456formed in the coating438C that has a partial oval cross-sectional shape.

A gas turbine engine (e.g., the gas turbine engine10) may include alternating stages of static vanes and rotating blades (e.g., the blades30) in compressor (e.g., the compressor14) and turbine (e.g., the turbine18) sections of the engine. The rotating blades may impart mechanical energy to the flowpath gasses in the compressor section, and they may extract mechanical energy from the flowpath gasses in the turbine section. In both the compressor and turbine sections, the blades may be fitted to a rotating disk (e.g., the disk28) or drum. In designs where a shroud (e.g., the turbine shroud24) is not integral to a blade, the tips of the blade may move past static blade tracks (e.g., the blade track34) that are positioned just radially outboard of the rotating blades.

The amount of clearance (or lack thereof) between the blade tips and the seal segments or blade tracks may have a substantial impact on aerodynamic efficiency and overall performance of the engine. Without a seal segment radially outboard of the blade, gasses may be free to migrate over the blade tip from a pressure side of the blade to a suction side of the blade without causing the blade to rotate. By minimizing the clearance between the blade tips and the seal segments, aerodynamic losses may be reduced.

Turbine seal segments may have a multi-layer coating system on the radially inboard surface (e.g., the primary track surface42) that forms an outer annulus of the flowpath. The coating system may include a bond coat applied to a metallic, ceramic (e.g., the base portion38B), or other suitable substrate, and an abradable coating (e.g., the coating38C) applied to the bond coat. In some applications, an environmental barrier coating may be applied after the bond coat and before the abradable coating.

The outer abradable coating's purpose may be to act as a sacrificial material so that the turbine blade tips can rub into the surface and leave a minimum gap between the blade tips and outer annulus surface formed by the abradable coating. Since managing tip clearance may be important for achieving high stage efficiencies, measuring the tip clearance at different operating conditions may be done to provide insight into the relative radial position of the blade tips and seal segments at different engine operating conditions. Such measurement may be accomplished by a variety of methods, including, but not limited to, installing tip clearance measurement probes or measuring incursion depth into the abradable coating after disassembly of the engine.

The present disclosure may provide designs for forming negative features (e.g., the rub depth indicators44,46) in the abradable coating surface. In one example, flat-bottomed holes (e.g., the indicators44,46having respective surfaces44as,44bs,44cs,44ds,46as,46bs,46cs,46ds) may be machined into the abradable coating surface. A series of separate holes (e.g., the apertures48,50,52,54,56,58,60,62) may be produced at varying depths (e.g., the depths44D1,44D2,44D3,44D4,46D1,46D2,46D3,46D4) so that the features successively get rubbed away by the blade tips as the incursion depths of the blade tips increase. The rub depth may be revealed by observing which holes are still visible during inspection since the pattern of features and their depths are known. Embodiments of the present disclosure provide for successive disappearance of the features with increasing depth such that the rub depth can be estimated during a borescope inspection by simply counting the remaining features. This does not require the segments to be disassembled from the engine.

One benefit of the flat-bottomed holes may be that the features are less complicated and therefore easier to manufacture with industry standard equipment than other designs. Additionally, the small diameter, flat-bottomed holes may be advantageous for some coatings such as ceramic-containing coatings because the holes can minimize stresses in such brittle, relatively-low bond strength coatings. In some embodiments, the hole feature may include a radius where the cylindrical surface of the hole meets the flat bottom of the hole. The size and shape of the holes may be unique to the abradable coating material itself, and some coatings may be more tolerant to other shapes.

The flat-bottomed holes may be produced in multiple rows of increasing or decreasing incremental depths (e.g., the row of indicators44a,44b,44c,44dand the row of indicators46a,46b,46c,46d). Multiple rows of flat-bottomed holes with depths varying in opposite directions (the directions D1, D2and the directions D1′, D2′) may provide indications of rub depth on forward and aft portions (e.g., the portions138F,138A) of blade track segments or on circumferentially spaced portions of blade track segments. Such configurations may enable rub depth consistency to be determined over the axial and circumferential dimensions of blade track segments to a greater degree than other configurations permit such rub depth consistency to be determined.

In one example, the depth of the flat-bottomed holes may vary as a function of circumferential position (e.g., the indicators44,46spaced circumferentially about the axis26as shown inFIG. 4). In another example, the depth of the flat-bottomed holes may vary as a function of axial position (e.g., the indicators144,146,148spaced along the axis126as shown inFIG. 5). A sectional view of one of the flat-bottomed holes (e.g., one of the indicators44,46or the indicators144,146,148) may be provided byFIG. 6.

In the latter example, the same pattern may be reproduced at differential circumferential positions in the abradable coating (e.g., the indicators144,146,148are circumferentially spaced about the axis126). This may be advantageous because the radius of curvature of the blade track segments may change as a result of thermal expansion such that tip clearance and rub depth may not be consistent along a segment's arc length at a given engine condition. A blade track segment's radius of curvature may be different from its radial position, which may be referred to as petalling or faceting depending on whether the blade track segment's radius of curvature is less than or greater than its radial position with respect to the engine centerline (e.g., the centerline defined by the axis26). Varying the depth of the flat-bottomed holes as a function of axial position may provide insight into the degree of mismatch between the blade track segment's curvature and radial position.

In yet another example, a series of successively smaller diameter and deeper holes (e.g., the apertures256,258,260defining the rub indicator244) may be produced in the abradable coating. One benefit of this design may be that multiple features (e.g., the rub indication surfaces244S1,244S2,244S3) occupy a small amount of space such that rub or interference at generally the same precise location may be observed at multiple incursion depths.

In yet another example still, a cone-shaped feature (e.g., the indicator344defined by the aperture356having a generally conical cross-sectional shape) may be produced in the abradable coating. In this example, the radius may vary with the depth of the machined feature, and the rub depth may be calculated as long as the diameter of the remaining feature can be measured at the coating surface and the correlation between feature depth and feature diameter is known. Other shapes (e.g., the indicator444defined by the aperture456having a partial oval cross-sectional shape) may offer similar benefits.

The assembly of blade track segments in an engine may form a full annular surface outboard of the blades. The negative coating features contemplated by the present disclosure can be produced in any number of segments forming the full annular surface. Including these features at various circumferential positions around the engine may provide insight into the variation of tip clearance as these positions.

While illustrative embodiments of the present disclosure include blade track segments comprising composite matrix materials, the teachings herein are applicable to metallic blade track segments. In addition, while illustrative blade tracks of the present disclosure are made up of segments, it is contemplated that the rub depth indication systems described herein may be included in full-hoop blade track designs.