CMC BOAS intersegment seal

A blade outer air seal assembly includes a support structure. A blade outer air seal extends circumferentially about an axis and is mounted in the support structure. A flow guide has a plurality of flow guide segments arranged between the blade outer air seal and the support structure. An intersegment seal is at a circumferential end of at least one of the flow guide segments.

BACKGROUND

This application relates to an intersegment seal for a blade outer air seal.

Gas turbine engines are known and typically include a compressor compressing air and delivering it into a combustor. The air is mixed with fuel in the combustor and ignited. Products of the combustion pass downstream over turbine rotors, driving them to rotate.

It is desirable to ensure that the bulk of the products of combustion pass over turbine blades on the turbine rotor. As such, it is known to provide blade outer air seals radially outwardly of the blades.

SUMMARY

In one exemplary embodiment, a blade outer air seal assembly includes a support structure. A blade outer air seal extends circumferentially about an axis and is mounted in the support structure. A flow guide has a plurality of flow guide segments arranged between the blade outer air seal and the support structure. An intersegment seal is at a circumferential end of at least one of the flow guide segments.

In a further embodiment of any of the above, the flow guide segments extend circumferentially to form an annulus about the axis. An intersegment seal is arranged between each of the flow guide segments.

In a further embodiment of any of the above, the intersegment seal has an anti-rotation feature in engagement with the flow guide.

In a further embodiment of any of the above, the anti-rotation feature is a protrusion that extends generally radially outward from the intersegment seal.

In a further embodiment of any of the above, the protrusion is generally rectangular shaped.

In a further embodiment of any of the above, the flow guide has a notch at the circumferential end for engagement with the anti-rotation feature.

In a further embodiment of any of the above, a gap is defined between the flow guide and the blade outer air seal. The intersegment seal fits into the gap at the circumferential end.

In a further embodiment of any of the above, the intersegment seal has an axial portion, a first radial portion, and a second radial portion each abutting the flow guide. The flow guide has a hook at a first axial end in engagement with the first radial portion of the intersegment seal.

In a further embodiment of any of the above, the flow guide has a lip at a second axial end in engagement with the second radial portion of the intersegment seal.

In a further embodiment of any of the above, the intersegment seal has a backer piece that extends from the second radial portion and in engagement with the lip.

In a further embodiment of any of the above, the backer piece is welded to the intersegment seal.

In a further embodiment of any of the above, a spacer is arranged between the flow guide and the blade outer air seal. The spacer has a notch that corresponds to the shape of the intersegment seal. The intersegment seal is in engagement with the spacer.

In a further embodiment of any of the above, the support structure has a first support member that engages a hook at a first axial side of the blade outer air seal. A second support member engages a lip at a second axial side of the blade outer air seal.

In a further embodiment of any of the above, the intersegment seal has a first radially extending portion engaged with the hook.

In a further embodiment of any of the above, the intersegment seal has a second radially extending portion engaged with the lip.

In a further embodiment of any of the above, the blade outer air seal is a ceramic matrix composite material.

In a further embodiment of any of the above, the blade outer air seal is a monolithic ceramic material.

In a further embodiment of any of the above, the intersegment seal is metallic.

In a further embodiment of any of the above, the intersegment seal is a ceramic matrix composite material.

In another exemplary embodiment, a turbine section for a gas turbine engine includes a turbine blade that extends radially outwardly to a radially outer tip and for rotation about an axis of rotation. A blade outer air seal extends circumferentially about the axis and is mounted in a support structure radially outward of the outer tip. The support structure has a first support member that engages a hook at a first axial side of the blade outer air seal. A second support member engages a lip at a second axial side of the blade outer air seal. A flow guide has a plurality of flow guide segments arranged circumferentially about the axis between the support structure and the blade outer air seal. The flow guide forms a gap between the flow guide and blade outer air seal. An intersegment seal is arranged between each of the flow guide segments. The intersegment seal has a first radial portion and a second radial portion joined by an axial portion. The first radial portion abuts the hook, the second radial portion abuts the lip, and the axial portion is in the gap.

DETAILED DESCRIPTION

FIG. 2schematically illustrates a portion100of the turbine section28. The portion100includes alternating series of rotating blades102and stationary vanes104that extend into the core flow path C of the gas turbine engine. Turbine blades102rotate and extract energy from the hot combustion gases that are communicated along the core flow path C of the gas turbine engine20. The turbine vanes104, which generally do not rotate, guide the airflow and prepare it for the next set of blades102. As is known, it is desirable to pass the bulk of products of combustion downstream of the combustor section26across the turbine blades. Thus, an assembly105having a blade outer air seal (“BOAS”)106is positioned slightly radially outwardly of the outer tip of the blades102. It should be understood that the turbine section portion100could be utilized in other gas turbine engines, and even gas turbine engines not having a fan section at all.

The BOAS assembly105is attached to the engine static structure36. The engine static structure36has a plurality of engagement features109,111,113for engagement with the BOAS assembly105. In an embodiment, engagement features109and111are at an axial position between leading and trailing edges of the blade102and engagement feature113is aft of the vane104. In another embodiment, engagement feature111is between the blade102and vane104. Fewer or additional engagement features may be contemplated within the scope of this disclosure.

FIG. 3shows the BOAS assembly105. The assembly105includes the BOAS106which is made up of a plurality of seal segments110that are circumferentially arranged in an annulus around the central axis A of the engine20. The seal segments110are mounted in a structure112, which is circumferentially continuous about the central axis A. The BOAS106is in close radial proximity to the tips of the blades102to reduce the amount of gas flow that escapes around the blades102.

The seal segments110may be monolithic bodies that are formed of a high thermal-resistance, low-toughness material, such as a ceramic matrix composite. In another embodiment, the seal segments110may be formed from another material, such as a metallic alloy or monolithic ceramic. BOAS seals that are ceramic matric composite, particularly 2D ply construction, may be difficult to mount in an engine. This disclosure may also apply to 3D and 4D ceramic matrix composite construction methods. The parts are designed so that the thermal expansion in the axial direction can more easily work with other part with different thermal expansion rations.

Each seal segment110is a body that defines radially inner and outer sides R1, R2, respectively, first and second circumferential ends C1, C2, respectively, and first and second axial sides A1, A2, respectively. The radially inner side R1faces in a direction toward the engine central axis A. The radially inner side R1is thus the gas path side of the seal segment110that bounds a portion of the core flow path C. The first axial side A1faces in a forward direction toward the front of the engine20(i.e., toward the fan42), and the second axial side A2faces in an aft direction toward the rear of the engine20(i.e., toward the exhaust end).

The seal segments110are mounted in the structure112, which includes a BOAS support portion114and a vane platform portion116. The BOAS support portion114includes a first support member118that radially supports a hook130on the seal segment110at an axially forward portion of the structure114and a second support member120that radially supports a lip132on the seal segment110at an axially aft portion of the seal segment110. The first support member118is the axially forward-most end of the structure112. In an embodiment, the second support member120is the radially innermost portion of the structure112.

The structure112may include a plurality of hooks for attachment to the engine static structure36, for example. The structure112may include a plurality of discrete hooks122extending radially outward from the BOAS support portion114. The hooks122engage the engagement feature109(shown inFIG. 2). The structure112may include a continuous hook structure aft of the BOAS106. In the illustrated embodiment, an attachment member124extends radially outward from the structure112for attachment to the engine20. The attachment member124may be at the same axially position as the second support member120, or may forward or aft of the second support member120. The attachment member124engages the engagement feature111(shown inFIG. 2). A vane platform attachment member126extends radially outward from the vane platform portion116.

In the illustrated embodiment, the vane platform attachment member126is axially aft of the vane104. The vane platform attachment member126may be the radially outermost portion of the structure112. The attachment member126engages the engagement feature113(shown inFIG. 2). Each of the attachment members122,124,126has a generally radially extending portion and a generally axially extending portion. Although three attachment members122,124,126and three engagement members109,111,113are shown, more or fewer may come within the scope of this disclosure.

In this embodiment, the BOAS support portion114and vane platform portion116form a unified part. The metallic vane platform portion116may be used in conjunction with a CMC vane104, so that the vane construction is multi-piece in nature. The BOAS support portion114is joined with the vane platform portion116to allow the architecture to seal more easily and use cooling air more efficiently. This architecture allows BOAS cooling air reuse so the cooling air can be used on an adjacent vane. Details of a support structure112are found in U.S. patent application Ser. No. 16/122,373, entitled “UNIFIED BOAS SUPPORT AND VANE PLATFORM” filed on even date herewith. Although a unified BOAS support portion114and vane platform portion116is illustrated, the disclosed assembly may be used in a BOAS support that is not integrated with a vane platform.

FIG. 4shows a cross-section of the blade outer air seal assembly105. A hook130is formed in seal segment110of the BOAS106near the first axial side A1for engagement with the first support member118. The hook130is at a forward-most portion of the seal segment110. The hook130includes a radially outwardly extending portion defining the first axial side A1and an axially extending portion that extends aft of the first axial side A1. A lip132is formed in the seal segment110near the second axial side A2for engagement with the second support member120. The lip132extends generally axially from the seal segment110. The BOAS106may be assembled in a forward to aft direction, as the hook130and lip132will be received in the first and second support members118,120, respectively.

A cooling air reuse port134extends between a vane chamber136and a BOAS chamber137. The vane chamber136is formed between the vane platform portion116and the engine structure36. The BOAS chamber137is formed between the BOAS support portion114and the BOAS106. Cooling air enters the BOAS chamber137through an inlet148in the BOAS106, and may be reused to cool the vane104by travelling through the cooling air port134. In one embodiment, the port134extends generally axially. In another embodiment, the port134may be a different orientation, such as generally radially, depending on the orientation of the hooks122and attachment member124. For example, the port134may extend generally perpendicular to the axis A. The support112may include a plurality of cooling air reuse ports134spaced circumferentially about the support112. The cooling air may be reused in adjacent vanes, which improves cycle efficiency. This allows for less total cooling air to be used than a non-reuse configuration. Further, cooling air from several BOAS may be reused to cool a single vane.

The port134re-uses cooling air that has been used for forced convection back side cooling of the BOAS106to cool an adjacent vane104. The used air can then be used to cool the adjacent vane104reducing the amount of cooling air required to be supplied by the compressor, which may improve engine cycle efficiency.

A flow guide138is arranged between the BOAS106and BOAS support portion114. The flow guide138generally tracks the shape of the BOAS106. The flow guide138has a hook140and lip142that generally correspond to a hook130and lip132on the BOAS106. The flow guide138forces convection along the radial surface R2of the BOAS106. A spacer144may be arranged between the flow guide138and the BOAS106. The spacer144defines and maintains a radially extending space between the spacer144and BOAS106. A gap146is formed between the BOAS106and flow guide138having a width w, which is defined and maintained by the geometry of the flow guide138. Cooling air enters the BOAS106through a BOAS inlet148, then travels radially inward through the spacer144into the gap146. Cooling air exits the gap146through an outlet150in the flow guide138, and through the port134. The flow guide138is made from a ceramic matrix composite compatible material, such as cobalt, or contains a ceramic matrix composite compatible coating. The flow guide138may be formed from sheet metal, for example. Details of a flow guide138and spacer144are found in U.S. patent application Ser. No. 16/122,431, entitled “CMC BOAS COOLING AIR FLOW GUIDE” filed on even date herewith.

FIG. 5shows a portion of the BOAS assembly105with an intersegment seal152. The intersegment seal152fits at the first circumferential side C1of the seal segment110, and seals the gap between adjacent seal segments110. The intersegment seal152fits between the flow guide138and the BOAS106between two adjacent seal segments110to seal the intersegment ends of each seal segment110. In one example, the intersegment seal152is the same thickness as the spacer144. The spacer144may have a notch145corresponding to the shape of the intersegment seal152, and the intersegment seal152is in engagement with the notch145.

The intersegment seal152has an axial portion154that extends in a generally axial direction and abuts the second radial side R2of the BOAS106. A first radial portion156extends in a generally radial direction. This first radial portion156is at a forward end of the axial portion154and abuts the hook130of the BOAS106and the hook140of the flow guide138. A second radial portion158extends at an aft end of the axial portion154and abuts the lip132of the BOAS106and lip142of the flow guide138.

A flow discourager159is incorporated into the second radial portion158. The flow discourager159is generally curved aftward. However, other shapes may come within the scope of this disclosure. The flow discourager159is between the lip132of the BOAS106and the lip142of the flow guide138. The geometry of the flow discourager159helps minimize leakage in the space left between the BOAS106and flow guide138.

There may be manufacturing limitations for the BOAS106, such as the radius153near the lip132. For example, there are limitations on how small the radius153can be on a ceramic matrix composite BOAS106. The flow discourager159is shaped to minimize such leakage.

In some embodiments, the flow guide138includes a backer piece160. This backer piece160decreases the size of the gap146between the BOAS106and the flow guide138near the radius153. The backer piece160may be welded to the flow guide138, for example.

The intersegment seal152may include an anti-rotation feature162that fits into a notch164on the flow guide138. The anti-rotation feature162protrudes generally radially outward from the axial portion154to engage with the notch164. This engagement prevents the intersegment seal152from shifting in the assembly105. In an embodiment, a top surface of the anti-rotation feature162is flush with a surface of the flow guide138. In another embodiment, the anti-rotation feature162may be above or below the surface of the flow guide138. In the illustrated embodiment, the anti-rotation feature162is generally rectangular in shape. However, the anti-rotation feature162may be other shapes, such as rounded. In one embodiment, the anti-rotation feature162is flat stock welded to the intersegment seal152. In another embodiment, the anti-rotation features162is a channel. The notch164and anti-rotation feature162have complementary shapes. The anti-rotation feature162allows the flow guide138to span multiple seal segments110for reduced leakage, since the anti-rotation feature162engages with the flow guide138, rather than the BOAS106. Thus, in some examples, there may be fewer flow guide segments than BOAS seal segments110.

FIG. 6shows the intersegment seal152. The first and second radial portions156,158and axial portion154generally form a C shape. The intersegment seal152may be a metallic material or may a ceramic matrix composite material. The intersegment seal152is more robust in size and nature than known feather seals, which are used for metal BOAS. The intersegment seal152takes advantage of the space left by the ceramic matrix composite BOAS106, and fills a larger area than feather seals.

FIG. 7Aschematically shows a cross-section taken along line7-7ofFIG. 5. The intersegment seal152fits between the flow guide138and the BOAS106between flow guide segments. In this illustration, the flow guide segments align with BOAS seal segments110. Cooling air may leak from the gap146between BOAS seal segments110or between flow guide segments. The intersegment seal152helps prevent leakage at these spots. Each segment of the flow guide138has a notch164for engagement with the anti-rotation feature162.

FIG. 7Bschematically shows a cross-section taken along line7-7of another example assembly205. In this example, segments of the flow guide238are offset from the BOAS seal segments210. An intersegment seal252is arranged between each flow guide238. The offset flow guide segments and seal segments210may provide better sealing. This arrangement also allows for a different number of flow guide segments and seal segments210about the engine central axis A. In one example, flow guide segments may be longer than BOAS seal segments210, so the assembly205includes fewer flow guide segments than BOAS seal segments210.