An inter-turbine duct includes a first annular wall with a ceramic composite material and including a first plurality of layers and a second plurality of layers, the first plurality of layers including a slot extending therethrough; and a first vane with a material of a metal alloy or a ceramic material. The first vane has a first end and a flange extending through the slot with the flange extending away from the first end and being retained between the first plurality of layers and the second plurality of layers of the first annular wall.

TECHNICAL FIELD

The inventive subject matter generally relates to engines, and more particularly relates to inter-turbine ducts for use in turbine sections of engines.

BACKGROUND

A gas turbine engine may be used to power various types of vehicles and systems. A particular type of gas turbine engine that may be used to power aircraft is a turbofan gas turbine engine. A turbofan gas turbine engine may include, for example, a fan section, a compressor section, a combustor section, a turbine section, and an exhaust section. The fan section induces air from the surrounding environment into the engine and accelerates a fraction of the air toward the compressor section. The remaining fraction of air is accelerated into and through a bypass plenum, and out the exhaust section.

The compressor section, which may include a high pressure compressor and a low pressure compressor, raises the pressure of the air it receives from the fan section to a relatively high level. The compressed air then enters the combustor section, where an annular wall of fuel nozzles injects a steady stream of fuel into a plenum. The injected fuel is ignited to produce high-energy compressed air. The air then flows into and through the turbine section causing turbine blades therein to rotate and generate energy. This energy is used to power the fan and compressor sections. The air exiting the turbine section is exhausted from the engine via the exhaust section, and the energy remaining in the exhaust air aids the thrust generated by the air flowing through the bypass plenum.

In some configurations, the turbine section includes a high pressure turbine section and a low pressure turbine section. An inter-turbine duct may be interposed between the two sections and may include a plurality of radially inwardly extending vanes adapted to guide airflow from the high pressure turbine section into the low pressure turbine section. Conventionally, the vanes and at least part of the inter-turbine duct (e.g., an inner wall or an outer wall of the duct) are cast as a single piece from high-temperature materials, such as nickel-based superalloys. To protect structures surrounding the inter-turbine duct from excessive heat, an insulation blanket is typically disposed around inner diameter of the inter-turbine duct. In other configurations, air flowing through the bypass plenum may be bled into cavities surrounding the inter-turbine duct. However, as the demand for more efficient engines has increased, the demands for increased engine operating temperatures and decreased engine weight have increased as well. As a result, use cooling air flow from the bypass plenum may not provide sufficient cooling for the inter-turbine duct.

Accordingly, it is desirable to have an improved inter-turbine duct, which may have improved performance over conventional inter-turbine ducts when exposed to high engine operating temperatures. In addition, it is desirable for the improved inter-turbine duct to be capable of being retrofitted into existing engines. Moreover, it is desirable for the improved inter-turbine duct to be relatively simple and inexpensive to manufacture. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter.

BRIEF SUMMARY

In accordance with an exemplary embodiment, an inter-turbine duct includes a first annular wall with a ceramic composite material and including a first plurality of layers and a second plurality of layers, the first plurality of layers including a slot extending therethrough; and a first vane with a material of a metal alloy or a ceramic material. The first vane has a first end and a flange extending through the slot with the flange extending away from the first end and being retained between the first plurality of layers and the second plurality of layers of the first annular wall.

In accordance with an exemplary embodiment, an inter-turbine duct includes a first annular wall including a first plurality of layers and a second plurality of layers each with a first ceramic material, the first plurality of layers including a plurality of slots extending therethrough. The duct further include a second annular wall with a ceramic material and including a plurality of openings extending between an inner surface and an outer surface of the second annular wall. The duct further includes a plurality of vanes extending between the first annular wall and the second annular wall, each vane having a material of a metal alloy or a ceramic material, each vane having a first end, a second end, and a flange. The second end of each vane extends through a corresponding opening of the plurality of openings of the second annular wall. The flange of each vane extends through a corresponding slot of the plurality of slots. The flange of each vane extends away from the first end of a corresponding vane and being retained between the first plurality of layers and the second plurality of layers of the first annular wall.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the inventive subject matter or the application and uses of the inventive subject matter. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

The inventive subject matter relates to inter-turbine ducts that may be employed in high temperature applications in which separate systems for cooling a turbine section may be omitted or cooling of the turbine section may be minimal. In particular, the inter-turbine ducts may include first and second annular walls that extend axially between two turbine stages. One or more of the annular walls comprises a ceramic composite. A plurality of vanes extends between the two annular walls, and each vane may include an end having a flange extending away from the vane. The flange may be retained between multiple layers of the first annular wall. By including first and/or second annular walls that include ceramic materials, where one annular wall serves as an inner wall and the other annular wall serves as an outer wall, the inter-turbine ducts may withstand operating temperatures that are higher than those that conventional inter-turbine ducts are designed to withstand. In any case, the inventive subject matter may be implemented into any type of engine in which an inter-turbine duct may be subjected to high operating temperatures. One example of such an engine is a turbofan jet engine.

FIG. 1is a partial cross-sectional side view of a turbofan jet engine100, according to an embodiment. The turbofan jet engine100is disposed in an engine case101and includes a fan section102, a compressor section104, a combustor and turbine assembly105, and an exhaust section108. The fan section102is positioned at the front, or “inlet” section of the engine100, and includes a fan110that induces air from the surrounding environment into engine100. The fan section102accelerates a fraction of the air toward the compressor section104, and a remaining fraction is accelerated into and through a bypass112, and out the exhaust section108. The compressor section104raises the pressure of the air it receives to a relatively high level.

The high-pressure compressed air enters combustor and turbine assembly105, where an annular wall of fuel nozzles (not shown) injects fuel into a combustor116. Combustion is initiated by an ignitor114which ignites the fuel in the high-pressure air to significantly increase the thermal energy of the air. This high-temperature, high-pressure air flows into a cooled high pressure turbine stage106and into un-cooled low pressure turbine assemblies118,120,122, causing the turbines to rotate as air flows over radially mounted turbine blades, thereby converting thermal energy from the air into mechanical energy. Although three low pressure turbine assemblies are shown inFIG. 1, fewer or more assemblies may be included in other embodiments.

The mechanical energy generated in the low pressure turbine assemblies118,120,122is used to power other portions of engine100, such as the fan section102and axial stages of the compressor section104. Air exiting the last turbine assembly122then leaves the engine100via the exhaust section108. Energy remaining in the exhaust air augments thrust generated by the air flowing through the bypass112.

FIG. 2is a cross-sectional view of a portion of the turbofan jet engine100ofFIG. 1indicated by dotted box2, according to an embodiment. The portion of the turbofan jet engine100includes an aft portion of a high pressure turbine stage202and a portion of a low pressure turbine stage204. In an embodiment, an inter-turbine duct206extends between the two turbine stages202,204and includes a plurality of vanes210. The inter-turbine duct206is annular and includes an inner annular wall212and an outer annular wall214, in an embodiment. Generally, both the inner and outer annular walls212,214may be cone-shaped, in an embodiment. In another embodiment, the inner and outer annular walls212,214may be concentric. In other embodiments, the inner and outer annular walls212,214alternatively may be cylindrical or another shape depending on particular configurations and dimensions of the high and low pressure turbine stages202,204. The vanes210extend between the inner and outer annular walls212,214. Although only one vane210is shown inFIG. 2, additional vanes are disposed circumferentially around the inter-turbine duct206.

To allow inter-turbine duct206to operate adequately in high engine operating temperature environments, at least a portion of the inter-turbine duct206may comprise ceramic composite materials. In another embodiment, the vanes210may comprise ceramic composite materials and/or metal alloy materials. In accordance with an embodiment, a suitable ceramic composite material from which one or both of the inner and outer annular walls212,214and/or one or more of the vanes210may include a composite including a reinforcement phase and a matrix phase. The reinforcement phase may include a plurality of reinforcement fibers that form a fabric to provide a structure of the composite for enhancing the tensile and flexural strength properties of the composite. The matrix phase impregnates the reinforcement fabric and bonds the fibers and layers of fabric together to enhance strength properties of the composite. As described below, these phases may be implemented by applying the material in the appropriate location and sintering at a relatively low temperature. In this regard, the ceramic composites may include but are not limited to, aluminum oxide ceramic composites, and silicon carbide materials. For example, the ceramic composites may be formed by a suitable ceramic fiber (e.g., carbon, silicon carbide (SiC), alumina and the like) embedded in a ceramic matrix (e.g., carbon, silicon carbide (SiC), alumina and the like). In some embodiments, the vanes210may comprise metal alloy materials, such as nickel-based superalloys, cobalt-based superalloys or other superalloys.

FIG. 3is a side cross-sectional view of an inter-turbine duct300, andFIG. 4is a cross-sectional view of a portion of the inter-turbine duct300ofFIG. 3taken along line4-4, in accordance with an embodiment. With reference toFIGS. 3 and 4, in an embodiment, the inter-turbine duct300includes a vane302, a first annular wall304(only a portion of which is shown), and second annular wall306(only a portion of which is shown). The vane302may comprise a metal alloy material or a ceramic composite described above. In accordance with an embodiment, the vane302may be formed by casting or growth from a seed crystal. In another embodiment, plies of ceramic composite fabric may be laid up within a mold, and the laid-up plies may be sintered to form the vane302. In still another embodiment, the vane302may have a portion that is cast from a metal alloy or ceramic composite material and may have a portion that comprises plies of ceramic composite fabric.

In an embodiment, the vane302includes a main body308, a first end310, and a second end312. The main body308may have a height that is sufficient to span a majority of the distance between the first and second annular walls304,306. In other embodiments, the height may be greater or less than the aforementioned range. To provide a sufficient surface area for directing airflow through the inter-turbine duct300as desired, the main body308also generally extends from a first edge314to a second edge316, either of which may be contoured to serve as leading or trailing edges. In an embodiment, a length between the first edge314to the second edge316may longer or shorter than the height of the main body308.

The first end310of the vane302is configured to be retained within the first annular wall304. In an embodiment, the first end310includes a flange320that extends outwardly from the first end310. According to an embodiment, the flange320may be rectangular, ovular, circular or another shape and is suitably dimensioned to be retained within the first annular wall304. To retain the flange320within the first annular wall304, the first annular wall304may comprise a first plurality of layers322and a second plurality of layers324. The first plurality of layers322makes up an inner portion of the first annular wall304and includes a slot326having dimensions that are smaller than those of the main body308of the vane302. The first end310of the vane302extends through the slot326in the first plurality of layers322so that the flange320, which has dimensions that are larger than those of the slot326, is disposed on one side of the first annular wall304between the first and second pluralities of layers322,324, and the main body308is disposed on an opposite side of the first annular wall304.

To provide sufficient structural integrity to the first annular wall304to thereby minimize relative movement of the vane302, each plurality of layers322,324may comprise a number of layers. In an embodiment, fewer layers may be included depending on the material selected for use as the ceramic composite material. In some embodiments, all of the layers may comprise the same ceramic composite material. In other embodiments, the first plurality of layers322may comprise a first ceramic composite material, and the second plurality of layers324may comprise a second ceramic composite material. In still another embodiment, one or both of the plurality of layers322,324may comprise two or more ceramic composite materials. In yet another embodiment, one or both of the plurality of layers322,324may be formed from a metal alloy and a ceramic composite material.

The second end312of the vane302extends through an opening338in the second annular wall306. In an embodiment, the second end312may include a post340that may generally extend along the same axis as the main body308. In another embodiment, the post340may have smaller and/or different dimensions and/or shape than the main body308. For example, a portion of the post340may have a cylindrical cross-sectional shape or another shape. To accommodate thermal expansion of the vane302, the second end312of the vane302and the opening338of the second annular wall306may form a slip joint, in an embodiment. Other embodiments may include other types of joints formed between the second end312of the vane302and the opening338of the second annular wall306.

The second annular wall304may comprise a ceramic composite material, in an embodiment. For example, the second annular wall304may include a plurality of layers formed with a ceramic composite material. In an embodiment, more or fewer layers may be included depending on the material selected for use as the ceramic composite material. In some embodiments, all of the layers may comprise the same ceramic composite material. In other embodiments, the plurality of layers may comprise two or more ceramic composite materials. In still another embodiment, the second annular wall304may be cast or formed from a metal alloy. In yet another embodiment, the second annular wall304may be formed from a metal alloy and a ceramic composite material.

Generally, a majority of the plurality of vanes (e.g., vanes210) included in the inter-turbine duct (e.g., assembly206) includes the above-described configuration. However, to further secure the inter-turbine duct within the engine (e.g., engine100), the vanes may include additional features.

Hollow vanes can also be used to permit passage of services or cooling air. Retention methods other than those illustrated may be used. Clamped flanges that permit radial slip, guided features that permit radial relative displacement, and other configurations may be used in conjunction with the configuration described herein.

As such, generally, the outer duct wall captures the retention feature on the outer diameter of the airfoil and the inner wall will form a guided slip joint. The aerodynamic forces on the vanes will be reacted by the captured features in the CMC end walls. Three to five of the vanes could incorporate a feature which extends through the outer wrap of the outer duct wall to position and react the loads of the assembly. This configuration accommodates relative radial displacement between the motion to accommodate temperature and thermal expansion between the supporting structure and the duct while supporting axial loads. Accurate centering and axial position is also provided.

FIG. 5is a side cross-sectional view of a portion of an inter-turbine duct500, andFIG. 6is a cross-sectional view of the portion of the inter-turbine duct500ofFIG. 5taken along line6-6, in accordance with an embodiment. Here, the inter-turbine duct500includes a vane502, a first annular wall504, and a second annular wall506. The vane502may be similar in configuration to vane302ofFIGS. 3 and 4, except that a first end510of the vane502includes a post518and extends through a corresponding opening528formed between inner and outer surfaces530,532of a second plurality of layers524making up an outer portion of the first annular wall504. According to another embodiment, the post518may generally extend along the same axis as a main body508of the vane502. In another embodiment, the post518may have smaller and/or different dimensions and/or shape than the main body508. For example, a portion of the post518may be cylindrical or have another shape. In some embodiments, the post518may be further configured to correspond to a capture feature236(FIG. 2) or536(shown in phantom inFIGS. 5 and 6) extending from an engine case220(FIG. 2). For example, the post518may have a cylindrical shape that is received by a cylindrical space defined by the capture feature536.

In accordance with an embodiment, one or more of the vanes of the plurality of vanes210(FIG. 2) may be configured to be received by the capture feature236,536. For example, three such vanes may be included and each may be interposed between two vanes configured according to the description associated withFIGS. 3 and 4. In other embodiments, fewer or more vanes having capture features236,536may be included.

FIG. 7is a cross-sectional view of a portion of an inter-turbine duct700, in accordance with another embodiment. In this embodiment, the portion of inter-turbine duct700includes first and second annular walls704,706that are configured in a manner similar to that described above for first and second annular walls304,306and504,506. However, the inter-turbine duct700includes a vane702that is at least partially comprised of a ceramic composite material. For example, the vane702may be formed such that an internal cavity750extends from a first end710of the vane to a second end712of the vane702. The internal cavity750may have an opening752on the first end710of the vane702. A flange720extends from the first end710of the vane702to define at least a portion of the first end710of the vane. Similar to above-described embodiments, the flange720is retained between a first plurality of layers722and a second plurality of layers724making up the first annular wall704. The second end712of the vane702extends through the second annular wall706in a manner similar to that described above.

FIG. 8is a cross-sectional view of a portion of an inter-turbine duct800, in accordance with still another embodiment. Here, the inter-turbine duct800is configured to correspond to a capture feature that may be provided on an engine. In such case, the inter-turbine duct800includes a vane802and first and second annular walls804,806that are configured in a manner similar to that described above for vane702and first and second annular walls704,706, except that a retention insert852is included. In an embodiment, the retention insert852includes a post818and an insertion section842. The post818is configured to correspond to a capture feature236(FIG. 2) or536(shown in phantom inFIGS. 5 and 6) extending from an engine case220(FIG. 2) and extends through a second plurality of layers824of the first annular wall804. For example, the post818may have a cylindrical shape that is received by a cylindrical space defined by the capture feature536. The insertion section842is configured to be disposed at least partially within an internal cavity850of the vane802and is dimensioned such that its outer surface corresponds to an inner surface defining the internal cavity850. Although the insertion section842is shown as extending partially into the internal cavity850, the insertion section842may extend an entire length of the internal cavity850in other embodiments.

For applications in which metallic airfoils do not have adequate temperature capability, those described in this embodiment with ceramic composite airfoils such as SiC/SiC typically provide this capability. The layup of the outer portion of the vane, beyond the gas path would be deformed prior to final matrix infiltration and sintering to yield the retention feature. This process yields a natural taper to the ends of the retention feature which enhances the joint with the oxide/oxide wraps. This configuration would typically employ the interfaces with adjacent hardware described in the previously and could be used as hollow vanes to permit the passage of services or cooling air.

Although the first annular walls304,504,704,804, are depicted as forming an outer annular wall, and the second annular walls306,506,706,806are depicted as forming an inner annular wall, other embodiments may include the first annular wall304,504,704,804as the inner annular wall and the second annular wall306,506,706,806as the outer annular wall. As such, the capture features and joints may have reversed positions.

FIG. 9is a flow diagram of a method900of forming an inter-turbine duct, according to an embodiment. Inter-turbine duct materials are prepared, step902. In an embodiment, one or more vanes are obtained or formed (e.g., cast or fabricated from metal alloys and/or laid up using a plurality of plies of ceramic composite material) according to the configurations described above (e.g., vanes210ofFIG. 2, vane302ofFIGS. 3 and 4, vane502ofFIGS. 5 and 6, vane702ofFIG. 7, and vane802ofFIG. 8). Additionally, a fixture having an outer diameter surface and an inner diameter surface, each configured to correspond to a desired shape of first and second annular walls (e.g., walls304,306ofFIGS. 3 and 4, walls504,506ofFIGS. 5 and 6, walls704,706ofFIG. 7, and walls804,806ofFIG. 8) of the inter-turbine duct, may be obtained.

A portion of a first annular wall and a second annular wall are formed around the fixture, step904. In an embodiment, plies of ceramic composite material may be used to line the inner and outer diameter surfaces of the fixture. According to an embodiment, the number of plies lining the fixture surfaces may depend on a desired resultant thickness of the first and second annular walls. In another embodiment, the thickness of the annular walls may depend on whether the inner annular wall is employed to retain a flange of the vane or whether the outer annular wall is employed to retain the flange of the vane. For example, in either case, the annular wall designated to include the vane flange may be formed such that a first plurality of plies are laid around the fixture surface. For ease of understanding, the annular wall designated to include the vane flange will be referred to as the “first annular wall”. In other embodiments, the first annular wall may comprise an inner annular wall of the inter-turbine duct. In another embodiment, the first annular wall may comprise an outer annular wall of the inter-turbine duct.

Vanes are installed between the first and second annular walls, step906. In an embodiment, slots are formed through the first annular wall and openings are formed in the second annular wall. In accordance with an embodiment, the slots and openings are formed at radial locations around the first and second annular walls at which corresponding vanes may be disposed. Accordingly, the number of slots and the number of openings correspond to a total number of vanes to be included in the inter-turbine duct. According to an embodiment, the slots and openings may be machined into the first and/or the second annular walls.

Each vane is placed between a corresponding slot and opening such that a main body of the vane is disposed on one side of the first annular wall and a flange is disposed on a second side of the first annular wall.

Separator fixtures may be employed to prevent the vanes from moving relative to the annular walls. In an embodiment, a separator fixture may be disposed between adjacent vanes.

Next, a second portion of the first annular wall is formed to retain the vanes in position, step908. For example, a second plurality of layers is applied over the first annular wall and over at least a portion of the flanges of the vanes. In an embodiment, the flanges of the vanes are completely covered by the second plurality of layers. In another embodiment in which a post extends from the vanes, the second plurality of layers may be laid such that an opening is formed through which the post can extend. In still another embodiment in which the vane includes an internal cavity and a retention insert is to be included, the second plurality of layers may be configured to include corresponding openings for a post section of the retention insert to extend. In other embodiments, more or fewer layers may be included. In another embodiment, if included, the retention insert is inserted into the internal cavity of the vane.

The first and second annular walls and the vanes extending between the annular walls are sintered to form a unitary component, step910. In an embodiment, the fixture, and, if included, the retention inserts and separator fixtures, are also included in the sintering process. Sintering may be performed by subjecting the inter-turbine duct structures to firing temperatures that are above an anticipated operating temperature of the inter-turbine duct. In still another embodiment in which the vanes comprise a single crystal superalloy, the firing temperatures may be greater than the anticipated operating temperature of the inter-turbine duct and less than a solutioning temperature of the single crystal superalloy. After sintering, the fixtures may be removed.

The materials selected may depend on the desired operating conditions. As examples, for engines in which the inter-turbine temperatures are in the range of 2100° F. or less, such as 1650° F., alumina based oxide/oxide ceramic composites with the higher temperature fiber typically have adequate structural capability and cost advantages relative to higher temperature ceramic composite systems such as SiC/SiC. Firing temperatures of these systems are typically in the in the range of 2250 to 2300 F, well below the solution heat treat temperatures of the bulk of single crystal superalloys. This would enable encapsulation of single crystal superalloy elements into the CMC structure prior to firing without damaging the properties. The alumina based oxide/oxide ceramics also have another unique property for this application. Their thermal conductivity is on the order of a tenth of that of a nickel base superalloy. The thermal conductivity is similar to that of the thermal barrier coatings and insulations currently used to reduce the conductance of heat from the gas path of a gas turbine to the surrounding structures and cooling air.

The firing temperature sets the ceramic geometry of the ceramic. At the firing temperature, the metallic is experiencing thermal expansion greater than that at the maximum operating temperature. The ceramic has a thermal expansion lower than that of the metallic this result in an interface with a small clearance at operating conditions and a larger clearance at room temperature. With multiple vanes, the small clearance in individual joints permits movement to preclude excessive thermal strains, but provides the restraint to maintain system alignment. In addition the clearance also accommodates transient thermal differences without excessive strains.

The unitary component may undergo final processing with any suitable process to form the inter-turbine duct, step912. Examples include stabilization and aging heat treatments.

Accordingly, the concepts discussed above may combine the capability of a single crystal superalloy, oxide dispersion strengthened, nitride strengthen, or similar metallic airfoil in conjunction with oxide/oxide ceramic composite end walls to provide a configuration which will provide the required high temperature strength and reduced thermal conductivity to avoid cooling of the duct walls and minimize insulation requirements.

The concepts outlined above can also be applied to the lower cost family alumina based oxide/oxide ceramic composites with the lower temperature fiber. At the appropriate firing and use temperatures, a large range of lower cost materials may be used for the attachment and/or interface elements. If higher temperature applications are desired, the SiC/SiC ceramic composites may be used. Embodiments discussed above may also be applicable to rear bearing support gas path elements, tip shrouds, and the like for attachment/interface configurations that may otherwise provide challenges with respect to wear and relative motion from thermal expansion differences and the complexity of fabrication. Exemplary embodiments address this issue with advantages with cost, usable life, maintainability, and weight.

By forming at least a portion of the inter-turbine duct from composite materials and by retaining a portion of a vane within a portion of the duct, the inter-turbine duct may be employed in applications in which exposure to high engine operating temperatures may be required. Moreover, by including the composite material inter-turbine ducts in some engine configurations, insulation blankets may be omitted from such engine configurations. Additionally, the inter-turbine duct may be capable of being retrofitted into existing engines and may be simpler and less expensive to manufacture than conventional inter-turbine ducts.