CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to and the benefit of U.S. Provisional Application No. 62/523,502, filed June 22, 2017, the entirety of which is incorporated by reference herein.

FIELD

[0002] Disclosed embodiments are generally related to turbine engines and in particular to components for securing blades within the turbine engine.

BACKGROUND

[0003] Gas turbines comprise a casing or cylinder for housing a compressor section, a combustion section, and a turbine section. A supply of air is compressed in the compressor section and directed into the combustion section. The compressed air enters the combustion inlet and is mixed with fuel. The air/fuel mixture is then combusted to produce high temperature and high pressure (working) gas. This working gas then travels through the transition and into the turbine section of the turbine.

[0004] The turbine section typically comprises rows of vanes which direct the working gas to the airfoil portions of the turbine blades. The working gas travels through the turbine section, causing the turbine blades to rotate, thereby turning a rotor attached thereto. The rotor is also attached to the compressor section, thereby turning the compressor and also operatively connected to an electrical generator for producing electricity.

[0005] High efficiency of a combustion turbine is improved by heating the gas flowing through the combustion section to as high a temperature as is practical. However, the hot gas may degrade various metal turbine components, such as the combustor, transition ducts, vanes, ring segments, and turbine blades as it flows through the turbine. [0006] High temperature resistant ceramic matrix composite (CMC) materials have been developed and increasingly utilized in gas turbine engines. Typically, CMC materials include a ceramic or a ceramic matrix material, either of which hosts a plurality of reinforcing fibers. The fibers may have a predetermined orientation(s) to provide the CMC materials with additional mechanical strength. Generally, fiber reinforced ceramic matrix composites are manufactured by the infiltration of a matrix slurry (e.g., alumina, mullite, silicon-containing polymers, molten silicon, or the like) into a fiber preform, but can be manufactured in a variety of other ways. While these CMC materials may offer a higher temperature resistance than superalloys, fiber grains of the CMC may coarsen and result in reduced strength over time. In addition, matrix grain coarsening can result in CMC embrittlement leading to a propensity for cracking and crack propagation as firing temperatures increase.

[0007] The blades used in gas turbine engines can provide improved performance by being shaped in certain ways. Having a curved CMC blade can improve performance. However attachment of curved CMC blades can be problematic and sometimes requires that concessions be made that can impact the structural integrity of the CMC blade. Therefore, improving the manner in which a curved CMC blade is attached can provide overall benefits.

SUMMARY

[0008] Briefly described, aspects of the present disclosure relate to providing an apparatus for attaching gas turbine engine blades.

[0009] An aspect of the present disclosure may be a root attachment for securing a gas turbine engine blade. The root attachment may comprise a plurality of clevis components, wherein each of the clevis components comprises a plurality of holes and a plurality of clevis pins for insertion into the plurality of holes, and wherein the assembled clevis components form arced slots for the receipt of the gas turbine engine blade. When the gas turbine engine blade is placed in the arced slots, the plurality of the clevis pins are inserted through the plurality of holes and the gas turbine engine blade, thereby securing the gas turbine engine blade to the root attachment.

[0010] Another aspect of the present disclosure may be an apparatus for attachment of a plurality of gas turbine engine blades. The apparatus may comprise a plurality of root attachments, wherein each root attachment comprises a plurality of clevis components wherein each of the clevis components comprises a plurality of holes and a plurality of clevis pins for insertion into the plurality of holes, wherein the assembled clevis components form arced slots for the receipt of the gas turbine engine blade. When the gas turbine engine blade is placed in the arced slots, the plurality of the clevis pins are inserted through the plurality of holes and the gas turbine engine blade thereby securing the gas turbine engine blade to the root attachment. The apparatus may comprise a plurality of modular platforms, wherein at least one of the plurality of modular platforms is inserted between two of the plurality of root attachments.

BRIEF DESCRIPTION OF THE DRAWINGS [0011] Fig. 1 shows a view of a root attachment.

[0012] Fig. 2 is another view of the root attachment with a curved CMC blade inserted.

[0013] Fig. 3 is a view illustrating the location of clevis pins through the curved CMC blade.

[0014] Fig. 4 is another view illustrating the location of the clevis pins through the curved CMC blade.

[0015] Fig. 5 is a view of the clevis pins through the plurality of clevis components.

[0016] Fig. 6 is a view of the modular platform used to secure a plurality of curved CMC blades.

[0017] Fig. 7 is view of the modular platforms securing curved CMC blades.

[0018] Fig. 8 is a view of a circumferential holder for the clevis components and modular platforms.

[0019] Fig. 9 is another view of the circumferential holder.

[0020] Fig. 10 shows the circumferential holder with curved blades secured to root attachments.

DETAILED DESCRIPTION [0021] To facilitate an understanding of embodiments, principles, and features of the present disclosure, they are disclosed hereinafter with reference to implementation in illustrative embodiments. Embodiments of the present disclosure, however, are not limited to use in the described systems or methods and may be utilized in other systems and methods as will be understood by those skilled in the art.

[0022] The components described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components that would perform the same or a similar function as the components described herein are intended to be embraced within the scope of embodiments of the present disclosure.

[0023] Oxide/Oxide ceramic matrix composites may be used in lieu of nickel or cobalt based superalloys as selected components within the hot gas path of turbines engines, e.g. rotating airfoils. A key strength criterion for a turbine blade is the specific strength (strength over density) of the material used for the construction of the blade. Nickel based superalloys have relatively high strength and high density (for example, 336 Mpa and about 8.1. g/cm ³ , for example) while Ox/Ox CMCs have relatively low strength and low density (for example, 81 MPa and 2.7 g/cm3). Based on the exemplary numbers, specific strength of nickel superalloys is roughly 38% higher than that of Ox/Ox CMCs. Therefore, in order to utilize an Ox/Ox CMC blade with a similar specific strength as a nickel based blade, the blade would need to have a cross-section capable of carrying its own centrifugal pull load.

[0024] Additionally, there needs to be an apparatus for attaching the CMC blade to the gas turbine engine in such a way that it can carry the high pull loads of the entire airfoil. While CMCs have very high strength in the direction of the ceramic fibers, the interlaminar tensile strength between CMC plies is weak (2-4 MPa) due to the load being carried by the matrix only. Therefore, the transition between the airfoil of the CMC blade and the root attachment should minimize the interlaminar tensile stresses.

[0025] Current blades are typically designed to handle pull loads by using tapered wall thickness along the radial length of the airfoil. Using a tapered wall thickness helps with the castability of Ni -based superalloy blades. When using a CMC blade use of tapered wall thicknesses is preferred.

[0026] Interlaminar tensile stresses in the transition region between the root of the CMC blade and airfoil of the CMC blade can be minimized if the curvature of the transition shape is minimized. In order to reduce the transition curvature, the CMC root can be either straight with an axial skew (angled relative to the engine centreline) or preferably curved to mimic the airfoil shape.

[0027] Referencing the figures, wherein embodiments of the present invention are shown, Fig. 1 shows a view of the root attachment 10 for a blade 30 having a curved root 32 and airfoil 34 (see FIG. 8). The root attachment 10 is comprised of a plurality of clevis components 14. Clevis pins 16 are arranged through holes 9 in each of the clevis components 14.

[0028] The clevis components 14 are advantageously made of metal, but could be made of other suitable materials. Each clevis component 14 is cast to be able to form the overall root attachment 10 when assembled. The clevis component has a base 7, a stem 11, and a head 13.

[0029] The stem 11 extends from the base 7 in a manner to properly orient the head 13 for each clevis component 14. The base 7 is similarly sized and shaped for each of the plurality of clevis components 14. When the clevis components 14 are assembled in order to form the root attachment 10, the bases 7 are arranged into aligned rows. In the embodiment shown in Fig. 1, there are three rows formed by the bases 7; there is the first row 21, the second row 22, and the third row 23. Each of the rows is formed with three bases 7 and thus three clevis components 14. Each of the formed rows is parallel with each other. However it should be understood that more (or less) than three rows could be formed, as well as using more than three bases 7 per a row. The resultant configuration is advantageously determined by the geometry (e.g. shape and size) of the curved blade 30 that is being attached.

[0030] Extending from each of the bases 7 are stems 11. The stems 11 vary in shape. The shape of the stems 11 are determined by the way in which the head 13 of the clevis component 14 is going to be facing. Some of the stems 11 are similarly shaped and oriented in the same manner as other of the stems 11 while some of the stems 11 are twisted in some manner in order to orient the heads 13 in the proper direction to form the arced slots that form the receiving areas for the root 32 of the blade 30.

[0031] The ultimate shape of the stems 11 is based upon the position of the head 13 within the one of the first row 21, the second row 22 and the third row 23. Also, the position of the head 13 within the first row 21, the second row 22, and the third row 23 determines the shape and orientation of the stem 11 plus head 13. For example, in one embodiment, the stems 11 in the first row 21 are all oriented in substantially the same direction. The stems 11 in the second row 22 vary in orientation with some of the stems 11 twisting in order to orient the head 13 in a different manner for the respective arced row in which the head 13 is located. Stems 11 in the third row 23 also vary in orientation based on the need to retain the root 32 of the blade 30 with some of the stems 11 twisting in one direction versus another direction.

[0032] Attached to each of the stems 11 are the heads 13 of the clevis components 14. The heads 13 are rectangular shaped structures that have holes 9 formed therein. The holes 9 pass through the heads 13 and receive the clevis pins 16. The holes 9 formed in the heads 13 vary in size and distribution. The holes 9 are varied in size in order to accommodate the proper alignment of the blade 30 and secure the blade 30 to accommodate the pressures impacting it. In Figs. 1 and 2, the distribution and size of the holes 9 are such that each head 13 has four rows of holes 9. The distribution and size of the holes 9 shown in Figs. 1 and 2 are the same for each of the heads 13. The largest holes 9 are located proximate to the stems 11. The size of the holes 9 decreases when approaching the portion of the head 13 furthest away from the stem 11. Each row of holes 9 is designed to carry a successively lower load. For example, moving from lower to upper, load split is 50 %, 27 %, 16 % and 7%. The CMC material may carry 93 % of the pull load from the bottom three rows of holes. This puts the CMC material near its strength limit and only has enough remaining strength to carry a small amount (7%) of additional load.

[0033] Additionally, the number of holes 9 located in each of the rows of holes 9 varies. In the heads 13 shown, there are three holes 9 in the row closest to the stem 11, two in the following row, then three, and then two. The number of holes 9 in each of the rows alternates. This results in ten holes 9 per head 13. It should be understood that the size, number and distribution of holes 9 in each of the heads 13 may vary depending on the structural characteristics of the blade 30 that is being implemented. When defining the location of the holes 9 and the clevis pins 16, net section stress should be about equal for each of the rows of holes 9 on the heads 13. Each successive row should carry its own force, plus the force of the clevis pins 16 below it. Each successive row of holes 9 should carry less of the load as a result. The embodiment of the root attachment 10 shown in Figs. 1 and 2 are for a CMC curved blade 30.

[0034] The clevis components 14 are subsequently arranged to form three arced rows 15, 17, 19 which define arced slots 115, 117 for attachment of the root 32. As shown in Fig. 5, the arrangement of clevis components 14 forms an inner arced row 15, a middle arced row 17, and an outer arced row 19. Each of the arced rows is curved in order to accommodate the shape of the blade 30. In this way, the assembled clevis components 14 form arced rows 15, 17, 19 which define arced slots 1 15, 117 for the receipt of the gas turbine engine blade 30 within the slots 115, 117. When the gas turbine engine blade is placed in the arced slots, the plurality of the clevis pins are inserted through the plurality of holes and the gas turbine engine blade, thereby securing the gas turbine engine blade.

[0035] In an embodiment, the inner arced row 15 is formed with three heads 13 that are roughly the same size and when assembled form an arc that complements the shape and size of the root 32 of the blade 30. The inner arced row 15 is formed by clevis components 14 that are also located in the first row 21 and the second row 22. There are no clevis components 14 from the third row 23 that are located in the inner arced row 15. This is due to the curvature of the inner arced row 15 that is to be achieved. The curvature needed by the inner arced row 15 is based upon the overall curvature of the blade 30 and its root 32.

[0036] The middle arced row 17 is formed from clevis components 14 that have heads 13 that are larger than the heads 13 of the clevis components 14 located in the inner arced row 15. The outer arced row 19 is formed from clevis components 14 that have heads 13 that are larger than the heads 13 of the clevis components 14 located in the middle arced row 17. Both the middle arced row 17 and the outer arced row 19 have clevis components 14 that are located in the first row 21. It should be understood that the particular arrangement of clevis components 14 described herein may vary depending on the size and shape of the blade 30 that is being attached to the root attachment 10.

[0037] The curved blade 30 is placed on the root attachment 10 so that the root 32 surrounds the middle arced row 17 and is located within the arced slots (115, 117) defined by the arced rows (15, 17, 19). Once the curved blade 30 is placed on the root attachment 10, clevis pins 16 are inserted through the holes 9, thereby securing the blade 30 to the root attachment 10.

[0038] Figs. 3 and 4 illustrate the location of the clevis pins 16 when inserted in the root 32 of the curved blade 30 through holes 39. The Figs. 3 and 4 show the distribution and arrangement of the clevis pins 16 for this particular arrangement. Larger clevis pins 16 are inserted through the base of the root 32 while smaller clevis pins 16 are located further away from the base of the root32. Larger clevis pins 16 carry more load, thus achieving the target load goals. The bottom row of clevis pins 16 is governed by the net section stress and the shear tearout. The shear tearout planes (i.e. the area that would be torn out should failure occur) for the different rows of clevis pins 16 should not align. The CMC thickness can be increased to gain increased load carrying capability.

[0039] Fig. 5 shows the clevis pins 16 inserted through the clevis components 14. Fig. 5 also shows the curvature of the inner arced row 15, the middle arced row 17, and the outer arced row 19. The curvatures of the arced rows are based upon the curve of the root 32. The clevis components 14 enable the existence of curved blades 30 that can be fully curved through the root 32 and the airfoil 34 and that do not have to make concessions to be attached. The proposed attachment of clevis pins 16 fans out such that the holes 39 on the blade 30 are evenly spaced on each of the pressure and suction sides of the blade 30. This causes the clevis pins 16 to potentially be at an angle relative to the surface normal of the blade 30. Over constraint of the assembly is minimized due to the non-lineraities of the CMC material and the segmentation of the clevis pin 16 array into three locations segments in the chordal direction.

[0040] Figs. 6 and 7 show views of the modular platform 40 that is used in securing the curved blades 30 to a circumferential holder 50 in the turbine engine. The modular platform 40 is placed between root attachments 10 in the turbine engine. The modular platform 40 is formed so that it is curved to accommodate the inner arced row 15 and the outer arced row 19. This is accomplished by having a platform surface 41 having an inwardly curved platform surface 42 and an outwardly curved platform surface 43. [0041] The inwardly curved platform surface 42 is curved so that it fits against the outer arced row 19. The outwardly curved platform surface 43 is curved so that it fits against the inner arced row 15. The modular platforms 40 are located between every root attachment 10 and help secure and space the curved blades 30 from one another. The bottom of the modular platform 40 has leg sockets 45 to receive legs 44, which are secured with a clevis pin 16. The legs 44 cooperate with the bases 7 of the root attachments 10 in order to form the circumferentially aligned arrangement of curved blades 30, modular platforms 40, and root attachments 10. This arrangement is shown in Fig. 8.

[0042] The modular platform 40 concept includes a clevis pin 16 at the attachment point between the leg 44 and the platform surface 41. Due to the circumferential holder 50 groove concept, the attachment points on the modular platform 40 can be staggered circumferentially such that any overhang is minimized. The modular platform 40 can be shaped such that it is possible to insert the modular platform 40 into a loading slot 52 in the circumferential holder 50, discussed below, and slide it circumferentially during assembly without interfering with the adjacent blade airfoil 34.

[0043] Figs. 8-10 show the circumferential holder 50 used in the connection of the curved blades 30 to the turbine engine. The circumferential holder 50 extends circumferentially forming a ring. The blades 30 are attached via the root attachments 10 around the circumferential holder 50. The circumferential holder 50 has a plurality of loading slots 52 that accommodate the bases 7 of the clevis components 14 and the legs 44 of the modular platforms 40. Cutaway 54 accommodates the placement of the modular platforms 40 around the circumferential holder 50. There may be multiple cutaways 54 located around the circumferential holder 50.

[0044] The pull load of the CMC blade 30 (including all metallic attachment hardware and modular platforms) is roughly 80% that of an equivalent metal blade. This pull load may be less depending on the arrangement. The proposed circumferential holder 50 has only loading slots 52 containing clevis components 14 supporting the CMC blade 30. The 1 ^st , 2 ^nd and 4 ^th loading slots 52 each carry a clevis component 14 to support the modular platform 40. The loading slots 52 are formed as circumferential grooves. Machining for the formation of the loading slots 52 can be less expensive than an axial groove attachment that may be used for a metal blade.

[0045] As a result of the root attachment 10 and the modular platforms 40 the interlaminar tensile stresses in the transition region between the root 32 and airfoil 34 of a CMC blade 30 will be minimized because it is curved to mimic the shape of the airfoil 34.

[0046] Furthermore, while blade platforms are typically integral to the blade casting itself. The modular platform 40 disclosed herein has benefits over the unitary casting. The curved root 32 of the CMC curved blade 30 can be made thicker while maintaining a smooth (low curvature) transition between the blade root 32 and airfoil 34. This improves strength and minimizes structural fatigue and potential damage.

[0047] Interlaminar stresses between CMC plies will be reduced due to the low curvature transition between the root 32 and the airfoil 34. Additionally, stress in the attachment region of the clevis pins 16 is reduced due to the larger bearing area. A higher wall taper can be achieved to carry the large pull load of the CMC blade 30. The use of metallic clevis components 14 accommodates thermal expansion differences between the clevis components 14 and the CMC blade 30. Three clevis components 14 may be located on each pressure side to accommodate the pull.

[0048] The root attachment 10 further forms a wide base to support airfoil bending loads. Excellent distribution of pull loads to all clevis pins 16 is due to material nonlinearity and pin flexibility. The root attachment 10 is also located in relatively colder environment away from the primary hot gas path to ensure safe operating temperatures.

[0049] While embodiments of the present disclosure have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents, as set forth in the following claims.