GB2508886A

GB2508886A - Aligning replacement aerofoil vane with platform

Info

Publication number: GB2508886A
Application number: GB1222551.2A
Authority: GB
Inventors: David Tucker; Adrian Lewis Harding; Mark F Foulkes; Gary J Wright
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2012-12-14
Filing date: 2012-12-14
Publication date: 2014-06-18
Also published as: GB201222551D0

Abstract

A method of assembling an aerofoil to a platform comprises providing a datum feature 70, 80 protruding from the platform, and a complementary datum feature 76, 78, 82, 84 on the vane. The aerofoil can therefore be aligned to the platform before joining e.g. using a braze. The datum features may comprise portions of the leading and/or trailing edge of the vane. The vane may include a fillet that flares outwardly from the aerofoil to a surface of the platform. The method may be used to join a replacement aerofoil to an existing platform, and the original aerofoil may be removed by waterjet or electrodischarge machining. The blade may be attached to a second platform (not shown) and be aligned by a further datum feature 90. Instead of a projecting datum feature, a cut-out may be provided through the platform and a rail (figures 11 and 12).

Description

Vanes and Vane Replacement For Gas Turbines

Technical Field of Invention

[001] The invention relates to vanes and particularly a method of replacing vanes for a gas turbine engine.

Background of Invention

[002] With reference to Figure 1, a ducted fan gas turbine engine generally indicated at 10 comprises, in axial flow series, an air intake 1, a propulsive fan 2, an intermediate pressure compressor 3, a high pressure compressor 4, combustion equipment 5, a high pressure turbine 6, an intermediate pressure turbine 7, a low pressure turbine Sand an exhaust nozzle 9.

[003] Air entering the air intake 1 is accelerated by the fan 2 to produce two air flows, a first air flow into the intermediate pressure compressor 3 and a second air flow that passes over the outer surface of the engine casing 12 and which provides propulsive thrust. The intermediate pressure compressor 3 compresses the air flow directed into it before delivering the air to the high pressure compressor 4 where further compression takes place.

[004] Compressed air exhausted from the high pressure compressor 4 is directed into the combustion equipmentS, where it is mixed with fuel that is injected from a fuel injector 14 and the mixture combusted. The resultant hot combustion products expand through and thereby drive the high 6, intermediate 7 and low pressure 8 turbines before being exhausted through the nozzle 9 to provide additional propulsive thrust. The high, intermediate and low pressure turbines respectively drive the high and intermediate pressure compressors and the fan by suitable interconnecting shafts.

[005] Vanes are used within a gas turbine to adjust the direction of the flow of air before it is presented to a downstream component such as a rotating blade. Sometimes vanes are provided downstream of a final row of blades to reduce swirl in the gas flow. The vanes typically have an aerofoil portion that is mounted to a platform. The aerofoil is presented within the gas flow whilst the platform can provide a circumferential surface which bounds the annulus in which the aerofoil is located.

[006] Some vanes have a single platform from which the aerofoil is cantilevered, but others have platforms at either end of the aerofoil. Both the aerofoil and the platforms have to be accurately formed. Because the aerofoil is located in the gas flow it is the part of the vane that is most likely to be damaged in use; either by foreign object damage or by the high temperatures of the gas flow.

[007] If the vane is damaged by specific impact to the aerofoil it is desirable to be able to replace just the aerofoil whilst reusing the platform. This is not a trivial task due to the accuracy of the platform and aerofoil and the large effects on efficiency and / or life of the component an incorrectly formed vane will have [008] It is an object of the present invention to seek to provide an improved method for repairing vanes by assembling an aerofoil section on preformed platform sections.

Statements of Invention

[009] According to a first aspect of the invention there is provided a method of assembling an aerofoil assembly comprising the steps of providing a first vane platform and an aerofoil, wherein the vane platform has a datum feature protruding from the platform, the datum feature engaging a complimentary datum feature on the aerofoil, aligning the aerofoil to the vane platform using the datum feature and complimentary datum feature, and securing the aerofoil to the vane platform.

[0010] Advantageously, the datum feature helps to align the aerofoil to the platform in a desired orientation. The datum feature may have a face that advantageously helps to locate the aerofoil in a orthogonal position relative to the platform.

[0011] Preferably the aerofoil has a leading edge and the datum feature engages the aerofoil to provide a portion of the leading edge. The aerofoil may also have a trailing edge and the datum feature engages the aerofoil to provide a portion of the trailing edge. The aerofoil may have both trailing edge and leading edge datum features.

[0012] A braze may be used between the datum feature and the complementary datum feature to secure the aerofoil to the vane platform.

[0013] Preferably the aerofoil has an outwardly flaring fillet that flares from a flank of the aerofoil to a surface of the platform.

[0014] Preferably the aerofoil is a replacement aerofoil, the method further comprises the step of removing an original aerofoil from the first vane platform before joining the replacement aerofoil to the vane platform.

[0015] The step of removing an original aerofoil may include the further steps of dividing the original aerofoil, determining an edge profile of the aerofoil at the interface of the aerofoil and the platform and cutting around the edge profile.

[0016] The edge profile may be cut by waterjet or electodischarge machining, which may use a wire to cut the profile. The edge profile preferably includes a blade fillet flaring from pressure and! or suction flanks of the aerofoil.

[0017] According to a second aspect of the invention there is provided an aerofoil assembly comprising a first vane platform and an aerofoil, wherein the vane platform has a preformed datum feature protruding from the platform, the datum feature engaging a complimentary datum feature on a separate aerofoil.

[0018] Preferably the datum feature engages the aerofoil to provide a portion of a leading edge of the aerofoil. The aerofoil preferably has a trailing edge and the datum feature may engage the aerofoil to provide a portion of the trailing edge.

[0019] A braze may be used between the datum feature and the complementary datum feature to secure the separate aerofoil to the vane platform.

[0020] The aerofoil preferably has an outwardly flaring fillet that flares from a flank of the aerofoil to a surface of the platform.

[0021] The assembly may further comprise a second platform at an opposite end of the aerofoil to the first platform, [0022] The second platform may have a preformed datum feature protruding from the platform that engages a further complimentary datum feature on a separate aerofoil.

[0023] The aerofoil may be ceramic or a ceramic matrix composite and the platform may be metallic. Alternatively, the aerofoil may be metallic.

Description of Drawings

[0024] Figure 1 depicts a schematic of a gas turbine; [0025] Fig. 2 depicts a vane assembly with an aerofoil and platform; [0026] Fig. 3 depicts a vane platform with a projecting datum stub; [0027] Fig. 4 depicts a replacement aerofoil; [0028] Fig. S depicts a vane assembly with the vane platform of Figure 3 and the joined aerofoil of Figure 4; [0029] Fig. 6 depicts a vane platform with two projecting datum stub; [0030] Fig. 7 depicts a replacement aerofoil prepared for joining to the platform of Figure 6; [0031] Fig. 8 depicts a vane assembly and a vane platform; [0032] Figure 9 shows a cross-section of the platform showing the positioning of the aerofoil; [0033] Fig. 10 shows a schematic of the vane assembly having a radially inner platform and a radially outer platform joined to the aerofoil of Fig. 7 [0034] Figure 11 depicts an alternative arrangement [0035] Figure 12 depicts an alternative aerofoil arrangement

Detailed Description of Invention

[0036] Figure 2 depicts a schematic of a typical vane 50 having a platform portion 54 and an aerofoil portion 52. The platform has one or more rails 56 that are used to mount the vane to the engine. In the embodiment of Figure 2 the vane has a single platform and a cantilevered aerofoil. The platform is an inner platform section which has a platform surface 58 that forms part of the radially inner surface of the annulus having the air which flows past the aerofoil 52.

[0037] The side surfaces of the platform section (60a, 60b) are adapted to abut against the sides of adjacent platform sections such that platform surfaces 58 of each platform together provide a circumferentially extending surface of the gas flow annulus.

[0038] In original manufacture the aerofoils and platforms are integrally formed as a fabricated assembly in a single casting. The aerofoil and platform are carefully machined with respect to each other such that the aerofoil surface is aligned at a predetermined position relative to an edge of the platform. Advantageously, the known profile and position of the aerofoil relative to the platform ensures the desired alignment and efficiency of the vane array.

[0039] Damage 62 to the aerofoil can occur during use of the vane within the gas turbine engine. The damage may occur when a foreign object such as dust, grit or other particle carried by the airflow through the engine impacts the aerofoil, or in rare cases during manufacture of the original equipment. Other forms of damage may relate to overheating, where the vane is used in a turbine section, and where internal passages used to supply cooling fluid to the aerofoil get blocked or otherwise do not supply the required cooling flow.

[0040] It will be appreciated that this damage is typically isolated to one or at most a few vanes within a vane set. The damaged vane is inspected either on-wing or following removal of the engine from an aircraft. The inspection is used to determine whether it is economical to replace just the aerofoil rather than the whole vane.

[0041] If, following inspection, it is determined to be viable to replace just the aerofoil section the aerofoil section is separated from the platform to leave a stub protruding from platform section. The stub preferably forms part of the leading edge of the aerofoil for reasons to be described later but can also provide part of the trailing edge and! or suction or pressure flanks.

[0042] Figure 3 depicts a platform 54 with a leading edge stub 70 following aerofoil removal. The aerofoil is removed by firstly machining off the rest of the blade above the stub and then machining around the stub to leave the stub whilst removing all the remaining aerofoil portion flush to the platform surface 58 and opening an aperture 72 through the vane platform. The machining is performed using any appropriate method and apparatus that gives the desired accuracy and integrity. Such methods include, but is not limited to, waterjet machining, chemical machining, electro-discharge machining, etc. [0043] The stub has a sufficient length along the suction and / or pressure flanks to mitigate damage to the rails 56 on the underside of the platform. The rails 56 provides structural strength to the platform and in some platform architectures, where the periphery of the aerofoil overlies the platform, complete removal of the aerofoil can result in unacceptable weakening of the platform.

[0044] Advantageously, the stub 70 also provides a datum feature, not just for the pressure and suction flanks but also for the radial height of the aerofoil on the platform 54. Figure 4 depicts a replacement aerofoil which matches the profile of the original aerofoil but which has a cut out which is complementary to the shape of the stub 70. One surface of the cut-out 78 provides a radial datum for the aerofoil relative to the platform.

[0045] The aerofoil is assembled to the platform as shown in Figure 5 such that the stub of the original aerofoil provides a portion of the replacement aerofoil. A braze material is applied between the replacement aerofoil 74 and the stub 70 and between the replacement aerofoil 74 and the platform 54 which secures the parts together. The assembly may be heated to join the vane and platform by diffusion bonding.

[0046] A further advantage of the stub is that it provides support to the aerofoil to resist the sideways torque generated by the airflow over the aerofoil surface. In the absence of the stubs the torque can cause the replacement aerofoil to fail by shearing from the vane platform. The radial join at around 9odegrees to the circumferential join along the platform surface 58 resists the shearing movement of the vane and more so when a stub 80 provided at the trailing edge of the aerofoil in addition to stub 70 at the leading edge as shown in Figure 6.

[0047] The datum stub 80 also has a radial datum face 82a which serves to locate the aerofoil. The leading edge stub and the trailing edge stub may be the same or of different heights. Where the aerofoil has embedded cooling passages the use of datum stubs can reduce the chance of these passages blocking when the braze material is applied to secure the respective parts.

[0048] Where the vane comprises both a radially inner and a radially outer platform there is additional benefit in the transfer of loads through the vane to provide a datum stub at the trailing edge that has a complementary cut-out 90. It will be appreciated that there may also be a leading edge stub on the radially outer platform [0049] The invention provides additional advantage in that it is possible to improve the functionality of current vanes by replacing the aerofoil section with an aerofoil section of a different material which offers better corrosion, high temperature or damage resistance.

One such material is a ceramic or ceramic matrix composite. An aerofoil moulded, cast or machined from this material is joined to the inner and! or outer platform by brazing, mechanical fixtures, pins, slots and dovetails etc, or by welding or using composite joining pastes. The aerofoil is kept in compression between the platforms [0050] For both the metallic replacement aerofoil and the ceramic replacement aerofoil it is desirable for the aerofoil to have a fillet that flares from both the suction and pressure surfaces. Figure 8 depicts the flare of a cross-section through a replacement aerofoil that flares from the suction 82 and pressure 80 surface of an aerofoil 52 to the pressure surface flare edge 84 and suction surface flare edge 86. The fillet edge profiles 84, S2from the original equipment part can be projected onto a plane aligned to an appropriate machine datum as shown by the dotted line in Figure 9. The fillet profile helps to define the cut line required on the platform surface. The projected profile can then be offset or adjusted to ensure that the cut line clears any existing fillet radius on the existing part. The profile is projected onto the platform to define the cut-out to be used.

[0051] Machining of the cut-out is achieved by directing a waterjet towards the platform surface and traversing it along the cut-out path. As an alternative to the use of a waterjet an electrodischarge machine may be used which uses an electrical current between an electrode and the platform to generate a spark that erodes the material of the platform.

[0052] The replacement aerofoil is then joined to the platform with a portion of the replacement aerofoil sitting within the cut-out. The braze material added and the joining process completed to join the aerofoil to the platform.

[0053] Fig. 10 shows a schematic of the vane assembly having a radially inner platform and a radially outer platform joined to the aerofoil of Fig. 7.

[0054] As an alternative arrangement the datum feature may protrude from the platform in a direction that is opposite to that of the aerofoil. In this arrangement the rails themselves form the datum feature, the rails being cut to provide a sloped datum feature against which a complementary datum feature protruding from the aerofoil interfaces. Figure 11 is a perspective view of this arrangement where the datum feature on the aerofoil protrudes past both an inner platform 58 to engage the rails 56 and past an outer platform to engage the outer rails. As seen in Figure 12, which is an idealised aerofoil datum projections 70, 80, 70a, 80a are provided at both the leading and trailing edges and at both the radially inner and the radially outer ends of the aerofoil portion 52.The sloped sides of the datum features assist with the radial alignment of the aerofoil as well as its circumferential position on the platform. One particular advantage of this arrangement is the alignment join is out of the airflow passing over the aerofoil.

S

[0055] The replacement aerofoil is preferably a compressor guide vane but the invention may be used to provide other vanes within a gas turbine engine including, but not limited to, variable stator vanes, turbine vanes, and nozzle guide vanes.

[0056] It will also be appreciated that the platform may also be part of a casting from which multiple vanes project. Typically these castings have two or three vanes formed as a single unit. Each vane may be replaced simultaneously with the other vanes or the vanes of the unit may be replaced independently.

Claims

Claims: 1. A method of assembling an aerofoil comprising the steps of providing a first vane platform and an aerofoil portion, wherein the vane platform has a datum feature protruding from the platform, the datum feature engaging a complimentary datum feature on the aerofoil portion, aligning the aerofoil to the vane platform using the datum feature and complimentary datum feature, and securing the aerofoil to the vane platform.
2. A method according to claim 1, wherein the aerofoil has a leading edge and the datum feature engages the aerofoil to provide a portion of the leading edge.
3. A method according to claim 1 or claim 2, wherein the aerofoil has a trailing edge and the datum feature engages the aerofoil to provide a portion of the trailing edge.
4. A method according to claim 1, wherein the platform has a rail for joining the platform to a gas turbine engine, wherein the datum feature is provided by a cut-out from the rail.
5. A method according to any preceding claim, wherein a braze is used between the datum feature and the complementary datum feature to secure the aerofoil to the vane platform.
6. A method according to any preceding claim, wherein the aerofoil has an outwardly flaring fillet that flares from a flank of the aerofoil to a surface of the platform.
7. A method according to any preceding claim, wherein the aerofoil is a replacement aerofoil, the method further comprises the step of removing an original aerofoil from the first vane platform before joining the replacement aerofoil to the vane platform.
8. A method according to claim 7, wherein the step of removing an original aerofoil includes the further steps of dividing the original aerofoil, determining an edge profile of the aerofoil at the interface of the aerofoil and the platform and cutting around the edge profile.
9. A method according to claim 8, wherein the edge profile is cut by waterjet or electodischarge machining.
10. A method according to claim 8 wherein the edge profile includes a blade fillet flaring from pressure and! or suction flanks of the aerofoil.
11. An aerofoil assembly, comprising a first vane platform and an aerofoil, wherein the vane platform has a preformed datum feature protruding from the platform, the datum feature engaging a complimentary datum feature on a separate aerofoil.
12. An aerofoil assembly according to claim 11, wherein the datum feature engages the aerofoil to provide a portion of a leading edge of the aerofoil.
13. An aerofoil assembly according to claim 11 or claim 12, wherein the aerofoil has a trailing edge and the datum feature engages the aerofoil to provide a portion of the trailing edge.
14. An aerofoil assembly according to any of claim 11 to claim 13, wherein a braze is used between the datum feature and the complementary datum feature to secure the separate aerofoil to the vane platform.
An aerofoil assembly according to any of claim 11 to claim 14, wherein the aerofoil has an outwardly flaring fillet that flares from a flank of the aerofoil to a surface of the platform.
16. An aerofoil assembly according to any of claim 11 to claim 14, wherein the assembly further comprises a second platform at an opposite end of the aerofoil to the first platform,
17. An aerofoil assembly according to claim 16, wherein the second platform has a preformed datum feature protruding from the platform that engages a further complimentary datum feature on a separate aerofoil.18 An aerofoil assembly according to any of claim 11 to claim 17, wherein the aerofoil is ceramic or a ceramic matrix composite and the platform is metallic.