Patent Publication Number: US-2017356298-A1

Title: Stator vane

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This specification is based upon and claims the benefit of priority from UK Patent Application Number 1610004.2 filed on 8 Jun. 2016, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates to a stator vane for a gas turbine engine, a stator vane stage, and a gas turbine engine. 
     2. Description of the Related Art 
     An axial compressor of a gas turbine engine comprises one or more rotor assemblies which carry rotor blades of aerofoil cross-section. The rotor is located by bearings, which are supported by a casing structure. The casing includes stator vanes, also of aerofoil cross-section. Each rotor and its downstream stator row form a stage. 
     Such vanes can be secured into the casing using a dovetail or T-slot fixing.  FIG. 1  shows schematically the fixing parts of two adjacent vanes  1  of a stator vane row. Each vane has an aerofoil  2  and a fixing portion  3  from which the body extends into the working gas passage of the engine. Front  4  and rear  5  tangs of the platform are for use in a T-slot fixing slot  8  (see  FIG. 2 ) within the casing. 
     In operation, aerodynamic loading on the aerofoil body induces a torque T (as illustrated in  FIG. 2 ) that tends to rotate the vane around the radial direction of the engine. Under this rotation, neighbouring lateral edges  6  (which may extend substantially axially in the engine) of adjacent platforms slide along each other until interference at reaction points  7  of the front  4  and rear  5  tangs with the casing slot  8  limits the rotation by reacting the torque, as shown schematically in  FIG. 2( a ) . 
     The casing slot  8  may be provided with a so-called anti-fret liner, for example around the face where the contact points  7  occur. However, excessive rotation of the metallic vanes  1  before contact  7  with such an anti-fret liner occurs may result in high contact loads, which may lead to excessive wear of the ant-fret liner and/or break-up of the anti-fret liner, which may cause material to be released. Such material release may cause damage to downstream parts of the engine, as well as to the anti-fret liner itself. 
     To limit the rotation, and thus try to reduce the damage to the casing and/or anti-fret liner, adjacent metallic vanes may be permanently joined (e.g. welded or brazed together) by a secondary manufacturing process at neighbouring lateral edges. As shown schematically in  FIG. 2( b ) , for a given vane-to-casing axial clearance A, the greater circumferential width W 2  of joined vanes substantially reduces the amount of rotation before contact  7  with the casing compared with that of the circumferential width W 1  of the individual vanes. 
     However such secondary manufacturing increases the cost of the vanes, not just because of the secondary process itself, but also because of the need to inspect the joint (e.g. using X-rays and/or penetrant dye for example) post-manufacture. In addition, secondary manufacturing processes such as welding and brazing can induce distortions of the platforms  3 , producing a mismatch between platforms that introduces local disturbances in the airflow and corresponding small performance losses within the stage. 
     A further disadvantage of permanently joining adjacent vanes is that it reduces the amount of frictional damping between vanes in a given vane row, thereby increasing vane amplitude/deflection for vibration modes that may be excited via upstream/downstream forcing. 
     It would be desirable to produce an improved stator vane, for example one which addresses at least one of the problems described above and/or facilitates a range of manufacturing methods, such as metal injection moulding (MIM). 
     SUMMARY 
     According to an aspect, there is provided an annular stator vane row as provided in claim  1 . 
     Such an arrangement may result in reduced angular rotation of the vanes before contact is made between the vane (for example the fixing portion thereof) and the casing/retaining slot (for example with an ant-fret liner), but without the disadvantages associated with joining vanes together to form multiple vane assemblies (such as that shown by way of example in  FIG. 2( b ) ). This may alleviate and/or substantially eliminate at least one of the problems with conventional single metallic vanes and multiple metallic vane assemblies discussed above and elsewhere herein. The increased circumferential extent of the stator vane resulting from the combination of the platform surface and the joggle surface may be responsible for the decreased angular rotation before contact with the casing/retaining slot, compared with a conventional stator vane. 
     The metallic vane may be said to be entirely metallic, for example it may comprise only metal. The metallic vane may be homogeneous, for example it may comprise the same, metallic, material throughout. 
     The radial direction, axial direction and circumferential direction as used herein have their conventional meaning in the field of gas turbine engine components, that is relative to the gas turbine engine itself. The radial direction may be substantially aligned with a thickness direction of the fixing portion and/or with the direction in which the aerofoil extends away from the platform surface. The circumferential direction may be substantially aligned with a lateral and/or width direction of the fixing portion. The axial direction may be substantially aligned with a length direction of the fixing portion. 
     Where the term “substantially perpendicular” to the radial surface is used (for example in relation to the platform surface and the joggle surface), this may mean that the surface is at least a segment of a cylindrical surface or at least a segment of a frusto-conical surface, for example. Thus, “substantially perpendicular to the radial surface” includes, for example, perpendicular to a direction that has a major component in a radial direction and a minor component in an axial direction. 
     The joggle surface may be said to be circumferentially offset from the platform surface. The joggle surface may be circumferentially and/or radially non-overlapping with the platform surface. The joggle surface and the platform surface may have surface normals that point in substantially the same direction. Surface normal of the joggle surface and/or the platform surface may be substantially aligned with a direction that points away from the platform surface, for example with the direction in which the aerofoil extends away from the platform surface. The joggle surface may be a segment of a cylindrical or frusto-conical surface and the platform surface may be a segment of a cylindrical or frusto-conical surface that is offset from the cylindrical or frusto-conical surface of the joggle surface. The radial offset of the joggle surface from the platform surface may be in substantially the opposite direction to the direction in which the aerofoil extends away from the platform surface. 
     The axial extent of the joggle surface may be substantially the same as the axial extent of the platform surface. Alternatively, the axial extent of the joggle surface may be less than the axial extent of the platform surface. 
     The recess may be formed in the underside of the fixing portion, the underside being on the radially opposite side to the platform surface. 
     The recess surface may have a surface normal (or surface normals) that points in the opposite direction to that of the joggle surface. 
     The joggle surface may comprise a circumferentially extending locking tooth. Such a locking tooth may extend away from the joggle surface in a circumferential direction. Such a locking tooth may extend over only a part of the axial extent of the joggle surface. 
     The platform surface may be a gas-washed surface in use. In other words, the platform surface may form a part of the boundary of the working fluid as it passes through the engine in use. 
     The term annular as used in the context of an annular stator vane row includes frusto-conical. 
     Each stator vane in such a stator vane row is independent of the other stator vanes. Independent may mean that each stator vane is not integral with and/or attached to and/or permanently joined to any other stator vane. Independent may mean that each stator vane is free to move in at least one degree of freedom relative to the other stator vanes. For example, each stator vane may be able to independently rotate about a substantially radial direction relative to the other stator vanes. 
     Each stator vane in such a stator vane row may be retained in a retaining slot. Such a retaining slot may be a circumferentially extending retaining slot and/or may be an annular retaining slot. The retaining slot may be part of and/or attached to a casing, for example an engine core casing. Each stator vane may be retained by its fixing portion. 
     Such a retaining slot may comprise an anti-fret liner. The fixing portion of the vanes may be engaged with the anti-fret liner, for example during use. The material of an anti-fret liner may be softer than the material of the fixing portion of the vanes to ensure that it wears in preference to the fixing portion. 
     For arrangements in which the fixing portion has a recess the joggle surface of one stator vane in a stator vane row may be provided in the recess of a neighbouring second stator vane so as to oppose the recess surface of the neighbouring stator vane. In some arrangements, the recess surface and the joggle surface may be engaged. 
     According to an aspect, there is provided a gas turbine engine comprising at least one stator vane row as described and/or claimed herein. The stator vane(s) and/or stator vane row(s) may be part of a compressor, turbine, or both, for example. 
     According to an aspect, there is provided a method of manufacturing a stator vane as described and/or claimed herein using metal injection moulding (MIM). MIM could be used to integrally form the aerofoil and the fixing portion. However, it will be appreciated that any manufacturing method could be used to manufacture a stator vane as described and/or claimed herein, for example forging and/or machining. 
     The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Arrangements will now be described by way of example only, with reference to the Figures, in which: 
         FIG. 1  shows schematically fixing portions of two adjacent vanes of a stator vane row; 
         FIG. 2  shows schematically platforms of two adjacent stator vanes located in a casing slot (a) for un-joined vanes, and (b) for vanes permanently joined at neighbouring axially-extending edges of their platforms; 
         FIG. 3  is a sectional side view of a gas turbine engine; 
         FIG. 4  is a schematic side view of a stator vane in accordance with an example of the present disclosure; 
         FIG. 5  is a schematic perspective view of the stator vane shown in  FIG. 4 ; 
         FIG. 6  is another schematic perspective view of the stator vane shown in  FIG. 4 ; 
         FIG. 7  is a schematic view showing part of a stator vane row comprising the stator vanes shown schematically in  FIGS. 4 to 6 ; 
         FIGS. 8A and 8B  are schematic views showing vanes rotating in a retaining slot; 
         FIG. 9  is a schematic showing leakage flow through a stator vane row; 
         FIG. 10  is a schematic perspective view showing a double-ended stator vane in accordance with an example of the present disclosure; 
         FIG. 11  is a schematic perspective view of a stator vane in accordance with an example of the present disclosure; 
         FIG. 12  is a schematic view showing part of a stator vane row comprising stator vanes shown schematically in  FIG. 11 ; 
         FIG. 13  is another schematic view showing part of a stator vane row comprising stator vanes shown schematically in  FIG. 11 ; 
         FIG. 14  is a schematic perspective view of another stator vane in accordance with an example of the present disclosure; 
         FIG. 15  is another schematic view of the stator vane shown in  FIG. 14 ; 
         FIG. 16  is a schematic view showing part of a stator vane row comprising stator vanes shown schematically in  FIGS. 14 and 15 ; and 
         FIG. 17  is another schematic view showing part of a stator vane row comprising stator vanes shown schematically in  FIGS. 14 and 15 . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     With reference to  FIG. 3 , a gas turbine engine is generally indicated at  10 , having a principal and rotational axis  11 . The engine  10  comprises, in axial flow series, an air intake  12 , a propulsive fan  13 , an intermediate pressure compressor  14 , a high-pressure compressor  15 , combustion equipment  16 , a high-pressure turbine  17 , an intermediate pressure turbine  18 , a low-pressure turbine  19  and an exhaust nozzle  20 . A nacelle  21  generally surrounds the engine  10  and defines both the intake  12  and the exhaust nozzle  20 . 
     The gas turbine engine  10  works in the conventional manner so that air entering the intake  12  is accelerated by the fan  13  to produce two air flows: a first air flow into the intermediate pressure compressor  14  and a second air flow which passes through a bypass duct  22  to provide propulsive thrust. The intermediate pressure compressor  14  compresses the air flow directed into it before delivering that air to the high pressure compressor  15  where further compression takes place. 
     The compressed air exhausted from the high-pressure compressor  15  is directed into the combustion equipment  16  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines  17 ,  18 ,  19  before being exhausted through the nozzle  20  to provide additional propulsive thrust. The high  17 , intermediate  18  and low  19  pressure turbines drive respectively the high pressure compressor  15 , intermediate pressure compressor  14  and fan  13 , each by suitable interconnecting shaft. 
     At least one of the compressors  14 ,  15  and the turbines  17 ,  18 ,  19  comprise stages having rotor blades in rotor blade rows (labelled  60  by way of example in relation to the intermediate pressure compressor in  FIG. 3 ) and stator vanes in stator vane rows (labelled  70  by way of example in relation to the intermediate pressure compressor in  FIG. 3 ). 
     Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan. 
     The geometry of the gas turbine engine  10 , and components thereof, is defined by a conventional axis system, comprising an axial direction  30  (which is aligned with the rotational axis  11 ), a radial direction  40 , and a circumferential direction  50  (shown perpendicular to the page in the  FIG. 3  view). The axial, radial and circumferential directions  30 ,  40 ,  50  are mutually perpendicular. 
     A metallic stator vane  100  in accordance with the present disclosure is shown in  FIGS. 4 to 6 . The stator vane  100  may be used in one or more stator vane rows  70  in a gas turbine engine  10  such as that shown in  FIG. 3 . 
     The stator vane  100  comprises an aerofoil  110  and a fixing portion  120 . The fixing portion  120  is arranged to fix the stator vane  100  in a gas turbine engine  10 , for example using tangs  122 . 
     The aerofoil  110  extends from a platform surface  130 . The platform surface  130  is considered to be part of the fixing portion  120 . The fixing portion  120  also comprises a joggle surface  140 . The joggle surface  140  may be said to be part of a joggle portion that extends circumferentially away from the platform surface  130 . 
     The joggle surface  140  is offset from the platform surface in the radial direction  40 . In the illustrated example, the fixing portion  120  is provided at the radially outer end of the stator vane  100 , and so the joggle surface  140  is radially outside (i.e. at a greater radial extent) than the platform surface  130 . The joggle surface  140  is offset from the platform surface  130  in the circumferential direction  50 . The overall circumferential extent C 2  of the vane  100 , for example the overall circumferential extent C 2  of the fixing portion  120 , is greater than the circumferential extent C 1  of the platform surface  130  alone. The combination of the circumferential offset and the radial offset of the joggle surface from the platform surface may be said to form a step in the fixing portion  120 . 
     The vane  100  also comprises a recess  150  in the fixing portion  120 , as shown in the example of  FIGS. 4 to 7 . The recess  150  may be said to be formed by circumferentially extending ledge that comprises a part of the platform surface  130 . The recess  150  defines a recess surface  155 . The recess surface  155  is substantially parallel to, and radially offset from, the platform surface  130 . The recess surface  155  is substantially parallel to, and circumferentially offset from, the joggle surface  140 . The geometry of the recess surface  155  and the joggle surface  140  may be substantially the same. 
       FIG. 7  shows a portion of a stator vane row  70  having a plurality of the stator vanes  100  assembled together. In the  FIG. 7  example, the joggle surface  140  (or joggle portion) is slotted into the recess  150 . The joggle surface  140  of one vane  100  may engage the recess surface of a neighbouring vane  100 , as shown in  FIG. 7 . Each vane  100  remains independent of the other vanes  100 . Even when assembled into a gas turbine engine  10 , each vane  100  may be moveable in at least one degree of freedom relative to the other vanes  100 . For example, each vane  100  may be rotatable about a radial direction  40  relative to the other vanes  100 , within a retaining slot. 
       FIG. 8A  shows a conventional vane  1  (such as that shown in  FIG. 1 , discussed above) that has rotated during use in its retaining slot  200  to a position in which the vane  1  contacts the retaining slot  200  at contact points  7 . The retaining slot  200  may comprise an anti-fret lining along the contact surface. As shown in  FIG. 8A , the conventional vane  1  rotates through an angle of θ 1  before contacting the retaining slot  200 . As mentioned above, the larger this angle, the greater the chance of damage and/or increased wear, for example due to greater forces being generated between the vane  1  and the retaining slot  200 . 
       FIG. 8B  shows a stator vane  100  in accordance with the present disclosure (such as that shown in  FIGS. 4 to 7 , discussed above) that has rotated during use in its retaining slot  200  to a position in which the vane  100  contacts the retaining slot  200  (which may be, for example, a T-shaped retaining slot  200 ) at contact points  207 . Compared with the conventional vane  1  shown in  FIG. 8B , the stator vane  100  rotates through a smaller angle, θ 2 , before contacting the retaining slot  200 . This is because of the increased effective width (that is, increased circumferential extent) C 2  of the stator vane  100  compared with the width C 1  of the conventional vane  1 . Any increase in effective width may be beneficial. Purely by way of example, the circumferential extent (or effective width) C 2  of the stator vane  100  may be in the range of from 1% to 100%, for example 10% to 90%, for example 20% to 75%, for example 25% to 50%, for example on the order of 30% greater than the circumferential extent (or effective width) C 1  of the stator vane  1 . 
     This reduced rotation before contact with the cases reduces the likelihood and/or magnitude of any wear/damage caused by the contact between the vane  100  and the casing  200 . Note that the size of the platform surface  130  (i.e. the surface from which the aerofoil  110  extends) may be the same for the convention vane  1  of  FIG. 8A  and the vane  100  in accordance with the present disclosure shown in  FIG. 8B . For example, the width (or circumferential extent) of the platform surface of both vanes  1 ,  100  may be C 1 . 
       FIG. 9  illustrates another potential advantage of stator vanes  100  in accordance with the present disclosure. In particular,  FIG. 9  illustrates a leakage path  250  for leakage flow to leak between the working fluid passing over the aerofoils  110  (and thus providing useful work, or energy output), and the region radially outside the vanes  100  (which does not provide useful work, or energy output). Such leakage flow may be problematic for all vane rows. However, as shown in  FIG. 9 , the leakage flow path  250  formed by arrangements in accordance with the present disclosure is tortuous. In the  FIG. 9  example, the leakage flow path turns from radial  40 , to circumferential  50 , then back to radial  40 . This may significantly reduce flow losses, and thus increase efficiency, compared to a conventional vane design, in which the leakage path is purely radial  40 . 
     A stator vane in accordance with the present disclosure may be either a singled ended vane (as in the example described above in relation to  FIGS. 4 to 7 ), or a double ended vane  300 , as in the example shown in  FIG. 10 . The double ended vane  300  shown in  FIG. 10  has a sealing tip  310 . The sealing tip  310  may help to reduce over-tip flow during use. Any sealing tip  310  may be used. In all other aspects, the double ended vane  300  shown in  FIG. 10  may be the same as the single ended vane shown in  FIGS. 4 to 7 , with like reference numerals representing like features. Any description provided herein in relation to a single ended vane  100  may also apply to a double ended vane  300  (for example in relation to the fixing portion  120 ), and so will not be repeated in relation to  FIG. 10 . 
       FIGS. 11 to 13  show a further example of a stator vane  400  in accordance with the present disclosure. The stator vane  400  shares many features with the stator vane  100  shown and described in relation to  FIGS. 4 to 7 . For example, the aerofoil  410 , platform surface  430  and tangs  422  may be substantially the same as the aerofoil  110 , platform surface  130  and tangs  122  described in relation to  FIGS. 4 to 7 , and so will not be described further in relation to  FIGS. 11 to 13 . 
     However, whereas the axial extent of the joggle surface  140  of the vane  100  shown in  FIGS. 4 to 7  is substantially the same as the axial extent of the platform surface  130 , the axial extent of the joggle surface  440  of the vane  400  shown in  FIGS. 11 to 13  is less than the axial extent of the platform surface  430 . Similarly, the axial extent of the recess surface  455  is less than the axial extent of the platform surface  430  in the vane  400  shown in the example of  FIGS. 11 to 13 . The axial extent of the recess surface  455  may be the same as the axial extent of the joggle surface  440 . More generally, the geometry of the recess surface  455  may be the same as the geometry of the joggle surface  440 . 
       FIGS. 12 and 13  show a plurality of the vanes  400  arranged together to form part of a stator vane row  70 . As shown in these Figures, the configuration of the recess surface  455  and the joggle surface  440  may create an interlocking feature that may help to lock neighbouring vanes  400  together and/or may help to reduce unwanted rotation of the vanes  400  (for example about a radial direction  40 . Stator vanes according to the present disclosure may, optionally, be provided with any suitable interlocking feature, of which the arrangement shown in  FIGS. 11 to 13  is just one example. 
       FIGS. 14 to 17  show a further example of a stator vane  500  in accordance with the present disclosure. The stator vane  500  shown in  FIGS. 14 to 17  shares many corresponding features with the stator vane  100  shown in, and described in relation to,  FIGS. 4 to 7 . For example, the aerofoil  510 , and platform surface  530  are substantially the same as the aerofoil  110  and platform surface  130  of the stator vane  100  shown in  FIGS. 4 to 7 , and will not be described in detail again here. 
     The joggle surface  540  of the stator vane  500  shown in  FIGS. 14 to 17  comprises a locking tooth  545 . The locking tooth  545  in this example is a circumferential extension  545  of the joggle surface  540 . The circumferential extension  545  may be an extension of the rest of the joggle surface and/or may form a continuous and/or contiguous surface with the rest of the joggles surface  540 . However, it will be appreciated that other geometries of locking tooth  545  may be used. 
     The recess surface  555  of the fixing portion  520  also has a circumferentially extending extension  557  in the  FIGS. 14 to 17  example. The extension  557  of the recess surface  555  may correspond to, for example have the same geometry as, the circumferential extension  545  of the joggle surface  540 . As shown in  FIGS. 16 and 17 , when more than one stator vane  500  are arranged together to form a stator vane row  70 , the joggle surface  540  of one vane may be adjacent (and optionally engaging) the recess surface  555  of an adjacent vane  500 , as with any arrangement. In the example of  FIGS. 14 to 17 , this means that the extension  557  of the recess surface  555  is adjacent (and optionally engaging) the extension  545  of the joggle surface  540 . 
     Any suitable method may be used to manufacture the metallic vanes  100 ,  400 ,  500  shown and described herein. For example, each individual vane  100 ,  400 ,  500  may be manufactured using metal injection moulding (MIM). 
     It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.