Abstract:
A system and method for reducing vibration and wear to adjacent platform surfaces and mounting locations of a vane segment in a gas turbine engine is disclosed. The present invention seeks to improve the interaction between mating faces of adjacent gas turbine vane assemblies by increasing the surface area where contact between the adjacent vanes occurs, so as to increase the damping capability and reduce the wear to the mating surfaces.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       TECHNICAL FIELD 
       [0003]    The present invention relates generally to gas turbine engines and more specifically to a vane configuration having reduced wear along mating surfaces. 
       BACKGROUND OF THE INVENTION 
       [0004]    A gas turbine engine typically comprises a multi-stage compressor that compresses air, which has been drawn into the engine, to a higher pressure and temperature. A majority of this air passes to the combustion system, which mixes the compressed and heated air with fuel and contains the resulting reaction that generates the hot combustion gases. These gases then pass through a multi-stage turbine, which, in turn drives the compressor, and possibly a shaft of an electrical generator. Exhaust from the turbine can also be channeled to provide thrust for propulsion of a vehicle. 
         [0005]    Typical compressors and turbines comprise a plurality of alternating rows of rotating and stationary airfoils. An example of a vane segment, or stator section, comprising a plurality of airfoils positioned between an inner platform and outer platform is shown in  FIG. 1 . In this embodiment of the prior art, the vane segment spans approximately 180 degrees where two vane segments together encompass an engine shaft (not shown) which runs along the engine centerline. A vane segment  10  of the prior art, is shown in  FIG. 1 , and comprises an inner platform  12 , an outer platform  14 , and vanes  16  extending between inner platform  12  and outer platform  14 . The vane segment  10  encompasses approximately 180 degree span and is in accordance with typical vane styles of the prior art. 
         [0006]    The stationary airfoils, or vanes, direct the flow of air in a compressor or hot combustion gases in a turbine onto a subsequent row of rotating airfoils, or blades, at the proper orientation in order to maximize the output of the compressor or turbine. To minimize manufacturing costs as well as to improve response to thermal gradients and thermal deflections, more recent engine designs utilize a plurality of vane assemblies in the compressor or turbine. These vane assemblies include at least one airfoil bounded on either end by a section of an outer platform and an inner platform, with the inner platform located closer to the engine centerline. Each of the vane assemblies typically span a few degrees and have a shorter arc length than the prior art half-ring segments. Depending on how the vane assemblies are mounted in the engine, significant movement can occur between adjacent vane assemblies causing undesirable contact and wear. When vane assemblies are mounted at or near their outer platform, thereby causing them to essentially hang free at the inner platform, relatively large movement can occur at the inner platform due to the distance of the inner platform from the mounting location, vibrations, and differences in thermal gradients between the adjacent vane assemblies. When such motion occurs between adjacent vane assemblies, significant wear can occur along the mating surfaces due to the mating surfaces essentially damping the vibrations. Significant wear is also found at the hooks that hold the vane assemblies in place due to the amount of movement at the inner platform and the surface-to-surface contact at the mounting location. This excessive wear can lead to premature repair or require replacement of the vane assemblies. 
         [0007]    What is needed is a vane assembly configuration that reduces the amount of wear that occurs along mating faces of adjacent vane assemblies and at the mounting location so as to increase the life of the vane assemblies. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is defined by the claims below. Embodiments of the present invention solve at least the above problems by providing a system and method for, among other things, reducing vibration and wear along adjacent platform surfaces and mounting locations of a plurality of vane assemblies in a gas turbine engine. 
         [0009]    The present invention seeks to improve the interaction between mating faces of adjacent gas turbine vanes by increasing the surface area where contact between the adjacent vanes occurs. In a first embodiment of the present invention, a gas turbine engine having a plurality of vane assemblies extending about an engine centerline having inner and outer arc-shaped platforms with at least one airfoil extending therebetween are disclosed. First and second extension plates extend radially inward from the inner platform and have a plurality of first openings, and are fixed to first and second side faces of the inner arc-shaped platform. Positioned between the extension plates, and having a plurality of second openings, is at least one shim plate. At least one fastener is positioned so as to secure the extension plates and shim plate together in a removable manner, thereby increasing the surface area along which adjacent vane assemblies interact. 
         [0010]    In an alternate embodiment of the invention, a shim plate assembly for use in a gas turbine engine is disclosed. The shim plate assembly comprises first and second extension plates having a first plurality of openings and at least one shim plate positioned therebetween, with the shim plate having a second plurality of openings. The axial length of the shim plate is greater than the length of the extension plates. A locating pin is positioned proximate the mid-span of the shim plate and extension plates so as to properly position the plates relative to one another while at least one fastener is positioned through the first and second plurality of openings in the plates so as to fix the extension plates and at least one shim plate together. 
         [0011]    In yet another alternate embodiment, a method of reducing wear along mating surfaces of a vane segment is disclosed. A slot is cut through a vane segment inner arc-shaped platform from the surface opposite of the airfoils and circumferentially between adjacent airfoils. A block, pre-machined to include a first plurality of openings, is fixed in the slot. The vane segment is then cut, between adjacent airfoils, through the inner and outer arc-shaped platforms, including the machined block. As a result, a plurality of vane assemblies are formed, with each vane assembly having an extension plate fixed to each side face of the vane assembly inner platform. A locating pin is then placed in one of the first plurality of openings and at least one shim plate is inserted between the extension plates. The extension plates are then fixed to the at least one shim plate by passing at least one fastener through the remaining openings in the extension plates and corresponding openings in the shim plate. 
         [0012]    In accordance with these and other objects, which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings. Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0013]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0014]      FIG. 1  is a perspective view of a vane segment of the prior art; 
           [0015]      FIG. 2  is a perspective view of a vane segment in accordance with an embodiment of the present invention; 
           [0016]      FIG. 3  is an exploded view of shim plate assembly for use with a vane assembly in accordance with an embodiment of the present invention; 
           [0017]      FIG. 4  is a perspective view of a shim plate in accordance with an embodiment of the present invention; 
           [0018]      FIG. 5  is a partial perspective view of the inner platform of a vane assembly in accordance with an embodiment of the present invention; and 
           [0019]      FIG. 6  is a cross section view of a shim plate assembly in a vane assembly in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The subject matter of the present invention is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different steps or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. Moreover, although the terms “step” and/or “block” may be used herein to connote different elements of methods employed, the terms should not be interpreted as implying any particular order among or between various steps herein disclosed unless and except when the order of individual steps is explicitly described. 
         [0021]    The present invention is shown in detail in  FIGS. 2-6  and is applicable to both individual vane assemblies as well as half-ring vane segments. While the present invention is directed primarily towards vane assemblies or vane segments for a compressor, other vane locations, such as in the engine inlet or the turbine section could also utilize such a design if desired. 
         [0022]    Referring initially to  FIG. 2 , an embodiment of the present invention comprises a vane segment  20  that extends circumferentially about an engine centerline and having a plurality of vane assemblies  22 . As previously discussed, the vane segments or assemblies that are supported from the outer platform are those that exhibit the greatest wear indications along the outer platform. The vane assemblies  22  comprise an outer arc-shaped platform  24 , at least one airfoil  26  extending radially inward from the outer-arc-shaped platform  24 . Fixed to the at least one airfoil  26 , opposite the outer arc-shaped platform  24 , is an inner arc-shaped platform  28 . Referring to  FIGS. 3 and 5 , the inner arc-shaped platform  28  comprises a first surface  30  and a second surface  32  located radially outward of the first surface  30 , to thereby form a platform thickness  34 . The inner arc-shaped platform  28  also comprises a forward face  36  and an aft face  38  spaced an axial distance from the forward face, thereby forming a platform length  40 . Referring now to  FIGS. 3 ,  5 , and  6 , the inner arc-shaped platform  28  also comprises a first side face  42  and a second side face  44 , with the sidefaces being generally parallel. 
         [0023]    As previously discussed, the present invention reduces wear on the mating platform surfaces by increasing the surface area at which contact occurs, so as to provide more damping. This is accomplished for a plurality of vane assemblies through a sim plate assembly  45 . A first extension plate  46  is fixed to the first side face  42 , while a second extension plate  48  is fixed to the second side face  44 . The extension plates  46  and  48  have a first axial length and are preferably fixed to the inner arc-shaped platform  28  by electron beam (EB) welding. Such a process ensures a clean and complete weld through the thickness of the platform and the extension plate. In order to have the best weld properties, it is preferred that the extension plate is fabricated from a material having similar properties as the vane assemblies. The extension plates  46  and  48  extend radially inward from the inner arc-shaped platform  28  and have a first plurality of openings  50  comprising at least two openings. The present invention also comprises at least one shim plate  52  that has a second axial length and second plurality of opening  54  with a plate thickness  56  and at least one fastener  58 . As it can be seen from  FIG. 3 , the second axial length is greater than the first axial length of the extension plates  46  and  48 . 
         [0024]    The at least one shim plate  52 , which is also fabricated from a material similar to the extension plates and the vane assembly, is positioned between the first and second extension plates,  46  and  48 , of adjacent vane assemblies. That is, with each vane assembly having a first side face  42  and a second side face  44 , the first and second side faces would normally contact one another, and therefore, the first and second extension plates,  46  and  48 , of adjacent vane assemblies provide increased areas for contact. The shim plate  52  is positioned such that the second plurality of openings  54 , which also comprises at least two openings, correspond to the first plurality of openings  50  and the at least one fastener  58  is positioned at least partially through the first and second openings,  50  and  54 , so as to fix the adjacent vane assemblies together. The shim plate  52 , as it can be seen from  FIG. 6 , extends substantially along the platform length  40 . This assembly arrangement is shown in cross section in  FIG. 6 . The at least one fastener  58  is removable to allow for disassembly of the vane assemblies for routing maintenance and overhaul. The shim plate  52  further comprises a wear reduction coating that is applied to at least the surfaces of the shim plate  52  that contact the first and second extension plates  46  and  48 . This coating is preferably an Aluminum Bronze and is applied in order to ensure that damping action of the shim plate will not diminish over time. 
         [0025]    Located through one of the at least two openings in extension plates  46  and  48  and through the shim plate  52  is a locating pin  60 . The locating pin  60  helps to position adjacent vane assemblies in the proper orientation while fasteners  58  are installed through the first and second plurality of openings  50  and  54  in the extension plates and the shim plate. The locating pin  60  is intended to be contained within the shim plate assembly  45  and not to become dislodged during engine operation. This can be accomplished by tack welding the locating pin  60  to one of the extension plates  46  or  48 . Alternatively, the locating pin  60  can be contained by a retaining plate  62 , through which at least one fastener  58  passes. 
         [0026]    In one embodiment of the present invention, an apparatus is disclosed for reducing wear caused by vibration along mating surfaces of adjacent turbine vane assemblies  22 . In another embodiment, a method of reducing wear along mating surfaces of a vane segment is provided. In this method, an existing vane segment  10 , similar to a half-ring segment of the prior art, is modified to incorporate one or more shim plate assemblies  45  to reduce wear on the inner platforms and along the mounting locations at the outer platform. The method comprises providing a vane segment  10  having an outer arc-shaped platform  14 , a plurality of airfoils  16  extending radially inward from the outer arc-shaped platform  14 , and an inner arc-shaped platform  12  fixed to the plurality of airfoils  16  opposite the outer arc-shaped platform  14 . 
         [0027]    Referring to  FIG. 3 , a cut is made through a surface of the inner arc-shaped platform that is opposite the plurality of airfoils, to form a slot  29 . That is, the slot  29  is cut from the radially inner-most surface outward towards the airfoils. Also, the slot is cut between adjacent airfoils. Next, a machined block is fixed in the slot  29 . The block is preferably fabricated from a material similar in properties to the vane segment and is machined to have a first plurality of openings  50 . The block is permanently fixed in the slot  29 , preferably by electron beam welding. However, alternate means to fix the block in the slot  29  are acceptable as long as a complete joint is achieved. 
         [0028]    Once the block is fixed in the slot  29 , the vane segment is cut between the adjacent airfoils, through both the inner and outer arc-shaped platforms and the machined block. The cutting of the vane segment  10  forms a plurality of vane assemblies  22  with the machined block split into two parts, thereby forming two extension plates  46  and  48 , with each extension plate remaining fixed to the inner arc-shaped platform  28 . 
         [0029]    As a result of cutting the vane segment into individual assemblies  22 , the natural tendency of an assembly  22  is to spring back to a more relaxed position and not maintain as much of the arc shape in the platforms. In order to help the vane assemblies  22  maintain their shape and to assist in properly re-aligning the vane assemblies  22  into a segment  20 , a locating pin  60  is placed in one of the first plurality of openings  50 . The locating pin  60  can be placed in any of the first openings  50 . However, if the first plurality of openings  50  comprises three openings, then it is preferred that the locating pin  60  be placed in the opening closest to the center of the extension plates  46  and  48 . Next, at least one shim plate  52  having a second plurality of openings  54  is inserted between the extension plates  46  and  48 . Depending on the vane assembly configuration and expected wear, the at least one shim plate  52  may also include a wear reduction coating, such as an Aluminum Bronze coating, applied to surfaces of the shim plate  52  that mate with the extension plates. The shim plate(s)  52  has a thickness that corresponds to the thickness of material lost when the vane segment was cut into individual assemblies  22 . Depending on the amount of material lost during the cutting process, more than one shim plate  52  may be required. The extension plates  46  and  48  and at least one shim plate  52  are fixed together by passing at least one fastener  58  through the remaining plurality of first and second openings  50  and  54 . 
         [0030]    From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. While the invention has been described in what is known as presently the preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment but, on the contrary, is intended to cover various modifications and equivalent arrangements within the scope of the following claims.