Abstract:
A compressor diaphragm for a gas turbine engine having improved wear capability, manufacturability, and assembly techniques is disclosed. The diaphragm includes a shiplap-type joint at an outer vane platform for connecting to adjacent vane assemblies and a clamshell-like assembly of a seal box secures and seals regions around the inner vane platform of the compressor diaphragm so as to reduce wear between the seal box and the vane assemblies. The inner platform of the diaphragm segments are fastened to each other through circumferentially-oriented fasteners at the inner diameter platform.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 61/117,313, filed on Nov. 24, 2008. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to a compressor diaphragm and vane configuration. More specifically, the compressor vane diaphragm includes improved assembly techniques that reduces operating stresses and wear at mating surfaces between adjacent compressor vanes. 
     BACKGROUND OF THE INVENTION 
     Gas turbine engines operate to produce mechanical work or thrust. Specifically, land-based gas turbine engines typically have a generator coupled thereto for the purposes of generating electricity. A gas turbine engine comprises an inlet that directs air to a compressor section which has stages of rotating compressor blades spaced between stage of stationary vanes. As the air passes through the compressor, the pressure of the air increases. The compressed air is then directed into one or more combustors where fuel is injected into the compressed air and the mixture is ignited. The hot combustion gases are then directed from the combustion section to a turbine section. As the hot combustion gases pass through the turbine, the stages of the turbine rotate, which in turn, causes the compressor to rotate. 
     The air from the inlet is directed through a compressor section, with the compressor having a plurality of alternating axial stages of rotating blades and stationary vanes. As the air travels through the compressor, its pressure increases as well as its temperature. An axial stage of vanes and mounting hardware forms a diaphragm that is secured to the engine and directs the flow of air onto the compressor blades. In prior designs, circular inner diameter and outer diameter rings were used with slots cut through the rings for airfoils to slide through the slots. The airfoils were then welded to the rings to form the vane diaphragms. The full-circle rings and vanes were split into two, 180-degree segments and each of these segments was then assembled into an engine. This assembly has numerous drawbacks including manufacturing and production issues, airfoil cracking at the weld joints during operation, and durability issues regarding seals associated with the diaphragm assembly. 
     SUMMARY 
     In accordance with the present invention, there is provided a novel configuration for a gas turbine engine compressor diaphragm having a plurality of vane segments fastened together to form a vane pack along with a clam shell-type seal box. The vane pack has a plurality of elastomeric seals located at the interfaces between fastened vane segments. The vane pack also engages a seal box at its inner diameter, the seal box having a forward and aft seal carrier portions coupled together and to the compressor diaphragm. 
     In an embodiment of the present invention, a vane pack assembly for a gas turbine comprises a plurality of vane assemblies coupled together by a first plurality of fasteners. The vane assemblies have an outer platform with a connecting plate extending from a first side and a recessed portion along the opposite side, an inner platform and one or more airfoils extending therebetween. Each of the connecting plates has a plurality of holes that correspond to a plurality of threaded holes in the recessed portion when a connecting plate is placed over a recessed portion of an adjacent vane assembly. The recessed portion in the outer platform also corresponds generally in dimension and shape to the connecting plate. A plurality of fasteners pass through the plurality of holes in the connecting plate and secure the connecting plate in the recessed portion through the plurality of threaded holes in the recessed portion. The vane pack assembly also includes an elastomeric seal that is located in the recessed portion to provide both sealing and vibration dampening capabilities. 
     In an alternate embodiment, an improved seal box for engaging a plurality of vane assemblies is provided that does not require modifications to an existing compressor case. The seal box is a region around the inner diameter of a vane pack assembly adjacent to a rotating disk. The seal box provides for increased durability at hook portions, increased damping in conjunction with the vanes, and improved assembly techniques. The seal box comprises a forward seal carrier segment having a first forward radially extending wall connected to a second forward radially extending wall by a first generally axial portion and an aft seal carrier segment having a first aft radially outward extending wall connected to a first aft radially inward extending wall by a second generally axial portion. The seal carrier segments are secured together by a plurality of fasteners passing through the first aft radially inward extending wall and the second forward radially extending wall so as to couple the forward seal carrier and aft seal carrier together and to a vane assembly. 
     In yet another embodiment of the present invention, an elastomeric seal for use in a compressor diaphragm is also disclosed. The elastomeric seal comprises a first sheet of metal, a silicone sheet, and a second sheet of metal. The silicone sheet is impregnated with fiberglass and is bonded to the first and second sheets of metal to form a reinforced solid bonded seal. The seal is generally used in a joint interface between mating platform portions of vane assemblies, such as between the connecting plate and recessed portions of the outer platform of a vane. 
     In a further embodiment of the present invention, a method of assembling a compressor diaphragm is disclosed. Adjacent vane assemblies are coupled together at the interface of connecting plates and recessed portions of the outer platforms and at the inner platforms by a plurality of fasteners. The resulting diaphragm assembly is then placed in a forward seal carrier segment and an aft seal carrier segment is then placed onto the diaphragm assembly. The seal carrier segments are then fastened to the diaphragm assembly. 
     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. The instant invention will now be described with particular reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The present invention is described in detail below with reference to the attached drawing figures, wherein: 
         FIG. 1  is a cross section of a portion of a compressor incorporating an embodiment of the present invention; 
         FIG. 2  is a perspective view of an embodiment of the present invention; 
         FIG. 3  is a perspective view of a vane assembly of a compressor diaphragm in accordance with an embodiment of the present invention; 
         FIG. 4  is a top elevation view of the vane assembly of  FIG. 3  in accordance with an embodiment of the present invention; 
         FIG. 5  is a perspective view of a partial assembly of components of a diaphragm assembly in accordance with an embodiment of the present invention; 
         FIG. 6  is an exploded view of a portion of a compressor diaphragm in accordance with an embodiment of the present invention; 
         FIG. 7  is a cross section view of a joint between a connecting plate and a recessed portion of an outer platform in accordance with an embodiment of the present invention; 
         FIG. 8  is a view of a joint between a connecting plate and the outer platform having multiple recessed surfaces in accordance with an alternate embodiment of the present invention; 
         FIG. 9  is a view of a joint between a connecting plate and the outer platform in accordance with an alternate embodiment of the present invention; 
         FIG. 10  is a view of a joint located along radially extending edges of platforms in accordance with yet another alternate embodiment of the present invention; 
         FIG. 11  is a top elevation view of an elastomeric seal in accordance with an embodiment of the present invention; 
         FIG. 12  is a cross section view of the elastomeric seal of  FIG. 11 ; 
         FIG. 13  is an exploded perspective view of the diaphragm to seal box interface in accordance with an embodiment of the present invention; 
         FIG. 14  depicts a cross section view of a the seal box in accordance with an embodiment of the present invention; and, 
         FIG. 15  is a flow diagram depicting an assembly sequence for a diaphragm assembly in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     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 components, combinations of components, steps, or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. 
     Referring initially to  FIG. 1 , a cross section of a portion of a gas turbine compressor is depicted. The compressor  100  includes a plurality of alternating stages of rotating compressor blades  102  and stationary stages of compressor vanes  104 . The stationary vanes  104  receive compressed air from a stage of rotating blades  102  and redirect the air in the proper direction towards a subsequent stage of rotating blades  102 . The compressor  100  serves to increase the pressure and temperature of air passing through it by passing the air through an increasingly smaller volume at each subsequent stage of the compressor  100 . 
     A compressor diaphragm in accordance with an embodiment of the present invention is shown in  FIGS. 2-7 . Referring to  FIG. 2 , the vane pack assembly  200  typically includes a radially outer surface  202 , relative to an engine centerline A-A, a radially inner surface  204 , and a series of airfoils  206  spaced between the surfaces. The outer surface  202  is formed from a series of outer vane platforms that are arc-shaped. These assemblies are exposed to varying temperatures, pressures, and vibrations that can wear and degrade over time. An individual vane assembly  300  used in the vane pack assembly  200  is shown in  FIG. 3 . The vane assembly  300  includes an outer vane platform  302  having a first sidewall  304 , an opposing second sidewall  306 , a forward wall  307   a , and an aft wall  307   b . The outer vane platform  302 , also includes a connecting plate  308  that extends away from the first side wall  304 . In  FIG. 4 , a top elevation view of a vane assembly  300  is shown where the connecting plate  308  has a plurality of through holes  310 . The outer platform  302  also has a recessed portion  312  adjacent the second sidewall  306  with the recessed portion  312  having a plurality of threaded holes  314 . An inner vane platform  316  is spaced radially inward from the first outer platform  306 . One or more airfoils  318  extend between the platforms  302  and  316 , with a flange  344  extending radially inward from the inner vane platform  316 . The one or more airfoils are preferably integral to the inner vane platform  316  and outer vane platform  302 . 
     To secure the vane assembly  300  to an adjacent vane assembly  330 , as depicted in  FIG. 5 , the connecting plate  308  is placed within the recessed portion  312  of the adjacent vane assembly  330  such that the holes  310  and  314  overlay on each other. The vane assembly  300  can be fastened to the adjacent vane assembly  330  with a plurality of fasteners  320 , such as a screw or bolt that can be removed for purposes of overhaul and repair of the individual vane assemblies. An exploded view of the diaphragm components at the outer vane platform joint is shown in  FIG. 6 . By dividing the overall compressor diaphragm into individual segments instead of half-ring segments, manufacturability and durability are improved since platforms and airfoils can be integrally cast and greater manufacturing tolerances can be controlled. Also, vibrations of the fastened assembly are controlled since the joint formed by the connecting plate  308  and recessed portion  312  is capable of having an elastomeric seal located therebetween. Features of an acceptable elastomeric seal are discussed below. 
     In order to minimize any gaps between adjacent vane assemblies  300  and  330 , the segments are also fastened to each other at the inner vane platform  316 , with the fasteners  340  extending in a generally circumferential direction. The fasteners  340  connect adjacent inner platforms  316  through a recessed portion  342  in the inner platform  316  (see  FIGS. 3 and 10 ). The fasteners  340  pass through openings in a sidewall of the inner vane platform  316  and extend to engage threaded holes of an adjacent inner vane platform  316  such that the fasteners  340  are generally perpendicular to the fasteners  320  which secure outer vane platforms  302  together. As a result of the geometric tolerances that are able to be held during manufacturing and use of fasteners  340  and  320  on the inner platform and outer platform, respectively, the individual vane assemblies  300  form a relatively smooth arc-shape diaphragm assembly free from steps between adjacent platforms. 
     The quantity of airfoils  306  that extend between the platforms  302  and  316  can vary. Vane assemblies  300  can have a single airfoil, two airfoils (doublets), or three airfoils (triplets) extending between the platforms, depending on the engine geometry The embodiment depicted in  FIG. 3 , shows a doublet arrangement. 
     Referring to  FIG. 7 , a seal  400  is located between the connecting plate  308  a bottom surface of the recessed portion  312 . The seal  400  provides for a flexible contact surface between a connecting plate  308  and recessed portion  312  of adjacent vane assemblies. This contact surface also serves as a damper given its multi-layer composite construction. The seal  400 , which is shown in more detail in  FIGS. 11 and 12 , comprises a first sheet of metal  402  having a first thickness, a second sheet of metal  404  having a second thickness, and an elastomeric sheet  406  positioned between the first and second sheets  402  and  404 , where the elastomeric sheet  406  is fiber reinforced. The elastomeric layer  406  provides flexibility to the seal  400  while the reinforcing fiber provides the necessary structural rigidity. The reinforced elastomer is bonded to the metal sheets  402  and  404  by an adhesive compound. In one embodiment, the metal plates consist of a stainless steel, but the material selection for the metal can vary depending on desired flexibility and temperature of the seal. For the embodiment of the present invention shown in  FIG. 7 , the seal  400  is approximately 0.062 inches thick, but the thickness can vary depending on the geometry of the connecting plate  308  and recessed portion  312 . The respective thickness of the metal sheets  402  and  404  will also vary depending on the desired stiffness of the seal  400 . 
     Referring to  FIGS. 8-10 , alternate embodiments of the outer vane platform region are shown. In  FIG. 8 , a portion of vane assemblies  800  and  830  are shown at the outer vane platforms  802  and  832 . In this embodiment, a recessed portion  812  is located adjacent the first sidewall  804  and the second sidewall  806 , such that when vane assemblies  800  and  830  are positioned adjacent to one another, the recessed portions  812  are capable of receiving a connecting plate  808  for joining vane assembly  800  to vane assembly  830 . Positioned between the connecting plate  808  and the recessed potions  812  is a seal  400 . Similar to the embodiment disclosed in  FIG. 6 , the vane assembly  800  is secured to the adjacent vane assembly  830  by a plurality of fasteners  820  that pass through a plurality of holes in the seal  400  and secure within openings in the recessed portion  812  of the outer vane platforms  802  and  832 . 
     Referring to  FIG. 9 , another alternate embodiment of the outer vane platform region is shown. A portion of vane assemblies  900  and  930  are shown at the outer vane platforms  902  and  932 . In this embodiment, the outer vane platforms  902  and  932  do not include a recessed portion, such that the connecting plate  908  and seal  400  are secured directly to an outermost surface of the outer vane platforms  902  and  932 . As with prior configurations, the connecting plate  908  and seal  400  are secured with a plurality of fasteners  920 . 
     Referring to  FIG. 10 , yet another alternate embodiment for securing adjacent vane assemblies together is shown. A portion of vane assemblies  1000  and  1030  are shown at the outer vane platforms  1002  and  1032 . In this embodiment, the outer vane platforms  1002  and  1032  each include a radially extending portion  1004  and  1034 , respectively, such that the adjacent vane assemblies can be secured to each other by one or more fasteners  1020  that passes through the radially extending portions  1004  and  1034  and at least a seal  400 . 
     Referring now to  FIGS. 13 and 14 , a seal box  500  of the compressor diaphragm is depicted. Specifically, the seal box  500  includes a forward seal carrier segment  502  having a first forward radially extending wall  504  connected to a second forward radially extending wall  506  by a first generally axial portion  508 . An aft seal carrier segment  510  has a first aft radially outward extending wall  512  connected to a first aft radially inward extending wall  514  by a second generally axial portion  516 . When positioned around the inner vane platform  316  of the diaphragm, the forward seal carrier segment  502  and aft seal carrier segment  510  essentially sandwich the inner vane platform  316  and a connecting flange  344 . The flange  344  is either an integrally machined feature of the inner vane platform  316  of each vane or welded to the inner vane platform  316 . A plurality of fasteners  520  are placed through openings in the first aft radially inward extending wall  514 , the flange  344 , and the second forward radially extending wall  506  to secure the forward and aft seal carriers  502  and  510  in an axial direction. Through this fastening arrangement, each of the vane assemblies are fastened to the seal box such that tighter axial and radial fits at the joints are maintained over prior art designs. 
     The inner vane platform  316  is also held radially by the seal box  500  through hooks  522  that extend from the first aft radially outward extending wall  512  and the first forward radially extending wall  504 . The hooks  522  extend laterally and engage slots  524  in the forward face  307   a  and aft face  307   b  of the inner vane platform  316 . To further reduce wearing at the interface between the slots  524  and hooks  522 , an anti-fretting coating is applied to the contact surfaces of the hooks  522  and slots  524 . One such type of anti-fretting coating is an Aluminum Bronze coating. Applying the wear coating to both surfaces creates a uniform wear surface between the inner vane platform  316  and the hooks  522 . To minimize any leakage around these interfaces, the hooks  522  and radially-extending walls  504  and  512  are designed to have a limiting axial fit against the inner platform  316  as well as a limiting radial fit with the flange  344 . 
     In yet another embodiment of the present invention, a method of assembling a compressor diaphragm is disclosed. Referring to  FIG. 15 , the method  1500  comprises a step  1502  in which an elastomeric seal is placed in a recessed portion of an outer vane platform of a vane assembly. In a step  1504 , the connecting plate of an adjacent vane assembly is placed over the elastomeric seal and recessed portion of the vane assembly. Then, in a step  1506 , the outer vane platforms of adjacent vane assemblies are fastened together with a first plurality of fasteners. In a step  1508 , the inner platforms of the adjacent vane assemblies are secured together with a second plurality of fasteners to form a diaphragm assembly. The diaphragm assembly is then placed onto a forward seal carrier segment in a step  1510 . A hook portion of the forward seal carrier segment interfaces with a slot in the forward face of the inner platforms. Then, in a step  1512 , an aft seal carrier segment is placed onto the diaphragm assembly such that a hook portion of the aft seal carrier segment engages with a slot in the aft face of the inner platforms. The forward seal carrier and aft seal carrier segments are then secured to the diaphragm assembly in a step  1514 . 
     The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those of ordinary skill in the art to which the present invention pertains without departing from its scope. 
     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. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.