Patent Publication Number: US-2007117480-A1

Title: Method and apparatus for increasing a durability of a body

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates generally to ceramic matrix composite materials, and more specifically to a method and apparatus for increasing a durability of a ceramic matrix composite material.  
      Gas turbine engines typically include a compressor, a combustor, and a turbine. Airflow entering the compressor is compressed and channeled to the combustor, wherein the air is mixed with a fuel and ignited within a combustion chamber to produce combustion gases. The combustion gases are channeled to a turbine that extracts energy from the combustion gases for powering the compressor. One turbine extracts energy from the combustion gases to power the compressor. Other turbines may be used to power an output shaft connected to a load, such as an electrical generator. In some applications, the combustion gases exiting the turbine(s) are channeled through an engine exhaust nozzle to produce thrust for propelling an aircraft in flight.  
      Some known gas turbine aircraft engines include an engine exhaust nozzle having a variable geometry configuration, wherein a cross-sectional area of the exhaust nozzle is adjustable. Variable geometry exhaust nozzles typically have a plurality of flaps and a plurality of seals mounted circumferentially about a centerline of the exhaust nozzle. The seals are mounted generally between adjacent nozzle flaps, such that the flaps and seals form a generally continuous interior surface that directs a flow of the combustion gases through the exhaust nozzle. As their name implies, the seals seal the spaces between the flaps and shield various components of the exhaust nozzle from high temperatures and high thermal gradients during flow of the combustion gases therein.  
      To facilitate extending a useful life at high temperature operation, some seals are fabricated from non-metallic composite materials, such as ceramic matrix composite materials. However, even such non-metallic materials experience wear and other damage due to the hostile operating environment in gas turbine engines. For example, the seal edges may erode due to frictional contact with the flaps as well as point contact rub caused by part deformation from the high thermal gradients the seals experience during operation.  
     SUMMARY OF THE INVENTION  
      In one aspect, an inseparable assembly is provided having a body including a ceramic matrix composite material, and a cover including a metallic wire mesh. The cover is bonded to the body so that the cover overlaps at least a portion of the body.  
      In another aspect, a variable geometry exhaust nozzle is provided for a gas turbine engine having an exhaust centerline. The nozzle includes a plurality of flaps arranged around the exhaust centerline, each of the flaps having a sealing surface, and a plurality of flap seals. Each seal has a body which includes a sealing surface. The body is positioned between a pair of flaps of the plurality of flaps so that the sealing surface of the seal engages the sealing surface of at least one of the adjacent flaps. At least one of the seals has a cover including a metallic wire mesh bonded to the body with an adhesive so that the cover overlaps at least a portion of an edge of the body.  
      In yet another aspect, a method is provided for increasing a durability of a body including a ceramic matrix composite material. The method includes the steps of positioning a cover including a metallic wire mesh over at least a portion of the body, and bonding the positioned cover to the body.  
      Other features of the present invention will be in part apparent and in part pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic of an exemplary gas turbine engine;  
       FIG. 2  is a perspective of a portion of the gas turbine engine shown in  FIG. 1  illustrating a portion of an exemplary exhaust nozzle assembly;  
       FIG. 3  is a cross section of the exhaust nozzle assembly shown in  FIG. 2  taken alone line  3 - 3  of  FIG. 2 ;  
       FIG. 4  is a perspective of an exemplary flap seal body for use with the exhaust nozzle assembly shown in  FIG. 2 ;  
       FIG. 5  is a perspective of the flap seal body shown in  FIG. 4  after a material removal process;  
       FIG. 6  is a cross-section of the flap seal body shown in  FIG. 5  taken along line  6 - 6  of  FIG. 5 ;  
       FIG. 7  is a cross-section of the flap seal body shown in  FIG. 5  taken along line  7 - 7  of  FIG. 5 ;  
       FIG. 8  is a perspective of an exemplary cover for use with the flap seal body shown in  FIG. 5 ;  
       FIG. 9  is a cross-section of the cover shown in  FIG. 8  taken along line  9 - 9  of  FIG. 8 ; and  
       FIG. 10  is a perspective view of the flap seal body shown in  FIG. 5  having a plurality of covers, such as the cover shown in  FIG. 8 , bonded thereto. 
    
    
      Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring now the to the drawings,  FIG. 1  is a schematic of a gas turbine engine  20  including a fan  22 , a high pressure compressor  24 , and a combustor  26 . The engine  20  also includes a high pressure turbine  28  and a low pressure turbine  30 . The fan  22  and the turbine  30  are coupled by a first shaft  34 , and the high pressure compressor  24  and the turbine  28  are coupled by a second shaft  36 . In one embodiment, the engine  20  is a F414 engine commercially available from GE Aircraft Engines, Evendale, Ohio.  
      In operation, air received through an inlet end  38  of the engine  20  is compressed by the fan  22  and channeled to the high pressure compressor  24 , wherein the compressed air is compressed even further. The highly compressed air from the high pressure compressor  22  is channeled to the combustor  26 , wherein it is mixed with a fuel and ignited to produce combustion gases. The combustion gases are channeled from the combustor  26  to drive the turbines  28  and  30 , and exit an outlet end  40  of the engine  20  through an exhaust nozzle assembly  42  to provide thrust.  
       FIG. 2  is a perspective of a portion of the gas turbine engine  20  illustrating a sector of the exhaust nozzle assembly  42 .  FIG. 3  is a cross section of the exhaust nozzle assembly  42  taken along line  3 - 3  of  FIG. 2 . The nozzle assembly  42  includes a plurality of flaps  70  and a plurality of flap seals  72 . The flaps  70  and the flap seals  72  are arranged circumferentially around a centerline  74  of the exhaust nozzle assembly  42 . Each flap seal  72  is positioned between a pair of adjacent flaps  70  and radially inwardly with respect to the flaps  70 , such that a portion of each flap seal  72  overlaps a portion of each adjacent flap  70 . More specifically, each flap  70  includes a body  76  having a sealing surface  78 , and each flap seal  72  includes a body, generally referred to by the reference numeral  80 , having a sealing surface  82 . The flap seals  72  overlap adjacent flaps  70  such that during operation of the engine  20  a portion of each flap sealing surface  78  contacts a portion of each corresponding sealing surface  82  generally along an axial length of the flaps  70  and the flap seals  72 . In one embodiment, the flap seal bodies  80  are fabricated from a ceramic matrix composite material. In another embodiment, the flap seal bodies  80  are fabricated from an oxide-based ceramic matrix composite material. Additionally, in one embodiment, the flap bodies  76  are fabricated from a ceramic matrix composite material.  
      Respective radially inner surfaces  86  and  88  of the flaps  70  and the flap seals  72  form a generally continuous interior surface defining an exhaust nozzle orifice  90 . The orifice  90  directs a flowpath of gases received from the turbine  30  (shown in  FIG. 1 ) out of the engine outlet end  40  to produce thrust. In the exemplary embodiment, the exhaust nozzle assembly  42  is a variable geometry exhaust nozzle, wherein a cross-sectional area of the nozzle orifice  90  is adjustable. A mounting assembly, generally referred to herein with the reference numeral  92 , couples each flap seal  72  to adjacent flaps  70 . The assembly  92  is movably coupled to an outer casing  94  of the engine  20  to facilitate adjustment of the cross-sectional area of the orifice  90 . Additionally, the assembly  92  allows relative motion between the flaps  70  and the flap seals  72  to facilitate contact between the sealing surfaces  78  and respective sealing surfaces  82 , and to facilitate adjustment of the cross-sectional area of the orifice  90 . In the exemplary embodiment, the exhaust nozzle orifice  90  is generally annular, however, it should be understood the orifice  90  may be any suitable shape. For example, in an alternative embodiment, the exhaust nozzle orifice  90  is generally rectangular.  
      During operation of the engine  20 , a pressure of the flowpath gases exiting through the exhaust nozzle orifice  90  urges the flap seals  72  against the flaps  70 , and more specifically, urges the sealing surfaces  82  of the seals  72  in contact with respective sealing surfaces  78  of the flaps  70 . As gases flow through the nozzle assembly  42 , and more specifically the exhaust nozzle orifice  90 , contact between the sealing surfaces  78  and respective sealing surfaces  82  substantially prevents leakage of gases between the flaps  70  and the flap seals  72 .  
       FIG. 4  is a perspective of an exemplary flap seal body  80  for use with the exhaust nozzle assembly  42  (shown in  FIG. 2 ). Generally, the body  80  includes a plurality of ends  100 ,  102 ,  104 , and  106 . The body  80  also includes the sealing surface  82 , the radially inner surface  88 , and a plurality of other surfaces  120 ,  122 ,  124 , and  126 . Any of the surfaces  82 ,  88 ,  120 ,  122 ,  124 , and  126  may be designated a first surface or a second surface. The body  80  also includes plurality of openings, generally referred to by the reference numeral  128 , for attachment to the mounting assembly  92 .  
       FIG. 5  is a perspective of the flap seal body  80  after a material removal process.  FIG. 6  is a cross-section of the flap seal body  80  taken along line  6 - 6  of  FIG. 5 .  FIG. 7  is a cross-section of the flap seal body  80  taken along line  7 - 7  of  FIG. 5 . Material is removed from the body  80  using any suitable machining process, such as, for example, cutting, grinding, planing, facing, and/or milling. After material removal, the body  80  generally includes the ends  100 ,  102 ,  104 , and  106 , the sealing surface  82 , the radially inner surface  88 , and a plurality of mating surfaces  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144 ,  146 ,  148 , and  150 . In the exemplary embodiment, the mating surfaces  130 ,  134 ,  138 ,  140 ,  142 , and  144  are generally perpendicular to the surfaces  132  and  136 . In addition, in the exemplary embodiment, the mating surfaces  132  and  136  are generally perpendicular to the surfaces  146 ,  148 , and  150 . Any of the surfaces  82 ,  88 ,  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144 ,  146 ,  148 , and  150  may be designated a first surface or a second surface.  
      A plurality of edges  152 ,  154 ,  156 ,  158 ,  160 ,  162 ,  164 ,  166 ,  168 ,  170 ,  172 , and  174  extend between corresponding surfaces  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144 ,  146 ,  148 , and  150  of the body  80 . More specifically, the edge  152  is defined at the intersection of the surfaces  130  and  132 , the edge  154  is defined at the intersection of the surfaces  132  and  134 , the edge  156  is defined at the intersection of the surfaces  134  and  136 , and the edge  158  is defined at the intersection of the surfaces  136  and  138 . Similarly, the edge  160  is defined at the intersection of the surfaces  140  and  132 , the edge  162  is defined at the intersection of the surfaces  132  and  142 , the edge  164  is defined at the intersection of the surfaces  142  and  136 , and the edge  166  is defined at the intersection of the surfaces  136  and  144 . Additionally, the edge  168  is defined at the intersection of the surfaces  150  and  136 , the edge  170  is defined at the intersection of the surfaces  136  and  148 , the edge  172  is defined at the intersection of the surfaces  148  and  132 , and the edge  174  is defined at the intersection of the surfaces  132  and  146 .  
       FIG. 8  is a perspective of an exemplary cover, generally referred to by the reference numeral  180 , for use with the flap seal body  80  (shown in  FIG. 5 ).  FIG. 9  is a cross-section of the cover  180  taken along line  9 - 9  of  FIG. 8 . The cover  180  includes a plurality of outer sides  182 ,  184 , and  186 , and a plurality of mating sides  188 ,  190 ,  192 ,  194 , and  196 . The cover  180  also includes end surfaces  198  and  200  generally defining respective ends, generally referred to by the reference numerals  202  and  204 , of the cover  180 . In the exemplary embodiment, the outer sides  182  and  186  are generally perpendicular to the outer side  184 , and the mating sides  188  and  192  are generally perpendicular to the mating sides  190 ,  194 , and  196 . The cover  180  has a predetermined durability that is greater than a predetermined durability of a portion of the flap seal body  80  adjacent one or more of the flap seal body ends  100 ,  102 ,  104 , and  106 . In one embodiment, the flap seal body  80  has a substantially uniform durability throughout that is less than the predetermined durability of the cover  180 .  
      In one embodiment, the cover  180  is a metallic wire mesh, however, it should be understood that the cover  180  may be any material, and may be fabricated in any material configuration, having a durability greater than a predetermined durability of a portion of the flap seal body  80 , and more specifically, a portion of the flap seal body  80  that includes the cover  180  bonded thereto, as described below. In one embodiment, the cover  180  is a metallic wire mesh fabricated from a nickel-based alloy, such as, for example, HAYNES® HASTELLOY X™ alloy, commercially available from Haynes International, Inc., Kokomo, Ind. In another embodiment, the cover  180  is a metallic wire mesh fabricated from a cobalt-based alloy, such as, for example, HAYNES® alloy  188 , commercially available from Haynes International, Inc., Kokomo, Ind. In yet another embodiment, the cover  180  is a metallic wire mesh fabricated from stainless steel, such as, for example, stainless steel grade  316  commercially available from Cleveland Wire Cloth, Cleveland, Ohio.  
       FIG. 10  is a perspective view of the flap seal body  80  having a plurality of the covers  180  bonded thereto to increase a durability of the seal body  80  generally adjacent the ends  102 ,  104 , and  106 . In the exemplary embodiment, a plurality of the covers  180  are bonded to the seal body  80 . However, it should be understood that the seal body  80  may have any number of the covers  180  bonded thereto. For example, in an alternative embodiment, the body  80  has only one cover  180  bonded thereto. Additionally, in the exemplary embodiment, the body  80  includes a plurality of the covers  180  that are each bonded to the seal body  80  adjacent a corresponding end  102 ,  104 , and  106 . However, it should be understood that the seal body  80  may include a cover  180  bonded thereto adjacent the body end  100 .  
      The covers  180 , referred to herein as the covers  180   a ,  180   b , and  180   c  with regard to  FIG. 10 , are bonded to the seal body  80  using an adhesive. In one embodiment, the adhesive used to bond the covers  180   a ,  180   b , and  180   c  to the seal body  80  is a ceramic adhesive, for example, a ceramic adhesive produced by combining a glass powder, for example, SP921® glass powder from Specialty Glass, Florida, and an alumina powder with a silica yielding polymer. Another example of a ceramic adhesive is Cotronics 901® adhesive, available from Cotronics Corporation, Brooklyn, N.Y. Additionally, prior to bonding the covers  180   a ,  180   b , and  180   c  to the flap seal body  80 , the seal body mating surfaces  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144 ,  146 ,  148 , and  150  are cleaned by slightly sanding the surfaces and applying a solvent, for example acetone or isopropanol, to provide a substantially wetable surface that facilitates adhesion between the adhesive and the mating surfaces.  
      After cleaning, the adhesive is applied to some or all of the mating sides  188 ,  190 ,  192 ,  194 , and  196  of each cover  180   a ,  180   b , and  180   c , in addition to the seal body mating surfaces  130 ,  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144 ,  146 ,  148 , and  150 . The covers  180   a ,  180   b , and  180   c  are then positioned on the seal body  80  over the respective ends  102 ,  104 , and  106 , as illustrated in  FIG. 10 . More specifically, the cover  180   a  is positioned over the end  102  such that the mating sides  188 ,  190 ,  192 ,  194 , and  196  of the cover  180   a  contact the respective mating surfaces  132 ,  148 ,  136 ,  150 , and  146  of the body  80 , and accordingly, the cover  180   a  overlaps the seal body edges  168 ,  170 ,  172 , and  174 . Additionally, the cover  180   b  is positioned over the end  104  such that the mating sides  188 ,  190 ,  192 ,  194 , and  196  of the cover  180   b  contact the respective mating surfaces  132 ,  134 ,  136 ,  138 , and  130  of the body  80 , and accordingly, the cover  180   b  overlaps the seal body edges  152 ,  154 ,  156 , and  158 . Furthermore, the cover  180   c  is positioned over the end  106  such that the mating sides  188 ,  190 ,  192 ,  194 , and  196  of the cover  180   c  contact the respective mating surfaces  136 ,  142 ,  132 ,  140 , and  144  of the body  80 , and accordingly, the cover  180   c  overlaps the seal body edges  160 ,  162 ,  164 , and  166 . Once dry, the adhesive bonds the covers  180  to the seal body  80 . The greater durability of the covers  180  with respect to the body  80  facilitates increasing the durability of the seal body ends  102 ,  104 , and  106  by reinforcing the body  80  adjacent the ends  102 ,  104 , and  106 .  
      In the exemplary embodiment, the covers  180   a ,  180   b , and  180   c  each substantially overlap the respective ends  102 ,  104 , and  106 . However, it will be understood that the covers  180   a ,  180   b , and  180   c  may each overlap only a portion of the respective ends  102 ,  104 , and  106 . Additionally, in the exemplary embodiment, the covers  180   a ,  180   b , and  180   c  each substantially overlap the respective edges  168 ,  170 ,  172 ,  174 ,  152 ,  154 ,  156 ,  158 ,  160 ,  162 ,  164 , and  166 . However, it will be understood that the covers  180   a ,  180   b , and  180   c  may each overlap only a portion of the respective edges  168 ,  170 ,  172 ,  174 ,  152 ,  154 ,  156 ,  158 ,  160 ,  162 ,  164 , and  166 .  
      Although the seal body  80  is herein described and illustrated in the exemplary manner, it should be understood that the seal body  80  may include any number of covers  180  each bonded to any portion of the body  80  such that at least one cover  180  overlaps at least a portion of the body  80 .  
      The above-described cover is cost-effective and reliable for increasing a durability of a ceramic matrix composite material. More specifically, the cover facilitates reinforcing a portion of the ceramic matrix composite material. As a result, the cover may increase the performance and useful life of the ceramic matrix composite material, and thereby reduce replacement costs. Additionally, the cover may increase a wear resistance and a strain to failure ratio of the ceramic matrix composite material, and may allow the ceramic matrix composite material to experience higher thermal gradients without failing. In the exemplary embodiment, the cover facilitates increasing the performance and useful life of a gas turbine engine exhaust seal. As a result, the exemplary cover facilitates reducing a number of exhaust nozzle seals that are replaced within a gas turbine engine to maintain a desired operational efficiency of the engine.  
      Although the invention is herein described and illustrated in association with a gas turbine engine, and more specifically, in association with an exhaust nozzle seal for use with a gas turbine engine, it should be understood that the present invention is applicable to any ceramic matrix composite material. Accordingly, practice of the present invention is not limited to gas turbine engine exhaust nozzle seals nor gas turbine engines generally. Additionally, practice of the present invention is not limited to gas turbine engine exhaust nozzle seals that are fabricated from ceramic matrix composite materials. Rather, it should be understood that the present invention is applicable to gas turbine engine seals that are fabricated from materials other than ceramic matrix composite materials.  
      Exemplary embodiments of gas turbine engine exhaust nozzle assemblies are described above in detail. The assemblies are not limited to the specific embodiments described herein, but rather, components of each assembly may be utilized independently and separately from other components described herein. Each exhaust nozzle assembly component can also be used in combination with other exhaust nozzle assembly components.  
      When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.  
      As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.