Patent Publication Number: US-10760500-B2

Title: Composite piston ring seal for axially and circumferentially translating ducts

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of, and claims priority to, U.S. application Ser. No. 14/727,475, filed Jun. 1, 2015 and titled “COMPOSITE PISTON RING SEAL FOR AXIALLY AND CIRCUMFERENTIALLY TRANSLATING DUCTS.” The &#39;475 application is hereby incorporated by reference in its entirety. 
    
    
     GOVERNMENT LICENSE RIGHTS 
     This disclosure was made with Government support under Contract No. FA8650-09-D-2923 awarded by the United States Air Force. The U.S. Government has certain rights in the disclosure. 
    
    
     FIELD 
     The present disclosure relates to gas turbine engines, and, more specifically, to gas path duct sealing for gas turbine engines. 
     BACKGROUND 
     Gas turbine engines may have various gas-flow streams that may be kept separate from one another. The gas-flow streams may be separated by components including cowls and seals. A pair of annular cowls may align with one another, but relative translation in axial and circumferential directions may create varying relative motion between the cowls during operation. The varying relative motion may be sealed to maintain separate gas-flow streams, but the varying relative may tear seals or render the seals ineffective. For example, finger seals in such a configuration may risk catching an edge of the nozzle since a cowl may move diagonally across the fingers. 
     SUMMARY 
     A gas turbine engine may comprise a compressor, a combustor disposed aft of the compressor and in fluid communication with the compressor, and a turbine aft of the combustor and in fluid communication with the combustor. An inner duct may be disposed radially outward from the turbine, and an outer duct may be disposed radially outward from the inner duct. A groove may be formed in the inner duct, and a piston may be configured to slideably engage the groove. 
     In various embodiments, the piston may comprise a fibrous material. The piston may also comprise at least one of a glass fiber-reinforced polymer (GFRP) or an aramid fiber-reinforced polymer (AFRP). A bumper may be bonded to the inner duct. The bumper may comprise at least one of a GFRP or an AFRP. The bumper may comprise an annular geometry. The bumper may be disposed in a recess in the inner duct. The piston may comprise an elliptical shape. A spring may be disposed in the groove. The piston may be configured to bottom in the groove and locate the inner duct separate from the outer duct. 
     A seal system may comprise a first duct having an annular geometry, a second duct overlapping the first duct in a radial direction, and a seal disposed between the first duct and the second duct. The seal may comprise a groove defined by the first duct and a piston configured to slideably engage the groove. 
     In various embodiments, the piston may include a fibrous material. The piston may comprise a GFRP or an AFRP. A bumper may be bonded to the first duct. The bumper may comprise at least one of a GFRP or an AFRP, and may also have an annular geometry. The bumper may be disposed in a recess in the first duct. The piston may comprise an elliptical shape. A spring may be disposed in the groove. 
     A seal may comprise a groove defined by a first duct. The groove may have metallic walls. A piston may include a composite material and configured to slideably engage the groove. 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the figures, wherein like numerals denote like elements. 
         FIG. 1  illustrates an exemplary gas-turbine engine, in accordance with various embodiments; 
         FIG. 2  illustrates a split ring seal axially adjacent to a cowl that is prone to axial and circumferential translation, in accordance with various embodiments; 
         FIG. 3  illustrates a cross section of a split ring seal coupled to an outer duct and comprising a wave spring, in accordance with various embodiments; 
         FIG. 4  illustrates a cross section of a split ring seal coupled to an outer duct and comprising composite bumper pads between the outer duct and inner duct, in accordance with various embodiments; 
         FIG. 5  illustrates a cross section of a split ring seal coupled to an outer duct and comprising a composite bumper ring between the inner duct and outer duct, in accordance with various embodiments; 
         FIG. 6  illustrates a cross section of a split ring seal coupled to an inner duct and comprising a wave spring, in accordance with various embodiments; 
         FIG. 7  illustrates a cross section of a split ring seal coupled to an inner duct and comprising composite bumper pads between the outer duct and inner duct, in accordance with various embodiments; and 
         FIG. 8  illustrates a cross section of a split ring seal coupled to an inner duct and comprising a composite bumper ring between the inner duct and outer duct, in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the exemplary embodiments of the disclosure, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this disclosure and the teachings herein. Thus, the detailed description herein is presented for purposes of illustration only and not limitation. The steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. 
     Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. Surface shading lines may be used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     As used herein, “aft” refers to the direction associated with the tail (e.g., the back end) of an aircraft, or generally, to the direction of exhaust of the gas turbine. As used herein, “forward” refers to the direction associated with the nose (e.g., the front end) of an aircraft, or generally, to the direction of flight or motion. 
     As used herein, “distal” refers to the direction radially outward, or generally, away from the axis of rotation of a turbine engine. As used herein, “proximal” refers to a direction radially inward, or generally, towards the axis of rotation of a turbine engine. 
     With reference to  FIG. 1 , an exemplary gas turbine engine  100  is shown, in accordance with various embodiments. Gas turbine engine  100  may comprise a fan  102  with a nose cone  104  disposed forward of fan  102 . Nose cone  104  may rotate with fan  102  as fan  102  drives airflow into compressor  106  and bypass ducts  110 . Compressor  106  may be in fluid communication with combustor  112  with the airflow exiting compressor  106  and entering combustor  112 . A fuel-air mixture may be ignited in combustor  112 . 
     In various embodiments, combustor  112  may be in fluid communication with turbine  108  disposed aft of combustor  112 . Combusted gas from combustor  112  expands across turbine  108  to provide rotational energy to compressor  106  and fan  102 . Rotating components of gas turbine engine  100  such as the turbine  108  and compressor  106  may be configured to rotate about axis A. 
     In various embodiments, tail cone  114  may be disposed aft of turbine  108 . An augmentor liner may also be disposed aft of turbine  108 . A nozzle comprising a divergent nozzle section  122  and a convergent nozzle section  126  may be disposed aft of augmentor liner  116 . A proximal bypass duct  120  may be disposed radially outward from compressor  106 , combustor  112 , and turbine  108 . A distal bypass duct  124  may be disposed radially outward from proximal bypass duct  120 . The ducting of proximal bypass duct  120  and distal bypass duct  124  may include sealing section  118 . 
     Large ducting that undergoes movement, such as proximal bypass duct  120  and distal bypass duct  124 , may implement sealing between ducts to maintain ducting during periods of movement. Sealing section  118  may comprise a split ring seal, as described in detail below, to maintain sealing while in duct sections when movement would otherwise cause fluid leaks. 
     With reference to  FIG. 2 , sealing section  118  is shown, in accordance with various embodiments. Sealing section  118  may comprise outer duct  146  and forward cowling  148 . Outer duct  146  and forward cowling  148  may both comprise a cylindrical or annular geometry. During operation, forward cowling  148  and outer duct  146  may translate relative to one another in an axial direction (i.e., forward and aft directions) as well as a circumferential direction (i.e., a rotational direction). Inner duct  140  may be disposed forward of outer duct  146 . Linkage system  142  may comprise swiveling, rigid arms that cause the outer duct  146  to move circumferentially relative to inner duct  140  in response to outer duct  146  moving axially relative to inner duct  140 . 
     With reference to  FIG. 3 , a seal system  150  is shown, in accordance with various embodiments. Seal system  150  may be a split ring seal (also referred to herein as a piston seal) disposed between a forward portion of outer duct  146  and an aft portion of inner duct  140  at a location where outer duct  146  and inner duct  140  overlap in a radial direction. Seal system  150  may comprise groove  168  formed in, and defined by, inner duct  140 . A piston  164  may contact and separate from outer duct  146  and slideably engage groove  168  of inner duct  140 . Inner duct  140  and outer duct  146  may each be made from metallic materials such as titanium, aluminum, stainless steel, alloyed metals, or other suitable metallic materials. The groove  168  defined by inner duct  140  may thus have metallic sidewalls. 
     In various embodiments, piston  164  may comprise a composite material having favorable wear characteristics when sliding against metals. For example, piston  164  may comprise glass fiber-reinforced polymer (GFRP) or an aramid fiber-reinforced polymer (AFRP). The resin used in piston  164  may be selected for performance at high temperatures. For example, the resin used in piston  164  may be selected to operate at temperatures of about 600° F. (315° C.), wherein the term about in this context means +/−50° F. Piston  164  may comprise an annular or ring-shaped flange protruding from outer duct  146  having a circular geometry. The annular shape of piston  164  may also be elongated in some locations so that the cross sectional shape of piston  164  is elliptical or otherwise varies from a circular geometry. The positions of groove  168  and piston  164  may be reversed with groove  168  disposed on outer duct  146  and piston  164  disposed on inner duct  140 . The fibers in piston  164  may be oriented to provide a desired stiffness in various directions (e.g., axially, circumferentially, and radially) at various locations of piston  164  so that piston  164  may deflect and deform in a desired, predetermined shape. 
     In various embodiments, a spring  162  may be disposed between groove  168  and piston  164  to provide mechanical resistance to piston  164  entering groove  168 . Spring  162  may become fully compressed in a radial direction in response to piston  164  traveling a predetermined distance into groove  168  with spring  162  becoming a load bearing member. Spring  162  may be omitted provided that piston  164  has sufficient dimensions to “bottom out” in groove  168  (i.e., translate to a bottom surface of the groove) before outer duct  146  contacts inner duct  140  and thereby locate outer duct  146  separate from inner duct  140 . Thus, seal system  150  may prevent or limit metal-to-metal contact between outer duct  146  and inner duct  140 . Piston  164  may be made of composite materials and may be lighter in weight than a metal piston. Piston  164  may have a ring configuration may have a diameter of approximately 50 inches (127 cm). 
     With reference to  FIG. 4 , seal system  150  comprising bumper  202  between the outer duct  146  and inner duct  190  is shown, in accordance with various embodiments. Seal system  150  of  FIG. 4  is similar to seal system  150  of  FIG. 3 . In  FIG. 4 , seal system  150  comprises groove  198  formed in inner duct  190 . Piston  194  may slideably engage groove  198  with a spring  192  disposed at a proximal end of piston  194 . Piston  194  may have dimensions to maintain gap  200  between outer duct  146  and inner duct  190  in response to outer duct  146  contacting bumper  202 . Bumper  202  may be made from a composite material similar to piston  194  such as a GFRP, AFRP, or other fibrous material within a resin matrix. Bumper  202  may thus exhibit advantageous wear characteristics in response to sliding and/or contacting outer duct  146 . 
     In various embodiments, bumper  202  may be bonded to inner duct  190  to limit deflection and prevent piston  194  from bottoming out in groove  198  (i.e., contacting the radial surface of the groove by traveling radially into the groove). Bumper  202  may be a plurality of discrete bumpers bonded about an outer diameter of inner duct  190 . Bumper  202  may extend forward of outer duct  146  in an axial direction so that bumper  202  is partially exposed from outer duct  146  when viewed in a radially inward direction. Bumper  202  may also be a continuous annular bumper disposed about an outer diameter of inner duct  190 . 
     With reference to  FIG. 5 , seal system  150  comprising bumper  222  recessed in a groove between the outer duct  146  and inner duct  210  is shown to maintain a spacing  220 , in accordance with various embodiments. Seal system  150  of  FIG. 5  is similar to seal system  150  of  FIG. 4 . In  FIG. 5 , seal system  150  comprises piston  214  slideably coupled to groove  218 . Groove  218  may be defined by inner duct  190 . Piston  214  may slideably engage outer duct  146 . Bumper  222  may comprise a bumper ring or annulus lodged in and/or bonded to a recess in inner duct  210  in axial series with piston  214  and groove  218 . Spring  212  may optionally be included to locate piston  214  radially relative to groove  218 . Outer duct  146  may contact bumper  222  to limit the deflection of piston  214  into groove  218 . Bumper  222  may be made from a composite material similar to piston  214  such as GFRP, AFRP, or other fibrous material within a resin matrix. Bumper  222  may thus exhibit advantageous wear characteristics in response to sliding and/or contacting outer duct  146 . 
     With reference to  FIG. 6 , a seal system  230  is shown, in accordance with various embodiments. Seal system  230  may include a piston seal disposed between a forward portion of outer duct  232  and an aft portion of inner duct  234  at a location where outer duct  232  and inner duct  234  overlap in a radial direction. Inner duct  234  and outer duct  232  may each be made from metallic materials such as titanium, aluminum, stainless steel, alloyed metals, or other suitable metallic materials. The groove  168  defined by inner duct  234  may thus have metallic sidewalls. Seal system  230  may comprise groove  236  formed in, and defined by, outer duct  232 . A piston  238  may contact and separate from inner duct  234  and slideably engage groove  236  of outer duct  232 . Outer duct  232  and inner duct  234  may each be made from metallic materials such as titanium, aluminum, stainless steel, alloyed metals, or other suitable metallic materials. The groove  236  defined by outer duct  232  may thus have metallic sidewalls. 
     In various embodiments, piston  238  may comprise a composite material having favorable wear characteristics when sliding against metals. For example, piston  238  may comprise GFRP or an AFRP. The resin used in piston  238  may be selected for performance at high temperatures. For example, the resin used in piston  238  may be selected to operate at temperatures of about 600° F. (315° C.), wherein the term about in this context means +/−50° F. Piston  238  may comprise an annular or ring-shaped flange protruding from inner duct  234  having a circular geometry. The annular shape of piston  238  may also be elongated in some locations so that the cross sectional shape of piston  238  is elliptical or otherwise varies from a circular geometry. The positions of groove  236  and piston  238  may be reversed with groove  236  disposed on inner duct  234  and piston  238  disposed on outer duct  232  (as shown in  FIG. 3 ). The fibers in piston  238  may be oriented to provide a desired stiffness in various directions (e.g., axially, circumferentially, and radially) at various locations of piston  238  so that piston  238  may deflect and deform in a desired, predetermined shape. 
     In various embodiments, a spring  240  may be disposed between groove  236  and piston  238  to provide mechanical resistance to piston  238  entering groove  236 . Spring  240  may become fully compressed in a radial direction in response to piston  238  traveling a predetermined distance into groove  236  with spring  240  becoming a load bearing member. Spring  240  may be omitted provided that piston  238  has sufficient dimensions to “bottom out” in groove  236  (i.e., translate to a bottom surface of the groove) before inner duct  234  contacts outer duct  232  and thereby locate inner duct  234  separate from outer duct  232 . Thus, seal system  230  may prevent or limit metal-to-metal contact between inner duct  234  and outer duct  232 . Piston  238  may be made of composite materials and may be lighter in weight than a metal piston. Piston  238  may have a ring configuration may have a diameter of approximately 50 inches (127 cm). 
     With reference to  FIG. 7 , seal system  250  comprising bumper  260  between the inner duct  254  and outer duct  252  is shown, in accordance with various embodiments. Seal system  250  of  FIG. 7  is similar to seal system  230  of  FIG. 6 . In  FIG. 7 , seal system  250  comprises groove  256  formed in outer duct  252 . Piston  258  may slideably engage groove  256 . Piston  258  may have dimensions to maintain gap  200  between inner duct  254  and outer duct  252  in response to inner duct  254  contacting bumper  260 . Bumper  260  may be made from a composite material similar to piston  258  such as a GFRP, AFRP, or other fibrous material within a resin matrix. Bumper  260  may thus exhibit advantageous wear characteristics in response to sliding and/or contacting inner duct  254 . 
     In various embodiments, bumper  260  may be bonded to outer duct  252  to limit deflection and prevent piston  258  from bottoming out in groove  256  (i.e., contacting the radial surface of the groove by traveling radially into the groove). Bumper  260  may be a plurality of discrete bumpers bonded about an outer diameter of outer duct  252 . Bumper  260  may extend forward of groove  256  in an axial direction so that bumper  260  is partially exposed from inner duct  254  when viewed in a radially outward direction. Bumper  260  may also be a continuous annular bumper disposed about an inner diameter of outer duct  252 . 
     With reference to  FIG. 8 , seal system  270  comprising bumper  280  recessed in a groove between the outer duct  272  and inner duct  274  is shown, in accordance with various embodiments. Seal system  270  is similar to seal system  250  of  FIG. 7 . In  FIG. 8 , seal system  270  comprises piston  276  slideably coupled to groove  278 . Groove  278  may be defined by outer duct  272 . Piston  276  may slideably engage with inner duct  274 . Bumper  280  may comprise a bumper ring or annulus lodged in and/or bonded to a recess in inner duct  274  in axial series with piston  276  and groove  278 . A spring may be included to locate piston  276  radially relative to groove  278 . Inner duct  274  may contact bumper  222  to limit the deflection of piston  276  into groove  278 . Bumper  222  may be made from a composite material similar to piston  276  such as GFRP, AFRP, or other fibrous material within a resin matrix. Bumper  222  may thus exhibit advantageous wear characteristics in response to sliding and/or contacting inner duct  274 . 
     In various embodiments, the seal systems  150  illustrated in  FIGS. 3-8  may be formed by rolling layers of fibrous material around an elliptical or circular spindle, depending on the desired shape of piston  164 . An elliptical spindle shape provides even diametric tension when compressed into a circular housing. A resin matrix may be deposited in and about the fibrous material and cured to form piston  164 . Fibrous material may be oriented to produce high modulus and tensile strength weave with a low modulus orientation on the compression side to reduce compressive stresses. 
     Benefits and other advantages have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, and any elements that may cause any benefit or advantage to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosure. The scope of the disclosure is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. 
     Systems, methods and apparatus are provided herein. In the detailed description herein, references to “various embodiments”, “one embodiment”, “an embodiment”. “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments. 
     Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112(f), unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.