Abstract:
Self-balancing face seals and gas turbine engine systems involving such seals are provided. In this regard, a representative self-balancing face seal assembly includes: a rotatable seal runner having a first seal runner face and an opposing second seal runner face; a first face seal operative to form a first seal with the first seal runner face, the first face seal being one of a hydrostatic seal and a hydrodynamic seal; and a second face seal operative to form a second seal with the second seal runner face, the first face seal being one of a hydrostatic seal and a hydrodynamic seal.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The disclosure generally relates to gas turbine engines. 
         [0003]    2. Description of the Related Art 
         [0004]    A gas turbine engine typically maintains pressure differentials between various components during operation. These pressure differentials are commonly maintained by various configurations of seals. In this regard, labyrinth seals oftentimes are used in gas turbine engines. As is known, labyrinth seals tend to deteriorate over time. By way of example, a labyrinth seal can deteriorate due to rub interactions from thermal and mechanical growths, assembly tolerances, engine loads and maneuver deflections. Unfortunately, such deterioration can cause increased flow consumption resulting in increased parasitic losses and thermodynamic cycle loss. 
       SUMMARY 
       [0005]    Self-balancing face seals and gas turbine engine systems involving such seals are provided. In this regard, an exemplary embodiment of a self-balancing face seal assembly comprises: a rotatable seal runner having a first seal runner face and an opposing second seal runner face; a first face seal operative to form a first seal with the first seal runner face, the first face seal being one of a hydrostatic seal and a hydrodynamic seal; and a second face seal operative to form a second seal with the second seal runner face, the second face seal being one of a hydrostatic seal and a hydrodynamic seal. 
         [0006]    An exemplary embodiment of a turbine assembly for a gas turbine engine comprises: a turbine having rotatable blades and a self-balancing face seal assembly; the self-balancing face seal assembly having a seal runner, a first face seal and a second face seal; the seal runner having a first seal runner face and a second seal runner face; the first face seal being operative to form a first seal with the first seal runner face, the first face seal being one of a hydrostatic seal and a hydrodynamic seal; and the second face seal being operative to form a second seal with the second seal runner face, the second face seal being one of a hydrostatic seal and a hydrodynamic seal. 
         [0007]    An exemplary embodiment of a gas turbine engine comprises: a compressor; a shaft interconnected with the compressor; and a turbine operative to drive the shaft, the turbine having a self-balancing face seal assembly having a seal runner, a first face seal and a second face seal; the seal runner having a first seal runner face and a second seal runner face; the first face seal being operative to form a first seal with the first seal runner face, the first face seal being one of a hydrostatic seal and a hydrodynamic seal; and the second face seal being operative to form a second seal with the second seal runner face, the second face seal being one of a hydrostatic seal and a hydrodynamic seal. 
         [0008]    Other systems, methods, features and/or advantages of this disclosure will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be within the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0010]      FIG. 1  is a schematic diagram depicting an exemplary embodiment of a self-balancing face seal. 
           [0011]      FIG. 2  is a schematic diagram depicting an exemplary embodiment of a gas turbine engine. 
           [0012]      FIG. 3  is a schematic diagram depicting a portion of the low-pressure turbine of  FIG. 2 , showing detail of the embodiment of the self-balancing face seal of  FIG. 1  installed therein. 
           [0013]      FIG. 4  is a schematic diagram depicting an exemplary embodiment of a self-balancing face seal using hydrostatic balancing forces. 
           [0014]      FIG. 5  is a schematic diagram depicting an exemplary embodiment of a self-balancing face seal using hydrodynamic balancing forces. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Self-balancing face seals and gas turbine engine systems involving such seals are provided, several exemplary embodiments of which will be described in detail. In this regard, self-balancing face seals use hydrostatic and/or hydrodynamic forces to position adjustable seal faces adjacent to the opposing sides of a seal runner. In some embodiments, a self-balancing face seal can be used at various locations of a gas turbine engine, for example, such as in association with a low-pressure turbine. 
         [0016]    An exemplary embodiment of a self-balancing face seal assembly is depicted schematically in  FIG. 1 . As shown in  FIG. 1 , face seal assembly  10  incorporates opposing face seals  12  and  14  that are formed by portions of a stationary stator assembly  16  and a portion of a rotating rotor assembly  18 . Specifically, rotor assembly  18  provides a seal runner  20 . 
         [0017]    Stator assembly  16  includes an arm  22  that facilitates attachment, removal and/or placement of the face seals. A carrier  24  of the stator assembly includes a carrier member  26  (which carries face seal  12 ) and a carrier member  28  (which carries face seal  14 ). Carrier  24  accommodates differential thermal growth of the rotor assembly and the stator assembly. Notably, each of the face seals is annular in shape. 
         [0018]    Each of the face seals  12 , 14  includes a seal face (i.e., a seal-forming surface). Specifically, face seal  12  includes a seal face  32  and face seal  14  includes a seal face  34 . Carrier member  26  is axially translatable so that seal face  32  can move, with carrier member  26 , away from or toward face  42  of seal runner  20 . Similarly, carrier member  28  is axially translatable so that seal face  34  can move, with carrier member  28 , away from or toward face  44  of seal runner  20 . 
         [0019]    In this embodiment, an anti-rotation feature  46  is provided to prevent circumferential displacement of carrier member  26  with respect to the arm  22  and to assist in aligning the carrier member  26  to facilitate axial translation. An anti-rotation feature  48  is provided to prevent circumferential displacement of carrier member  28  with respect to carrier member  26 . 
         [0020]    A biasing member  50 , which is provided as a spring in this embodiment, biases the carrier members  26 ,  28  together to establish a defined clearance between the seal faces  32 ,  34 . In this regard, the defined clearance can be selected to maintain a desired pressure differential between a high-pressure side (P HIGH ) and a low-pressure side (P LOW ) of the seal assembly. Notably, multiple biasing members may be spaced about the carrier. Additionally, a secondary seal  52  (e.g., a piston ring) is captured between opposing surfaces  54 ,  56  of the arm  22  and carrier member  26 , respectively, to control gas leakage between the arm and the carrier. 
         [0021]    In operation, interaction between seal face  32  and seal runner face  42  results in pneumatic forces urging seal face  32  away from seal runner face  42 . Simultaneously, however, interaction between seal face  34  and seal runner face  44  results in other pneumatic forces urging seal face  34  away from seal runner face  44 . These competing pneumatic forces, when balanced, tend to cause centering of the seal runner between the opposing seal faces  42 ,  44 , thereby establishing the desired sealing between the low-pressure side (P LOW ) and the high-pressure side (P HIGH ) of the seal assembly  10 . 
         [0022]    Notably, either or both of face seals  12  and  14  can be hydrostatic seals or hydrodynamic seals. In this regard, a hydrostatic seal is a seal that uses balanced static pressure forces as opening and closing forces to maintain a desired separation between a seal face and a corresponding seal runner. A hydrodynamic seal is a seal that uses balanced dynamic pressure forces as opening and closing forces to maintain a desired separation between a seal face and a corresponding seal runner. In a hydrodynamic seal, one or both of the seal face and corresponding seal runner can include surface features for generating the dynamic pressure forces when the seal runner rotates relative to the seal face. Typically, both face seals of a particular seal assembly are of the same type. 
         [0023]    During normal operating conditions, the seal faces  32 ,  34  and the seal runner faces  42 ,  44  should not contact each other. In this regard, a material containing carbon can be used as a seal face material. It should be noted, however, that carbon can fracture or otherwise be damaged due to unintended contact (e.g., excessively forceful contact) between the seal face and the seal runner as may be caused by severe pressure fluctuations and/or vibrations, for example. It should also be noted that carbon may be susceptible to deterioration at higher temperatures. Therefore, carbon should be used in locations where predicted temperatures are not excessive such as in the low-pressure turbine. By way of example, use of such a material may not be appropriate, in some embodiments, in a high-pressure turbine. 
         [0024]      FIG. 2  is a schematic diagram depicting an exemplary embodiment of a gas turbine engine that incorporates at least one self-balancing face seal. As shown in  FIG. 2 , engine  100  is configured as a turbofan gas turbine engine that incorporates a fan  102 , a compressor section  104 , a combustion section  106  and a turbine section  108 . Although the embodiment of  FIG. 2  is configured as a turbofan, there is no intention to limit the concepts described herein to use with turbofans. That is, self-balancing face seals can be used in various other configurations of gas turbine engines, as well as in other systems in which maintaining a pressure differential between rotating and non-rotating components is desired. 
         [0025]    In the embodiment of  FIG. 2 , engine  100  is a dual spool engine that includes a high-pressure turbine  110  interconnected with a high-pressure compressor  112  via a shaft  114 , and a low-pressure turbine  120  interconnected with a low-pressure compressor  122  via a shaft  124 . 
         [0026]    As shown in  FIG. 3 , low-pressure turbine  120  defines a primary gas flow path  130  along which multiple rotating blades (e.g., blade  132 ) and stationary vanes (e.g., vane  134 ) are located. In this embodiment, the blades are mounted to turbine disks, the respective webs and bores of which extend into a high-pressure cavity  140 . For instance, disk  142  includes a web  144  and a bore  146 , each of which extends into cavity  140 . 
         [0027]    A relatively lower-pressure cavity  148  is oriented between high-pressure cavity  140  and turbine hub  150 , with a self-balancing face seal assembly  10  (described in detail before with respect to  FIG. 1 ) being provided to maintain a pressure differential between the high-pressure cavity and the lower-pressure cavity. It should also be noted that although this embodiment is described as incorporating a self-balancing face seal in association with a low-pressure turbine, such seals are not limited to use with low-pressure turbines when used in gas turbine engines. 
         [0028]    In the implementation of  FIG. 3 , the rotor assembly  18  (which includes the seal runner  20 ) is provided by a removable bracket that is mounted to the low-pressure turbine hub  150 . The stator assembly  16  (which provides arm  22  and carrier  24 ) is provided by a removable bracket that is mounted to a stationary portion of the engine. By providing seal assembly  10  as a removable assembly, the location of which can be adjusted axially and/or radially, thrust balance trimming of engine  100  can be at least partially accommodated by altering the position of the seal assembly to adjust the volume of cavities  140  and  148 . 
         [0029]    Another exemplary embodiment of a self-balancing face seal assembly is depicted schematically in  FIG. 4 . As shown in  FIG. 4 , face seal assembly  210  incorporates opposing hydrostatic face seals  212  and  214  that are formed by portions of a stationary stator assembly  216  and a portion of a rotating rotor assembly  218 . Specifically, rotor assembly  218  provides a seal runner  220 . 
         [0030]    Stator assembly  216  includes an arm  222  that facilitates attachment, removal and/or placement of the face seals. A carrier  224  of the stator assembly includes a carrier member  226  (which carries face seal  212 ) and a carrier member  228  (which carries face seal  214 ). 
         [0031]    Hydrostatic face seal  214  includes a seal face  234 , a seal dam  239 , and an air bearing  243  that is fed via air passage  241  with air from the high-pressure side (P HIGH ) of the seal assembly  210 . Air bearing air and leakage air passing air dam  239  will be discharged into a plenum  280  formed between hydrostatic face seal  214 , hydrostatic face seal  212 , rotor assembly  218 , and carrier  224 . Air pressure in plenum  280  will be at an intermediate pressure (P INT ) that is smaller than the high pressure side (P HIGH ) but larger than the low pressure side (P LOW ) of assembly  210 . Hydrostatic face seal  212  includes a seal face  232 , which incorporates a seal dam  233 , and air bearing  237  that is fed via air passage  235  with air from the intermediate-pressure plenum  280 . Air bearing air and leakage air passing air dam  233  will be discharged to the low pressure side (P LOW ) of assembly  210 . 
         [0032]    In operation, interaction between seal face  232  and seal runner face  242  results in hydrostatic forces urging seal face  232  away from seal runner face  242 . Simultaneously, however, interaction between seal face  234  and seal runner face  244  results in other hydrostatic forces urging seal face  234  away from seal runner face  244 . These competing hydrostatic forces can be balances by compensating the decrease in air bearing supply pressure from P HIGH  at hydrostatic face seal  214  to P INT  at hydrostatic face seal  212  with a corresponding increase in air bearing size from air bearing  243  to air bearing  237 . Hydrostatic forces, when balanced, tend to cause centering of the seal runner between the opposing seal faces  242 ,  244 , thereby establishing the desired sealing between the low-pressure side (P LOW ) and the high-pressure side (P HIGH ) of the seal assembly  210 . 
         [0033]    Carrier member  226  is axially translatable so that seal face  232  can move, with carrier member  226 , away from or toward face  242  of seal runner  220 . Similarly, carrier member  228  is axially translatable so that seal face  234  can move, with carrier member  228 , away from or toward face  244  of seal runner  220 . 
         [0034]    An anti-rotation feature  246  is provided to prevent circumferential displacement of carrier member  226  with respect to the arm  222  and to assist in aligning the carrier member  226  to facilitate axial translation. An anti-rotation feature  248  is provided to prevent circumferential displacement of carrier member  228  with respect to carrier member  226 . 
         [0035]    A biasing member  250 , biases the carrier members  226 ,  228  together to establish a defined clearance between the seal faces  232 ,  234 . Additionally, a piston ring  252  is captured between opposing surfaces  254 ,  256  of the arm  222  and carrier member  226 , respectively, to control gas leakage between the arm and the carrier. 
         [0036]    Another exemplary embodiment of a self-balancing face seal assembly is depicted schematically in  FIG. 5 . As shown in  FIG. 5 , face seal assembly  310  incorporates opposing hydrodynamic face seals  312  and  314  that are formed by portions of a stationary stator assembly  316  and a portion of a rotating rotor assembly  318 . Specifically, rotor assembly  318  provides a seal runner  320 . 
         [0037]    Stator assembly  316  includes an arm  322  that facilitates attachment, removal and/or placement of the face seals. A carrier  324  of the stator assembly includes a carrier member  326  (which carries face seal  312 ) and a carrier member  328  (which carries face seal  314 ). 
         [0038]    Hydrodynamic face seal  312  includes a seal face  332 , and hydrodynamic face seal  314  includes a seal face  334 . Carrier member  226  is axially translatable so that seal face  332  can move, with carrier member  326 , away from or toward face  342  of seal runner  320 . Similarly, carrier member  328  is axially translatable so that seal face  334  can move, with carrier member  328 , away from or toward face  344  of seal runner  320 . Notably, one or both of seal face  332  and seal runner face  342  can include surface features for generating hydrodynamic forces when the seal runner rotates relative to the seal face. Additionally, one or both of seal face  334  and seal runner face  344  can include surface features for generating hydrodynamic forces. 
         [0039]    An anti-rotation feature  346  is provided to prevent circumferential displacement of carrier member  326  with respect to the arm  322  and to assist in aligning the carrier member  326  to facilitate axial translation. An anti-rotation feature  348  is provided to prevent circumferential displacement of carrier member  328  with respect to carrier member  326 . 
         [0040]    A biasing member  350 , biases the carrier members  326 ,  328  to establish a defined clearance between the seal faces  332 ,  334 . Additionally, a secondary seal  352  is positioned between opposing surfaces  354 ,  356  of the arm  322  and carrier member  326 , respectively, to control gas leakage between the arm and the carrier. 
         [0041]    In operation, interaction between seal face  332  and seal runner face  342  results in hydrodynamic forces urging seal face  332  away from seal runner face  342 . Simultaneously, however, interaction between seal face  334  and seal runner face  344  results in other hydrodynamic forces urging seal face  334  away from seal runner face  344 . These competing forces, when balanced, tend to cause centering of the seal runner between the opposing seal faces  342 ,  344 , thereby establishing the desired sealing between the low-pressure side (P LOW ) and the high-pressure side (P HIGH ) of the seal assembly  310 . 
         [0042]    Notably, It should be emphasized that the above-described embodiments are merely possible examples of implementations set forth for a clear understanding of the principles of this disclosure. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the accompanying claims.