Abstract:
Gas turbine engine systems involving hydrostatic face seals with integrated back-up seals are provided. In this regard, a representative seal assembly for a gas turbine engine includes: a stator assembly and a rotor assembly configured to operatively engage each other to form a first seal and a second seal; the first seal being provided by a hydrostatic seal having a seal face and a seal runner; and the second seal being provided by a back-up seal such that responsive to a failure of the first seal, the back-up seal maintains at least a portion of a pressure differential established by the first seal prior to the failure.

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]    Gas turbine engine systems involving hydrostatic face seals with integrated back-up seals are provided. In this regard, an exemplary embodiment of a seal assembly for a gas turbine engine comprises: a stator assembly and a rotor assembly configured to operatively engage each other to form a first seal and a second seal; the first seal being provided by a hydrostatic seal having a seal face and a seal runner; and the second seal being provided by a back-up seal such that responsive to a failure of the first seal, the back-up seal maintains at least a portion of a pressure differential established by the first seal prior to the failure. 
         [0006]    An exemplary embodiment of a turbine assembly for a gas turbine engine comprises: a turbine having a hydrostatic seal and a back-up seal; the hydrostatic seal having a carrier, a seal face and a seal runner, the carrier being operative to position the seal face relative to the seal runner; the back-up seal having a first seal-forming component and a second seal-forming component, one of first seal-forming component and a second seal-forming component being mounted to the carrier, the back-up seal being operative such that responsive to a failure of the hydrostatic seal, the back-up seal maintains at least a portion of a pressure differential established by the hydrostatic seal prior to the failure. 
         [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 hydrostatic seal and an integrated back-up seal; wherein, in a normal mode of operation of the hydrostatic seal, interaction of the seal face and the seal runner maintains a pressure differential within the gas turbine engine and, in a failure mode of operation of the hydrostatic seal, the back-up seal maintains at least a portion of the pressure differential within the gas turbine engine. 
         [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 hydrostatic face seal with integrated back-up 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 hydrostatic face seal with integrated back-up seal of  FIG. 1  installed therein. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Gas turbine engine systems involving hydrostatic face seals with integrated back-up seals are provided, several exemplary embodiments of which will be described in detail. In this regard, hydrostatic face seals can be used at various locations of a gas turbine engine, such as in association with a low-pressure turbine. Notably, a hydrostatic seal is a seal that uses balanced opening and closing forces to maintain a desired separation between a seal face and a corresponding seal runner. Unanticipated pressure fluctuations and/or vibrations could cause undesired contact between the seal face and the corresponding seal runner that can cause damage to the seal, e.g., carbon fracture. To mitigate the potential consequence of a damaged hydrostatic face seal, a back-up seal can be provided that is integrated with one or more components forming the hydrostatic seal. 
         [0014]    An exemplary embodiment of a hydrostatic face seal with an integrated back-up seal (collectively referred to herein as a “seal assembly”) is depicted schematically in  FIG. 1 . As shown in  FIG. 1 , seal assembly  10  incorporates a hydrostatic face seal  12  and a back-up seal  14  that are provided by a stationary stator assembly  16  and a rotating rotor assembly  18 . In general, the stator assembly incorporates the seal face of the associated hydrostatic face seal, as well as one or more of the primary components of the back-up seal. In contrast, the rotor assembly incorporates the seal runner of the hydrostatic face seal and others of the primary components of the back-up seal. Notably, when the back-up seal is a labyrinth seal, the stator assembly carries either the honeycomb lands or the knife edges, whereas the rotor carries the corresponding feature of the seal. In the embodiment of  FIG. 1 , the stator assembly incorporates the honeycomb lands and the rotor assembly incorporates the knife edges as will be described in detail. 
         [0015]    With respect to the stator assembly, stator assembly  16  includes an arm  17  that extends from a mounting bracket  19 . Mounting bracket  19  facilitates attachment, removal and/or position adjustment of the stator assembly. Notably, other embodiments may not incorporate mounting brackets for ease of installation and/or removal. 
         [0016]    Stator assembly  16  incorporates a carrier  20  that carries face seal  22 , which is annular in shape. Face seal  22  includes a seal face  24 , which is one of the seal-forming surfaces of the hydrostatic seal. Carrier  20  is axially translatable so that seal face  24  can move, with the carrier, away from or toward (e.g., into contact with) a seal runner  26  (which is the other of the seal-forming components of the hydrostatic seal) of rotor assembly  18 . In this embodiment, an anti-rotation lock  28  is provided to prevent circumferential displacement and to assist in aligning the seal carrier to facilitate axial translation. 
         [0017]    A biasing member  30 , which is provided as a spring in this embodiment, biases the seal face against the seal runner until overcome by gas pressure. In this regard, the biasing force of the biasing member 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. Multiple biasing members may be spaced about the stator and carrier. Notably, a piston ring  32  is captured between opposing surfaces  34 ,  36  of the stator assembly and carrier, respectively, to control gas leakage between the arm of the stator assembly and the carrier. 
         [0018]    Surface  40  of the carrier mounts lands  42 ,  44  of the labyrinth-type back-up seal  14 . The lands may be comprised of an abradable structure such as honeycomb. Corresponding knife edges  52 ,  54  of the labyrinth-type back-up seal are carried by the rotor assembly. 
         [0019]    With respect to the rotor assembly, rotor assembly  18  supports the seal runner  26 , which is annular in shape. Specifically, the rotor assembly includes an arm  56  that extends from a mounting bracket  58 . Mounting bracket  58  facilitates attachment, removal and/or position adjustment of the rotor assembly. 
         [0020]    The knife edges  52 ,  54  of the labyrinth-type back-up seal are supported by an annular extension  60  that extends from the arm of the rotor assembly. Thus, extension  60  assists in defining an intermediate-pressure cavity  62  that is located between the hydrostatic seal and the back-up seal. Note also that extension  60  can assist in preventing debris (e.g., debris that may by attributable to unintended damage of the hydrostatic seal) from passing beyond the back-up seal. 
         [0021]    In a normal mode of operation (i.e., when the hydrostatic face seal is properly seated), the desired pressure differential is maintained, at least primarily, across the hydrostatic face seal  12 . However, in a failure mode of operation (i.e., when the hydrostatic face seal fails due to unintended circumstances), a corresponding pressure differential is maintained, at least primarily, across the back-up seal  14 . Thus, in the failure mode of operation, intermediate-pressure cavity  62  typically exhibits P HIGH . 
         [0022]      FIG. 2  is a schematic diagram depicting an exemplary embodiment of a gas turbine engine, in which an embodiment of a hydrostatic face seal with integrated back-up seal can be used. As shown in  FIG. 2 , engine  100  is configured as a turbofan 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, as various other configurations of gas turbine engines can be used. 
         [0023]    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 . It should also be noted that although various embodiments are described as incorporating hydrostatic face seals in low-pressure turbines, such seals are not limited to use with low-pressure turbines. 
         [0024]    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 . 
         [0025]    A relatively lower-pressure cavity  148  is oriented between high-pressure cavity  140  and turbine hub  150 , with a 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. Seal assembly  10  incorporates a hydrostatic face seal  12  and a back-up seal  14  that are provided by a stator assembly  16  and a rotor assembly  18 . Notably, the stator assembly is mounted to a non-rotating structure of the turbine, whereas the rotor assembly is mounted to a rotating structure. In the implementation of  FIG. 3 , the rotor assembly is mounted to the low-pressure turbine hub  150 . Additionally, an intermediate-pressure cavity  151  is defined between hydrostatic face seal  12  and back-up seal  14 . 
         [0026]    It should be noted that seal assembly  10  is provided as a removable assembly, the location of which can be adjusted axially and radially. As such, 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   
         [0027]    In operation, the seal face intermittently contacts the seal runner. By way of example, contact between the seal face and the seal runner can occur during sub-idle conditions and/or during transient conditions. That is, contact between the seal face and the seal runner is maintained until gas pressure in the high-pressure cavity is adequate to overcome the biasing force, thereby separating the seal face from the seal runner. During normal operating conditions, however, the seal face and the seal runner should not contact each other. 
         [0028]    Since the embodiments described herein are configured as lift-off seals (i.e., at least intermittent contact is expected), materials forming the surfaces that will contact each other are selected, at least in part, for their durability. 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. 
         [0029]    In a normal mode of operation (i.e., when the hydrostatic seal is properly functioning), a nominal pressure differential exists between intermediate-pressure cavity  151  and lower-pressure cavity  148 . That is, the pressure differential between the high-pressure cavity and the lower-pressure cavity is maintained, at least primarily, across the hydrostatic face seal  12 . However, in a failure mode of operation (i.e., the hydrostatic seal fails), the pressure of the high-pressure cavity  140  is depleted to a level lower than during the normal mode of operation but higher than that of intermediate cavity  151  during normal operation. The increase in pressure differential across the back-up seal  14  is due to the increased flow rate imposed on the back-up seal during failure of the primary seal. Thus, in the failure mode of operation, pressure in intermediate cavity  151  increases and a corresponding pressure differential is maintained, at least primarily, across the back-up seal  14 . 
         [0030]    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. By way of example, although the embodiments described herein are configured as lift-off seals, other types of seals can be used. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the accompanying claims.