Abstract:
Gas turbine engine systems involving hydrostatic face seals with anti-fouling provisioning are provided. In this regard, a representative turbine assembly for a gas turbine engine comprises: a turbine having a hydrostatic seal; the hydrostatic seal having a seal face, a seal runner, a carrier, and a biasing member; the seal face and the seal runner defining a high-pressure side and a lower-pressure side of the seal; the carrier being operative to position the seal face relative to the seal runner; and the biasing member being located on the lower-pressure side of the seal and being operative to bias the carrier such that interaction of the biasing member and gas pressure across the seal causes the carrier to position the seal face relative to the seal runner.

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure generally relates to gas turbine engines. 
     2. Description of the Related Art 
     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 
     Gas turbine engine systems involving hydrostatic face seals with anti-fouling provisioning are provided. In this regard, an exemplary embodiment of a hydrostatic seal for a gas turbine engine comprises: a face seal having a seal face; a seal runner; and means for reducing a potential for debris to foul the hydrostatic seal formed by the seal face and the seal runner. 
     An exemplary embodiment of a turbine assembly for a gas turbine engine comprises: a turbine having a hydrostatic seal; the hydrostatic seal having a seal face, a seal runner, a carrier, and a biasing member; the seal face and the seal runner defining a high-pressure side and a lower-pressure side of the seal; the carrier being operative to position the seal face relative to the seal runner; and the biasing member being located on the lower-pressure side of the seal and being operative to bias the carrier such that interaction of the biasing member and gas pressure across the seal causes the carrier to position the seal face relative to the seal runner. 
     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; the hydrostatic seal having a seal face, a seal runner and a biasing member; the seal face and the seal runner defining a high-pressure side and a lower-pressure side of the seal; the biasing member being located on the lower-pressure side of the seal and being operative to bias positioning of the seal face relative to the seal runner. 
     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 
       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. 
         FIG. 1  is a schematic diagram depicting an exemplary embodiment of a hydrostatic face seal with anti-fouling provisioning. 
         FIG. 2  is a schematic diagram depicting an exemplary embodiment of a gas turbine engine. 
         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 anti-fouling provisioning of  FIG. 1  installed therein. 
     
    
    
     DETAILED DESCRIPTION 
     Gas turbine engine systems involving hydrostatic face seals with anti-fouling provisioning 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. Use of a hydrostatic face seal requires maintaining a metered airflow through orifices of the seal in order to produce desired seal characteristics. Such a metered airflow can be altered (e.g., interrupted) by the introduction of debris, which may be present in the gas turbine engine for a variety of reasons. 
     In order to reduce the possibility of a seal being fouled by debris, some embodiments incorporate the use of one or more anti-fouling provisions. By way of example, such provisions can include locating one or more potential debris-producing components of the seal to the lower-pressure side of the seal. Additionally or alternatively, an air bearing supply channel of the seal that limits the potential for debris to become stuck in the channel can be used. For instance, in some embodiments, the channel does not incorporate bends. Additionally or alternatively, an air bearing supply channel can be shielded to prevent debris from entering the channel. 
     An exemplary embodiment of a hydrostatic face seal with anti-fouling provisioning is depicted schematically in  FIG. 1 . As shown in  FIG. 1 , hydrostatic face seal  10  is provided by a stationary stator assembly  12  and a rotating rotor assembly  14 . The stator assembly includes an arm  16  that extends from a mounting bracket  18 , which facilitates attachment, removal and/or position adjustment of the stator assembly in the engine. Notably, other embodiments may not incorporate such a mounting bracket. 
     Stator assembly  12  also incorporates a carrier  20  that carries a face seal  22 . Face seal  22  is annular in shape and includes a seal face  24 , which is one of the seal-forming surfaces of the hydrostatic seal. A vent  25  also is provided through face seal  22 . 
     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  14 . In this embodiment, an anti-rotation lock  28  is provided to prevent circumferential movement and assist in aligning the seal carrier to facilitate axial translation of the carrier. 
     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. Multiple springs may be disposed about the circumference of the seal. In this regard, the biasing force of the biasing member can be selected to maintain a desired pressure differential between a high-pressure cavity (P HIGH ) and a lower-pressure cavity (P LOW ) of the seal. 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. 
     With respect to the rotor assembly  14 , rotor assembly  14  supports the seal runner  26 , which is annular in shape. Specifically, the rotor assembly  14  includes an arm  40  that extends from a mounting bracket  42 , which facilitates attachment, removal and/or position adjustment of the rotor assembly  14 . Notably, other embodiments may not incorporate such a mounting bracket. 
     With respect to anti-fouling provisions, the embodiment of  FIG. 1  incorporates several such means. For instance, seal  10  locates the biasing member  30  in the lower-pressure cavity side (P LOW ) of the seal. Notably, the biasing member has the potential to produce debris. By locating the biasing member on the lower-pressure cavity side of the seal, any debris produced by the biasing member will have a tendency to move away from the seal face and the seal runner and, therefore, should not foul the seal. This is in contrast to a seal that locates the biasing member on the high-pressure side. In such an embodiment, debris from the biasing member can be drawn (due to the pressure differential and corresponding gas flow across the seal) between the seal face and seal runner, thus fouling the seal. 
     As another example, seal  10  incorporates an air bearing supply channel  46  that limits the potential for debris to become stuck in the channel. Specifically, air bearing supply channel  46  is formed through face seal  22  from a side  48  (which includes seal face  24 ) to an opposing side  50  (which is attached to carrier  20 ). Notably, carrier  20  includes an orifice  52  that is aligned with the air bearing supply channel. So configured, air can be provided from the high-pressure side of the seal, through orifice  52 , then through air bearing supply channel  46  to seal location  54 , which is located between side  48  and seal runner  26 . 
     In order to reduce the potential for debris to become stuck in the air bearing supply channel, channel  46  of the embodiment of  FIG. 1  does not incorporate bends. That is, the channel is a substantially straight through-hole. While a constant diameter straight through-hole is less susceptible to debris accumulation when compared with internal passages that have sharp bends, it is preferable to tailor the diameter along the tube towards a desired pressure distribution. Thus, in the embodiment of  FIG. 1 , channel  46  includes a cylindrical portion  45  that is interconnected with a cylindrical portion  47  (of smaller diameter) via a conical portion  49  such that the channel exhibits a non-uniform diameter along its length. It should be noted that the cylindrical portion  47  could be connected to orifice  52  without incorporation of a cylindrical portion  45 . In this case, the non-uniform diameter of the channel inside face seal  22  consists of a lead-in conical portion  49  and the cylindrical section  47 . Connecting cylindrical portions  45  and  47  with a conical portion  49  accelerates the flow and reduces residence times of any debris particles. Therefore, the potential for debris accumulation is reduced. 
     Alternatives to straight through-hole configurations that may reduce a tendency for debris to get stuck in the internal face seal channels could involve internal cavities that serve reservoirs. These could be formed by relatively large diameter holes drilled radially inward and deeper than that needed to feed an axial air bearing supply hole, which is typically similar to cylindrical portion  47 . 
     Seal  10  also incorporates a shield for reducing the potential of debris to enter the air bearing supply channel. Specifically, a shield  60  is provided that extends outwardly from carrier  20  in a vicinity of orifice  52 . The shield forms a physical barrier that discourages debris travelling on a radially inward trajectory from entering the orifice. Additionally, for debris to enter orifice  52  of the embodiment of  FIG. 1 , the debris is required to pass through a narrow opening  62  defined by the shield and a surface  64  of the carrier. Notably, since the orifice is located radially outboard of surface  64 , the tortuous path formed by the shield and the orifice location may prevent debris from entering the air bearing supply channel. 
       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 anti-fouling provisioning 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. 
     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 with anti-fouling provisioning in low-pressure turbines, such seals are not limited to use with low-pressure turbines. 
     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 . 
     A relatively lower-pressure cavity  148  is oriented between high-pressure cavity  140  and turbine hub  150 , with a seal  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. Recall that seal assembly  10  incorporates a stator assembly  12  and a rotor assembly  14 . 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 turbine hub  150 . 
     It should be noted that seal  10  is provided as a removable assembly, the location of which can be adjusted. As such, thrust balance trimming of engine  100  can be at least partially accommodated by altering the position of the seal assembly. 
     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. 
     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 comprising carbon can be used as a seal face material. It should be noted, however, that carbon can fracture or otherwise be damaged due to unwanted contact (e.g., excessively forceful contact) between the seal face and the seal runner as may be caused by 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. By way of example, use of such a material may not be appropriate, in some embodiments, in a high-pressure turbine. 
     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.