Abstract:
Aspects of the disclosure are directed to a system associated with an engine of an aircraft, the system comprising: a fluid source that is configured to provide a fluid at a first pressure value, a carbon seal, a seal plate that includes at least one lift-off feature that interfaces to the carbon seal, and a pressure boosting mechanism configured to obtain the fluid from the fluid source, increase the pressure of the fluid to a second pressure value, and provide the fluid at the second pressure value to the at least one lift-off feature.

Description:
BACKGROUND 
       [0001]    Gas turbine engines, such as those which power aircraft and industrial equipment, employ a compressor to compress air that is drawn into the engine and a turbine to capture energy associated with the combustion of a fuel-air mixture. The compressor and turbine employ rotors that include multiple airfoil blades mounted on, or formed integrally with, rims of a plurality of disks mounted on a shaft. Typically, such shafts are rotatably supported on bearings and are lubricated with a lubricant. For example, oil may be disposed within an interior of a bearing compartment. 
         [0002]    Referring to  FIG. 2 , it is known to provide a system  200  that includes a bearing compartment  204  with mechanical seals, such as non-contacting face seals, to reduce (e.g., minimize) the escape of lubricating fluid from forward and aft ends of the bearing compartment. The air outside of these ends is typically at a higher pressure than the pressure of an air-oil mixture inside the bearing compartment  204 . Face seals typically employ a stationary carbon seal  210  and a rotatable seal plate  216  mounted on a rotor shaft  222 . The carbon seal  210  is usually provided with a smooth, continuous (uninterrupted) sealing surface which is disposed in a face-to-face, opposed relationship to a sealing surface of the seal plate  216 . A spacer  228  maintains the seal plate  216  in axial alignment. Like the seal plate  216 , the shaft  222  and the spacer  228  are configured to rotate. 
         [0003]    The sealing surface of the seal plate  216  is often equipped with hydrodynamic (so-called “lift-off”) features  234 , such as with a pattern of spiral grooves. A source  240  of fluid (e.g., air), which is taken from the compressor or a core primary/combustion flowpath, enters the grooves  234  at the entrainment location  246 . The fluid then exits the grooves  234  and consumes at least a portion of a space between the carbon seal  210  and the seal plate  216  from outside the bearing compartment  204 . The fluid is pumped within the spiral grooves  234 , raising the pressure thereof such that the elevated pressure of the fluid within the grooves  234  fauns a fluid barrier between the carbon seal  210  and the seal plate  216  thereby restricting the leakage of the air-oil mixture from inside the bearing compartment  204  into the space between the carbon seal  210  and the seal plate  216 . The pumping characteristics of the grooves  234  to provide the elevated pressure fluid seal between the carbon seal  210  and the seal plate  216  is a function of the geometry of the grooves  234 , the rotational speed of the seal plate  216  and the characteristics of the fluid supplied to the grooves  234  at the entrainment location  246 . 
         [0004]    Since gas turbine engines operate at a wide range of rotational speeds, the ability of the grooves  234  to provide the pressurization of sealing fluid between the carbon seal  210  and the seal plate  216  over a wide range of rotational shaft  222  speeds is imperative. However, when the pressure of the source fluid  240  is relatively low (such as for example at high altitude, sub-ambient pressure conditions) the low density of the fluid  240  compromises the ability of the grooves  234  to generate sufficient pressure. 
       BRIEF SUMMARY 
       [0005]    The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosure. The summary is not an extensive overview of the disclosure. It is neither intended to identify key or critical elements of the disclosure nor to delineate the scope of the disclosure. The following summary merely presents some concepts of the disclosure in a simplified form as a prelude to the description below. 
         [0006]    Aspects of the disclosure are directed to a system associated with an engine (e.g., of an aircraft or otherwise), the system comprising: a fluid source that is configured to provide a fluid at a first pressure value, a carbon seal, a seal plate that includes at least one lift-off feature that interfaces to the carbon seal, and a pressure boosting mechanism configured to obtain the fluid from the fluid source, increase the pressure of the fluid to a second pressure value, and provide the fluid at the second pressure value to the at least one lift-off feature. In some embodiments, the fluid source includes a compressor of the engine. In some embodiments, the at least one lift-off feature includes a plurality of grooves formed in a seal plate face of the seal plate. In some embodiments, at least one of the grooves is formed as a recess in the seal plate face. In some embodiments, the recess is approximately  0 . 001  inches deep. In some embodiments, the system further comprises: a shaft of the engine, and a spacer coupled to the shaft and located radially outward of the shaft. In some embodiments, the pressure boosting mechanism includes a gap defined between a first surface of the seal plate and a second surface of the spacer. In some embodiments, the pressure boosting mechanism includes a cavity formed in the seal plate coupled to the gap. In some embodiments, the fluid at the second pressure value in the cavity is provided to the at least one lift-off feature via at least one hole formed in the seal plate. In some embodiments, a ratio of an axial length of the gap to a radial width of the gap has a value within the range of 2.50 and 3.33. In some embodiments, the pressure boosting mechanism includes at least one hole formed through the spacer. In some embodiments, the pressure boosting mechanism includes a cavity formed in the seal plate coupled to the at least one hole formed through the spacer. In some embodiments, the fluid at the second pressure value in the cavity is provided to the at least one lift-off feature via at least one hole formed in the seal plate. In some embodiments, the pressure boosting mechanism includes an o-ring seal configured to prevent a backflow of the fluid at the second pressure value to the fluid source. In some embodiments, the pressure boosting mechanism includes at least one hole formed in the seal plate. In some embodiments, the at least one hole is angled relative to a radial reference direction and has a value within a range of 0 to 90 degrees. 
         [0007]    Aspects of the disclosure are directed to a system comprising: a fluid source that is configured to provide a fluid, a carbon seal, a seal plate having a seal plate face that interfaces to the carbon seal, and a plurality of grooves formed in the seal plate face, where the seal plate at least partially defines a cavity coupled to the fluid source, where the seal plate at least partially defines a plurality of holes that are coupled to the cavity and the plurality of grooves. In some embodiments, the system further comprises: a spacer, where the spacer and the seal plate define a gap that couples the fluid source and the cavity. In some embodiments, the system further comprises: a spacer, where the spacer defines a second plurality of holes that couple the fluid source and the cavity. 
         [0008]    Aspects of the disclosure are directed to a system comprising: a fluid source that is configured to provide a fluid, a carbon seal, a seal plate having a seal plate face that interfaces to the carbon seal, and a plurality of grooves formed in the seal plate face, where the seal plate defines a plurality of holes that couple the fluid source and the plurality of grooves, where the holes are angled relative to a radial reference direction and each hole has a value within a range of 0 to 90 degrees. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present disclosure is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements. 
           [0010]      FIG. 1  is a side cutaway illustration of a geared turbine engine. 
           [0011]      FIG. 2  illustrates a system incorporating a prior art hydrodynamic face seal. 
           [0012]      FIGS. 3-5  illustrate systems incorporating seals with various fluid pressure boosting mechanisms in accordance with aspects of this disclosure. 
           [0013]      FIG. 6A  illustrates a prior art seal plate face incorporating lift-off features. 
           [0014]      FIG. 6B  illustrates a seal plate face incorporating lift-off features in accordance with aspects of this disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    It is noted that various connections are set forth between elements in the following description and in the drawings (the contents of which are included in this disclosure by way of reference). It is noted that these connections are general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. A coupling between two or more entities may refer to a direct connection or an indirect connection. An indirect connection may incorporate one or more intervening entities. 
         [0016]    In accordance with various aspects of the disclosure, apparatuses, systems and methods are described for increasing (e.g., maximizing) a pressure of a sealing/buffer fluid as the fluid is taken into the interior of a sealing member (e.g., a rotating sealing member). The fluid at the elevated pressure may be provided to one or more hydrodynamic features, such as for example one or more spiral grooves. The increase in pressure of the fluid may be obtained by rotating the fluid as it is delivered through holes at a circumferentially inclined angle. 
         [0017]    Aspects of the disclosure may be applied in connection with a gas turbine engine.  FIG. 1  is a side cutaway illustration of a geared turbine engine  10 . This turbine engine  10  extends along an axial centerline  12  between an upstream airflow inlet  14  and a downstream airflow exhaust  16 . The turbine engine  10  includes a fan section  18 , a compressor section  19 , a combustor section  20  and a turbine section  21 . The compressor section  19  includes a low pressure compressor (LPC) section  19 A and a high pressure compressor (HPC) section  19 B. The turbine section  21  includes a high pressure turbine (HPT) section  21 A and a low pressure turbine (LPT) section  21 B. 
         [0018]    The engine sections  18 - 21  are arranged sequentially along the centerline  12  within an engine housing  22 . Each of the engine sections  18 - 19 B,  21 A and  21 B includes a respective rotor  24 - 28 . Each of these rotors  24 - 28  includes a plurality of rotor blades arranged circumferentially around and connected to one or more respective rotor disks. The rotor blades, for example, may be formed integral with or mechanically fastened, welded, brazed, adhered and/or otherwise attached to the respective rotor disk(s). 
         [0019]    The fan rotor  24  is connected to a gear train  30 , for example, through a fan shaft  32 . The gear train  30  and the LPC rotor  25  are connected to and driven by the LPT rotor  28  through a low speed shaft  33 . The HPC rotor  26  is connected to and driven by the HPT rotor  27  through a high speed shaft  34 . The shafts  32 - 34  are rotatably supported by a plurality of bearings  36 ; e.g., rolling element and/or thrust bearings. Each of these bearings  36  is connected to the engine housing  22  by at least one stationary structure such as, for example, an annular support strut. 
         [0020]    During operation, air enters the turbine engine  10  through the airflow inlet  14 , and is directed through the fan section  18  and into a core gas path  38  and a bypass gas path  40 . The air within the core gas path  38  may be referred to as “core air”. The air within the bypass gas path  40  may be referred to as “bypass air”. The core air is directed through the engine sections  19 - 21 , and exits the turbine engine  10  through the airflow exhaust  16  to provide forward engine thrust. Within the combustor section  20 , fuel is injected into a combustion chamber  42  and mixed with compressed core air. This fuel-core air mixture is ignited to power the turbine engine  10 . The bypass air is directed through the bypass gas path  40  and out of the turbine engine  10  through a bypass nozzle  44  to provide additional forward engine thrust. This additional forward engine thrust may account for a majority (e.g., more than 70 percent) of total engine thrust. Alternatively, at least some of the bypass air may be directed out of the turbine engine  10  through a thrust reverser to provide reverse engine thrust. 
         [0021]      FIG. 1  represents one possible configuration for a geared turbine engine  10 . Aspects of the disclosure may be applied in connection with other environments, including additional configurations for engines. Aspects of the disclosure may be applied in the context of a non-geared engine. 
         [0022]    Referring now to  FIG. 3 , a system  300  is shown. The system  300  is shown as including some of the features of the system  200  of  FIG. 2  described above. As such, a complete re-description of the common features is omitted for the sake of brevity. 
         [0023]    The system  300  is shown as having a clearance/gap  306  formed between a surface (e.g., a radially inner surface)  312  of the seal plate  216  and a surface (e.g., a radially outer surface)  318  of the spacer  228 . The fluid  240  may traverse the axial length of the gap  306  (illustratively in an aft-to-forward direction as shown in  FIG. 3 ), such that when the fluid  240  reaches an end  324  of the gap  306  proximate a seal cavity  330  (formed in the seal plate  216 ) the fluid  240  may have a rotational component imparted upon it by wall shear forces at the inner and outer diameter of the gap  306 . This rotation of the fluid may persist within the seal cavity  330 . The rotation of the fluid imparted by the gap  306  and the seal cavity  330  may cause the pressure of the fluid in the seal cavity  330  to be greater than the pressure of the fluid at the start  336  of the gap  306 . The pressurized fluid within the seal cavity  330  may be delivered to grooves  234 ′ via one or more holes  342  formed in the seal plate  216 . 
         [0024]    In some embodiments, the gap  306  may have an axial length within a range of about 0.050 inches and about 0.100 inches (1.27 millimeters and 2.54 millimeters). The gap  306  may have a radial width within a range of about 0.020 inches and about 0.030 inches (0.51 millimeters and 0.76 millimeters). Using the exemplary values described above, the ratio of the axial length to radial width may range from 0.05/0.02=2.50 to 0.100/0.030=3.33. 
         [0025]    Referring to  FIG. 4 , a system  400  is shown. In the system  400 , one or more holes  406  may be formed in/through the spacer  228 . The fluid  240  may traverse the holes  406  (illustratively aft-to-forward in  FIG. 4 ) before reaching the seal cavity  330 . Much like the system  300 , the pressure of the fluid may increase as a result of the rotation in the seal cavity  330  in the system  400 . The pressurized fluid may be delivered by the holes  342  to the grooves  234 ′ in the system  400  in a substantially similar manner as described above in connection with the system  300 . 
         [0026]    The system  400  may include an o-ring seal  414 . The o-ring seal  414  may be used to prevent or minimize a spill-back/backflow of the pressurized fluid in the seal cavity  330  towards the fluid source  240 . In other words, the o-ring seal  414  may encourage the pressurized fluid in the seal cavity  330  to flow to the grooves  234 ′ via the holes  342 . The o-ring seal  414  is one example of a sealing member (e.g., a static sealing member); other types of sealing members may be used. 
         [0027]    Referring now to  FIG. 5 , a system  500  is shown. In the system  500 , the holes  342  convey the pressurized fluid to the grooves  234 ′. The holes  342  are shown in  FIG. 5  as being oriented at an angle  508  relative to the radial reference direction. The angle  508  may assume a value within one or more ranges, such as for example a value within a range of 0 to 90 degrees. One skilled in the art would appreciate that the particular value, or range of values, that is used for the angle  508  may be based in part on one or more dimensions of the holes  342  relative to one or more dimensions of the grooves  234 ′. 
         [0028]    The holes  342  shown in systems  300 ,  400  and  500  as well as the holes  406  in system  400 , although shown in the cross-sectional views in  FIGS. 3-5  as being confined within the same circumferential plane each, may be inclined in the circumferential direction in order to enhance the pressure build-up effect by the action of rotation. This enhanced hydrodynamic pressurization is analogous to the spiral grooves shown in  FIGS. 6A and 6B , which build up the pressure due to the combined effect of their circumferential inclination and rotation. 
         [0029]    At least some of features shown in the systems  300 ,  400 , and  500  may be fully circumferential. For example, in some embodiments all of the features may be fully circumferential with the exception of the holes  342  and the grooves  234 ′. 
         [0030]    Referring now to  FIG. 6A , a closer view of the grooves  234  associated with  FIG. 2  is shown: In particular, the grooves  234  are shown in relation to a seal plate face  600  of the seal plate  216 . Also superimposed in  FIG. 6A  is a rotational reference direction  602 . The fluid that enters the grooves  234  is entrained at the radially innermost location  608  of the grooves  234 . In  FIGS. 2 and 6A , the fluid that enters the grooves  234  may be at approximately the same pressure as the source/buffer fluid  240 . 
         [0031]    In contrast to  FIG. 6A ,  FIG. 6B  provides a closer view of the grooves  234 ′ associated with  FIGS. 3-5 . In particular, the grooves  234 ′ are shown in relation to a seal plate face  600 ′ of the seal plate  216 . Also superimposed in  FIG. 6B  is a rotational reference direction  602 ′, which may correspond to the rotational reference direction  602 . The fluid that enters the grooves  234 ′ may enter through holes  342  formed (e.g., drilled, electrical discharge machined, etc.) in the seal plate  216  (see  FIGS. 3-5 ); the dots  658  may represent the interface from the holes  342  to the grooves  234 ′. The grooves  234 ′ may be configured as recesses in the seal plate face  600 ′; the recesses may be approximately 0.001 inches (approximately 25.4 micrometers) deep. 
         [0032]    The pressurized fluid that enters the grooves  234 ′ at the dots  658  may be distributed throughout the length/span of the grooves  234 ′. At least a portion of the fluid within each of the grooves  234 ′ may escape the groove ‘ 234  proximate an outer diameter (OD)  666  of the groove  234 ’. This escaped fluid may create the lift-off in relation to the carbon seal  210  and the seal plate  216 . 
         [0033]    Technical effects and benefits of this disclosure include a seal that may be incorporated as part of one or more sections of an engine, such as for example as part of a bearing compartment. Relative to a conventional seal, a seal in accordance with this disclosure may have an extended usable lifetime due to the avoidance or minimization of wear. For example, an increase in the pressure of the fluid delivered to lift-off features (e.g., grooves) of a seal may increase the hydrodynamic lift for a given shaft speed. This increase in lift may result in less wear of the carbon seal portion of the seal, particularly at low shaft speeds. Still further, a reduction in seal leakage may be obtained due to an increase in differential pressure across the carbon seal and the seal plate. 
         [0034]    Aspects of the disclosure have been described in terms of illustrative embodiments thereof. Numerous other embodiments, modifications, and variations within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art from a review of this disclosure. For example, one of ordinary skill in the art will appreciate that the steps described in conjunction with the illustrative figures may be performed in other than the recited order, and that one or more steps illustrated may be optional in accordance with aspects of the disclosure. One or more features described in connection with a first embodiment may be combined with one or more features of one or more additional embodiments.