Abstract:
A turbomachine seal includes, among other things, a sealing member configured to be influenced by both hydrostatic and hydrodynamic forces when providing a seal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 61/704,105, which was filed on 21 Sep. 2012 and is incorporated herein by reference. 
    
    
     BACKGROUND 
     Turbomachines, such as gas turbine engines, typically include a fan section, a compression section, a combustion section, and a turbine section. Turbomachines may employ a geared architecture connecting portions of the compression section to the fan section. Turbomachines include various seals. The seals may be lift-off seals. 
     Some lift-off seals rely exclusively on hydrodynamic forces to move the seal to a position appropriate for establishing a sealing film of air. At low pressures, low speeds, high biasing loads, etc., the hydrodynamic forces may be inadequate. The lift-off seal may undesirably touchdown if the hydrodynamic forces are inadequate. 
     Other lift-off seals rely exclusively on hydrostatic forces to move the seal to a position appropriate for establishing the sealing film of air. Under some operating conditions, the hydrostatic forces are inadequate and touchdown may undesirably occur. 
     SUMMARY 
     A turbomachine seal according to an exemplary aspect of the present disclosure includes, among other things, a sealing member configured to be influenced by both hydrostatic and hydrodynamic forces when providing a seal. 
     In a further non-limiting embodiment of the foregoing turbomachine seal, the sealing member may limit flow of a turbomachine fluid when providing the seal. 
     In a further non-limiting embodiment of either of the foregoing turbomachine seals, the sealing member may lift off from a rotating seal face when providing the seal. 
     A seal assembly according to another exemplary aspect of the present disclosure includes, among other things, a first seal member movable from a first position to a second position in response to both a hydrostatic and a hydrodynamic force. The first seal member contacting a second seal member when in the first position, the first seal member spaced from the second seal member when in the second position. 
     In a further non-limiting embodiment of the foregoing turbomachine seal assembly, the first and second seal members may provide a sealing interface when the first seal member is in the second position, the sealing interface limiting flow of a fluid from a first side of the sealing interface to an opposing, second side of the sealing interface. 
     In a further non-limiting embodiment of either of the foregoing turbomachine seal assemblies, the fluid may be a first fluid, and a different second fluid is communicated to the sealing interface to provide the hydrostatic and hydrodynamic forces. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, the second seal member may be rotated relative to the first seal member when providing the sealing interface. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, the sealing interface may be an annular sealing interface. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, the first fluid may be an oil of a bearing compartment within a turbomachine. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, the first seal member may be spring biased toward the first position. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, the first seal member may be a lift-off seal. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, one of the first or the second seal members may provide a at least one conduit that directs a fluid toward the other of the first or the second seal to provide the hydrostatic forces. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, the first seal may be configured to rotate relative to the second seal about an axis, and the at least one conduit directs the fluid toward the other of the first or second seal in an axial direction. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, the fluid may be first fluid, and one of the first or the second seal member provides a plurality of grooves that communicates a second fluid that is different from the first fluid to the sealing interface to provide the hydrodynamic forces. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, the first seal may be configured to rotate relative to the second seal about an axis, and the plurality of grooves are provided by the first seal. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, the plurality of grooves may extend from the first side and terminate partially within the sealing interface.= 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, one of the first or the second seal members may provide at least one conduit that directs the second fluid from the second side to the sealing interface to provide the hydrostatic forces. 
     In a further non-limiting embodiment of any of the foregoing turbomachine seal assemblies, the plurality of grooves may communicate the second fluid to a first area of the sealing interface, and the at least one conduit directs the second fluid to a different second area of the sealing interface. 
     A method of sealing an interface according to another exemplary aspect of the present disclosure includes, among other things, moving a seal member to a sealing position using both hydrostatic and hydrodynamic forces, and limiting movement of a turbomachine fluid when the seal member is in the sealing position. 
     In a further non-limiting embodiment of the foregoing method of sealing an interface, the method may include moving including moving the seal member to the sealing position from a position wherein the sealing member is contacting a seal face, the sealing member spaced from the seal face when in the sealing position. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
         FIG. 1  shows a cross section view of an example turbomachine. 
         FIG. 2  shows a close-up view of a sealed area of the turbomachine of  FIG. 1 . 
         FIG. 3  shows an example seal assembly from the sealed area of  FIG. 2  in a first position. 
         FIG. 4  shows an example seal assembly from the sealed area of  FIG. 2  in a second position. 
         FIG. 5  shows a seal face of the assembly of  FIGS. 3 and 4 . 
         FIG. 6  shows another seal face of the assembly of  FIGS. 3 and 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates an example turbomachine, which is a gas turbine engine  20  in this example. The gas turbine engine  20  is a two-spool turbofan gas turbine engine that generally includes a fan section  22 , a compression section  24 , a combustion section  26 , and a turbine section  28 . 
     Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans. That is, the teachings may be applied to other types of turbomachines and turbine engines including three-spool architectures. Further, the concepts described herein could be used in environments other than a turbomachine environment and in applications other than aerospace applications. 
     In the example engine  20 , flow moves from the fan section  22  to a bypass flowpath. Flow from the bypass flowpath generates forward thrust. The compression section  24  drives air along a core flowpath. Compressed air from the compression section  24  communicates through the combustion section  26 . The products of combustion expand through the turbine section  28 . 
     The example engine  20  generally includes a low-speed spool  30  and a high-speed spool  32  mounted for rotation about an engine central axis A. The low-speed spool  30  and the high-speed spool  32  are rotatably supported by several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively, or additionally, be provided. 
     The low-speed spool  30  generally includes a shaft  40  that interconnects a fan  42 , a low-pressure compressor  44 , and a low-pressure turbine  46 . The shaft  40  is connected to the fan  42  through a geared architecture  48  to drive the fan  42  at a lower speed than the low-speed spool  30 . 
     The high-speed spool  32  includes a shaft  50  that interconnects a high-pressure compressor  52  and high-pressure turbine  54 . 
     The shaft  40  and the shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A, which is collinear with the longitudinal axes of the shaft  40  and the shaft  50 . 
     The combustion section  26  includes a circumferentially distributed array of combustors  56  generally arranged axially between the high-pressure compressor  52  and the high-pressure turbine  54 . 
     In some non-limiting examples, the engine  20  is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6 to 1). 
     The geared architecture  48  of the example engine  20  includes an epicyclic gear train, such as a planetary gear system or other gear system. The example epicyclic gear train has a gear reduction ratio of greater than about 2.3 (2.3 to 1). 
     The low-pressure turbine  46  pressure ratio is pressure measured prior to inlet of low-pressure turbine  46  as related to the pressure at the outlet of the low-pressure turbine  46  prior to an exhaust nozzle of the engine  20 . In one non-limiting embodiment, the bypass ratio of the engine  20  is greater than about ten (10 to 1), the fan diameter is significantly larger than that of the low-pressure compressor  44 , and the low-pressure turbine  46  has a pressure ratio that is greater than about 5 (5 to 1). The geared architecture  48  of this embodiment is an epicyclic gear train with a gear reduction ratio of greater than about 2.5 (2.5 to 1). It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans. 
     In this embodiment of the example engine  20 , a significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. This flight condition, with the engine  20  at its best fuel consumption, is also known as “Bucket Cruise” Thrust Specific Fuel Consumption (TSFC). TSFC is an industry standard parameter of fuel consumption per unit of thrust. 
     Fan Pressure Ratio is the pressure ratio across a blade of the fan section  22  without the use of a Fan Exit Guide Vane system. The low Fan Pressure Ratio according to one non-limiting embodiment of the example engine  20  is less than 1.45 (1.45 to 1). 
     “Low Corrected Fan Tip Speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)]^0.5. The Temperature represents the ambient temperature in degrees Rankine. The Low Corrected Fan Tip Speed according to one non-limiting embodiment of the example engine  20  is less than about 1150 fps (351 m/s). 
     Referring to  FIGS. 2-6  with continuing reference to  FIG. 1 , the bearing systems  38  within the engine  20  typically hold a lubricating fluid, such as a lubricating oil. A seal assembly  60  is used, in this example, to keep the lubricating fluid within the bearing system  38 . The seal assembly is within a sealed area of the engine  20 . 
     The example seal assembly  60  is a lift-off seal that utilizes a film of air to limit movement of the lubricating fluid from a first side  64  of the seal assembly  60  to a second side  68  of the seal assembly  60  and to reduce undesirable heat generation at the sealing interface  72  due to absence of contact of the seal with the mating runner in the lifted position. 
     During operation of the engine  20 , a film of air communicates across a sealing interface  72  from the second side  68  to the first side  64  to limit movement of the lubricating fluid. In this example, the lubricating fluid is a first fluid, and the air is a second fluid. 
     Air on the second side  68  is at a relatively higher pressure than the first side  64 . The pressure differential causes movement of air from the second side  68  to the first side  64 . The compression section  24  of the engine  20  provides the high-pressure air to the second side  68  in this example. 
     The example seal assembly  60  includes a first seal member  76  and a second seal member  80 . A seal face  84  of the first seal member  76  faces a seal face  88  of the second seal member  80 . The sealing interface  72  is provided by the facing portions of the seal face  84 , the seal face  88 , and air communicated therebetween. 
     The example first seal member  76  is biased by a spring  92  toward the seal face  88  in an axial direction. Air communicated through the sealing interface  72  overcomes at least some of the spring biasing force. Overcoming the biasing force causes the first seal member  76  to separate from the seal face  88  such that the first seal member  76  is spaced from the second seal member  80 . The air communicated through the sealing interface  72  overcomes the biasing force and moves first seal member  76  from a first position ( FIG. 3 ) where the first seal member  76  contacts the second seal member  80  to a second position ( FIG. 4 ) where the first seal member  76  is spaced from the second seal member  80 . The first seal member  76  utilizes both hydrostatic and hydrodynamic forces to overcome the spring biasing force. 
     In this example, the first seal member  76  includes a at least one conduits  96 . Air from the second side  68  communicates through the at least one conduit  96  to directly contact the seal face  88  at a location L. Directing air toward the seal face  88  from the first seal member  76  in this way helps overcome the spring bias force and moves the first seal member  76  axially away from the second seal member  80 . The at least one conduit  96  helps provide the hydrostatic force to the first seal member  76  in this example. A hydrostatic pressure peak is applied directly to the sealing interface  72 . 
     The second seal member  80  includes a plurality of grooves  100  (or relatively shallow trenches) that open to the seal face  84 . The grooves  100  extend radially from the second side  68  to at least the sealing interface  72 . The grooves may be spiral grooves that are angled relative to a radial direction r, or the grooves may be of various other forms that create the hydrodynamic lift force. The second seal member  80  rotates about the axis A during operation of the engine  20  in a direction D. The grooves  100  are angled away from the direction of rotation of the second seal member  80 . 
     Air from the second side  68  fills the grooves  100 . When the second seal member  80  rotates, the pressure of this air increases. The higher pressure air within the grooves  100  helps overcome the spring biasing force and helps to move the first seal member  76  away from the second seal member  80 . The grooves  100  help provide the hydrodynamic force to the first seal member  76  in this example. The grooves  100  provide the hydrodynamic pressure peak to the sealing interface  72 . 
     Air from the at least one conduit  96  exits the first seal member  76  at outlets  104 . In this example, these outlets  104  are radially outside a radially outer end  108  of the plurality of grooves  100 . In other examples, the outlets  104  may radially overlap some portion of the plurality of grooves  100 . 
     Air that has exited the conduits  96  and the grooves  100  flows radially along the sealing interface  72  to the first side  64 . The movement of air from the second side  68  to the first side  64  provides a film seal that limits movement of oil from the first side  64  to the second side  68 . 
     Although the example seal assembly includes at least one conduit  96  in the first seal member  76 , the at least one conduit  96  may be located within the second seal member  80  in another example. In still other examples, both the first seal member  76  and the second seal member  80  may include conduits. 
     Also, although grooves  100  are incorporated into the second seal member  80 , the grooves may be incorporated elsewhere in other examples. 
     The first seal member  76  is carbon based in this example. The first seal member  76  is considered a wear member. Touching down the first seal member  76  such that the seal face  84  contacts the seal face  88  causes the first seal member  76  to wear. The hydrostatic forces and the hydrodynamic forces move the first seal member  76  away from the second seal member  80  to limit such wear while still providing a film seal. 
     Features of the disclosed examples include a hybrid lifting scheme for a mechanical seal that utilizes a combination of concurrent hydrostatic and hydrodynamic forces to move a seal. Since both lift mechanisms are used, the seal may perform in a relatively wider design space (speeds, pressures, temperatures, etc.) than prior art seals. 
     The hybrid lift-off seal may also be better at handling inherent variations in the design features of either the hydrodynamic or the hydrostatic seal prior arts, thereby reducing part tolerances and thus manufacturing costs. The disclosed examples may be used in applications where conventional hydrodynamic or hydrostatic seals are used. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.