Abstract:
A gas turbine engine includes a fan, a compressor section, a combustor, and a turbine section. The engine also includes a rotating element and at least one bearing compartment including a bearing for supporting the rotating element, a seal for resisting leakage of lubricant outwardly of the bearing compartment and for allowing pressurized air to flow from a chamber adjacent the seal into the bearing compartment. A method and section for a gas turbine engine are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. application Ser. No. 14/053,648, filed Oct. 15, 2013, which is a continuation of U.S. application Ser. No. 13/787919, filed Mar. 7, 2013. 
     
    
     BACKGROUND 
       [0002]    Gas turbine engines are known and, when utilized in aircraft applications, typically include a fan delivering air into a bypass duct and into a core engine flow. The core engine flow passes into a compressor where the air is compressed and then delivered into a combustion section. The air is mixed with fuel in the combustion section and ignited. Products of that combustion pass downstream over turbine rotors, driving them to rotate. 
         [0003]    Historically, a fan drive turbine drove the fan through a direct drive, such that they rotated at the same speed. This restricted the speed available for the fan drive turbine, as the fan speed was limited. 
         [0004]    More recently, it has been proposed to include a gear reduction between the fan drive turbine and the fan. With this change, the speed of the fan drive turbine can increase. 
         [0005]    In gas turbine engines, there are a number of bearing compartments which are desirably sealed. In the prior art, operating at slower speeds, contact seals have been utilized, which directly contacted surfaces rotating with the shaft to seal the bearing compartments. Such contact seals were typically cooled using oil or other lubricant, which was circulated through a cooling system. For geared engines, in which certain components are enabled to rotate faster than corresponding components in non-geared engines, to achieve the same amount of cooling a larger volume of lubricant would be needed. Moreover, a larger volume of lubricant would require a larger holding tank and correspondingly larger cooling system fluid pumping apparatus. All of the larger volume of lubricant, the larger holding tank, and the larger fluid pumping apparatus would add undesirable weight to the engine. 
       SUMMARY 
       [0006]    A gas turbine engine according to an example of the present disclosure includes a fan, a compressor section, a combustor, and a turbine section, a rotating element and at least one bearing compartment including a bearing for supporting the rotating element, a seal for resisting leakage of lubricant outwardly of the bearing compartment and for allowing pressurized air to flow from a chamber adjacent the seal into the bearing compartment. The seal has a seal face facing a rotating face rotating with the rotating element, and the seal is a non-contact seal. The bearing compartment has a seal associated with each of two opposed axial ends on either axial side of the bearing. 
         [0007]    In a further embodiment of the foregoing embodiment, a grooved area is formed in one of the faces. The grooved area has a plurality of circumferentially spaced grooves for generating hydrodynamic lift-off forces and allows leakage of pressurized air across the faces and into the bearing compartment to resist leakage of lubricant from the bearing compartment. 
         [0008]    In a further embodiment of either of the foregoing embodiments, the seal is formed with a plurality of passages to allow tapping of additional pressurized air to be delivered to the faces at a location in the proximity of the grooved area for generating hydrostatic lift-off forces. 
         [0009]    In a further embodiment of any of the foregoing embodiments, the grooved area is spaced radially from the plurality of passages at the seal face. 
         [0010]    In a further embodiment of any of the foregoing embodiments, each of the plurality of passages is positioned radially outward of the grooved area. 
         [0011]    In a further embodiment of any of the foregoing embodiments, the rotating element is a shaft rotating with a rotor having an axial face facing the seal face. 
         [0012]    In a further embodiment of any of the foregoing embodiments, the grooved area is formed in the rotor. 
         [0013]    In a further embodiment of any of the foregoing embodiments, the turbine section includes a fan drive turbine driving the fan through a gear reduction. The rotating element is driven by the fan drive turbine. At least one bearing compartment is associated with the gear reduction. 
         [0014]    In a further embodiment of any of the foregoing embodiments, the seal is a carbon seal. 
         [0015]    In a further embodiment of any of the foregoing embodiments, the rotating element is a shaft rotating with a rotor having a circumferential face facing the seal face. 
         [0016]    In a further embodiment of any of the foregoing embodiments, the seal face faces radially inwardly. 
         [0017]    In a further embodiment of any of the foregoing embodiments, a grooved area is formed in one of the faces, with the grooved area having a plurality of circumferentially spaced grooves for generating hydrodynamic lift-off forces and allowing leakage of pressurized air across the faces and into the bearing compartment to resist leakage of lubricant from the bearing compartment. 
         [0018]    In a further embodiment of any of the foregoing embodiments, the grooved area is formed in the rotor. 
         [0019]    In a further embodiment of any of the foregoing embodiments, the seal is a circumferentially segmented carbon seal. 
         [0020]    In a further embodiment of any of the foregoing embodiments, the seal is a controlled gap carbon seal having a full hoop seal and a metal band shrunk fit onto the seal, and positioned in a seal carrier. 
         [0021]    In a further embodiment of any of the foregoing embodiments, the rotating element is driven by a fan drive turbine. At least one bearing compartment is associated with a gear reduction for driving the fan. 
         [0022]    A method of designing a section of a gas turbine engine according to an example of the present disclosure includes configuring a bearing compartment to include a bearing designed to support a rotating element, configuring the rotating element to define a rotating face, the rotating face configured to rotate with said rotating element, configuring the bearing compartment to include a seal designed to resist leakage of lubricant outwardly of the bearing compartment and to allow air to flow from a chamber adjacent the seal and into the bearing compartment configuring the seal to define a seal face facing the rotating face, designing the seal to be a non-contact seal, and configuring the bearing compartment to have a seal associated with each of two opposed axial ends, on either axial side of said bearing. 
         [0023]    A further embodiment of the foregoing embodiment includes the step of designing the faces to define a grooved area in one of the faces. The grooved area has a plurality of circumferentially spaced grooves for generating hydrodynamic lift-off forces and allows leakage of pressurized air across the faces and into the bearing compartment to resist leakage of lubricant from the bearing compartment. 
         [0024]    In a further embodiment of either of the foregoing embodiments, the rotating element is designed to be a shaft rotating with a rotor having an axial face facing the seal face. 
         [0025]    In a further embodiment of any of the foregoing embodiments, the grooved area is formed in the rotor. 
         [0026]    A further embodiment of any of the foregoing embodiments includes the step of designing the seal to define a plurality of passages to allow tapping of additional pressurized air to be delivered to the faces at a location in the proximity of the grooved area for generating hydrostatic lift-off forces. 
         [0027]    In a further embodiment of any of the foregoing embodiments, the rotating element is designed to be a shaft rotating with a rotor having a circumferential face facing the seal face. 
         [0028]    In a further embodiment of any of the foregoing embodiments, the seal is designed to be a controlled gap carbon seal having a full hoop seal and a metal band shrunk fit onto the seal, and positioned in a seal carrier. 
         [0029]    A section for a gas turbine engine according to an example of the present disclosure includes a rotating element and at least one bearing compartment configured to be secured to a static structure. The bearing compartment includes a bearing for supporting the rotating element and a seal for resisting leakage of lubricant outwardly of the bearing compartment and for allowing pressurized air to flow from a chamber across the seal into the bearing compartment. The seal has a seal face facing a rotating face rotating with the rotating element. The seal is a non-contact seal where the bearing compartment has a seal associated with each of two opposed axial ends, on either axial side of the bearing. 
         [0030]    In a further embodiment of the foregoing embodiment, a grooved area is formed in one of the faces. The grooved area has a plurality of circumferentially spaced grooves for generating hydrodynamic lift-off forces and allows leakage of pressurized air across the faces and into the bearing compartment to resist leakage of lubricant from the bearing compartment. 
         [0031]    In a further embodiment of either of the foregoing embodiments, the seal is formed with a plurality of passages to allow tapping of additional pressurized air to be delivered to the faces at a location in the proximity of the grooved area for generating hydrostatic lift-off forces. 
         [0032]    In a further embodiment of any of the foregoing embodiments, the rotating element is a shaft rotating with a rotor having an axial face facing the seal face. 
         [0033]    In a further embodiment of any of the foregoing embodiments, the rotating element is a shaft rotating with a rotor having a circumferential face facing the seal face. 
         [0034]    In a further embodiment of any of the foregoing embodiments, the seal is a circumferentially segmented carbon seal. 
         [0035]    In a further embodiment of any of the foregoing embodiments, the seal is a controlled gap carbon seal having a full hoop seal and a metal band shrunk fit onto the seal, and positioned in a seal carrier. 
         [0036]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  schematically shows a gas turbine engine. 
           [0038]      FIG. 2  schematically shows example locations of bearing compartments. 
           [0039]      FIG. 3A  is a first embodiment of a non-contact seal according to the present invention. 
           [0040]      FIG. 3B  shows a second embodiment of a non-contact seal according to the present invention. 
           [0041]      FIG. 3C  shows a third embodiment of a non-contact seal according to the present invention. 
           [0042]      FIG. 3D  shows a fourth embodiment of a non-contact seal assembly according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0043]      FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section  22  drives air along a bypass flow path B in a bypass duct defined within a nacelle  15 , while the compressor section  24  drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the 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 two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
         [0044]    The exemplary engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, and the location of bearing systems  38  may be varied as appropriate to the application. 
         [0045]    The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in exemplary gas turbine engine  20  is illustrated as 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 an outer shaft  50  that interconnects a high pressure compressor  52  and high pressure turbine  54 . A combustor  56  is arranged in exemplary gas turbine  20  between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  further supports bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
         [0046]    The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow path C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and geared architecture  48  may be varied. For example, geared architecture  48  may be located aft of combustor section  26  or even aft of turbine section  28 , and fan section  22  may be positioned forward or aft of the location of geared architecture  48 . 
         [0047]    The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), 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 five (5:1). 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. The geared architecture  48  may be an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
         [0048]    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. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “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 “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second. 
         [0049]      FIG. 2  shows an embodiment of an arrangement of bearing compartments  100  associated with the gas turbine engine, such as the gas turbine engine  20  illustrated in  FIG. 1 . As shown, a bearing compartment  102  is associated with a low speed shaft  92  at a location associated with the low pressure turbine. Bearings  106  are shown schematically as is a seal  104 . 
         [0050]    A bearing compartment  108  is associated with a high speed rotor  90  and at the high pressure turbine of  FIG. 1 . Bearing compartment  108  includes seals  110  at each axial end and a central bearing  112 . 
         [0051]    Another bearing compartment  114  is also associated with the high speed rotor  90  and the high pressure compressor and includes a bearing  118  and seals  116 . 
         [0052]    Finally, a bearing compartment is associated with a fan drive gear system  122  at location  120  and with and the fan at location  123 . Seals  126  and  128  mechanically seal the axial ends of the bearing compartment  120  and are associated with the fan rotor  127  and the low speed rotor  92 . The seals  126 ,  128  are also respectively associated with the bearings  124  and  130  that are positioned within the bearing compartment  120 / 123 . 
         [0053]    There are challenges with sealing the bearing compartments in a geared turbofan engine. Accordingly, various embodiments disclosed herein relate to the use of non-contacting seals such as lift-off seals at any one or more of the locations of the seals shown in  FIG. 2  or in any other bearing compartment on a gas turbine engine. In some embodiments, the seals may be lift-off seals and, more particularly, may be carbon lift-off seals. Of course, in other embodiments other non-contacting seals, including other lift-off seals may be used. 
         [0054]    Thus, as shown in  FIG. 3A , a shaft  140 , which could be any rotating shaft in a gas turbine engine, has a mating rotor  142 . An axial face  147  of this mating rotor  142  is sealed relative to a face  145  from a seal  144 . The faces  145  and  147  face each other to form a mechanical seal. The seal  144  may be a non-contact seal such as a carbon seal lift-off seal. The interface between faces  145  and  147  experiences high velocities, especially when compared to the prior art. The high velocity is a combination of a high rotational speed of the shaft  140  and a relatively large diameter for the seal  144 . Velocities greater than or equal to about 450 ft/second  (137.16 meters/second) may be seen. 
         [0055]    In the  FIG. 3A  embodiment seal  144 , a set of shallow grooves  152  is provided by cutting into the face  147  of the rotor  142 , as shown at circumferentially spaced grooves  154 . A spring  146  biases the seal  144  toward the face  147 . A higher pressure air is available in a chamber  148 , which is on an opposed side of the seal  144  from the bearing compartment  150 . The bearing compartment  150  is at a lower pressure than the chamber  148 , and this higher pressure air passes through the grooved area  152 , such that the air flow levitates (lifts-off) the sealing surface  145  of the non-rotating seal  144  from the sealing surface  147  of the rotor  142 . The levitation is a result of hydrodynamic lifting force as the air passes into the bearing compartment  150 , preventing oil from escaping the bearing compartment  150 . 
         [0056]    Another embodiment is illustrated in  FIG. 3B .  FIG. 3B  provides the mechanical sealing between face  168  of a non-rotating seal  162  and a face  170  of a rotor in a manner somewhat similar to the  FIG. 3A  embodiment. There is a grooved area  172  having circumferentially spaced grooves  174  with the features as described for the first embodiment that generate hydrodynamic lifting force as the gas passes from a high pressure chamber  160  into the bearing compartment  274 . Furthermore, the non-rotating seal  162  has an inlet  166 , a passage  164 , and an outlet  180  which delivers additional high pressure air generating hydrostatic lifting forces at a radial location in the proximity of the grooved area  172 , thereby providing a stronger and more stable lift-off seal compared to the first embodiment. As shown, there is a plurality of circumferentially spaced outlets  180 . The non-rotating seal  162 , which is biased toward the rotor  170  by a spring  161 , may be a carbon lift-off seal. 
         [0057]      FIG. 3C  shows another embodiment  182 , wherein the seal  186  has a plurality of circumferentially segmented members biased by spring  184  toward a face  185  of a rotor  142  rotating with the shaft  140 . Seal  186  has a radially inwardly facing face  183  providing the seal face with the mating face  185 . One of the sealing faces, either  183  or  185 , has a set of shallow, circumferentially spaced grooves  210  in a grooved area  211 , somewhat similar to those described in the earlier embodiments that generate a hydrodynamic force that levitates (lifts-off) the non-rotating sealing surface  183  from the rotating mating surface  185  when the high pressure chamber  188  delivers pressurized air across the seal  186  to prevent leakage of oil from the bearing compartment  190 . 
         [0058]      FIG. 3D  shows an embodiment of a controlled gap non-contacting seal assembly  201 . The shaft  140  has an outer surface spaced by a small gap  196  from two carbon seals  192 . The gap is controlled by design, typically by sizing the sealing diameters of the seals  192  and the rotor  140  such that a small gap is maintained under all conditions. The shaft outer surface  193  and a radially inward facing surfaces  191  of the seals  192  provide the seal faces. In one embodiment, the carbon seals  192  are full hoop members extending around the entire circumference of the shaft  140 . A metal band  194  is shrunk fit onto the seal  192 . A carrier  195  mounts the seals  192 . A high pressure chamber  198  is spaced from the bearing compartment  200 , such that high pressure air passes through the gap  196  to prevent the leakage of lubricant. 
         [0059]    All of the disclosed embodiments reduce the friction between the seal and the rotating components. This reduces heat generation due to friction, increases the durability of the seals, minimizes loss of oil, and increases the efficiency in fuel consumption of the overall engine. Moreover, as a result of the reduction in friction, less lubricant can be used, thereby also reducing the size of the applicable fluid storage tank (not shown) and the applicable cooling system fluid pumping apparatus (also not shown). Accordingly, the overall weight of the engine may be greatly reduced, thereby increasing the engine&#39;s fuel efficiency. 
         [0060]    The disclosed embodiments may be useful at any bearing compartment in a gas turbine engine. Although shafts are shown supported by the bearings, the disclosure would extend to other rotating elements supported by a bearing. 
         [0061]    Although various embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.