Abstract:
A method facilitates assembling a gas turbine engine. The method comprises coupling a seal assembly including a brush seal and a plurality of seal bristles to a first rotatable shaft, and positioning the seal assembly such that the seal bristles contact a second rotatable shaft to facilitate sealing between the first and second rotatable shafts during gas turbine engine operation.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to gas turbine engines, and more specifically to seal assemblies used with gas turbine engine rotor assemblies. 
     At least some known gas turbine engines include a core engine having, in serial flow arrangement, a fan assembly and a high pressure compressor which compress airflow entering the engine, a combustor ignites a fuel-air mixture which is then channeled towards low and high pressure turbines which each include a plurality of rotor blades that extract rotational energy from airflow exiting the combustor. The high pressure compressor is coupled by a shaft to the high pressure turbine. 
     To facilitate sealing between rotor shafts, at least some known turbines include a plurality of seal assemblies to facilitate containing fluid within predetermined locations. For example, at least some known engines include a bearing compartment that is filled with an oil mist to provide lubrication to bearings that support an inner and outer rotor shaft. The inner and outer shafts are separated by a gap that may be filled with a working fluid used to cool the shafts. A seal assembly is used to prevent the oil mist from leaking into the gap defined between the shafts. 
     At least some known seal assemblies include a first portion that is coupled to the first rotor shaft and a second portion that is coupled to the second rotor shaft. However, because both seal assembly portions are rotating independently, such seal assemblies may be susceptible to leaking when thermal, mechanical, and centrifugal forces are induced to either or both rotor shafts. Other known seal assemblies include a first seal portion that is mounted to a stationary structure between the rotor shafts, such as an engine frame, and a second portion that is mounted to one of the rotor shafts. Because of the limited space between shafts, such seal assemblies are typically only used near an end of a shaft, and as such, may  also be susceptible to deflections and/or rotor excursions cased by thermal, centrifugal, and/or gyroscopic forces induced to the rotor shaft. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, a method for assembling a gas turbine engine is provided. The method comprises coupling a seal assembly including a brush seal and a plurality of seal bristles to a first rotatable shaft, and positioning the seal assembly such that the seal bristles contact a second rotatable shaft to facilitate sealing between the first and second rotatable shafts during gas turbine engine operation. 
     In another aspect, a seal assembly for a gas turbine engine including a first rotatable shaft and a second rotatable shaft is provided. The seal assembly includes a brush seal and a plurality of seal projections extending outwardly from the brush seal. The brush seal is sealingly coupled to the first rotatable shaft such that the plurality of seal projections contact the second rotatable shaft to facilitate sealing between the first and second rotatable shafts. 
     In a further aspect, a gas turbine engine is provided. The engine includes a first rotatable shaft, a second rotatable shaft, and a seal assembly that extends between said first and second rotatable shafts to facilitate preventing leakage through a gap defined between the first and second rotatable shafts. The seal assembly includes a brush seal and a plurality of seal projections extending outwardly from the brush seal. The brush seal is sealingly coupled to the first rotatable shaft such that the plurality of seal projections contact the second rotatable shaft to facilitate sealing between the first and second rotatable shafts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic illustration of a gas turbine engine; and 
         FIG. 2  is an enlarged partial cross-sectional view of a portion of rotor assembly that may be used with the gas turbine engine shown in  FIG. 1 .  
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic illustration of a gas turbine engine  10  including a low pressure compressor  12 , a high pressure compressor  14 , and a combustor  16 . Engine  10  also includes a high pressure turbine  18  and a low pressure turbine  20 . Compressor  12  and turbine  20  are coupled by a first shaft  24 , and compressor  14  and turbine  18  are coupled by a second shaft  26 . In one embodiment, the gas turbine engine is a GE90 available from General Electric Company, Cincinnati, Ohio. 
     In operation, air flows through low pressure compressor  12  and compressed air is supplied from low pressure compressor  12  to high pressure compressor  14 . The highly compressed air is delivered to combustor  16 . Airflow from combustor  16  drives turbines  18  and  20  before exiting gas turbine engine  10 . 
       FIG. 2  is an enlarged partial cross-sectional view of a portion of a rotor assembly  40  that may be used with gas turbine engine  10 . As is known in the art, engine  10  also includes a stator assembly (not shown) that extends longitudinally through engine  10 . Rotor assembly  40  cooperates with the stator assembly and includes a radially inner rotor shaft  42  and a radially outer rotor shaft  44 . In the exemplary embodiment, rotor shafts  42  and  44  are co-axial and are counter-rotating such that first rotor shaft  42  rotates in a first direction that is opposite a second direction that second rotor shaft  44  rotates during engine operation. In an alternative embodiment, first rotor shaft  42  and second rotor shaft  44  are co-rotating and each shaft  42  and  44  rotates in the same direction. 
     Shafts  42  and  44  are spaced radially apart such that a gap  50  is defined therebetween. Gap  50  may be filled with a working medium gas supplied from a compressor, such as compressor  14 , to facilitate cooling shafts  42  and  44 . In the exemplary embodiment, gap  50  is filled with parasitic secondary air for use in cooling shafts  42  and  44 . 
     An intershaft seal assembly  60  extends across gap  50  to facilitate preventing the working medium gas from leaking out of gap  50 . In addition,  seal  60  extends across gap  50  to facilitate preventing other fluids, such as oil mist, from being channeled downstream and into gap  50 . For example, in the exemplary embodiment, a compartment  62  upstream from seal assembly  60  may be filled with oil mist to facilitate lubricating a component (not shown), such as a bearing, housed within compartment  62 . Seal assembly  60  facilitates preventing the parasitic secondary air from leaking into compartment  62 , and also prevents oil mist from leaking into gap  50 . 
     Seal assembly  60  includes a brush seal  70  and a plurality of flexible seal members  72  that project radially outward from seal  70 . In the exemplary embodiment, seal members  72  are a plurality of brush bristles which are formed integrally with brush seal  70  and extend substantially perpendicularly from brush seal  70 . 
     Brush seal  70  is annular and extends in substantial sealing contact circumferentially around inner rotor shaft  42 . In the exemplary embodiment, a fastener assembly  80  retains brush seal  70  against an abutment  82  extending outwardly from rotor shaft  42  such that seal  70  rotates concurrently with, and at the same rotational speed of, rotor shaft  42 . In an alternative embodiment, brush seal  70  is coupled to shaft  44  rather than shaft  42 . More specifically, when brush seal  70  is coupled in position relative to radially inner shaft  42 , seal members  72  extend substantially radially outward towards outer shaft  44 . In the exemplary embodiment, when seal assembly  60  is coupled in position relative to shafts  42  and  44 , brush seal  70  circumscribes shaft  42  intermediate upstream and downstream ends (not shown) of inner shaft  42 , and seal members  72  contact shaft  44  in substantial sealing contact intermediate upstream and downstream ends (not shown) of outer shaft  44 . Accordingly, seal assembly  60  is known as an intershaft seal assembly. 
     During operation, brush seal  70  rotates simultaneously with, and at the same rotational speed as, inner shaft  42 . Moreover, as brush seal  70  is rotated, because seal members  72  extend radially outward from brush seal  70 , during rotation of shaft  42 , seal members  72  are maintained in close proximity to outer shaft  44 , regardless of a direction of rotation of outer shaft  44  with respect to inner shaft  42 .  Moreover, seal members  72  remain in close proximity to outer shaft  44  during engine operation, regardless of forces induced to seal assembly  60  or to shafts  42  and/or  44 . Accordingly, seal assembly  60  is facilitated to be compliant to deflections and rotor excursions due to thermal, centrifugal, and/or gyroscopic forces. Furthermore, because brush seal  70  is coupled to rotor shaft  42 , brush seal  70  and seal members  72  are substantially insensitive to rotor speed and centrifugal forces induced to seal assembly  60  during rotor operation. Accordingly, sealing contact is facilitated to be maintained between seal members  72  and shaft  44 , such that leakage past seal assembly  60  is facilitated to be reduced in comparison to other known intershaft seal assemblies. Furthermore, because seal assembly  60  is not coupled to a stationary support structure, the mounting locations for seal assembly  60  are not as limited as compared to other known intershaft seal assemblies. Accordingly, seal assembly  60  facilitates extending a useful life of rotor assembly  40 . 
     The above-described interstaft seal assemblies are cost-effective and highly reliable. The interstaft seal assembly includes a brush seal and a plurality of seal members that extend outwardly from the brush seal. The brush seal is coupled in sealing contact to a first rotor shaft such that the seal members extend towards the second shaft. Because the seal assembly is rotated concurrently with the first shaft, the seal members are maintained in close proximity to the second shaft regardless of the rotational speed or rotational direction of either of the shafts. Accordingly, the seal assembly is insensitive to rotor speed and centrifugal forces. Moreover, the seal configuration facilitates reducing leakage into and from the gap defined between the shafts at an intershaft location, without the requirement for a stationary support structure. As a result, the interstaft seal assembly facilitates extending a useful life of the turbine rotor assembly in a cost-effective and reliable manner. 
     Exemplary embodiments of rotor assemblies are described above in detail. The rotor assemblies are not limited to the specific embodiments described herein, but rather, components of each assembly may be utilized independently and separately from other components described herein. For example,  each interstaft seal assembly component can also be used in combination with other interstaft seal assembly components and with other rotor assemblies. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.