Patent Publication Number: US-7717667-B2

Title: Method and apparatus for operating gas turbine engines

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to turbine engines and more specifically to clearance control systems used with gas turbine engines. 
   Known gas turbine engines include an engine casing that extends circumferentially around a compressor, and a turbine that includes a rotor assembly and a stator assembly. Known rotor assemblies include at least one row of rotating blades that extend radially outward from a blade root to a blade tip. A radial tip clearance is defined between the rotating blade tips and a stationary shroud attached to the engine casing. 
   During engine operation, the thermal environment variations in the engine may cause thermal expansion or contraction of the rotor and stator assemblies. Such thermal expansion or contraction may not occur uniformly in magnitude or rate. As a result, inadvertent rubbing, such as between the rotor blade tips and the casing may occur, or radial clearances may be created that are wider than the design clearances which may adversely affect engine performance. Continued rubbing between the rotor blade tips and engine casing may lead to premature failure of the rotor blade. 
   To facilitate minimizing inadvertent rubbing between the rotor blade tips and the surrounding shroud or undesirable large radial clearances, at least some known engines include an active clearance control system. The clearance control system channels cooling air to the engine casing to facilitate controlling thermal growth of the engine casing and to facilitate minimizing inadvertent blade tip rubbing. Such cooling air may be channeled from a fan assembly, a booster, or from compressor bleed air sources. The effectiveness of the clearance control system is at least partially dependent upon controlling pressure losses that may occur while the cooling air is channeled towards the engine casing. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a method for operating a gas turbine engine is provided. The gas turbine engine includes a fan, a high pressure turbine coupled downstream from the fan, and a low pressure turbine downstream from the high pressure turbine. The method includes channeling a portion of air discharged from the fan through a clearance control system including an inlet assembly that includes a plurality of louvers, and directing air from the inlet assembly into a first pipe and a second pipe coupled to the inlet assembly such that pressure losses associated with the airflow are facilitated to be reduced. 
   In a further aspect, a turbine assembly is provided. The turbine assembly includes a first rotor assembly including a first case manifold, a second rotor assembly including a second case manifold wherein the second rotor assembly is disposed downstream from the first rotor assembly. The turbine assembly also includes a clearance control system coupled within the turbine assembly and located upstream from the first and second rotor assemblies. The clearance control system includes an inlet assembly, an inlet tube, a first transfer pipe, and a second transfer pipe. The inlet assembly includes a plurality of louvers oriented to direct cooling air into the clearance control system. The inlet tube is coupled to the inlet assembly. The first pipe and the second pipe are coupled in flow communication to the inlet tube such that substantially all of the cooling air discharged from the inlet assembly is channeled into the first and second pipes such that pressure losses of the airflow entering the inlet assembly are facilitated to be reduced. 
   In a further aspect, a clearance control system for use with a gas turbine engine assembly including a fan, a first rotor assembly downstream from the fan, and a second rotor assembly downstream from the first rotor assembly is provided. The system includes an inlet assembly including a plurality of louvers oriented to channel air discharged from the fan into the inlet assembly. The system also includes a first pipe extending downstream from the inlet assembly and configured to couple to a portion of the high pressure turbine. The system also includes a second pipe extending downstream from the inlet assembly for channeling air discharged from the inlet assembly towards the second rotor assembly. The clearance control system facilitates active clearance control between the first and second rotor assemblies and a stationary component positioned adjacent to the first and second rotor assemblies. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of an exemplary gas turbine engine; 
       FIG. 2  is an enlarged schematic illustration of a portion of the gas turbine engine shown in  FIG. 1 ; 
       FIG. 3  is a front view of a portion of a clearance control system shown in  FIG. 2 ; 
       FIG. 4  is a perspective view of a portion of the clearance control system shown in  FIG. 2  and including an inlet assembly; and 
       FIG. 5  is a perspective view of the portion of the clearance control system shown in  FIG. 4  without the inlet assembly. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic illustration of an exemplary gas turbine engine  10  that includes a fan assembly  12  and a core engine  13  including a high pressure compressor  14 , a combustor  16 , and a high pressure turbine  18 . Engine  10  also includes a low pressure turbine  20 . Fan assembly  12  includes an array of fan blades  24  that extend radially outward from a rotor disk  26 . Engine  10  has an intake side  28  and an exhaust side  30 . Fan assembly  12  and low pressure turbine  20  are coupled by a low speed rotor shaft  31 , and compressor  14  and high pressure turbine  18  are coupled by a high speed rotor shaft  32 . 
   Generally, during operation, air flows axially through fan assembly  12 , in a direction that is substantially parallel to a central axis  34  extending through engine  10 , and compressed air is supplied to high pressure compressor  14 . The highly compressed air is delivered to combustor  16 . Combustion gas flow (not shown in  FIG. 1 ) from combustor  16  drives turbines  18  and  20 . Turbine  18  drives compressor  14  by way of shaft  32  and turbine  20  drives fan assembly  12  by way of shaft  31 . 
   Gas turbine engine  10  also includes an active clearance control system  100 . In the exemplary embodiment, clearance control system  100  is coupled to a fan frame hub  40  associated with fan blades  24 , and clearance control system  100  includes an inlet assembly  102  and at least two active clearance control supply pipes  104  and  106 . Specifically, in the exemplary embodiment, a first active clearance control supply pipe  104  and a second active clearance control supply pipe  106  extend downstream from inlet assembly  102  to channel airflow towards a portion of high pressure turbine  18  and low pressure turbine  20 , respectively. Specifically, in the exemplary embodiment, first pipe  104  is coupled to high pressure turbine casing manifold  108 , and second pipe  106  is coupled to low pressure turbine casing manifold  110 . In the exemplary embodiment, first pipe  104  includes a first control valve  112  and second pipe  106  includes a second control valve  114 . Valves  112  and  114  each modulate airflow during engine operation. 
     FIG. 2  is an enlarged schematic illustration of a portion of clearance control system  100 , and  FIG. 3  is a front view of a portion of clearance control system  100 .  FIG. 4  is a perspective view of a portion of clearance control system  100  including inlet assembly  102 , and  FIG. 5  is the same perspective view of the clearance control system  100  illustrated in  FIG. 4  but without inlet assembly  102 . 
   Inlet assembly  102  is coupled to a portion of fan frame hub  40  to channel air discharged from fan assembly  12  towards high pressure turbine  18  and low pressure turbine  20  to facilitate controlling thermal expansion of first and second casing manifolds  108  and  110 . More specifically, as shown in  FIG. 4 , inlet assembly  102  is sealingly coupled to an inlet tube  121  to enable air entering inlet assembly  102  to enter a partitioned supply plenum  125  through inlet tube  121 . Plenum  125  is coupled to first and second pipes  104  and  106  such that air entering plenum  125  is directed into first and second pipes  104  and  106 . In the exemplary embodiment, plenum  125  circumscribes the exterior of pipes  104  and  106 . As such, all air entering plenum  125  is directed into pipes  104  and  106  and plenum  125  facilitates supporting pipes  104  and  106  in proper alignment with respect to each other. 
   In the exemplary embodiment, a portion of air discharged from the fan blades  24 , is channeled through an intake side  122  of inlet assembly  102  for delivery into pipes  104  and  106 . Specifically, in the exemplary embodiment, air intended for use with pipes  104  and  106  enters inlet assembly  102  from the same circumferential location, i.e. a single inlet location, for use with both high pressure turbine  18  and low pressure turbine  20 . The use of a single inlet location facilitates reducing the complexity of clearance control system  100 . In one embodiment, the single inlet location is located adjacent an outlet guide vane hub exit. 
   Inlet assembly  102  includes a plurality of louvers  130  that are aerodynamically designed and oriented to channel air from the fan discharge stream into inlet assembly  102  such that the air captured maintains a higher pressure facilitating optimizing dynamic head recovery of the captured air. Specifically, in the exemplary embodiment, louvers  130  are oriented at an angle with respect to central axis  34  of engine  10  that enables air to be “scooped” or channeled from the fan discharge stream. In the exemplary embodiment, louvers  130  are semi-elliptically-shaped and are oriented to channel a portion of the fan discharge stream into inlet assembly  102 . Alternatively, louvers  130  may be of any suitable shape and/or may be positioned at any suitable angle within inlet assembly  102  that enables clearance control system  100  to function as described herein. The shape and position of louvers  130  facilitates increasing the pressure of the air that may be captured from the fan discharge stream. Additionally, as shown in  FIG. 4 , in the exemplary embodiment, a separator  132  extends across inlet assembly  102  such that a first set of louvers  134  and a second set of louvers  136  are defined with inlet assembly  102 . In the exemplary embodiment, first set of louvers  134  channel airflow into first pipe  104  and second set of louvers  136  channel airflow into second pipe  106 . In the exemplary embodiment, first and second pipes  104  and  106  each have a substantially constant cross-sectional area along the length of first pipe  104  and second pipe  106 . 
   Inlet assembly  102  also includes an anchor plate  140  that circumscribes inlet assembly  102  adjacent intake side  122 . More specifically, in the exemplary embodiment, anchor plate  140  is positioned upstream from louvers  130 . Anchor plate  140  includes a plurality of openings  141  that are sized to receive at least one fastening mechanism (not shown) therethrough for coupling inlet assembly  102  to fan frame hub  40 . In the exemplary embodiment, anchor plate  140  also includes a contoured inlet wall  142  that assists in channeling air into inlet assembly  102  with an enhanced pressure recovery. Countered inlet wall  142  extends into both sets of louvers  134  and  136 . Inlet tube  121  extends in sealing contact between anchor plate  140  and plenum  125 . The combination of inlet tube and plenum  125  facilitates reducing significant pressure losses of air by channeling the air directly from inlet assembly  102  into pipes  104  and  106  without passing through a dead air gap, as is common in known active control systems. 
   In the exemplary embodiment, each pipe  104  and  106  extends from plenum  125  and includes at least one bend  152  that turns air flowing therein. In the exemplary embodiment, the smooth curvature of each bend  152  facilitates channeling air through pipes  104  and  106  while minimizing pressure losses therein. Furthermore, the orientation, configuration, and size of contoured inlet wall  142 , inlet tube  121 , and plenum  125  also facilitate preventing pressure losses of air channeled therethrough. 
   In the exemplary embodiment, plenum  125  also includes retaining member  160  that circumscribes the exterior of pipes  104  and  106 , and plenum  125 . Retaining member  160  facilitates enhancing the structural support to pipes  104  and  106  and facilitates aligning pipes  104  and  106  with respect to each other. Specifically, in the exemplary embodiment, pipes  104  and  106  are adjacent each other near inlet assembly  102  and separate a distance apart as pipes  104  and  106  extend outward from inlet assembly  102  towards turbines  18  and  20 . 
   In the exemplary embodiment, retaining member  160  is coupled to fan frame hub  40 . Specifically, retaining member  160  circumscribes plenum  125  and includes a lip  162  that includes a plurality of openings  166  that are each sized to receive retaining mechanisms (not shown) therethrough to enable retaining member  160  to be coupled to fan frame hub  40 . 
   During assembly, inlet assembly  102  is coupled to inlet tube  121  in a sealed joint. Inlet tube  121  is then coupled to plenum  125  and pipes  104  and  106  are each coupled to plenum  125 . In the exemplary embodiment, plenum  125  is coupled to pipes  104  and  106  in a sealed joint to facilitate preventing air from leaking out of inlet assembly  102  and into a cowl support plenum  150 . 
   Clearance control system  100  is then coupled to fan frame hub  40  with a plurality of retaining mechanisms (not shown) inserted through openings  141 . Additionally, retaining mechanisms are inserted through openings  166  to couple plenum  125  and retaining member  160  to fan frame hub  40 . Specifically, retaining member  160  is positioned adjacent an inner portion  172  of fan frame hub  40  and retaining mechanisms are used to secure retaining member  160  to inner portion  172  such that lip  162  contacts inner portion  172 . 
   During operation, a portion of air discharged from fan blades  24  is channeled from fan assembly  12  towards clearance control system  100 . Specifically, air discharged from fan assembly  12  is directed into clearance control system  100  through inlet assembly  102  and at a single inlet location. Air entering inlet assembly  102  is discharged downstream towards high pressure turbine casing manifold  108  and low pressure turbine casing manifold  110 . Louvers  130  facilitate channeling air discharged from fan assembly  12  into clearance control system  100 . The aerodynamic shape of louvers  130  facilitates capturing air from the fan discharge stream while maintaining an enhanced pressure recovery for the air entering clearance control system  100 . The efficiency of clearance control system  100  is at least partially dependent on system pressure ratio and pressure recovery. Additionally, contoured inlet wall  142  aids in channeling a portion of the fan discharge stream into inlet system  102  such that the captured air from the fan stream has enhanced pressure when the air enters into clearance control system  100 . Once air has entered inlet assembly  102 , air is channeled through inlet tube  121  and into plenum  125 . Plenum  125  provides a sealed area for air to flow into first and second pipes  104  and  106 . Moreover, tube  121  and plenum  125  prevent air entering inlet assembly  102  from leaking out of clearance control system  100 . Air is then channeled from plenum  125  into pipes  104  and  106 . 
   In the exemplary embodiment, air flows through each pipe  104  and  106  towards turbines  18  and  20 . The smooth curvature of bends  152  facilitates guiding the air into pipes  104  and  106  such that pressure losses associated with channeling the airflow are facilitated to be reduced. Air in pipes  104  and  106  flows toward each respective control valve  112  and  114 . In the exemplary embodiment, control valves  112  and  114  are fully modulated and each valve  112  and  114  may be in either an open position or a closed position. When in the open position, cooling air continues to flow through pipes  104  and  106  towards respective manifolds  108  and  110 . Directing cooling air towards manifolds  108  and  110  facilitates controlling thermal expansion of the rotor and stator assemblies. As a result, tighter blade clearances within turbines  18  and  20  are achieved through enhanced control and cooling of case manifold  108  and  110 . As such, engine  10  performance is enhanced. 
   The method for operating a gas turbine engine herein includes channeling a portion of air discharged from the fan through a clearance control system including an inlet assembly that includes a plurality of louvers, and directing air from the inlet assembly into a first pipe and second pipe coupled to the inlet assembly such that pressure losses associated with the airflow are facilitated to be reduced. 
   The clearance control system described herein facilitates maintaining a clearance gap defined between static casing assemblies and adjacent rotating components. Cooling air supplied towards the static casing assemblies from the clearance control system can come from any cooling source inside the engine. Moreover, the clearance control system facilitates enhanced control of thermal expansion rates, which ultimately facilitates maintaining tighter clearances during engine operation. 
   The above-described clearance control system provides a cost-effective and reliable means for increasing the source pressure for turbines than known bleed air systems without negatively impacting bypass fan efficiency. This is achieved by directing air from the fan stream into bleed air system at the same bleed location to increase the amount of pressure within the air captured from the fan stream. Additionally, the shape and position of louvers increases the pressure captured from the fan stream. Furthermore, contoured inlet wall, inlet tube, and gentle bend prevent pressure loss once air from the fan stream has entered bleed air system. Thus, the clearance control system facilitates increasing turbine efficiency a cost-effective and reliable manner. 
   An exemplary embodiment of a bleed air system for a clearance control system is described above in detail. The system illustrated is not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. 
   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.