Abstract:
A method for operating a gas turbine engine includes channeling compressed air from the gas turbine engine to a noise suppression system, and selectively operating the noise suppression system such that air discharged from the noise suppression system generates a plurality of flow control mechanisms in the gas turbine exhaust flowpath.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to gas turbine engines, more particularly to methods and apparatus for operating gas turbine engines.  
         [0002]     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 which burns a mixture of fuel and air, and low and high pressure rotary assemblies which each include a plurality of rotor blades that extract rotational energy from airflow exiting the combustor.  
         [0003]     Combustion gases are discharged from the core engine through an exhaust assembly. More specifically, within at least some known turbofan engines, a core exhaust nozzle discharges core exhaust gases radially inwardly from a concentric fan exhaust nozzle which exhausts fan discharge air therefrom for producing thrust. Generally during engine operation, both exhaust flows approach their maximum velocity during high power engine operations, such as during take-off operations. During such operations, as the high velocity flows interact with each other and with ambient air flowing past the engine, substantial noise may be produced along the take-off path of the aircraft.  
         [0004]     To facilitate reducing such noise, at least some known turbine engine exhaust assemblies utilize noise suppression equipment which includes at least one of tabs, mixing lobes, and/or a plurality of chevrons to enhance mixing the core and bypass exhaust flows. Although the tabs, mixing lobes, and chevrons facilitate suppressing noise during high power engine operating conditions, because the tabs, mixing lobes, and chevrons are mechanical devices which remain positioned in the flow path during all flight conditions, such devices may adversely impact engine performance during non-take-off operating conditions. Specifically, during cruise conditions, the tabs, the mixing lobes, and/or the chevrons may adversely impact specific fuel consumption (SFC) of the engine.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0005]     In one aspect, a method for operating a gas turbine engine is provided. The method includes channeling compressed air from the gas turbine engine to a noise suppression system, and selectively operating the noise suppression system such that air discharged from the noise suppression system generates a plurality of flow control mechanisms in the gas turbine exhaust flowpath.  
         [0006]     In another aspect, an assembly for a gas turbine engine is provided. The assembly includes a gas turbine nozzle, and a noise suppression system coupled to the gas turbine nozzle, the noise suppression system is selectively operable to facilitate generating a plurality of flow control mechanisms in the gas turbine nozzle flowpath.  
         [0007]     In a further aspect, a gas turbine engine is provided. The gas turbine engine includes a core engine nozzle, a fan nozzle, and a noise suppression system coupled to at least one of the core engine nozzle and the fan nozzle, the noise suppression system is selectively operable to facilitate generating a plurality of flow control mechanisms in at least one of the core engine nozzle exhaust flowpath and the fan nozzle exhaust flowpath. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic illustration of an exemplary gas turbine engine;  
         [0009]      FIG. 2  is a side view of an exemplary noise suppression system that may be used with the gas turbine engine shown in  FIG. 1 ;  
         [0010]      FIG. 3  is a perspective view of the noise suppression system shown in  FIG. 2 ;  
         [0011]      FIG. 4  is a side view of an alternative embodiment of a noise suppression system that may be used with the gas turbine engine shown in  FIG. 1 ; and  
         [0012]      FIG. 5  is a perspective view of the noise suppression system shown in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]      FIG. 1  is a schematic illustration of a gas turbine engine  10  including a fan assembly  12  and a core engine  13  including a high pressure compressor  14 , and a combustor  16 . Engine  10  also includes a high pressure turbine  18 , and a low pressure turbine  20 . Fan assembly  12  includes an array of fan blades  24  extending radially outward from a rotor disc  26 . Engine  10  has an intake side  28  and an exhaust side  30 . In one embodiment, the gas turbine engine is a GE90 available from General Electric Company, Cincinnati, Ohio. Fan assembly  12  and turbine  20  are coupled by a first rotor shaft  31 , and compressor  14  and turbine  18  are coupled by a second rotor shaft  32 .  
         [0014]     An exhaust assembly  33  extends downstream from core engine  13  and includes an annular fan exhaust nozzle  34  that extends around, and is spaced radially outwardly from, a core engine exhaust nozzle  35 . More specifically, fan exhaust nozzle  34  is positioned upstream from core exhaust nozzle  35  and is spaced radially outwardly from core engine exhaust nozzle  35  such that an annular bypass stream outlet  36  is defined between fan exhaust nozzle  34  and an engine cowling  37  extending circumferentially around core engine  13 .  
         [0015]     Core engine exhaust nozzle  35  also has an annular outlet  38  defined between an inner surface  39  of cowling  37  and an outer surface  40  of a centerbody or center plug  41 . In an alternative embodiment, core engine exhaust nozzle  35  is known as a long-ducted mixed flow exhaust and is discharged into stream outlet  36  upstream from centerbody  41 , such that core combustion gases are mixed with bypass stream flow prior to the mixture being discharged from exhaust assembly  33 . In the exemplary embodiment, centerbody  41  extends aftward from core engine  13  such that core exhaust nozzle outlet  38  is upstream from an aft end  42  of centerbody  48 . In an alternative embodiment, centerbody  41  does not extend downstream from nozzle outlet  38 , and rather nozzle outlet  38  is downstream from centerbody  41 .  
         [0016]     During operation, air flows through fan assembly  12  and compressed air is supplied to high pressure compressor  14 . The highly compressed air is delivered to combustor  16 . Airflow (not shown in  FIG. 1 ) from combustor  16  drives turbines  18  and  20 , and turbine  20  drives fan assembly  12  by way of shaft  31 . More specifically, to produce thrust from engine  10 , fan discharge flow is discharged through fan exhaust nozzle  34 , and core combustion gases are discharged from engine  10  through core engine exhaust nozzle  35 . In one embodiment, engine  10  is operated at a relatively high bypass ratio which is indicative of the amount of fan air which bypasses core engine  13  and is discharged through fan exhaust nozzle  34 . In an alternative embodiment, gas turbine engine  10  is operable with a low bypass ratio.  
         [0017]      FIG. 2  is a side view of an exemplary noise suppression system  50  that can be used with gas turbine engine  10 .  FIG. 3  is a perspective view of noise suppression system  50 . In an exemplary embodiment, noise suppression system  50  is operably coupled to core engine exhaust nozzle  35 . Noise suppression system  50  includes a manifold  52  coupled to core engine exhaust nozzle  35  such that manifold  52  circumscribes core engine exhaust nozzle  35 . Compressed air is channeled from an air source  54  through an actuation valve  56  into manifold  52 . In the exemplary embodiment, air is supplied to manifold  52  from at least one of fan assembly  12 , high pressure compressor  14 , high pressure turbine  18 , or low pressure turbine  20 .  
         [0018]     Noise suppression system  50  also includes a plurality of tubes  60  coupled to manifold  52  and operated such that air is discharged from manifold  52  through plurality of tubes  60  and into a core engine exhaust stream  85 . In other embodiments, noise suppression system  50  does not utilize tubes  60 , but rather air is discharged into core engine exhaust stream  85  through other means. Accordingly, in the exemplary embodiment, each tube  60  includes an upstream end  62 , a downstream end  64 , and a length  66  that is measured between upstream end  62  and downstream end  64 , respectively. In the exemplary embodiment, length  66  is sized such that upstream end  62  is coupled to manifold  52  and downstream end  64  is coupled to an end  68  of engine exhaust nozzle  35 . In the exemplary embodiment, tubes  60  are arranged in tube pairs  70  wherein each tube pair  70  includes a first tube  72  and a second tube  74 .  
         [0019]     In the exemplary embodiment, noise suppression system  50  includes eight pairs  70  of tubes  60  arranged azimuthally around an outer periphery of engine exhaust nozzle  35 . In an alternative embodiment, tubes  60  are not arranged in pairs. In the exemplary embodiment, each tube  60  is substantially hollow, has a substantially circular cross-sectional profile, and includes an opening  76  that extends along length  66  of tube  60 . Alternatively, tube  60  does not have a circular cross-sectional profile. In the exemplary embodiment, noise suppression system  50  includes four pairs  70  of tubes  60  arranged azimuthally around an outer periphery of core engine exhaust nozzle  35 . Tubes  72  and  74  are separated by a first angle  78 . In the exemplary embodiment, first angle  78  is approximately equal to thirty degrees. In another embodiment, tubes  72  and  74  are separated by a first angle  78  that is approximately equal to sixty degrees. Furthermore, each tube pair  70  is oriented at an injection angle  80  that is measured with respect to a centerline axis  82 . Although noise suppression system  50  is shown as coupled to an outer periphery of core engine exhaust nozzle  35 , it should be realized that noise suppression system  50  could also be coupled to an inner periphery of core engine exhaust nozzle  35 .  
         [0020]     During operation, air discharged from each tube pair  70  is discharged into core engine exhaust stream  85  such that the compressed air entering core engine exhaust stream  85  generates a flow control mechanism. For example, in the exemplary embodiment, each tube pair  70  generates a streamwise vorticity that is substantially analagous to a similar streamwise vorticity that is generated by a mechanical chevron nozzle. However, unlike mechanical chevrons, noise suppression system  50  can be operated in either an activated mode or a de-activated mode. When noise suppression system  50  is operated in the activated mode, air is supplied into manifold  52  and distributed substantially uniformly among the plurality of tube pairs  70 . Since each tube pair  70  includes a first tube  72  and a second tube  74  that are offset by a pre-defined angle  78  and a predefined angle  80 , air discharged from each tube pair  70  simulates that discharged from a mechanical chevron nozzle. When noise suppression system  50  is deactivated, no air is channeled through tube pairs  70 .  
         [0021]      FIG. 4  is a side view of an exemplary noise suppression system  150  that can be used with gas turbine engine  10 .  FIG. 5  is a perspective view of noise suppression system  150 . Noise suppression system  150  is substantially similar to noise suppression system  50 , (shown in  FIGS. 3 and 4 ) and components of noise suppression system  150  that are identical to components of noise suppression system  50  are identified in  FIGS. 4 and 5  using the same reference numerals used in  FIGS. 3 and 4 .  
         [0022]     In an exemplary embodiment, noise suppression system  150  is operably coupled to fan nozzle  34 . Noise suppression system  150  includes a manifold  52  coupled to engine exhaust nozzle  35  such that manifold  52  circumscribes core engine exhaust nozzle  35 . Compressed air is channeled from an air source  54  through an actuation valve  56  into manifold  52 . In the exemplary embodiment, air is supplied to manifold  52  from at least one of fan assembly  12 , high pressure compressor  14 , high pressure turbine  18 , or low pressure turbine  20 . Alternatively, air may be supplied from any other pressurized air source. In another alternative embodiment, synthetic jets are utilized within noise suppression system  50 , and as such, no pressurized air is supplied to noise suppression system  50 .  
         [0023]     Noise suppression system  150  also includes a plurality of tubes  60  coupled to manifold  52  and operated such that air is discharged from manifold  52  through plurality of tubes  60  and into a fan nozzle exhaust stream  87 . Accordingly, each tube  60  includes an upstream end  62 , a downstream end  64 , and a length  66  that is measured between upstream end  62  and downstream end  64 , respectively. In the exemplary embodiment, length  66  is sized such that upstream end  62  is coupled to manifold  52  and downstream end  64  is coupled to an end  36  of fan nozzle  35 . In the exemplary embodiment, tubes  60  are arranged in tube pairs  70  wherein each tube pair  70  includes a first tube  72  and a second tube  74 .  
         [0024]     In the exemplary embodiment, noise suppression system  150  includes eight pairs  70  of tubes  60  arranged azimuthally around an outer periphery of engine exhaust nozzle  35 . Each tube  60  is substantially hollow and includes an opening  76  that extends along length  66  of tube  60 . In one embodiment opening  76  is approximately 0.125 inches in diameter. In another embodiment, opening  76  is approximately 0.0625 inches in diameter. In the exemplary embodiment, noise suppression system  50  includes four pairs  70  of tubes  60  arranged azimuthally around an outer periphery of core engine exhaust nozzle  35 . Tubes  72  and  74  are separated by a first angle  78 . In the exemplary embodiment, first angle  78  is approximately equal to thirty degrees. In another embodiment, tubes  72  and  74  are separated by a first angle  78  that is approximately equal to sixty degrees. Furthermore, each tube pair  70  is oriented at an injection angle  80  that is measured with respect to a centerline axis  82 . Although noise suppression system  150  is shown as coupled to an outer periphery of fan nozzle  34 , it should be realized that noise suppression system  150  could also be coupled to an inner periphery of fan nozzle  34 .  
         [0025]     During operation, air discharged from each tube pair  70  is discharged into fan nozzle exhaust stream  87  such that the compressed air entering fan nozzle exhaust stream  87  simulates a streamwise vorticity that is analagous to a similar streamwise vorticity that is generated by a mechanical chevron nozzle. However, unlike mechanical chevron nozzles, noise suppression system  150  can be operated in either an activated mode or a de-activated mode. When noise suppression system  50  is operated in the activated mode, air is supplied into manifold  52  and distributed substantially uniformly among the plurality of tube pairs  70 . Since each tube pair  70  includes a first tube  72  and a second tube  74  that are offset by a predefined angle  78  and a predefined angle  80 , the air discharged from each tube pair  70  into fan nozzle exhaust stream  87  simulates a similar streamwise vorticity that is generated by a mechanical chevron nozzle. When noise suppression system is deactivated, no air is channeled through tube pairs  70 .  
         [0026]     The above-described noise suppression system includes a manifold and plurality of pairs of hollow injection tubes coupled to the manifold. Each pair of tubes discharges air into either the fan nozzle exhaust stream or the core engine exhaust stream such that the discharged air enables the tubes to simulate the function of a mechanical eight-lobed chevron nozzle. Accordingly, the tubes facilitate decreasing engine noise when the noise suppression system is activated. More specifically, the above-described noise suppression system includes a manifold and plurality of pairs of hollow tubes that are oriented at complex angles which are selected to enable the air discharged into either the core engine exhaust stream or the fan engine exhaust stream to be discharged at a desired injection velocity, a desired relative velocity, and a desired mass-flow-rate that are variably selected to simulate the effects that may be generated by a mechanical chevron.  
         [0027]     The injection flow can be controlled to facilitate maximizing the effect during take-off and landing, and can also be activated when desired or deactivated when not desired, e.g. during cruise, to facilitate eliminating performance penalties during most of the flight duration. Moreover, the noise suppression system can be operated either continuously or by pulsating control valve  56 . Operating the noise suppression system by pulsating valve  56  facilitates increasing effective amount of secondary airflow injected into the exhaust stream by reducing the quantity of air required. Accordingly, the noise suppression system described herein facilitates reducing noise during takeoff or landing, and reducing or eliminating engine performance losses during cruise conditions. Moreover, the noise suppression system described herein can also be operated to facilitate reducing an infra-red signature generated by engine  10 .  
         [0028]     In other words, the fluidic injection system described herein includes a plurality of opposed vortex pairs that are distributed azimuthally around the jet shear layer of the gas turbine engine. The vortex pairs inject small “jets” of compressed air into the jet shear layer at an angle to the main flow which induces the formation of relatively small longitudinal vortices. The relatively small longitudinal vortices facilitate enhancing mixing between the core and fan flow, and between the fan and ambient flows and thereby facilitate reducing jet noise. Moreover, the enhanced mixing also facilitates reducing an infra-red signature generated by engine  10 .  
         [0029]     In the exemplary embodiment, the noise suppression system described herein facilitates reducing the gas turbine noise at substantially all operational frequencies. Additionally, increasing the injection velocity of air channeled through the tube pairs facilitates reducing the gas turbine noise.  
         [0030]     Exemplary embodiments of noise suppression systems and exhaust assemblies are described above in detail. The noise suppression systems 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 noise suppression component can also be used in combination with other exhaust assemblies and/or with other noise suppression systems. Moreover, and for example, each noise suppression component can also be used in combination with engine assemblies that include mixing lobes and/or tabs to facilitate noise suppression and/or infra-red signature reduction.  
         [0031]     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.