Abstract:
A method of assembling a gas turbine engine includes coupling an annular exhaust duct to the gas turbine engine, coupling a plurality of chevrons to the annular exhaust duct, and coupling a chevron actuation system to the annular exhaust duct such that selective operation of the chevron actuation system repositions the plurality of chevrons to adjust an amount convergence of the annular exhaust duct.

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. Typically, both exhaust flows have a maximum velocity when the engine is operated during high power 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 jet noise, at least some known turbine engine exhaust assemblies include a plurality of chevron nozzles to enhance mixing the core and bypass exhaust flows. Although the chevron nozzles do provide a noise benefit during take-off conditions, because the nozzles 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, chevron nozzles may adversely impact specific fuel consumption (SFC) of the engine.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0005]     In one aspect, a method of assembling a gas turbine engine is provided. The method includes coupling an annular exhaust duct to the gas turbine engine, coupling a chevron actuation system to the annular exhaust duct such that selective operation of the chevron actuation system repositions the plurality of chevrons to adjust an amount convergence of the annular exhaust duct.  
         [0006]     In another aspect a method of operating a gas turbine engine that includes an annular exhaust duct and a plurality of chevrons coupled to the annular exhaust duct is provided. The method includes coupling a chevron actuation system to the annular exhaust duct wherein at least a portion of the chevron actuation system is fabricated from a shape memory alloy that has a memorized activation configuration and such that the plurality of chevrons are oriented in a first configuration during engine operation, and passively or actively heating the shape memory alloy such that the plurality of chevrons are reconfigured from the first configuration to an activation configuration.  
         [0007]     In a further aspect, a gas turbine engine is provided. The gas turbine engine includes an annular exhaust duct for discharging exhaust from an aft end thereof, a plurality of circumferentially adjoining chevrons extending from the duct aft end, and a chevron actuation system coupled to the annular exhaust duct, a portion of the chevron actuation system fabricated from a shape memory alloy material. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic illustration of a gas turbine engine;  
         [0009]      FIG. 2  is a side view of an exemplary nozzle that may be used with the gas turbine engine shown in  FIG. 1 ;  
         [0010]      FIG. 3  is a perspective view of an exemplary chevron actuation system that may be used with the nozzle shown in  FIG. 2 ; and  
         [0011]      FIG. 4  is a perspective view of an exemplary chevron actuation system that may be used with the nozzle shown in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]      FIG. 1  is a perspective view of a turbofan aircraft gas turbine engine  10  coupled to a wing of an aircraft  12  using a pylon  14 , for example. Engine  10  includes a core engine exhaust nozzle  16  and a fan exhaust nozzle  18  which discharge combustion gas exhaust  20  and pressurized fan air exhaust  22 , respectively. Engine  10  also includes a fan  24  having at least one row of rotor blades mounted inside a corresponding fan nacelle at a forward end of engine  10 . Fan  24  is driven by a core engine  26  which is mounted concentrically inside the fan nacelle along an axial or centerline axis  28 . Core engine  26  includes a high pressure turbine (not shown) coupled to a compressor (not shown) which extracts energy from the combustion gases for powering the compressor. A low pressure turbine (not shown) is disposed downstream from the high pressure turbine and is coupled to fan  24  by a shaft (not shown) that is rotated by extracting additional energy from the combustion gases which are discharged as combustion gas exhaust  20  from core engine exhaust nozzle  16 .  
         [0013]     An annular centerbody  30  is spaced radially inwardly from core engine exhaust nozzle  16  and converging in the aft direction downstream therefrom. Core engine exhaust nozzle  16  and fan exhaust nozzle  18  each include an annular exhaust duct  32 . In the exemplary embodiment, each annular exhaust duct  32  is a one-piece or substantially unitary ring positioned concentrically around centerline axis  28 . In an alternative embodiment, engine  10  includes, but is not limited to, at least one of an internal plug nozzle, a long duct mixed flow nozzle, and a convergent/divergent (CD) variable area nozzle. A plurality of circumferentially adjoining chevrons  34  extend axially aft from an aft end of annular exhaust duct  32  preferably in a unitary and coextensive configuration therewith.  
         [0014]     During operation, to produce thrust from engine  10 , fan discharge flow is discharged through fan exhaust nozzle  18 , and combustion gases are discharged from engine  10  through core engine exhaust nozzle  16 . In one embodiment, engine  10  is operated at a relatively high bypass ratio which is indicative of the amount of fan air which bypasses engine  10  and is discharged through fan exhaust nozzle  18 . In an alternative embodiment, engine  10  is operable with a low bypass ratio.  
         [0015]      FIG. 2  is a side view of an exemplary nozzle  50  that can be used with gas turbine engine  10 , (shown in  FIG. 1 ) in a first operational configuration.  FIG. 3  is a side view of nozzle  50  in a second operational configuration. Nozzle  50  is substantially similar to core engine exhaust nozzle  16  and fan nozzle exhaust  18 , (shown in  FIG. 1 ) and components in nozzle system  50  that are identical to components of core engine exhaust nozzle  16  and fan nozzle exhaust  18  are identified in  FIG. 2  and  FIG. 3  using the same reference numerals used in  FIG. 1 . Accordingly, in one embodiment, nozzle  50  is a core engine exhaust nozzle. In another embodiment, nozzle  50  is a fan nozzle.  
         [0016]     Nozzle  50  includes a plurality of circumferentially or laterally adjoining chevrons  52  integrally disposed at an aft end  54  of annular exhaust duct  32 . Each chevron  52  has a geometric shape  56 . In the exemplary embodiment, each chevron  52  has a substantially triangular shape and includes a base  58  fixedly coupled or integrally joined to annular exhaust duct  32 . Each chevron  52  also includes an axially opposite apex  60 , and a pair of circumferentially or laterally opposite trailing edges  62  or sides converging from base  58  to each respective apex  60  in the downstream, aft direction. Each chevron  52  also includes a radially outer surface  63 , and a radially opposite inner surface  64  bounded by trailing edges  62  and base  58 .  
         [0017]     Trailing edges  62  of adjacent chevrons  52  are spaced circumferentially or laterally apart from the bases  58  to apexes  60  to define respective slots or cut-outs  65  diverging laterally and axially, and disposed in flow communication with the inside of annular exhaust duct  32  for channeling flow radially therethrough. In the exemplary embodiment, slots  65  are also triangular and complementary with triangular chevrons  52  and diverge axially aft from a slot base  66 , which is circumferentially coextensive with chevrons bases  58 , to chevron apexes  60 .  
         [0018]     In one exemplary embodiment, each chevron outer surface  63  is disposed approximately parallel to centerline axis  28  to form a diverging exhaust nozzle as shown in  FIG. 2 . Moreover, as shown in  FIG. 3 , each chevron outer surface  63  can be re-positioned to adjust an amount convergence of the annular exhaust duct. Accordingly, repositioning each chevron  52  facilitates mixing effectiveness while at the same time providing an aerodynamically smooth and non-disruptive profile for minimizing losses in aerodynamic efficiency and performance.  
         [0019]      FIG. 4  is a perspective view of an exemplary chevron actuation system  70  that can be used with nozzle  50  (shown in  FIGS. 2 and 3 ). Chevron actuation system  70  includes an actuator or shape memory alloy band  72  coupled to annular exhaust duct  32 . In the exemplary embodiment, actuator  72  is positioned forward of chevrons  52  and circumferentially around an outer periphery  76  of annular exhaust duct  32 .  
         [0020]     In the exemplary embodiment, single actuator  72  is fabricated from a shape memory alloy  74  having a memorized activated configuration. Shape memory alloy  74  is used to reposition chevrons  52  and thereby either increase or decrease the convergence of annular exhaust duct  32 . As used herein a shape memory alloy is defined as a material which can be formed into any desired shape.  
         [0021]     Various metallic materials are capable of exhibiting shape-memory characteristics. These shape-memory capabilities occur as the result of the metallic alloy undergoing a reversible crystalline phase transformation from one crystalline state to another crystalline state with a change in temperature and/or external stress. In particular, alloys of nickel and titanium exhibit these properties of being able to undergo energetic crystalline phase changes at ambient temperatures, thus giving them a shape-memory. These shape-memory alloy materials, if plastically deformed while cool, will revert to their original, undeformed shape when warmed. These energetic phase transformation properties render articles made from these alloys highly useful in a variety of applications. For example, the shape “training” of SMA&#39;s is accomplished by holding the SMA into their desired shape and then heating and holding to a higher temperature. Upon cooling, the SMA will retain the desired shape. When the SMA is mechanically deformed at a lower temperature, the SMA will revert to its “trained shape” upon subsequent heating. An article made of an alloy having shape-memory properties can be deformed at a low temperature from its original configuration, but the article “remembers” its original shape, and returns to that shape when heated. More specifically, and in the exemplary embodiment,  
         [0022]     For example, in nickel-titanium alloys possessing shape-memory characteristics, the alloy undergoes a reversible transformation from an austenitic state to a martensitic state with a change in temperature. This transformation is often referred to as a thermoelastic martensitic transformation. The reversible transformation of the NiTi alloy between the austenite to the martensite phases occurs over two different temperature ranges which are characteristic of the specific alloy. As the alloy cools, it reaches a temperature M s  at which the martensite phase starts to form, and finishes the transformation at a still lower temperature M f . Upon reheating, it reaches a temperature A s  at which austenite begins to reform and then a temperature A f  at which the change back to austenite is complete. In the martensitic state, the alloy can be easily deformed. When sufficient heat is applied to the deformed alloy, it reverts back to the austenitic state, and returns to its original configuration. Accordingly, in the exemplary embodiment actuator  72  is fabricated from a material such as, but not limited to, NiTi, NiTi—Pt, TiRu, NiTiCu, CuZnAl, CuAlNi, NiTiFe, CuAlNiTiMn, TiNiPd, TiNiPt, NiTiPd, and TiNiHf. In the exemplary embodiment, the lower temperature chevrons used for the fan chevrons are fabricated from a Ni—Ti alloy, and the higher temperature chevrons used for the core engine chevrons are fabricated from a Ni—Ti—Pt alloy.  
         [0023]     During operation, chevron actuation system  70  is operable in at least one of an active mode and a passive mode. In the active mode, an electrical current is input to actuator  72 , i.e. shape memory alloy  74 , such that actuator  72  is contracted around outer periphery  76  of annular exhaust duct  32 . Contracting actuator  72  causes shape memory alloy band  72  to reconfigure from a first length  77  to a second length  78 , shorter than first length  77 , thus causing plurality of chevrons  52  to deflect inwardly toward central axis  28  (shown in  FIG. 3 ). More specifically, shape memory alloy band  72  contracts around outer periphery  76  such that a convergence of nozzle  50  is increased. When actuator  72  is de-energized, plurality of chevrons  52  deflect outwardly from central axis  28  such that plurality of chevrons  52  are substantially parallel to outer periphery  76  of annular exhaust duct  32 , thus decreasing the convergence of nozzle  50  (shown in  FIG. 4 ).  
         [0024]     In the passive mode, heat is input to actuator  72 , i.e. shape memory alloy  74 , such that actuator  72  is contracted around outer periphery  76  of annular exhaust duct  32 . In the exemplary embodiment, heat is supplied from engine  10  during takeoff or landing, for example. More specifically, engine exhaust flow, during operations other than take-off, flows past chevrons  52  but does not result in activation of actuator  72  since the temperature of the exhaust is not great enough to activate shape memory alloy  74 . During take-off operations, engine exhaust flow, having an increased temperature, flows past chevrons  52  and actuates shape memory alloy  74  resulting in an increased convergence of exhaust nozzle  50 . When the airplane has reached a cruise condition, the temperature of the exhaust flow is reduced, resulting in chevrons  52  deflecting away from central axis  28 , such that a convergence of nozzle  50  is decreased.  
         [0025]      FIG. 5  is a perspective view of an exemplary chevron actuation system  80  that can be used with nozzle  50  (shown in  FIGS. 2 and 3 ). Chevron actuation system  80  includes a plurality of actuators  82  coupled to annular exhaust duct  32 . In the exemplary embodiment, each actuator  82  includes a mounting portion  84  and a finger  86  coupled to mounting portion  84  and extending along outer surface  63  of each chevron  52 . In the exemplary embodiment, a plurality of fingers  86  are positioned along outer surface  63  of each chevron  52  and circumferentially around outer perimeter  76  of annular exhaust duct  32 .  
         [0026]     In the exemplary embodiment, fingers  86  are fabricated from shape memory alloy  74  having a memorized activated configuration. In the exemplary embodiment, shape memory alloy  74  is activated to reposition chevrons  52  and thereby either increase or decrease a convergence of the nozzle. As used herein a shape memory alloy is defined as a material which can be formed into any desired shape as described previously herein. Accordingly, in the exemplary embodiment actuator fingers  86  are fabricated from material such as, but not limited to, NiTi, TiRu, NiTiCu, CuZnAl, CuAlNi, NiTiFe, CuAlNiTiMn, TiNiPd, TiNiPt, NiTiPd, and TiNiHf.  
         [0027]     During operation, chevron actuation system  80  is operable in at least one of an active mode and a passive mode. In the active mode, an electrical current is input to each finger  86 , i.e. shape memory alloy  74 , such that each finger  86  is contracted around outer periphery  76  of annular exhaust duct  32 . Contracting fingers  86  causes plurality of chevrons  52  to deflect inwardly toward central axis  28  (shown in  FIG. 3 ). Accordingly, actuating fingers  86  increases a convergence of nozzle  50 . When fingers  86  are de-energized, plurality of chevrons  52  deflect outwardly from central axis  28  such that plurality of chevrons  52  are substantially parallel to outer periphery  76  of annular exhaust duct  32 , thus decreasing the convergence of nozzle  50  (shown in  FIG. 5 ).  
         [0028]     In the passive mode, heat is applied to fingers  86  to activate shape memory alloy  74 . In the exemplary embodiment, heat is supplied from the engine during engine takeoff or landing, for example. More specifically, engine exhaust flow, during operations other than take-off, flows past chevrons  52  but does not result in activation of fingers  86  since the temperature of the exhaust is not great enough to activate shape memory alloy  74 . During take-off operations, engine exhaust flow, having an increased temperature, flows past chevrons  52  and actuates shape memory alloy  74  thereby increasing a convergence of exhaust nozzle  50  (shown in  FIG. 3 ). When the airplane has reached a cruise condition, the temperature of the exhaust flow is reduced, resulting in chevrons  52  deflecting away from central axis  28 , such that a convergence of nozzle  50  is decreased (shown in  FIG. 5 ).  
         [0029]     In another exemplary embodiment, nozzle  50  includes a plurality of circumferentially or laterally adjoining chevrons  52  integrally disposed at an aft end  54  of annular exhaust duct  32 . Each chevron  52  has a geometric shape  56 . In the exemplary embodiment, each chevron  52  has a substantially triangular shape and is fabricated from a shape memory alloy material. Additionally, the shape metal alloy chevrons may be operated in either a passive or active mode as described previously herein. Accordingly, fabricating each chevron from a shape memory alloy material facilitates reducing a quantity of parts used to fabricate nozzle  50  and thereby facilitates reducing the time required to fabricate the nozzle.  
         [0030]     The above-described nozzle exhaust system includes a plurality of chevrons which can be repositioned to either increase a convergence of the exhaust nozzle during takeoff or decrease a convergence of the exhaust nozzle during cruise conditions using a shape memory alloy. The shape memory alloy is selectably operable using either electrical current supplied to the shape memory alloy or using engine exhaust heat. According, the shape memory alloy reconfigures the exhaust nozzle chevrons only when required, during takeoff for example, and streamlines the exhaust nozzle chevrons when not required, during cruise conditions for example. Accordingly, the nozzle system described herein facilitates reducing noise during takeoff or landing, and reducing or eliminating engine performance losses during cruise conditions.  
         [0031]     Exemplary embodiments of noise suppression systems and exhaust assemblies are described above in detail. The exhaust 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 noise suppression component can also be used in combination with other exhaust assemblies.  
         [0032]     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.