Abstract:
A method for assembling a gas turbine engine includes providing a core engine, and providing a flade system including a flade stream augmentor positioned within a flade duct. The method also includes channeling airflow through the core engine to produce engine thrust, channeling airflow through the flade duct to produce engine thrust, and igniting a portion of the airflow channeled through the flade duct using the flade stream augmentor to increase the amount of thrust produced by the flade system.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to gas turbine engines and more particularly, to methods and apparatus for assembling fladed engines.  
         [0002]     Variable cycle engines are conventionally known for powering high performance aircraft from subsonic to supersonic speeds while attempting to obtain countervailing objectives such as high specific thrust and low fuel consumption. In other words, ideal aircraft jet engines attempt to operate through various modes of thrust and speed requirements while minimizing fuel consumption.  
         [0003]     Known variable cycle engines are generally operable over a range of operating conditions. In particular, conventional variable cycle combined turbojet or turbofan and ramjet engines generally attempt to provide for a range of operation from low subsonic Mach numbers to high supersonic Mach numbers of about Mach 6. However such turbofan-ramjet engines are relatively complex and generally include varying disadvantages. For example, at least one known turbofan-ramjet engine includes a ram burner which is wrapped around a core engine, thus creating an undesirably large diameter engine.  
         [0004]     Other known variable cycle engines include variable coannular exhaust nozzles that are relatively complex and difficult to schedule the flow area thereof. Additionally, these known engines have a high level of base drag associated with the exhaust nozzles. Moreover, other known variable cycle engines include coannular, separate flow paths including a coannular inlet which creates an undesirably large inlet and which typically requires an inlet diverter valve for selectively channeling inlet air flow. These known engines may have high levels of spillage around the engine inlet. Other known engines may include one or more of such undesirable structures, thus resulting in an engine that is relatively complex, heavy, large, and inefficient.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     In one aspect, a method is provided for operating a gas turbine engine. The method includes providing a core engine, and providing a flade system including a flade stream augmentor positioned within a flade duct. The method also includes channeling airflow through the core engine to produce engine thrust, channeling airflow through the flade duct to produce engine thrust, and igniting a portion of the airflow channeled through the flade duct using the flade stream augmentor to increase the amount of thrust produced by the flade system.  
         [0006]     In another aspect, a flade system for a gas turbine engine is provided. The gas turbine engine includes a core engine including an inner fan duct for channeling airflow through a portion of the core engine, and at least one inner fan section including at least one row of inner fan blades positioned in the inner fan duct. The engine also includes a flade system including a flade duct surrounding the inner fan duct and defining a flade stream, at least one fladed fan positioned in the flade duct and producing a flade stream airflow, wherein the fladed fan includes at least one row of fladed fan blades radially outward of and coupled to the inner fan section such that the fladed fan blades are driven by the inner fan section, and a flade stream augmentor positioned within the flade duct.  
         [0007]     In a further aspect, a gas turbine engine is provided. The gas turbine engine includes a core engine including an inner fan duct for channeling airflow through a portion of the core engine, and at least one inner fan section including at least one row of inner fan blades positioned in the inner fan duct. The engine also includes a flade system including a flade duct surrounding the core engine and defining a flade stream, at least one fladed fan positioned in the flade duct and producing a flade stream airflow, wherein the fladed fan includes at least one row of fladed fan blades radially outward of and coupled to the inner fan section such that the fladed fan blades are driven by the inner fan section, and a flade stream augmentor positioned within the flade duct.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is an end view of an aircraft including an exemplary engine.  
         [0009]      FIG. 2  is a schematic illustration of an exemplary fladed engine that may be used with the aircraft shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]      FIG. 1  is a schematic illustration of a jet aircraft  10  including a plurality of engines  12  and a plurality of nozzle assemblies  14 . Aircraft  10  includes an aircraft inlet  16  for channeling airflow to engines  12 .  
         [0011]      FIG. 2  is a schematic illustration of an exemplary “fan-on-blade” or fladed engine  12  having an axially oriented engine centerline axis  18 . Engine  12  includes a flade inlet  20  and an inner fan inlet  22  through which engine inlet airflow  24  enters during engine operations. In the exemplary embodiment, airflow  24  entering flade inlet  20  flows along a flade duct  26 , and airflow  24  entering inner fan inlet  22  flows along an inner fan duct  28 . Flade inlet  20  facilitates capturing additional airflow  24  that would otherwise spill around engine  12  leading to spillage drag losses on engine  12 . Accordingly, the airflow captured by flade inlet  20  is channeled through engine  12  to improve engine  12  performance by increasing thrust through additional exhaust. Moreover, the airflow captured by flade inlet  20  is channeled by flade duct  26  to facilitate cooling portions of engine  12 .  
         [0012]     In the exemplary embodiment, fan duct  28  is defined by a fan casing  30  that extends circumferentially around the core engine along centerline axis  18  from fan inlet  22 . Fan casing  30  separates fan duct  28  and flade duct  26 . As such, flade duct  26  is defined by fan casing  30  and a flade casing  32 , positioned radially outward from fan casing  30 . Fan duct  28  and flade duct  26  channel airflow  24  through a fan assembly  34  wherein airflow  24  is compressed and discharged downstream as flade discharge airflow  36  and fan discharge airflow  38 . Discharge airflows  36  and  38  facilitate generating thrust to power engine  12 .  
         [0013]     Fan assembly  34  includes a plurality of fan blades  40 . Each fan blade  40  includes a leading edge and a trailing edge and extends radially between a root and a tip. In the exemplary embodiment, fan blades  40  are arranged in a two-stage configuration such that fan assembly  34  includes a first fan stage  50  having a first row  52  of circumferentially-spaced fan blades  40 , and a second fan stage  54  having a second row  56  of circumferentially-spaced fan blades  40 . In an alternative embodiment, fan assembly  34  includes more or less than two fan stages and includes more or less than two rows of fan blades.  
         [0014]     A shroud  60  extends circumferentially around, and is coupled to, each fan blade tip within second stage  54 . In one embodiment, shroud  60  is a single annular member that is coupled to each fan blade tip within second stage  54 . In another embodiment, fan assembly  34  includes a plurality of tip shrouded airfoils such that shroud  60  includes a plurality of arcuate members each coupled to at least one fan blade tip such that the arcuate members extend circumferentially around second stage  54 . Specifically, each arcuate member is positioned adjacent other arcuate members to facilitate reducing an amount of air transfer between flade stream  26  and fan duct  28 . Shroud  60  facilitates preventing airflow flowing from fan duct  28  to flade duct  26 , or vice-versa. In an alternative embodiment, shroud  60  is coupled to another stage, such as, for example, first stage  50 .  
         [0015]     In the exemplary embodiment, fan assembly  34  is a counter rotating fan assembly such that first stage  50  is rotatably coupled to, and driven by, a first shaft  70 , and second stage  54  is rotatably coupled to, and driven by, a second shaft  72 . First and second shafts  70  and  72  operate independently with respect to each other, such that first shaft  70  operates with a first rotational speed that is different than a second rotational speed of second shaft  72 . Accordingly, first stage  50  and second stage  54  have different operational speeds. In the exemplary embodiment, second shaft  72  rotates in an opposite direction than first shaft  70 . In an alternative embodiment, first stage  50  and second stage  54  operate in the same rotational direction.  
         [0016]     A fan stream  74  flows through fan duct  28 . Specifically, fan stream  74  enters engine  12  at fan inlet  22  and flows between fan casing  30  and a rotor hub  76 . In operation, fan stream  74  is channeled through a plurality of inlet guide vanes  78  towards first stage  50  between fan casing  30  and hub  76 . As fan stream  74  is channeled through first row  52  of fan blades  40 , the density of fan stream  74  is increased. Fan stream  74  is then channeled through second row  56  of fan blades  40  wherein the density of fan stream  74  is further increased. Once fan stream  74  is channeled through fan assembly  34 , the airflow is divided by a splitter  80  into a core stream  82  and a bypass stream  84 . More specifically, splitter  80  is oriented downstream of fan assembly  34  to facilitate dividing fan stream  74  to enable engine  12  to meet engine overall performance requirements relating to thrust and airflow pressure ratios. Core stream  82  continues through the core engine towards a downstream end  86  of fan duct  28 . Additionally, bypass stream  84  continues through fan duct  28  towards downstream end  86 . In the exemplary embodiment, core and bypass streams  82  and  84  are mixed together upstream of downstream end  86  prior to the addition of fuel to the mixture. The fuel-air mixture is then ignited by a plurality of augmentors  87  prior to being exhausted through downstream end  86 .  
         [0017]     In the exemplary embodiment, fan assembly  34  also includes a fladed fan assembly  88  that includes a plurality of fladed rotor blades  90  positioned within flade duct  26 . Each fladed blade  90  includes a leading edge and a trailing edge and extends radially between a root and a tip. In the exemplary embodiment, fladed blades  90  are arranged in a row that extends circumferentially around shroud  60 . Fladed blades  90  produce flade discharge airflow  36  that is channeled through flade duct  26 .  
         [0018]     Each fladed blade  90  is drivenly coupled to shroud  60  at blade root  96  and extends radially outward from shroud  60 . In one embodiment, each fladed blade  90  is coupled to shroud  60  via, for example, a welding process, such as, but not limited to, an inductive welding process. In another embodiment, fladed blades  90  are unitarily formed with shroud  60 . Fladed blades  90  have a radial height extending between the blade root and the blade tip  98 , that is selected to facilitate improving an efficiency potential of flade stream  74 , while reducing the risk of exceeding tip speed constraints.  
         [0019]     A row of circumferentially spaced variable area inlet guide vanes  104  are positioned within flade duct  26  upstream of fladed blades  90 . Inlet guide vanes are operable to channel airflow towards fladed blades  90  and meter the volume of airflow entering flade stream  26 . As the airflow is channeled through fladed blades  90  the airflow is compressed. The airflow discharged from fladed blades  90  passes through a row  106  of circumferentially spaced outlet guide vanes  108  which change the direction of the airflow to facilitate reducing the rotary velocity component of the airflow. Flade stream  26  is then channeled downstream through flade duct  26  prior to being exhausted. Accordingly, flade stream  26  increases an amount of high pressure airflow available, thus facilitating increasing the overall performance and/or thrust of engine  12 .  
         [0020]     In the exemplary embodiment, engine  12  includes a flade stream augmentor  110  to facilitate increasing the thrust output, and therefore the overall performance of engine  12 . Augmentor  110  is positioned in flade duct  26  such that a portion of flade stream  74  is mixed with a fuel, ignited and then exhausted downstream of augmentor  110 . Specifically, flade stream  74  is exhausted into a nozzle assembly  112  positioned at a downstream end of engine  12 . Additionally, the discharge airflow from fan duct  28  is exhausted into nozzle assembly  112 . Accordingly, the discharge from flade and fan ducts  26  and  28  are mixed in nozzle assembly  112  and exhausted from engine  12 . In the exemplary embodiment, nozzle assembly  112  includes an upper nozzle section  114  and a lower nozzle section  116 . A throat area  118  is defined by the inner surface of a nozzle liner  120  between the upper and lower nozzle sections  114  and  116 . Additionally, a front flap  122  and a rear flap  124  are coupled to lower nozzle section  116  and are moveable such that throat area  118  is variable. Specifically, throat area  118  is increased and/or decreased depending on the mode of operation and/or the required thrust output of engine  12 .  
         [0021]     Flade duct  26  includes a flade duct scroll  130  that channels a portion of flade stream  74  from a lower flade section  132  to an upper flade section  134 . A portion of flade duct  26  continues downstream from flade duct scroll  130  such that flade stream  74  in that portion facilitates cooling fan casing  30  and/or nozzle assembly  112  proximate the downstream end of engine  12 . In one embodiment, by way of example only, approximately 20%-30% of flade stream  74  continues downstream of flade duct scroll  130  in the corresponding flade duct  26 . In other embodiments, more or less of flade stream  74  continues downstream of flade duct scroll  130  to facilitate improving the cooling potential of flade duct  26 . In the exemplary embodiment, flade duct scroll  130  extends to upper flade section  134  and is positioned upstream of augmentor  110 . Specifically, flade duct scroll  130  channels flade stream  74  upstream of augmentor  110  to facilitate increasing the amount of flade stream  74  airflow that enters augmentor  110  for ignition. As such, the overall thrust potential of engine  12  is increased.  
         [0022]     Augmentor  110  includes a fuel spraybar  140 , a plurality of burners  142 , and a burner cavity  144  extending downstream from burners  142 . An inlet  146  is positioned at an upstream end  148  of augmentor  110  and is defined by an inner burner cavity liner  150  and an outer burner cavity liner  152 . Outer liner  152  is positioned radially outward from inner liner  150  and defines burner cavity  144  therebetween. Additionally an inner flade bypass duct  154  extends between inner liner  150  and fan casing  30 , and an outer flade bypass duct  156  extends between outer liner  152  and flade casing  32 . Flade bypass ducts  154  and  156  facilitate channeling the excess flade stream  74  airflow around augmentor  110 . Additionally, flade bypass ducts  154  and  156  facilitate channeling a portion of flade stream  74  around augmentor  110  for cooling burner cavity  144  and/or fan duct  28 .  
         [0023]     In the exemplary embodiment, fuel spray bar  140  delivers fuel to augmentor  110  to mix with the air in flade stream  74 . Specifically, the fuel is mixed with the portion of flade stream  74  entering augmentor inlet  146 . Burners  142  are positioned downstream of spray bar  140  and facilitate igniting and/or maintaining ignition of the fuel air mixture. Once ignited, the fuel-air mixture expands and the temperature is increased to facilitate increasing the overall thrust produced by engine  12 . The hot gas produced is channeled through a flade burner throat  160  into the nozzle assembly  112 . Specifically, the hot gas is channeled into a common secondary nozzle system to facilitate filling the nozzle base area and reduce nozzle base drag.  
         [0024]     In one embodiment, a cooling cavity  162  is formed between flade casing  32  and a radially outer engine casing  164 . Flade casing  32  is supported by a strut  166  extending between engine casing  164  and flade casing  32 . In the exemplary embodiment, strut  166  controls the area defined by flade burner throat  160 . Flade casing  32  is also supported by a support member  168 . In the exemplary embodiment, support member  168  extends between engine casing  164  and fan casing  30  to facilitate supporting fan casing  30 , inner liner  150 , outer liner  152 , and flade casing  32 . In one embodiment, burners  142  are coupled to support member  168  between inner and outer burner cavity liners  150  and  152 .  
         [0025]     The above-described fladed engines are cost-effective and highly reliable. The fladed engine includes a flade stream for capturing a portion of the airflow spilled around fan inlet. The increased airflow through the engine increases the amount of thrust generated by the engine. Additionally, the engine includes a flade duct scroll for channeling a significant portion of the airflow upstream of a flade stream augmentor. As a result, a portion of the flade stream is ignited to produce additional thrust generation by the engine, thereby increasing the engines overall performance.  
         [0026]     Exemplary embodiments of fladed engines are described above in detail. The fladed engines are not limited to the specific embodiments described herein, but rather, components of each fladed engine may be utilized independently and separately from other components described herein. For example, each fladed engine component can also be used in combination with other fladed engine components described herein.  
         [0027]     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.