Abstract:
A method for assembling a fan assembly for a gas turbine engine includes coupling a plurality of fan blades in a row to a rotor disk, wherein each fan blade includes an airfoil having a first sidewall and a second sidewall connected together at a leading edge and a trailing edge, and wherein each airfoil extends radially between a root and a tip. The method also includes coupling at least one shroud to at least one of the plurality of rows of fan blades, such that the shroud is coupled to at least one fan blade tip extending within the same row of fan blades, and coupling at least one row of rotor blades to the shroud, such that the rotor blades extend radially outward from the shroud.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to gas turbine engines, and more particularly to methods and apparatus for assembling fan assemblies for gas turbine engines.  
         [0002]     One key factor in aircraft engine design may be the installation and integration of the propulsion system with the aircraft system. For example, the cross-sectional area at the leading edge of the propulsion system, known as the frontal area of the propulsion system, may significantly impact the overall performance of an aircraft system. Specifically, a reduced engine frontal area generally simplifies the installation of the propulsion system into the fuselage or the engine nacelle. Moreover, if the engine frontal area is reduced, then the overall weight of the engine is also reduced.  
         [0003]     Within at least some known engines, a fan assembly influences and/or dictates the size of the frontal area. More specifically, known fan assemblies are sized to enable predetermined operational requirements, such as fan inlet radius ratio and/or specific flow to be achieved. The fan inlet radius ratio is generally a mechanical constraint, wherein the airflow output available from the fan assembly is directly linked to the wheel speed of the stage and may be limited by the materials used in fabricating the fan assembly. In contrast, the specific flow of the fan assembly may be limited by aerodynamic constraints.  
         [0004]     Other known engines include a “fan-on-blade”, known as a flade, to enable overall aircraft system requirements, such as reduced noise for commercial supersonic aircraft and engine-to-inlet airflow compatibility. In these engines, fan blades are generally coupled to the last stage of the fan assembly due to the increased inlet radius ratio of these downstream stages. Although beneficial, the use of flades may be limited, and more specifically, flades may not be available for use in engines having a reduced engine frontal area, because of the relatively high tip speed of the downstream rotors in engines having a reduced engine frontal area.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0005]     In one aspect, a method is provided for assembling a gas turbine engine. The method includes coupling a plurality of fan blades in a row to a disk, wherein each fan blade includes an airfoil having a first sidewall and a second sidewall connected together at a leading edge and a trailing edge, and wherein each airfoil extends radially between a root and a tip. The method also includes coupling at least one shroud to at least one of the plurality of rows of fan blades, such that the shroud is coupled to at least one fan blade tip extending within the same row of fan blades, and coupling at least two rows of rotor blades to the shroud, such that the rotor blades extend radially outward from the shroud, and wherein each rotor blade includes an airfoil having a first sidewall and a second sidewall connected together at a leading edge and a trailing edge.  
         [0006]     In another aspect, a fan assembly for a gas turbine engine is provided. The fan assembly includes a plurality of fan blades coupled together such that the fan blades are arranged in a circumferential row extending around a rotor disk, wherein each fan blade includes an airfoil including a first sidewall and a second sidewall connected together at a leading edge and a trailing edge and extends radially between a root and a tip. The fan assembly also includes at least one shroud coupled to at least one of the plurality of fan blade tips and extending circumferentially around the rotor disk, and at least one row of rotor blades extending radially outward from the at least one shroud. Each rotor blade includes an airfoil including a first sidewall and a second sidewall connected together at a leading edge and a trailing edge.  
         [0007]     In a further aspect, a gas turbine engine is provided that includes a fan blade assembly including a plurality of fan blades coupled together such that the fan blades are arranged in a circumferential row extending around a rotor disk, wherein each fan blade includes an airfoil including a first sidewall and a second sidewall connected together at a leading edge and a trailing edge and extends radially between a root and a tip. The fan assembly also includes at least one shroud coupled to at least one of the plurality of fan blade tips and extending circumferentially around the rotor disk, and at least two rows of rotor blades extending radially outward from the at least one shroud. Each rotor blade includes an airfoil including a first sidewall and a second sidewall connected together at a leading edge and a trailing edge. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic illustration of an exemplary fladed engine.  
         [0009]      FIG. 2  is a schematic illustration of a portion of the fladed engine shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]      FIG. 1  is a schematic illustration of an exemplary “fan-on-blade” or fladed engine  16  having an axially oriented engine centerline axis  18 .  FIG. 2  is a schematic illustration of a portion of fladed engine  16 . Engine  16  includes a flade inlet  20  and a 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 stream  26 , and airflow  24  entering fan inlet  22  flows along a fan stream  28 . Flade stream  26  and fan stream  28  are separated by a fan casing  30  extending downstream from fan inlet  22 . Fan stream  28  and flade stream  26  are channeled through a fan assembly  32  wherein airflow  24  is compressed and discharged downstream as flade discharge airflow  34  and fan discharge airflow  36 . Discharge airflows  34  and  36  facilitate generating thrust to power engine  16 .  
         [0011]     Fan assembly  32  includes a plurality of fan blades  40 . Each fan blade  40  includes a leading edge  42  and a trailing edge  44  and extends radially between a root  46  and a tip  48 . In the exemplary embodiment, fan blades  40  are arranged in a two-stage configuration such that fan assembly  32  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 . First and second rows  52  and  56 , respectively, are spaced apart an axial distance  58 . Distance  58  is variably selected to enable fan assembly  32  to meet operational requirements and to facilitate reducing wake generated in airflow  22  between first and second rows  52  and  56 , respectively.  
         [0012]     In the exemplary embodiment, a shroud  60  extends circumferentially around, and is coupled to, each fan blade tip  48  within first stage  50 . In one embodiment, shroud  60  is a single annular member that is coupled to each fan blade tip  48  within first stage  50 . In another embodiment, fan assembly  32  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  48  such that the arcuate members extend circumferentially around first stage  50 . Specifically, each arcuate member is positioned adjacent other arcuate members to facilitate reducing an amount of air transfer between flade stream  26  and fan stream  28 . Shroud  60  is positioned within a cavity  62  defined in fan casing  30  such that shroud  60  is substantially aligned with fan casing  30 . In the exemplary embodiment, shroud  60  extends between an upstream side  64  and a downstream side  66 , and includes a plurality of seal members  68  extending between each respective shroud side  64  and  66 , and fan casing  30 . As such, shroud  60  facilitates preventing airflow flowing from fan stream  28  to flade stream  26 , or vice-versa.  
         [0013]     Fan assembly first stage  50  is rotatably coupled to, and driven by, a first shaft  70 , and fan assembly 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  operates with a faster rotational speed than first shaft  70 , such that second stage  54  operates at a faster rotational speed than first stage  50 . Moreover, 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 with the same rotational speed and/or in the same rotational direction.  
         [0014]     In the exemplary embodiment, fan stream  28  is defined between fan casing  30  and a rotor hub  74 . Moreover, fan stream  28  has a fan inlet radius ratio that is defined as an inlet hub radius  78  divided by an inlet tip radius  76 , wherein inlet tip radius  76  is measured with respect to centerline axis  18  and fan blade tips  48 , and inlet hub radius  78  is measured with respect to centerline axis  18  and an intersection of hub  74  and blade roots  46 . In the exemplary embodiment, the first stage fan inlet radius ratio is smaller than the second stage fan inlet radius ratio as necessitated by the increased density into second stage  54 . In one embodiment, first stage  50  is designed with a fan inlet radius ratio that is between approximately 0.1 and 0.3. In another embodiment, first stage fan inlet radius ratio is between approximately 0.1 and 0.15. First stage fan inlet radius ratio is selected to facilitate improving a flow per unit frontal area and the overall performance of engine  16 , while satisfying overall engine performance requirements. Accordingly, because the fan inlet radius ratio is reduced in comparison to other known engines, first stage  50  has a reduced rotational speed and a reduced fan blade tip speed. Moreover, because of the reduced rotational speed of first stage  50 , first stage  50  has a reduced pressure ratio. Accordingly, in order for engine  16  to satisfy overall performance requirements, second stage  54  has a higher rotational speed and a higher fan blade tip speed than that of first stage  50 .  
         [0015]     In operation, fan stream  28  flows through fan inlet  22  and is channeled towards first stage  50  between fan casing  30  and hub  74 . As fan stream  28  is channeled through first row  52  of fan blades  40 , the density of fan stream  28  is increased. Fan stream  28  is then channeled through second row  56  of fan blades  40  wherein the density of fan stream  28  is further increased.  
         [0016]     In the exemplary embodiment, engine  16  includes a splitter  80  downstream from second row  56 . Splitter  80  facilitates dividing fan stream  28  into a core stream  82  and a bypass stream  84 . More specifically, splitter  80  is oriented to facilitate dividing fan stream  28  to enable engine  16  to meet engine overall performance requirements relating to thrust and airflow pressure ratios.  
         [0017]     Fan assembly  32  also includes a plurality of fladed rotor blades  90 . Each fladed blade  90  includes a leading edge  92  and a trailing edge  94  and extends radially between a root  96  and a tip  98 . In the exemplary embodiment, blades  90  are arranged in a two stage configuration such that fan assembly  32  includes a first flade stage  100  having a first row  102  of circumferentially spaced fladed blades  90  and a second flade stage  104  having a second row  106  of circumferentially spaced fladed blades  90 . In one embodiment, first stage blade tips  98  have an axial length  108  that enables multiple flade stages to be coupled within engine  16 , such as, but not limited to, first and second flade stages  100  and  104 , respectively.  
         [0018]     In the exemplary embodiment, each blade  90  within flade stage  100  and  104  is 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 . In the exemplary embodiment, flade stages  100  and  104  are coupled to fan assembly first stage  50 . In an alternative embodiment, each blade  90  within flade stages  100  and  104  is coupled to another stage of fan blades  40 . In yet another alternative embodiment, flade stages  100  and  104  are coupled to different stages of fan blades  40  other than first stage  50  or second stage  54 . In yet another alternative embodiment, fan assembly  32  includes more or less than two flade stages. Moreover, in the exemplary embodiment, because of the relatively low rotational speed of blades  40  within first stage  50 , fladed blades  90  have a radial height  110 , extending between blade root  96  and blade tip  98 , that is selected to facilitate improving an efficiency potential of flade stream  28 , while reducing the risk of exceeding tip speed constraints.  
         [0019]     In the exemplary embodiment, fan assembly  32  includes a row  112  of circumferentially spaced variable area inlet guide vanes  114 . Inlet guide vanes  114  are positioned upstream of first flade stage  100  and are operable to channel airflow towards first stage  100  of fladed blades  90 . Inlet guide vanes  114  meter the volume of airflow entering flade stream  26  and direct the airflow towards first flade stage  100 . As the airflow is channeled through first flade stage  100 , the airflow is compressed. Airflow discharged from first flade stage  100  passes through a row  116  of circumferentially spaced intermediate guide vanes  118  which changes the direction of airflow to facilitate reducing the rotary velocity component of the airflow. The airflow is then channeled towards second flade stage  104 . As the airflow is channeled through second flade stage  104 , the airflow is compressed. The airflow discharged from second flade stage  104  passes through a row  120  of circumferentially spaced outlet guide vanes  122  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 a flade duct  124  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  16 .  
         [0020]     The above-described flade engine includes a reduced diameter fan assembly. The fan assembly includes first and second rows of flades coupled to a first row of fan blades. The multiple stages of flades facilitate increasing an amount of pressurized airflow available for the engine. Accordingly, the amount of pressurized airflow that is required for the fan blades to produce is reduced. As a result, the overall diameter of the fan assembly is reduced, thereby decreasing the overall weight of the engine, and increasing the ease of installation of the engine.  
         [0021]     Exemplary embodiments of a fan assembly are described above in detail. The fan assembly is not limited to the specific embodiments described herein, but rather, components of each fan assembly may be utilized independently and separately from other components described herein. For example, each fan assembly component can also be used in combination with other fan assembly components.  
         [0022]     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.