Abstract:
A gas turbine engine includes an inlet duct that is formed with a generally elliptical shape. The inlet duct includes a vertical centerline and a fan section that has an axis of rotation. The axis of rotation is spaced from the vertical centerline and is disposed within an inlet duct orifice.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/971,037, which was filed on Mar. 27, 2014 and is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    This invention was made with government support under Contract No. NNC07CB59C, awarded by NASA. The Government has certain rights in this invention. 
     
    
     BACKGROUND 
       [0003]    This application relates to an inlet wall design for use in an embedded gas turbine engine. 
         [0004]    Gas turbine engines are known and typically include a fan delivering air into a bypass duct and into a core engine. In the core engine the air is compressed at a compressor and then mixed with fuel and ignited in a combustion section. Products of the combustion pass downstream over turbine rotors, driving them to rotate. 
         [0005]    Gas turbine engines have historically been mounted on a tail or beneath the wings of an aircraft. However, a next generation of aircraft seeks to dramatically increase fuel efficiency, reduce emissions, and decrease fuel burn. A design for such aircraft utilizes a blended wing design wherein the body and wing merge smoothly into each other. Such designs have typically been proposed with embedded engines, which are mounted within a fuselage or body of the aircraft. 
         [0006]    In such an engine, the area upstream of an inlet to the engine is different on circumferential locations adjacent to the body than at locations spaced away from the body. A boundary layer or area of low momentum air will be formed leading into the inlet and the fan at circumferential locations associated with the body. 
       SUMMARY 
       [0007]    In one exemplary embodiment, a gas turbine engine includes an inlet duct that is formed with a generally elliptical shape. The inlet duct includes a vertical centerline and a fan section that has an axis of rotation. The axis of rotation is spaced from the vertical centerline and is disposed within an inlet duct orifice. 
         [0008]    In a further embodiment of the above, the axis of rotation is spaced a first distance from the vertical centerline at a throat of the inlet duct. The axis of rotation is spaced a second distance from the vertical centerline at an intermediate location along the inlet duct. The first distance is greater than the second distance. 
         [0009]    In a further embodiment of any of the above, the axis of rotation is spaced a third distance from the vertical centerline at an axial location adjacent the fan section. The third distance is less than the second distance. 
         [0010]    In a further embodiment of any of the above, the axis of rotation is spaced a first distance from the vertical centerline at a first axial position in the inlet duct. The axis of rotation is spaced a second distance from the vertical centerline at a second axial position in the inlet duct. The first distance is greater than the second distance. 
         [0011]    In a further embodiment of any of the above, the first axial position is upstream of the second axial position. 
         [0012]    In a further embodiment of any of the above, the axis of rotation is spaced from the vertical centerline in a direction of rotation of an upper fan blade of the fan section. 
         [0013]    In another exemplary embodiment, a blended wing aircraft includes a blended wing fuselage and at least one embedded gas turbine engine in the fuselage. The gas turbine engine includes an inlet duct formed with a generally elliptical shape with a vertical centerline and a fan section that has an axis of rotation. The axis of rotation is spaced from the vertical centerline. 
         [0014]    In a further embodiment of the above, the axis of rotation is spaced a first distance from the vertical centerline at a throat of the inlet duct. The axis of rotation is spaced a second distance from the vertical centerline at an intermediate location along the inlet duct. The first distance is greater than the second distance. 
         [0015]    In a further embodiment of the above, the axis of rotation is spaced a third distance from the vertical centerline at an axial location adjacent the fan section. The third distance is less than the second distance. 
         [0016]    In a further embodiment of the above, the axis of rotation is spaced a first distance from the vertical centerline at a first axial position in the inlet duct. The axis of rotation is spaced a second distance from the vertical centerline at a second axial position in the inlet duct. The first distance is greater than the second distance. 
         [0017]    In a further embodiment of the above, the first axial position is upstream of the second axial position. 
         [0018]    In a further embodiment of the above, the axis of rotation is spaced from the vertical centerline in a direction of rotation of an upper fan blade of the fan section. 
         [0019]    In a further embodiment of the above, the axis of rotation is disposed within an inlet duct orifice. 
         [0020]    In a further embodiment of the above, the at least one embedded gas turbine engine includes a first gas turbine engine that is configured to rotate in a first direction. A second gas turbine engine is configured to rotate in a second opposite direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  illustrates a blended wing aircraft. 
           [0022]      FIG. 2  illustrates an inlet duct for a gas turbine engine as may be included in the  FIG. 1  embodiment. 
           [0023]      FIG. 3  illustrates a cross-sectional view of the gas turbine engine from  FIG. 2 . 
           [0024]      FIG. 4  illustrates a top view of the inlet duct. 
           [0025]      FIG. 5  illustrates a side view of the inlet duct. 
           [0026]      FIG. 6  illustrates a perspective view of the inlet duct. 
           [0027]      FIG. 7  illustrates a perspective view of the inlet duct. 
           [0028]      FIG. 8A  illustrates the inlet duct at a throat. 
           [0029]      FIG. 8B  illustrates the inlet duct at an intermediate location. 
           [0030]      FIG. 8C  illustrates the inlet duct adjacent the fan. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    An aircraft  20  is illustrated in  FIG. 1  having a blended wing body or fuselage  22  and a plurality of embedded gas turbine engines  24 . As known, the embedded gas turbine engines  24  include a fan  30  ( FIG. 2 ) at an upstream location delivering air into a compressor and into a bypass duct. The air is mixed with fuel and ignited in a combustor downstream of the compressor and products of that combustion pass downstream over turbine rotors driving them to rotate. 
         [0032]    There are challenges with regard to the embedded gas turbine engines  24 . As an example, as shown in  FIG. 2 , an inlet end  26  of the embedded gas turbine engine  24  includes an inlet duct  28  that will sit on the fuselage  22 . There will be a boundary layer leading into a bottom surface  32  of the inlet duct  28  for the gas turbine engine  24 . A duct centerline DC of the inlet duct  28  is shifted horizontally from an axis of rotation A of the fan  30 . For example, the duct centerline DC is shifted horizontally in the direction of rotation R of a fan blade located at a top of the fan  30 . As shown in this design, the inlet duct  28  includes a throat T at the inlet end  26  that is generally elliptical. The inlet duct  28  becomes generally more circular downstream of the throat T towards the fan  30 . Applicant has designed the shape of the inlet duct by utilizing ellipses and optimizing the curves, lengths and shape of the overall duct. 
         [0033]    As shown in  FIGS. 3 and 4 , the duct centerline DC is spaced from the axis of rotation A at the throat T. The duct centreline DC gradually approaches the axis of rotation A downstream of the throat T. Although a single fan blade is shown in  FIGS. 4-7  to illustrate the direction of rotation of the fan  30 , one of ordinary skill in the art would recognize that multiple fan blades would surround the fan  30 . 
         [0034]    As shown in  FIG. 5 , a first vertical dimension V 1  at the throat T of the inlet duct  28  generally increases downstream towards the fan  30  to a second vertical dimension V 2  adjacent the fan  30 . The second vertical dimension V 2  is greater than the first vertical dimension V 1 . 
         [0035]    As shown in  FIG. 8A , the throat T of the inlet duct  28  includes a very small lower ellipse  62  and an upper ellipse  64 , which is much larger. This may be at the upstream most point of the inlet duct  28  and immediately downstream of the fuselage  22 . The axis of rotation A is spaced horizontally a distance D 1  from the duct centerline DC and extends through the inlet duct  28 . In this example, the axis of rotation extends through an upper left quadrant of the inlet duct  28 . 
         [0036]      FIG. 8B  shows another location  70  which is generally intermediate in the inlet duct  28  as shown in  FIG. 5 . At the location  70 , the inlet duct  28  includes a lower ellipse  72  that is much larger than the lower ellipse  62  shown in  FIG. 8A . An upper ellipse  74  is slightly narrower than the upper ellipse  64  shown in  FIG. 8A . The axis of rotation A is spaced horizontally a distance D 2  from the duct centerline DC and extends through an upper left quadrant of the inlet duct  28 . The distance D 2  is less than the distance D 1 . 
         [0037]      FIG. 8C  shows a downstream location  80  adjacent the fan  30 . An upper ellipse  84  is generally the same size as a lower ellipse  82  and the upper and lower ellipses  84  and  82  are generally circular. The axis of rotation A generally extends through the duct centreline DC or is spaced a distance from the duct centreline DC that is less than the distance D 1  or the distance D 2  shown in  FIGS. 8A and 8B , respectively. 
         [0038]    By designing the inlet duct  28  according to the teachings above, the airflow will be more uniform by the time it reaches the fan  30 , and the effects of the boundary layer from the fuselage  22  will be dramatically reduced. In particular, air entering the inlet duct  28  along the inlet area IA ( FIG. 2 ) will have a reduced angle of incidence. The inlet area IA is generally located between the 6 and 9 o&#39;clock position when the fan  30  is rotating clockwise and between the 6 and 3 o&#39;clock position when the fan  30  is rotating counterclockwise. Air entering the inlet duct  28  with a high angle of incidence reduces the operational margin of the gas turbine engine  24  and can decrease the life of the fan blades. 
         [0039]    A worker of ordinary skill in this art would recognize when either of the inlet shape options would be most efficient to utilize. Of course, other shapes may be utilized as well. 
         [0040]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.