Patent Publication Number: US-11649834-B2

Title: Engine systems and methods

Description:
RELATED APPLICATION 
     This patent claims the benefit of U.S. patent application Ser. No. 15/887,340, filed Feb. 2, 2018, which is hereby incorporated herein by reference in its entirety. Priority to U.S. patent application Ser. No. 15/887,340, is hereby claimed. 
     FIELD 
     The subject matter described herein relates to aircraft systems. 
     BACKGROUND 
     During operation of a gas turbine engine assembly, airflow is channeled from a fan assembly to a fan stream exhaust. Rotating fan blades of the fan assembly generate air wakes that interfere with outlet guide vanes downstream from the fan blades. The outlet guide vanes may reduce an amount of swirl that is present in the air wake by turning the flow of air from the fan. Additionally, the air wake interferes with the outlet guide vanes to generate aerodynamic noise. Such aerodynamic noise may be seen as a nuisance or discomfort to aircraft passengers, or may exceed a noise ordinance law or requirement. 
     In addition to turning the fan airflow, the outlet guide vanes may also provide structural stiffness to the fan frame. More specifically, the outlet guide vanes may be integrated with the fan frame, forming an integrated fan frame assembly. 
     Known systems for reducing an amount of aerodynamic noise include outlet guide vane sweeps at leading and trailing edges of the outlet guide vane. Sweeping the leading and trailing edges also maintains the outlet guide vane chord length between the leading and trailing edges. Although sweeping the leading and trailing edges reduces a level of aerodynamic noise generated by the outlet guide vanes, sweeping the leading and trailing edges also reduces an amount of structural stiffness provided by the outlet guide vanes that are integrated with the fan frame assembly. 
     BRIEF DESCRIPTION 
     In one embodiment, a system includes an airfoil configured to be disposed inside of an engine assembly. The airfoil is shaped to direct air inside the engine assembly. The airfoil includes a pressure side and a suction side that are coupled together at a leading edge of the airfoil and that are coupled together at a trailing edge of the airfoil that is located downstream from the leading edge. The airfoil extends a radial length away from a central axis of the engine assembly between a hub end of the airfoil and an opposite tip end of the airfoil. The airfoil includes a sweep feature disposed at the leading edge of the airfoil. The sweep feature is shaped to alter the air inside the engine assembly. Altering the air inside the engine assembly reduces a surface unsteady pressure level on the airfoil relative to the leading edge not including the sweep feature. The system also includes a fan frame assembly comprising an inner surface and an outer surface. The hub end of the airfoil is configured to be operably coupled with the inner surface of the fan frame assembly and the tip end of the airfoil is configured to be operably coupled with the outer surface of the fan frame assembly. The airfoil is configured to be integrated with the fan frame assembly of the system such that the airfoil increases a structural load supporting capability of the fan frame assembly relative to the airfoil not being integrated with the fan frame assembly. 
     In one embodiment, an airfoil is configured to be disposed inside of an engine assembly including a fan frame assembly. The airfoil is shaped to direct air inside the engine assembly. The airfoil includes a pressure side and a suction side that are coupled together at a leading edge of the airfoil and that are coupled together at a trailing edge of the airfoil that is located downstream from the leading edge. The airfoil extends a radial length away from a central axis of the engine assembly between a hub end of the airfoil and an opposite tip end of the airfoil. The leading edge of the airfoil includes a sweep feature that is shaped to alter the air inside the engine assembly. Altering the air inside the engine assembly reduces a surface unsteady pressure level on the airfoil relative to the leading edge not including the sweep feature. The hub end of the airfoil is configured to be operably coupled with an inner surface of the fan frame assembly and the tip end of the airfoil is configured to be operably coupled with an outer surface of the fan frame assembly. The airfoil is configured to be integrated with the fan frame assembly such that the airfoil increases a structural load supporting capability of the fan frame assembly relative to the airfoil not be integrated with the fan frame assembly. 
     In one embodiment, a method includes integrating an airfoil configured to be disposed inside an engine assembly with a fan frame assembly. The airfoil is shaped to direct air inside the engine assembly. The airfoil includes a pressure side and a suction side that are coupled together at a leading edge of the airfoil and that are coupled together at a trailing edge of the airfoil that is located downstream from the leading edge. The airfoil extends a radial length away from a central axis of the engine assembly between a hub end of the airfoil and an opposite tip end of the airfoil. The airfoil includes a sweep feature disposed at the leading edge of the airfoil. The sweep feature is shaped to alter the air inside the engine assembly. The fan frame assembly includes an inner surface and an outer surface. The hub end of the airfoil is configured to be operably coupled with the inner surface of the fan frame assembly and the tip end of the airfoil is configured to be operably coupled with the outer surface of the fan frame assembly. The airfoil integrated with the fan frame assembly increases a structural load supporting capability of the fan frame assembly relative to the airfoil not being integrated with the fan frame assembly. The method also includes altering the air inside the engine assembly with the sweep feature of the leading edge of the airfoil. Altering the air inside the engine assembly reduces a surface unsteady pressure level on the airfoil relative to the leading edge not including the sweep feature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present inventive subject matter will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below: 
         FIG.  1    illustrates a cross-sectional view of a gas turbine engine assembly in accordance with one embodiment; 
         FIG.  2    illustrates a partial cross-sectional view of a system of the gas turbine engine assembly of  FIG.  1    in accordance with one embodiment; 
         FIG.  3    illustrates a perspective view of an airfoil in accordance with one embodiment; 
         FIG.  4    illustrates unsteady surface pressure exerted by air inside the engine assembly of  FIG.  1    in accordance with one embodiment; 
         FIG.  5    illustrates a perspective view of an airfoil in accordance with one embodiment; and 
         FIG.  6    illustrates a flowchart of a method in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments of the inventive subject matter described herein relates to systems and methods that include an airfoil that is integrated with a fan frame assembly disposed inside of an engine assembly. Integrating the airfoil with the fan frame assembly improves a structural load supporting capability of the fan frame assembly relative to the airfoil not being integrated with the fan frame assembly. Additionally, a sweep feature can be provided at a leading edge of the airfoil that alters the air inside the engine assembly. Altering the air flow inside the engine assembly with the sweep feature improves the reduction of an amount of surface pressure exerted on the airfoil by the air and reduces the noise generated by the engine assembly relative to the leading edge of the airfoil not including the sweep feature. 
       FIG.  1    illustrates a partial cross-sectional view of a gas turbine engine assembly  12  in accordance with one embodiment. The gas turbine engine assembly  12  is elongated along a central axis  11 . The engine assembly  12  includes a fan assembly  16  and a core gas turbine engine  13 . The engine  13  includes, among other things, a high pressure compressor  14 , a combustor (not shown), and a high pressure turbine (not shown). The engine assembly  12  may also include, among other things, a low pressure turbine, a multi-stage booster compressor  22 , and a splitter  44  that substantially circumscribes the booster  22 . 
     The fan assembly  16  includes an array of fan blades  24  extending radially outward from a rotor disk  26 . The engine assembly  12  includes an intake side  28  and an exhaust side (not shown). In operation, air flows in to the engine assembly  12  at the intake side  28  and through the fan assembly  16 . A first portion  50  of the airflow is channeled through the booster  22 . The compressed air that is discharged from the booster  22  is channeled through the compressor  14  wherein the airflow is further compressed and is delivered to a combustor (not shown). Hot products of combustion (not shown) from the combustor are utilized to drive turbines of the engine assembly  12 . The engine assembly  12  is operable at a range of operating conditions between design operating conditions, off-design operating conditions, or the like. 
     A second portion  52  of the airflow discharged from the fan assembly  16  is channeled through a bypass duct  40  to bypass a portion of the airflow from the fan assembly  16  and around the core gas turbine engine  13 . The bypass duct  40  extends between a fan casing or shroud  42  and the splitter  44 . For example, the first portion  50  of the airflow from the fan assembly  16  is channeled through the booster  22  and then into the compressor  14 , and the second portion  52  of the airflow from the fan assembly  16  is channeled through the bypass duct  40  to provide thrust for an aircraft. The engine assembly  12  also includes a fan frame assembly  60  that includes, among other things, the fan casing or shroud  42 , and provides structural support for the fan assembly  16  to the core gas turbine engine  13 . The fan frame assembly  60  may also include a plurality of outlet guide vanes that typically extend substantially radially, between a radially-outer mounting flange and a radially-inner mounting flange, and are circumferentially-spaced within the bypass duct  40 . The fan frame assembly  60  may also include a plurality of struts that are coupled between a radially outer mounting flange and a radially inner mounting flange. The fan frame assembly  60  will be described in more detail with reference to  FIG.  2   . 
       FIG.  2    illustrates a partial cross-sectional view of a system  10  of the engine assembly  12  in accordance with one embodiment.  FIG.  3    is a perspective view of an airfoil  70  in accordance with one embodiment.  FIGS.  2  and  3    will be described in detail together. 
     The system  10  includes the fan frame assembly  60  and a plurality of airfoils  70 . The airfoils  70  may also be referred to herein as outlet guide vanes  70 . In the illustrated embodiment, a single airfoil  70  is shown, however the engine assembly  12  may include any number of airfoils  70  that are disposed circumferentially about the central axis  11 . 
     The airfoil  70  is shaped such that it directs the second portion  52  of air inside the engine assembly  12 . For example, the outlet guide vanes  70  turn the airflow that is directed downstream from the rotating fan blades  24  of  FIG.  1   . The airfoil  70  extends an axial length  226  between a leading edge  71  and a trailing edge  73  of each of the airfoils  70 . Optionally, the axial length  226  may be referred to herein as a chordwise length or chord length between the leading and trailing edges  71 ,  73 . The leading edge  71  is disposed proximate the fan blade  24  (of  FIG.  1   ) relative to the trailing edge  73  along the axial length  226 . For example, the trailing edge  73  is located downstream from the leading edge  71  of the airfoil  70  as the second portion  52  of the airflow moves inside of the engine assembly  12 . 
     The airfoil  70  includes a pressure side  214  and a suction side  216  that is opposite the pressure side  214 . The pressure side  214  and the suction side  216  are interconnected by the leading edge  71  and the trailing edge  73  that is opposite the leading edge  71 . The pressure side  214  is generally concave in shape, and the suction side is generally convex in shape between the leading and trailing edges  71 ,  73 . For example, the generally concave pressure side  214  and the generally convex suction side  216  provide an aerodynamic surface over which the second portion  52  of the compressed working fluid (e.g., the air inside the engine assembly  12 ) flows through the engine assembly  12 . 
     The airfoil  70  extends substantially or predominantly radially in a radial direction  224  between a hub end  114  of the airfoil  70  and an opposite tip end  112  of the airfoil  70 . Additionally, the leading edge  71  and the trailing edge  73  extend substantially radially about the central axis  11 . The airfoil  70  is integrated with the fan frame system  60  such that the hub end  114  is operably coupled with an inner surface  104  of the fan frame assembly  60  and the tip end  112  is operably coupled with an outer surface  102  of the fan frame assembly  60 . For example, the inner surface  104  of the fan frame assembly  60  may be a surface of the splitter  44 , and the outer surface  102  of the fan frame assembly  60  may be a surface of the fan casing  42 . Optionally, the inner surface  104  may be referred to as a radially-outward flow path surface and the outer surface  102  may be referred to as a radially-inner flow path surface. For example, the inner surface  104  is a radially-outward facing flow path surface such that the inner surface  104  faces a direction away from the central axis  11  in the radial direction  224  and the flow of the air through the fan frame assembly  60  passes over the inner surface  104 . Additionally, the outer surface is a radially-inward facing mounting flange such that the outer surface  102  faces a direction towards the central axis  11  in the radial direction  224  and the flow of the air through the fan frame assembly  60  passes inside of the outer surface  102 . 
     The leading edge  71  of each of the plural airfoils  70  includes a sweep feature  80 . Optionally, the sweep feature  80  may also be referred to herein as a sweep structure, sweep body, or the like. The sweep feature  80  is shaped to alter the air (e.g., the second portion  52  of the airflow) in the engine assembly  12 . The sweep feature  80  extends between an inner edge  88  and an interference edge  82  along the axial length  226 . Optionally, the interference edge  82  may also be referred to herein as a new leading edge  82 . The inner edge  88  is operably coupled with the leading edge  71  of the airfoil  70 . For example, the inner edge  88  and the leading edge  71  share a mating surface. 
     In one or more embodiments, the sweep feature  80  and the airfoil  70  may be formed as a unitary body. For example, the sweep feature  80  may be cast, machined, stamped, or the like, with the airfoil  70 . Additionally or alternatively, the sweep feature  80  may be fitted onto (e.g., coupled with, or the like) a new or an existing airfoil  70  For example, the existing airfoil may have been previously used in one or more test simulation cycles or may have been previously used in service during one or more normal operating duty cycles, or the like. The sweep feature  80  may be retrofitted onto the airfoil  70  by any attachment methods such as, but not limited to, welding, bolting, adhering, or the like. 
     The interference edge  82  (e.g., the new leading edge  82 ) of the sweep feature  80  includes a non-zero sweep angle  84  relative to a line  86  that is substantially or predominantly perpendicular to the central axis  11  of the engine assembly  12 . For example, the interference edge  82  is distinctly unrelated to the shape of the trailing edge  73  of the airfoil  70 . In the illustrated embodiment, the interference edge  82  has a positive non-zero sweep angle  84  that is substantially uniform between the hub end  114  and the tip end  112  of the airfoil  70  along the radial length  224 . Additionally, the trailing edge  73  is substantially radial between the hub end  114  and the tip end  112  of the airfoil  70  along the radial length  224 . Optionally, the new leading edge  82  may have a non-zero sweep angle  84  that may be non-uniform or may change at different radial positions along the new leading edge  82  between the hub end  114  and the tip end  112  of the airfoil  70  along the radial length  224 . For example, the non-zero sweep angle  84  may be a positive and/or negative non-zero sweep angle, may increase then decrease, decrease then increase, or any combination therein along the radial length  224 . 
     The sweep feature  80  is separated from the trailing edge  73  of the airfoil  70  by a variable chord length  116 . The variable chord length  116  extends generally chord-wise between the trailing edge  73  and the interference edge  82  of the sweep feature  80 . The variable chord length  116  varies (e.g., is different or changes) at different radial positions of the airfoil  70 . For example, the variable chord length between the trailing edge  73  and the interference edge  82  of the sweep feature varies with respect to the shape of the sweep feature  80 . In the illustrated embodiment of  FIGS.  2  and  3   , the variable chord length  116  extends a first length  116   a  at a first radial position  118   a  of the airfoil  70  along the radial length  224  of the airfoil  70 . Additionally, the variable chord length  116  extends a different, second length  116   b  at a different, second radial position  118   b  of the airfoil  70  along the radial length  224  of the airfoil  70 . In the illustrated embodiment, the first length  116   a  extends a distance between the trailing edge  73  and the interference edge  82  of the sweep feature  80  along the axial direction  226  that is less than the second length  116   b . The variable chord length between the trailing edge  73  and the interference edge  82  decreases from the hub end  114  to the tip end  112  of the airfoil  70 . For example, the sweep feature  80  has a variable chord length  116  that is longer at a radial position near the hub end  114  of the airfoil  70  relative to the variable chord length  116  that is shorter at a radial position near the tip end  112  of the airfoil  70 . Optionally, the variable chord length may increase from the hub end  114  to the tip end  112  of the airfoil  70  along the radial length  224 . Optionally, the sweep feature  80  may have any alternative shape such that the variable chord length  116  may increase and/or decrease at different radial positions of the airfoil  70  along the radial length  224 . 
     In one or more embodiments, one or more of the plural airfoils  70  may include a common or unique sweep feature  80  at the leading edge  71  of each of the plural airfoils  70 . Optionally, each of the sweep features  80  of each of the plural airfoils  70  may have common and/or unique shapes, sizes, or the like. Optionally, each of the airfoils  70  about the central axis  11  may include sweep features that may have any alternating or patterned configuration (e.g., common or unique shape and/or size). Optionally, one or more of the airfoils  70  may include sweep features having any configuration of shape and/or size. 
     The fan frame assembly  60  is one of various frame and support assemblies of the gas turbine engine assembly  12  that are used to facilitate maintaining an orientation of various components within the gas turbine engine assembly  12 . For example, the frame and support assemblies interconnect stationary components and provide rotor bearing supports, structural load support, or the like. The fan frame assembly  60  is coupled downstream from the fan assembly  16  within the bypass duct  40  such that the outlet guide vanes  70  are circumferentially spaced apart around the outlet of the fan assembly  16  and extend across the airflow path of the second portion  52  of the airflow that is discharged from the fan assembly  16 . For example, looking rearward from the front of the gas turbine engine assembly  12  (not shown), a plurality of airfoils  70  are circumferentially distributed about the central axis  11  of the engine assembly  12 . 
     In one or more embodiments, the fan frame assembly  60  may also include a plurality of struts (not shown) that are coupled between the inner and outer surfaces  104 ,  102 . Optionally, the fan frame assembly  60  may be fabricated in arcuate segments in which flanges are coupled to the outlet guide vanes  70  and/or the struts. Optionally, the outlet guide vanes  70  and/or the struts may be coupled coaxially within the bypass duct  40 . 
     The airfoils  70  integrated with the fan frame assembly  60  increase a structural load support level or a structural load supporting capability of the fan frame assembly  60  relative to the airfoils  70  not being integrated with the fan frame assembly  60 . The tip ends  112  and the hub ends  114  of each of the plural airfoils  70  are operably coupled with the outer surface  102  and the inner surface  104 , respectively, of the fan frame assembly  60 . For example, the plural airfoils  70  may be formed as unitary bodies with one or more components of the fan frame assembly  60 . 
     The trailing edge  73  of the airfoil  70  that is substantially or predominantly radial provides a substantially radial load path between the inner surface  104  and the outer surface  102  of the fan frame assembly  60 . For example, the substantially radial trailing edge  73  increases a structural stiffness of the integrated airfoil  70  and fan frame assembly  60  relative to the trailing edge  73  including a sweep feature or a trailing edge that is also swept. 
       FIG.  4    illustrates unsteady surface pressure that is exerted onto the airfoil  70  by air inside the engine assembly  12  in accordance with one embodiment. Unsteady surface pressure at each point refers to the difference between the surface pressure at any instant in time and the average surface pressure over the time it takes for a fan blade to rotate an extent corresponding to the angular extent between two adjacent outlet guide vanes (e.g., the airfoils  70 ). Airfoil  402  illustrates the airfoil  70  that includes the sweep feature  80  and airfoil  404  illustrates a baseline airfoil that does not include a sweep feature. The interference edge  82  (e.g., the new leading edge  82 ) of the sweep feature  80  interferes with and alters the second portion  52  of the air that is received from the fan assembly  16 . 
     Illustrated in  FIG.  4   , the areas shaded in the hatching pattern  601  have a high level of negative unsteady surface pressure, while the hatch pattern  602  denotes areas of moderately negative unsteady surface pressure. Similarly, areas shown by the hatch patterns  605  and  604  have high and moderate levels of positive unsteady surface pressure, respectively. The areas that have no hatching, represented by  603  have an unsteady surface pressure that is substantially zero. For example, the areas of no hatching  603  are quieter than the levels indicated by patterns  601 ,  602  and patterns  604 ,  605  such that the unsteady surface pressure levels of  603  are negligible in comparison to the unsteady surface pressure levels of  601 ,  602 ,  604 , and  605 . High values of unsteady surface pressure, whether positive or negative, generally result in higher levels of noise radiated from the airfoils  70 . With the inclusion of the sweep feature  80 , the air inside the engine assembly  12  is altered and areas of high and low unsteady surface pressure are substantially reduced relative to the leading edge  71  not including the sweep feature  80 . Therefore, the sweep feature  80  substantially reduces the interaction noise between the upstream fan assembly  16  and the airfoils  70  (e.g., the outlet guide vanes  70 ). 
     Additionally, the sweep feature  80  is shaped in order to change a noise level that is generated by the engine assembly  12 . For example, the airfoil  70  including the sweep feature  80  and the substantially radial trailing edge  73  reduces a noise level that is generated by the engine assembly  12  relative to the leading edge  71  of the airfoil  70  not including the sweep feature  80 . The interference edge  82  of the sweep feature  80  causes destructive interference in acoustic waves that emanate from the airfoil  70  due to the interaction with wakes in the airflow generated by the upstream fan assembly  16 . Altering the flow of air inside the engine assembly  12  reduces a noise level that is generated by the engine assembly  12  relative to the airfoil  70  not including the sweep feature  80 . 
     Introducing the sweep feature  80  changes the effective chord length of the airfoil  70  and can result in increased skin friction losses at the expense of reduced noise levels and increased stiffness. To minimize the skin friction penalty caused by the sweep feature, the sweep feature may be made variable as shown in  FIG.  5   , which illustrates a perspective view of the airfoil  70  in accordance with one embodiment. The leading edge  71  of the airfoil  70  includes a sweep feature  580 . The sweep feature  580  extends between an inner edge  588  and an interference edge  582  along the axial length  226  (of  FIG.  2   ). Optionally, the interference edge  582  may be referred to herein as a new leading edge  582 . The new leading edge  582  of the sweep feature  580  includes a non-zero sweep angle relative to a line perpendicular to the central axis  11  (of  FIG.  2   ). For example, the interference edge  582  is distinctly unrelated to the shape of the trailing edge  73  of the airfoil  70 . In the illustrated embodiment, the non-zero sweep angle is substantially non-uniform between the hub end  114  and the tip end  112  of the airfoil  70  along the radial length  224 . 
     The sweep feature  580  is separated from or is disposed at a position away or apart from the trailing edge  73  of the airfoil  70  by a distance of a variable chord length  516 . For example, the variable chord length  516  varies (e.g., is different or changes) at different radial positions of the airfoil  70 . In the illustrated embodiment of  FIG.  5   , the variable chord length  516  extends a first length  516   a  at a first radial position  518   a  of the airfoil  70  along the radial length  224 , extends a different, second length  516   b  at a different, second radial position  518   b  of the airfoil  70  along the radial length  224 , and extends a different, third length  516   c  at a different, third radial position  518   c  of the airfoil  70  along the radial length  224 . In the illustrated embodiment, the variable chord length  516  increases then decreases from the hub end  114  to the tip end  112  of the airfoil  70  along the radial length  224 . For example, the sweep feature  580  has a variable chord length  516  that is longer at a radial position between the hub end  114  and the tip end  112  (e.g., the second length  516   b ) relative to the variable chord length  516  that is shorter at a radial position near the hub end  114  (e.g., the third length  516 C) and near the tip end  112  (e.g., the first length  516   a ). Optionally, the sweep feature  580  may have a uniform or non-uniform wavy shape along the radial length  224 . Optionally, the sweep feature  580  may have any alternative shape along the radial length  224  between the hub end  114  and the tip end  112  of the airfoil  70 . 
       FIG.  6    illustrates a flowchart of a method  600  in accordance with one embodiment. At  602 , an airfoil (e.g., the airfoil  70 ) that is disposed inside of an engine assembly is integrated with a fan frame assembly (e.g., the fan frame assembly  60 ). The airfoil  70  may be a guide vane, a blade, or the like. Optionally, the airfoil may be integrated with the fan frame assembly inside of any mechanical assembly. 
     At  604 , a sweep feature (e.g., sweep features  80  or  580 ) is coupled with a leading edge of the airfoil  70 . In one or more embodiments, the sweep feature  80  may be formed as a unitary body with the airfoil  70  at the leading edge  71  of the airfoil  70 . Additionally or alternatively, the sweep feature may be coupled with a new or existing airfoil  70 . For example, the sweep feature  80  may be retrofitted to a new or existing airfoil  70 . The new airfoil  70  may be an airfoil that has not been used for test simulation cycles or has not been used in service during operating duty cycles. The existing airfoil may have been previously used in one or more test simulation cycles or may have been previously used in service during one or more normal operating duty cycles, or the like. The sweep feature  80  may be retrofitted onto the airfoil  70  by any attachment methods such as, but not limited to, welding, bolting, adhering, or the like. 
     At  606 , the sweep feature  80  alters the air inside of the engine assembly. For example, the sweep feature  80  may alter or change the flow of the second portion  52  of the air that is received from the fan assembly  16  (of  FIG.  2   ). Altering the air inside the engine assembly with the sweep feature  80  reduces an unsteady pressure level on the airfoil  70  relative to the leading edge not including the sweep feature  80 . Additionally, altering the air inside the engine assembly with the sweep feature  80  reduces a noise level that is generated by the airfoil  70  relative to the leading edge of the airfoil not including the sweep feature  80 . 
     In one embodiment of the subject matter described herein, a system includes an airfoil configured to be disposed inside of an engine assembly. The airfoil is shaped to direct air inside the engine assembly. The airfoil includes a pressure side and a suction side that are coupled together at a leading edge of the airfoil and that are coupled together at a trailing edge of the airfoil that is located downstream from the leading edge. The airfoil extends a radial length away from a central axis of the engine assembly between a hub end of the airfoil and an opposite tip end of the airfoil. The airfoil includes a sweep feature disposed at the leading edge of the airfoil. The sweep feature is shaped to alter the air inside the engine assembly. Altering the air inside the engine assembly reduces a surface unsteady pressure level on the airfoil relative to the leading edge not including the sweep feature. The system also includes a fan frame assembly comprising an inner surface and an outer surface. The hub end of the airfoil is configured to be operably coupled with the inner surface of the fan frame assembly and the tip end of the airfoil is configured to be operably coupled with the outer surface of the fan frame assembly. The airfoil is configured to be integrated with the fan frame assembly of the system such that the airfoil increases a structural load supporting capability of the fan frame assembly relative to the airfoil not being integrated with the fan frame assembly. 
     Optionally, the sweep feature comprises an interference edge having a non-zero sweep angle relative to a line perpendicular to the central axis. The non-zero sweep angle is configured to one or more of increase or decrease along the radial length of the airfoil between the hub end and the tip end. 
     Optionally, the sweep feature is configured to be retrofitted to the airfoil. 
     Optionally, the sweep feature of the leading edge is configured to reduce a noise level that is generated by the airfoil relative to the leading edge of the airfoil not including the sweep feature. 
     Optionally, the trailing edge does not include the sweep feature but is configured to increase a structural stiffness level of the airfoil relative to the trailing edge of the airfoil including a sweep feature. 
     Optionally, the trailing edge of the airfoil is configured to provide a substantially radial load path between the inner surface and the outer surface of the fan frame assembly along the trailing edge of the airfoil. 
     Optionally, the sweep feature of the leading edge is separated from the trailing edge by a variable chord length. The variable chord length is configured to extend a first length between the sweep feature and the trailing edge at a first radial position of the airfoil along the radial length of the airfoil and extend a different, second length between the sweep feature and the trailing edge at a different, second radial position of the airfoil along the radial length of the airfoil. 
     Optionally, the airfoil is one or more of a guide vane or a blade. 
     In one embodiment of the subject matter described herein, an airfoil is configured to be disposed inside of an engine assembly including a fan frame assembly. The airfoil is shaped to direct air inside the engine assembly. The airfoil includes a pressure side and a suction side that are coupled together at a leading edge of the airfoil and that are coupled together at a trailing edge of the airfoil that is located downstream from the leading edge. The airfoil extends a radial length away from a central axis of the engine assembly between a hub end of the airfoil and an opposite tip end of the airfoil. The leading edge of the airfoil includes a sweep feature that is shaped to alter the air inside the engine assembly. Altering the air inside the engine assembly reduces a surface unsteady pressure level on the airfoil relative to the leading edge not including the sweep feature. The hub end of the airfoil is configured to be operably coupled with an inner surface of the fan frame assembly and the tip end of the airfoil is configured to be operably coupled with an outer surface of the fan frame assembly. The airfoil is configured to be integrated with the fan frame assembly such that the airfoil increases a structural load supporting capability of the fan frame assembly relative to the airfoil not be integrated with the fan frame assembly. 
     Optionally, the sweep feature comprises an interference edge having a non-zero sweep angle relative to a line perpendicular to the central axis. The non-zero sweep angle is configured to one or more of increase or decrease along the radial length of the airfoil between the hub end and the tip end. 
     Optionally, the sweep feature is configured to be retrofitted to the airfoil. 
     Optionally, the sweep feature of the leading edge is configured to reduce a noise level that is generated by the airfoil relative to the leading edge of the airfoil not including the sweep feature. 
     Optionally, the trailing edge does not include the sweep feature but is configured to increase a structural stiffness level of the airfoil relative to the trailing edge of the airfoil including a sweep feature. 
     Optionally, the trailing edge of the airfoil is configured to provide a substantially radial load path between the inner surface and the outer surface of the fan frame assembly along the trailing edge of the airfoil. 
     Optionally, the sweep feature of the leading edge is separated from the trailing edge by a variable chord length. The variable chord length is configured to extend a first length between the sweep feature and the trailing edge at a first radial position of the airfoil along the radial length of the airfoil and extend a different, second length between the sweep feature and the trailing edge at a different, second radial position of the airfoil along the radial length of the airfoil. 
     In one embodiment of the subject matter described herein, a method includes integrating an airfoil configured to be disposed inside an engine assembly with a fan frame assembly. The airfoil is shaped to direct air inside the engine assembly. The airfoil includes a pressure side and a suction side that are coupled together at a leading edge of the airfoil and that are coupled together at a trailing edge of the airfoil that is located downstream from the leading edge. The airfoil extends a radial length away from a central axis of the engine assembly between a hub end of the airfoil and an opposite tip end of the airfoil. The airfoil includes a sweep feature disposed at the leading edge of the airfoil. The sweep feature is shaped to alter the air inside the engine assembly. The fan frame assembly includes an inner surface and an outer surface. The hub end of the airfoil is configured to be operably coupled with the inner surface of the fan frame assembly and the tip end of the airfoil is configured to be operably coupled with the outer surface of the fan frame assembly. The airfoil integrated with the fan frame assembly increases a structural load supporting capability of the fan frame assembly relative to the airfoil not being integrated with the fan frame assembly. The method also includes altering the air inside the engine assembly with the sweep feature of the leading edge of the airfoil. Altering the air inside the engine assembly reduces a surface unsteady pressure level on the airfoil relative to the leading edge not including the sweep feature. 
     Optionally, the method also includes retrofitting the sweep feature to the airfoil. 
     Optionally, the sweep feature includes an interference edge having a non-zero sweep angle relative to a line perpendicular to the central axis. The non-zero sweep angle is configured to one or more of increase or decrease along the radial length of the airfoil between the hub end and the tip end. 
     Optionally, the method also includes reducing a noise level that is generated by the engine assembly with the sweep feature of the leading edge relative to the leading edge of the airfoil not including the sweep feature. 
     Optionally, the method also includes increasing a structural stiffness level of the airfoil with the trailing edge that does not include the sweep feature relative to the trailing edge of the airfoil including a sweep feature. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the presently described subject matter are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the subject matter set forth herein without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the disclosed subject matter, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the subject matter described herein should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112(f), unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further feature. 
     This written description uses examples to disclose several embodiments of the subject matter set forth herein, including the best mode, and also to enable a person of ordinary skill in the art to practice the embodiments of disclosed subject matter, including making and using the devices or systems and performing the methods. The patentable scope of the subject matter described herein is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.