Patent Publication Number: US-2018029719-A1

Title: Drag reducing liner assembly and methods of assembling the same

Description:
BACKGROUND 
     The field of the disclosure relates generally to drag reduction, and, more particularly, to a drag reducing liner assembly and methods of assembling the same. 
     At least some known engines, such as some known jet engines and turbofan jet engines, are surrounded by a generally barrel-shaped nacelle and a core casing that covers the core engine. Such engines, and the airflow moving therethrough, generate an undesired amount of noise. As such, at least some known engines include an acoustic liner mounted on exposed surfaces of the engine, nacelle, and housing to dampen the noise level. More specifically, such acoustic liners include a honeycomb core coupled to a facesheet including a plurality of holes defined therethrough. In at least some known acoustic liners, the holes are either circular or elongated in the direction of the airflow. Sound waves generated inside the engine propagate forward and enter the cells of the honeycomb core through the facesheet and reflect from a backsheet at a phase different from the entering sound waves to facilitate damping the incoming sound waves and attenuating the overall noise level. 
     However, the air flowing over the holes defined in the facesheet cause an undesired amount of surface drag, which can reduce the efficiency of the engine. Additionally, the cost and time required to form the amount of holes in the facesheet required to achieve the desired acoustic performance is extensive. 
     BRIEF DESCRIPTION 
     In one aspect, a liner assembly is provided. The liner assembly includes a core and a septum coupled to the core. The liner assembly also includes a facesheet coupled to the septum. The facesheet includes a plurality of slots defined therethrough. Each slot of the plurality of slots includes a major axis oriented perpendicular to a centerline of the liner assembly. 
     In another aspect, an aircraft engine housing having a centerline and an axis extending through the engine housing parallel to the centerline is provided. The aircraft engine housing includes a nacelle including an inner surface and a core casing including an outer surface. The inner surface and the outer surface are configured to be exposed to an airflow traveling in a direction generally parallel to the axis. The aircraft engine housing also includes a liner assembly coupled to at least one of the inner surface and the outer surface. The liner assembly includes a core and a septum coupled to the core. The liner assembly also includes a facesheet coupled to the septum. The facesheet includes plurality of slots defined therethrough, wherein each slot of the plurality of slots includes a major axis oriented perpendicular to the centerline. 
     In another aspect, a method of assembling a liner assembly is provided. The method includes coupling a septum to a core and coupling a facesheet to the septum. The facesheet includes a plurality of slots defined therethrough, wherein each slot of the plurality of slots includes a major axis oriented perpendicular to a centerline of the liner assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of an embodiment of an aircraft engine including an engine housing; 
         FIG. 2  is an exploded perspective view of an exemplary liner assembly that may be used with the engine housing shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the liner assembly shown in  FIG. 2 ; 
         FIG. 4  is an exploded side view of the liner assembly shown in  FIG. 2  illustrating an exemplary facesheet, a septum, and a core; 
         FIG. 5  is top view of the facesheet shown in  FIG. 4  illustrating a plurality of slots defined therethrough; and 
         FIG. 6  is a flowchart of an embodiment of a method of assembling the liner assembly shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The implementations described herein provide an apparatus and method for noise attenuation and drag reduction in an engine housing. The implementations describe a liner assembly that includes a core, a septum coupled to the core, and a facesheet coupled to the septum. The facesheet includes a plurality of slots defined therethrough. Each slot is elongated in a direction perpendicular to the direction of an airflow that is configured to travel over the facesheet. Furthermore, the septum is coupled to a top surface of the core such that the septum and the facesheet are in direct contact with one another. The embodiments described herein provide improvements over at least some known noise attenuation systems for engine housings. As compared to at least some known noise attenuation systems, the embodiments described herein facilitate reducing the drag induced by the slots during operation. More specifically, as described above, estimates and experimental testing have shown that orienting the slots in a direction perpendicular to the airflow direction reduces drag. Furthermore, combining the perpendicular orientation of the slots with the position of the septum being directly adjacent the facesheet further reduces the drag to unexpected levels comparable to that of a smooth facesheet having no slots or holes. 
     Referring more particularly to the drawings, implementations of the disclosure may be described in the context of an aircraft engine assembly  10  shown schematically in cross-section in  FIG. 1 . In an embodiment, engine assembly  10  includes a housing  12  including a nacelle  14  and a core casing  16 . Nacelle  14  and core casing  16  enclose a turbofan engine for use with an aircraft. It should be understood, however, that the disclosure applies equally to nacelles and core casings for other types of engines, as well as to other structures subjected to noise-generating fluid flow in other applications, including but not limited to automobiles, heavy work vehicles, and other vehicles. 
     In the illustrated implementation, nacelle  14  and core casing  16  extend generally circumferentially about a centerline  18 . Nacelle  14  includes a forward end  20 , an aft end  22 , and an inner surface  24  extending between ends  20  and  22 . Nacelle  14  also includes, in a sequential forward to aft arrangement, a lip portion  26 , an inlet portion  28 , a fan case portion  30 , and a fan duct portion  32 . Inner surface  24  extends axially along each of lip portion  26 , inlet portion  28 , fan case portion  30 , and fan duct portion  32 . Similarly, core casing  16  includes a forward end  34 , an aft end  36 , and an outer surface  38  extending between ends  34  and  36 . Core casing  16  also includes a nozzle portion  40  including an outer surface  42 . 
     In the implementation, engine housing  12  includes a liner assembly  100  coupled to at least one of inner surface  24  of nacelle  14 , outer surface  38  of core casing  16 , and outer surface  42  of nozzle  40 . During operation, liner assembly  100  is exposed to an airflow  44  traveling through housing  12  in the axial direction, that is, along an axis  19 , which is parallel to centerline  18 . As described herein, liner assembly  100  both attenuates noise generated by engine assembly  10  and also reduces drag created by airflow  44  along inner surface  24  and outer surface  38  and by an airflow  45  through core casing  16  and along outer surface  42 . In one implementation, liner assembly  100  is coupled along an entire length of inner surface  24  between ends  20  and  22  of nacelle  14  and is also coupled along an entire length of at least one of outer surface  38  between ends  34  and  36  of core casing  16 . In another implementation, liner assembly  100  is coupled to only a portion of at least one of inner surface  24  and outer surface  38 . Generally, liner assembly  100  extends along at least one of inner surface  24  and outer surface  38  any length required to achieve the desired noise attenuation and drag reduction. 
       FIG. 2  is an exploded perspective view of liner assembly  100  that may be used with engine housing  12  (shown in  FIG. 1 ).  FIG. 3  is a cross-sectional view of liner assembly  100 .  FIG. 4  is an exploded side view of liner assembly  100 , and  FIG. 5  is top view of liner assembly  100 . 
     Liner assembly  100  includes a core  102 , a septum  104 , and a facesheet  106  coupled to one another. Core  102  is coupled to at least one of inner surface  24  (shown in  FIG. 1 ) and outer surface  38  (shown in  FIG. 1 ), and facesheet  106  is exposed to airflows  44  and  45  when engine assembly  10  (shown in  FIG. 1 ) is in an operational state. Liner assembly  100  also includes a backsheet  108  coupled to core  102  opposite facesheet  106 . Backsheet  108  provides a cap to the individual cells of core  102  to facilitate noise attenuation. Backsheet  108 , core  102 , septum  104 , and facesheet  106  are coupled together using diffusion bonding. Backsheet  108 , core  102 , septum  104 , and facesheet  106  may be brazed or welded together, or in another implementation, may be coupled together using an adhesive. Generally, backsheet  108 , core  102 , septum  104 , and facesheet  106  may be coupled together in any suitable fashion that enables liner assembly  100  to function as described herein. 
     As shown in  FIGS. 2-5 , core  102  includes a first surface  110  and an opposing second surface  112  having cell openings defined therethrough. First surface  110  is coupled to backsheet  108  and second surface  112  is coupled to septum  104 . In one implementation, backsheet  108  closes first surface  110  such that first surface  110  is impermeable to air and, therefore, acoustic flow. 
     Furthermore, core  102  includes a plurality of cells  114  extending between surfaces  110  and  112  and arranged in a honeycomb pattern wherein each cell  114  has a generally hexagonal cross-section and includes a channel  116  defined therethrough. Generally, cells  114  may be shaped and arranged in any suitable pattern that enables core  102  to function as described herein. In the exemplary implementation, core cells  114  are full-depth cells, that is, cells  114  are continuous through core  102  between surfaces  110  and  112 . 
     In one implementation, core  102  includes a thickness T 1  in a range of approximately 0.1 in. (2.54 mm.) to approximately 4.0 in. (101.6 mm.). Generally, core  102  may have any thickness that facilitates operation of liner assembly  100  as described herein. More specifically, the thickness T 1  of core  102  may be tuned to provide optimum noise attenuation for various jet engine and nacelle configurations. More specifically, the thickness T 1  of core  102  may be based on the location of liner assembly within engine assembly  10 . Additionally, core  102  is formed from fiberglass-reinforced phenolic resin. In alternative embodiments, core  102  is formed from another fiber-reinforced resin. In still other alternative embodiments, core  102  is formed from at least one of a plastic material, a metal, a coated paper material, or any other suitable material that enables core  102  to function as described herein. 
     In the exemplary implementation, septum  104  includes a first surface  118  and an opposing second surface  120 . First surface  118  is coupled to second surface  112  of core  102  and second surface  120  is coupled to facesheet  106 . As such, septum  104  is coupled between core  102  and facesheet  106  such that core  102  does not contact facesheet  106  and septum  104  is directly coupled to facesheet  106 . In another implementation is septum  104  covers only the open areas of facesheet  106  such that facesheet  106  is directly coupled to core  102 . In the illustrated implementation, septum  104  is coupled to core  102  using an adhesive. In certain implementations, the adhesive is a reticulated film adhesive to facilitate avoiding interference with the acoustic coupling of cells  114  and septum  104 . In other implementations, septum  104  is coupled to core  102  in any suitable fashion that enables liner assembly  100  to function as described herein. 
     Septum  104  is formed at least partially from a material that provides substantially linear acoustic attenuation. In certain implementations, septum  104  is formed from a woven fabric, such as a fabric woven from thermoplastic fibers in the polyaryletherketone (PAEK) family. In an implementation, septum  104  is formed from at least one of a polyetherketoneketone (PEKK) and a polyether ether ketone (PEEK) woven fabric. As used herein, the term “linear material” is meant to describe any material that responds substantially the same to acoustic waves regardless of the sound pressure (i.e., amplitude) of the waves, to facilitate noise attenuation. With a linear material, the pores or passages defined therein may be configured such that resistance to pressure waves does not vary with the noise level, and the pressure drop across the material is relatively constant with respect to the pressure wave velocity. This is a result of the pressure losses primarily due to viscous or friction losses through the material. 
     Additionally, in certain implementations, septum  104  has a thickness T 2  in a range of about 0.003 inches (0.0762 mm) to about 0.100 inches (2.54 mm). In an embodiment, septum  104  has a thickness T 2  of about 0.005 inches (0.127 mm). In alternative implementations, septum  104  is formed from any suitable material and has any suitable thickness that enables septum  104  to function as described herein. 
     Liner assembly  100  includes facesheet  106  including a first surface  122  and an opposing second surface  124 . First surface  122  is coupled to second surface  120  of septum  104  and second surface  124  is exposed to axially-oriented airflow  44 . As best shown in  FIG. 5 , facesheet  106  includes a plurality of slots  126  extending therethrough from first surface  122  to second surface  124 . Each slot  126  includes a major axis  128  that is oriented perpendicular to the direction of airflow  44 . That is, each slot  126  is elongated such that each slot  126  defines a length L in a direction perpendicular to the direction of airflow  44  over facesheet  106 . In an implementation, slots  126  include a length in a range of approximately 0.250 (6.35 mm) inches to approximately 1.500 inches (38.1 mm). As such, as liner assembly  100  extends circumferentially along inner surface  24  (shown in  FIG. 1 ) of nacelle  14  (shown in  FIG. 1 ) and/or outer surface  38  (shown in  FIG. 1 ) of core casing  16  (shown in  FIG. 1 ), slots  126  are oriented circumferentially with respect to centerline  18  (shown in  FIG. 1 ). In the exemplary implementation, each slot  126  also defines a width W extending in the direction of airflow  44 . More specifically, each slot  126  defines a width of approximately 0.005 inches (0.127 mm) to approximately 0.06 inches (1.524 mm). In another implementation, the width W of each slot  126  is a maximum of 0.06 inches (1.524 mm). 
     As shown in  FIG. 5 , slots  126  are elongated in a direction perpendicular to centerline  18  and, thus, airflow direction  44 . Such a perpendicular orientation facilitates minimizing drag created by slots  126  for a certain open area. More specifically, experimental testing has shown that orienting slots  126  in a direction perpendicular to airflow direction  44  reduces drag. Furthermore, combining the perpendicular orientation of slots  126  with the position of septum  118  being directly adjacent facesheet  106  further reduces the drag to levels below that as would be expected according to estimates. Such experimental drag levels are comparable to that of a facesheet having no slots. Tests have shown that the smaller the width W of slots  126  oriented a direction perpendicular to centerline  18  (and airflow direction  44 ), the lower the measured drag levels. 
     In one implementation, slots  126  are spaced on facesheet  106  such that facesheet  106  has a porosity in a range of between approximately 5 percent open area (POA) to approximately 40 POA, and more specifically, between approximately 15 POA to approximately 30 POA. In an embodiment, slots  126  are spaced such that facesheet  106  has a porosity of approximately 20 POA. The relatively high porosity of facesheet  106  reduces the pressure loss through slots  126 . Accordingly, the pressure within core  102  is approximately equal to the pressure along second surface  124  of facesheet  106 , and slots  126  do not significantly affect the flow of air into and out of core  102  as sound waves pass over surface of facesheet  106 . In some implementations, the percent open area of facesheet  106  is based on a percent open area of septum  104  such that facesheet  106  and septum  104  generate a predetermined combined flow resistance. For example, in implementations where septum  104  has a low percentage open area, facesheet  106  will have a high percent open area such that the combined flow resistance of facesheet  106  and septum  104  is within a predetermined range. Moreover, in the illustrated embodiment, slots  126  are disposed in a staggered pattern such that they alternate in axial position along a circumference of facesheet  106 . In alternative embodiments, slots  126  may be disposed in any suitable pattern that enables facesheet  106  to function as described herein. 
     Facesheet  106  is made of a metallic material, such as, but not limited to, titanium, aluminum, or any other metallic material. Additionally, in another implementation, facesheet  106  is made of composite, resin, wood, or any material that holds stress and facilitates operation of liner assembly  100  as described herein. Furthermore, facesheet  106  includes a thickness T 3  in a range of between approximately 0.05 inches (1.27 mm.) and approximately 0.1 inches (2.54 mm.). Generally, facesheet  106  may have any thickness T 3  that facilitates operation of liner assembly  100  as described herein. 
     In at least some embodiments, a shape and spacing of slots  126  on facesheet  106  facilitate an increased linearity of, and acoustic attenuation by, liner assembly  100 , as compared to at least some known perforated facesheets. Additionally, alignment of slots  126  perpendicular to centerline  18  (and the direction of airflow  44 ) facilitates minimizing drag created by slots  126 . The shape and spacing of slots  126  also facilitates a decreased cost and time required to manufacture facesheet  106 . For example, in a particular embodiment, facesheet  106  is used as part of nacelle  14  (shown in  FIG. 1 ) for a turbofan engine, and facesheet  106  includes about 96,000 slots  126 , wherein millions of perforations are required for a conventional facesheet in a similar application. 
       FIG. 6  is a flowchart of an embodiment of a method  200  of assembling a liner assembly, such as liner assembly  100 . Method  200  includes coupling  202  a septum, such as septum  104 , to a core, such as core  102 , and then coupling  204  a facesheet, such as facesheet  106 , to the septum. The facesheet includes a plurality of slots, such as slots  126 , defined therethrough that each includes a major axis oriented perpendicular to a centerline, such as centerline  18 , and thus perpendicular to an airflow, such as airflow  44 , configured to be channeled across the facesheet. Method  200  further includes coupling  206  the core to at least one of an inner surface of an engine nacelle, such as inner surface  24  of nacelle  14 , and an outer surface of a core casing, such as outer surface  38  of core casing  16 . 
     Each of the processes of method  200  may be performed or carried out by a system integrator, a third party, and/or a customer. For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and a customer may be an airline, leasing company, military entity, service organization, and so on. Moreover, although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry. 
     The embodiments described herein provide an apparatus and method for noise attenuation and drag reduction in an engine housing. The embodiments describe a liner assembly that includes a core, a septum coupled to the core, and a facesheet coupled to the septum. The facesheet includes a plurality of slots defined therethrough. Each slot is elongated in a direction perpendicular to the direction of an airflow that is configured to travel over the facesheet. Furthermore, the septum is coupled to a top surface of the core such that the facesheet and the core do not contact one another. The embodiments described herein provide improvements over at least some known noise attenuation systems for engine housings. As compared to at least some known noise attenuation systems, the embodiments described herein facilitate reducing the drag induced by the slots during operation. More specifically, as described above, experimental testing has shown that orienting the slots in a direction perpendicular to the airflow direction reduces drag. Furthermore, combining the perpendicular orientation of the slots with the position of the septum being directly adjacent the facesheet further reduces the drag to unexpected levels comparable to that of a facesheet having no slots. 
     This written description uses examples to disclose various implementations, which include the best mode, to enable any person skilled in the art to practice those implementations, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled 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 language of the claims.