BACKGROUND OF THE INVENTION

[0001] Contemporary aircraft engines can include acoustic attenuation panels in aircraft engine nacelles to reduce noise emissions from aircraft engines. These acoustic attenuation panels generally have a sandwich structure comprising liners enclosing a cellular honeycomb-type inner structure.

BRIEF DESCRIPTION OF THE INVENTION

[0002] In one aspect, an embodiment of the invention relates to an acoustic liner having a support layer that includes a set of partitioned cavities with open faces, a perforated sheet that includes a set of perforations with corresponding inlets, the perforated sheet supported by the support layer such that perforations are in overlying relationship with the open faces to form paired perforations and cavities that define acoustic resonator cells, and a coating applied to the perforated sheet and having a portion, at least upstream relative to the through air flow of the inlets, with a reducing thickness to define a transition area leading up to the inlets.

[0003] In another aspect, an embodiment of the invention relates to a method of shaping an inlet of an acoustic liner, the method includes applying a coating to the perforated sheet to form a portion of the coating with a reducing cross section leading up to the inlet along an air flow direction across the acoustic liner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] In the drawings:

[0005] FIG. 1 is a schematic view of an aircraft engine assembly with a portion of the outer nacelle cut away for clarity.

[0006] FIG. 2 is a detail view of section A of the acoustic panel of FIG. 1 illustrating a partitioned support structure with facing and backing sheets.

[0007] FIG. 3 is perspective view of the acoustic panel of FIG. 1 with portions of the support structure and facing sheet removed for clarity.

[0008] FIG. 4 is a sectional view showing a coating applied to the perforated sheet of FIG. 3 according to an embodiment of the invention.

[0009] FIGS. 5A - 5C illustrate a coating applied to a perforated sheet according to embodiments of the invention. DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0010] FIG. 1 illustrates an aircraft engine assembly 10 having a turbine engine 12, a fan assembly 13, and a nacelle 14. Portions of the nacelle 14 have been cut away for clarity. The nacelle 14 surrounds the turbine engine 12 and has an inlet section 17 that defines an inlet 19 open to ambient air and an annular airflow path or annular bypass duct 16 through the aircraft engine assembly 10 to define a generally forward-to-aft bypass airflow path as schematically illustrated by the arrow 18. The turbine engine 12 can have a fan section 21 that includes an annular fan case 23 and an aft duct 25 of a thrust reverser (not shown). The fan section can be provided within the nacelle wherein the fan section 21 is in fluid communication with the inlet 19. An annular acoustic panel 20 is provided within the nacelle in at least a portion of the inlet 19 or the fan section 21. The acoustic panel 20 forms a liner for attenuating noise in the aircraft engine assembly 10 and defines the through air flow.

[001 1] FIG. 2 shows a detailed view of the annular acoustic panel of FIG. 1. The annular acoustic panel 20 includes an open framework 22 disposed between an imperforate backing sheet 26 and a front perforated sheet 24. The open framework 22 forms a support layer having a set of partitioned cavities or cells 28 with open faces. Including that the open framework 22 has open faces on opposing front and rear sides of the open framework 22. In this manner, the open framework 22 forms a set of cells 28 in the open spaces between the open framework 22, the backing sheet 26, and the perforated sheet 24.

[0012] As illustrated more clearly in FIG. 3, the cells 28 formed by the open framework 22 disposed between the backing sheet 26 and the perforated sheet 24 each have a predetermined volume defined by the geometry of the open framework 22 and the spacing between the backing sheet 26 and the perforated sheet 24. The open framework 22 can include a honeycomb structure wherein the cells have six walls formed by the open frame work 22, a top wall formed by the backing sheet 26 and a bottom wall formed by the perforated sheet 24. The backing sheet 26 can be impervious with respect to air. More specifically, the backing sheet 26 can be an imperforate sheet supported by the support layer or open framework 22 on an opposite side of the open framework 22 than the perforated sheet 24. In this manner, the imperforate sheet is on a back side of the open framework 22 and closes off the open faces on the back side.

[0013] The perforated sheet 24 can be perforated such that a set of perforations 30, which form inlets, in a predetermined pattern are formed in the perforated sheet 24 to allow air into selected cells 28. The perforated sheet 24 can be operably coupled to the open framework 22 such that perforations 30 are in overlying relationship with the open faces of the open framework 22 to form paired perforations 30 and cavities that define the acoustic resonator cells 28. The perforated sheet can be directly supported on the open framework 22. Alternatively, an intervening layer can be utilized. The perforated sheet 24 can be formed from any suitable material including, but not limited to, a composite material. The perforations can be sized in order to attenuate various frequencies. For instance, the perforations can be between 0.005 and 0.010 inches in diameter. The backing sheet 26 and perforated sheet 24 and open framework 22 can be formed such that there are no seams present in backing sheet 26 and perforated sheet 24 and open framework 22.

[0014] Cells 28 can form a portion of an acoustic resonator. For instance, the area of the perforation 30 and thickness of the perforated sheet 24 can define neck portions of Helmholtz resonators, and the volume of the cells 28 can define the cavity volume. In addition, the acoustic resonators can be tuned to attenuate engine sounds. For example, the resonators can be tuned to attenuate predetermined frequencies associated with engine sounds entering the acoustic resonators. The honeycomb cells 28 can be a single layer of hexagonal geometry or multiple layers of the same or different geometry separated by a porous layer, typically identified as a septum. In addition, alternate geometries other than hexagonal can be envisaged including random size cells formed by open cell foams or similar materials.

[0015] FIG. 4 illustrates a coating 40 applied to the perforated sheet 24 and having a portion with a reducing thickness 42 leading up to a perforation 30, to define a transition area leading up to the perforation 30 according to an embodiment of the invention. In this manner, the portion with a reducing thickness 42 can be upstream relative to the through air flow 44 of the perforations 30 or can be constant around the circumference of the perforation. The portion with the reducing thickness 42 can have any suitable shape, profile or contour including, but not limited to, that the portion with the reducing thickness 42 can have a radius, a continuously reducing thickness, a linear step-wise reducing thickness, etc. In this manner, it will be understood that the coating 40 having the reducing thickness 42 leading up to the perforations 30 can be shaped in any suitable manner so as to modify the geometry into the perforation 30 to improve the flow of acoustic energy into the resonator cells 28. For example, as shown in FIG. 4, the portion with the reducing thickness 42 can form a radius 46 when viewed in cross section. In the illustrated example, the perforations 30 have an approximately 90 degree transition angle 48 at the perforation 30 relative to an upper surface 49 of the perforated sheet 24 and the portion with the reducing thickness 42 increases the transition angle to greater than 90 degrees. The increased transition angle results in improved flow of acoustic energy into the resonator cells 28 [0016] The coating 40 can be formed from any suitable material including, but not limited to, that the coating 40 can include at least one of fluoropolymers, polymers, hydrophobic, icephobic, low friction, or anti-erosion coating. Other commercially available coating materials are also possible. By way of non-limiting example a siloxane-based nano-composite sprayable coating, which was thinned up to 10% using Naptha or Xylene can be utilized. Further still, the coating 40 can be applied in any suitable manner including, but not limited to, that the coating 40 can be a sprayed coating 40 or a vapor deposited coating 40. It will be understood that the perforation 30 can be shaped by applying a coating 40 to the perforated sheet to form a portion of the coating 40 with a reducing cross section leading up to the inlet along an air flow direction across the acoustic liner and that this can be done in any suitable manner. For example, the coating 40 can be sprayed in a direction relative to the perforated sheet 24 to form an acute angle 45 relative to the perforated sheet 24. For example, the acute angle can be 45 degrees or less. In the illustrated example, spray 47 is illustrated as being sprayed at an acute angle of 45 degrees. The coating 40 can be applied with a spraying process using conventional spray equipment. The thickness of the coating 40 can depend on the particular application and the type of coating material used, but generally, thicknesses ranging between approximately 0.001 inch to 0.030 inch will be used. The thinnest coating that achieves the desired entry geometry can be utilized to minimize weight/cost. Any suitable spray techniques utilizing different spray parameters, numbers of coats, and angles of application can be used. To achieve the desired spray characteristics and resultant geometry the coatings can be thinned and/or cured at elevated temperatures. In addition to improving acoustic performance the coating 40 can serve multiple purposes including improved corrosion, erosion, impact or wear resistance and exhibit anti-ice or reduced friction characteristics.

Sidewall(s) 32 of the perforation 30 can have some coating 40 applied to them and the coating 40 on the sidewalls 32 of the perforations 30 can reduce the cross-sectional area of the perforations 30. The perforations 30 can be intentionally oversized to allow for a reduction in diameter due to spray build up.

[0017] It will be understood that the coating can be used, applied or otherwise fashioned to create, form, or otherwise generate virtually any variety of shapes beneficial to improved flow into the perforation 30. By way of non-limiting examples, FIGS. 5A - FIG. 5C illustrate coatings 50, 60, 70, having portions with reducing thickness 52, 62, 72, which have been applied to achieve a number of different geometries leading into the perforation 30. It will be understood that the application of a coating can form a number of geometries including a variety of radii, as well as tapers, and chamfers. [0018] It will be understood that the above mentioned surface treatments, modifications and applications according to the various embodiments can be applied only to a portion of the perforated sheet 24 or to the entire perforated sheet 24. It will further be understood that the above mentioned surface treatments, modifications and applications according to the various embodiments can be applied at any stage of the annular acoustic panel manufacturing process. Further, it will be understood that coating the perforated sheet 24 is generally independent of the configuration of the perforated sheet 24 or the process by which the perforated sheet 24 is manufactured. The coating can be applied to composite perforated sheet 24 in which the perforations were molded during the curing process or were created after curing by drilling or punching.

[0019] The embodiments described above provide for a variety of benefits including that the aircraft engine assembly that includes the acoustic liner can provide improved acoustic performance. The above-described embodiments utilize a coating to modify the geometry of the perforation in the acoustic liner, which can improve the flow of acoustic energy into and out of the resonator cells of the acoustic panel. The geometries achieved by the coatings cannot be achieved by the current industrial perforated hole manufacturing techniques such as drilling, punching, grit blasting or laser generation. Further, the above-described embodiments can be formed by a relatively inexpensive, conventional manufacturing technique of spray coating, which can be automated. Another benefit can be the reduction of skin perforation size and the associated reduced skin friction and drag penalty while maintaining acoustic performance associated with larger uncoated acoustic panels and perforations. The above-described embodiments provide the benefits of increased flow, reduced flow velocity, and potentially reduced discharge turbulence.

[0020] To the extent not already described, the different features and structures of the various embodiments may be used in combination with each other as desired. That one feature may not be illustrated in all of the embodiments is not meant to be construed that it may not be, but is done for brevity of description. Thus, the various features of the different embodiments may be mixed and matched as desired to form new embodiments, whether or not the new embodiments are expressly described. All combinations or permutations of features described herein are covered by this disclosure.

[0021] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention 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 languages of the claims.