Acoustic liners for use in a turbine engine

An acoustic liner for a turbine engine, the acoustic liner includes a support layer that includes a set of partitioned cavities with open faces, a facing sheet operably coupled to the support layer such that the facing sheet overlies and closes the open faces, a set of perforations located in the facing sheet and in fluid communication with a corresponding one of the cavities to form a set of acoustic resonators, and at least a subset of the perforations have an axially-oriented, relative to the axial flow path, inlet.

BACKGROUND OF THE INVENTION

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 that includes liners enclosing a cellular honeycomb-type inner structure.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, an embodiment of the invention relates to an acoustic liner for a turbine engine including a support layer that includes a set of partitioned cavities with open faces, a facing sheet operably coupled to the support layer such that the facing sheet overlies and closes the open faces, a set of perforations located in the facing sheet and in fluid communication with a corresponding one of the cavities to form a set of acoustic resonators, and at least a subset of the perforations have an axially-oriented, relative to an axial flow path defined by the turbine engine, inlet having an elongated cross section in the axial flow path direction.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1illustrates an aircraft engine assembly10having a turbine engine12, a fan assembly13, and a nacelle14. Portions of the nacelle14have been cut away for clarity. The nacelle14surrounds the turbine engine12and has an inlet section17that defines an inlet19open to ambient air and an annular airflow path or annular bypass duct16through the aircraft engine assembly10to define a generally forward-to-aft bypass airflow path as schematically illustrated by the arrow18. The turbine engine12can have a fan section21that includes an annular fan case23and an aft duct25of a thrust reverser (not shown). The fan section can be provided within the nacelle wherein the fan section21is in fluid communication with the inlet19. An annular acoustic panel20is provided within the nacelle in at least a portion of the inlet19or the fan section21. The acoustic panel20forms a liner for attenuating noise in the aircraft engine assembly10and defines the through air flow.

FIG. 2shows a detail view of the annular acoustic panel ofFIG. 1. The annular acoustic panel20includes an open framework22disposed between an imperforate backing sheet26and a facing sheet or perforated sheet24. The open framework22forms a support layer having a set of partitioned cavities or cells28with open faces. Including that the open framework22has open faces on opposing front and rear sides of the open framework22. In this manner, the open framework22forms a set of cells28in the open spaces between the open framework22, the backing sheet26and the perforated sheet24.

As illustrated more clearly inFIG. 3, the cells28formed by the open framework22disposed between the backing sheet26and the perforated sheet24each have a predetermined volume defined by the geometry of the open framework22and the spacing between the backing sheet26and the perforated sheet24. The open framework22can include a honeycomb structure wherein the cells have six walls formed by the open frame work22, a top wall formed by the backing sheet26and a bottom wall formed by the perforated sheet24. The backing sheet26can be impervious with respect to air. More specifically, the backing sheet can be an imperforate sheet operably coupled to the support layer or open framework22on an opposite side of the open framework22than the perforated sheet24. In this manner, the imperforate sheet is on a back side of the open framework22and closes off the open faces on the back side.

The perforated sheet24can be perforated such that a set of perforations30, which form inlets, in a predetermined pattern are formed in the perforated sheet24to allow air into selected cells28. The perforated sheet24can be operably coupled to the open framework22such that the perforations30are in overlying relationship with the open faces of the open framework22to form paired perforations30and cavities that define the acoustic resonator cells28. The perforated sheet can be directly supported on the open framework22. Alternatively, an intervening layer can be utilized. The perforated sheet24can be formed from any suitable material including, but not limited to, a composite material. The perforations can be identical in area or can vary in area in different zones of the perforated sheet. The backing sheet26and perforated sheet24and open framework22can be formed such that there are no seams present in backing sheet26and perforated sheet24and open framework22.

Cells28can form a portion of an acoustic resonator. For instance, the area of the perforation30and thickness of the perforated sheet24can define neck portions of the Helmholtz resonators, and the volume of the cells28can define the cavity volume. In addition, the acoustic resonators can be tuned to attenuate engine sounds. For example, the acoustic resonators can be tuned to attenuate predetermined frequencies associated with engine sounds entering the acoustic resonators. The honeycomb cells28can 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.

As illustrated inFIG. 3, the perforations30have an axially-oriented inlet32. As used in this description an axially-oriented inlet includes an inlet having an elongated cross section in the axial flow path direction (illustrated by arrow18). As used herein an axially-oriented inlet can alternatively include any shape, profile, or contour with a frictional drag less than a perforation having a circular inlet of the same cross-sectional area. While all of the perforations30have been shown as having an inlet32with an elongated cross section it will be understood that any number of the perforations30can be shaped in this manner. While the inlets32are shaped as ovals, it will be understood that the inlets of the perforations can be shaped in any suitable manner so long as the inlet has an elongated cross section in the axial flow path direction. By way of further non-limiting examples, the shape of the inlets can alternatively include a tapered geometry or teardrop shape132(FIG. 4A), a triangular shape232(FIG. 4B), etc.

It will be understood that the cross-sectional shape need not be a geometrical shape and that aerodynamic shapes can be utilized including that the inlet can include a NACA scoop shaped inlet332(FIG. 5A). In this manner, it will be understood that any suitable axially-oriented inlet having reduced drag compared to a circular inlet can be utilized.

As illustrated inFIG. 5B, the NACA scoop shaped inlet332extends from an upper surface340of the perforated sheet24into a portion of the perforated sheet24below the upper surface340of the perforated sheet24. The NACA scoop shaped inlet and other axially elongated perforations can be normal to the surface of the perforated sheet24or can incorporate an angled edge or ramp as shown inFIG. 5Bto enhance entry of the sound waves into the cells28to improve the acoustic characteristics of the panel.

In yet another example, such inlets with minimal drag can be utilized with at least one discontinuity, which can be included in the facing sheet upstream of the inlet. By way of non-limiting example, the at least one discontinuity can include at least one riblet included in the facing sheet. Several riblets400have been illustrated as recesses in the upper surface340of the perforated sheet24while alternatively riblets404have been illustrated as protrusions extending from the upper surface340of the perforated sheet24. It is contemplated that the riblet(s) can be shaped in any suitable manner including, but not limited to, that any number of riblets can be included and that the riblet(s) can have any suitable cross-section. Further, the riblets can be continuous riblets or discontinuous riblets that can be interspersed with the perforations. It is contemplated that the riblet(s) can be formed in any suitable manner, including by way of non-limiting example via a grit blasting process. It is contemplated that any number of riblets can be located between the perforations to enhance the continuation of laminar flow and reduce skin friction resulting from circumferential flow of vortices from the perforations.

The embodiments described above provide for a variety of benefits including that the aircraft engine assembly that includes the acoustic liner can provide improved aerodynamic performance versus conventional acoustic panels. The above-described embodiments with the axially oriented perforations provide for reduced skin friction and resultant reduced drag as compared to conventional or micro perforated round perforations. Such improved aerodynamic performance can result in improved engine fuel consumption and still provide the benefits of acoustic attenuation. Further, the above-described embodiments can have reduced manufacturing complexity and cost versus micro perforated liners (perforation size range 0.005 to 0.008 diameter) or linear liners (0.040 diameter and above where the sheet is combined with wire or fabric mesh to create what is identified in the industry as a linear liner).

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.