Acoustic liner

An acoustic liner that may be for a turbofan engine includes a first panel that may be non-permeable and a permeable panel spaced from the first panel. A non-permeable wall located between the first panel and the permeable panel faces in a first direction away from the first panel and a non-permeable wall, also between the panels, faces in a second direction away from the first panel and traversing the first direction. The liner may further include a plurality of sidewalls spaced from one-another, extending between the panels, and through the walls.

BACKGROUND

The present disclosure relates to an acoustic liner and more particularly to an acoustic liner that extends noise attenuation capability to a lower frequency range.

A gas turbine engine may include an acoustic liner for attenuating noise generated during engine operation. A typical acoustic liner includes a honeycomb core connected between a solid face sheet and a perforated face sheet, also known as a single degree of freedom (SDOF), local reacting, liner. This honeycomb core includes a plurality of resonating cavities. The honeycomb core may have a height that tunes the resonating cavities to a specific target frequency of the noise to be attenuated.

New aircraft engine designs are facing increasing noise restrictions within the boundaries of airports by many government regulatory agencies. Accordingly, recent trends in aircraft engine design (i.e. higher bypass ratios, large fan diameter, slower rotating fans, and/or less fan blades) have highlighted the need for acoustic liners that provide sound suppression, such as tonal and broadband sound absorption at relatively low frequencies while utilizing substantially the same or less space than previous liners. Therefore, there is a need in the art for an improved noise attenuating acoustic panel with reduced acoustic liner thickness.

SUMMARY

An acoustic liner according to one, non-limiting, embodiment of the present disclosure includes a first panel; a permeable panel spaced from the first panel; a first wall located between the first and permeable panels and facing in a first direction away from the first panel; and a permeable wall located between the first and permeable panels and facing in a second direction away from the first panel and traversing the first direction.

Additionally to the foregoing embodiment, the first panel is a non-permeable back panel.

In the alternative or additionally thereto, in the foregoing embodiment, the first wall is non-permeable.

In the alternative or additionally thereto, in the foregoing embodiment, the liner includes a plurality of sidewalls spaced from one-another, extending between and engaged to the first panel and the permeable panel, and through the first and permeable walls.

In the alternative or additionally thereto, in the foregoing embodiment, each one of a plurality of cells are defined between the first and permeable panels and adjacent sidewalls of the plurality of sidewalls, and the first and permeable walls are each one of a plurality of first and permeable walls with each one of the plurality of first and permeable walls being generally in a respective one of the plurality of cells.

In the alternative or additionally thereto, in the foregoing embodiment, an angle measured between the first wall and the first panel is about forty-five degrees.

In the alternative or additionally thereto, in the foregoing embodiment, the plurality of first walls each have opposite first and second edges with the first edge engaged to the first panel and the second edge engaged to the permeable panel.

In the alternative or additionally thereto, in the foregoing embodiment, the plurality of permeable walls each have opposite first and second edges with the first edge engaged to the first edge of the first wall and the second edge engaged to the second edge of an adjacent first wall of the plurality of first walls.

In the alternative or additionally thereto, in the foregoing embodiment, the plurality of first and permeable walls are one continuous, folded, panel.

In the alternative or additionally thereto, in the foregoing embodiment, the plurality of permeable walls each have opposite first and second edges with the first edge engaged to the first panel, and parallel to and spaced from the first edge of the first wall, and wherein the second edge of the permeable wall is engaged to the permeable panel and spaced from the second edge of an adjacent first wall of the plurality of first walls.

In the alternative or additionally thereto, in the foregoing embodiment, the permeable panel includes a plurality of non-permeable segments defined and spanning between the second edge of the first wall and the second edge of the adjacent permeable wall.

In the alternative or additionally thereto, in the foregoing embodiment, the plurality of permeable walls each have opposite first and second edges with the first edge engaged to the first wall and the second edge engaged to the permeable panel.

In the alternative or additionally thereto, in the foregoing embodiment, the permeable panel includes a plurality of non-permeable segments defined and spanning between the second edge of the first wall and the second edge of the adjacent permeable wall.

In the alternative or additionally thereto, in the foregoing embodiment, the plurality of permeable walls each have opposite first and second edges with the first edge engaged to the first wall and the second edge engaged to an adjacent first wall of the plurality of first walls.

A liner for a turbofan engine according to another, non-limiting, embodiment includes a non-permeable panel; a permeable panel spaced from the non-permeable panel; a non-permeable wall located between the non-permeable and permeable panels and facing in a first direction away from the non-permeable panel; a permeable, DDOF septum, wall located between the non-permeable and permeable panels and facing in a second direction away from the non-permeable panel and traversing the first direction; and a plurality of sidewalls spaced from one-another, extending between and engaged to the non-permeable and permeable panels, and through the non-permeable and permeable walls.

DETAILED DESCRIPTION

Referring toFIG. 1, a turbofan engine20is illustrated as one example of an application using an acoustic liner22of the present disclosure. The engine20is centered about an axis A, and includes a nacelle intake cowling24, a fan section26downstream of the intake cowling24, an annular air bypass flowpath28downstream of the fan section26and generally defined between radial inner and outer walls30,32, an engine core34located radially inward of the inner wall30, and an exhaust nozzle36located downstream of the engine core34. The acoustic liner22may be carried by a radially inward facing wall of the intake cowling24; the inner and/or outer walls30,32; and/or, the exhaust nozzle36to suppress noise in the respective vicinities. It is further contemplated and understood that the acoustic liner22may be applied to any other application where noise suppression, and particularly low frequency noise suppression, is desirable.

Referring toFIGS. 2 and 3, the acoustic liner22may have a non-permeable back panel38and permeable panel40that is parallel to and spaced from the panel38by a distance (see arrow42). A plurality of elongated sidewalls44extend laterally between and engage to the panels38,40. The sidewalls44are spaced from one-another, may substantially be parallel to one-another, and may be substantially normal to the panels38,40. A plurality of elongated non-permeable walls46extend longitudinally through the plurality of sidewalls44and have opposite first and second edges48,50, with the first edge48being engaged to the non-permeable panel38and the second edge50being engaged to the permeable panel40. A plurality of cells52of the liner22are defined by and between the panels38,40, adjacent non-permeable walls46, and adjacent sidewalls44. A plurality of elongated permeable walls54extend longitudinally through the plurality of sidewalls44and have opposite first and second edges56,58. The first edge56may be engaged to the first edge48of the non-permeable wall46and/or engaged to the non-permeable panel38. The second edge58of each permeable wall54may be engaged to the second edge50of each respective and adjacent non-permeable wall46and/or engaged to the non-permeable panel38. A permeable segment60of the plurality of permeable walls54is in each one of the plurality of cells52. The plurality of non-permeable walls46and plurality of permeable walls54may be one continuous fold panel, folded along the respective first edges48,56and again at the respective second edges50,58.

The non-permeable wall46and the permeable wall54are generally angled with respect to the non-permeable panel38and the permeable panel40. More specifically, the non-permeable wall46faces in an outward direction (see arrow62) normal to the wall46and away from the non-permeable panel38and through the permeable panel40. The permeable wall54faces in an outward direction (see arrow64) normal to the wall54and away from the non-permeable panel38, through the permeable panel40, and such that the directions62,64traverse one-another (i.e. are transverse to one-another). An angle (see arrow66) taken between the panel38and non-permeable wall46may be about forty-five degrees, and generally, the smaller the angle66, the greater is the attenuation of lower frequency noise.

The permeable panel40has a plurality of holes68with at least one hole communicating with each respective cell52. The permeable wall54has a plurality of holes70and each wall segment60may have a multiple of holes70. It is further contemplated and understood that the holes68,70may be, or achieved through, perforations, a mesh layer, a combination of a perforated layer and a mesh layer, a screen or other type of skin that permits the passage of air. It is also understood that with the combination of the permeable panel40and the permeable wall54, the acoustic liner22may behave as a double degree of freedom (DDOF) liner with the wall54being a DDOF septum, and use of the sidewalls44generally make the liner a local reacting liner.

With further regard to the turbofan engine20application (seeFIG. 1), the permeable panel40of the acoustic liner22is a perforated panel having an outer face72that may define, in-part, an air passage such as, for example, the generally cylindrical intake passage74of the intake cowling24. Alternatively, the face72may define, at least in-part, the bypass flowpath28and/or an exhaust channel76of the exhaust nozzle36. It should be appreciated to those skilled in the art that the physical dimensions of the acoustic liner22may be altered or tuned to suppress targeted resonating frequency bandwidths without departing from the novelties of the present disclosure. For instance, the liner22may be tuned to suppress the relatively high frequency bandwidths emitted from a turbine section of the engine core34, or may be tuned to suppress the lower frequency bandwidths emitted from a combustor section of the engine core34.

The acoustic liner22may be made of any variety of materials depending upon a particular application including metals, composites and ceramics. For instance, if the acoustic liner22is applied to the exhaust nozzle36of the turbofan engine20, a liner made of ceramic may be desirable to withstand exposure to high temperatures. The liner may be manufactured using any variety and combinations of known manufacturing techniques; and, for more complex liner structures may be manufactured using, at least in-part, an additive manufacturing process.

In operation, an airstream flows across the outer face72and in a shearing direction (see arrow78) with respect to the acoustic liner22. Noise from this airstream generally enters each cell52along an air/sound path (see arrow80), through the hole(s)68in the permeable panel40, into the cell52, and through the holes70in the wall segment60of the permeable wall54. Because of the angular relationship of the non-permeable wall46with the panels38,40a general length (see arrow82) of the air/sound path80is greater than the length42between the panels38,40. This length difference (or increase in path length from more traditional acoustic panels) is advantageous for attenuating low frequency noise increasingly more common in current gas turbine engines due to higher bypass ratios, slower fan speeds and less fan blades. Furthermore, the acoustic liner22may be thinner than more traditional acoustic liners thereby improving the liner application for the next generation, slimmer, nacelle designs.

Referring toFIG. 4, a second embodiment of an acoustic liner is illustrated wherein like elements to the liner22have like identifying element numbers except with the addition of a prime symbol. In a given cell52′ of a liner22′, a first edge56′ of a permeable wall54′ and a first edge48′ of a first non-permeable wall46′ are both engaged to a non-permeable panel38′ and are spaced from one-another. Similarly, a second edge58′ of the permeable wall54′ and a second edge50′ of an adjacent, second, non-permeable wall46′ are both engaged to a permeable panel40′ and spaced from one-another. The second edge58′ of the permeable wall54′ is upstream of the second edge50′ of the second non-permeable wall46′ and with respect to an airstream flow direction78′. An elongated non-permeable segment84of the permeable panel40′ is generally defined laterally between the second edges50′,58′, and defines in-part the given cell52′. The greater the segment's width between edges the larger is the effective cell volume, thereby enhancing attenuation capability of low frequency noise.

Referring toFIG. 5, a third embodiment of an acoustic liner is illustrated wherein like elements to the first and second liners22,22′ have like identifying element numbers except with the addition of a double prime symbol. An acoustic liner22″ may have a plurality of cells52″ that include cells of varying orientations. For instance, cells52″ may have a cell52a″, a cell52b″ and a cell52c″. Cell52a″ is similar to the cell of the second embodiment (i.e. cell52′) except that a first edge56a″ of a permeable wall54a″ is engaged to a first non-permeable panel46a″ and is space from a non-permeable panel38″. Cell52b″ may be similar to the cell of the first embodiment (i.e. cell52) except that a second edge58b″ of a permeable wall54b″ is engaged to the non-permeable wall46a″ and spaced inward from a permeable panel40″. Cell52c″ may generally be a combination of cell52a″ and cell52b″ attributes such that a permeable wall54c″ has opposite edges56c″,58c″ engaged to respective, adjacent, non-permeable walls46c″,46b″, and spaced from respective panels38″,40″. The variety of cell structures is a means of fine tuning the noise attenuation efficiency of the liner for a given application. The positioning of the permeable walls54a″,54b″,54c″ will vary the area of each wall and alter an angle66″ between the permeable walls and the respective non-permeable walls46a″,46b″,46c″.

Acoustic characteristics of the liner22″ may further be adjusted by varying the porosity of the permeable panel40″ and/or the porosity of the permeable wall or septum54b″ (as one example). Yet further, re-positioning of the wall54b″ along a centerline or direction (signified by arrow86) so as to adjust or shift the volumes of respective fore and aft cell portions88,90of the cell52″ is also a means to adjust the acoustic characteristics.

It is understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude and should not be considered otherwise limiting. It is also understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will also benefit. Although particular step sequences may be shown, described, and claimed, it is understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure.

The foregoing description is exemplary rather than defined by the limitations described. Various non-limiting embodiments are disclosed; however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For this reason, the appended claims should be studied to determine true scope and content.