阅读说明：本技术 具有增强的声吸收和减小的阻力特性的声衬 (Acoustic liner with enhanced acoustic absorption and reduced drag characteristics ) 是由 S.穆鲁加潘 M.M.马丁内斯 E.吉尔特塞马 R.K.马吉吉 R.D.塞达 林玟玲 R 于 2020-03-27 设计创作，主要内容包括：本发明涉及具有增强的声吸收和减小的阻力特性的声衬。一种声衬可包括具有谐振单元的阵列的声芯,以及横跨谐振单元的阵列而设置的声屏障。谐振单元包括多个单元壁和由多个单元壁限定的谐振空间。声芯可包括折叠的声芯。另外或在备选方案中,谐振单元中的至少一些可包括斜多面体蜂窝结构和/或多个声音衰减突起。声屏障可包括网状膜和支承网格。(The present invention relates to an acoustic liner having enhanced acoustic absorption and reduced drag characteristics. An acoustic liner may include an acoustic core having an array of resonant cells, and an acoustic barrier disposed across the array of resonant cells. The resonance unit includes a plurality of unit walls and a resonance space defined by the plurality of unit walls. The acoustic core may comprise a folded acoustic core. Additionally or in the alternative, at least some of the resonant cells may include a slanted polyhedral honeycomb structure and/or a plurality of sound attenuating protrusions. The sound barrier may comprise a mesh membrane and a support mesh.)

1. An acoustic liner, comprising:

an acoustic core comprising an array of resonant cells, the resonant cells comprising a plurality of cell walls and a resonant space defined by the plurality of cell walls, wherein the acoustic core comprises a folded acoustic core and/or at least some of the resonant cells comprise:

a slanted polyhedral honeycomb structure; and/or

A plurality of sound attenuating protrusions; and

a sound barrier disposed across the array of resonant cells, the sound barrier comprising a mesh membrane and a support grid.

2. The acoustic liner of claim 1, wherein the acoustic liner comprises:

at least part of the acoustic core and at least part of the acoustic barrier have been integrally formed using additive manufacturing techniques.

3. The acoustic liner of claim 1 wherein the mesh membrane comprises:

a plurality of webs passing through the membrane matrix.

4. The acoustic liner of claim 3 wherein the mesh membrane has a thickness of from 0.1 millimeters to 2.0 millimeters.

5. The acoustic liner of claim 4 wherein the plurality of webs have a cross-sectional width of from 1.0 micron to 2.0 millimeters.

6. The acoustic liner of claim 3 wherein the mesh membrane is rigid or flexible.

7. The acoustic liner of claim 1 wherein the mesh membrane and/or the support mesh comprises:

polymeric materials, metal alloys, and/or composite materials.

8. The acoustic liner of claim 1 wherein the support mesh includes a plurality of apertures extending through the support mesh.

9. The acoustic liner of claim 8 wherein the resonant cells include a resonant space, and wherein the apertures of the support mesh provide an open area from 20% to 100% of a surface area of the resonant space.

10. The acoustic liner of claim 1 wherein the support mesh and/or the mesh membrane comprise a curved surface comprising an aerodynamic profile and/or a coanda surface.

Technical Field

The present disclosure relates to acoustic cores having enhanced acoustic absorption and reduced drag characteristics, and methods of making such acoustic cores and acoustic liners.

Background

The acoustic liner may be used to attenuate or attenuate acoustic waves. For example, acoustic liners are commonly used to attenuate or dampen noise from turbines such as turbofan engines. A typical acoustic liner includes an acoustic core positioned between a perforated sound barrier and a substantially non-perforated back plate. The perforated sound barrier allows sound waves to enter the sound core. The acoustic core includes a plurality of resonant cells intended to attenuate or damp the acoustic waves. However, existing perforated sound barriers may affect sound absorption to different degrees, which may differ across the entire frequency spectrum. Indeed, some acoustic cores may have perforated sound barriers that exhibit unsatisfactory sound absorption properties, either overall or with respect to at least some absorption frequencies. In addition, existing perforated sound barriers can cause undesirable resistance to varying degrees. Furthermore, the degree and nature to which existing perforated sound barriers affect sound absorption and resistance may also vary depending on the velocity of the tangential flow across the surface of the perforated sound barrier and depending on the configuration of the sound core, such that some existing perforated sound barriers may be less suitable at certain velocities and/or for certain sound core configurations.

Accordingly, there is a need for an improved acoustic liner that includes an improved sound barrier for an acoustic liner that exhibits enhanced sound absorption and/or reduced drag. Additionally, there is a need for an improved method of forming an acoustic liner having such improved acoustic absorption and/or reduced resistance characteristics.

Disclosure of Invention

Aspects and advantages will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the presently disclosed subject matter.

In one aspect, the present disclosure includes an acoustic liner. An exemplary acoustic liner may include an acoustic core having an array of resonant cells, and an acoustic barrier disposed across the array of resonant cells. The resonance unit includes a plurality of unit walls and a resonance space defined by the plurality of unit walls. The acoustic core may comprise a folded acoustic core. Additionally or in the alternative, at least some of the resonant cells may include a slanted polyhedral honeycomb structure and/or a plurality of sound attenuating protrusions. The sound barrier may comprise a mesh membrane and a support mesh. The support grid may include a plurality of apertures extending through the support grid.

The reticulated film may include a plurality of webs that pass through the film matrix. The reticulated film may have a thickness of from 0.1 to 2.0 millimeters. The plurality of webs may have a cross-sectional width of from 1.0 micron to 2.0 millimeters. The reticulated film may be rigid or flexible. The resonance unit comprises a resonance space, and the apertures of the support grid may be provided as an open area of from 20% to 100% of the surface area of the resonance space.

In some embodiments, the support grid and/or the reticulated film may comprise a curved surface, and the curved surface may comprise an aerodynamic profile and/or a Coanda (Coanda) surface. In other embodiments, the reticulated film may additionally or alternatively include intra-film resonating elements and/or intra-film curved surfaces.

At least part of the acoustic core and/or at least part of the acoustic barrier may be integrally formed using additive manufacturing techniques. By way of example, the reticulated film and/or the supporting mesh may be formed from a polymeric material, a metal alloy, and/or a composite material. The reticulated film includes a first reticulated film material and a second reticulated film material, the first reticulated film material being different from the second reticulated film material.

In another aspect, the present disclosure includes a turbine including an acoustic liner. An exemplary turbomachine may include a turbine, a fan rotor, a casing or nacelle defining a duct wall surrounding the turbine and/or fan rotor, and one or more acoustic liners annularly disposed along the duct wall. At least one of the one or more acoustic liners may include an acoustic core having an array of resonant cells, and an acoustic barrier disposed across the array of resonant cells. The resonance unit includes a plurality of unit walls and a resonance space defined by the plurality of unit walls. The acoustic core may comprise a folded acoustic core. Additionally or in the alternative, at least some of the resonant cells may include a slanted polyhedral honeycomb structure and/or a plurality of sound attenuating protrusions. The sound barrier may comprise a mesh membrane and a support mesh. The support grid may include a plurality of apertures extending through the support grid.

In yet another aspect, the present disclosure includes a method of forming an acoustic liner. An example method may include attaching a sound barrier to a sound core. The acoustic barrier may include a mesh membrane and a support grid, and the acoustic core may include an array of resonant cells having a plurality of cell walls and a resonant space defined by the plurality of cell walls. The acoustic core may comprise a folded acoustic core. Additionally or in the alternative, at least some of the resonant cells may include a slanted polyhedral honeycomb structure and/or a plurality of sound attenuating protrusions.

In some embodiments, an example method may include forming a reticulated film and/or a support mesh, at least in part, using an additive manufacturing technique. Additionally or in the alternative, an example method may include forming the acoustic core at least in part using an additive manufacturing technique. Further, the example method may additionally or alternatively include forming a sound attenuating protrusion on at least a portion of the sound barrier and/or forming a sound attenuating protrusion on at least a portion of the resonant cell. In still other embodiments, the exemplary method may additionally or alternatively include forming the acoustic core at least in part using a folded core technique.

Technical solution 1. an acoustic liner, comprising:

an acoustic core comprising an array of resonant cells, the resonant cells comprising a plurality of cell walls and a resonant space defined by the plurality of cell walls, wherein the acoustic core comprises a folded acoustic core and/or at least some of the resonant cells comprise:

a slanted polyhedral honeycomb structure; and/or

A plurality of sound attenuating protrusions; and

a sound barrier disposed across the array of resonant cells, the sound barrier comprising a mesh membrane and a support grid.

Solution 2. the acoustic liner according to any preceding solution, characterized in that the acoustic liner comprises:

at least part of the acoustic core and at least part of the acoustic barrier have been integrally formed using additive manufacturing techniques.

Solution 3. the acoustic liner according to any of the preceding claims, wherein the mesh membrane comprises:

a plurality of webs passing through the membrane matrix.

Claim 4. the acoustic liner of any of the preceding claims, wherein the mesh membrane has a thickness of from 0.1 mm to 2.0 mm.

Solution 5. the acoustic liner of any of the preceding claims, wherein the plurality of webs have a cross-sectional width of from 1.0 micron to 2.0 millimeters.

Claim 6. the acoustic liner of any of the preceding claims, wherein the mesh membrane is rigid or flexible.

Solution 7. the acoustic liner according to any preceding solution, wherein the mesh membrane and/or the support mesh comprise:

polymeric materials, metal alloys, and/or composite materials.

Claim 8 the acoustic liner of any preceding claim wherein the support mesh comprises a plurality of apertures extending through the support mesh.

Solution 9. the acoustic liner according to any preceding solution, wherein the resonant cells comprise a resonant space, and wherein the apertures of the support grid provide an open area of from 20% to 100% of the surface area of the resonant space.

Solution 10. the acoustic liner of any preceding solution wherein the support mesh and/or the mesh membrane comprise a curved surface comprising an aerodynamic profile and/or a coanda surface.

Claim 11 the acoustic liner of any preceding claim wherein the mesh membrane comprises a first mesh membrane material and a second mesh membrane material, the first mesh membrane material being different from the second mesh membrane material.

Claim 12. the acoustic liner of any preceding claim, wherein the mesh membrane comprises intra-membrane resonant cells.

Solution 13. the acoustic liner of any of the preceding claims, wherein the mesh membrane comprises an in-membrane curved surface.

The invention according to claim 14 provides a turbine comprising:

a turbine;

a fan rotor;

a casing or nacelle surrounding the turbine and/or the fan rotor, the casing or nacelle defining a duct wall; and

one or more acoustic liners annularly disposed along the conduit wall, at least one of the one or more acoustic liners comprising:

an acoustic core comprising an array of resonant cells, wherein the acoustic core comprises a folded acoustic core and/or at least some of the resonant cells comprise:

a slanted polyhedral honeycomb structure; and/or

A plurality of sound attenuating protrusions; and

a sound barrier disposed across the array of resonant cells, the sound barrier comprising a mesh membrane and a support grid.

Solution 15. a method of forming an acoustic liner, the method comprising:

attaching a sound barrier to an acoustic core, the sound barrier comprising a mesh membrane and a support grid, and the acoustic core comprising an array of resonant cells comprising a plurality of cell walls and a resonant space defined by the plurality of cell walls, wherein the acoustic core comprises a folded acoustic core and/or at least some of the resonant cells comprise:

a slanted polyhedral honeycomb structure; and/or

A plurality of sound attenuating protrusions.

The method of any of the preceding claims, further comprising:

forming the mesh membrane and/or the support grid at least in part using additive manufacturing techniques.

The method of any of the preceding claims, further comprising:

sound attenuating protrusions are formed on at least a portion of the sound barrier.

The method of any of the preceding claims, further comprising:

the acoustic core is formed, at least in part, using additive manufacturing techniques.

The method according to any of the preceding claims, characterized in that the method comprises:

sound attenuating protrusions are formed on at least a portion of the resonance unit.

The method of any of the preceding claims, further comprising:

the acoustic core is formed at least in part using folded core techniques.

These and other features, aspects, and advantages will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and together with the description, serve to explain certain principles of the presently disclosed subject matter.

Drawings

A full and enabling disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 schematically depicts a perspective partial cut-away view of a turbine with an acoustic liner;

2A-2D schematically depict isometric, partial cross-sectional views of portions of an example acoustic liner;

fig. 3A-3H schematically depict partial cross-sectional views of an exemplary sound liner, further illustrating features of an exemplary sound barrier;

fig. 4A-4F schematically depict partial cross-sectional views of exemplary reticulated films;

fig. 5 schematically depicts an exemplary configuration of apertures for a support grid and/or an exemplary configuration of a mesh for a mesh membrane;

FIG. 6 schematically depicts an isometric perspective view of a portion of an example acoustic liner with a sound barrier removed to show an example acoustic core;

FIGS. 7A-7C depict top, side, and bottom perspective views, respectively, of an acoustic core having a parallel polyhedral honeycomb structure;

8A-8C depict top, side, and bottom perspective views, respectively, of an acoustic core having an oblique polyhedral honeycomb structure;

FIG. 9 schematically depicts several additional exemplary oblique polyhedral cells that may be included in an acoustic core;

FIGS. 10A and 10B depict converging and diverging polyhedral cells, respectively, from the exemplary acoustic core depicted in FIGS. 8A-8C projected onto a two-dimensional space;

FIG. 10C schematically depicts an exemplary strip of core material, a plurality of strips of core material being selectively adhered and folded or expanded to form an acoustic core;

FIG. 10D schematically depicts a perspective view of an acoustic core formed using folded core technology using a strip of core material configured as shown in FIG. 10C;

FIG. 11A schematically depicts another exemplary core material strip, a plurality of which may be selectively adhered and folded or expanded to form an acoustic core;

11B-11D depict top, side, and bottom perspective views, respectively, of an acoustic core formed using a folded core technique using a strip of core material configured as shown in FIG. 11A;

12A and 12B schematically depict an exemplary acoustic core having sound attenuating protrusions;

13A and 13B schematically depict an exemplary tool path that may be used to additively manufacture an acoustic core having sound attenuating protrusions;

FIG. 14 schematically depicts an exemplary outer profile and an inner profile adjacent to the outer profile, the outer profile having overlapping tool paths (pass) intended to form sound attenuating protrusions;

FIG. 15 schematically depicts a perspective view of an acoustic core having a combination of parallel polyhedral honeycomb structures and oblique polyhedral honeycomb structures; and

16A-16C show a flow chart depicting an exemplary method of forming an acoustic liner.

Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the present disclosure.

Detailed Description

Reference will now be made in detail to exemplary embodiments of the presently disclosed subject matter, one or more examples of which are illustrated in the accompanying drawings. The various examples are provided by way of illustration and should not be construed to limit the present disclosure. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Accordingly, the disclosure is intended to cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

Acoustic liners for attenuating or attenuating acoustic waves are described herein. Acoustic liners may be used, for example, to attenuate or dampen noise generated or emitted by various aspects or components of turbomachinery, such as turbofan engines commonly used in aircraft, including commercial, military, and civilian aircraft. Acoustic liners can be used to attenuate and dampen noise from a wide variety of turbomachines, including turbojet engines, turbofan engines, turboprop engines, turboshaft engines, ramjet engines, rocket jet engines, impulse jet engines, turbines, gas turbines, steam turbines, marine engines, and the like. More broadly, the acoustic liner may be used to attenuate or attenuate acoustic waves from any source that may be within the contemplation of those skilled in the art.

The presently disclosed acoustic liner includes an array of resonant cells having a plurality of cell walls and a resonant space 207 defined by the plurality of cell walls, and an acoustic barrier disposed across the array of resonant cells. The sound barrier comprises a mesh membrane and a support grid. The presently disclosed sound barrier may be configured to provide a relatively constant acoustic impedance across the entire frequency spectrum, meaning that the acoustic impedance of the sound barrier is substantially unaffected by the magnitude of the sound pressure level and the tangential flow mach number.

The presently disclosed acoustic liner is in contrast to conventional acoustic liners as follows: the conventional acoustic liner has a perforated acoustic barrier, such as one having many small perforations or holes that are known to exhibit acoustic impedance that is greatly affected by both the sound pressure level and the tangential flow mach number. The presently disclosed acoustic liner also contrasts with conventional acoustic liners as follows: this conventional acoustic liner has a wire mesh acoustic barrier adhered to an array of resonant cells, without a supported perforated acoustic barrier, which can provide a relatively linear acoustic impedance, but generally requires an undesirably small resonant cell, and the wire mesh may easily become damaged or displaced by debris, and the adhesive used to adhere the wire mesh tends to become partially blocked by the adhesive material used to adhere the wire mesh to the resonant cell. A conventional perforated sound barrier may be placed on top of the wire mesh to provide support; however, such conventional perforated sound barriers may undesirably introduce variable acoustic impedance properties that depend on the sound pressure level and the tangential flow mach number.

The presently disclosed exemplary embodiments of the acoustic liner may be produced, at least in part, using additive manufacturing techniques. The use of additive manufacturing techniques allows for novel resonant cell configurations, geometries, and/or features, as well as novel sound barriers that avoid the aforementioned disadvantages of conventional sound liners. In an exemplary embodiment, the sound barrier may be integrally formed with the array of resonant cells using additive manufacturing techniques, thereby eliminating the need for adhesives while also permanently securing the sound barrier to the array of resonant cells. For example, additive manufacturing techniques may be used to provide an additive manufactured acoustic core or an additive manufactured acoustic core segment comprising an array of additive manufactured resonant cells and/or an additive manufactured acoustic barrier. The additively manufactured sound barrier may comprise an additively manufactured reticulated film and/or an additively manufactured supporting mesh. In some embodiments, the array of additively-manufactured resonant cells and the additively-manufactured sound barrier may be formed using the same additive manufacturing technique and/or as part of the same additive build process.

It is understood that the terms "upstream" and "downstream" refer to relative directions with respect to fluid flow in the fluid pathway. For example, "upstream" refers to the direction from which the fluid flows, and "downstream" refers to the direction to which the fluid flows. It is also understood that terms such as "top," "bottom," "outward," "inward," and the like are words of convenience and are not to be construed as limiting terms. As used herein, the terms "first," "second," and "third" may be used interchangeably to distinguish one component from another component, and are not intended to denote the position or importance of the individual components. The terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

Here and throughout the specification and claims, range limitations are combined and interchanged, and such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. For example, all ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about", "approximately" and "substantially", will not be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value, or of a method or machine for constructing or manufacturing the component and/or system.

Exemplary embodiments of the present disclosure will now be described in more detail. As shown in fig. 1, one or more acoustic liners 100 may provide a system for attenuating or attenuating sound waves, such as sound waves associated with turbofan engine 102. As shown, turbofan engine 102 includes a casing or nacelle 104 that surrounds a turbine 106 and/or a fan rotor 108, with fan rotor 108 including a plurality of circumferentially spaced fan blades 110 powered by turbine 106. The exemplary housing or nacelle 104 includes an inlet 112 and a duct having a duct wall 114 that generally guides an airflow 116 downstream through the fan rotor 108 along a longitudinal axial centerline 118. In some embodiments, one or more acoustic liners provide a system for attenuating or attenuating acoustic waves. An exemplary system may include one or more acoustic liners 100 disposed annularly along the conduit wall 114. One or more acoustic liners 100 may have a position along duct wall 114 upstream of fan blades 110. One or more acoustic liners may also be positioned downstream of fan blades 110. For example, the acoustic liner may be positioned at or aft of the inner barrel 120 portion of the nacelle 104. Additionally or alternatively, one or more acoustic liners 100 may be positioned at or aft of a fan casing portion 122 and/or a transcowl portion 124 of the nacelle 104. In some embodiments, turbofan engine 102 may include a plurality of casings that surround turbine 106. In some embodiments, multiple housings may be annularly configured and arranged with respect to one another. Each such housing may include an inner conduit wall 114 and an outer conduit wall 114. The one or more acoustic liners 100 may be positioned around the inner conduit wall 114 and/or the outer conduit wall 114 of any one or more of the plurality of enclosures. Additionally, one or more acoustic liners 100 may be positioned adjacent to a non-rotating portion of the fan casing portion 122 or other component of the turbofan engine 102. These locations include ducts or casings within turbofan engine 102 where the acoustic liner may effectively suppress (e.g., attenuate or attenuate) noise at various frequency ranges, including the entire frequency spectrum. For example, one or more acoustic liners 100 may be positioned at the core cowl portion 126. Those skilled in the art will recognize that the acoustic liner 100 may be positioned to further areas of attenuation or attenuation of noise generated or emitted by various aspects of the turbofan engine 102, all of which are within the scope of the present disclosure.

In operation, the turbofan engine 102 generates a significant amount of noise. To illustrate a typical source of noise for turbofan engine 102, it will be appreciated that fan rotor 108 rotates within fan casing portion 122, producing discrete tonal noise primarily at the Blade Pass Frequency (BPF) and multiples thereof. During takeoff of the aircraft, fan blades 110 reach transonic and supersonic rotational speeds, thereby generating noise that propagates outwardly from the fan duct into the surrounding environment. In an exemplary embodiment, the one or more acoustic liners 100 are constructed and arranged to suppress noise that resonates at BPFs and harmonics of BPFs. One or more of the acoustic liners 100 or portions thereof may be configured to attenuate or attenuate acoustic waves and thereby reduce sound at particular frequencies or over the entire frequency range. Some aspects of the acoustic liner 100 may be configured to reflect incident acoustic waves multiple times before the acoustic waves exit the acoustic liner 100. These multiple reflections can reduce the amplitude of the sound waves. Additionally, some aspects of the acoustic liner 100 may be configured to cause the acoustic waves to become out of phase. As the sound waves become out of phase, various portions of the sound waves tend to cancel each other, thereby reducing at least some of the energy in the sound waves.

Fig. 2A-2D illustrate isometric partial cross-sectional views of portions of an exemplary acoustic liner 100. The acoustic liner 100 shown in fig. 2A-2D may be configured for use with the turbofan engine 102 shown in fig. 1, or for attenuating noise from any other source within contemplation of those skilled in the art. In some embodiments, the acoustic liner 100 may be disposed proximate the air flow 116 (also shown in FIG. 1). The acoustic liner 100 may be secured within the turbofan engine 102 by a flange or other means of attachment to the duct wall 114 and/or the fan case portion 122. The acoustic liner 100 includes an acoustic core 200 positioned between an acoustic barrier 202 and a substantially non-perforated backplate 204. The sound barrier 202 and the back plate 204 form planes having a substantially parallel orientation with respect to each other. The acoustic core 200 is comprised of a hollow honeycomb or resonant cell 206 disposed between the acoustic barrier 202 and the backplate 204. The resonance unit 206 comprises a plurality of unit walls defining hollow resonance spaces 207, 207. The sound barrier 202 includes a mesh membrane 208 and a support grid 210. In an exemplary embodiment, the mesh membrane 208 may be disposed proximal to the acoustic core 200 and the support grid 210 is disposed distal to the acoustic core 200. However, in some embodiments, at least a portion of the support mesh 210 may be disposed proximal to the acoustic core, with at least a portion of the mesh membrane 208 disposed distal to the acoustic core 200 relative to such at least a portion of the support mesh 210. Additionally or in the alternative, at least a portion of the support grid 210 may be disposed flush with at least a portion of the mesh membrane 208. For example, the top surface of the support grid 210 may lie in a plane that is substantially planar with the top surface of the mesh membrane 210. Additionally or in the alternative, at least a portion of the support grid 210 may pass through or interrupt the mesh membrane 208 relative to the normal 214.

The mesh film 208 may include a plurality of meshes 400 (fig. 4A-4F) through a film base 401. Exemplary mesh membrane 208 may include a mesh having any desired shape, including oval and/or polyhedral shaped meshes. The mesh may pass directly through the mesh film 208, and/or the mesh may define a complex network of interconnected meshes throughout the mesh film 208. The mesh may have a well-defined shape and/or size, or a distribution of shapes and/or sizes, such as a random distribution. In some embodiments, the mesh film 208 may have a mesh or fibrous composition, and may include sound attenuating protrusions as described herein.

The mesh film 208 may be rigid or flexible, and may include one or more layers that may be different from each other. In some embodiments, the mesh membrane 208 may include a pre-load tension, such as by stretching the mesh membrane 208 across the array of resonant cells 206 and/or by subjecting the mesh membrane 208 to a thermal or chemical curing process that introduces such a pre-load tension. Such a pre-load tension may increase the sound absorbing properties of the acoustic liner 100. For example, tangential flow (such as tangential flow from air flow 116) and/or fluid within resonant cell 206 may interact with pre-loaded mesh membrane 208, and the pre-loaded tension may allow mesh membrane 208 to absorb a greater amount of acoustic energy and thereby provide enhanced acoustic impedance. Additionally or in the alternative, energy absorption may be enhanced by providing a degree of flexibility in the mesh membrane 208 such that tangential flow within the resonant cell 206 (such as tangential flow from the air flow 116) and/or fluid activates the flexibility of the mesh membrane 208 and thereby provides enhanced acoustic impedance. The reticulated film 208 may be formed from a polymeric material (e.g., a thermoplastic and/or elastomeric material), a metal alloy, and/or a composite material, and may be in the form of a mesh, netting, or woven or non-woven fibrous material (e.g., synthetic fibers) having a netting applied thereto or having reticulated characteristics when formed.

The mesh membrane 208 may have a thickness of from about 0.1 millimeters (mm) to about 2.0 mm (such as from about 0.1 mm to about 1.0 mm, such as from about 0.5 mm to about 1.5mm, such as from about 1.0 mm to about 2.0 mm, or such as from about 1.5mm to about 2.0 mm). The mesh membrane 208 may have a thickness of at least about 0.1 mm (such as at least about 0.5 mm, such as at least about 1.0 mm, or such as at least about 1.5 mm). The mesh membrane 208 may have a thickness of less than about 2.0 mm (such as less than about 1.5mm, such as less than about 1.0 mm, or such as less than about 0.5 mm).

The webs in the mesh membrane 208 may have a cross-sectional width of from about 1.0 micrometers (μm) to about 2.0 millimeters (mm), such as from about 1 μm to about 1000 μm, such as from about 50 μm to about 1000 μm, such as from about 100 μm to about 500 μm, such as from about 250 μm to about 750 μm, such as from about 750 μm to about 1.5mm, such as from about 1.0 mm to about 2.0 mm, or such as from about 1.5mm to about 2.0 mm. The webs in the reticulated film 208 may have a cross-sectional width of at least about 1.0 μm (such as at least about 50 μm, such as at least about 100 μm, such as at least about 250 μm, such as at least about 500 μm, such as at least about 750 μm, such as at least about 1.0 mm, or such as at least about 1.5 mm). The webs in the reticulated film 208 may have a cross-sectional width of less than about 2.0 mm (such as less than about 1.5mm, such as less than about 1.0 mm, such as less than about 0.5 mm, such as less than about 1.0 mm, such as less than about 750 μm, such as less than about 500 μm, such as less than about 250 μm, such as less than about 100 μm, such as less than about 50 μm).

The support grid 210 provides support to the mesh membrane 208 and may also be formed of a polymer material (e.g., a thermoplastic material or an elastomeric polymer), a metal alloy, and/or a composite material. The support mesh 210 includes a plurality of apertures 212 extending through the support mesh 210 to allow acoustic waves to interact with the mesh membrane 208 and enter the resonant cells 206 of the acoustic core 200. The orifices 212 may be positioned and arranged in at least one of a repeating pattern and a random pattern. In an exemplary embodiment, the apertures 212 may be positioned and spaced in a manner corresponding to the positioning and spacing of the array of resonant cells 206 comprising the acoustic core 200. The apertures 212 and the resonance units 206 may have a one-to-one or many-to-one relationship. For example, in some embodiments, the acoustic liner 100 may include one aperture 212 positioned adjacent to a respective resonant cell 206 to allow fluid to interact with the mesh membrane 208 and enter such resonant cell 206. Other embodiments may include a plurality of apertures 212 positioned adjacent to respective resonant cells 206.

The mesh membrane 208 and/or the support grid 210 may be formed separately from or simultaneously with each other as part of an additive manufacturing technique or any other suitable process. The mesh membrane 208 and/or the support grid 210 may additionally or alternatively be formed separately from or simultaneously with the acoustic core 200 as part of an additive manufacturing technique. Additionally or in the alternative, the mesh membrane 208 may be combined with the support mesh 210 and/or the acoustic core 200 using a bonding process, and/or the support mesh 210 may be combined with the mesh membrane and/or the acoustic core 200 using a bonding process. Alternatively, the mesh membrane 208 may be secured to the sound barrier 202 using an adhesive process. For example, a thermal, sonic, or electric welding process may be used. As another example, diffusion bonding may be used. Alternatively, an adhesive formulation or adhesive tape, such as a thermoset or pressure sensitive adhesive, may be used to secure the mesh film 208 to the support grid 210. Such a bonding process may also be used to secure the support mesh and/or the mesh membrane 208 to the acoustic core 200.

The exemplary sound barrier 202 may include a support mesh 210 having apertures 212, the apertures 212 being sufficiently large to provide linear acoustic impedance properties while minimizing or eliminating undesirable dependence on sound pressure level and tangential flow mach number. For example, the sound barrier 202 may comprise a support grid 210 having apertures 212, the apertures 212 providing an open area of at least 20% up to or close to 100% of the surface area of the resonance space 207, such as from about 20% to about 100%, such as from about 20% to about 90%, such as from about 20% to about 80%, such as from about 20% to about 60% or such as from about 20% to about 40% of the surface area of the resonance space 207 of the resonance unit 206.

The support grid 210 may include apertures 212 having any desired shape, including oval-shaped and/or polyhedral shaped apertures 212. For example, fig. 2A and 2B illustrate the example acoustic liner 100 having a support grid 210, the support grid 210 including apertures 212 having an elliptical shape, and fig. 2C and 2D illustrate the example acoustic liner 100 having a support grid 210, the support grid 210 including apertures 212 having a polyhedral shape. In some embodiments, the apertures 212 in the support grid 210 may correspond to the shape of the top surface 216 of the resonant cells 206. For example, as shown in fig. 2D, an acoustic liner 100 having an array of resonant cells 206 with hexagonal top surfaces 216 may be utilized in combination with an acoustic barrier 202 having a support grid 210 with corresponding hexagonal shaped apertures 212.

The thickness or height of the acoustic core 200 may be defined by the distance taken along axis R214 (also shown in fig. 1) between the inner surface of the acoustic barrier 202 and the inner surface of the back plate 204. The top surface 216 defines a first linear or curved surface of the acoustic core 200 and the bottom surface 218 defines a second linear or curved surface of the acoustic core. The top surface 216 is located adjacent to and oriented toward the inner surface of the sound barrier 202, and the bottom surface 218 is located adjacent to and oriented toward the inner surface of the back plate 204. Axis R214 represents a normal to a normal surface corresponding to top surface 216 and/or bottom surface 218. The axis R may be a radial axis or other axis as the context requires. In the exemplary embodiment, the terms "inner" and "outer" refer to the orientation of the respective layers relative to longitudinal axial centerline 118 shown in FIG. 1.

The sound barrier 202, the backplate 204, and the acoustic core 200 may together form an arcuate, cylindrical acoustic liner 100 (see, e.g., fig. 1), portions of which are shown in fig. 2A. Thus, a noise source (e.g., fan blades 110 of fan rotor 108) is positioned within arcuate cylindrical acoustic liner 100. The sound-lined sound barrier 202 is typically oriented towards a noise source, with the back plate 204 typically being further from the noise source relative to the sound barrier 202. In an alternative embodiment, the sound barrier 202, the back plate 204, and the acoustic core 200 may together form the acoustic liner 100 having a substantially flat planar profile. For example, but not limiting of, an enclosed space such as a room or engine housing may house a noise source such as a noisy machine, and one or more walls or other aspects of such an enclosed space may be lined with a substantially flat acoustic liner 100.

In still other embodiments, the sound barrier 202, the back plate 204, and the acoustic core 200 may together form a complexly curved acoustic liner 100. For example, but not limiting of, one or more complex curved walls or other aspects of the nacelle or a room or space housing the noise source may be at least partially lined with a complex curved acoustic liner 100 (such as that shown in fig. 1). The curve may be configured to correspond to a contour of an installation location, such as locations 114, 120, 122, 124, 126 within the nacelle 104 of the turbofan engine 102.

Turning now to fig. 3A-3H, partial cross-sectional views of the exemplary sound liner 100 are shown to further illustrate features of the exemplary sound barrier 202. The acoustic liner 100 shown in fig. 3A-3H includes an acoustic barrier 202 having apertures 212, the apertures 212 being large enough to provide linear acoustic impedance properties while minimizing or eliminating undesirable dependence on sound pressure level and tangential flow mach number. For example, the aperture 212 may be provided as an open area of at least 20% up to or near 100% of the surface area of the resonance space 207. As shown in fig. 3A-3D, the example sound liner 100 may include a sound barrier 202 having a mesh membrane 208 disposed proximal to the sound core 200 and a support mesh 210 disposed distal to the sound core 200. Additionally or in the alternative, as shown in fig. 3E-3H, the example acoustic liner 100 may include an acoustic barrier 202 in which at least a portion of the support mesh 210 is disposed flush with at least a portion of the mesh membrane 208. For example, as shown, the top surface of the support grid 210 may lie in a plane that is substantially planar with the top surface of the mesh membrane 208. Also, as shown, at least a portion of the support grid 210 may pass through or interrupt the mesh membrane 208.

The acoustic liner 100 shown in fig. 3A-3H may reflect an embodiment of the acoustic barrier 202 in which the acoustic barrier 202 includes apertures 212 and resonant cells 206 having one-to-one or many-to-one relationships depending on the orientation of the cross-section depicted. The acoustic liner 100 shown in fig. 3C reflects the barrier 202 with the apertures 212 and the resonant cells 206 having a many-to-one relationship.

In some embodiments, as shown in fig. 3D, the support grid 210 of the sound barrier 202 may include aspects having curved surfaces 300. Such curved surfaces 300 may have an aerodynamic profile that reduces drag from tangential flow (such as from the airflow 116), and may include convex and/or concave aspects. Additionally or in the alternative, such curved surfaces 300 may comprise "coanda surfaces" that may direct tangential flow (such as from the air flow 116) into a resonating unit immediately downstream. "coanda surface" refers to a curved surface as follows: a region of reduced pressure is created in the immediate vicinity of such a curved surface. This pressure drop entrains and accelerates the fluid along the contour of the surface, which is sometimes referred to as the "coanda effect". The coanda effect is a phenomenon as follows: the flow attaches itself to nearby surfaces and remains attached even when the surface curves away from the initial direction of flow. As is characteristic of the coanda effect, the accelerating fluid tends to flow tightly over the surface, as if "attached" or "clinging" to the surface. As such, the coanda surface may increase the amount of fluid that interacts with the mesh membrane 208 and enters the resonant cell 206, thereby increasing the fluid interaction with the resonant cell 206, which may result in an increase in sound absorption.

In still other embodiments, as shown in fig. 3G and 3H, the mesh membrane 208 of the sound barrier 202 may include aspects having curved surfaces. The mesh membrane 208 may include a convex curved surface 302 (fig. 3G) and/or a concave curved surface 304 (fig. 3H). Such convex curved surfaces 302 and/or concave curved surfaces 304 may have aerodynamic profiles that reduce drag from tangential flow, such as from the air flow 116. Additionally or in the alternative, such convex curved surfaces 302 and/or concave curved surfaces 304 may comprise coanda surfaces that may direct a tangential flow (such as a tangential flow from the air flow 116) into the resonant unit 206. The convex curved surface 302 may increase the interaction between the reticulated film 208 and the tangential flow (such as the tangential flow from the air stream 116), for example, by protruding a convex portion of the reticulated film 208 into the tangential flow (such as the tangential flow from the air stream 116). Additionally, the convex curved surface 302 of the mesh membrane 208 may draw tangential flow (such as tangential flow from the air stream 116) into the adjacent resonant cell 206, for example, by providing a coanda surface such as at the downstream side of the adjacent resonant cell 206. Such coanda surfaces can direct a tangential flow (such as a tangential flow from the air stream 116) along the downstream cell wall into the resonant cell 206, which can introduce sound attenuating vortices in the resonant cell 206.

While the acoustic liner 100 having the support grid 210 with the curved surface 300 is described with reference to fig. 3D, it will be appreciated that the support grid 210 with the curved surface 300 may be incorporated into any acoustic liner 100 according to the present disclosure. For example, the support grid 210 of any of the acoustic liners 100 described with reference to fig. 1, 2A-2D, and 3A-3H may include aspects having curved surfaces 300, all of which are within the scope of the present disclosure. Additionally, while the acoustic liner 100 having the mesh membrane 208 with the convex curved surface 302 or the concave curved surface 304 is described with reference to fig. 3G and 3H, respectively, it will be appreciated that the mesh membrane 208 with the convex curved surface 302 and/or the concave curved surface 304 may be incorporated into any acoustic liner 100 according to the present disclosure. For example, the mesh membrane 208 of any of the acoustic liners 100 described with reference to fig. 1, 2A-2D, and 3A-3H may include aspects having convex curved surfaces 302 and/or concave curved surfaces 304, all within the scope of the present disclosure. The acoustic liner 100 may include a resonant cell 206 adjacent to a portion of the mesh membrane 208 that includes a convex curved surface 302 and/or a concave curved surface 304. Such portions of the mesh membrane 208 may include a convex curved surface 302, a concave curved surface 304, or both the convex curved surface 302 and the concave curved surface 304. In some embodiments, the acoustic liner may have an acoustic barrier 202 with a support member that includes a curved surface 300, and a mesh membrane 208 that includes a convex curved surface 302 and/or a concave curved surface 304.

Still referring to fig. 3A-3H, in an exemplary embodiment, the acoustic core 200, the mesh membrane 208, and/or the support mesh 210 may be formed using additive manufacturing techniques, which may allow for acoustic barriers 202 having novel configurations, geometries, and/or features that avoid certain disadvantages of conventional acoustic liners. Such additive manufacturing techniques may be utilized alone or with other manufacturing techniques to provide the acoustic liner 100 having the configuration as shown.

In an exemplary embodiment, the acoustic liner 100 may be formed entirely using additive manufacturing techniques. For example, the sequential layers of the acoustic core 200, the mesh membrane 208, and the acoustic barrier 202 may be additively manufactured using suitable additive manufacturing techniques. Such additive manufacturing techniques may allow for configurations such as: a support grid 210 disposed flush with at least a portion of the mesh membrane 208 (e.g., as shown in fig. 3E-3H), and a sound barrier 202 including curved surfaces 300, 302, 304, such as the support grid 210 having the curved surface 300 and/or the mesh membrane 208 having curved surfaces such as a concave curved surface 302 and/or a convex curved surface 304. Additionally, additive manufacturing techniques may provide the reticulated film 208 with sufficient structure so that the presently disclosed support grid 210 may be utilized rather than a conventional perforated top plate.

In some embodiments, the mesh membrane 208 may be applied to the top surface 216 of the acoustic core 200, such as from a roll or sheet of mesh membrane material, and the support grid 210 may then be additively printed on the mesh membrane 208. The support grid 210 may penetrate the mesh membrane material and be integrally bonded with the cell walls of the acoustic core 200 and the mesh membrane material, thereby providing the acoustic liner 100 comprising the acoustic core 200 and the acoustic barrier 202 integrally formed with one another. Such an integrally formed acoustic liner 100 may include a mesh membrane 208 integrally formed with the support mesh 210 and the acoustic core 200, and the support mesh 210 integrally formed with the acoustic core 200.

In an exemplary embodiment, the acoustic core 200, the mesh membrane 208, and the support mesh 210 may be additively manufactured so as to be the same component without seams or the like that separate the elements from one another. However, the mesh membrane 208 may be identified by the mesh present therein, and the support mesh 210 may be identified by a non-mesh material disposed over the cell walls of the acoustic core 200 and/or between portions of the mesh membrane 208.

Turning now to fig. 4A-4F, the construction of an exemplary reticulated film 208 will be described in more detail. Fig. 4A-4F illustrate cross-sectional views of configurations of exemplary mesh films 208. As shown in fig. 4A, the mesh film 208 may include a plurality of meshes 400 passing through a film base 401. As shown in fig. 4B, exemplary reticulated film 208 may include a combination of different materials and/or a combination of reticulated film material configurations. For example, the mesh membrane 208 may include a first mesh membrane material 402 and a second mesh membrane material 404. The first web of film material 402 may be substantially impermeable and the second web of film material 404 may include a plurality of webs 400. Alternatively, both the first web of film material 402 and the second web of film material 404 may comprise a plurality of webs 400. In some embodiments, the webs 400 in the first web of film material 402 may be different than the webs 400 in the second web of film material 404. For example, the first web of film material 402 may include sound attenuating protrusions 1200 (fig. 12A and 12B), and the second web of film material 404 may include a plurality of webs 400. Such sound attenuating protrusions 1200 may be located at any portion of the mesh membrane 208, such as the surface facing the resonance space 207 of the acoustic core 200.

As shown in fig. 4C-4F, the mesh membrane 208 may include an intra-membrane resonant unit 406. Such an intra-film resonating unit 406 may be located between a first mesh film layer 408 and a second mesh film layer 410. The middle mesh film layer 412 may define sidewalls of the in-film resonant cell 406. The in-film resonating unit may define an in-film resonating space 407. The sound attenuating protrusions 1200 may be located at any part of the mesh membrane 208, such as the surface facing the in-membrane resonant unit 406 and/or the surface facing the resonance space 207 of the acoustic core 200.

As shown in fig. 4D, in some embodiments, the mesh membrane 208 may include an in-membrane curved surface 414. The in-film curved surface 414 may be oriented outward so as to interact with a tangential flow, such as the tangential flow from the air stream 116. The in-film curved surface 414 may increase the interaction between the reticulated film 208 and a tangential flow (such as the tangential flow from the air stream 116), for example, by protruding into the tangential flow. Additionally or in the alternative, the in-film curved surface 414 may be oriented facing inward so as to interact with fluid in the resonant space 207 of the acoustic core 200 and/or so as to interact with fluid in the in-film resonant space 407 of the mesh membrane 208. Such interaction may introduce acoustic attenuation eddy currents within resonating unit 206 and/or in-film resonating unit 406.

In some embodiments, the in-film curved surface 414 may have an aerodynamic profile that reduces drag from tangential flow (such as from the air flow 116). While a convex aspect is shown, it will be appreciated that the in-film curved surface 414 may include convex and/or concave aspects. In some embodiments, the in-film curved surface 414 may comprise a coanda surface that may direct a tangential flow (such as a tangential flow from the air stream 116) through the mesh 400 in the mesh-like film material 404 and into the in-film resonant space 407 defined by the in-film resonant cell 406 and/or into the resonant space 207 defined by the resonant cell 206.

As shown in fig. 4E and 4F, in some embodiments, the mesh membrane 208 may include a first mesh membrane material 402, which may be substantially impermeable, defining a plurality of intra-membrane resonant cells 406. In some embodiments, as shown in fig. 4E, a second mesh film material 404, which may include a plurality of meshes 400, may define pathways into and/or out of an in-film resonant cell 406. Alternatively or additionally, as shown in fig. 4F, first mesh film material 402 may include a plurality of intra-film apertures 416 that define passageways into and/or out of intra-film resonant cells 406. Such intra-film apertures 416 may additionally or alternatively define a passageway into and/or out of the resonant cells 206 of the acoustic core 200.

The exemplary mesh film 208 shown in fig. 4A-4F may be formed using any desired technique, including: additive manufacturing techniques, adhesive processes, thermal welding, sonic or electric welding processes, or diffusion bonding, and combinations thereof. In some embodiments, the first mesh material 402 and the second mesh material 404 may be formed using additive manufacturing techniques. Alternatively, the first web-like film material 402 may be formed using additive manufacturing techniques, and such first web-like film material 402 may be combined with the second web-like film material 404 formed in a separate process. For example, the first web-like film material 402 may be additively printed onto the second web-like film material 404. Alternatively or additionally, the second web-like film material 404 may be secured to the first web-like film material 402 during and/or after such additive printing.

Turning now to fig. 5, an exemplary configuration of the apertures 212 for the support grid 210 and/or a configuration of the mesh 400 for the mesh membrane 208 is shown, any one or more of which may be incorporated into the sound barrier 202. Any one or more of the configurations of the orifices 212 and/or mesh 400 shown in fig. 5 may be incorporated into the mesh membrane 208 and/or the support grid 210. As shown in fig. 5, the surface 500 includes a plurality of apertures 212 or webs 400 that define a plurality of passages 502 extending through the surface 500. The passages 502 may represent apertures 212 extending through the support grid 210. Additionally or in the alternative, the passageways 502 may represent a mesh 400 defined by a mesh membrane 208. The passageways 502 for the mesh membrane 208 may be different in configuration and/or orientation than the passageways 502 for the support grid 210.

The surface 500 and/or the via 500 may be formed using additive manufacturing techniques and/or subtractive manufacturing techniques, or a combination thereof. For example, surface 500 may be formed using additive manufacturing techniques, leaving a via 502 extending through surface 500. Additionally or in the alternative, a subtractive process may be used to form the passages 502 extending through the surface 500.

As shown in fig. 5, exemplary passageways may include polyhedral and/or elliptical cross-sectional shapes. For example, surfaces 500 (a), (b), (c) (e), (f), (h), (i), (j), (l), and (n) comprise polyhedral passageways 502, and surfaces 500(d), (g), (k), (m), (o), and (p) comprise elliptical passageways 502. More particularly, surfaces 500 (a), (e), (f), (h), (j), and (n) include rectangular vias 502; surface 500 (b) includes a tear-drop shaped passage 502; surfaces 500 (c), (i), and (l) include hexagonal vias 502; surfaces (d) and (i) comprise elongated passages 502; and surfaces (g), (m), (o), and (p) include circular vias 502. It will be appreciated that combinations of polyhedral and/or elliptical passageways 502 are also within the scope of the present disclosure.

The vias 502 may be arranged in any desired orientation (including ordered or random or semi-random orientations) around the surface 502. Vias 502 may be oriented to include an equidistant array (e.g., having adjacent vias 502 equidistant from each other in the vertical direction, as shown with respect to surfaces 500 (a) and (c)) or a staggered array (e.g., having adjacent vias 502 unequal distances from each other in the vertical direction, as shown with respect to surfaces 500 (l) and (m)).

Turning now to fig. 6, an exemplary acoustic core 200 will be described. As mentioned, the acoustic core 200 includes an array of resonant cells 206. The resonant cells 206 may have any polyhedral structure or combination of structures, including parallel polyhedral honeycomb structures and/or oblique polyhedral honeycomb structures. In exemplary embodiments, the acoustic core 200, the acoustic barrier 202, and the back plate 204 may together form a complex curved acoustic liner 100 that, for example, may conform to complex curved walls or other aspects of the nacelle 104 or other room or space housing a noise source. For example, fig. 6 illustrates an exemplary curved acoustic liner 100 in which the acoustic barrier 202 is omitted to further illustrate the acoustic core 200. As mentioned, the curvature of the acoustic liner 100 may conform to the contour of the installation location (such as locations 114, 120, 122, 124, 126 within the nacelle 104 of the turbofan engine 102).

The acoustic core 200 may include resonant cells 206 having any polyhedral configuration, including parallel polyhedral honeycomb and/or slanted polyhedral honeycomb. The parallel polyhedral honeycomb structures typically have geometric features that reflect straight prisms or substantially straight prisms. A right prism refers to a polyhedron made up of an n-sided polygonal top surface 216, a bottom surface 218, which is a rotationally-translationally-free copy of the top surface 216, and n rectangular side surfaces, which are bisected by the top surface 216 and the bottom surface 218. Given these characteristics of a straight prism or substantially straight prism, a parallel polyhedral honeycomb structure has sides that are substantially parallel to normal 214, represented by axis R. For example, fig. 7A-7C illustrate an acoustic core 200 having a parallel polyhedral honeycomb structure.

As shown in fig. 7A-7C, the acoustic core 200 has a plurality of polyhedral resonant cells 702 that exhibit the geometric characteristics of a hexagonal prism or "honeycomb" structure. The polyhedral resonant cell 702 has a plurality of polygonal sides 704 bisected by a top surface 706 and a bottom surface 708. The top surface 706 and the bottom surface 708 are substantially parallel to each other and have substantially the same surface area as each other. The side 704 is substantially parallel to the normal 214 and has a convergence angle θ (theta) 220 of zero or approximately zero. However, the parallel polyhedral honeycomb structure is not limited to those having rectangular sides of the same size, nor is the parallel polyhedral honeycomb structure limited to those having the same inner angle between the adjacent rectangular sides. In contrast, parallel honeycomb structures include those having rectangular sides of different sizes and correspondingly different interior angles between adjacent rectangular sides. However, such parallel honeycomb structures have top 706 and bottom 708 surfaces with substantially the same surface area. Also, it will be appreciated that parallel honeycomb structures may not exhibit complete symmetry due to incomplete symmetry on the honeycomb structure resulting from minor inaccuracies in fabrication techniques, etc.

In contrast to parallel honeycombs, oblique polyhedral honeycombs have polyhedral cells with at least one side that converges or diverges at a convergence angle θ (theta) 220 greater than zero degrees with respect to the normal 214 represented by axis R. A wide variety of convergence and/or divergence angles may be provided. For example, in various embodiments, the convergence angle θ (theta) 220 may fall within a range from greater than zero to 45 degrees, such as from 1 to 10 degrees, such as from 1 to 20 degrees, such as from 1 to 30 degrees, or such as from 1 to 45 degrees. In some embodiments, the convergence angle θ (theta) 220 may fall within a range from 2 to 30 degrees (such as from 2 to 10 degrees, such as from 5 to 15 degrees, such as from 10 to 20 degrees, or such as from 15 to 30 degrees). The convergence angle θ (theta) 220 may be greater than zero degrees, such as greater than 1 degree, such as greater than 2 degrees, such as greater than 5 degrees, such as greater than 10 degrees, such as greater than 15 degrees, such as greater than 20 degrees, such as greater than 25 degrees, such as greater than 30 degrees, such as greater than 35 degrees, or such as greater than 40 degrees. The convergence angle θ (theta) 220 may be less than 45 degrees, such as less than 40 degrees, such as less than 35 degrees, such as less than 30 degrees, such as less than 25 degrees, such as less than 20 degrees, such as less than 15 degrees, such as less than 10 degrees, such as less than 5 degrees, or such as less than 1 degree.

The exemplary acoustic core shown in fig. 6 gives one example of a tilted polyhedral honeycomb structure. Fig. 8A-8C illustrate another exemplary diagonal polyhedral honeycomb structure 800. The oblique polyhedral honeycomb structure 800 includes a plurality of converging polyhedral cells 802 and a plurality of diverging polyhedral cells 804 bisected by a top surface 806 and a bottom surface 808. As shown, top surface 806 and bottom surface 808 are substantially parallel to each other. Each of the converging polyhedral cell 802 or the diverging polyhedral cell 804 has a plurality of polygonal sides 810. These polygonal sides include at least a first side 812 that converges at a convergence angle θ (theta) 220 greater than zero degrees with respect to the normal 214 represented by axis R. Additionally or in the alternative, the polygonal sides include at least a first side 812 that converges with respect to at least a second side 814. In some embodiments, the first side 812 may additionally or alternatively diverge with respect to the normal 214 and/or with respect to at least the third side 816.

The converging polyhedral cell 802 and/or the diverging polyhedral cell 804 have asymmetry in at least one such converging or diverging side and/or in different cross-sectional areas as between two substantially parallel planes (i.e., top surface 806 and bottom surface 808) bisecting the cell. Depending on the configuration of a particular cell, the substantially parallel planes of the top surface 806 and the bottom surface 808 may bisect the oblique polyhedral cell into planes, lines, or points. For convenience, such planes, lines or points may sometimes be referred to more generally as faces. For example, top surface 806 bisects both converging polyhedral cell 802 and diverging polyhedral cell 804 into planes, and bottom surface 808 bisects converging cell 802 into a line and diverging cell 804 into planes.

In addition to the exemplary pitched polyhedron honeycomb shown in fig. 5 and 8A-8C, the acoustic core may also include many other pitched polyhedron honeycombs. For example, fig. 9 illustrates a number of exemplary diagonal polyhedrons that may be incorporated into a diagonal polyhedral honeycomb structure according to the present disclosure.

As shown in fig. 9, the oblique-polyhedron honeycomb structure may comprise all or part of any one or more oblique polyhedrons. Exemplary oblique polyhedral honeycomb structures can include frustums, rhomboids, inverse prisms, twisted prisms, cupola (including star-shaped cupola), wedges, pyramids, and combinations or portions of these. By way of example, the frustum may comprise a triangular frustum, a quadrangular frustum, a pentagonal frustum, a hexagonal frustum, a heptagonal frustum, an octagonal frustum, a nine-cornered frustum, a ten-cornered frustum, an eleven-cornered frustum, a twelve-cornered frustum, any other frustum-polyhedron, and combinations of these. Frustum polyhedrons include a frustum combined with another polyhedron, including any of the aforementioned frustum shapes combined with another polyhedron. For example, the rhomboids may be formed of any rhomboid shape, thereby providing a rhomboid polyhedron. As a further example, the rhomboid may be combined with a frustum to form a rhomboid frustum.

An anti-prism comprises a polyhedron made up of a polygonal top face 216, a polygonal bottom face 218, and a sequence of adjacent triangular side faces with alternating orientations that are bisected by the top face 216 and the bottom face 218. By way of example, the inverse prism may include a triangular inverse prism, a tetragonal inverse prism, a hexagonal inverse prism, an inverse prismatic polyhedron, and combinations of these. An anti-prismatic polyhedron comprises an anti-prism in combination with another polyhedron. In some embodiments, the anti-prism may include an n-sided top surface 216 and an n-sided bottom surface 218. Alternatively, the anti-prism may include n-sided top surfaces 216 and bottom surfaces 218 having more or less than n sides.

The twisted prism comprises a polyhedron made up of a polygonal top face 216, a polygonal bottom face 218, and a plurality of side faces including at least some side faces bisected on a diagonal, wherein the top face 216 and the bottom face 218 are twisted with respect to each other such that at least some adjacent side faces are recessed with respect to each other. By way of example, the distorted prisms may include schnhardt polyhedrons, four-sided distorted prisms, hexagonal distorted prisms, distorted prismatic polyhedrons, and combinations of these. The twisted prisms have one or more sides that bisect adjacent diagonals or subsequent diagonals. For example, fig. 9 shows a hexagonal twisted prism with sides bisected on adjacent diagonals, and a hexagonal twisted prism with sides bisected on a second diagonal. A distorted prismatic polyhedron comprises a distorted prism in combination with another polyhedron.

The turret comprises a polyhedron made up of a polygonal top surface 216, a polygonal bottom surface 218, and a plurality of sides comprising an alternating sequence of triangular sides and quadrilateral sides. In some embodiments, the top surface 216 of the turret has twice as many edges as the bottom surface 218 of the turret, or vice versa. By way of example, a tower comprises: a triangular tower having a quadrilateral top surface 216 and a hexagonal bottom surface 218, or a hexagonal top surface 216 and a quadrilateral bottom surface 218; and a pentagonal tower having a pentagonal top surface 216 and a decagonal bottom surface 218, or vice versa. The tower also includes a star tower, which is a tower that utilizes adjacent concave triangular sides instead of quadrilateral sides. The star tower includes a pentagram type tower body (cuploid) and a heptagram type tower body. The pentagram-like turret body has a pentagram base 218 and a pentagram top 216, or vice versa. The heptagonal tower body has a heptagonal top surface 216 and a heptagonal bottom surface 218, or vice versa. As a further example, a tower includes a tower-like configuration having a number of sides, including configurations that approach a frustoconical shape as the number of sides increases. For example, a tower includes an octagon having eighty sides. The tower also includes a tower-like polyhedron comprising a tower or tower-like body in combination with another polyhedron.

The wedge comprises a polyhedron having a polygonal top face 216 and a plurality of polygonal side faces converging in a line. By way of example, the wedges may include four-sided wedges, obtuse-sided wedges, acute-sided wedges, and wedge-shaped polyhedrons, as well as combinations of these. The tetrahedral wedge has two triangular sides and two quadrangular sides. The sides are bisected by the quadrilateral planes on one side and converge into a line on the other side. The obtuse wedges converge into a line wider than the opposite quadrilateral plane. The acute wedges converge to a line narrower than the opposing quadrilateral planes. A wedge-shaped polyhedron comprises a wedge in combination with another polyhedron.

A pyramid comprises a polyhedron with a polygonal base bisected by a plurality of triangular sides converging into points. By way of example, a pyramid comprises a four-corner pyramid consisting of four quadrilateral faces bisected by four triangular sides that converge into a point. Pyramids also include star pyramids, which consist of a star polygonal base and a plurality of triangular sides that converge to a point. By way of example, star pyramids include pentagonal star pyramids.

Any one or more of these oblique polyhedral configurations (including combinations or portions thereof) can be included in various exemplary oblique honeycomb structures. In one aspect, the converging polyhedral cell 802 illustrated in fig. 8A-8C reflects the aspect of an inverse prism combined with the aspect of a wedge. For example, the converging polyhedral cell 802 includes polygonal (hexagonal) top faces 806, and, like the inverse prism, a plurality of triangular side faces are bisected by bottom faces 808. Similar to a wedge, the bottom surface 808 has a wired form. On the other hand, the converging polyhedral cell 802 reflects an aspect of a "flipped inverse prism" (i.e., an inverse prism that has been twisted 180 degrees about its vertical axis). The converging polyhedral cell 802 has flipped or twisted at its midpoint 703. The diverging polyhedral cell 804 reflects the aspect of an anti-prism combined with the aspect of a frustum and/or a tower. For example, the diverging polyhedral cell 804 includes a polygonal (hexagonal) top surface 806, the top surface 806 being bisected by a plurality of sides, similar to an inverse prism, having a plurality of adjacent triangular sides, and having an alternating sequence of triangular sides and quadrilateral sides similar to a tower.

The acoustic core 200 may be formed from a polymer material (e.g., a thermoplastic material or an elastomeric polymer), a synthetic fiber, a metal alloy, or a composite material, and may be formed separately from or simultaneously with the mesh membrane 208 and/or the support grid 210 as part of an additive manufacturing technique or any other suitable process. Additionally, the backplate 204 may be formed from any one or more of such materials, separately from or simultaneously with the acoustic core 200, the mesh membrane 208, and/or the support mesh 210 as part of an additive manufacturing technique or any other suitable process. Alternatively, the acoustic core 200 may be secured between the acoustic barrier 202 and the back plate 204 using a bonding process. For example, a thermal, sonic, or electric welding process may be used. As another example, diffusion bonding may be used. Alternatively, adhesive formulations such as thermosetting or pressure sensitive adhesives or adhesive tapes may be used to secure the acoustic core 200 in place. Additionally, the acoustic core may be formed from any other suitable technique and/or material known in the art, all of which are within the scope of the present disclosure.

Exemplary polymeric materials may include thermoplastic materials and/or thermoset materials. Exemplary thermosetting materials include, for example, epoxy, resin, acrylic, phenolic, polyester, polyurethane, polyimide, polyamide-imide (PAI), polysiloxane bismaleimide, cyanate ester, phenolic, benzoxazine, phthalonitrile. Exemplary thermoplastic materials include, for example, Acrylonitrile Butadiene Styrene (ABS), polyester, polyamide imide (PAI), Polyetherimide (PEI), polyphenylsulfone (PPSF), Polycarbonate (PC), polylactic acid (PLA), High Impact Polystyrene (HIPS), Thermoplastic Polyurethane (TPU), aliphatic polyamide (nylon), Polyaryletherketone (PAEK), Polyetherketoneketone (PEKK), or Polyetheretherketone (PEEK), and combinations thereof.

Exemplary synthetic fibers include extruded polymeric filaments such as Polyetherimide (PEI), polycarbonate, acrylonitrile butadiene styrene, aramid fibers, meta-aramid fibers, para-aramid fibers, polyethylene fibers, rayon, polyester, or nylon, and combinations of these.

Exemplary metal alloys include aluminum alloys, steel alloys, titanium alloys, or nickel alloys (e.g., superalloys, such as austenitic nickel-chromium-based superalloys), and combinations of these.

Exemplary composite materials include Ceramic Matrix Composite (CMC) materials and/or Polymer Matrix Composite (PMC) materials. CMC materials include a ceramic matrix material and reinforcing fibers or cloth. Exemplary ceramic matrix materials include silicon carbide (SiC) and/or carbon (C). Exemplary CMC materials include carbon fiber reinforced carbon (C/C), carbon fiber reinforced silicon carbide (C/SiC), or silicon carbide reinforced silicon carbide (SiC/SiC). PMC materials include a polymer matrix material and reinforcing fibers or cloth. Exemplary PMC materials include fiber reinforced plastics and advanced composites. Exemplary polymeric matrix materials include thermoset materials such as epoxy, phenolic, polyurethane, polyimide, bismaleimide, cyanate ester, phenolic, benzoxazine, phthalonitrile. In some embodiments, polyimides may be particularly suitable. Exemplary polyimides include phenylethynyl terminated imide (PETI) oligomer, biphenyl dianhydrides 2, 2' -dimethylbenzidine, ultra high temperature HFPE. In some embodiments, exemplary polyimides can include end-capping agents (end caps), such as 4-phenylethynylphthalic anhydride (PEPA) and/or asymmetric oxydiphthalic anhydride (a-ODPA) end-capping agents.

Exemplary reinforcing fibers or fabrics that may be utilized in the CMC or PMC material include carbon fibers, ceramic fibers, glass fibers, graphite fibers, and aramid fibers. Exemplary reinforcing fibers include monofilaments, yarns, whiskers or fibers and/or particles. In some embodiments, the ceramic fibers may be formed of materials such as silicon carbide (SiC), carbon fibers (C), sapphire, aluminum silicate, and/or oxides of Si, Al, Zr, Y, and combinations thereof. The reinforcing fibers may additionally include inorganic fillers such as silica, quartz, pyrophyllite, wollastonite, mica, talc, kyanite, and/or montmorillonite, and combinations thereof.

The various aspects of the presently disclosed acoustic liner 100 may be manufactured using any suitable additive manufacturing technique. Exemplary additive manufacturing techniques include, but are not limited to: a Directed Energy Deposition (DED) system, such as a Chemical Vapor Deposition (CVD) system, a Laser Metal Deposition (LMD) system, a Directed Metal Deposition (DMD) system, a Laser Engineered Net Shape (LENS) system, an Electron Beam Additive Melting (EBAM) system, or a Rapid Plasma Deposition (RPD) system; a Powder Bed Fusion (PBF) system, such as a Direct Metal Laser Melting (DMLM) system, an Electron Beam Melting (EBM) system, a Directed Metal Laser Sintering (DMLS) system, a Selective Laser Melting (SLM) system, or a Selective Laser Sintering (SLS) system; laminate Object Manufacturing (LOM) systems, such as ultrasonic manufacturing (UAM) systems; a Material Extrusion (ME) system, such as a Fused Deposition Modeling (FDM) system or a fuse fabrication (FFF) system; material Jetting (MJ) systems, such as Smooth Curvature Printing (SCP) systems, multiple jet forming (MJM) systems; and 3D printing, such as 3D printing by inkjet and laser jetting, including adhesive jetting (BJ) systems; photopolymer Jetting (PJ) systems, Stereolithography (SLA) systems, and Hybrid Processes (HP).

Other suitable techniques that may be used to manufacture the various aspects of the presently disclosed acoustic liner 100 include, but are not limited to, forming (e.g., rolling, stamping, joining, etc.), extruding (e.g., sheet extrusion), subtractive manufacturing (e.g., machining, drilling, laser cutting, etc.), forging or casting, and combinations thereof, or any other manufacturing technique.

Turning now to fig. 10A-10D and 11A-11D, in some embodiments, the acoustic core 200 may be manufactured using a folded core technique, which may utilize a band of core material 1000. The folded core technique may include adhering a plurality of strips of core material 1000 to one another at a plurality of adhesion areas 1002, the adhesion areas 1002 being positioned at selected length intervals along the respective strips of core material 1000. The folded core technique may additionally include expanding the strips of core material 1000 relative to one another at a plurality of expansion regions 1004 respectively located between the plurality of adhesion regions 1002.

In one embodiment, the acoustic core 200 shown in fig. 8A-8C may be formed using folded core technology, providing a folded acoustic core 1006. By way of illustration, fig. 10A shows a converging polyhedral cell 802 from the acoustic core 200 shown in fig. 8A-8C projected onto a two-dimensional space, and fig. 10B shows a diverging polyhedral cell 804 from the acoustic core shown in fig. 8A-8C projected onto a two-dimensional space. The plurality of strips of core material 1000 may be configured as shown in fig. 10A and/or fig. 10B. For example, a plurality of strips of core material 1000 configured as shown in fig. 10A and/or 10B may be joined together in an alternating pattern (as shown in fig. 10C). A plurality of strips of core material 1000 configured as shown in fig. 10C may be used to form a folded acoustic core 1006 as shown in fig. 10D. As shown in fig. 10C, the strip of core material 1000 includes a plurality of fold lines 1008, the fold lines 1008 configured to form a skewed polyhedral cell structure 800 having a plurality of converging polyhedral cells 802 and a plurality of diverging polyhedral cells 804 bisected by a top surface 806 and a bottom surface 808.

Fig. 11A-11D illustrate another example folded acoustic core 1006. Fig. 11A shows a side view of a ribbon 1000 of core material having a plurality of fold lines 1008. A plurality of strips 1000 of core material configured as shown in fig. 11A may be used to form a folded acoustic core 1006 as shown in fig. 11B-11D. The resulting folded acoustic core 1006 shown in fig. 11B-11D includes an oblique polyhedral honeycomb structure 1001 having a plurality of converging polyhedral cells 1102 and a plurality of diverging polyhedral cells 1104 bisected by a top surface 1106 and a bottom surface 1108.

A strip of core material 1000 (such as the strip of core material 1000 shown in fig. 10C and 11A) may be cut from a supply, such as a roll. A strip of core material 1000 having a generally circular configuration prior to folding (such as the strip of core material 1000 shown in fig. 10C) may be wound in an edge direction around the roll. A strip of core material 1000 having a generally linear configuration prior to folding (such as the strip of core material 1000 shown in fig. 11A) may be wound lengthwise around the roll. Several strips of core material 1000 may be selectively adhered to one another at a plurality of adhesion regions 1002 positioned at selected length intervals along the respective strips of core material 1000. The roll of core material may be cut to provide a strip of core material 1000, and the strip of core material 1000 may be folded and/or expanded away from each other at a plurality of expansion regions 1004 respectively located between the plurality of adhesion regions 1002. When folded and/or expanded, the core material strip 1000 may form the acoustic core 200 having any desired profile, including a substantially flat planar profile, a curved planar profile, or a complexly curved planar profile. The desired profile may be provided by: the core material strip 1000 is selectively configured, for example, to correspond to the profile of an installation location, such as locations 114, 120, 122, 124, 126 within the nacelle 104 of the turbofan engine 102. As further examples, the ribbon of core material 1000 in its unfolded state may exhibit a generally circular configuration (fig. 10C), a generally linear configuration (fig. 11A), a curvilinear configuration, an elliptical configuration, a helical configuration, or a wavy or oscillating configuration, as well as combinations of these.

It will be appreciated that in some embodiments, it may be advantageous to avoid scrap or unused material when cutting the strip of core material 1000 from a larger supply of core material. In some embodiments, a strip of core material 1000 having a circular, spiral, or curved configuration may result in waste or unused material. However, in some embodiments, the strip of core material 1000 may be cut from a larger supply of core material, such as a roll, to provide a skewed polyhedral honeycomb structure that reduces scrap material. For example, in some embodiments, the oblique polyhedral cells may be cut from a wavy or oscillating strip of core material 1000, the wavy or oscillating strip of core material 1000 being configured such that the respective edges of the subsequently cut strips 1000 are aligned with one another. Additionally, in some embodiments, oblique polyhedral cells may be cut from the linear core material strip 1000.

Turning now to fig. 12A and 12B, in some embodiments, an exemplary acoustic core 200 may include a resonant cell 206 having sound attenuating protrusions 1200. The sound attenuating protrusion 1200 may be integrally formed with the cell wall of the acoustic core 200. Any one or combination of additive manufacturing techniques may be used to additively manufacture the acoustic core 200 having the sound attenuating protrusions 1200. The integral formation of the sound attenuating protrusion 1200 may intentionally accompany the formation of the acoustic core 200 using additive manufacturing techniques. By "intentionally piggyback" is meant that the plurality of sound attenuating protrusions 1200 will typically not be integrally formed with the acoustic core 200 when using additive manufacturing techniques, but that intentional modifications to additive manufacturing techniques as described herein incidentally form the plurality of sound attenuating protrusions 1200 as the intended integral feature of the acoustic core 200.

The sound attenuating protrusions 1200 or intentionally incidental properties of their formation may provide random or semi-random orientation and/or dimensions of the sound attenuating protrusions 1200 over at least a portion of the acoustic core 200, such as over at least a portion of the cell walls of the resonant cells 206 that make up the acoustic core 200. This random or semi-random orientation and/or size may not necessarily be achievable by other means, such as direct additive manufacturing of the individual protrusions 1200. For example, in some embodiments, at least a portion of the sound attenuating protrusion 1200 may have one or more dimensions (such as height, width, and/or length) that are less than a corresponding minimum dimensional resolution provided by the additive manufacturing technique used to produce the acoustic core 200.

As shown in fig. 12A and 12B, an exemplary resonant cell 206 may include a plurality of sound attenuating protrusions 1200 protruding from a nominal surface 1202 of the cell wall into the resonant space 207. As shown, the resonant cell 206 has sound attenuating protrusions 1200 on the entire cell wall. However, to achieve the benefits of sound attenuation, the sound attenuating protrusions 1200 need not be provided on the entire cell wall, nor on each resonant cell 206 of the array. Indeed, in some embodiments, improved sound attenuation may be achieved by providing sound attenuating protrusions 1200 only on specific areas of the cell walls, only on portions of the cell walls, and only on portions of the array. Likewise, the corresponding remaining portion of the cell wall, or portion of the array of resonant cells 206 may be devoid of sound attenuating protrusions at all. Thus, according to the present disclosure, at least some of the resonant cells 206 may have a plurality of sound attenuating protrusions 1200.

The sound attenuating protrusions 1200 take the form of an additive manufactured material of the cell walls that integrally protrudes into the resonance space 207 in a random or semi-random orientation around at least part of the cell walls. The example sound attenuating protrusions 1200 may include any one or more of a combination of protrusion features having a variety of shapes and configurations, including nodules, loops, hooks, bumps, nubs, plaques, lumps, bumps, protrusions, bumps, bulges, outgrowths, nodules, bubbles, spikes, and the like. These sound attenuating protrusions 1200 appear in a random or semi-random manner as a result of the particular manner in which the resonant cells 206 are formed. However, the particular configuration, arrangement, or orientation of the sound attenuating protrusions 1200 may be selectively controlled or modified by adjusting the manner in which the resonant cells 206 are formed.

Regardless of its shape, the sound attenuating protrusion 1200 may be provided in any desired size. The sound attenuating protrusions 1200 protrude from the nominal surface 1202 of the cell wall in terms of height (h) 1204, width (w) 1206, and length (l) 1208. In some embodiments, the plurality of sound attenuating protrusions 1200 may have an average height, width, and/or length of from about 5 to 10000 microns. The dimensions of the sound attenuating protrusion 1200 may be selected based on the desired sound attenuating properties of the resonant unit 206.

The plurality of sound attenuating protrusions 1200 may have an average height (h) 1204 of from about 5 to 10000 microns as measured from a nominal surface 1202 of the cell wall from which the sound attenuating protrusion 1200 protrudes. For example, the average height 1204 of the sound attenuating protrusions 1200 may be from about 10 μm to 5000 μm, such as from about 10 μm to 1000 μm, such as from about 10 μm to 500 μm, such as from about 25 μm to 300 μm, such as from about 50 μm to 200 μm, or such as from about 75 μm to 150 μm. The plurality of sound attenuating protrusions 1200 may have an average height 1204 of 10000 μm or less (such as 5000 μm or less, such as 1000 μm or less, such as 500 μm or less, such as 300 μm or less, such as 200 μm or less, such as 100 μm or less, such as 75 μm or less, such as 50 μm or less, such as 25 μm or less, or such as 10 μm or less). The plurality of sound attenuating protrusions 1200 may have an average height 1204 of 10 μm or more (such as 25 μm or more, such as 50 μm or more, such as 75 μm or more, such as 100 μm or more, such as 150 μm or more, such as 200 μm or more, such as 300 μm or more, such as 500 μm or more, such as 1000 μm or more, or such as 5000 μm or more).

The plurality of sound attenuating protrusions 1200 may have an average width (w) 1206 from 5 to 500 microns as measured laterally across the surface of the cell wall from which the sound attenuating protrusion 1200 protrudes. For example, the average width 1206 of the sound attenuating protrusions 1200 may be from 10 μm to 5000 μm, such as from 10 μm to 1000 μm, such as from 10 μm to 500 μm, such as from 25 μm to 300 μm, such as from 50 μm to 200 μm, such as from 75 μm to 150 μm. The plurality of sound attenuating protrusions 1200 may have an average width 1206 of 10000 μm or less (such as 5000 μm or less, such as 1000 μm or less, such as 500 μm or less, such as 300 μm or less, such as 200 μm or less, such as 100 μm or less, such as 75 μm or less, such as 50 μm or less, such as 25 μm or less, or such as 10 μm or less). The plurality of sound attenuating protrusions 1200 may also have an average width 1206 of 10 μm or more (such as 25 μm or more, such as 50 μm or more, such as 75 μm or more, such as 100 μm or more, such as 150 μm or more, such as 200 μm or more, such as 300 μm or more, such as 500 μm or more, such as 1000 μm or more, or such as 5000 μm or more).

The plurality of sound attenuating protrusions 1200 may have an average length (l) 1208 from 5 to 500 microns as measured longitudinally along the surface of the cell wall from which the sound attenuating protrusion 1200 protrudes. For example, the average length 1208 of the sound attenuating protrusions may be from 10 μm to 5000 μm, such as from 10 μm to 1000 μm, such as from 10 μm to 500 μm, such as from 25 μm to 300 μm, such as from 50 μm to 200 μm, or such as from 75 μm to 150 μm. The plurality of sound attenuating protrusions 1200 may have an average length 1208 of 10000 μm or less (such as 5000 μm or less, such as 1000 μm or less, such as 500 μm or less, such as 300 μm or less, such as 200 μm or less, such as 100 μm or less, such as 75 μm or less, such as 50 μm or less, such as 25 μm or less, or such as 10 μm or less). The plurality of sound attenuating protrusions 1200 may have an average length 1208 of 10 μm or more (such as 25 μm or more, such as 50 μm or more, such as 75 μm or more, such as 100 μm or more, such as 150 μm or more, such as 200 μm or more, such as 300 μm or more, such as 500 μm or more, such as 1000 μm or more, or such as 5000 μm or more).

Referring now to fig. 13A and 13B, an exemplary embodiment of an intentional incidental formation of the sound attenuating protrusion 1200 will be described. The additive manufacturing technique may be configured to orient the additive manufacturing tool relative to the tool path 1300. Typically, tool path 1300 follows a contour that occupies a two-dimensional space, however tool path 1300 may alternatively be oriented relative to a contour that occupies a three-dimensional space. In either case, the acoustic core 200 may be formed in sequential profiles applied one above the other separated by a profile spacing. Each sequential profile may be formed by orienting an additive manufacturing tool relative to a tool path such that the acoustic core 200 is formed by the additive manufacturing material bonding or otherwise solidifying in the domains 1201 occupied by the respective profile. The field 1201 corresponding to the respective contour includes a three-dimensional volume defined by the contour spacing, i.e., the space occupied by the contour. It will be appreciated that any acoustic core 200 may be formed in the manner described herein so as to integrally form the sound attenuating protrusion 1200 on at least a portion of the acoustic core 200. In this regard, the acoustic core 200 described herein is provided by way of example only and not in a limiting sense. Further, in addition to the acoustic core 200, it may also be desirable to provide sound attenuating protrusions 1200 on other surfaces of the acoustic liner 100, including: a mesh membrane 208, a support grid 210, or a back plate 204, and combinations of these, all within the spirit and scope of the present disclosure.

As shown in fig. 13A, an additive manufacturing tool is oriented relative to a tool path 1300 that includes a plurality of tool path lanes. For example, the tool path 1300 may include a first tool path way 1302 and a second tool path way 1304, which may each represent a portion of the tool path 1300. A plurality of tool path lanes (e.g., first tool path lane 1302 and second tool path lane 1304) overlap one another at a tool path overlap region 1306. In some embodiments, the sound attenuating protrusion 1200 may be formed by introducing additional additive manufacturing material to the acoustic core 200. Additional additive manufacturing material may be introduced to the acoustic core 200 within the tool path overlap region 1306. Additionally or in the alternative, additional additive manufacturing material may be introduced at locations other than the tool path overlap region 1306 (such as the region of the acoustic core 200 adjacent to the tool path overlap region).

As shown in fig. 13B, wherever additional additive manufacturing material is introduced, the overlapping tool paths cause portions of the additive manufacturing material to be introduced to the acoustic core 200 in the form of incidental projections 1200 that protrude from the walls of the acoustic core 200. These protrusions 1200 have sound attenuating properties and as such are referred to herein as sound attenuating protrusions 1200. The sound attenuating protrusions 1200 are formed with attendant properties that impart random or semi-random orientations to the sound attenuating protrusions 1200. The size, shape, and/or configuration of the sound attenuating protrusion 1200 and/or its presence may depend, at least in part, on the degree of overlap in the tool path overlap region 1306, as between multiple tool path lanes.

The degree of overlap in the tool path overlap region 1306 as between two tool path lanes (e.g., first tool path lane 1302 and second tool path lane 1304) may be described with reference to a tool path gap 1308 that describes the distance between a first lane centerline 1310 and a second lane centerline 1312. The tool path gap 1308 may be described with respect to a tool path width 1314 and/or a profile width 1316. The tool path lane width 1314 refers to the average width of a tool path lane (such as the first tool path lane 1302) regardless of the presence of the sound attenuating protrusion 1200. The contour width 1316 refers to an average width of a plurality of tool path lanes defining the tool path overlap region 1306, such as an average width of the first tool path lane 1302 and the second tool path lane 1304, regardless of the presence of the sound attenuating protrusion 1200. In some embodiments, the amount of additional additive manufacturing material introduced to the acoustic core 200 may be proportional to the tool path gap 1308.

The integral formation of the sound attenuating protrusion 1200 may depend on providing a tool path gap 1308 of sufficient size to introduce sufficient additional additive manufacturing material to the acoustic core 200. The dimensions of the tool path gap 1308 may be described with reference to a tool path gap ratio, which refers to the ratio of the profile width 1316 to the tool path lane width 1314. In some embodiments, the amount of additional additive manufacturing material introduced may depend at least in part on the tool path gap ratio. The particular tool path gap ratio that may be appropriate for a given acoustic core 200 may be selected by evaluating the sound attenuating properties of the sound attenuating protrusions 1200 produced thereby.

The tool path gap ratio may range from 1.0 to less than 2.0. A tool path gap ratio of 1.0 corresponds to completely overlapping tool path lanes. A tool path gap ratio of 2.0 corresponds to adjacent and contiguous tool path lanes that do not overlap. In some embodiments, the sound attenuating protrusion 1200 may be integrally formed by providing a tool path to gap ratio of from 1.0 to less than 2.0 (such as from 1.1 to 1.9, such as from 1.1 to 1.8, such as from 1.1 to 1.5, such as from 1.1 to 1.3, such as from 1.2 to 1.7, such as from 1.5 to 1.9, such as from 1.5 to 1.7). The tool path gap ratio may be 1.0 or greater, such as 1.1 or greater, such as 1.2 or greater, such as 1.3 or greater, such as 1.4 or greater, such as 1.5 or greater, such as 1.6 or greater, such as 1.7 or greater, such as 1.8 or greater, or such as 1.9 or greater. The tool path gap ratio may be less than 2.0, such as less than 1.9, such as less than 1.8, such as less than 1.7, such as less than 1.6, such as less than 1.5, such as less than 1.4, such as less than 1.3, such as less than 1.2, or such as less than 1.1.

The sequential profile of the acoustic core 200 including the sound attenuating protrusions 1200 may be formed by orienting the additive manufacturing tool relative to the sequential tool path 1300. Sequential profiles may be applied one above the other, increasing in a step-wise manner to additively build the acoustic core 200. All or a portion of the sequential tool path 1300 may include overlapping tool path lanes, which provide a tool path overlap region 1306. However, it is not necessary that each tool path 1300 provide a tool path overlap region 1306, and it is also not necessary that a tool path overlap region 1306 exist with respect to the entire tool path 1300. In practice, the tool path overlap region 1306 may exist in an intermittent or variable manner. Additionally or in the alternative, additional additive manufacturing material may be introduced within tool path overlap region 1306 in an intermittent or variable manner. As an example, the additive manufacturing tool may follow a variable or irregular tool path 1300 or tool path lanes such that the tool path overlap region 1306 exhibits variable or irregular properties. As a further example, the additive manufacturing tool may cause the introduction of additive manufacturing material to occur in a variable or irregular manner (such as by cycling the tool speed or material introduction rate).

The specific nature of the sound attenuating protrusion 1200 integrally formed in an intentionally incidental manner may depend on the particular additive manufacturing technique used. Additive manufacturing techniques may be grouped according to the nature of the input from the additive manufacturing tool. For example, the additive manufacturing tool may introduce an additive manufacturing material and/or an additive energy beam to additively manufacture the acoustic core 200. The additive manufacturing material may be an amorphous material, such as a powder, a liquid, a gel, a polymer, and the like. Additive manufacturing techniques include conforming amorphous material to solid acoustic core 200 through processes such as melting, fusing, curing, and the like.

Additive manufacturing techniques that utilize additive manufacturing tools incorporating additive manufacturing materials are sometimes referred to herein as additive manufacturing techniques. Additive material techniques include material extrusion (e.g., Fusion Deposition Modeling (FDM), fuse fabrication (FFF), etc.), Material Jetting (MJ) (e.g., Smooth Curvature Printing (SCP), Multiple Jet Modeling (MJM), etc.), adhesive jetting (BJ), and Directed Energy Deposition (DED) (e.g., Laser Metal Deposition (LMD), Laser Engineered Net Shaping (LENS), Directed Metal Deposition (DMD), etc.).

In the case of material extrusion, the additive manufacturing material may be provided in the form of filaments. For example, the filaments may comprise a thermoplastic material or a ceramic material. In the case of Material Jetting (MJ), the additive manufacturing material may comprise a light sensitive material, such as a thermoset material. The photosensitive material may be supplied in the form of a liquid, gel, or the like, and may solidify when exposed to an additive energy source such as ultraviolet light. In the case of Binder Jetting (BJ), the additive manufacturing material may comprise binder material jetted into a bed of powder material. The adhesive material may be applied in the form of a liquid, gel, or the like. Exemplary binder materials include thermosetting materials or thermoplastic materials. Exemplary powder materials for adhesive jetting (BJ) may include, for example, metals or metal alloys, thermoplastics, and ceramics. In the case of Directed Energy Deposition (DED), the additive manufacturing material may be provided in the form of a thread, filament or powder. Exemplary materials for Directed Energy Deposition (DED) may include, for example, metals or metal alloys, thermoplastics, and ceramics.

Additive manufacturing techniques that utilize additive manufacturing tools that introduce an additive energy beam to solidify (e.g., melt, fuse, cure, etc.) an amorphous additive manufacturing material (e.g., powder, liquid, gel, etc.) are sometimes referred to herein as additive energy techniques. Additive energy techniques include powder bed fusion (PFB) (e.g., Selective Laser Sintering (SLS), direct metal laser Sintering (SLM), Laser Melting (LM), Electron Beam Melting (EBM), Selective Heat Sintering (SHS), Multiple Jet Fusion (MJF), etc.) and in-container photopolymerization (e.g., stereolithography apparatus (SLA), Digital Light Processing (DLP), scanning, spin and selective photocuring (3SP), Continuous Liquid Interface Production (CLIP), etc.). In the case of powder bed fusion (PFB), the additive manufacturing material may be provided in the form of a powder. Exemplary powder materials for powder bed fusion (PFB) may include, for example, metals or metal alloys, polymeric materials (e.g., thermoset and/or thermoplastic materials), and ceramics. In the case of photo-polymerization within the container, the additive manufacturing material may comprise a photosensitive material. Exemplary photosensitive materials that can be utilized with additive manufacturing techniques (e.g., additive material techniques or additive energy techniques) include formulations that include, for example, a binder, a monomer, and a photoinitiator. Exemplary binders include styrene, methacrylate, vinyl alcohol, olefins, glycerin, and propylene. Exemplary monomers include acrylic acid, methacrylic acid, isodecyl acrylate (isodecenyl acrylate), and N-vinyl pyrrolidone. Exemplary photoinitiators include: free radical photoinitiators, such as isopropyl thioxanthone, benzophenone, and 2, 2-azobisisobutyronitrile; and cationic photoinitiators, such as diaryliodonium salts and triarylsulfonium salts.

In some embodiments, the sound attenuating protrusions 1200 may be integrally formed in an intentional incidental manner using additive material technology. One suitable additive material technique includes Fused Deposition Modeling (FDM) or fuse fabrication (FFF), although other additive material techniques may also be used. In the case of additive material technology, the additive manufacturing tool introduces additive manufacturing material to the acoustic core 200. The overlapping tool path lanes cause excess additive manufacturing material to be introduced into the field 1201 occupied by the profile defined by the tool path 1300. As additional contours are applied to the acoustic core 200, the adjacent contours push excess additive manufacturing material outward from the respective contours, thereby intentionally forming the incidental protrusions 1200 of the additional additive manufacturing material to have a random or semi-random orientation. For example, in the case of Fused Deposition Modeling (FDM) or fuse fabrication (FFF), excess material is extruded and deposited in the overlapping tool path lanes, causing the excess material to accumulate in the tool path overlap region 1306, pushing the extruded material outward from the corresponding profile. The additive manufacturing material comprising protrusion 1200 may be from any portion of the additive manufacturing material, including any one or more tool paths 1300 and/or any one or more tool path streets 1302, 1304, and including material originating within or outside of tool path overlap region 1306. In some embodiments, at least a portion of the sound attenuating protrusion 1200 may have one or more dimensions that are less than a corresponding minimum dimensional resolution provided by the additive manufacturing technique used to produce the acoustic core 200. For additive material technology, the dimensional resolution may be defined by the dimensions of the incoming material. For example, in the case of Fused Deposition Modeling (FDM) or fuse fabrication (FFF), the dimensional resolution may be defined by the cross-sectional dimensions of the filament as extruded during the fused deposition modeling process.

In some embodiments, the sound attenuating protrusions 1200 may be integrally formed in an intentional incidental manner using additive energy techniques. One suitable additive energy technique includes Selective Laser Sintering (SLS), however, other additive energy techniques may also be used. In the case of an additive energy technique, the additive manufacturing tool introduces a beam of additive energy to the acoustic core 200, which solidifies the amorphous additive manufacturing material. The overlapping tool path lanes cause excess additive energy to be introduced into the field 1201 occupied by the profile defined by the tool path 1300. This excess energy propagates outward from the respective profile, thereby intentionally forming the incidental protrusions 1200 of additional additive manufacturing material to have a random or semi-random orientation. For example, in the case of Selective Laser Sintering (SLS), the heat generated by the laser melts the powder material. To form the sound attenuating protrusions 1200, excess laser energy is intentionally introduced by providing overlapping tool path lanes and causes adjacent powder particles outside the domains 1201 occupied by the respective profiles to incidentally melt in a random or semi-random orientation. In some embodiments, at least a portion of the sound attenuating protrusion 1200 may have one or more dimensions that are less than a corresponding minimum dimensional resolution provided by the additive manufacturing technique used to produce the acoustic core 200. For additive energy techniques, the dimensional resolution may be defined by the cross-sectional dimensions of the amorphous additive manufacturing material and/or the cross-sectional dimensions of the additive energy beam. For example, in the case of Selective Laser Sintering (SLS), the dimensional resolution may be defined by the cross-sectional dimensions of the particles of amorphous additive manufacturing material and/or the cross-sectional dimensions of the laser beam used to melt the particles. As another example, for in-vessel photopolymerization, the dimensional resolution may be defined by the cross-sectional dimensions of the laser or other energy beam used to cure the photopolymer.

In some embodiments, the sound attenuating protrusions 1200 may be integrally formed using a combination of additive material technology and additive energy technology. For example, it will be appreciated that Directed Energy Deposition (DED) utilizes an additive manufacturing tool that introduces both additive manufacturing material and additive energy. Additionally or in the alternative, different additive manufacturing techniques may be combined with one another, such as by using different additive manufacturing techniques for different portions of the acoustic core 200, and/or by using different additive manufacturing techniques in combination, simultaneously, sequentially, or otherwise, to integrally form the sound attenuating protrusion 1200 in the acoustic core 200.

Referring now to fig. 14, it will be appreciated that not every tool path or tool path way need overlap to form a sound attenuating protrusion 1200. For example, as shown in fig. 14, one or more outer contours 1400 defining the cell walls may include overlapping tool paths to form sound attenuating protrusions 1200 (fig. 12A and 12B) on the cell walls, while one or more inner contours 1402 defining the internal structure may not necessarily have overlapping tool paths. However, it will be appreciated that some nominal overlap may be provided, such as for the purpose of adequately bonding the domains 1201 of additive manufacturing material corresponding to adjacent tool paths. However, such nominal overlap will typically not form a sound attenuating protrusion 1200 as described herein, in addition to providing a sufficient tool path gap ratio.

The present disclosure provides a number of configurations for honeycomb structures that may be included in the acoustic core 200. It will be recognized that many additional configurations are within the spirit and scope of the present disclosure. In some embodiments, the array of resonant cells 206 may include a combination of differently configured polyhedral cells. The combination may include both oblique and parallel polyhedral cells, as well as a variety of different configurations of the polyhedral cells. For example, fig. 15 shows a perspective view of an exemplary acoustic core 200, the acoustic core 200 having a combination of differently configured units. As shown in fig. 15, the acoustic core 200 may include a converging polyhedral cell 1502 having a first configuration and a diverging polyhedral cell 1504 having a first configuration. The acoustic core 200 shown in fig. 15 further includes a converging polyhedral cell 1506 having a second configuration and a diverging polyhedral cell 1508 having a second configuration. As shown, in some embodiments, the acoustic core 200 may further include a converging polyhedral unit 1510 having a third configuration, and in some embodiments may even include an additional converging polyhedral unit 1512 having a fourth configuration. Additionally or in the alternative, the acoustic core 200 may further include diverging polyhedral cells 1514 having a third configuration, and may even include additional diverging polyhedral cells 1516 having a fourth configuration in some embodiments. In some embodiments, the acoustic core 200 may also include parallel polyhedral cells 1518. The parallel polyhedral cells can be combined with the oblique polyhedral cells in any desired configuration. For example, as shown in fig. 15, parallel polyhedral cells may be adjacent to the convergence cells 1514, 1516. Alternatively or additionally, the parallel polyhedral cells may be adjacent to the diverging cells.

Turning now to fig. 16A-16C, an exemplary method 1600 of forming the acoustic liner 100 will be described. The example method 1600 may include forming the acoustic core 200 and/or forming the acoustic barrier 202. Additionally or in the alternative, the acoustic core 200 and/or the acoustic barrier 202 may be provided separately and utilized in the exemplary method 1600. For example, the exemplary method 1600 may include: attaching the sound barrier 202 to the acoustic core 200; forming the sound barrier 202 and attaching the sound barrier 202 to the sound core 200; forming the acoustic core 200 and attaching the acoustic core 200 to the acoustic barrier 202; or forming the sound barrier 202 and the acoustic core 200 and attaching the sound barrier 202 to the acoustic core 200. In an exemplary embodiment, the sound barrier 202 and the acoustic core 200 may be integrally formed, such as using additive manufacturing techniques.

As shown in fig. 16A, an exemplary method 1600 of forming the acoustic liner 100 may include: at block 1602, an acoustic core 200 including an array of resonant cells 206 is formed. The resonant cell 206 may include a plurality of cell walls and a resonant space 207 defined by the plurality of cell walls. At least some of the resonant cells 206 may include a slanted polyhedral honeycomb structure 800 and/or a plurality of sound attenuating protrusions 1200. The exemplary method may additionally include: at block 1604, forming the sound barrier 202 including the mesh membrane 208 and the support grid 210; and at block 1606, attaching the sound barrier 202 to the acoustic core 200. For example, the sound barrier 202 and the acoustic core 200 may be integrally formed using additive manufacturing techniques. The exemplary method may additionally include: at block 1608, the acoustic core 200 is attached to the backplate 204.

In exemplary method 1600, forming an acoustic core at block 1602 may include forming acoustic core 200 at block 1610 using, at least in part, an additive manufacturing technique. Additionally or in the alternative, block 1602 may include forming the acoustic core 200 at block 1612 at least in part using a folded core technique. In some embodiments, block 1602 may include forming the sound attenuating protrusion 1200 on at least a portion of the resonant unit 206 at block 1614.

Still referring to fig. 16A, exemplary method 1600 may additionally or alternatively include: at block 1616, the reticulated film 208 and/or the support grid 210 is formed, at least in part, using additive manufacturing techniques. In some embodiments, exemplary method 1600 may include: at block 1618, sound attenuating protrusions 1200 are formed on at least a portion of the sound barrier 202, such as on at least a portion of the mesh membrane 208 and/or at least a portion of the support lattice 210.

Turning now to fig. 16B, an exemplary method 1600 that includes forming the acoustic core 200 using folded core techniques at block 1612 will be described. As shown in fig. 16B, the example method 1600 may include forming a plurality of strips of core material 1000 at block 1620. The core material strip 1000 may be configured to provide an array of slanted polyhedral honeycomb structures 800. Additionally or in the alternative, the band of core material 1000 may include sound attenuating protrusions 1200. The example method 1600 may additionally include: at block 1622, a plurality of strips of core material 1000 are selectively adhered to one another, such as at a plurality of adhesion regions 1002. The adhesion areas 1002 may be positioned at selected length intervals along the respective strips of core material 1000.

The exemplary method may further include simultaneously or subsequently folding a plurality of strips of core material 1000 at block 1624. The respective strips of core material 1000 may thus be separated or expanded from each other at the plurality of expanded regions 1004. Such extended regions 1004 may be located between the plurality of adhesion regions 1002, respectively. Such folding and/or expanding may provide an array of diagonal polyhedral honeycomb structures 800. For example, the core material strip 1000 may be configured according to the present disclosure to provide an array of resonant cells 206 that includes a plurality of converging polyhedral cells and a plurality of diverging polyhedral cells.

Turning now to fig. 16C, an exemplary method 1600 that includes a block 1614 (forming the sound attenuating protrusion 1200 on at least a portion of the resonant cell 206) and a block 1618 (forming the sound attenuating protrusion 1200 on at least a portion of the sound barrier 202) will be described. As shown in fig. 16C, an exemplary method 1600 may include: at block 1626, the additive manufacturing tool is oriented relative to a tool path to form a profile, wherein the tool path includes a plurality of overlapping tool path lanes 1302, 1304. The profile may correspond to at least a portion of the acoustic core 200 and/or at least a portion of the acoustic barrier 202.

The overlapping tool path lanes may be configured such that the overlapping tool path lanes 1302, 1304 intentionally introduce an amount of additive manufacturing material beyond the field 1201 occupied by the profile at block 1628. When the amount of additive manufacturing material intentionally introduced exceeds the area 1201 occupied by the profile, at block 1630, portions of additive manufacturing material may be incidentally formed into a plurality of sound attenuating protrusions 1200 having random or semi-random orientations and/or sizes.

The sequential profile of the acoustic core 200 and/or the acoustic barrier 202 may be formed by orienting the additive manufacturing tool relative to a sequential tool path, wherein at least a portion of the sequential tool path includes overlapping tool path lanes. The formation of the sound attenuating protrusion 1200 may be intentionally incidental to the formation of the acoustic core 200. In some embodiments, the additive manufacturing tool may utilize additive manufacturing techniques that introduce additive manufacturing materials to form the sequential profile of the acoustic core 200 and/or the sequential profile of the acoustic barrier 202. The overlapping tool-path lanes may cause excess additive manufacturing material to be introduced into respective domains 1201 occupied by respective profiles corresponding to the overlapping tool- path lanes 1302, 1304. The adjacent profiles may push the excess additive manufacturing material outward to incidentally form the plurality of sound attenuating protrusions 1200. Additive manufacturing techniques may include material extrusion, material jetting, adhesive jetting, and/or directed energy deposition. For example, additive manufacturing techniques may include Fused Deposition Modeling (FDM) or fuse fabrication (FFF).

In other embodiments, the additive manufacturing tool may utilize additive manufacturing techniques that introduce additive energy to the amorphous additive manufacturing material. The additive energy may solidify portions of the amorphous additive manufacturing material to form sequential contours of the acoustic core 200 and/or the acoustic barrier 202. The overlapping tool- path lanes 1302, 1304 may cause excess additive energy to be introduced into the respective domains 1201 occupied by the respective contours corresponding to the overlapping tool- path lanes 1302, 1304. Excess additive energy may propagate outward from the respective profiles to incidentally form the plurality of sound attenuating protrusions 1200. Additive manufacturing techniques may include powder bed fusion or in-vessel photopolymerization. For example, the additive manufacturing technique may comprise selective laser sintering.

The presently disclosed acoustic liner may be used, for example, in a turbomachine, such as turbofan engine 102. An exemplary turbomachine may include: turbine 106 and fan rotor 108; and a casing or nacelle 104 surrounding turbine 106 and/or fan rotor 108, casing or nacelle 104 defining a duct wall 114; and one or more acoustic liners 100 annularly disposed along the conduit wall 114. At least one of the one or more acoustic liners 100 may include an acoustic core 200 that includes an array of resonant cells 206. At least some of the resonant cells 206 may include a slanted polyhedral honeycomb structure 800 and/or a plurality of sound attenuating protrusions 1200. The acoustic liner 100 may further include an acoustic barrier 202 disposed across the array of resonant cells 206, and the acoustic barrier 202 may include a mesh membrane 208 and a support mesh 210.

This written description uses exemplary embodiments to describe the presently disclosed subject matter (including the best mode) and also to enable any person skilled in the art to practice such subject matter (including making and using any devices or systems and performing any incorporated methods). The patentable scope of the presently disclosed subject matter 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 include 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.