Patent Description:
Acoustic panels may be used for noise suppression or attenuation in aerospace applications and other fields. The panels typically comprise two skin surfaces that sandwich between them at least one layer of a core material or structure. The two skins and the core structure may be bonded together or cured or otherwise formed together, but mechanical fastening is also used in some applications. The core structure ties the skins together structurally and can form a very rigid, efficient and lightweight structure for noise suppression or attenuation useful in aerospace applications, such as for example, in cabins or other areas of passenger aircraft. The panels may be given acoustic properties by perforating one skin (typically an air washed side of the panel) with specifically sized volumes. This enables the cells of the core structure to act like individual Helmholtz or quarter-wave resonators that attenuate a certain tone or tones, at specific or broadband frequencies or wavelengths, of noise generated outside an aircraft - e.g., by an engine or airflow over the fuselage - or noise generated within an aircraft - e.g., by personal audio/visual equipment, galley equipment or air management equipment. These acoustic panels, where the resonators are sandwiched by a single pair of skins, are typically referred to as single-degree of freedom (SDOF) liners or panels. Acoustic panels may also be constructed as double-degree of freedom (DDOF) or multiple-degree of freedom (MDOF) liners or panels, comprising two or more layers of resonators, that provide broader frequency noise reduction.

<CIT> discloses a prior art noise attenuation panel as set forth in the preamble of claim <NUM>.

<CIT>, which is prior art under Article <NUM> (<NUM>) EPC, discloses a nacelle liner comprising unit cell resonator networks.

<CIT> discloses a prior art acoustic liner with non-uniform volumetric distribution.

From a first aspect, there is provided a noise attenuation panel for a structure within a propulsion system as recited in claim <NUM>.

There is also provided a gas turbine engine component as recited in claim <NUM>.

While these various embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that changes may be made from the figures or the description without departing from the scope of the claims.

Referring now to <FIG>, a side cutaway illustration of a gas turbine engine <NUM> is provided. The gas turbine engine <NUM> extends along an axial centerline A between an airflow inlet <NUM> and a core exhaust system <NUM>. The gas turbine engine <NUM> includes a fan section <NUM>, a low-pressure compressor section <NUM> (LPC), a high-pressure compressor section <NUM> (HPC), a combustor section <NUM>, a high-pressure turbine section <NUM> (HPT) and a low-pressure turbine section (LPT) <NUM>. The various engine sections are typically arranged sequentially along the axial centerline A. In various embodiments, the low-pressure compressor section <NUM> (LPC), the high-pressure compressor section <NUM> (HPC), the combustor section <NUM>, the high-pressure turbine section <NUM> (HPT) and the low-pressure turbine section <NUM> (LPT) form a core <NUM> (or an engine core) of the gas turbine engine <NUM>.

Air enters the gas turbine engine <NUM> through the airflow inlet <NUM>, and is directed through the fan section <NUM> and into a core gas flow path C and a bypass gas flow path B. The air within the core gas flow path C may be referred to as "core air. " The air within the bypass gas flow path B may be referred to as "bypass air. " The core air is directed through the low-pressure compressor section <NUM>, the high-pressure compressor section <NUM>, the combustor section <NUM>, the high-pressure turbine section <NUM> and the low-pressure turbine section <NUM> and exits the gas turbine engine <NUM> through the core exhaust system <NUM>, which includes an exhaust center body <NUM> surrounded by an exhaust nozzle <NUM>. Within the combustor section <NUM>, fuel is injected into and mixed with the core air and ignited to provide a hot airstream that drives the turbine sections. The bypass air is directed through the bypass gas flow path B, and out of the gas turbine engine <NUM> through a bypass exhaust nozzle <NUM> to provide forward engine thrust. The bypass air may also or alternatively be directed through a thrust reverser, positioned, for example, at or proximate the bypass exhaust nozzle <NUM>, to provide reverse engine thrust. A fan nacelle <NUM> is typically employed to surround the various sections of the gas turbine engine <NUM> and a core nacelle <NUM> is typically employed to surround the various sections of the core <NUM>. The gas turbine engine <NUM> is typically secured to an airframe (e.g., a fuselage or a wing) via a pylon <NUM>.

Referring now to <FIG>, schematic views of a noise attenuation panel (or an acoustic attenuation structure) are provided; the noise attenuation panels described and illustrated in these figures are oversimplified to explain various features of the panels. Referring specifically to <FIG>, a noise attenuation panel <NUM> is illustrated having a unit cell <NUM> sandwiched between a facesheet <NUM> and a back plate <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings <NUM> to communicate acoustic waves or energy to the unit cell <NUM>, which acts as a resonator to damp or attenuate the acoustic waves or energy. The back plate <NUM> typically is non-perforated and, together with the facesheet <NUM>, provides a support structure for the unit cell <NUM>; note that while the back plates described and illustrated in this disclosure are described as typically being non-perforated, there is no requirement that perforations may not be incorporated into or through the back plates. In various embodiments, and as will be described in further detail below, the unit cell <NUM> includes a pair of axial tubes, including, for example, a first axial tube <NUM> connected to the facesheet <NUM> and a second axial tube <NUM>, opposite the first axial tube <NUM> (e.g., the first axial tube <NUM> being axially aligned with the second axial tube <NUM>), connected to the back plate <NUM>. In various embodiments, the unit cell <NUM> further includes a first pair of lateral tubes, such as, for example, a first lateral tube <NUM> and a second lateral tube <NUM>, opposite the first lateral tube <NUM> (e.g., the first lateral tube <NUM> being axially aligned with the second lateral tube <NUM>). In various embodiments, the unit cell <NUM> further includes a second pair of lateral tubes, such as, for example, a third lateral tube <NUM> and a fourth lateral tube <NUM>, opposite the third lateral tube <NUM> (e.g., the third lateral tube <NUM> being axially aligned with the fourth lateral tube <NUM>). As also described further below, while the various tubes (or tubular structures) are illustrated in <FIG> as having an opening into a central body <NUM> of the unit cell <NUM>, the various tubes may be connected to the tubes of adjacent unit cells (see, e.g., <FIG>) or may be completely or partially closed (or sealed) via a wall or a mesh, which may include a perforated or a similar structure, the wall or the mesh being configured to block or partially restrict, respectively, a flow of fluid therethrough.

Further, it is noted that while the unit cell <NUM> may comprise a structure that exhibits various degrees of symmetry (e.g., a cubic symmetry typical of a Schwarz P surface), the various tubes or central bodies among a plurality of interconnected unit cells may be sized or shaped identically or exhibit different sizes or shapes among such plurality of interconnected unit cells. For example, the first axial tube <NUM> may exhibit a first axial tube size (e.g., a first diameter or first length), the second axial tube <NUM> may exhibit a second axial tube size (e.g., a second diameter or second length), the first lateral tube <NUM> may exhibit a first lateral tube size (e.g., diameter or length), the second lateral tube <NUM> may exhibit a second lateral tube size (e.g., diameter or length), the third lateral tube <NUM> may exhibit a third lateral tube size (e.g., diameter or length) and the fourth lateral tube <NUM> may exhibit a fourth lateral tube size (e.g., diameter or length) and at least one of the first axial tube size, the second axial tube size, the first lateral tube size, the second lateral tube size, the third lateral tube size or the fourth lateral tube size exhibits a first size and at least one of the first axial tube size, the second axial tube size, the first lateral tube size, the second lateral tube size, the third lateral tube size or the fourth lateral tube size exhibits a second size that is different from the first size. Note also that in various embodiments, each of the first axial tube <NUM>, the second axial tube <NUM>, the first lateral tube <NUM>, the second lateral tube <NUM>, the third lateral tube <NUM> and the fourth lateral tube <NUM> are in fluid communication with each other via the central body <NUM>.

Referring now to <FIG>, with continued reference to <FIG>, a noise attenuation panel <NUM> is illustrated having a plurality of unit cells <NUM>, each having the shape of the unit cell <NUM>, interconnected and sandwiched between a facesheet <NUM> and a back plate <NUM>. In various embodiments, the plurality of unit cells <NUM> is formed by interconnecting adjacent lateral tubes of adjacent unit cells together. For example, as illustrated in <FIG>, a first unit cell <NUM> having a first lateral tube <NUM> may be interconnected to a second unit cell <NUM> having a second lateral tube <NUM> by interconnecting the first lateral tube <NUM> to the second lateral tube <NUM>. In similar fashion, a third unit cell <NUM> and a fourth unit cell <NUM> may be interconnected to each other and to, respectively, the first unit cell <NUM> and to the second unit cell <NUM>. In such fashion, a periodic structure having a plurality of resonators configured to damp or attenuate acoustic waves or energy results. As described in further detail below, note the periodic structure of the plurality of unit cells <NUM>, interconnected as described, results in a volume <NUM> at the center of the periodic structure and extending axially between the facesheet <NUM> and the back plate <NUM>. In various embodiments, the volume <NUM> may be sized to damp or attenuate acoustic waves or energy at different frequencies as do the plurality of unit cells <NUM>.

Referring now to <FIG>, schematic views of a noise attenuation panel <NUM>, similar to the noise attenuation panels described above, are provided. The noise attenuation panel <NUM> is illustrated as having a plurality of unit cells <NUM> sandwiched between a facesheet <NUM> and a back plate <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings <NUM> to communicate acoustic waves or energy to the plurality of unit cells <NUM>, which acts as a resonator to damp or attenuate the acoustic waves or energy. The back plate <NUM> typically is non-perforated and, together with the facesheet <NUM>, provides a support structure for the plurality of unit cells <NUM>. Each member of the plurality of unit cells <NUM> has properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, and so such properties and characteristics, including the manner of interconnecting the unit cells within the plurality of unit cells <NUM> is not repeated here.

One difference between the embodiments described with reference to <FIG> and those described with reference to <FIG> is the layered structure exhibited by the noise attenuation panel <NUM>. For example, while the noise attenuation panel <NUM> described above with reference to <FIG> comprises a single layer of unit cells (or a first periodic structure), the noise attenuation panel <NUM> comprises a plurality of layers of unit cells, including, for example, a first lateral layer of unit cells <NUM> (or a first periodic structure), a second lateral layer of unit cells <NUM> (or a second periodic structure), a third lateral layer of unit cells <NUM> (or a third periodic structure) and a fourth lateral layer of unit cells <NUM> (or a fourth periodic structure). In various embodiments, each lateral layer of unit cells exhibits an NxM structure of unit cells, where N is the number of unit cells in a first direction (e.g., a first unit cell, a second unit cell. an Nth unit cell in the x-direction) and M is the number of unit cells in a second direction (e.g., a first unit cell, a second unit cell. an Mth unit cell in the y-direction). A similar arrangement applies to the layers of unit cells in the axial or the z-direction, which may be P in number, and include a first axial layer of unit cells <NUM> (or a first periodic structure), a second axial layer of unit cells <NUM> (or a second periodic structure), a third axial layer of unit cells <NUM> (or a third periodic structure) and a fourth axial layer of unit cells <NUM> (or a fourth periodic structure). Note that while each of M, N and P equals four (<NUM>) in <FIG>, there is no requirement that M, N and P equal one another in any particular noise attenuation panel or embodiment thereof.

With primary reference now to <FIG>, and with continued reference to <FIG>, the second lateral layer of unit cells <NUM> is illustrated from an overhead (or axial or z-direction) perspective. Given the generally periodic structure of the noise attenuation panel <NUM>, the second lateral layer of unit cells <NUM> may be considered representative of any of the lateral or axial layers of unit cells identified above. The layer of unit cells comprises an NxM plurality of unit cells <NUM> interconnected together (via a plurality of lateral tubes as described above) and an (N-<NUM>)x(M-<NUM>) plurality of volumes <NUM> disposed between the unit cells. The layer also comprises an NxM plurality of axial tubes <NUM> that extend into an NxM plurality of central bodies <NUM> of the unit cells (e.g., a first central body, a second central body. an NxMth central body). As discussed further below, one or more of the individual members of the (N-<NUM>)x(M-<NUM>) plurality of volumes <NUM>, the NxM plurality of axial tubes <NUM> and the plurality of lateral tubes may be either completely or partially sealed or restricted to tune the noise attenuation panel <NUM> to attenuate various frequencies of the acoustic energy spectrum that the noise attenuation panel <NUM> is being subjected during operation.

Referring now to <FIG>, sectional schematic views of a portion of a noise attenuation panel <NUM>, similar to any of the noise attenuation panels described above, are provided. Referring to <FIG>, for example, a schematic view of a volume <NUM>, similar to the volume <NUM> illustrated in <FIG> or one of the (N-<NUM>)x(M-<NUM>) plurality of volumes <NUM> illustrated in <FIG>, is provided. As described above, the volume <NUM> is defined by a plurality of unit cells <NUM> that are interconnected via the interconnecting of lateral or axial tubes associated with the plurality of unit cells <NUM>. As illustrated, the volume <NUM> is partially restricted via a volume filler <NUM>, disposed throughout the space exterior to the unit cells, that is configured to act as a bulk absorber to reduce or restrict the flow of air through the volume <NUM>. Note that in various embodiments, the volume filler <NUM> may comprise a plurality of layers of mesh-like materials, perforated structures or even acoustic foams so the resulting structure exhibits properties of a bulk material or a foam that either partially restricts or completely restricts the flow of air (or acoustic waves) within the space that is exterior to the plurality of unit cells <NUM>. The partial or complete restriction provided by the volume filler <NUM> facilitates additional tuning of the noise attenuation panel <NUM> to attenuate over a broader frequency range of the acoustic energy spectrum. Similarly, referring to <FIG>, a schematic view of an isolated one of the plurality of unit cells <NUM>, similar to one of the plurality of unit cells <NUM> illustrated in <FIG> or one of the plurality of unit cells <NUM> illustrated in <FIG>, is provided. As described above, the isolated one of the plurality of unit cells <NUM> includes a tube <NUM>, either lateral or axial, depending on the orientation of the unit cell. As illustrated, the tube <NUM> is partially restricted via a tube mesh <NUM>, which may include properties similar to those identified for the volume filler <NUM>, that is configured to reduce or restrict the flow of air through the tube <NUM>. The partial restriction provided by the tube mesh <NUM> facilitates tuning the noise attenuation panel <NUM> to attenuate specific frequencies of the acoustic energy spectrum the noise attenuation panel <NUM> is being subjected to during operation.

Referring now to <FIG>, a model <NUM> that facilitates mathematical design of a noise attenuation panel <NUM> is described. As illustrated, the model <NUM> approximates the behavior or response of the noise attenuation panel <NUM> via a dynamical system that includes (i) a mass (e.g., M<NUM> and M<NUM>) that represents the mass of air associated with an acoustic wave <NUM> that oscillates within a tube of a unit cell; (ii) a stiffness (e.g., K<NUM> and K<NUM>) that represents the density of the air within the central body of the unit cell; and (iii) a dashpot (e.g., R<NUM> and R<NUM>) that represents the energy dissipation associated with the air moving in the tubes. The dynamical system facilitates development of a set of differential equations that may be solved to approximate the behavior or response of the noise attenuation panel <NUM>. The dynamical system may also account for complete or partial restriction of the various axial or lateral tubes associated with the unit cell. While the model <NUM> illustrated in <FIG> is representative of a simple two unit-cell system as illustrated in <FIG>, such models may be extended to arbitrarily large numbers of unit cells.

Referring now to <FIG>, computational results are provided that illustrate various benefits of the noise attenuation panels presented and described in this disclosure. Referring to <FIG>, a graph <NUM> showing absorption coefficient as a function of frequency is illustrated for a conventional single degree of freedom noise attenuation panel <NUM> (SDOF) having a facesheet <NUM> and a back plate <NUM> defining a height (h) of the panel, filled with a honeycomb structure <NUM>. By way of comparison, <FIG> illustrate a graph <NUM> showing absorption coefficient as a function of frequency for a noise attenuation panel <NUM> (NAP) having the same facesheet and a back plate as employed in the conventional single-degree of freedom noise attenuation panel <NUM>. In this regard, the core material of noise attenuation panel <NUM> differs from the core material of noise attenuation panel <NUM>, in accordance with various embodiments. The facesheet and back plate of noise attenuation panel <NUM> may be similar to that of noise attenuation panel <NUM>, though in various embodiments the facesheet and/or back plate of noise attenuation panel <NUM> is structurally different from that of noise attenuation panel <NUM>. As indicated in the graph <NUM>, the noise attenuation panel <NUM> provides a greater magnitude of noise attenuation at the design frequency and an extended attenuation bandwidth with more broadband absorption at higher frequencies, than the conventional single-degree of freedom noise attenuation panel <NUM> having a height (h) less than <NUM>% of the height (h) of the conventional panel, thus providing a substantial space and potential weight savings and an increase in attenuation of noise over the conventional panel.

Referring now to <FIG>, schematic views of a noise attenuation panel of the present disclosure and a performance graph illustrating improvements over more conventional single-degree of freedom cell-based structures are provided, in accordance with various embodiments. Referring to <FIG>, a noise attenuation panel <NUM>, similar to the noise attenuation panel <NUM> described above, is depicted. Rather than having a height (h) equal to <NUM> of the height (h) of the conventional single-degree of freedom noise attenuation panel <NUM>, also described above, the noise attenuation panel <NUM> has a height (h) equal to the height (h) of the conventional single-degree of freedom noise attenuation panel <NUM>. This enables a more direct comparison between the noise attenuation panel <NUM> and the conventional single-degree of freedom noise attenuation panel <NUM> when constructed to have the same dimension (e.g., the same height (h)). As illustrated in <FIG>, for example, a graph <NUM> showing absorption coefficient as a function of frequency for the noise attenuation panel <NUM> (NAP) and the conventional single-degree of freedom noise attenuation panel <NUM> (SDOF) is provided. As indicated in the graph <NUM>, the noise attenuation panel <NUM> provides a greater magnitude of noise attenuation at the design frequency and at both higher and lower frequencies surrounding the design frequency than the conventional single-degree of freedom noise attenuation panel <NUM>, thus providing an extended attenuation bandwidth with more broadband absorption at both higher and lower frequencies than the design frequency where the two noise attenuation panels share the same dimensional characteristics.

Referring now to <FIG>, schematic views of various embodiments of the noise attenuation panels of the present disclosure, and a graph illustrating relative performance, are provided. Referring to <FIG>, a first noise attenuation panel <NUM> and a second noise attenuation panel <NUM> are illustrated. Similar to the various embodiments described above, both the first noise attenuation panel <NUM> and the second noise attenuation panel <NUM> include a plurality of unit cells <NUM> and a plurality of volumes <NUM> defined by the spaces in between the individual unit cells comprising the plurality of unit cells <NUM>. The only difference between the first noise attenuation panel <NUM> and the second noise attenuation panel <NUM> is each of the plurality of volumes <NUM> in the second noise attenuation panel <NUM> is partially restricted or completely restricted via a volume filler <NUM>, similar to the volume filler <NUM> described above. Note that where complete restriction is provided, the volume filler <NUM> may be completely solid - e.g., the space exterior to the plurality of unit cells <NUM> is completely filled with material. Referring now to <FIG>, a graph <NUM> showing absorption coefficient as a function of frequency for the first noise attenuation panel <NUM> and the second noise attenuation panel <NUM> is provided. As depicted in the graph <NUM>, the second noise attenuation panel <NUM> exhibits an extended attenuation bandwidth with greater broadband absorption throughout the range of frequencies, which illustrates the enhanced noise absorption characteristics provided by the volume filler <NUM> used to partially restrict the flow of air through each of the plurality of volumes <NUM>.

Referring now to <FIG>, schematic illustrations of a noise attenuation panel <NUM> are provided, in accordance with various embodiments. Similar to the various embodiments described above, the noise attenuation panel <NUM> includes a plurality of unit cells <NUM> sandwiched between a facesheet <NUM> and a back plate <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings <NUM> to communicate acoustic waves or energy to the plurality of unit cells <NUM>. Each member of the plurality of unit cells <NUM> has properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, and so such properties and characteristics, including the manner of interconnecting the unit cells within the plurality of unit cells <NUM> is not repeated here. In various embodiments, the noise attenuation panel <NUM> includes a gap <NUM> adjacent the back plate <NUM> at each of the unit cells positioned adjacent the back plate <NUM>, where the gap <NUM> provides an opening or spacing away from the back plate <NUM>, thereby allowing fluid communication between the interior of the unit cells positioned adjacent the back plate <NUM> and the exterior of the unit cells comprising the plurality of unit cells <NUM>.

Referring more particularly now to <FIG>, and with continued reference to <FIG>, a panel section <NUM> of the noise attenuation panel <NUM> is illustrated as comprising a single row of unit cells sandwiched between the facesheet <NUM> and the back plate <NUM>. As illustrated, during operation, acoustic waves or energy impinge upon the facesheet <NUM> and enter the first unit cell of the panel section <NUM> via a perforation <NUM> (or via a plurality of such perforations). The acoustic waves or energy then traverse the plurality of unit cells <NUM> where acoustic attenuation occurs as described above. In various embodiments, the acoustic waves or energy then exit the interiors of the plurality of unit cells at the gap <NUM> adjacent the back plate <NUM>. Once exited, the acoustic waves or energy then traverse back to the facesheet <NUM> via a plurality of volumes <NUM> defined by the spaces in between the individual unit cells comprising the plurality of unit cells <NUM>. The acoustic waves or energy then may exit the facesheet <NUM> via the plurality of perforations or openings <NUM>. Note that in various embodiments, one or more or even all of the plurality of perforations or openings <NUM> may be closed to alter the frequency range of attenuation. In the case where all of the plurality of perforations or openings <NUM> is completely closed or sealed, it is possible to shift the peak absorption frequency to a lower frequency range than would otherwise occur. In such case, the volume of space exterior to the plurality of unit cells <NUM> - i.e., the plurality of volumes <NUM> - acts as a closed volume or resonator.

Referring now to <FIG>, schematic illustrations of a noise attenuation panel <NUM> are provided, in accordance with various embodiments. Similar to the various embodiments described above, the noise attenuation panel <NUM> includes a plurality of unit cells <NUM> sandwiched between a facesheet <NUM> and a back plate <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings configured to communicate acoustic waves or energy to the plurality of unit cells <NUM>. Each member of the plurality of unit cells <NUM> has properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, and so such properties and characteristics, including the manner of interconnecting the unit cells within the plurality of unit cells <NUM> is not repeated here. In various embodiments, various members of the plurality of unit cells <NUM> exhibit different sizes and, particular to the illustrated embodiment, different sized tubes used to interconnect the unit cells comprising the plurality of unit cells <NUM> (e.g., the axial tubes and the lateral tubes described above with reference to the various figures). For example, as illustrated with reference to a panel section <NUM>, a plurality of lateral tubes includes a first lateral tube <NUM><NUM>, a second lateral tube <NUM><NUM>, a third lateral tube <NUM><NUM> and a fourth lateral tube <NUM><NUM>, with each of the lateral tubes disposed between and surrounded by various members of a plurality of volumes <NUM>. Each of the first lateral tube <NUM><NUM>, the second lateral tube <NUM><NUM>, the third lateral tube <NUM><NUM> and the fourth lateral tube <NUM><NUM> exhibit a tube size (e.g., a diameter) that decreases from a first tube size associated with the first lateral tube <NUM><NUM> to a fourth tube size associated with the fourth lateral tube <NUM><NUM>. While the various lateral tubes are illustrated as having tube sizes that decrease in diameter proceeding from the facesheet <NUM> to the back plate <NUM>, the disclosure contemplates alternative embodiments, such as, for example, tube sizes that increase in diameter proceeding from the facesheet <NUM> to the back plate <NUM> or tube sizes that both decrease and increase in diameter proceeding from the facesheet <NUM> to the back plate <NUM>.

Referring now to <FIG>, schematic illustrations of a noise attenuation panel <NUM> are provided, in accordance with various embodiments. Similar to the various embodiments described above, the noise attenuation panel <NUM> includes a plurality of unit cells <NUM> sandwiched between a facesheet <NUM> and a back plate <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings configured to communicate acoustic waves or energy to the plurality of unit cells <NUM>. Each member of the plurality of unit cells <NUM> has properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, and so such properties and characteristics, including the manner of interconnecting the unit cells within the plurality of unit cells <NUM> is not repeated here. In various embodiments, various of the plurality of unit cells <NUM> exhibit different sizes and, particular to the illustrated embodiment, different sized tubes used to interconnect the unit cells comprising the plurality of unit cells <NUM> (e.g., the axial tubes and the lateral tubes described above with reference to the various figures). For example, as illustrated with reference to a panel section <NUM>, a plurality of axial tubes includes a first axial tube <NUM><NUM>, a second axial tube <NUM><NUM>, a third axial tube <NUM><NUM>, and a fourth axial tube <NUM><NUM>, with each of the axial tubes disposed between and surrounded by various members of a plurality of volumes <NUM>. Each of the first axial tube <NUM><NUM>, the second axial tube <NUM><NUM>, the third axial tube <NUM><NUM> and the fourth axial tube <NUM><NUM> exhibit a tube size (e.g., a diameter) that decreases from a first tube size associated with the first axial tube <NUM><NUM> to a fourth tube size associated with the fourth axial tube <NUM><NUM>. The panel section terminates at a fifth axial tube <NUM><NUM>, which may be positioned adjacent the back plate <NUM>. While the various tubes are illustrated as having tube sizes that decrease in diameter from the facesheet <NUM> to the back plate <NUM>, the disclosure contemplates alternative embodiments, such as, for example, tube sizes that increase in diameter from the facesheet <NUM> to the back plate <NUM> or tube sizes that both decrease and increase in diameter from the facesheet <NUM> to the back plate <NUM>. Further, while the illustrations show an outer diameter or exterior of each axial tube being sized the same, with the internal diameter having different sizes (e.g., progressively decreasing internal diameters from the first tube size to the fourth tube size), the disclosure contemplates size variations of the exteriors of the axial tubes to vary in the same or a similar manner as the above-described lateral tubes.

Referring now to <FIG>, schematic illustrations of a noise attenuation panel <NUM> are provided, in accordance with various embodiments. Similar to the various embodiments described above, the noise attenuation panel <NUM> includes a plurality of unit cells <NUM> sandwiched between a facesheet <NUM> and a back plate <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings configured to communicate acoustic waves or energy to the plurality of unit cells <NUM>. Each member of the plurality of unit cells <NUM> has properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, and so such properties and characteristics, including the manner of interconnecting the unit cells within the plurality of unit cells <NUM> is not repeated here. In various embodiments, the plurality of perforations or openings in the facesheet <NUM> exhibit different sizes. For example, as illustrated with reference to <FIG>, the facesheet <NUM> includes a first perforation <NUM><NUM>, a second perforation <NUM><NUM>, a third perforation <NUM><NUM>, a fourth perforation <NUM><NUM> and a fifth perforation <NUM><NUM>. Each of the first perforation <NUM><NUM>, the second perforation <NUM><NUM>, the third perforation <NUM><NUM>, the fourth perforation <NUM><NUM> and the fifth perforation <NUM><NUM> exhibit a perforation size (e.g., a diameter) that decreases from a first perforation size associated with the first perforation <NUM><NUM> to a fifth perforation size associated with the fifth perforation <NUM><NUM>. While the various perforations are illustrated as having perforation sizes that decrease in diameter proceeding from a left side (or an upstream side) of the facesheet <NUM> to a right side (or a downstream side) of the facesheet <NUM>, the disclosure contemplates alternative embodiments, such as, for example, perforation sizes that increase in diameter proceeding from the left side of the facesheet <NUM> to the right side of the facesheet <NUM>, or perforation sizes that both decrease and increase in diameter proceeding from the left side of the facesheet <NUM> to the right side of the facesheet <NUM>.

Referring now to <FIG>, a schematic illustration of a noise attenuation panel <NUM> is provided, in accordance with various embodiments. Similar to the various embodiments described above, the noise attenuation panel <NUM> includes a plurality of unit cells <NUM> sandwiched between a facesheet <NUM> and a back plate <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings configured to communicate acoustic waves or energy to the plurality of unit cells <NUM>. Each member of the plurality of unit cells <NUM> has properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, and so such properties and characteristics, including the manner of interconnecting the unit cells within the plurality of unit cells <NUM> is not repeated here. In various embodiments, various of the plurality of unit cells <NUM> exhibit different sizes and, particular to the illustrated embodiment, different sized tubes used to interconnect the unit cells comprising the plurality of unit cells <NUM> (e.g., the axial tubes and the lateral tubes described above with reference to the various figures) and different sized volumes that surround the exterior surfaces of the unit cells comprising the plurality of unit cells <NUM>.

For example, a plurality of lateral tubes includes a first lateral tube <NUM><NUM>, a second lateral tube <NUM><NUM>, a third lateral tube <NUM><NUM> and a fourth lateral tube <NUM><NUM>. Each of the first lateral tube <NUM><NUM>, the second lateral tube <NUM><NUM>, the third lateral tube <NUM><NUM> and the fourth lateral tube <NUM><NUM> exhibit a tube size (e.g., a diameter) that decreases from a first tube size associated with the first lateral tube <NUM><NUM> to a fourth tube size associated with the fourth lateral tube <NUM><NUM>. While the various lateral tubes are illustrated as having tube sizes that decrease in diameter proceeding from a left side (or an upstream side) of the noise attenuation panel <NUM> to a right side (or a downstream side) of the noise attenuation panel <NUM>, the disclosure contemplates alternative embodiments, such as, for example, tube sizes that increase in diameter proceeding from the left side of the noise attenuation panel <NUM> to the right side of the noise attenuation panel <NUM>, or tube sizes that both decrease and increase in diameter proceeding from the left side of the noise attenuation panel <NUM> to the right side of the noise attenuation panel <NUM>.

Still referring to <FIG>, the volumes that surround the exterior surfaces of the unit cells exhibit different sizes. For example, a plurality of volumes includes a first volume <NUM><NUM>, a second volume <NUM><NUM>, a third volume <NUM><NUM>, a fourth volume <NUM><NUM> and a fifth volume <NUM><NUM>. Each of the first volume <NUM><NUM>, the second volume <NUM><NUM>, the third volume <NUM><NUM>, the fourth volume <NUM><NUM> and the fifth volume <NUM><NUM> exhibit a volume size (e.g., a characteristic dimension) that increases from a first volume size associated with the first volume <NUM><NUM>, to a second volume size associated with the second volume <NUM><NUM>. to a fifth volume size associated with the fifth volume <NUM><NUM>. While the various volumes are illustrated as having volume sizes that increase in characteristic dimension proceeding from a left side (or an upstream side) of the noise attenuation panel <NUM> to a right side (or a downstream side) of the noise attenuation panel <NUM>, the disclosure contemplates alternative embodiments, such as, for example, volume sizes that decrease in characteristic dimension proceeding from the left side of the noise attenuation panel <NUM> to the right side of the noise attenuation panel <NUM>, or volume sizes that both decrease and increase in characteristic dimension proceeding from the left side of the noise attenuation panel <NUM> to the right side of the noise attenuation panel <NUM>. Note that where the volumes comprising the plurality of volumes are of varying or different sizes, in general, the unit cells comprising the plurality of unit cells that define the various volumes will also be of different sizes (e.g., where one or more of a first unit cell size, a second unit cell size, a third unit cell size or a fourth unit cell size exhibits a different characteristic dimension or dimensions from that of its neighboring unit cells).

For example, a plurality of lateral tubes includes a first lateral tube <NUM><NUM>, a second lateral tube <NUM><NUM>, a third lateral tube <NUM><NUM> and a fourth lateral tube <NUM><NUM>. Each of the first lateral tube <NUM><NUM>, the second lateral tube <NUM><NUM>, the third lateral tube <NUM><NUM> and the fourth lateral tube <NUM><NUM> exhibit a tube size (e.g., a diameter) that decreases from a first tube size associated with the first lateral tube <NUM><NUM> to a fourth tube size associated with the fourth lateral tube <NUM><NUM>. While the various lateral tubes are illustrated as having tube sizes that decrease in diameter proceeding from the facesheet <NUM> to the back plate <NUM>, the disclosure contemplates alternative embodiments, such as, for example, tube sizes that increase in diameter proceeding from the facesheet <NUM> to the back plate <NUM> or tube sizes that both decrease and increase in diameter proceeding from the facesheet <NUM> to the back plate <NUM>.

Still referring to <FIG>, the volumes that surround the exterior surfaces of the unit cells exhibit different sizes. For example, a plurality of volumes includes a first volume <NUM><NUM>, a second volume <NUM><NUM>, a third volume <NUM><NUM>, a fourth volume <NUM><NUM> and a fifth volume <NUM><NUM>. Each of the first volume <NUM><NUM>, the second volume <NUM><NUM>, the third volume <NUM><NUM>, the fourth volume <NUM><NUM> and the fifth volume <NUM><NUM> exhibit a volume size (e.g., a characteristic dimension) that increases from a first volume size associated with the first volume <NUM><NUM> to a fifth volume size associated with the fifth volume <NUM><NUM>. While the various volumes are illustrated as having volume sizes that increase in characteristic dimension proceeding from the facesheet <NUM> to the back plate <NUM>, the disclosure contemplates alternative embodiments, such as, for example, volume sizes that decrease in characteristic dimension proceeding from the facesheet <NUM> to the back plate <NUM> or volume sizes that both decrease and increase in characteristic dimension proceeding from the facesheet <NUM> to the back plate <NUM>.

Referring now to <FIG>, schematic views of various noise attenuation panels (or acoustic attenuation structures) are provided; the noise attenuation panels described and illustrated in these figures are oversimplified to explain various features of the panels, but the disclosure contemplates that any or all of the various acoustic attenuation structures illustrated in <FIG> may be incorporated into the noise attenuation panels described above and below. Referring, for example, to <FIG>, a noise attenuation panel <NUM> is illustrated having a first unit cell <NUM> and a second unit cell <NUM> sandwiched between a facesheet <NUM> and a back plate <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings to communicate acoustic waves or energy to the first unit cell <NUM> and then to the second unit cell <NUM>, which together act as a resonator to damp or attenuate the acoustic waves or energy. The back plate <NUM> typically is non-perforated and, together with the facesheet <NUM>, provides a support structure for the noise attenuation panel <NUM>. In various embodiments, a septum <NUM> separates the first unit cell <NUM> and the second unit cell <NUM>, with the septum <NUM> including a plurality of perforations or openings to communicate acoustic waves or energy between the first unit cell <NUM> and the second unit cell <NUM>. In various embodiments, a connector <NUM> (e.g., a tubular member) is used to connect the first unit cell <NUM> and the second unit cell <NUM>, with the septum <NUM> being disposed between the connector <NUM> and the second unit cell <NUM>. Note, as illustrated, the first unit cell <NUM> and the second unit cell <NUM> may exhibit different shapes or sizes to further assist in tuning the noise attenuation panel <NUM>.

Referring now to <FIG>, a noise attenuation panel <NUM> is illustrated having a first unit cell <NUM> and a second unit cell <NUM> sandwiched between a facesheet <NUM> and a back plate <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings to communicate acoustic waves or energy to the first unit cell <NUM> and then to the second unit cell <NUM>, which together act as a resonator to damp or attenuate the acoustic waves or energy. The back plate <NUM> typically is non-perforated and, together with the facesheet <NUM>, provides a support structure for the noise attenuation panel <NUM>. In various embodiments, a septum <NUM> separates the first unit cell <NUM> and the second unit cell <NUM>, with the septum <NUM> including a plurality of perforations or openings to communicate acoustic waves or energy between the first unit cell <NUM> and the second unit cell <NUM>. In various embodiments, a connector <NUM> (e.g., a tubular member) is used to connect the first unit cell <NUM> and the second unit cell <NUM>, with the septum <NUM> being disposed between the connector <NUM> and the first unit cell <NUM>.

Referring now to <FIG>, a noise attenuation panel <NUM> is illustrated having a unit cell <NUM>, a facesheet <NUM>, a back plate <NUM> and a septum <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings to communicate acoustic waves or energy to an open chamber <NUM> and then to the unit cell <NUM>, which together act as a resonator to damp or attenuate the acoustic waves or energy. The back plate <NUM> typically is non-perforated and, together with the facesheet <NUM>, provides a support structure for the noise attenuation panel <NUM>. In various embodiments, the septum <NUM> separates the unit cell <NUM> and the open chamber <NUM>, with the septum <NUM> including a plurality of perforations or openings to communicate acoustic waves or energy between the unit cell <NUM> and the open chamber <NUM>. In various embodiments, a connector <NUM> (e.g., a tubular member) is used to connect the unit cell <NUM> and the open chamber <NUM>, with the septum <NUM> being disposed between the connector <NUM> and the open chamber <NUM>.

Referring now to <FIG>, a noise attenuation panel <NUM> is illustrated having a unit cell <NUM>, a facesheet <NUM>, a back plate <NUM> and a septum <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings to communicate acoustic waves or energy to an open chamber <NUM> and then to the unit cell <NUM>, which together act as a resonator to damp or attenuate the acoustic waves or energy. The back plate <NUM> typically is non-perforated and, together with the facesheet <NUM>, provides a support structure for the noise attenuation panel <NUM>. In various embodiments, the septum <NUM> separates the unit cell <NUM> and the open chamber <NUM>, with the septum <NUM> including a plurality of perforations or openings to communicate acoustic waves or energy between the unit cell <NUM> and the open chamber <NUM>. In various embodiments, a connector <NUM> (e.g., a tubular member) is used to connect the unit cell <NUM> and the open chamber <NUM>, with the septum <NUM> being disposed between the connector <NUM> and the open chamber <NUM>. Note, in contrast with the noise attenuation panel <NUM>, the unit cell <NUM> may not, in various embodiments, have a tube (e.g., a lateral tube <NUM>) in contact with the back plate <NUM>.

Referring now to <FIG>, a noise attenuation panel <NUM> is illustrated having a first unit cell <NUM>, a second unit cell <NUM>, a facesheet <NUM>, a back plate <NUM> and a septum <NUM>. The facesheet <NUM> typically includes a plurality of perforations or openings to communicate acoustic waves or energy to an open chamber <NUM> and then to the first unit cell <NUM> and to the second unit cell <NUM>, which together act as a resonator to damp or attenuate the acoustic waves or energy. The back plate <NUM> typically is non-perforated and, together with the facesheet <NUM>, provides a support structure for the noise attenuation panel <NUM>. In various embodiments, the septum <NUM> separates the first unit cell <NUM> and the open chamber <NUM>, with the septum <NUM> including a plurality of perforations or openings to communicate acoustic waves or energy between the first unit cell <NUM> and the open chamber <NUM>. Note, in contrast with, for example, the noise attenuation panel <NUM>, the noise attenuation panel <NUM>, the noise attenuation panel <NUM>, and the noise attenuation panel <NUM>, the first unit cell <NUM> and the second unit cell <NUM> are smaller in comparison to the sizes of the unit cells comprising the previous attenuation panels, thereby allowing for attenuation of noise at relatively higher frequencies.

Referring briefly now to <FIG>, schematic views of various structures used for the facesheets and septa and other perforated structures described throughout the disclosure are provided. Referring to <FIG>, for example, a perforated structure <NUM> (e.g., a facesheet or a septum) includes a slot <NUM> (or a plurality of slots) that is aligned in a generally axial direction with respect to a longitudinal axis A. In various embodiments, the slot <NUM> exhibits an aspect ratio that may vary from a generally square-shaped configuration (e.g., <NUM>:<NUM> aspect ratio) to an elongated rectangular-shaped configuration (e.g., <NUM>:<NUM> aspect ratio). Referring to <FIG>, a perforated structure <NUM> includes a slot <NUM> (or a plurality of slots) that is aligned in a generally non-axial direction (or angled direction) with respect to a longitudinal axis A. In various embodiments, the slot <NUM> exhibits an aspect ratio that may vary from a generally square-shaped configuration (e.g., <NUM>:<NUM> aspect ratio) to an elongated rectangular-shaped configuration (e.g., <NUM>:<NUM> aspect ratio). Further, the disclosure contemplates the non-axial direction may exhibit an angle <NUM> with respect to the axial direction from plus ninety degrees (+<NUM>°) to minus ninety degrees (-<NUM>°). Referring to <FIG>, a perforated structure <NUM> includes a plurality of perforations <NUM> (e.g., circular holes) spaced about the surface of the perforated structure <NUM>. The plurality of perforations <NUM> may exhibit a regular spacing (as illustrated) or a non-regular orientation. Referring to <FIG>, a perforated structure <NUM> includes a mesh structure <NUM>. In various embodiments, the mesh structure <NUM> may be formed by weaving various materials to have warp and weft interaction (e.g., longitudinal warp materials interwoven with transverse weft materials). Without loss of generality, each of the perforated structures just described may exhibit various percent openings with respect to the non-open portions of the perforated structures. For example, in various embodiments, the percent openings may range from about two percent (<NUM>%) to about ninety percent (<NUM>%) or any range of values therebetween.

The foregoing disclosure provides an acoustic metamaterial (e.g., a material engineered to have a property or properties not found in naturally occurring materials) consisting of a periodic lattice structure made of a unit cell bulb-like structure that divides a space into two or more separated but intertwined fluid networks (e.g., the volumes and the tubes described above). The fluid networks are locally coupled at the junctions of the lattice structure to create arrays of resonator networks. The resonator networks may be varied in length, width or height to satisfy particular target frequencies for maximum sound absorption or attenuation. Distributed networks of various dimensions may be constructed for broadband absorption. Hybrid concepts include various forms of restrictions or space fillers for tuning the resulting noise attenuation panel. These space-fillers can act as bulk absorbers to extend the bandwidth and frequency range of acoustic attenuation or they can be partially or completely solid (or filled) for improved structural performance. Further, the unit cells may be constructed of different forms, sizes or shapes or may have similar, repeating shapes of the same size, such as, for example, including the Schwarz P periodic minimal surface. Advantageously, the various resonator networks, including networks exhibiting repeating and identically shaped unit cells, or networks exhibiting non-repeating and non-identically shaped unit cells, or networks comprising various restrictions (complete or partial) distributed throughout various tubes or volumes described above, may be fabricated using additive manufacturing techniques and dynamically modeled via acoustic performance analysis prior to manufacture. Other benefits of the disclosure include noise attenuation panels exhibiting greater damping or attenuation per unit volume as compared to conventional honeycomb liners. This benefit translates into potential weight reduction or fuel savings over existing technology. The noise attenuation panels described herein also provides an ability to replace conventional structural honeycomb liners with liners having better attenuation and structural properties. Additional embodiments of noise attenuation panels that include many of the features described above are described below, followed by applications in various combustors for gas turbine engines.

Referring now to <FIG>, schematic illustrations of various components of a noise attenuation panel <NUM> are provided. The noise attenuation panel <NUM> (<FIG>) is illustrated as having a first plurality of unit cells <NUM> (<FIG>) and a second plurality of unit cells <NUM> (<FIG>) merged within the first plurality of unit cells <NUM>. More specifically, the first plurality of unit cells <NUM> takes the form, for example, of the first plurality of unit cells <NUM> described above with reference to <FIG> and includes a plurality of volumes <NUM> disposed between the unit cells, similar to the plurality of volumes <NUM> described above with reference to <FIG>. The second plurality of unit cells <NUM> is merged within the first plurality of unit cells <NUM> by disposing a unit cell (from the second plurality of unit cells <NUM>) within a volume (from the plurality of volumes <NUM>), such that each of the plurality of volumes <NUM> has a unit cell disposed within its interior space. In addition, the size of the exterior surface of each unit cell disposed within the second plurality of unit cells <NUM> is sized smaller than the corresponding volume within which the unit cell resides or is disposed. The relative sizing provides a space between the exterior surfaces of the first plurality of unit cells <NUM> and second plurality of unit cells <NUM>. The spacing provides a flow path <NUM> (FIG. 3C) or a cooling fluid flow path for a cooling fluid to flow between the exterior surfaces of the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM>. To be clear, each of the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM> is a solid lattice structure while the flow path <NUM> is a fluid lattice structure (e.g., an open spacing or volume between the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM>). In various embodiments, the open spacing or volume is attributable to the additive manufacturing process used to construct the noise attenuation panel <NUM>, whereby the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM> are constructed simultaneously with the flow path <NUM> resulting thereby.

During operation, acoustic waves or energy <NUM> impinge upon the noise attenuation panel <NUM> (e.g., upon a facesheet <NUM> of the noise attenuation panel <NUM>). The acoustic waves or energy enter a first plurality of axial tubes <NUM> of the first plurality of unit cells <NUM> and traverse the interiors of the various unit cells as indicated by a first noise attenuation flow path <NUM>. Similarly, the acoustic waves or energy <NUM> enter a second plurality of axial tubes <NUM> of the second plurality of unit cells <NUM> and traverse the interiors of the various unit cells as indicated by a second noise attenuation flow path <NUM>. At the same time, a cooling fluid traverses the flow path <NUM> between the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM> as indicated by a cooling fluid flow path <NUM>. Further operational details are provided in the drawings that follow to clarify operation of the noise attenuation panel <NUM>. Note that while the disclosure describes the cooling fluid traversing the flow path <NUM>, the disclosure contemplates other manners of cooling the noise attenuation panel <NUM>. For example, in various embodiments, the cooling fluid may be introduced directly through the interior of a single one of the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM>, while the other of the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM> is used for noise attenuation.

Referring now to <FIG>, <FIG>, <FIG>, a noise attenuation panel <NUM>, similar to the noise attenuation panel <NUM>, is illustrated. The noise attenuation panel <NUM> includes a first plurality of unit cells <NUM> and a second plurality of unit cells <NUM> merged within the first plurality of unit cells <NUM> with a flow path <NUM> existing between the exterior surfaces of the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM>. During operation (referring to <FIG>), acoustic waves or energy <NUM> impinge upon the noise attenuation panel <NUM> (e.g., upon a facesheet <NUM> of the noise attenuation panel <NUM>). The acoustic waves or energy enter a first plurality of axial tubes <NUM> of the first plurality of unit cells <NUM> and traverse the interiors of the various unit cells as indicated by a first noise attenuation flow path <NUM>. Similarly (referring to <FIG>), the acoustic waves or energy <NUM> enter a second plurality of axial tubes <NUM> of the second plurality of unit cells <NUM> and traverse the interiors of the various unit cells as indicated by a second noise attenuation flow path <NUM>. At the same time (referring to <FIG>), a cooling fluid traverses the flow path <NUM> between the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM> as indicated by a cooling fluid flow path <NUM>, which, in various embodiments, completely fills the volume of space exiting between the exterior surfaces of the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM>. Benefits of the dual noise attenuation flow paths and cooling fluid flow path, based on the differing sizes of the unit cells comprising the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM>, include being able to cool the two pluralities of unit cells and the ability to attenuate different frequency ranges within the acoustic waves or energy <NUM>, with the larger of the unit cells (e.g., the first plurality of unit cells <NUM>) attenuating lower frequencies than the smaller of the unit cells (e.g., the second plurality of unit cells <NUM>).

Referring now to <FIG>, <FIG>, cross-sectional and axial views of a combustor <NUM>, similar to the combustor section <NUM> described above with reference to <FIG> are provided. Referring more specifically to <FIG>, in various embodiments, the combustor <NUM> may generally include an outer liner assembly <NUM>, an inner liner assembly <NUM> and a diffuser case module <NUM> that surrounds the outer liner assembly <NUM> and the inner liner assembly <NUM>. A combustion chamber <NUM>, positioned within the combustor <NUM>, has a generally annular configuration, defined by and comprising the outer liner assembly <NUM>, the inner liner assembly <NUM> and a bulkhead liner assembly <NUM>. The outer liner assembly <NUM> and the inner liner assembly <NUM> are generally cylindrical and radially spaced apart, with the bulkhead liner assembly <NUM> positioned generally at a forward end of the combustion chamber <NUM>. The outer liner assembly <NUM> is spaced radially inward from an outer diffuser case <NUM> of the diffuser case module <NUM> to define an outer annular plenum <NUM>. The inner liner assembly <NUM> is spaced radially outward from an inner diffuser case <NUM> of the diffuser case module <NUM> to define, in-part, an inner annular plenum <NUM>. Although a particular combustor is illustrated, it should be understood that this disclosure is also applicable to other combustor types having various combustor liner arrangements, various of which are described below. During operation, compressed air from a core flow path C enters the forward section of the combustion chamber <NUM> and is mixed with fuel while the remainder of the compressed air enters the outer annular plenum <NUM> and the inner annular plenum <NUM>.

Still referring to <FIG>, the combustor includes one or more pairs of noise attenuation panels, including for example, a forward outer cooling flow noise attenuation panel <NUM> and a forward inner cooling flow noise attenuation panel <NUM>, an aft outer cooling flow noise attenuation panel <NUM> and an aft inner cooling flow noise attenuation panel <NUM>, and an outer diffuser case noise attenuation panel <NUM> and an inner diffuser case noise attenuation panel <NUM>. As illustrated in <FIG>, the pairs of noise attenuation panels, in various embodiments, are spaced about the combustor <NUM> in the circumferential direction (e.g., at <NUM>° intervals, as illustrated in <FIG>, or at other suitable intervals), but the disclosure contemplates other configurations, including embodiments where one or more noise attenuation panels are configured to extend up to the entire <NUM>° about the combustor. In addition, while not expressly illustrated in the figures, the disclosure contemplates perforations placed in or through the various liner assemblies and diffuser cases such that the acoustic waves or energy generated in the combustion chamber <NUM> (e.g., combustor tones <NUM>, <NUM> and <NUM>) is able to interact with the noise attenuation panels. Note that while pairs of noise attenuation panels are described and illustrated, the disclosure contemplates the use of single noise attenuation panels as well, positioned in the various locations just described. Further, while any of the noise attenuation panels previously described may be employed in the combustor <NUM> to attenuate acoustic waves or energy generated in the combustion chamber <NUM> (e.g., combustor tones <NUM>, <NUM> and <NUM>), beneficially, the forward outer cooling flow noise attenuation panel <NUM> and the forward inner cooling flow noise attenuation panel <NUM> and the aft outer cooling flow noise attenuation panel <NUM> and the aft inner cooling flow noise attenuation panel <NUM> may be cooled by the compressed air from the core flow path C by employing the structures described above with reference to <FIG> and <FIG>. The outer diffuser case noise attenuation panel <NUM> and the inner diffuser case noise attenuation panel <NUM> are considered far enough away from the combustion chamber <NUM> such that no cooling is required, but cooling may be incorporated nonetheless - e.g., via compressed air supplied by a low-pressure or high-pressure compressor. In addition, one potential advantage of using one or more of the aft outer cooling flow noise attenuation panel <NUM>, the aft inner cooling flow noise attenuation panel <NUM>, the outer diffuser case noise attenuation panel <NUM> or the inner diffuser case noise attenuation panel <NUM> is these panels exhibit reduced or eliminated pressure drop through the outer annular plenum <NUM> and the inner annular plenum <NUM> when compared with the pressure drop introduced by use of one or both of the forward outer cooling flow noise attenuation panel <NUM> and the forward inner cooling flow noise attenuation panel <NUM>.

Referring now more specifically to <FIG>, and with continued reference to <FIG>, the combustor <NUM> may include a noise attenuation panel <NUM>, such as, for example, one or more of the forward outer cooling flow noise attenuation panel <NUM>, the forward inner cooling flow noise attenuation panel <NUM>, the aft outer cooling flow noise attenuation panel <NUM> and the aft inner cooling flow noise attenuation panel <NUM> described above. The noise attenuation panel <NUM> is typically positioned in one of the outer annular plenum <NUM> and the inner annular plenum <NUM>. Attached to the noise attenuation panel <NUM> and positioned radially outside of the diffuser case module <NUM> is an extended noise attenuation panel <NUM>, which provides additional attenuation of acoustic waves and energy (e.g., combustor tones <NUM>). For example, where lower frequency ranges are targeted for attenuation, it is beneficial to increase the volume of the noise attenuation panel <NUM>, which may be accomplished via addition of the extended noise attenuation panel <NUM>. As described above, while any of the noise attenuation panels previously described may be employed in the combustor <NUM> to attenuate acoustic waves or energy generated in the combustion chamber <NUM>, beneficially, the noise attenuation panel <NUM> (as well as the extended noise attenuation panel <NUM>) may be cooled by the compressed air from the core flow path C by employing the structures described above with reference to <FIG> and <FIG>.

Referring now to <FIG>, a combustor <NUM> is illustrated and described. In various embodiments, the combustor <NUM> may be employed downstream of the combustor section <NUM> described above or may be used as a stand-alone unit. In various embodiments, the combustor <NUM> may generally include an annular liner assembly <NUM> surrounded by and spaced radially from an annular casing <NUM>, which together define an annular cooling passage <NUM> that extends radially and longitudinally between the annular liner assembly <NUM> and the annular casing <NUM>. A combustion chamber <NUM> is provided radially inward of the annular liner assembly <NUM>. In various embodiments, the combustion chamber <NUM> receives fuel from a plurality of injectors <NUM> positioned upstream of the combustion chamber <NUM> and the annular cooling passage <NUM> receives compressed air from a core flow path C, where the compressed air is used to both cool the annular liner assembly <NUM> and to provide an oxidant to the combustion chamber <NUM>. Similar to the combustor <NUM> described above, the combustor <NUM> may include one or more noise attenuation panels, such as, for example, a first cooling flow noise attenuation panel <NUM> and a second cooling flow noise attenuation panel <NUM> spaced radially opposite the first cooling flow noise attenuation panel <NUM>. As illustrated, the first cooling flow noise attenuation panel <NUM> and the second cooling flow noise attenuation panel <NUM>, in various embodiments, are spaced about the combustor <NUM> in the circumferential direction (e.g., at <NUM>° intervals, as illustrated, or at other suitable intervals). Note that while any of the noise attenuation panels previously described may be employed in the combustor <NUM> to attenuate acoustic waves or energy generated in the combustion chamber <NUM> (e.g., combustor tones <NUM>), beneficially, the first cooling flow noise attenuation panel <NUM> and the second cooling flow noise attenuation panel <NUM> may be cooled by the compressed air from the core flow path C by employing the structures described above with reference to <FIG> and <FIG>.

Referring now to <FIG>, a combustor <NUM> is illustrated and described. In various embodiments, the combustor <NUM> is disposed downstream of a compressor section (e.g., the high-pressure compressor section <NUM> (HPC)) and upstream of a turbine section (e.g., the high-pressure turbine section <NUM> (HPT)). In various embodiments, the combustor <NUM> may generally include an annular inner casing <NUM> surrounded by and spaced radially from an annular outer casing <NUM>, which together define an annular combustion chamber <NUM> that extends radially and longitudinally between the annular inner casing <NUM> and the annular outer casing <NUM>. In various embodiments, the combustor <NUM> in the form described is representative of a rotating detonation combustor <NUM>, which receives fuel and oxidant and supports a detonation wave that travels circumferentially about the annular combustion chamber <NUM>. As illustrated, upstream running combustor tones <NUM> and downstream running combustor tones <NUM> are generated by the combustion occurring in the annular combustion chamber <NUM>. An outer forward noise attenuation panel <NUM> and an inner forward noise attenuation panel <NUM> may be positioned radially outside and radially inside, respectively, of a core flow path C and configured to attenuate the upstream running combustor tones <NUM>. Similarly, an outer aft noise attenuation panel <NUM> and an inner aft noise attenuation panel <NUM> may be positioned radially outside and radially inside, respectively, of an exhaust flow path E and configured to attenuate the downstream running combustor tones <NUM>. As with the foregoing embodiments, note that while any of the noise attenuation panels previously described may be employed in the combustor <NUM> to attenuate acoustic waves or energy generated in the combustion chamber <NUM> (e.g., the upstream running combustor tones <NUM> and the downstream running combustor tones <NUM>), beneficially, one or more of the outer forward noise attenuation panel <NUM>, the inner forward noise attenuation panel <NUM>, the outer aft noise attenuation panel <NUM> and the inner aft noise attenuation panel <NUM> may be cooled by the compressed air from the core flow path C by employing the structures described above with reference to <FIG> and <FIG>.

Referring now to <FIG>, a sectional schematic view of a portion of a noise attenuation panel <NUM>, similar to any of the noise attenuation panels described above, are provided. Referring to <FIG>, a schematic view of an isolated one of the plurality of unit cells <NUM>, similar to one of the plurality of unit cells <NUM> illustrated in <FIG> or one of the plurality of unit cells <NUM> illustrated in <FIG>, is provided. Referring to <FIG>, and except as otherwise denoted, in various embodiments each member of the plurality of unit cells <NUM> has properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, and so such properties and characteristics are not repeated here.

One difference between the embodiments described with reference to <FIG> and those described with reference to <FIG> is the unit cell <NUM> includes a solid core material <NUM> (also referred to herein as a mass element) located in the volume <NUM> defined by central body <NUM>. Interior surfaces of the plurality of unit cells <NUM> define a plurality of volumes wherein the plurality of mass elements <NUM> are disposed. Mass element <NUM> may completely fill volume <NUM>, though in various embodiments mass element <NUM> only partially fills volume <NUM>. In various embodiments, each mass element <NUM> comprises a relatively solid and dense material, including metals or metal alloys such as aluminum, steel, and nickel alloys, among others.

Another difference between the embodiments described with reference to <FIG> and those described with reference to <FIG> is the tube <NUM>, either lateral or axial, depending on the orientation of the unit cell, is not necessarily hollow. In various embodiments, each tube <NUM> is solid. In this regard, "tube" as used herein may refer to a hollow structure or a solid structure. In various embodiments, each tube <NUM> comprises a relatively flexible and less dense material such as a plastic material or an elastomer. Each tube <NUM> may be made from an additively manufactured metal foam-like structure which is flexible. Each tube <NUM> may act as a spring element connecting the mass elements <NUM>. In various embodiments, the mass element <NUM> may be sized to damp or attenuate vibration at different frequencies.

The mass inclusions (i.e., mass elements <NUM>) and the elastic frame (i.e., the plurality of tubes <NUM> and central bodies <NUM>) together constitute a multiple-degree-of-freedom (MDOF) mass-spring system. When attached to a structure, this MDOF mass-spring system may absorb the vibrations at specific frequencies corresponding to the natural frequencies of the mass-spring system. The values of the natural frequencies may depend on the weight of the masses and the effective spring constants of the elastic frame. For a given elastic frame, using heavier masses tends to result in lower natural frequencies while using lighter masses tends to result in higher natural frequencies. Similarly, for given mass inclusions, a softer elastic frame tends to give lower natural frequencies while harder elastic frame tends to give higher natural frequencies.

Similar to the layer of unit cells described with respect to <FIG>, exterior surfaces of the first plurality of unit cells <NUM> define a noise attenuation flow path for a flow of air therebetween. The plurality of unit cells <NUM> of <FIG> comprises an NxM plurality of unit cells <NUM> interconnected together (via a plurality of lateral tubes as described above) and an (N-<NUM>)x(M-<NUM>) plurality of volumes <NUM> disposed between the unit cells <NUM>. As discussed with respect to at least <FIG>, one or more of the individual members of the (N-<NUM>)x(M-<NUM>) plurality of volumes <NUM> may be either completely or partially sealed or restricted to tune the noise attenuation panel <NUM> to attenuate various frequencies of the acoustic energy spectrum that the noise attenuation panel <NUM> is being subjected during operation. In various embodiments, each of the plurality of volumes <NUM> may be sized to damp or attenuate acoustic waves or energy at different frequencies. In this manner, noise attenuation panel <NUM> may simultaneously control acoustic waves or energy (i.e., via the plurality of volumes <NUM>) and vibration (i.e., via the mass elements <NUM>).

Referring now to <FIG>, a schematic illustration of a noise attenuation panel <NUM> is provided, in accordance with various embodiments. Similar to the various embodiments described above, the noise attenuation panel <NUM> includes a plurality of unit cells <NUM> sandwiched between a facesheet and a back plate (see <FIG>). Each member of the plurality of unit cells <NUM> may have properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, and so such properties and characteristics are not repeated here. In various embodiments, the plurality of mass members or elastic frame may exhibit different sizes. For example, as illustrated with reference to <FIG>, the noise attenuation panel <NUM> may include a plurality of mass members <NUM> and one or more larger mass members <NUM>.

A first pair of axial tubes <NUM> and a second pair of axial tubes <NUM>, opposite the first pair of axial tubes <NUM> (e.g., each of the first axial pair of tubes <NUM> being axially aligned with a respective one of the second pair of axial tubes <NUM>), may be connected to the mass member <NUM>. A first pair of lateral tubes <NUM> and a second pair of lateral tubes <NUM>, opposite the first lateral tube <NUM> (e.g., each of the first pair pf lateral tubes <NUM> being axially aligned with a respective one of the second pair of lateral tubes <NUM>), may be connected to the mass member <NUM>. Each of the axial tubes <NUM>, <NUM> and the lateral tubes <NUM>, <NUM> may extend from a single mass member <NUM>, though in various embodiments one or more of the axial tubes <NUM>, <NUM> and the lateral tubes <NUM>, <NUM> may be connected to a facesheet or a back plate, depending on the desired number of layers of the plurality of unit cells <NUM>. In various embodiments, mass member <NUM> may at least partially define one or more of the plurality of volumes <NUM>.

Referring now to <FIG>, a schematic illustration of a noise attenuation panel <NUM> is provided, in accordance with various embodiments. Similar to the various embodiments described above, the noise attenuation panel <NUM> includes a plurality of unit cells <NUM> sandwiched between a facesheet and a back plate (see <FIG>). Each member of the plurality of unit cells <NUM> may have properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, and so such properties and characteristics are not repeated here. In various embodiments, the plurality of mass members or elastic frame may exhibit different sizes. For example, as illustrated with reference to <FIG>, the noise attenuation panel <NUM> may include a first plurality of mass members <NUM>, a second plurality of mass members <NUM>, and a third plurality of mass members <NUM>, each comprising different size mass members.

In various embodiments, the first plurality of mass members <NUM>, the second plurality of mass members <NUM>, and/or the third plurality of mass members <NUM> may be periodically displaced within noise attenuation panel <NUM>. In various embodiments, the first plurality of mass members <NUM>, the second plurality of mass members <NUM>, and/or the third plurality of mass members <NUM> may be alternatingly displaced within noise attenuation panel <NUM>. For example, a mass member <NUM> of the first plurality of mass members <NUM> may be located between mass member <NUM> along a first direction (i.e., lateral direction in <FIG>). Similarly, a mass member <NUM> of the first plurality of mass members <NUM> may be located between mass members <NUM> along a second direction (i.e., axial direction in <FIG>).

In various embodiments, as described herein, the elastic frame of noise attenuation panel <NUM> (or any other noise attenuation panel described herein) comprises a plurality of central bodies <NUM> connected together by elastic necks <NUM> (also referred to herein as tubes). The central bodies <NUM> and/or elastic necks <NUM> may exhibit different sizes as described herein, for example as described with reference to <FIG>. Moreover, in various embodiments when the elastic necks <NUM> are hollow, the openings into the elastic necks <NUM> may exhibit different sizes as described herein, for example as described with reference to <FIG>, and <FIG> through <FIG>, and <FIG> through <FIG>. In this regard, it should be understood that the features of the various noise attenuation panels described herein may be combined in various embodiments.

Referring now to <FIG>, a schematic illustration of a portion of a noise attenuation panel <NUM> is provided, in accordance with various embodiments. Similar to the various embodiments described above, the noise attenuation panel <NUM> includes a plurality of unit cells <NUM> sandwiched between a facesheet and a back plate (see <FIG>). Each member of the plurality of unit cells <NUM> may have properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, or any other of the plurality of unit cells described herein, and so such properties and characteristics are not repeated here. In various embodiments, the volumes <NUM> that surround the exterior surfaces of the unit may be separated by a plurality of elastic disks <NUM>, each comprising an orifice <NUM>. For example, each of the orifices <NUM> may exhibit a size (e.g., a characteristic dimension) that varies to meter the air movement between each of the volumes <NUM>. Depending on the size of the orifice <NUM> diameter, the frequency of the acoustic absorption may change. Note that this elastic disk <NUM> with orifice <NUM> is a way to change the narrowness of the open area between volumes <NUM> (e.g., rather than directly changing the geometry of the unit cells). In this manner, the elastic disks <NUM> may provide a means for varying the openings between volumes <NUM>, while maintaining the size of the volumes <NUM> substantially the same. In this regard, an elastic disk <NUM> may be embedded and/or integrated into the elastic lattice structure (also referred to herein as an elastic frame). Each of the plurality of orifices <NUM> may be at least partially defined by the associated elastic disk <NUM>. Each of the plurality of volumes <NUM> may be at least partially defined by at least one associated elastic disk <NUM>. The elastic disk <NUM> may be used to control the size of the orifice <NUM> to attenuate various frequencies of the acoustic energy spectrum that the noise attenuation panel <NUM> is being subjected to during operation. The size of the elastic disk <NUM> may be varied to vary the size of the volume <NUM> as desired, for example similar to the volumes described with reference to <FIG> or as illustrated in <FIG>.

Noise attenuation panel <NUM> may further comprise a plurality of mass elements <NUM>. Each of the mass elements <NUM> may have properties and characteristics similar to the mass elements <NUM> described above with reference to <FIG>, or any other of the plurality of mass elements described herein, and so such properties and characteristics are not repeated here. In this manner, noise attenuation panel <NUM> may simultaneously control acoustic waves or energy (i.e., via the plurality of volumes <NUM>) and vibration (i.e., via the mass elements <NUM>).

Referring now to <FIG>, schematic illustrations of a portion of a noise attenuation panel <NUM> is provided, in accordance with the main embodiment. Similar to the various embodiments described above, the noise attenuation panel <NUM> includes a plurality of unit cells <NUM> sandwiched between a facesheet and a back plate (see <FIG>). Each member of the plurality of unit cells <NUM> may have properties and characteristics similar to the unit cell <NUM> and to the plurality of unit cells <NUM> described above with reference to <FIG>, or any other of the plurality of unit cells described herein, and so such properties and characteristics are not repeated here. A flow path <NUM> is defined by each of the plurality of unit cells <NUM> which define a plurality of volumes <NUM>. Each of the plurality of unit cells <NUM> may be a solid lattice structure while the flow path <NUM> is a fluid lattice structure (e.g., an open spacing or volume between each of the plurality of unit cells <NUM>). In various embodiments, the open spacing or volume is attributable to the additive manufacturing process used to construct the noise attenuation panel <NUM>, whereby the plurality of unit cells <NUM> are constructed simultaneously with the flow path <NUM> resulting thereby.

Noise attenuation panel <NUM> further comprises one or more solid perforated plates <NUM> intertwined and/or interposed with the solid lattice structure. Each perforated plate <NUM> may comprise a planar body. Perforated plates <NUM> may be decoupled from the solid lattice structure (i.e., perforated plates <NUM> and the solid lattice structure (i.e., plurality of unit cells <NUM>) may be two separate pieces of material). The intertwining of the plurality of unit cells <NUM> with the perforated plates <NUM> is attributable to the additive manufacturing process used to construct the noise attenuation panel <NUM>, whereby the plurality of unit cells <NUM> are constructed simultaneously with the perforated plates <NUM>.

Perforated plates <NUM> comprise a first plurality of apertures <NUM> configured to accommodate each of the plurality of necks or tubes <NUM>. In this regard, a tube <NUM> of a unit cell <NUM> passes through each of the plurality of apertures <NUM>. The perforated plates <NUM> may include a first perforated plate <NUM><NUM>, a second perforated plate <NUM><NUM>, and a third perforated plate <NUM><NUM>. The plurality of unit cells <NUM> may include a first layer of unit cells <NUM><NUM> (also referred to herein as a first plurality of unit cells), a second layer of unit cells <NUM><NUM> (also referred to herein as a second plurality of unit cells), a third layer of unit cells <NUM><NUM>, and a fourth layer of unit cells <NUM><NUM>. The first perforated plate <NUM><NUM> is disposed between the first layer of unit cells <NUM><NUM> and the second layer of unit cells <NUM><NUM>. The second perforated plate <NUM><NUM> may be disposed between the second layer of unit cells <NUM><NUM> and the third layer of unit cells <NUM><NUM>. The third perforated plate <NUM><NUM> may be disposed between the third layer of unit cells <NUM><NUM> and the fourth layer of unit cells <NUM><NUM>. Any number (N) of layers of unit cells and any number (N-<NUM>) of perforated plates may be used to form the noise attenuation panel <NUM>.

Perforated plates <NUM> further comprise a second plurality of apertures <NUM> configured to meter a flow of air through each of the flow paths <NUM>. In this manner, perforated plates <NUM> and the second plurality of apertures <NUM> may meter the flow of air between the volumes <NUM> to attenuate various frequencies of the acoustic energy spectrum that the noise attenuation panel <NUM> is being subjected to during operation. The size of the apertures <NUM> may be varied depending on the frequency of the acoustic energy spectrum that the noise attenuation panel <NUM> is being subjected to during operation. The size of the volumes <NUM> may be varied, for example similar to the volumes described with reference to <FIG> or as illustrated in <FIG>. Second plurality of apertures <NUM> may be sized smaller than first plurality of aperture <NUM> in various embodiments.

Noise attenuation panel <NUM> may further comprise a plurality of mass elements <NUM>. Each of the mass elements <NUM> may have properties and characteristics similar to the mass elements <NUM> described above with reference to <FIG>, or any other of the plurality of mass elements described herein, and so such properties and characteristics are not repeated here. In this manner, noise attenuation panel <NUM> may simultaneously control acoustic waves or energy (i.e., via the plurality of volumes <NUM> and perforated plates <NUM>) and vibration (i.e., via the mass elements <NUM>).

Referring now to <FIG>, schematic views of a noise attenuation panel <NUM>, similar to the noise attenuation panels described above, are provided. The noise attenuation panel <NUM> includes a first plurality of unit cells <NUM> and a second plurality of unit cells <NUM> intertwined with the first plurality of unit cells <NUM>. The first plurality of unit cells <NUM> may target vibration attenuation and the second plurality of unit cells <NUM> may target noise attenuation. In various embodiments, the first plurality of unit cells <NUM> are similar to the plurality of unit cells <NUM> described above with reference to <FIG>. In this regard, first plurality of unit cells <NUM> comprises a plurality of mass elements <NUM>. In various embodiments, the second plurality of unit cells <NUM> are similar to the plurality of unit cells <NUM> illustrated in <FIG>, or the plurality of unit cells <NUM> illustrated in <FIG>, or any other of the plurality of unit cells illustrated in <FIG>. In this regard, second plurality of unit cells <NUM> comprises a periodic structure having a plurality of resonators configured to damp or attenuate acoustic waves or energy results. In this manner, noise attenuation panel <NUM> may simultaneously control acoustic waves or energy (i.e., via the second plurality of unit cells <NUM>) and vibration (i.e., via first plurality of unit cells <NUM>).

The second plurality of unit cells <NUM> may extend through each of the plurality of volumes <NUM> (e.g., see also volumes <NUM> of <FIG>) of the first plurality of unit cells <NUM>. Noise attenuation panel <NUM> may be manufactured using additive manufacturing methods. The first plurality of unit cells <NUM> may be interlocked with the second plurality of unit cells <NUM> as each row and/or layer of the unit cells is successively manufactured using the additive manufacturing method(s). The first plurality of unit cells <NUM> may be separate from the second plurality of unit cells <NUM> (i.e., comprising two discrete members), though in various embodiments the first plurality of unit cells <NUM> and the second plurality of unit cells <NUM> may be manufactured as a unitary member connected at the sidewalls or in various embodiments with the sidewalls merged together such that each of the plurality of unit cells <NUM>, <NUM> share sidewalls.

Although various embodiments of noise attenuation panels are described herein with respect to combustor application, it should be understood that noise attenuation panels of the present disclosure may be used for various components for a gas turbine engine, including nacelles, turbine sections, fan sections, exhaust sections, or any other section utilizing panels where noise and/or vibration attenuation is desired.

The scope of the invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more.

Numbers, percentages, or other values stated herein are intended to include that value, and also other values that are about or approximately equal to the stated value, as would be appreciated by one of ordinary skill in the art encompassed by various embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable industrial process, and may include values that are within <NUM>%, within <NUM>%, within <NUM>%, within <NUM>%, or within <NUM>% of a stated value. Additionally, the terms "substantially," "about" or "approximately" as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the term "substantially," "about" or "approximately" may refer to an amount that is within <NUM>% of, within <NUM>% of, within <NUM>% of, within <NUM>% of, and within <NUM>% of a stated amount or value.

Claim 1:
A noise attenuation panel (<NUM>) for a structure (<NUM>) within a propulsion system (<NUM>), comprising:
a first plurality of unit cells (<NUM>); and
a first plurality of mass elements (<NUM>) disposed within the first plurality of unit cells (<NUM>),
wherein the first plurality of unit cells (<NUM>) includes a first periodic structure having a first unit cell (<NUM>), a second unit cell (<NUM>), a third unit cell (<NUM>), and a fourth unit cell (<NUM>), and
wherein each of the first unit cell (<NUM>), the second unit cell (<NUM>), the third unit cell (<NUM>), and the fourth unit cell (<NUM>) includes a central body (<NUM>) interconnected via a plurality of lateral tubes (<NUM>) extending from the central body (<NUM>), the first periodic structure forming a first lateral layer of unit cells,
wherein exterior surfaces of the first plurality of unit cells (<NUM>) define a noise attenuation flow path for a flow of air therebetween,
characterised in that
the noise attenuation panel (<NUM>) further comprises:
a second plurality of unit cells (<NUM><NUM>);
a perforated plate (<NUM><NUM>) disposed between the first plurality of unit cells (<NUM><NUM>) and the second plurality of unit cells (<NUM><NUM>);
a first plurality of apertures (<NUM>) disposed in the perforated plate (<NUM><NUM>) and configured to accommodate a plurality of tubes (<NUM>) extending from the first plurality of unit cells (<NUM><NUM>) to the second plurality of unit cells (<NUM><NUM>); and
a second plurality of apertures (<NUM>) disposed in the perforated plate (<NUM><NUM>) and at least partially defining the noise attenuation flow path (<NUM>).