Patent Description:
An aircraft propulsion system directs air into a fan section of a gas turbine engine through an inlet flowpath. Sound waves (e.g., noise) generated by the fan section during propulsion system operation may travel out of the aircraft propulsion system through the inlet flowpath. An inner barrel forming an outer peripheral boundary of the inlet flowpath may be configured with structures for attenuating sound waves. While known sound attenuating structures have various advantages, there is still room in the art for improvement. In particular, there is a need in the art for sound attenuation structures for an inner barrel (as well as other structures) capable of attenuating low frequency sound waves while maintaining structural integrity.

Prior art includes <CIT>, <CIT>, <CIT> and <CIT>.

According to an aspect of the present invention, an apparatus is provided for an aircraft propulsion system as claimed in claim <NUM>. Various embodiments of the invention are defined by the claims dependent thereon.

<FIG> illustrates a propulsion system <NUM> for an aircraft such as, but not limited to, a commercial airliner or cargo plane. This aircraft propulsion system <NUM> includes a gas turbine engine <NUM> and a nacelle <NUM>.

The gas turbine engine <NUM> may be configured as a high-bypass turbofan engine. The gas turbine engine <NUM> of <FIG>, for example, includes a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM> and a turbine section <NUM>. The compressor section <NUM> may include a low pressure compressor (LPC) section 27A and a high pressure compressor (HPC) section 27B. The turbine section <NUM> may include a high pressure turbine (HPT) section 29A and a low pressure turbine (LPT) section 29B.

The engine sections <NUM>-<NUM> are arranged sequentially along an axial centerline <NUM> (e.g., a rotational axis) of the gas turbine engine <NUM> within an aircraft propulsion system housing <NUM>. This propulsion system housing <NUM> includes an outer housing structure <NUM> and an inner housing structure <NUM>.

The outer housing structure <NUM> includes an outer case <NUM> (e.g., a fan case) and an outer structure <NUM> of the nacelle <NUM>; e.g., an outer nacelle structure. The outer case <NUM> houses at least the fan section <NUM>. The outer nacelle structure <NUM> houses and provides an aerodynamic cover for the outer case <NUM>. The outer nacelle structure <NUM> also covers a portion of an inner structure <NUM> of the nacelle <NUM>; e.g., an inner nacelle structure, which may also be referred to as an inner fixed structure. More particularly, the outer nacelle structure <NUM> axially overlaps and extends circumferentially about (e.g., completely around) the inner nacelle structure <NUM>. The outer nacelle structure <NUM> and the inner nacelle structure <NUM> thereby at least partially or completely form a bypass flowpath <NUM>. This bypass flowpath <NUM> extends axially along the centerline <NUM> within the aircraft propulsion system <NUM> to a bypass nozzle outlet <NUM>, where the bypass flowpath <NUM> is radially between the nacelle structures <NUM> and <NUM>.

The inner housing structure <NUM> includes an inner case <NUM> (e.g., a core case) and the inner nacelle structure <NUM>. The inner case <NUM> houses one or more of the engine sections 27A-29B, which engine sections 27A-29B may be collectively referred to as an engine core. The inner nacelle structure <NUM> houses and provides an aerodynamic cover for the inner case <NUM>. A downstream / aft portion of the inner housing structure <NUM> such as, for example, a core nozzle <NUM> of the inner nacelle structure <NUM> also covers at least a portion of an exhaust center body <NUM>. More particularly, the inner nacelle structure <NUM> and its core nozzle <NUM> axially overlap and extend circumferentially about (e.g., completely around) the exhaust center body <NUM>. The core nozzle <NUM> and the exhaust center body <NUM> collectively form a downstream / aft portion of a core flowpath <NUM>. This core flowpath <NUM> extends axially within the aircraft propulsion system <NUM>, through the engine sections 27A-29B, to a core nozzle outlet <NUM> at a downstream / aft end of the aircraft propulsion system <NUM>.

Each of the engine sections <NUM>, 27A, 27B, 29A and 29B of <FIG> includes a respective bladed rotor <NUM>-<NUM>. Each of these bladed rotors <NUM>-<NUM> includes a plurality of rotor blades arranged circumferentially around and connected to one or more respective rotor disks.

The fan rotor <NUM> and the LPC rotor <NUM> are connected to and driven by the LPT rotor <NUM> through a low speed shaft <NUM>. The HPC rotor <NUM> is connected to and driven by the HPT rotor <NUM> through a high speed shaft <NUM>. The shafts <NUM> and <NUM> are rotatably supported by a plurality of bearings (not shown). Each of these bearings is connected to the aircraft propulsion system <NUM> housing by at least one stationary structure such as, for example, an annular support strut.

During operation, air enters the aircraft propulsion system <NUM> through an airflow inlet <NUM>. This air is directed through the fan section <NUM> and into the core flowpath <NUM> and the bypass flowpath <NUM>. The air within the core flowpath <NUM> may be referred to as "core air". The air within the bypass flowpath <NUM> may be referred to as "bypass air".

The core air is compressed by the compressor rotors <NUM> and <NUM> and directed into a combustion chamber of a combustor in the combustor section <NUM>. Fuel is injected into the combustion chamber and mixed with the compressed core air to provide a fuel-air mixture. The rotation of the turbine rotor <NUM> also drives rotation of the fan rotor <NUM>, which propels bypass air through and out of the bypass flowpath <NUM>. The propulsion of the bypass air may account for a majority of thrust generated by the turbine engine <NUM>. The present disclosure, however, is not limited to the exemplary gas turbine engine configuration described above.

Sound waves (e.g., engine noise) generated by the fan rotor <NUM> as well as other engine components during turbine engine operation may propagate in a downstream direction through the bypass flowpath <NUM> as well as in an upstream direction through an inlet flowpath <NUM> formed by an inlet structure <NUM> of the outer nacelle structure <NUM>. These sound waves, if unmitigated, can be disruptive to people and/or animals within a certain proximity of the aircraft propulsion system <NUM>. Various aircraft propulsion system components forming (e.g., lining) the inlet flowpath <NUM> and/or the bypass flowpath <NUM> therefore may be configured with one or more acoustic panels <NUM> for attenuating the sound waves. An example of such an aircraft propulsion system component is an inner barrel <NUM> of the inlet structure <NUM>. Other examples of the aircraft propulsion system component include, but are not limited to, an inner panel of a translating sleeve for a thrust reverser and/or a variable area nozzle, a bifurcation panel of the inner nacelle structure <NUM> and an inner barrel panel of the inner nacelle structure <NUM>. However, for ease of description, the acoustic panel(s) <NUM> are described below with reference to the inner barrel <NUM> of the inlet structure <NUM>.

The inner barrel <NUM> of <FIG> extends axially along the axial centerline <NUM> between a forward, upstream end <NUM> of the inner barrel <NUM> and an aft, downstream end <NUM> of the inner barrel <NUM>. The inner barrel <NUM> extends circumferentially about (e.g., completely around) the axial centerline <NUM>, which may thereby provide the inner barrel <NUM> with a full-hoop, tubular body. The inner barrel <NUM> extends radially between and to a radial inner surface <NUM> of the inner barrel <NUM> and a radial outer surface <NUM> of the inner barrel <NUM>. The barrel inner surface <NUM> forms an outer peripheral boundary of the inlet flowpath <NUM> within the inlet structure <NUM>. Referring to <FIG>, the inner barrel <NUM> includes the one or more acoustic panels <NUM> (e.g., a single tubular acoustic panel, or an array of arcuate acoustic panels) and a mount <NUM>.

Each acoustic panel <NUM> of <FIG> may be configured as a multi-degree of freedom acoustic panel. For example, the acoustic panel <NUM> of <FIG> is configured as a multi-core structural, acoustic panel with a plurality of cellular cores <NUM> and <NUM>. This acoustic panel <NUM> also includes a radial inner perforated (e.g., fluid permeable) face skin <NUM>, a radial outer non-perforated (e.g., fluid impermeable) back skin <NUM> and a perforated (e.g., fluid permeable) intermediate layer <NUM>; e.g., a septum.

The face skin <NUM> is configured as an exterior skin of the acoustic panel <NUM>. The face skin <NUM>, for example, may be formed from a relatively thin sheet or layer of material; e.g., a layer of composite material (e.g., a fiber-reinforced polymer), or alternatively sheet metal. This face skin <NUM> of <FIG> extends axially along the axial centerline <NUM> to (or about) the barrel downstream end <NUM>. The face skin <NUM> extends circumferentially about (e.g., partially or completely around) the axial centerline <NUM>. The face skin <NUM> of <FIG> forms at least a portion or an entirety of the barrel inner surface <NUM>; see also <FIG>. The face skin <NUM> includes a plurality of face skin perforations <NUM>; e.g., apertures such as through-holes. Each of these face skin perforations <NUM> extends through the face skin <NUM>.

The back skin <NUM> is configured as an interior skin of the acoustic panel <NUM>. The back skin <NUM>, for example, may be formed from a relatively thin sheet or layer of (e.g., continuous, uninterrupted and/or non-porous) material; e.g., a layer of composite material (e.g., a fiber-reinforced polymer), or alternatively sheet metal. This back skin <NUM> of <FIG> extends axially along the axial centerline <NUM> to (or about) the barrel downstream end <NUM>. The back skin <NUM> extends circumferentially about (e.g., partially completely around) the axial centerline <NUM> and (e.g., partially or completely) circumscribes each of the acoustic panel elements <NUM>-<NUM> and <NUM>. The back skin <NUM> of <FIG> is configured as a continuous, uninterrupted and/or non-porous skin; e.g., a skin without any perforations aligned with the outer cellular core <NUM>.

The intermediate layer <NUM> is configured as an intra-core septum for the acoustic panel <NUM>. The intermediate layer <NUM>, for example, may be formed from a relatively thin sheet or layer of material; e.g., a layer of composite material (e.g., a fiber-reinforced polymer), or alternatively sheet metal. This intermediate layer <NUM> of <FIG> extends axially along the axial centerline <NUM> towards the barrel downstream end <NUM> and, for example, to (or about) an aft, downstream end <NUM> of the outer cellular core <NUM>, where the outer core downstream end <NUM> is axially recessed from the barrel downstream end <NUM>. The intermediate layer <NUM> extends circumferentially about (e.g., partially or completely around) the axial centerline <NUM> and (e.g., partially or completely) circumscribes each of the acoustic panel elements <NUM> and <NUM>. The intermediate layer <NUM> of <FIG> includes a plurality of intermediate layer perforations <NUM>; e.g., apertures such as through-holes. Each of these intermediate layer perforations <NUM> extends through the intermediate layer <NUM>.

The inner cellular core <NUM> of <FIG> extends axially along the axial centerline <NUM> to (or about) the barrel downstream end <NUM>. The inner cellular core <NUM> extends circumferentially about (e.g., partially or completely around) the axial centerline <NUM>. The inner cellular core <NUM> is generally arranged radially between the face skin <NUM> and the back skin <NUM>. More particularly, referring to <FIG>, a forward, upstream section <NUM> of the inner cellular core <NUM> extends radially between and to the face skin <NUM> and the intermediate layer <NUM>. This inner core upstream section <NUM> is connected (e.g., bonded and/or otherwise attached) to the face skin <NUM> and the intermediate layer <NUM>. Referring to <FIG>, an aft, downstream section <NUM> of the inner cellular core <NUM> extends radially between and to the face skin <NUM> and the back skin <NUM>. This inner core downstream section <NUM> is connected (e.g., bonded and/or otherwise attached) to the face skin <NUM> and an aft, downstream section <NUM> of the back skin <NUM>. The inner core downstream section <NUM> of <FIG> extends axially along the axial centerline <NUM> between and to the inner core upstream section <NUM> and the barrel downstream end <NUM>.

The inner cellular core <NUM> of <FIG> and <FIG> is configured to form one or more internal inner core chambers <NUM> (e.g., acoustic resonance chambers, cavities, etc.) radially between the face skin <NUM> and the intermediate layer <NUM> or the back skin <NUM>, respectively. The inner cellular core <NUM> of <FIG> and <FIG>, for example, includes an inner cellular core structure. This inner cellular core structure may be configured as a honeycomb core structure. The inner cellular core structure of <FIG>, for example, includes a plurality of corrugated sidewalls <NUM>. These corrugated sidewalls <NUM> are arranged in a side-by-side array and are connected to one another such that each adjacent (e.g., neighboring) pair of the corrugated sidewalls <NUM> forms an array of the inner core chambers <NUM> laterally therebetween. The inner cellular core structure and its corrugated sidewalls <NUM> are constructed from or otherwise include core material such as metal; e.g., sheet metal. The present disclosure, however, is not limited to such an exemplary core material.

Each of the inner core chambers <NUM> of <FIG> extends radially within / through the inner cellular core <NUM> and its upstream section <NUM> between and to the face skin <NUM> and the intermediate layer <NUM>. One or more or all of the inner core chambers <NUM> in the inner core upstream section <NUM> may thereby each be fluidly coupled with a respective set of one or more of the face skin perforations <NUM> and a respective set of one or more of the intermediate layer perforations <NUM>. Each of the inner core chambers of <FIG> extends radially within / through the inner cellular core <NUM> and its downstream section <NUM> between and to the face skin <NUM> and the back skin <NUM>.

Each of the inner core chambers <NUM> has a first inner core chamber sectional geometry (e.g., shape, size, etc.) when viewed in a first inner core chamber reference plane; e.g., the plane of <FIG>, <FIG>. This first inner core chamber sectional geometry may have a polygonal shape; e.g., a rectangular shape. Referring to <FIG>, each of the inner core chambers <NUM> has a second inner core chamber sectional geometry (e.g., shape, size, etc.) when viewed in a second inner core chamber reference plane; e.g., the plane of <FIG>. This second inner core chamber sectional geometry may have a polygonal shape; e.g., a hexagonal shape. The present disclosure, however, is not limited to foregoing exemplary inner cellular core configuration. For example, one or more or all of the inner core chambers <NUM> may each have a circular, elliptical or other non-polygonal cross-sectional geometry. Furthermore, various other types of honeycomb cores and, more generally, various other types of cellular cores for an acoustic panel are known in the art, and the present disclosure is not limited to any particular ones thereof.

The outer cellular core <NUM> of <FIG> extends axially along the axial centerline <NUM> to its outer core downstream end <NUM>. The outer cellular core <NUM> extends circumferentially about (e.g., partially or completely around) the axial centerline <NUM>. The outer cellular core <NUM> of <FIG> is arranged radially between the intermediate layer <NUM> and a forward, upstream section <NUM> of the back skin <NUM>. The outer cellular core <NUM> of <FIG>, more particularly, extends radially between and to the intermediate layer <NUM> and the back skin <NUM>. The outer cellular core <NUM> is connected (e.g., bonded and/or otherwise attached) to the intermediate layer <NUM> and/or the back skin upstream section <NUM>.

The outer cellular core <NUM> is configured to form one or more internal outer core chambers <NUM> (e.g., acoustic resonance chambers, cavities, etc.) radially between the intermediate layer <NUM> and the back skin <NUM> and its upstream section <NUM>. Each of these outer core chambers <NUM> may extend radially within / through the outer cellular core <NUM> between and to the intermediate layer <NUM> and the back skin <NUM> and its upstream section <NUM>. One or more or all of the outer core chambers <NUM> may thereby each be fluidly coupled with a respective set of one or more of the intermediate layer perforations <NUM>. Thus, one or more or all of the outer core chambers <NUM> may be fluidly coupled with a respective set of one or more of the inner core chambers <NUM> in the inner core upstream section <NUM> through the respective intermediate layer perforations <NUM>. However, while each outer core chamber <NUM> of <FIG> may be fluidly coupled with multiple inner core chambers <NUM>, each inner core chamber <NUM> in the inner core upstream section <NUM> may only be fluidly coupled with a single one of the outer core chambers <NUM>. For example, while each outer core chamber <NUM> may axially (see <FIG>) and/or circumferentially (see <FIG>) overlap multiple inner core chambers <NUM>, each inner core chamber <NUM> may only axially (see <FIG>) and/or circumferentially (see <FIG>) overlap a single one of the outer core chambers <NUM>. The present disclosure, however, is not limited to such an exemplary relationship between the inner and the outer cellular cores <NUM> and <NUM>.

Referring to <FIG>, <FIG> and <FIG>, the outer cellular core <NUM> includes one or more corrugated structures <NUM> and one or more (e.g., planar) chamber sidewalls <NUM> (see <FIG> and <FIG>). These outer core components <NUM> and <NUM> are arranged together to provide the outer core chambers <NUM>. The outer core chambers <NUM> of <FIG> are arranged in one or more linear chamber arrays 116A and 116B (generally referred to as "<NUM>"), where each chamber array <NUM> of <FIG> may extend axially along the axial centerline <NUM> (or alternatively in a circumferential direction). Each chamber array <NUM> includes a plurality of the outer core chambers <NUM>.

The chamber sidewalls <NUM> of <FIG> and <FIG> may be arranged parallel with one another. The chamber sidewalls <NUM> are spaced laterally (e.g., circumferentially) from one another so as to respectively form the outer core chambers <NUM> laterally between the chamber sidewalls <NUM>. Each of the chamber sidewalls <NUM> thereby respectively forms lateral peripheral sides of the outer core chambers <NUM> in at least one of the chamber arrays <NUM>. Each intermediate sidewall (e.g., 114I) (e.g., a chamber sidewall laterally disposed between two other chamber sidewalls), for example, forms the lateral peripheral sides of the respective outer core chambers <NUM> in a first of the chamber arrays <NUM> (e.g., 116A) as well as the lateral peripheral sides of the respective outer core chambers <NUM> in a second of the chamber arrays <NUM> (e.g., 116B) that laterally neighbors (e.g., is immediately adjacent, next to) the first of the chamber arrays <NUM> (e.g., 116A). Each intermediate sidewall (e.g., 114I) is located laterally between the respective laterally neighboring pair of chamber arrays <NUM> (e.g., the first and the second chamber arrays 116A and 116B). Each intermediate sidewall (e.g., 114I) may therefore fluidly separate the outer core chambers <NUM> in the respective laterally neighboring pair of chamber arrays <NUM> (e.g., 116A and 116B) from one another.

Referring to <FIG>, each of the chamber sidewalls <NUM> extends vertically between and to the intermediate layer <NUM> and the back skin <NUM>. Each of the chamber sidewalls <NUM> may also be connected (e.g., bonded and/or otherwise attached) to the intermediate layer <NUM> and/or the back skin <NUM>. Each of the chamber sidewalls <NUM> may be orientated substantially perpendicular to the intermediate layer <NUM> and the back skin <NUM>.

Each corrugated structure <NUM> of <FIG> and <FIG> includes one or more first panels <NUM> (e.g., members, segments, etc.) and one or more second panels <NUM> (e.g., members, segments, etc.). These corrugated structure panels <NUM> and <NUM> are arranged together and are interconnected (e.g., in a zig-zag pattern) to provide a corrugated ribbon <NUM> (see also <FIG>); e.g., a longitudinally elongated corrugated panel, layer, body, etc. The first panels <NUM> of <FIG> are configured as baffles; e.g., non-perforated (e.g., fluid impermeable) segments of the corrugated ribbon <NUM>. The second panels <NUM> of <FIG> are configured as septums; e.g., perforated (e.g., fluid permeable) segments of the corrugated ribbon <NUM>. Each of these second panels <NUM>, for example, includes one or more panel perforations <NUM>; e.g., apertures such as through-holes. Each of these panel perforations <NUM> extends through the respective second panel <NUM>. However, referring to <FIG>, one or more or all of the second panels <NUM> may alternatively each be configured as another baffle; e.g., another fluid impermeable (e.g., non-perforated) segment of the corrugated ribbon <NUM>.

Referring to <FIG>, the first panels <NUM> (e.g., the baffles) and the second panels <NUM> (e.g., the septums) are arranged together into a longitudinally extending linear array to provide the respective corrugated ribbon <NUM>. The first panels <NUM> are interspersed with the second panels <NUM>. Each first panel <NUM> (unless configured at a longitudinal end of the chamber sidewall <NUM>; see <FIG>), for example, is disposed and may extend longitudinally between and to a respective longitudinally neighboring pair of the second panels <NUM>. Similarly, each second panel <NUM> (unless configured at a longitudinal end of the chamber sidewall <NUM>; see <FIG>) is disposed and may extend longitudinally between and to a respective longitudinally neighboring pair of the first panels <NUM>.

The corrugated structure <NUM> of <FIG> includes one or more corrugations <NUM>. Each of these corrugations <NUM> includes a longitudinally neighboring pair of the first and second panels <NUM> and <NUM>.

Referring to <FIG>, within the same corrugation <NUM>, each first panel <NUM> is connected to and may meet a respective second panel <NUM> at a peak <NUM> adjacent the back skin <NUM>. Each first panel <NUM>, for example, extends to a first end <NUM> thereof. Each second panel <NUM> extends to a first end <NUM> thereof. Each first panel first end <NUM> is (e.g., directly) connected to the first end <NUM> of the second panel <NUM> in the same corrugation <NUM> at the back skin peak <NUM>; see also <FIG>. The first panel <NUM> is angularly offset from the respective second panel <NUM> by an included angle <NUM>; e.g., an acute angle. This back skin peak angle <NUM> of <FIG>, for example, may be between twenty degrees (<NUM>°) and seventy degrees (<NUM>°); e.g., thirty degrees (<NUM>°), forty-five degrees (<NUM>°), seventy degrees (<NUM>°). The present disclosure, however, is not limited to such an exemplary back skin peak angle.

Each first panel <NUM> is connected to and may meet the second panel <NUM> in a longitudinally neighboring corrugation <NUM> at a peak <NUM> adjacent the intermediate layer <NUM>. Each first panel <NUM>, for example, extends to a second end <NUM> thereof. Each second panel <NUM> extends to a second end <NUM> thereof. Each first panel second end <NUM> is (e.g., directly) connected to the second end <NUM> of the second panel <NUM> in the longitudinally neighboring corrugation <NUM> at the intermediate layer peak <NUM>; see also <FIG>. The first panel <NUM> is angularly offset from the respective second panel <NUM> by an included angle <NUM>; e.g., an acute angle. This intermediate layer peak angle <NUM> may be equal to or otherwise complementary with the back skin peak angle <NUM>. The intermediate layer peak angle <NUM> of <FIG>, for example, may be between twenty degrees (<NUM>°) and seventy degrees (<NUM>°); e.g., thirty degrees (<NUM>°), forty-five degrees (<NUM>°), seventy degrees (<NUM>°). The present disclosure, however, is not limited to such an exemplary intermediate layer peak angle.

Each corrugation <NUM> at its back skin peak <NUM> radially engages (e.g., contacts) and may be connected (e.g., bonded and/or otherwise attached) to the back skin <NUM>. Each first panel <NUM> is angularly offset from the back skin <NUM> by a back skin-first panel included angle <NUM>; e.g., an acute angle. The back skin-first panel included angle <NUM> of <FIG>, for example, may be between twenty degrees (<NUM>°) and seventy degrees (<NUM>°); e.g., thirty degrees (<NUM>°), forty-five degrees (<NUM>°), seventy degrees (<NUM>°). Each second panel <NUM> is angularly offset from the back skin <NUM> by a back skin-second panel included angle <NUM>; e.g., a right angle. The present disclosure, however, is not limited to such exemplary angles. For example, in other embodiments, the back skin-second panel included angle <NUM> may be an acute angle equal to or different than the back skin-first panel included angle <NUM>.

Each corrugation <NUM> at one or each of its intermediate layer peaks <NUM> radially engages (e.g., contacts) and may be connected (e.g., bonded and/or otherwise attached) to the intermediate layer <NUM>. Each first panel <NUM> is angularly offset from the intermediate layer <NUM> by an intermediate layer-first panel included angle <NUM>; e.g., an acute angle. The intermediate layer-first panel included angle <NUM> of <FIG>, for example, may be between twenty degrees (<NUM>°) and seventy degrees (<NUM>°); e.g., thirty degrees (<NUM>°), forty-five degrees (<NUM>°), seventy degrees (<NUM>°). Each second panel <NUM> is angularly offset from the intermediate layer <NUM> by an intermediate layer-second panel included angle <NUM>; e.g., right angle. The present disclosure, however, is not limited to such exemplary angles. For example, in other embodiments, the intermediate layer-second panel included angle <NUM> may be an acute angle equal to or different than the intermediate layer-first panel included angle <NUM>.

With the foregoing configuration, each corrugated structure <NUM> and each of its corrugations <NUM> extend across a radial height <NUM> of the outer cellular core <NUM> between the back skin <NUM> and the intermediate layer <NUM>. Each corrugated structure <NUM> may thereby divide the one or more outer core chambers <NUM> within a respective chamber array <NUM> into one or more first sub-chambers 154A (e.g., cavities) and one or more corresponding second sub-chambers 154B (e.g., cavities). The first sub-chambers 154A of <FIG> are located within the outer cellular core <NUM> on an inner side (e.g., intermediate layer side) of the respective corrugated structure <NUM>. The second sub-chambers 154B are located within the outer cellular core <NUM> on an outer side (e.g., back skin side) of the respective corrugated structure <NUM>.

Each of the first sub-chambers 154A of <FIG> is fluidly coupled with a respective one of the second sub-chambers 154B through the respective panel perforations <NUM>. Each respective set of fluidly coupled sub-chambers 154A and 154B collectively forms a respective one of the outer core chambers <NUM> within the outer cellular core <NUM>. Each outer core chamber <NUM> of <FIG> extends diagonally (e.g., radially and longitudinally) from the back skin <NUM>, along a respective neighboring pair of the first panels <NUM> and through a respective second panel <NUM> (via the respective panel perforations <NUM>), to the intermediate layer <NUM>. Each outer core chamber <NUM> of <FIG> extends longitudinally (e.g., axially), along each of the acoustic panel elements <NUM>, <NUM> and <NUM>, between and to the respective neighboring pair of the first panels <NUM>. Each outer core chamber <NUM> of <FIG> extends laterally (e.g., circumferentially), along each of the first and the second panels <NUM> and <NUM> (see <FIG>), between and to a respective neighboring pair of the chamber sidewalls <NUM>.

With the foregoing configuration, the respective outer core chamber <NUM> of <FIG> may have a length <NUM> within the outer cellular core <NUM> that is longer than the outer core height <NUM>. This may facilitate tuning the outer cellular core <NUM> and, more generally, the acoustic panel <NUM> for attenuating sound (e.g., noise) with relatively low frequencies without changing (e.g., proportionally increasing) an overall radial height of the acoustic panel <NUM> as may be required via a traditional acoustic panel only with a honeycomb core.

Each of the outer core chambers <NUM> of <FIG> has a first outer core chamber sectional geometry (e.g., shape, size, etc.) when viewed in a first outer core chamber reference plane (e.g., the plane of <FIG>), which plane may be parallel with (e.g., co-planar with) the first inner core chamber reference plane described above. The first outer core chamber sectional geometry may have a polygonal shape; e.g., a parallelogram shape (see dashed line box). Referring to <FIG>, each of the outer core chambers <NUM> has a second outer core chamber sectional geometry (e.g., shape, size, etc.) when viewed in a second outer core chamber reference plane, which plane may be perpendicular to the first outer core chamber reference plane and/or parallel with (but, radially spaced from) the second inner core chamber reference plane described above. This second outer core chamber sectional geometry may have a polygonal shape; e.g., a rectangular shape (see dashed line box). The present disclosure, however, is not limited to foregoing exemplary outer cellular core configuration. Furthermore, various other types of cellular cores for an acoustic panel are known in the art, and the present disclosure is not limited to any particular ones thereof.

An upstream section of the acoustic panel <NUM> of <FIG> and <FIG> is configured as a multi-degree of freedom (MDOF) acoustic panel section, whereas a downstream section of the acoustic panel <NUM> of <FIG> and <FIG> is configured as a single-degree of freedom (SDOF) acoustic panel section. Referring to <FIG>, sound waves entering the MDOF acoustic panel section may follow a plurality of trajectories 158A-C (generally referred to as "<NUM>"), select examples of such trajectories are schematically illustrated. These trajectories <NUM> are included to depict which chambers <NUM>, <NUM> / sub-chambers 154A, 154B are involved, rather than depicting specific sound wave paths. The sound waves, of course, may also follow one or more additional trajectories not shown in <FIG>. For example, one or more additional sound wave trajectories may exist due to interactions between the chambers / sub-chambers that produce additional reflections.

The first trajectory 158A extends away from the respective face skin perforations <NUM>, is reversed by the intermediate layer <NUM> (e.g., a septum layer), and extends back to the respective face skin perforations <NUM>. The second trajectory 158B extends away from the respective face skin perforations <NUM> and through the respective intermediate layer perforations <NUM>, is reversed by the respective corrugated structure <NUM> (e.g., solid, non-interrupted portion(s) of the respective second panel <NUM>), and extends back through the respective intermediate layer perforations <NUM> to the respective face skin perforations <NUM>. The third trajectory 158C extends away from the respective face skin perforations <NUM> and sequentially through the respective intermediate layer perforations <NUM> and the respective panel perforations <NUM>, is reversed by the back skin <NUM>, and extends back sequentially through the respective panel perforations <NUM> and the respective intermediate layer perforations <NUM> to the respective face skin perforations <NUM>. With such an arrangement, the acoustic panel <NUM> may reverse phase of a plurality of different frequencies of the sound waves using known acoustic reflection principles and subsequently direct the reverse phase sound waves out of the acoustic panel <NUM> through the face skin perforations <NUM> to destructively interfere with other incoming sound waves; e.g., noise waves.

One or more or all of the outer cellular core components <NUM> and <NUM> may be formed from composite material (e.g., a fiber-reinforced polymer), or alternatively metal. The outer cellular core components <NUM> and <NUM>, for example, may be laid up and formed from composite material as a monolithic body. The present disclosure, however, is not limited to the foregoing exemplary materials or formation techniques.

Referring to <FIG>, an intermediate section <NUM> of the back skin <NUM> is axially between and interconnects the back skin upstream section <NUM> to the back skin downstream section <NUM>. The back skin intermediate section <NUM> of <FIG>, for example, extends diagonally (e.g., axially aft and radially inward) from the back skin upstream section <NUM> to the back skin downstream section <NUM>, where the back skin <NUM> meets and is connected to the inner cellular core <NUM>. With this arrangement, a continuous sheet of material - the back skin material - may extend axially along and provide a continuous structural reinforcement / backing for the inner cellular core <NUM> and the outer cellular core <NUM>. Here, the intermediate layer <NUM> may terminate at the outer core downstream end <NUM> so as not to provide an intermediate member between the back skin <NUM> and the inner core downstream section <NUM>.

The mount <NUM> is configured to secure the inner barrel <NUM> and its acoustic panel <NUM> to another component of the aircraft propulsion system; e.g., the outer case <NUM> of <FIG>. This mount <NUM> may be configured as an A-flange. The mount <NUM> of <FIG>, for example, includes a mount base <NUM> and a mount flange <NUM>. The mount base <NUM> extends axially along and circumferentially about (e.g., partially or completely around) the axial centerline <NUM>. The mount base <NUM> is attached to the inner barrel <NUM> and its acoustic panel <NUM>. The mount base <NUM> of <FIG>, for example, is mechanically fastened to the back skin <NUM> and its downstream section <NUM> with one or more fasteners <NUM>. Each of these fasteners <NUM> may project through the back skin <NUM> and partially into the inner core downstream section <NUM>. Each of the fasteners <NUM>, for example, may be configured as a composi-lok fastener. The mount flange <NUM> is arranged at (e.g., on, adjacent or proximate) the barrel downstream end <NUM>. The mount flange <NUM> is connected to (e.g., formed integral with) the mount base <NUM>. The mount flange <NUM> of <FIG> projects radially out from the mount base <NUM> to a radial outer distal end of the mount flange <NUM>. This mount flange <NUM> extends circumferentially about (e.g., partially or completely around) the axial centerline <NUM> and (e.g., partially or completely) circumscribes the mount base <NUM>. With such an arrangement, the mount <NUM> may structurally tie the acoustic panel <NUM> and its structurally robust back skin <NUM> to the outer case <NUM> (see <FIG>) to the without, for example, imparting additional loads on other acoustic panel components (e.g., <NUM>-<NUM> and <NUM>). Of course, in other embodiments, one or more of the fasteners <NUM> may alternatively each be configured as a thru-fastener which extends radially through or otherwise into the acoustic panel <NUM> and each of its elements <NUM>, <NUM> and <NUM>.

In some embodiments, referring to <FIG>, one or more or all of the second panels <NUM> may each be configured as another baffle; e.g., another fluid impermeable (e.g., non-perforated) segment of the corrugated ribbon <NUM>. Each second panel <NUM> of <FIG> thereby fluidly decouples (e.g., separates, divides, etc.) the respective inner and outer sub-chambers 154A and 154B. With such an arrangement, each outer core chamber <NUM>' (e.g., the sub-chamber 154A) of <FIG> extends radially between and to the intermediate layer <NUM> and the respective first panel <NUM>. Each outer core chamber <NUM>' (e.g., the sub-chamber) of <FIG> extends longitudinally (e.g., axially) between the respective neighboring first and second panels <NUM> and <NUM>. The first outer core chamber sectional geometry of <FIG> may thereby have a triangular shape (see dashed line box) rather than a parallelogram shape as in the embodiments of <FIG>.

The acoustic panel <NUM> is described above with different cellular core configurations. However, in other embodiments, the inner cellular core <NUM> and the outer cellular core <NUM> may be configured with a common or similar configuration. For example, both the inner cellular core <NUM> and the outer cellular core <NUM> may each be configured with a corrugate structure.

While the acoustic panel <NUM> is described above as part of the inner barrel <NUM>, the acoustic panel <NUM> of the present disclosure is not limited to such an exemplary application. The acoustic panel <NUM> of the present disclosure, for example, may be configured for sound attenuation in other structures of the aircraft propulsion system. The acoustic panel <NUM> may also or alternatively be arranged in other orientations where, for example, the face skin <NUM> forms an inner peripheral boundary or a side peripheral boundary of a flowpath. Furthermore, the acoustic panel <NUM> and its components are not limited to the specific materials and/or construction techniques described above.

Claim 1:
An apparatus for an aircraft propulsion system (<NUM>), comprising:
an acoustic panel (<NUM>) including a perforated face skin (<NUM>), a back skin (<NUM>), a perforated intermediate layer (<NUM>), a first cellular core and a second cellular core;
the first cellular core including a first section (<NUM>) and a second section (<NUM>), the first section (<NUM>) between and connected to the perforated face skin (<NUM>) and the perforated intermediate layer (<NUM>), and the second section (<NUM>) between and connected to the perforated face skin (<NUM>) and the back skin (<NUM>);
the second cellular core between and connected to the perforated intermediate layer (<NUM>) and the back skin (<NUM>); and
a mount (<NUM>) attached to the back skin (<NUM>) along the second section (<NUM>),
characterised in that:
the second cellular core comprises a plurality of corrugations (<NUM>);
a first of the plurality of corrugations (<NUM>) comprises a first panel (<NUM>) and a second panel (<NUM>);
the first of the plurality of corrugations (<NUM>) is connected to the back skin (<NUM>) at an interface between the first panel (<NUM>) and the second panel (<NUM>);
the first panel (<NUM>) is connected to the perforated intermediate layer (<NUM>) at a first location; and
the second panel (<NUM>) is connected to the perforated intermediate layer (<NUM>) at a second location.