Patent Description:
Embodiments of the subject disclosure relate to acoustical damping systems and methods, such as additively manufactured, integral acoustic damping systems and methods within a propulsion flow path duct of an aircraft.

Various air vehicles include propulsion systems that generate noise. On commercial aircraft, for example, engine nacelle inlets include fan blades and other components that generate noise. To reduce the generated noise, acoustic liners have been installed in such areas to dampen the sound. For example, known liners include porous or mesh face sheets, typically made of titanium, stainless steel, or aluminum, laid over air cavities with a rigid backing. In some applications, the air cavities form a honeycomb structure to provide some rigidity to the liners. Some applications can include two air cavities, separated by a mesh material. In general, the liners act as damping and phase cancellation mechanisms for noise.

However, the known liners are typically mounted to primary structure and add complexity to the overall design.

<CIT>, in accordance with its abstract, states an acoustic liner that includes a support layer with a set of partitioned cavities defining a set of cells with open faces, a first facing sheet operably coupled to the support layer such that the first facing sheet overlies and closes the open faces, and a set of internal separator structures within at least some of the set of partitioned cavities.

<CIT>, in accordance with its abstract, states a propulsion system that comprises a turbine engine, and an engine nacelle including an SPF/DB inner wall having a hot side face sheet against the engine and a cold side face sheet that has noise attenuation openings.

<CIT>, in accordance with its abstract, states a structured panel that includes a first skin with a plurality of perforations, a second skin and a core. The core forms a plurality of cavities vertically between the first skin and the second skin. Each of the cavities is respectively fluidly coupled with one or more of the perforations. The cavities include a first cavity. An element of the core is configured with a multi-layered structure. The multi-layered structure includes a first layer and a second layer attached to the first layer. The first layer is configured with a first rib projecting into the first cavity.

<CIT>, in accordance with its abstract, states a composite panel assembly that includes first and second elastic membranes and a structure. The structure has a first side mounted to the first elastic membrane and a second side mounted to the second elastic membrane. The structure includes a first honeycomb layer, a second honeycomb layer, and a plurality of necks. The first honeycomb layer has partition walls defining resonance cavities that are covered by the first elastic membrane along the first side. The second honeycomb layer has partition walls defining resonance cavities that are covered by the second elastic membrane along the second side. The necks are disposed between and connect the first and second honeycomb layers. Each neck defines a channel that is fluidly connected to a corresponding one of the resonance cavities of the first honeycomb layer and a corresponding one of the resonance cavities of the second honeycomb layer.

<CIT>, in accordance with its abstract, states a panel for attenuating noise. This panel includes a first skin, a second skin and a cellular core. The cellular core may be connected to and form a plurality of cavities between the first skin and the second skin. The cellular core may include a wall and a septum. The cavities may include a first cavity and a second cavity. The septum may fluidly divide the first cavity into a first sub-cavity and a second sub-cavity. One or more perforations in the first skin may be fluidly coupled with the first sub-cavity. One or more perforations in the wall may fluidly couple the first sub-cavity with at least a region of the second cavity.

<CIT>, in accordance with its abstract, states a panel for attenuating sound. This panel includes a perforated first skin, a second skin and a core. The core forms a plurality of cavities vertically between the perforated first skin and the second skin. The core includes an array of corrugations that include a first baffle, a second baffle and a first septum. The cavities include a first cavity formed longitudinally between the first baffle and the second baffle. The first cavity is fluidly coupled with perforations in the first skin. The first septum extends from the first skin and the first baffle to the second skin and the second baffle. The first septum divides the first cavity into fluidly coupled sub-cavities. At least one element of the panel includes at least one first rib and at least one second rib, the first rib extends along a first trajectory and the second rib extends along a second trajectory that is non-parallel with the first trajectory.

<CIT>, in accordance with its abstract, states a structural panel for attenuating noise. This panel includes a first skin, a second skin and a core forming a plurality of cavities vertically between the first skin and the second skin. The core may include a wall connected to and extending vertically between the first skin and the second skin. The wall may be laterally between and fluidly separate at least a first of the cavities from a second of the cavities. The wall may include a vertical stiffener. One or more perforations in the first skin may be fluidly coupled with the first of the cavities.

A need exists for a system and method for efficiently and effectively reducing noise in relation to various components, such as within propulsion systems of aircraft. Further, a need exists for a less complex system and method for reducing noise with respect to engine of aircraft, for example.

With those needs in mind, certain embodiments of the subject disclosure provide a flow path duct system for a propulsion system of an aircraft in accordance with claim <NUM>.

In at least one embodiment, the base, the plurality of supports, and the backing surface may be integrally formed together as a monolithic, load-bearing structure. For example, the base, the plurality of supports, and the backing surface may be additively manufactured together.

In at least one embodiment, each of the plurality of cavities may be in fluid communication with at least one of the plurality of perforations. As a further example, the plurality of cavities and the plurality of perforations may cooperate to provide a plurality of Helmholtz resonators.

In at least one embodiment, the plurality of cavities may be shaped as one or more of triangles, diamonds, circles, or hexagons. In at least one embodiment, the plurality of perforations may be shaped as one or more of ellipses, circles, squares, rounded squares, diamonds, rounded diamonds, rectangles, rounded rectangles, parallelograms, or rounded parallelograms.

In at least one embodiment, the plurality of perforations may define a flow surface porosity within the base that ranges from <NUM>% to <NUM>%.

In at least one embodiment, the flow path duct system may include one or both of an inlet or an outlet nozzle having a high aspect ratio.

Certain embodiments of the subject disclosure provide a method of forming a flow path duct system for a propulsion system of an aircraft in accordance with claim <NUM>.

Certain embodiments of the subject disclosure provide an aircraft including a propulsion system including a flow path duct system, as described herein.

The foregoing summary, as well as the following detailed description of certain embodiments will be better understood when read in conjunction with the appended drawings. Further, references to "one embodiment" are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments "comprising" or "having" an element or a plurality of elements having a particular condition can include additional elements not having that condition.

In certain smaller vehicles, such as certain unmanned aerial vehicles (UAVs), or for configurations where a separate liner is not practical, a solution integral to the underlying structure is needed. As a result, there is a need for an integrated propulsion flow path in which acoustic treatments can be incorporated directly into the propulsion flow path structure, in contrast to be being separately secured to the structure.

Certain embodiments of the subject disclosure provide a quiet propulsion flow path duct system that includes a base having a flow surface, a plurality of supports joined together to define a plurality of cavities isolated from each other, and a backing surface. The supports are between the base and the backing surface. The base defines a plurality of perforations. An underlying cavity is in fluid communication with an internal volume of a duct via one or more perforations. In at least one embodiment, the base, supports, and backing surface together form a monolithic, load bearing structure.

In at least one embodiment, instead of separately forming portions, the flow path duct system is integrally formed as a monolithic structure. For example, the flow path duct system is integrally molded and formed as a single, monolithic piece (instead of having separate components formed and secured together). As another example, the flow path duct system, including all component parts, is integrally formed through additive manufacturing.

In at least one embodiment, the plurality of cavities and the perforations together form a plurality of Helmholtz resonators for sound attenuation. In at least one embodiment, the plurality of cavities define a distribution of shapes including triangles, diamonds, circles, hexagons (honeycomb), or a combination thereof. Further, in at least one embodiment, the plurality of cavities can define a distribution of diamond shapes. In some ducts, the perforations can be ellipses, circles, squares, rounded squares, diamonds, rounded diamonds, rectangles, rounded rectangles, parallelograms, rounded parallelograms, or a combination thereof. In at least one embodiment, the perforations can be circles. For some embodiments, the perforations can define a flow surface porosity. The porosity can range from <NUM>% to <NUM>%, for example. In some ducts, the perforations can define a flow surface porosity, the porosity ranging from <NUM>% to <NUM>%, for example.

In at least one embodiment, the depth of the plurality of cavities can define a continuous distribution, a constant distribution, or, according to the claimed subject matter, a step distribution with at least one step. In at least one embodiment, the depth of the plurality of cavities can define a constant distribution or, according to the claimed subject matter, a step distribution with at least one step. In at least one embodiment, the duct can be formed of titanium, titanium alloys, aluminum, aluminum alloys, stainless steel, or polymer. For some ducts, the duct can include a polymer. For some duct embodiments, the duct can be a variable geometry with at least one high aspect ratio inlet or exit.

<FIG> illustrates a perspective top view of an aircraft <NUM>, such as an unmanned aerial vehicle (UAV), according to an embodiment of the subject disclosure. In at least one embodiment, the UAV <NUM> includes a main body or fuselage <NUM>, wings <NUM>, and canards <NUM>. The main body <NUM> defines an inlet <NUM>. The inlet <NUM> leads into a flow path duct system of a propulsion system. The flow path duct system extends into and through at least a portion of the UAV <NUM>. The flow path duct system is described herein.

Optionally, the UAV <NUM> can be sized, shaped, and configured differently than shown in <FIG>. For example, the UAV <NUM> may not include canards. As another example, the wings <NUM> can be disposed at locations that are forward from the wings <NUM> as shown. As another example, the UAV <NUM> may not include wings. Instead, the UAV <NUM> can include one or more helicopter-like rotors, for example.

<FIG> illustrates a front perspective view of an aircraft <NUM>, according to an embodiment of the subject disclosure. The aircraft <NUM> includes a propulsion system <NUM> that includes two engines <NUM>, for example, such as two turbofan or turbojet engines. Optionally, the propulsion system <NUM> may include more engines <NUM> than shown. The engines <NUM> are carried by wings <NUM> of the aircraft <NUM>. In other embodiments, the engines <NUM> are carried by a fuselage <NUM> and/or an empennage <NUM>. The empennage <NUM> may also support horizontal stabilizers <NUM> and a vertical stabilizer <NUM>. The fuselage <NUM> of the aircraft <NUM> defines an internal cabin, including a flight deck. The engines <NUM> include flow path duct systems, such as described herein.

The aircraft <NUM> can be sized, shaped, and configured differently than shown in <FIG>. The aircraft <NUM> shown in <FIG> is merely an example.

<FIG> illustrates a lateral perspective view of an engine <NUM>, according to an embodiment of the subject disclosure. In at least one embodiment, the engine <NUM> is a turbofan or turbojet engine having a case <NUM> that includes an engine inlet <NUM>, which leads into a flow path duct system, as described herein. The engine inlet <NUM> may include a leading edge <NUM> and an inner barrel section <NUM> located aft of the leading edge <NUM> of the engine inlet <NUM>. The inner barrel section <NUM> can provide a boundary surface or wall for directing airflow (not shown) entering the engine inlet <NUM> and passing through the engine <NUM>. The inner barrel section <NUM> can be located in relatively close proximity to one or more fan blades (not shown in <FIG>). In at least one embodiment, the inner barrel section <NUM> can also be configured to serve as an acoustic structure having a plurality of perforations in an inner face sheet of the inner barrel section <NUM> for absorbing noise generated by the rotating fan blades and/or noise generated by the airflow entering the engine inlet <NUM> and passing through the engine <NUM>. In at least one embodiment, the inner barrel section <NUM> includes, and or can be configured as, a flow path duct system, as described herein.

<FIG> illustrates a perspective internal view of a flow path duct system <NUM>, according to an embodiment of the subject disclosure. <FIG> illustrates a perspective external view of the flow path duct system <NUM> with a backing surface removed to expose supports and resulting cavities, according to an embodiment of the subject disclosure.

Referring to <FIG>, in at least one embodiment, the flow path duct system <NUM> is within the UAV <NUM> shown in <FIG>. For example, the inlet <NUM>, shown in <FIG>, leads into, or forms an inlet of, the flow path duct system <NUM>. In at least one other embodiment, the flow path duct system <NUM> is within the engine <NUM> shown in <FIG> and <FIG>. For example, the engine inlet <NUM>, shown in <FIG>, leads into, or forms an inlet of, the flow path duct system <NUM>.

The flow path duct system <NUM> provides a quiet propulsion flow path system. The flow path duct system <NUM> includes an internal surface <NUM>, which defines a flow surface <NUM>. For example, a base <NUM> includes the internal surface <NUM> that defines the flow surface <NUM>. Fluid, for example, air, travels over and along the flow surface <NUM>. Supports <NUM> extend opposite from the base <NUM>, such as at edges <NUM> and an external surface. The supports <NUM> can include frames, beams, ribs, fins, walls, or the like.

The supports <NUM> define a plurality of cavities <NUM>. For example, a cavity 421a is defined between a first support 420a and a second support 420b. A cavity 421b is defined between the second support 420b and a third support 420c. The supports <NUM> can be sized and shaped the same. The supports <NUM> can be upstanding fins, walls, beams, ribs, and/or or the like.

The flow path duct system <NUM> also includes a backing surface <NUM> and a plurality of perforations <NUM>. For example, the backing surface <NUM> is disposed over external portions of the supports <NUM>, the cavities <NUM>, and/or the perforations <NUM>. The perforations <NUM> can be formed in the base <NUM>, for example. As an example, the supports <NUM> extend from the base <NUM>, which provides the flow surface <NUM>. In at least one embodiment, the supports <NUM> are or otherwise include fins <NUM> that extend from the base <NUM>. The cavities <NUM> are defined between the base <NUM> and the fins <NUM>. The perforations <NUM> are formed into and/or through the base <NUM>. As such, a fluid flow path extends between the cavities <NUM>, the perforations <NUM>, and the internal volume <NUM> of the flow path duct system <NUM>. The backing surface <NUM> can be a sheet, skin, or the like, disposed over the supports <NUM> and the cavities <NUM>.

The cavities <NUM> extend from external surfaces of the base <NUM>, opposite from the flow surface <NUM>, thereby extending away from the internal volume <NUM>. The perforations <NUM> are formed in the base <NUM> and are in fluid communication with the internal volume <NUM>. As such, the fluid flow path extends from the cavities <NUM>, through the perforations <NUM> in the base <NUM>, and into the internal volume <NUM>.

In at least one exemplary embodiment not forming the claimed subject matter, the depth <NUM> of the cavities <NUM> is constant throughout the flow path duct system <NUM>. That is, the distribution of depths <NUM> of the cavities <NUM> can be the same throughout the flow path duct system <NUM>. Optionally, the depths of certain cavities <NUM> can differ. In at least one embodiment, the flow path duct system <NUM> shown in <FIG> provides a monolithic, complex geometry inlet structure can be fabricated that provides sound attenuation.

In at least one embodiment, as shown in <FIG>, the supports <NUM> include intersecting, beams, ribs, panels, walls, or fins <NUM> that intersect to form a plurality of repeating cavities <NUM>. The supports <NUM> define outer boundaries for the cavities <NUM>, which can have various shapes and sizes.

In at least one embodiment, the flow path duct system <NUM> is for a propulsion system of an aircraft. The flow path duct system <NUM> includes the base <NUM> defining the flow surface <NUM> (such as on an internal surface <NUM>). The base <NUM> includes the internal surface <NUM> and an external surface <NUM>. A plurality of perforations <NUM> are formed through the base <NUM> between the internal surface <NUM> and the external surface <NUM>. The supports <NUM> define the cavities <NUM>. The supports <NUM> extend outwardly from the external surface <NUM> of the base <NUM>. One or more of the plurality of cavities <NUM> are in fluid communication with the one or more of the plurality of perforations <NUM>. The backing surface <NUM> is secured to the plurality of supports <NUM>. The supports <NUM> are disposed between the base <NUM> and the backing surface <NUM>. One or more of the plurality of cavities <NUM> are in fluid communication with an internal volume <NUM> defined by the internal surface <NUM> of the base <NUM> through one or more of the plurality of perforations <NUM>.

In at least one embodiment, the base <NUM>, the supports <NUM>, and the backing surface <NUM> are integrally formed together as a monolithic, load-bearing structure. For example, the base <NUM>, the supports <NUM>, and the backing surface <NUM> are additively manufactured together. That is, the flow path duct system <NUM>, including the components thereof, are integrally formed through an additive manufacturing process.

In at least one embodiment, each of the cavities <NUM> is in fluid communication with at least one the perforations <NUM>, and/or vice versa. In at least one embodiment, cavities <NUM> and the perforations <NUM> cooperate to provide a plurality of Helmholtz resonators.

<FIG> illustrates a transverse partial cross-sectional view of the flow path duct system <NUM> having constant depth cavities, according to an exemplary embodiment not forming part of the claimed subject matter. As shown in <FIG>, the flow path duct system <NUM> can be an inlet <NUM>. The depth (or height) <NUM> of the cavities <NUM> can be constant along a length <NUM> of the flow path duct system <NUM>.

<FIG> illustrates a transverse partial cross-sectional view of the flow path duct system <NUM> having constant depth cavities <NUM>, according to an exemplary embodiment not forming part of the claimed subject matter. As shown in <FIG>, the flow path duct system <NUM> can be an outlet nozzle <NUM>. Again, the depth (or height) <NUM> of the cavities <NUM> can be constant along a length <NUM> of the flow path duct system <NUM>.

Referring to <FIG>, while the depths <NUM> of the cavities <NUM> can be the same throughout the flow path duct system <NUM>, the widths <NUM> can differ. For example, a first set of cavities <NUM> can have a first width that differs from a second set of cavities <NUM>. Optionally, the width <NUM> of the cavities <NUM> can be the same throughout.

<FIG> illustrates transverse partial cross-sectional view of a flow path duct system <NUM> having cavities 421c and 421d with a single step distribution in depth <NUM>, or two constant depths, according to an embodiment of the subject disclosure. For example, a first set of cavities 421c has a depth <NUM> that differs from a depth <NUM> of a second set of cavities 421d. A step <NUM> defines a transition between the first set of cavities 421c and the second set of cavities 421d. As shown, the depth <NUM> of the first set of cavities 421c is greater than the depth <NUM> of the second set of cavities 421d. Optionally, the depth <NUM> of the second set of cavities 421d can be greater than the depth <NUM> of the first set of cavities 421c.

<FIG> illustrates a transverse partial cross-sectional view of a flow path duct system <NUM> having cavities 421e, 421f, and <NUM> with a double step distribution in depth, or three constant depths, according to an embodiment of the subject disclosure. For example, a first set of cavities 421e has a depth <NUM> that differs from a depth <NUM> of a second set of cavities 421f, which differs from a depth <NUM> of a third set of cavities <NUM>. A step <NUM> defines a transition between the first set of cavities 421e and the second set of cavities 421f. A step <NUM> defines a transition between the second set of cavities 421f and the third set of cavities <NUM>. As shown, the depth <NUM> of the first set of cavities 421e is greater than the depth <NUM> of the second set of cavities 421f. Further, the depth <NUM> of the second set of cavities <NUM> is greater than the depth <NUM> of the third set of cavities <NUM>. Optionally, the depth <NUM> of the second set of cavities 421f can be greater than the depth <NUM> of the first set of cavities 421e, and/or the depth <NUM> of the third set of cavities <NUM> can be greater than the depth <NUM> of the second set of cavities 421f.

Referring to <FIG>, certain embodiments provide a flow path duct system <NUM>, and a method of making the flow path duct system <NUM>. In at least one embodiment, the method includes additively manufacturing a duct geometry as a monolithic structure, in which the geometry includes the flow surface <NUM>, the supports <NUM> defining the plurality of cavities <NUM> isolated from each other, and the backing surface <NUM>. In at least one embodiment, the supports <NUM> are between the flow surface <NUM> and the backing surface <NUM>.

In at least one embodiment, the flow path duct system <NUM>, and the method of forming the flow patch duct <NUM>, also includes the plurality of perforations <NUM>. The perforations <NUM> are in fluid communication with one or more cavities <NUM>. In at least one embodiment, the plurality of perforations <NUM> can be added to the flow surface <NUM>, as opposed to adding them during an additive manufacturing step.

As noted, the supports <NUM> are between the base <NUM> and the backing surface <NUM>. In at least one embodiment, the supports <NUM> can be joined together. For example, the supports <NUM> can be fastened together. In at least one embodiment, the flow surface <NUM>, the supports <NUM>, and the backing surface <NUM> define the cavities <NUM>, which are internal to the flow path duct system <NUM>. The cavities <NUM> are isolated from one another. In at least one embodiment, the base <NUM>, the supports <NUM>, and the backing surface <NUM> together form a monolithic, load bearing structure. In at least one embodiment, the monolithic structure can be additively manufactured. In at least one embodiment, the flow path duct system <NUM> can be a primary load bearing structure, thereby resulting in an integrated design with reduced part count and reduced complexity.

The base <NUM> includes a plurality of perforations <NUM>. One or more cavities <NUM> are in fluid communication with an internal volume <NUM> of the flow path duct system <NUM> through the perforations <NUM>. The perforations <NUM> provide an acoustic flow path to the underlying isolated cavities <NUM> to effectively attenuate sound energy. In at least one embodiment, the cavities <NUM> and the perforations <NUM> together form a plurality of Helmholtz resonators that are configured to attenuate sound.

The perforations <NUM> can have a variety of sizes and shapes. For example, the perforations <NUM> can be formed as ellipses, circles, squares, rounded squares, diamonds, rounded diamonds, rectangles, rounded rectangles, parallelograms, rounded parallelograms, or a combination thereof. A rounded perforation <NUM> has junctions, edges, and the like that are filleted to provide a smooth transition. In at least one embodiment, the perforations <NUM> can be circular.

In at least one embodiment, the number of size of the perforations <NUM> (for example, a surface area and volume of perforation) defines a porosity of the flow surface <NUM>. For example, the porosity (that is, the total volume of open space within the flow path duct system <NUM>), as defined by the perforations <NUM>, ranges from about <NUM>% (for example, between <NUM>%-<NUM>%), about <NUM>% (for example, between <NUM>%-<NUM>%), about <NUM>% (for example, between <NUM>%-<NUM>%), about <NUM>% (for example, between <NUM>%-<NUM>%), about <NUM>% (for example, between <NUM>%-<NUM>%), or about <NUM>% (for example, between <NUM>%-<NUM>%), to about <NUM>% (for example, between <NUM>%-<NUM>%), or any combination thereof. In at least one embodiment, the porosity ranges from about <NUM>% to about <NUM>%, or about <NUM>%, for example.

In at least one embodiment, the plurality of cavities <NUM> define a distribution of shapes including triangles, diamonds, circles, hexagons (honeycomb), or a combination thereof. For example, as shown in <FIG>, the cavities <NUM> have shapes <NUM> in the form of diamonds. In at least one embodiment, the cavities <NUM> define a distribution of diamond shapes, as shown in <FIG>, for example. The supports <NUM> define the outer envelopes of the shapes of the cavities <NUM>. As such, the supports <NUM> provide load transmission and structural support for the flow path duct systems <NUM>, and define the envelopes of the cavities <NUM>.

In at least one embodiment, the size and spacing of the perforations <NUM> and the cavities <NUM> is tuned for tailored frequency attenuation using methods known in the art, for example noise propagation codes (one example being ACoustic TRANsmission (ACTRAN®)), or theoretical methods described in <NPL>). In at least one embodiment, the depth of cavities can be varied for sound attenuation optimization. In some embodiments, the depths <NUM> of the cavities <NUM> define a continuous distribution, a constant distribution, a step distribution with at one step for example, one step, two steps, or more).

In at least one embodiment, the material of the flow path duct system <NUM> can vary depending on actual use and environmental conditions. For example, the flow path duct system <NUM> is formed of titanium, titanium alloys, aluminum, aluminum alloys, stainless steel, one or more polymers, and/or the like.

In at least one embodiment, the flow path duct system <NUM> includes a variable geometry. For example, the flow patch duct system <NUM> includes an inlet flow path, an exit, a nozzle, a partial flow path, and/or a complete flow path. In at least one embodiment, at least one of the inlet (such as the inlet <NUM> shown in <FIG>) or the exit (such as the nozzle outlet <NUM> shown in <FIG>) includes a high aspect ratio. The aspect ratio is defined as a ratio of width/height of the flow path duct system <NUM>, with an aspect ratio greater than two (that is, the width being at least twice the height) being a high aspect ratio for a flow path duct system <NUM>. In at least one embodiment, both the inlet <NUM> and nozzle outlet <NUM> have high aspect ratios.

While the fluid path duct systems <NUM> described herein can be monolithic in terms of the construction of the acoustic treatment and the load bearing structure, the complete assembled flow path duct systems <NUM> as integrated into a vehicle (such as an aircraft) can include several different monolithic duct geometry sections (for example, inlet, nozzle, upper half, lower half) as opposed to one large section due to additive manufacturing and installation constraints.

In at least one embodiment, instead of additively manufacturing the flow surface <NUM> with a plurality of perforations <NUM>, different methods can be used to form the perforations <NUM>. For example, the perforations <NUM> can be formed through drilling cutting, laser cutting, vaporization, ablation, chemical treatment, and/or the like.

As described herein, certain embodiments of the subject disclosure provide a quiet propulsion flow path duct system <NUM>, which includes the flow surface <NUM>, a plurality of supports <NUM> defining a plurality of cavities <NUM> isolated from each other, and a backing surface <NUM>. The supports <NUM> are between the flow surface <NUM> and the backing surface <NUM>. For example, the supports <NUM> are sandwiched between the flow surface <NUM> and the backing surface <NUM>. The base <NUM> having the flow surface <NUM> includes a plurality of perforations <NUM>, such that at least one underlying cavity <NUM> is in fluid communication with the internal volume <NUM> through the perforations <NUM>. In at least one embodiment, the flow surface <NUM>, the supports <NUM>, and the backing surface <NUM> together form a monolithic, load bearing structure.

<FIG> illustrates a flow chart of a method of forming a flow path duct system for a propulsion system of an aircraft, according to an embodiment of the subject disclosure. Referring to <FIG>, the method includes forming, at <NUM>, a plurality of perforations <NUM> through a base <NUM> defining a flow surface <NUM> between an internal surface <NUM> and an external surface <NUM>; extending, at <NUM>, a plurality of supports <NUM> defining a plurality of cavities <NUM> from the external surface <NUM> of the base <NUM>; fluidly coupling, at <NUM>, one or more of the plurality of cavities <NUM> with one or more of the plurality of perforations <NUM>, wherein said fluidly coupling <NUM> includes fluidly coupling the one or more of the plurality of cavities <NUM> with an internal volume <NUM> defined by the internal surface <NUM> of the base <NUM> through the one or more of the plurality of perforations <NUM>; and securing, at <NUM>, a backing surface <NUM> to the plurality of supports <NUM>, wherein said securing <NUM> includes disposing the plurality of supports <NUM> between the base <NUM> and the backing surface <NUM>.

In at least one embodiment, the method further includes integrally forming the base <NUM>, the plurality of supports <NUM>, and the backing surface <NUM> together as a monolithic, load-bearing structure. As a further example, said integrally forming includes additively manufacturing the base <NUM>, the plurality of supports <NUM>, and the backing surface <NUM> together.

In at least one embodiment, said fluidly coupling <NUM> includes fluidly coupling each of the plurality of cavities <NUM> with at least one of the plurality of perforations <NUM>.

In at least one embodiment, said forming <NUM> includes forming the plurality of perforations <NUM> to define a flow surface porosity within the base that ranges from <NUM>% to <NUM>%.

In at least one embodiment, the method includes forming the flow path duct system <NUM> as one or both of an inlet or an outlet nozzle having a high aspect ratio.

It has been discovered that the embodiments of the flow path duct systems <NUM> described herein reduce acoustic noise, as well as being able to serve as a primary, load-bearing structure.

Also provided are the following illustrative, non-exhaustive examples of further non-claimed embodiments that are compatible with the claimed subject matter:
In the claimed method, said integrally forming may comprise additively manufacturing the base, the plurality of supports, and the backing surface together.

The method may further comprise forming the flow path duct system as one or both of an inlet or an outlet nozzle having a high aspect ratio.

As described herein, embodiments of the present disclosure provide systems and methods for efficiently and effectively reducing noise in relation to various components, such as an engine of aircraft. Further, embodiments of the present disclosure provide relatively simple systems and methods for reducing noise with respect to aircraft, for example.

While various spatial and directional terms, such as top, bottom, lower, mid, lateral, horizontal, vertical, front and the like can be used to describe embodiments of the subject disclosure, it is understood that such terms are merely used with respect to the orientations shown in the drawings.

It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) can be used in combination with each other. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the various embodiments of the disclosure without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments of the disclosure, the embodiments are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the various embodiments of the disclosure should, therefore, be determined with reference to the appended claims. In the appended claims and the detailed description herein, the terms "including" and "containing" are used as the plain-English equivalents of the term "comprising" and the term "in which" is used as the plain-English equivalents of the term "wherein. " Moreover, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on <NUM> U. § <NUM>(f), unless and until such claim limitations expressly use the phrase "means for" followed by a statement of function void of further structure.

Claim 1:
A flow path duct system (<NUM>) for a propulsion system (<NUM>) of an aircraft (<NUM>), the flow path duct system (<NUM>) comprising:
a base (<NUM>) defining a flow surface (<NUM>) having a length (<NUM>) along which a fluid travels, wherein the base (<NUM>) has an internal surface (<NUM>) and an external surface (<NUM>), wherein a plurality of perforations (<NUM>) are formed through the base (<NUM>) between the internal surface (<NUM>) and the external surface (<NUM>);
a plurality of supports (<NUM>) defining a plurality of cavities (<NUM>), wherein the plurality of supports (<NUM>) extend outwardly from the external surface (<NUM>) of the base (<NUM>) defining a height (<NUM>) of the cavities (<NUM>), and wherein one or more of the plurality of cavities (<NUM>) are in fluid communication with one or more of the plurality of perforations (<NUM>); and
a backing surface (<NUM>) secured to the plurality of supports (<NUM>);
wherein the plurality of supports (<NUM>) are disposed between the base (<NUM>) and the backing surface (<NUM>);
wherein the one or more of the plurality of cavities (<NUM>) are in fluid communication with an internal volume (<NUM>) defined by the internal surface (<NUM>) of the base (<NUM>) through the one or more of the plurality of perforations (<NUM>);
characterised in that the plurality of cavities (<NUM>) comprises a first set of cavities (421c) defined by the first height (<NUM>), and a second set of cavities (421d) defined by a second height (<NUM>) that differs from the first height (<NUM>); and
in that a step transition (<NUM>) between the first set of cavities (421c) and the second set of cavities (421d) is formed along the length (<NUM>) of the flow path duct system (<NUM>).