Patent Description:
Gas turbine engines often include a bypass duct, especially engines used for commercial aerospace applications. A fan assembly can draw air into the engine, and a portion of that air is diverted through the bypass duct. Fan exit guide vanes (FEGVs) extend into the bypass duct downstream of the fan assembly. These FEGVs provide an aerodynamic function in straightening or otherwise interacting with airflow from the fan assembly, and a structural function in delivering mechanical support in a generally radial direction across the bypass duct.

However, noise produced by gas turbine engines is a concern. Noise generated by fan-wake/vane interaction is a significant contributor to the effective perceived noise level (EPNL) of gas turbine engines. Such noise problems can occur when wakes of the upstream fan assembly impinge on the FEGVs, thereby providing a mechanism for converting non-acoustic vortical disturbances (i.e., the fan wake) into propagating pressure disturbances (i.e., sound).

Acoustic liners may be applied to airfoils to reduce the amount of noise generated by operation of gas turbine engine fans. Conventional acoustic liners rely on quarter-wave resonances of straight constant-area channels. This type of liner is the current industry standard for engine and nacelle acoustic treatment, typically constructed by bonding a perforated face sheet to a honeycomb structure. The honeycomb cells in such architectures form an array of quarter-wave resonators.

Practical space constraints often preclude use of optimum resonator length (e.g., honeycomb cell depth). In particular, deployment of acoustic treatment in Fan Exit Guide Vanes (FEGVs) poses a challenge due to constraints on airfoil thickness, requiring specific, non-optimal, orientation of the resonator channels. Additionally, an inherent drawback of such architectures is that only a fraction of the exposed airfoil surface can be treated. Accordingly, it may be beneficial to have improved acoustic treatment for airfoils and other gas turbine engine structures (e.g., nacelles).

<CIT> discloses a lining for a fluid-flow duct incorporating resonators of a Helmholtz type. <CIT> discloses a ventilation and heat sound insulating structure including Helmholtz resonators in a periodic arrangement. <CIT> discloses a cooled acoustic liner which includes a resonator chamber with a neck and a chamber. <CIT> discloses a noise control cassette for an airfoil of a gas turbine engine including a perforated face sheet configured for exposure to an airflow, a non-perforated backing sheet and a core which together define a cavity configured to provide acoustic reactance control.

According to the invention, an acoustic impedance control feature for airfoils of gas turbine engines is provided. The acoustic impedance control feature comprises an acoustic resonator comprising an acoustic resonator cell having a backing chamber defining a respective volume and a neck arranged relative to the backing chamber and defining an opening, wherein the neck has a length and a cross-sectional area. The acoustic resonator cell satisfies the following relationships: (<NUM>) l/L = <NUM>-<NUM>, where l is the length of the neck and L is a depth of the backing chamber and (<NUM>) a/A = <NUM>-<NUM>, where a is the cross-sectional area of the neck and A is a cross-sectional area of the backing chamber characterized by at least one of: (i) the acoustic resonator includes a first acoustic resonator cell and a second acoustic resonator cell , wherein: the first acoustic resonator cell comprises the backing chamber and the neck; and the second acoustic resonator cell comprises a respective second backing chamber and a respective second neck, wherein the first acoustic resonator cell is stacked on the second acoustic resonator cell and the first backing chamber and the second backing chamber are fluidly connected through the second neck; (ii) the neck is arranged outward from the backing chamber and does not extend into the backing chamber; and (iii) the acoustic resonator is integrally formed with the airfoil.

Embodiments of the acoustic impedance control feature may include that a plurality of acoustic resonator cells are arranged to form an acoustic resonator insert.

The acoustic resonator insert may be installed to the airfoil.

In some embodiments the neck is arranged inside the backing chamber.

In some embodiments the opening is the only fluid connection from an external environment into the backing chamber.

In some embodiments the neck is arranged outward from the backing chamber and does not extend into the backing chamber and the opening may have a rectangular slot.

Some embodiments of the acoustic impedance control feature may include a face sheet, wherein the opening is defined in the face sheet and an outer perforated sheet arranged opposite the backing chamber relative to the face sheet. A second volume may be defined between the face sheet and the outer perforated sheet and the outer perforated sheet may be configured to be exposed to an external environment during operation.

According to some embodiments, an acoustic resonator insert for an airfoil of a gas turbine engine is provided. The acoustic resonator insert may include a face sheet, an insert frame, wherein the face sheet is attached to the insert frame, and an acoustic resonator arranged between the face sheet and a back of the insert frame. The acoustic resonator includes a backing chamber defining a respective volume and a neck arranged relative to the backing chamber and defining an opening, wherein the neck has a length and a cross-sectional area. The acoustic resonator cell satisfies the following relationships: (<NUM>) l/L = <NUM>-<NUM>, where l is the length of the neck and L is a depth of the backing chamber and (<NUM>) a/A = <NUM>-<NUM>, where a is the cross-sectional area of the neck and A is a cross-sectional area of the backing chamber characterized by at least one of: (i) the acoustic resonator includes a first acoustic resonator cell and a second acoustic resonator cell, wherein: the first acoustic resonator cell comprises the backing chamber and the neck; and the second acoustic resonator cell comprises a respective second backing chamber and a respective second neck, wherein the first acoustic resonator cell is stacked on the second acoustic resonator cell and the first backing chamber and the second backing chamber are fluidly connected through the second neck; (ii) the neck is arranged outward from the backing chamber and does not extend into the backing chamber; and (iii) the acoustic resonator is integrally formed with the airfoil.

A plurality of acoustic resonator cells may be arranged within the acoustic treatment insert.

The acoustic resonator insert may be installed to an airfoil.

Optionally, the neck may be arranged inside the backing chamber.

The opening may be the only fluid connection from an external environment into the backing chamber.

Optionally, embodiments of the acoustic resonator inserts may include that the opening is defined in the face sheet and an outer perforated sheet is arranged opposite the backing chamber relative to the face sheet, wherein a second volume is defined between the face sheet and the outer perforated sheet and the outer perforated sheet is configured to be exposed to an external environment during operation.

The face sheet may be attached to the insert frame during assembly to define the neck.

The foregoing features and elements may be executed or utilized in various combinations without exclusivity, unless expressly indicated otherwise.

The exemplary gas turbine engine <NUM> is a two-spool turbofan engine that generally incorporates a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM>, and a turbine section <NUM>. The fan section <NUM> drives air along a bypass flow path B, while the compressor section <NUM> drives air along a core flow path C for compression and communication into the combustor section <NUM>. Hot combustion gases generated in the combustor section <NUM> are expanded through the turbine section <NUM>. Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to turbofan engines and these teachings could extend to other types of engines.

The gas turbine engine <NUM> generally includes a low speed spool <NUM> and a high speed spool <NUM> mounted for rotation about an engine centerline longitudinal axis A. The low speed spool <NUM> and the high speed spool <NUM> may be mounted relative to an engine static structure <NUM> via several bearing systems <NUM>. It should be understood that other bearing systems <NUM> may alternatively or additionally be provided.

The inner shaft <NUM> can be connected to the fan <NUM> through a geared architecture <NUM> to drive the fan <NUM> at a lower speed than the low speed spool <NUM>. The high speed spool <NUM> includes an outer shaft <NUM> that interconnects a high pressure compressor <NUM> and a high pressure turbine <NUM>. In this embodiment, the inner shaft <NUM> and the outer shaft <NUM> are supported at various axial locations by bearing systems <NUM> positioned within the engine static structure <NUM>.

A combustor <NUM> is arranged between the high pressure compressor <NUM> and the high pressure turbine <NUM>. A mid-turbine frame <NUM> may be arranged generally between the high pressure turbine <NUM> and the low pressure turbine <NUM>. The mid-turbine frame <NUM> can support one or more bearing systems <NUM> of the turbine section <NUM>. The mid-turbine frame <NUM> may include one or more airfoils <NUM> that extend within the core flow path C.

The inner shaft <NUM> and the outer shaft <NUM> are concentric and rotate via the bearing systems <NUM> about the engine centerline longitudinal axis A, which is co-linear with their longitudinal axes. The core airflow is compressed by the low pressure compressor <NUM> and the high pressure compressor <NUM>, is mixed with fuel and burned in the combustor <NUM>, and is then expanded over the high pressure turbine <NUM> and the low pressure turbine <NUM>. The high pressure turbine <NUM> and the low pressure turbine <NUM> rotationally drive the respective high speed spool <NUM> and the low speed spool <NUM> in response to the expansion.

Each of the compressor section <NUM> and the turbine section <NUM> may include alternating rows of rotor assemblies and vane assemblies (shown schematically) that carry airfoils that extend into the core flow path C. For example, the rotor assemblies can carry a plurality of rotating blades <NUM>, while each vane assembly can carry a plurality of vanes <NUM> that extend into the core flow path C. The blades <NUM> of the rotor assemblies add or extract energy from the core airflow that is communicated through the gas turbine engine <NUM> along the core flow path C. The vanes <NUM> of the vane assemblies direct the core airflow to the blades <NUM> to either add or extract energy.

Various components of a gas turbine engine <NUM>, including but not limited to the airfoils of the blades <NUM> and the vanes <NUM> of the compressor section <NUM> and the turbine section <NUM>, may be subjected to repetitive thermal cycling under widely ranging temperatures and pressures. The hardware of the turbine section <NUM> is particularly subjected to relatively extreme operating conditions. Therefore, some components may require internal cooling circuits for cooling the parts during engine operation. Example cooling circuits that include features such as airflow bleed ports are discussed below.

Although a specific architecture for a gas turbine engine is depicted in the disclosed non-limiting example embodiment, it should be understood that the concepts described herein are not limited to use with the shown and described configuration, as the teachings may be applied to other types of engines such as, but not limited to, turbojets, turboshafts, and other turbofan configurations (e.g., wherein an intermediate spool includes an intermediate pressure compressor ("IPC") between a low pressure compressor ("LPC") and a high pressure compressor ("HPC"), and an intermediate pressure turbine ("IPT") between the high pressure turbine ("HPT") and the low pressure turbine ("LPT")).

<FIG> is a schematic view of a turbine section that may employ various embodiments disclosed herein. Turbine <NUM> includes a plurality of airfoils, including, for example, one or more blades <NUM> and vanes <NUM>. The airfoils <NUM>, <NUM> may be hollow bodies with internal cavities defining a number of channels or cavities, hereinafter airfoil cavities, formed therein and extending from an inner diameter <NUM> to an outer diameter <NUM>, or vice-versa. The airfoil cavities may be separated by partitions within the airfoils <NUM>, <NUM> that may extend either from the inner diameter <NUM> or the outer diameter <NUM> of the airfoil <NUM>, <NUM>. The partitions may extend for a portion of the length of the airfoil <NUM>, <NUM>, but may stop or end prior to forming a complete wall within the airfoil <NUM>, <NUM>. Thus, each of the airfoil cavities may be fluidly connected and form a fluid path within the respective airfoil <NUM>, <NUM>. The blades <NUM> and the vanes <NUM> may include platforms <NUM> located proximal to the inner diameter thereof. Located below the platforms <NUM> may be airflow ports and/or bleed orifices that enable air to bleed from the internal cavities of the airfoils <NUM>, <NUM>. A root of the airfoil may connected to or be part of the platform <NUM>.

The turbine <NUM> is housed within a case <NUM>, which may have multiple parts (e.g., turbine case, diffuser case, etc.). In various locations, components, such as seals, may be positioned between airfoils <NUM>, <NUM> and the case <NUM>. For example, as shown in <FIG>, blade outer air seals <NUM> (hereafter "BOAS") are located radially outward from the blades <NUM>. As will be appreciated by those of skill in the art, the BOAS <NUM> can include BOAS supports that are configured to fixedly connect or attach the BOAS <NUM> to the case <NUM> (e.g., the BOAS supports can be located between the BOAS and the case). As shown in <FIG>, the case <NUM> includes a plurality of hooks <NUM> that engage with the hooks <NUM> to secure the BOAS <NUM> between the case <NUM> and a tip of the blade <NUM>.

Turning now to <FIG>, an airfoil <NUM> that has an acoustic treatment. As shown, the airfoil <NUM> includes an acoustic resonator insert <NUM> installed thereto. The airfoil <NUM> has an airfoil shape that defines a concave pressure side <NUM> and an opposite convex suction side <NUM>. The airfoil <NUM> extends in an engine-axis axial direction between a leading edge <NUM> and a trailing edge <NUM>. The acoustic resonator insert <NUM> is attached to the airfoil <NUM> along the pressure side <NUM>, at a location intermediate between the leading edge <NUM> and the trailing edge <NUM>. In alternative configurations, the acoustic resonator insert <NUM> can be attached to an airfoil at other locations (e.g., along the suction side <NUM>). In some embodiments, the airfoil is a fan exit guide vane for a gas turbine engine. It will be appreciated that acoustic resonator insert may be used on other types of airfoils and/or components that are employed in gas turbine engines or associated structures (e.g., nacelle components and structures). Some such acoustic resonator inserts are disclosed in <CIT>, entitled "Airfoil Acoustic Impedance Control". It will be appreciated that airfoil <NUM> of <FIG> generally represents an airfoil having an acoustic resonator insert installed therein, with some such insert incorporating embodiments of the present disclosure. That is, the acoustic resonator insert <NUM> illustrated in <FIG> may incorporate features described herein.

Turning to <FIG>, a perspective view of a portion of an airfoil <NUM> having an acoustic resonator insert <NUM> installed thereto is shown in <FIG>, and a cross-sectional view of the airfoil <NUM> is shown in <FIG>. The configuration shown in <FIG> is representative of prior acoustic resonator insert configurations. The airfoil <NUM> has an airfoil shape that defines a concave pressure side <NUM> and an opposite convex suction side <NUM>. The airfoil <NUM> extends in an engine-axis axial direction between a leading edge <NUM> and a trailing edge <NUM>.

The acoustic resonator insert <NUM> defines a plurality of internal cells that define resonator cavities <NUM> which are bounded, in part, by a face sheet <NUM>. The face sheet <NUM> defines part of an external flow surface of the airfoil <NUM> when the acoustic resonator insert <NUM> is installed to the airfoil <NUM>. The resonator cavities <NUM> are fluidly connected to an external environment through one or more openings <NUM> in the face sheet <NUM>. The openings <NUM> may be perforations formed in the face sheet <NUM>, or may be a perforated sub-sheet assembled with the face sheet <NUM>.

As shown, the openings <NUM> are grouped in rows or columns as perforated regions <NUM> with non-perforated (solid) regions <NUM> of the face sheet <NUM> located between the perforated regions <NUM> of the openings <NUM>. In the illustrated embodiment, the perforated regions <NUM> extend in a generally radial direction (e.g., root to tip direction), although in other configurations the perforated regions may extend in a generally axial direction (e.g., leading edge to trailing edge direction). In the illustrated configuration, each perforated region <NUM> is arranged at a forward side of a respective resonator cavity <NUM> of the acoustic resonator insert <NUM>. Each perforated region <NUM> has a width W. The resonator cavities <NUM> are generally cuboid-shaped (i.e., generally rectangular boxes) extending aftward (toward the trailing edge <NUM>) from the location of a respective perforated region <NUM>. The resonator cavities <NUM> of the acoustic resonator insert <NUM> have a length L in a direction from leading edge <NUM> to trailing edge <NUM> along the face sheet <NUM>. The length L is the length of a resonator cavity and may be optimized to be a quarter wave resonator. In some configurations, the internal cells may define or have cavities that are straight or constant cross-section area geometries (e.g., in a spanwise direction).

Each resonator cavity <NUM> has a thickness T in a direction from the pressure side <NUM> to the suction side <NUM>. Because of the relatively small or low thickness of airfoils, the resonator cavities <NUM> extend in a generally axial direction, with an entrance to each resonator cavity <NUM> defined by the perforations of the perforated regions <NUM> that are exposed to the external environment of the airfoil <NUM> such that fluid communication (at least acoustic communication) may be provided into the resonator cavities <NUM>. These limitations of available space can limit the fraction of the airfoil <NUM> that can be treated with acoustic treatment. The fraction of the airfoil that is treatable scales with T/L, and if L is optimized for acoustic damping, the treatment has a lower limit of coverage.

The formation of the acoustic resonator insert <NUM> typically involves the attachment of the face sheet <NUM> to a resonator structure, which, in some configurations is a honeycomb structure. The honeycomb structure can maximize the number of cells that are present within the treated component. In some configurations, the honeycomb cells will form an array of quarter-wave resonators. As such, the resonator cavities <NUM> may have a generally honeycomb (e.g., pentagon) cross-sectional geometry. The length L of the resonator cavities <NUM> is arranged in a leading edge-to-trailing edge direction to enable the quarter-wave length optimization to be achieved. Because of this and the amount of physical space each resonator cavity occupies to be functional, the number of resonator cavities in a given treatment may be limited.

In accordance with embodiments of the present invention, the length of a cavity of an internal cell may be reduced through the principles of Helmholtz resonance. As such, a modified, and improved, internal cell or cavity of an acoustic treatment insert (or acoustic treatment of any component, integrally formed therewith or as an insert/attachment) may be achieved. In accordance with some embodiments of the present invention, in addition to a quarter-wave resonator cavity, one or more relatively thin tubes are combined with the resonator cavity. This has the effect of adding acoustic inertia and reducing the resonance frequency for a given cell length (or depth).

Turning now to <FIG>, a schematic geometric representation of a resonator <NUM> in accordance with an embodiment of the present invention is shown. The geometric representation of a resonator <NUM> does not represent a physical structure, per se, but rather is provided for illustrative purposes of the principles of the structures of the resonator cavities in accordance with the present disclosure. The resonator <NUM> is formed of two resonator cells <NUM>, <NUM>, which are stacked. A first resonator cell <NUM> includes a respective first neck <NUM> and a respective first backing chamber <NUM>. A second resonator cell <NUM> includes a respective second neck <NUM> and a respective second backing chamber <NUM>. The first neck <NUM> has a respective first length l<NUM> and a respective first cross-sectional area a<NUM>. As such, the volume of the first neck <NUM> is defined as the first length l<NUM> times the first cross-sectional area a<NUM>. The second neck <NUM> has a respective second length l<NUM> and a respective second cross-sectional area a<NUM>. As such, the volume of the second neck <NUM> is defined as the second length l<NUM> times the second cross-sectional area a<NUM>. Further, the first backing chamber <NUM> of the first resonator cell <NUM> has a respective first volume V<NUM> and the second backing chamber <NUM> of the second resonator <NUM> has a respective second volume V<NUM>. The first backing chamber <NUM> has a respective first cross-sectional area A<NUM> and first backing chamber length L<NUM>. The second backing chamber <NUM> has a respective second cross-sectional area A<NUM> and second backing chamber length L<NUM>.

By implementing a neck-configuration, the depth required for optimum acoustic damping tuning can be reduced by the principles of Helmholtz resonance. The backing chambers define a backing volume as would be done in a typical or convention acoustic resonator cell. However, the addition of a thin tube of length l and cross-sectional area a, reduced total volume may be achieved. The neck of the acoustic resonator cells of the present disclosure adds acoustic inertia and reduces the resonance frequency for a given depth, thus allowing for shorter depth backing chambers.

Each acoustic resonator cell may satisfy the following relationships: (<NUM>) l/L = <NUM>-<NUM>, where l is a neck length and L is a backing cavity depth or length and (<NUM>) a/A = <NUM>-<NUM>, where a is the cross-sectional area of the neck and A is the cross-sectional area of the backing cavity.

Turning now to <FIG>, schematic illustrations of a resonator <NUM> in accordance with an embodiment of the present disclosure are shown. <FIG> illustrates an elevation cross-sectional view of the resonator <NUM> and <FIG> illustrates an isometric illustration of the resonator <NUM>. The resonator <NUM> may be a single resonator that is part of an insert, cartridge, or formed within a component of a gas turbine engine (e.g., airfoil, nacelle, etc.). The resonator <NUM> is arranged such that a portion of the resonator <NUM> is exposed to a flow of air, as indicated in <FIG>. Similar to the geometric illustration of <FIG>, the resonator <NUM> is formed of two resonator cells <NUM>, <NUM>, which are stacked. A first resonator cell <NUM> includes a respective first neck <NUM> and a respective first backing chamber <NUM>. A second resonator cell <NUM> includes a respective second neck <NUM> and a respective second backing chamber <NUM>. The first neck <NUM> has a respective first length l<NUM> and a respective first cross-sectional area a<NUM> and extends into a respective first volume V<NUM> of the first backing chamber <NUM>. The volume of the first neck <NUM> is defined as the first length l<NUM> times the first cross-sectional area a<NUM>. The second neck <NUM> has a respective second length l<NUM> and a respective second cross-sectional area a<NUM> and extends into a respective second volume V<NUM> of the second backing chamber <NUM>. The volume of the second neck <NUM> is defined as the second length l<NUM> times the second cross-sectional area a<NUM>. The first neck <NUM> extends inside or into the first backing chamber <NUM> and the second neck <NUM> extends inside or into the second backing chamber <NUM>. In this configuration, both the first resonator cell <NUM> and the second resonator cell <NUM> have a cross-sectional area A which is also the cross-sectional area of the backing chambers <NUM>, <NUM> or the first and second volumes V<NUM>, V<NUM>.

The respective necks <NUM>, <NUM> are formed as hollow cylinders that extend into the respective backing chambers <NUM>, <NUM> of the first and second resonator cells <NUM>, <NUM>. The resonator <NUM> has an opening <NUM> that fluidly connects the interior of the resonator <NUM> with an external flow of air. As such, the complete interior of the resonator <NUM> is fluidly connected to the exterior environment. Air (or vibrations) will enter into the first neck <NUM> and pass into the first volume V<NUM>. The air (or vibrations) may continue to pass into the second neck <NUM> and pass into the second volume V<NUM>.

Although the resonator <NUM> of <FIG> is a generally cylindrical shape those of skill in the art will appreciate that other geometries may be used without departing from the scope of the present disclosure. For example, the resonators of the present disclosure may have circular, square, rectangular, polygonal, or other geometric cross-sectional shapes. Further, although shown in <FIG>, with a dual-resonator cell stack, other configurations are possible without departing from the present disclosure. For example, a single resonator cell (e.g., components <NUM>, <NUM>, <NUM> as a single resonator is encompassed herein). As such, the illustrative embodiments described herein are merely for illustrative and explanatory purposes and are not to be limiting.

With reference to <FIG>, a total length Lt of the resonator <NUM> may be equivalent to a conventional length of a quarter-wave resonator cell. That is, as illustrated, two effective resonator cells (of the present disclosure) may be stacked to enable installation in a location where only a single convention resonator cell may have previously been installed. As such, improved tuning and acoustic damping may be achieved through embodiments of the present invention. Furthermore, although only two resonator cells <NUM>, <NUM>, in accordance with other embodiments, any number of resonator cells may be stacked to achieve a desired vibrational and acoustic damping.

Turning now to <FIG>, schematic illustrations of an airfoil <NUM> in accordance with an embodiment of the present invention are shown. <FIG> illustrates a cross-section of the airfoil <NUM> and the interior structure thereof, <FIG> is a partial elevation view of the airfoil <NUM>, and <FIG> illustrates an enlarged view of a portion of the airfoil <NUM>. The airfoil <NUM> has an airfoil shape that defines a concave pressure side <NUM> and an opposite convex suction side <NUM>. The airfoil <NUM> extends in an engine-axis axial direction between a leading edge <NUM> and a trailing edge <NUM>. An acoustic resonator insert <NUM> is installed into the airfoil <NUM> and defines a plurality of resonator cells <NUM>. The acoustic resonator insert <NUM> includes a face sheet <NUM> that defines a portion of the airfoil flow surfaces (e.g., exterior surface of the airfoil <NUM>). Although discussed herein as a face sheet construction, such configuration is not to be limiting. In other embodiments of the present disclosure, the acoustic resonator insert <NUM> may be a uniformly and integral piece that is formed, for example, by additive manufacturing, molds, machining, or other manufacturing processes, as will be appreciated by those of skill in the art. That is, in some embodiments, the illustrated and labeled face sheet <NUM> may be an integral piece with the rest of the acoustic resonator insert <NUM>, and not necessarily a separately formed and installed piece attached to a backing structure.

The face sheet <NUM> defines part of an external flow surface of the airfoil <NUM> when the acoustic resonator insert <NUM> is installed to the airfoil <NUM>. The resonator cells <NUM> are fluidly connected to an external environment through one or more openings <NUM> formed in the face sheet <NUM>. The openings <NUM> may be perforations formed in the face sheet <NUM>, or may be a perforated sub-sheet assembled with the face sheet <NUM>.

As shown in <FIG>, each resonator cell <NUM> includes a neck <NUM> and a respective backing chamber <NUM>. The neck <NUM> includes and defines the opening <NUM> of the respective resonator cell <NUM>, and fluidly connects the exterior environment to a volume V<NUM> defined within the backing chamber <NUM>. In this illustrative embodiment, the neck <NUM> has a length of l<NUM> and a cross-sectional area of a<NUM>. The backing chamber <NUM> has a volume V<NUM> with the neck <NUM> extending into the backing chamber <NUM>. In some embodiments, the openings <NUM> may be the equivalent of a single perforation in a typical acoustic treatment (e.g., about <NUM> (<NUM> inches) in diameter). In accordance with some embodiments of the present invention, each resonator cell <NUM> may be polygonal in cross-section (e.g., honeycomb) and each resonator cell <NUM> has one, and only one, opening <NUM> associated therewith. In some embodiments, the neck <NUM> may have a circular or non-circular cross-sectional geometry, and the illustrative and discussed geometries are not intended to be limiting, but rather are merely for illustrative and explanatory purposes.

Turning now to <FIG>, schematic illustration of an airfoil <NUM> in accordance with an embodiment of the present disclosure are shown. <FIG> illustrates a cross-section of the airfoil <NUM> and the interior structure thereof. <FIG> illustrates an enlarged view of a resonator cell <NUM> of the acoustic resonator insert <NUM>, <FIG> illustrates an assembly process for an acoustic resonator insert <NUM> of the airfoil <NUM>, and <FIG> illustrates a partial elevation view of the airfoil <NUM>. The airfoil <NUM> has an airfoil shape that defines a concave pressure side <NUM> and an opposite convex suction side <NUM>. The airfoil <NUM> extends in an engine-axis axial direction between a leading edge <NUM> and a trailing edge <NUM>. An acoustic resonator insert <NUM> is installed into the airfoil <NUM> and defines a plurality of resonator cells <NUM>. The acoustic resonator insert <NUM> includes a face sheet <NUM> that defines a portion of the airfoil flow surfaces (e.g., exterior surface of the airfoil <NUM>).

As shown in <FIG>, each resonator cell <NUM> includes a neck <NUM> and a respective backing chamber <NUM>. The neck <NUM> includes and defines the opening <NUM> of the respective resonator cell <NUM>, and fluidly connects the exterior environment to a volume V<NUM> defined within the backing chamber <NUM>. In this illustrative embodiment, the neck <NUM> has a length of l<NUM> and a cross-sectional area of a<NUM>. The backing chamber <NUM> has a volume V<NUM> and a cross-sectional area A<NUM>. In contrast to the prior embodiment, the neck <NUM> is arranged outward from the backing chamber <NUM> and does not extend into the backing chamber <NUM>. In some embodiments, the openings <NUM> may be the equivalent of a single perforation in a typical acoustic treatment (e.g., about <NUM> (<NUM> inches) in diameter). In accordance with some embodiments of the present disclosure, each resonator cell <NUM> may be polygonal in cross-section (e.g., honeycomb) and each resonator cell <NUM> has one, and only one, opening <NUM> associated therewith. In some embodiments, the neck <NUM> may have a circular or non-circular cross-sectional geometry, and the illustrative and discussed geometries are not intended to be limiting, but rather are merely for illustrative and explanatory purposes. For example, in the configuration of <FIG>, it may be advantageous to have a neck structure that is a slot (e.g., having a high aspect ratio, rectangular cross-sectional geometry).

<FIG> illustrates the cross-sectional area A<NUM> and the rectangular slot shape of the openings <NUM>. In this illustrative embodiment, the openings <NUM> are arranged at an aft-end of each resonator cell <NUM>, with the opening into the backing chamber <NUM> being forward thereof. However, in other embodiments, the openings exposed to the external air may be arranged at a forward end and/or may be angled (instead of the radial orientation as shown). That is, the openings exposed to the external air may have any geometric shape and/or orientation which may be influenced, at least in part, by desired acoustic properties, part-life properties (e.g., thermal considerations, fatigue, etc.), and/or manufacturing/producibility constraints.

<FIG> illustrates a construction of the acoustic resonator insert <NUM>. Specifically, as shown the face sheet <NUM> is installed to an insert frame <NUM>. The insert frame <NUM> may have an exterior surface configured to be installed and attached to a receiving portion of an airfoil, as will be appreciated by those of skill in the art. Further, the insert frame <NUM> may define, in part, a portion of the walls or structure that defines the necks <NUM>, once assembled. The other portion of the walls or structure that defines the necks <NUM> is provided by the face sheet <NUM>. When the face sheet <NUM> is installed to the insert frame, the necks <NUM> will be defined and provide acoustic damping, as described above. Each resonator cell <NUM> is defined between the face sheet <NUM> and a back of the insert frame <NUM>, when the face sheet <NUM> is installed to the insert frame <NUM>. Although described with respect to this specific embodiment, it will be appreciated that the resonators cells of the present disclosure are defined between a face sheet and a back of an insert frame or between a face sheet and a material of a component defining a back wall of a respective backing chamber.

It is noted that the resonator cell <NUM> of <FIG> satisfies the geometric requirements and relationships described with respect to <FIG> and as otherwise described herein. As will be appreciated, in accordance with embodiments of the present invention, a resonator cell is constructed having a neck that is arranged relative to a backing chamber. In operation, acoustic vibrations will travel through air or other fluid into the neck, and then into the backing chamber, regardless of specific orientation, geometry, or arrangement of components. The primary functionality is achieved by a neck acoustically upstream relative to a backing chamber, with the backing chamber having a greater volume than the neck. The change in internal volumes from the upstream neck to the downstream backing chamber provides improved acoustic damping within a reduced total volume as compared to prior quarter wavelength acoustic resonator cells.

Turning now to <FIG>, a portion of an acoustic resonator <NUM> is schematically illustrated. The illustrated portion of the acoustic resonator <NUM> may be a portion of an acoustic resonator insert, such as shown and described above, or may be an integral part of a component, such as an airfoil or nacelle part. In the integral configurations of the present disclosure, the integral nature means that the acoustic resonator is formed as part of the structure of the component, such as by machining or additive manufacturing. More specifically, an integrally formed acoustic resonator of the present disclosure that cannot be removed from the component to which it is treating. This is in comparison to an insert which can be separately manufactured and installed and potentially removed therefrom after installation, as a complete and separate unit.

The acoustic resonator <NUM> of <FIG> includes a perforated outer sheet <NUM>, a face sheet <NUM>, and one or more resonator cells <NUM> arranged opposite the face sheet <NUM> from the perforated outer sheet <NUM>. Between the face sheet <NUM> and the perforated outer sheet <NUM> is a conventional resonator region <NUM>. When installed to a component and in operation, the perforated outer sheet <NUM> is exposed to the external environment and the face sheet <NUM> of the resonator cells <NUM> is not exposed directly to the external environment.

Each resonator cell <NUM> includes a neck <NUM> and a backing chamber <NUM>. In this configuration, the neck <NUM> extends into the backing chamber <NUM>. However, in other embodiments, the resonator cells <NUM> can have a neck-and-backing chamber configuration similar to that shown and described in <FIG>, or some other geometry and configuration, without departing from the scope of the present disclosure. The neck <NUM> has a length l<NUM> and a cross-sectional area of a<NUM>. Similarly, the backing chamber <NUM> defines an interior volume of V<NUM>.

In operation, vibration waves from an external environment may pass through perforations <NUM> in the perforated outer sheet and enter an outer volume V<NUM> defined by the conventional resonator region <NUM>. The vibrational waves will then enter the necks <NUM> of the acoustic resonator cells <NUM> through openings <NUM> and travel into the interior volume V<NUM> of the acoustic resonator cells <NUM>. This configuration allows for reduced impact to the face sheet <NUM> (e.g., due to hot gases) and/or reduce the amount of turbulence present at the openings <NUM> of the necks <NUM>.

As shown in <FIG>, there are two distinct resonator regions <NUM> with discrete or respective outer volumes V<NUM> associated therewith. In some alternative configurations, the divider <NUM> between the separate outer volumes V<NUM> may be eliminated such that a single large and open space is present between the perforated outer sheet <NUM> and the face sheet <NUM>. As shown in <FIG>, the outer volume V<NUM> has a depth of L<NUM> and the acoustic resonator cells <NUM> have a depth of L<NUM>. A length l<NUM> of the necks <NUM> is selected to enable a reduction in, at least, the depth L<NUM> of the acoustic resonator cells <NUM>, thus allowing for a reduced total size of the acoustic resonator <NUM>. Advantageously, such configuration can be used to enable reduced sizes of the components to which the acoustic resonator is a part of (e.g., an airfoil). This illustrative configuration can enable both a reduced resonator depth while maintaining aerodynamic benefits of an outer sheet having numerous small scale perforation, as opposed to a single large preformation/aperture.

Similar to that shown and described with respect to <FIG>, the acoustic resonator <NUM> of <FIG> includes a perforated outer sheet <NUM>, a face sheet <NUM>, and one or more resonator cells <NUM> arranged opposite the face sheet <NUM> from the perforated outer sheet <NUM>. Between the face sheet <NUM> and the perforated outer sheet <NUM> is a conventional resonator region <NUM>. When installed to a component and in operation, the perforated outer sheet <NUM> is exposed to the external environment and the face sheet <NUM> of the resonator cell <NUM> is not exposed directly to the external environment.

The resonator cell <NUM> includes a neck <NUM> and a backing chamber <NUM>. In this configuration, the neck <NUM> extends into the backing chamber <NUM>. The neck <NUM> has a length l<NUM> and a cross-sectional area of a<NUM>. Similarly, the backing chamber <NUM> defines an interior volume of V<NUM>, a backing chamber depth L<NUM>, and a backing chamber cross-sectional area A<NUM>. In this configuration, the geometry, shape, and orientation of the acoustic resonator <NUM> of <FIG> is skewed as compared to prior configuration. The skewing may be employed for various reasons, including, not limited to, tailoring the acoustic damping for a specific application and/or to allow or facilitate certain manufacturing or producibility aspects (e.g., may allow for and/or facilitates additive manufacturing).

In accordance with embodiments of the present invention, the improved acoustic resonator cells have certain distinct features. For example, each acoustic resonator cell of the present disclosure has a backing chamber that defines a specific volume, a neck is arranged relative to the backing chamber, and the neck has a single opening, such that each acoustic resonator cell has one, and only one, opening to allow acoustic vibrations or waves to travel along the neck into the backing chamber.

Advantageously, embodiments described herein provide improved acoustic treatments and configurations for components of gas turbine engines. For example, embodiments of the present disclosure may enable a reduction of up to <NUM>% of the required depth for acoustic damping as compared to convention quarter-wave resonator cells. Further, advantageously, embodiments of the present disclosure can maintain and/or improve the absorption bandwidth of acoustic vibrations, as compared to conventional quarter-wave resonator cells. Advantageously, a highly effective acoustic treatment may be applied to areas or surfaces in gas turbine engines (e.g., airfoils, nacelle components, etc.) for improved acoustic damping. Moreover, embodiments of the present invention enable the application of acoustic treatments to be applied to surfaces and structures where depth/space is a limiting factor.

As used herein, the term "about" is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, "about" may include a range of ± <NUM>%, or <NUM>%, or <NUM>% of a given value or other percentage change as will be appreciated by those of skill in the art for the particular measurement and/or dimensions referred to herein.

It should be appreciated that relative positional terms such as "forward," "aft," "upper," "lower," "above," "below," "radial," "axial," "circumferential," and the like are with reference to normal operational attitude and should not be considered otherwise limiting.

While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions, combinations, sub-combinations, or equivalent arrangements not heretofore described, but which are commensurate with the scope of the appended claims. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments.

Claim 1:
An acoustic impedance control feature for airfoils of a gas turbine engine (<NUM>), the acoustic impedance control feature comprising:
an acoustic resonator (<NUM>, <NUM>, <NUM>, <NUM>) comprising an acoustic resonator cell (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having:
a backing chamber (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) defining a respective volume (V); and
a neck (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) arranged relative to the backing chamber and defining an opening (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), wherein the neck has a length (l) and a cross-sectional area (a),
wherein the acoustic resonator cell (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) satisfies the following relationships:
(<NUM>) l/L = <NUM>-<NUM>, where l is the length of the neck (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and L is a depth of the backing chamber (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>); and
(<NUM>) a/A = <NUM>-<NUM>, where a is the cross-sectional area of the neck and A is a cross-sectional area of the backing chamber
characterized by at least one of:
(i) the acoustic resonator (<NUM>, <NUM>) includes a first acoustic resonator cell (<NUM>, <NUM>) and a second acoustic resonator cell (<NUM>, <NUM>), wherein: the first acoustic resonator cell (<NUM>, <NUM>) comprises the backing chamber (<NUM>, <NUM>) and the neck (<NUM>, <NUM>); and the second acoustic resonator cell (<NUM>, <NUM>) comprises a respective second backing chamber (<NUM>, <NUM>) and a respective second neck (<NUM>, <NUM>), wherein the first acoustic resonator cell (<NUM>, <NUM>) is stacked on the second acoustic resonator cell (<NUM>, <NUM>) and the first backing chamber (<NUM>, <NUM>) and the second backing chamber (<NUM>, <NUM>) are fluidly connected through the second neck (<NUM>, <NUM>);
(ii) the neck (<NUM>, <NUM>, <NUM>) is arranged outward from the backing chamber (<NUM>, <NUM>, <NUM>) and does not extend into the backing chamber (<NUM>, <NUM>, <NUM>); and
(iii) the acoustic resonator (<NUM>, <NUM>) is integrally formed with the airfoil.