Abstract: A gas turbine engine comprises a fan, a core turbine engine coupled to the fan, a fan case housing the fan and the core turbine engine, a plurality of outlet guide vanes extending between the core turbine engine and the fan case, and an acoustic spacing. The fan comprises a plurality of fan blades that define a fan diameter and a BEAL. The fan case comprises an inlet and an inlet length between the inlet and the fan. The acoustic spacing comprises a distance between the fan and the plurality of outlet guide vanes, and in combination with the BEAL determines an acoustic spacing ratio of the gas turbine engine.

Abstract: An acoustic core may include an array of resonant cells configured as a plurality of resonant cell groups. The resonant cell groups may include a plurality of resonant cells configured as a partitioned resonant cell that include a converging resonant cell and a diverging resonant cell. The converging resonant cell and the diverging resonant cell may be defined by a plurality of cell walls integrally formed with one another and a partition integrally formed with the plurality of cell walls. The partition may at least partially delimit the converging resonant cell from the diverging resonant cell. The converging resonant cell may define an upper resonant space delimited by the partition and a top face of the array of resonant cells. The diverging resonant cell may define a lower resonant space delimited by the partition and a bottom face of the array of resonant cells.

Abstract: A gas turbine engine is provided, having a turbomachine and a rotor assembly driven by the turbomachine and operable at a first blade passing frequency (f1) greater than or equal to 2,500 hertz and less than or equal to 5,000 hertz during a high power operating condition; a heat exchanger positioned within an annular duct and extending substantially continuously along the circumferential direction, wherein an effective transmission loss (ETL) for the heat exchanger positioned within the annular duct is between 5 decibels and 1 decibels for a high power operating condition, and wherein the heat exchanger comprises a heat transfer section defining an acoustic length (Li), and wherein an Operational Acoustic Reduction Ratio (OARR) is greater than or equal to 0.75 to achieve the ETL at the high power operating condition, the OARR equal to: sin ? ? ( 2 × ? × f 1 a 1 × L i ) 2 wherein a1 is equal to 13,200 inches per second during the high power operating condition.

Abstract: An inlet duct for a nacelle of a ducted fan engine includes an inlet portion at an upstream end of the inlet duct, an acoustic liner arranged downstream of the inlet portion, and a fan section arranged downstream of the acoustic liner. The inlet portion and the acoustic liner are coupled together at an inlet-acoustic liner interface extending circumferentially about the inner surface of the inlet duct, and the acoustic liner and the fan section are coupled together at a fan section hardwall-acoustic liner interface extending circumferentially about the inner surface of the inlet duct. At least one of the acoustic liner, the inlet-acoustic liner interface, and the fan section hardwall-acoustic liner interface having a structure that circumferentially alters a magnitude and a phase of an acoustic wave reflection of the inlet duct to attenuate flutter bite of a fan.

Abstract: An aircraft engine includes a low pressure spool, a high pressure spool, and an alternative power source. The alternative power source is configured to add power to the high pressure spool. A controller is configured to determine a noise sensitive condition; and control, in response to determining the noise sensitive condition, the alternative power source to add power to the high pressure spool.

Abstract: A gas turbine engine is provided. The gas turbine engine includes a turbomachine having a compressor section, a combustion section, and a turbine section arranged in serial flow order and together defining a working gas flowpath, the turbomachine including an acoustic liner, the acoustic liner having: a flowpath wall exposed to the working gas flowpath, the flowpath wall defining an opening; and a duct wall extending from the flowpath wall defining at least in part an acoustic passage defining a volume, the acoustic passage operable to attenuate noise through the working gas flowpath during an operating condition of the gas turbine engine.

Abstract: A blended wing body aircraft includes a body section having an aerodynamic lifting surface. The body section includes an upper body and a lower body. The blended wing body aircraft also includes a plurality of blended wing sections further defining the body section. The blended wing body aircraft includes one or more grooves in the body section. The one or more grooves extend from the upper body towards the lower body. The blended wing body aircraft further includes one or more open-fan engines mounted at least partially within the one or more grooves. The one or more open-fan engines ingest a portion of a boundary layer of the blended wing body aircraft.

Abstract: An acoustic core includes an array of resonant cells. The array may include a plurality of coupled resonant cells respectively defining an antecedent resonant space and a subsequent resonant space, with at least one cell wall having one or more wall-apertures defining a pathway between the antecedent resonant space and the subsequent resonant space. The array may include a plurality of high-frequency resonant cells respectively defining a high-frequency resonant space and being matched with respective ones of the plurality of coupled resonant cells. A cross-sectional dimension of the one or more wall-apertures defining the pathway between the antecedent resonant space and the subsequent resonant space may be less than a cross-sectional dimension of the antecedent resonant space and/or a cross-sectional dimension of the subsequent resonant space.

Abstract: A propulsion system is provided. The propulsion system defines a radial direction and includes a rotating element; a stationary element; an inlet assembly defining an inlet positioned between the rotating element and the stationary element and positioned inward of the stationary element along the radial direction, the inlet assembly comprising an inlet duct located downstream of the inlet; and a ducted fan comprising a plurality of fan blades positioned at least partially in the inlet duct; wherein the inlet duct divides into a first duct and a second duct separate from the first duct, wherein the first duct is a core duct downstream of the ducted fan, wherein the second duct is a fan duct downstream of the ducted fan, and wherein the second duct includes an exhaust nozzle having a plurality of chevrons disposed at an aft end of the exhaust nozzle to define an exhaust outlet.

Abstract: Systems and methods for controlling an unducted turbofan engine to limit noise. The unducted turbofan engine may include an unducted fan drivingly coupled with a low-pressure turbine and a plurality of unducted outlet guide vanes. The unducted fan may include a plurality of fan blades and a pitch angle of the fan blades may be variable. A pitch angle of the unducted outlet guide vanes may be variable. A controller is configured to control the engine to limit noise based on a noise sensitive condition.

Abstract: A gas turbine engine is provided including a turbomachine having a compressor section, a combustion section, and a turbine section arranged in serial flow order; a rotor assembly driven by the turbomachine, the rotor assembly, the turbomachine, or both comprising a substantially annular duct relative to the centerline of the gas turbine engine, the annular duct defining a flowpath; a heat exchanger positioned within the annular duct and extending substantially continuously along the circumferential direction, the heat exchanger comprising a first material defining a heat exchange surface exposed to the flowpath, wherein the first material defines a heat exchange coefficient and wherein the heat exchange surface defines a surface area (A), and wherein the heat exchanger has an effective transmission loss (ETL) of between 5 decibels and 1 decibel for an operating condition.

Abstract: An aircraft includes a fuselage, a wing connected to and extending outward from the fuselage, and an engine mounted to the wing. The engine includes turbomachine defining a centerline axis, a fan, and an exhaust section with an outlet nozzle. The turbomachine defines a centerline axis. The fan is connected to and is disposed upstream from the turbomachine. The fan is disposed to rotate about the centerline axis. During operation of the engine, an exhaust stream is expelled from the outlet nozzle of the exhaust section. The exhaust stream defines a mean direction of flow in the downstream direction from the exhaust section. The mean direction of flow defines a first angle with the centerline axis of the turbomachine that is greater than zero such that the centerline axis is oriented downwardly along the vertical direction relative to the mean direction of flow of the exhaust stream.

Abstract: An acoustic core may include an array of resonant cells configured as a plurality of resonant cell groups. The resonant cell groups may include a plurality of resonant cells configured as a partitioned resonant cell that include a converging resonant cell and a diverging resonant cell. The converging resonant cell and the diverging resonant cell may be defined by a plurality of cell walls integrally formed with one another and a partition integrally formed with the plurality of cell walls. The partition may at least partially delimit the converging resonant cell from the diverging resonant cell. The converging resonant cell may define an upper resonant space delimited by the partition and a top face of the array of resonant cells. The diverging resonant cell may define a lower resonant space delimited by the partition and a bottom face of the array of resonant cells.

Abstract: A turbomachinery engine includes an unducted rotor assembly, a low-pressure turbine, a low-pressure shaft, a gearbox, and an engine correlation parameter. The unducted rotor assembly includes a plurality of rotor blades arranged in a single row and defining a blade diameter. The gearbox includes an input, an output, and a gear ratio. The input of the gearbox is coupled to the low-pressure shaft (which is coupled to the LPT), and the output of the gearbox is coupled to the unducted rotor assembly. The engine correlation parameter is greater than 0.17 and less than 0.83. The engine correlation parameter equals D/N/GR, where D is the blade tip diameter measured in feet, N is the stage count of the low-pressure turbine, and GR is the gear ratio of the gearbox. The unducted propulsor assembly optionally includes a disk loading within a range of 60-180 HP/ft2 at a takeoff flight condition.

Abstract: An acoustic core includes an array of resonant cells. The array may include a plurality of coupled resonant cells respectively defining an antecedent resonant space and a subsequent resonant space, with at least one cell wall having one or more wall-apertures defining a pathway between the antecedent resonant space and the subsequent resonant space. The array may include a plurality of high-frequency resonant cells respectively defining a high-frequency resonant space and being matched with respective ones of the plurality of coupled resonant cells. A cross-sectional dimension of the one or more wall-apertures defining the pathway between the antecedent resonant space and the subsequent resonant space may be less than a cross-sectional dimension of the antecedent resonant space and/or a cross-sectional dimension of the subsequent resonant space.

Abstract: An acoustic liner (20) with perforation (30) and method of constructing (100) an acoustic liner including forming perforations in the facing sheet by grit blasting (104) the facing sheet and mounting (106) the facing sheet to one side of a support layer having a set of partitioned cavities wherein the facing sheet closes an open face of the cavities except for the perforations to form a set of acoustic resonator cells.

Abstract: An acoustic liner for a turbine engine, the acoustic liner includes a support layer that includes a set of partitioned cavities with open faces, a facing sheet operably coupled to the support layer such that the facing sheet overlies and closes the open faces, a set of perforations located in the facing sheet and in fluid communication with a corresponding one of the cavities to form a set of acoustic resonators, and at least a subset of the perforations have an axially-oriented, relative to the axial flow path, inlet.

Abstract: An acoustic liner for a turbine engine, the acoustic liner includes a support layer that includes a set of partitioned cavities with open faces, a perforated sheet that includes a set of perforations with corresponding inlets, the perforated sheet supported by the support layer such that perforations are in overlying relationship with the open faces to form paired perforations and cavities that define acoustic resonator cells, and a coating applied to the perforated sheet.

Abstract: An acoustic liner (20) with perforation (30) and method of constructing (100) an acoustic liner including forming perforations in the facing sheet by grit blasting (104) the facing sheet and mounting (106) the facing sheet to one side of a support layer having a set of partitioned cavities wherein the facing sheet closes an open face of the cavities except for the perforations to form a set of acoustic resonator cells.

Abstract: An acoustic liner for a turbine engine, the acoustic liner includes a support layer that includes a set of partitioned cavities with open faces, a perforated sheet that includes a set of perforations with corresponding inlets, the perforated sheet supported by the support layer such that perforations are in overlying relationship with the open faces to form paired perforations and cavities that define acoustic resonator cells, and a coating applied to the perforated sheet.