Abstract: A nacelle inlet may comprise an aft bulkhead, an attachment ring extending in an aft direction from the aft bulkhead, an acoustic liner disposed radially inward from the attachment ring, the acoustic liner comprising a proximal skin, a distal skin, and a core disposed between the proximal skin and the distal skin, and a shroud extending longitudinally between a forward side of the shroud and an aft side of the shroud and extending circumferentially between a first end of the shroud and a second end of the shroud, wherein the shroud defines a plenum disposed between the acoustic liner and the shroud, the plenum is in fluid communication with the core via perforations in the distal skin. The plenum may serve to attenuate low frequency noise known as “buzz saw” tones and/or alleviate pressure resonance conditions that may cause structural damage to the engine fan blades.

Abstract: A sound attenuation device includes an acoustic panel having a first end and a second end spaced from the first end. The first end is configured for attachment to a first mount and the second end is configured for attachment to a second mount. The acoustic panel comprises a permeable skin and a septum, the septum having a length extending between the first end and the second end.

Abstract: A nacelle inlet may comprise an aft bulkhead, an attachment ring extending in an aft direction from the aft bulkhead, an acoustic liner disposed radially inward from the attachment ring, the acoustic liner comprising a proximal skin, a distal skin, and a core disposed between the proximal skin and the distal skin, and a shroud extending longitudinally between a forward side of the shroud and an aft side of the shroud and extending circumferentially between a first end of the shroud and a second end of the shroud, wherein the shroud defines a plenum disposed between the acoustic liner and the shroud, the plenum is in fluid communication with the core via perforations in the distal skin. The plenum may serve to attenuate low frequency noise known as “buzz saw” tones and/or alleviate pressure resonance conditions that may cause structural damage to the engine fan blades.

Abstract: A sound attenuation device includes an acoustic panel having a first end and a second end spaced from the first end. The first end is configured for attachment to a first mount and the second end is configured for attachment to a second mount. The acoustic panel comprises a permeable skin and a septum, the septum having a length extending between the first end and the second end.

Abstract: A structural panel for an aircraft nacelle may comprise a core between a perforated skin and a septum. A plurality of dividing walls may extend between the septum and a backskin to define a plurality of cavities. Each cavity may be in fluid communication with a plurality of cells in the core through the septum. The cells and the cavities may attenuate noise.

Abstract: A sound-absorbing exhaust nozzle center plug for an aircraft gas turbine engine can include an outer skin and at least one forward cavity within the outer skin. At least one aft cavity can be located within the outer skin and substantially aft of the forward cavity. A perforated wall including a plurality of first openings can be disposed between the forward and aft cavities. The outer skin can include a second plurality of openings providing an acoustic pathway through the outer skin and into the forward cavity. The forward and aft cavities can be configured to absorb and dissipate relatively low-frequency sound energy emitted from an aircraft gas turbine engine's combustor.