Abstract: A sound absorbing structure 38, 52 for a gas turbine engine 10 is disclosed. The sound absorbing structure 52 includes a wall element 54 and a casing 34 of the engine or nacelle 12. The casing is spaced from the wall element leaving a cavity 62 therebetween which is compartmentalized by partitions 64, 66. In one embodiment the partitions are attached to either the wall element or the casing element. In another embodiment the partitions are all attached to the wall element and spaced from the casing element or are all attached to the casing element and spaced from the wall element. In another embodiment the partitions are alternately spaced from the casing element and the wall element such that every other partition 64a is spaced from the wall and the remaining partitions 64b are spaced from the casing.

Abstract: A high efficiency broadband acoustic resonator and absorption panel used for reducing engine noise from high bypass fan jet engines mounted on an aircraft. The panel uses a single layer of cellular honeycomb core with a pair of parallel acoustic septums formed internally in the core for attenuating high and medium frequency sounds during all engine operations as well as the low frequency combination tone and "buzzsaw" noise experienced during high power aircraft takeoff and cutback engine power settings.

Abstract: An acoustic noise elimination assembly having a capability for disrupting the continuity of fields of sound pressures forwardly projected from fans or rotors of a type commonly found in the fan or compressor first stage for air-breathing engines, when operating at tip speeds in the supersonic range. The assembly incudes a tubular cowl 12 defining a duct for delivering an airstream axially into the intake for a jet engine E and a sound barrier 14, defined by a plurality of intersecting flat plates or struts 14a-14d having a line of intersection coincident with a longitudinal axis of the tubular cowl, which serves to disrupt the continuity of rotating fields of multiple pure tonal components of noise.

Abstract: Disclosed is a turbulence control structure for use during static noise testing of jet aircraft engines. A flow transparent substantially spherical geodesic dome defined by a modified 9-frequency icosahedral frame encloses the intake of a jet engine on a test stand. The surface of the dome is covered by flat flow panels constructed of aluminum honeycomb adhesively bonded to stainless steel perforated sheet. The combination of perforated sheet and honeycomb attenuate streamwise and transverse components of inflow distortions in the intake air entering the engine. As a result, clear inflow is achieved, engine speed is stabilized, and engine intake noise approximating that of in-flight operation are achieved.

Abstract: Combination bulk absorber-honeycomb acoustic panels particularly adapted for use in the inlet and fan air duct of a fan jet engine are disclosed. Each panel comprises a broadband noise-suppressing bulk absorber layer mounted between a back sheet and a perforated septum; and, a narrow band noise-suppressing honeycomb layer mounted between the septum and a perforated face sheet. The panels are mounted in an engine such that the perforated face sheet interfaces with airflow in the inlet or the fan air duct, as the case may be, whereby the face sheet, honeycomb layer and septum protect the bulk absorber from deterioration by isolating the high speed inlet and fan air duct airflows from the bulk absorber layer.

Abstract: An inlet for a gas turbine engine is disposed about a curved centerline for the purpose of accepting intake air that is flowing at an angle to engine centerline and progressively turning that intake airflow along a curved path into alignment with the engine. This curved inlet is intended for use in under-the-wing locations and similar regions where airflow direction is altered by aerodynamic characteristics of the airplane. By curving the inlet, aerodynamic loss and acoustic generation and emission are decreased.

Abstract: A noise-reducing jet engine air inlet duct contoured to control air flow such that sound waves (noise) propagating upstream from the engine toward the entryway of the air inlet duct are refracted to the duct wall and/or engine inlet centerbody is disclosed. The inlet duct wall and/or engine inlet centerbody are contoured to establish a cross-sectional duct region having substantial airflow velocity gradients in a direction transverse to the direction of the airflow. Starting at the inlet duct entryway, the contoured duct region includes a parallel or diverging section followed by a rapidly contracting section before a final diffusion section extending to the engine. The velocity gradients created in the region of the contracting section refract the sound waves toward the wall and/or engine centerbody of the air inlet duct.

Abstract: An inlet for a gas turbine engine is provided with a fixed geometry upstream lip defining the primary inlet flow passage, and a variable position downstream lip partially defining an efficient auxiliary fluid flow passage through the inlet. The upstream lip is sized to pass all of the engine flow requirements at a near-sonic average Mach number during engine approach operating conditions. Apparatus is provided to position the variable lip for modulating flow through the auxiliary passage during higher engine power settings.

Abstract: The inlet of a gas turbine is provided with a mechanism for varying the throat area which may be selectively adjusted to maintain the velocity of an incoming air stream at a high level during aircraft takeoff and climbout to thereby reduce forward propagated noise.