Abstract: In accordance with the present invention, an aircraft engine is provided with a component which helps reduce the noise generated by the engine. The component has a first aerodynamic surface, a second aerodynamic surface, and a system for reducing noise without altering a pressure differential between the first aerodynamic surface and the second aerodynamic surface.

Abstract: The present invention relates to a gas turbine engine exhaust nozzle for suppressing jet noise. The nozzle has an arrangement of tabs that extend in radially inward and outward directions. The tabs cause the formation of vortices which pull into mixing engagement the exhaust gas streams from the core and fan ducts and the ambient air. In addition, various construction details are developed for the tab arrangement including tabs that are directed radially inwardly and outwardly, and tabs that are continuous with the nozzle duct therebetween.

Abstract: The blades (38) of a gas turbine engine fan rotor (32) are uniquely distributed in the rotor hub (48) so that combination tone noise attributable to one or more physical nonuniformities in the blades is mitigated. The invention recognizes that the frequency spectrum of the combination tone noise includes both decay prone harmonics and decay resistant harmonics and that allocation of acoustic energy into the decay prone harmonics and out of the decay resistant harmonics is effective for mitigating combination tone noise. In particular, the blades are distributed so that the spatial or circumferential spectrum of the physical nonuniformity is dominated by circumferential harmonics whose order is no greater than the order of the highest decay prone harmonic of the combination tone noise spectrum.

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.