Thrust nozzles are mounted in vertically stacked array on the aft end of an aircraft jet engine nacelle, and thrust reversing doors are mounted on opposite sides of the nozzles for movement between: (1) a stowed position adjacent to said nozzles; (2) a partially deployed position wherein the doors are translated rearwardly from their stowed position so as to deflect slipstream air against exhaust gas issuing from said nozzles; and (3) a fully deployed position wherein the doors abut downstream from the nozzles and deflect exhaust gas forwardly.
A sound suppression apparatus for a jet engine mounted in a nacelle wherein the exhaust nozzle duct comprises a variable ramp as the lower surface thereof and a pair of clamshell doors as the enclosure thereof. The clamshell doors are pivotally mounted about a longitudinal hinge on each side of the engine nacelle and when they are in the closed position, the interior surface of the duct, formed by the closed clamshell doors, conforms to the predetermined shape of the high speed cruise nozzle and externally, the shape of the doors conform to the configuration of the streamlined nacelle. When the clamshell doors are opened outwardly from the top, they form an upward opening exhaust nozzle with a pair of clamshell deflecting surfaces extending laterally outwardly and upwardly about the exhaust nozzle flow for the sound suppression mode of airplane operation during low speed flight of takeoff and landing.
A noise abating improvement for jet engines including the provision of apparatus in the primary flow stream of gas turbine engines such as turbojet, turbofan, turboprop, and other jet engines such as ram jets, scram jets and hybrid jet engines, or in either the primary and/or secondary flow streams of turbofan engines or the like, for imparting to the exhaust gases a component rotation or swirl about the engine's longitudinal axis. The rotary component in the exhaust gases has the effect of substantially suppressing the build up on sound energy normally produced by an axial flow exhaust system.
A low noise mixer apparatus for mixing the turbine exhaust effluent of a turbofan gas turbine engine with a portion of the air flowing from the engine fan stage prior to discharge from the engine is disclosed. The mixer is of the daisy variety, having a tubular mixer section that includes a number of axially extending, circumferentially spaced lobes with the tubular mixer section coaxially mounted around the engine plug. An outer duct coaxially surrounds the plug and mixer section. The turbine exhaust flows through an annular passage formed between the exterior surface of the plug and the interior wall of the mixer section and the fan air flows through an annular passage formed between the inner surface of the outer duct and the outer surface of the mixer section. As in previous daisy type mixers, the turbine exhaust and fan air are mixed as the two gaseous streams flow past the exit plane of the mixer section to thereby increase the thrust produced by the engine and also decrease the component of noise known as jet noise. To further reduce the overall engine noise level, the mixer of this invention includes a first acoustically absorbent material mounted along the crests of the axially extending mixer lobes and a second acoustically absorbent material axially mounted in the interlobal regions. The first acoustic material is selected to dissipate low frequency noise energy associated with the turbine exhaust gases (commonly called core noise) and the cross-sectional geometry of the mixer lobes are established to match the impedance of the first acoustically absorbent material to the characteristic impedance of the core noise traveling through the mixer. The second acoustically absorbent material is selected to dissipate the higher frequency noise associated with the flowing fan air. Advantageously, shaping the lobes for the impedance matching of the core noise to the impedance of the first acoustic material also tends to match the impedance of the second acoustic material to the impedance of the fan noise.
Noise perceived below a turbofan is reduced by providing a thicker fan flow below the turbofan primary exhaust flow than is present in conventional turbofans having generally circular and concentric fan and exhaust flows. To thicken the fan flow, the exhaust nozzle is offset upward in the fan nozzle, or the exhaust nozzle discharge end is canted to offset the exhaust flow upward, or the exhaust nozzle is flattened to a generally rectangular or an elliptical shape having a major horizontal axis. In any of these cases, the thickness of the fan flow below the primary exhaust flow is increased and less noise is perceived below the turbofan than if circular concentric fan and exhaust flows were produced. In one embodiment a noise-suppressing thickened fan flow is used in combination with a conventional noise-suppressing multilobe or multitube mixing nozzle to further reduce noise perceived below the turbofan.
A discharge nozzle of a jet engine has lobes, tubes or deflectors for promoting mixing of the engine discharge flow with ambient air to reduce jet noise. By providing the lobes, tubes or deflectors at only the upper portion of the discharge nozzle, jet noise perceived below the engine is reduced substantially without shifting the noise spectrum to include a higher proportion of piercing and irritating high frequency noise components. Additionally, in a turbofan, the fan or secondary flow is discharged below the primary exhaust flow to further reduce noise perceived below the turbofan.
