GB1207194A - Jet engines having means for reducing the noise level - Google Patents

Abstract

1,207,194. Jet propulsion nozzles. UNITED AIRCRAFT CORP. Dec.11, 1967 [Dec.28, 1966], No.56151/67. Heading F1J. A jet engine arranged for the suppression of jet sound comprises a pod or nacelle surrounding a duct for exhaust gas flow, flaps positioned to form a converging section adjacent the end of the duct, blow-in doors pivotally mounted at the end of the pod or nacelle to move inwardly, an annular body positioned rearwardly of the pod or nacelle with the inner surface of the body forming an inlet passageway with each blow-in door, and turbulenceinducing means to produce a shear layer surrounding the expanding exhaust flow. An engine having a primary flow between a wall 20, Fig.8, and a centre core 22 and a by-pass flow through an annular duct 6 extending rearwardly of a fan and bounded by walls 8, 13, comprises a circumferential series of pivoted doors 37 extending rearwardly from a pod or nacelle 35, pivoted flaps 41 extending rearwardly from an annular shroud 39, and the two clamshells 43 of a clamshell nozzle mounted within the shroud 39. The members 37, 41, 43 occupy the dotted position during supersonic flight and the full-line positions during subsonic flight. Flaps 33 are slidably mounted on a track mechanism 30 to provide a nozzle of variable convergency. The rear ends of the walls 13, 20 are connected by a flat annular base 28 which promotes a turbulent layer between the primary and by-pass flows, the turbulence being increased by directing gas through slots or holes 51a from an annular manifold 58 fed via a conduit 55 with gas under pressure, e.g. air from the engine compressor. A further turbulent region downstream of the doors 37 is induced by gas discharged from an annular manifold 57 through openings 59. The turbulent regions reduce noise during take-off. Each door 37 comprises a front section 37a pivoted to the pod or nacelle 35 and a rear section 37b hinged to the front section at 54, a roller 56 at the hinge travelling in a cam opening which is part of a linkage connecting the doors 37 and the clamshells 43. The clamshells may, however, be arranged to be movable independently of the doors 37. The engine may be of non-bypass form, with doors 44, Fig.3, extending rearwardly from a pod or nozzle around a jet duct 26 terminating in a nozzle formed by fixed or movable flaps 10. The doors 44 are shown in the inward position. Gas for promoting turbulence downstream of the doors 44 is discharged through a long narrow slot 66 or a line of holes formed in each of a number of manifold sections 62. The rear end of the duct 26 is of polygonal form with each side of the polygon having a mounting sleeve 60 containing one of the manifold sections 62. The manifold sections 62 can be pivoted in unison by the linkage shown to adjust the direction of discharge from the slot 66. In other constructions, the direction of discharge is fixed. The outside surface of the door 44 may be roughened to promote turbulence. The doors 44 and pivoted flaps (46), Fig .1 (not shown) extending rearwardly from an annular shroud (40) may be either power-actuated or freely floating.