A Silencer for Jet Systems

1,193,372. Jet propulsion nozzles. SOC. NATIONALE D'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION. Jan. 17, 1968 [Jan. 18, 1967], No. 2637/68. Heading F1J. A silencer for a jet system, e.g. a propulsion nozzle, of the kind in which controllable elements distributed around the jet can be moved into a silencing position in which they project into the jet to produce undulations in the flow has secondary elements carried by at least some of the controllable elements so that when the latter are moved into the silencing position the secondary elements produce additional undulations in the flow between the undulations produced by consecutive controllable elements. The jet system comprises a primary hot gas duct 1 surrounded by a fairing 4 to form a secondary air duct 10. Hollow triangular section silencing elements 11 are pivotally mounted around the fairing 4 such that in the inoperative position they nestle within the hollow wall of the fairing. The elements 11 can be swung about generally longitudinal axes 11c into a silencing position in which each element 11 projects into the jet 3 leaving the primary duct 1 to produce an undulation 18 in the flow and assist mixing of the jet with the secondary air from duct 10. Mixing is further assisted by a stream of air 12 flowing through the interior of each element 11 into the jet 3. Additional undulations 18a in the flow are set up by plates 15 secured by flat bars 16, 17 to respective elements 11 so as to be movable therewith. In a modification, Figs. 5, 6(not shown), the additional undulations 18a are produced by fluid injectors (23) mounted on the elements 11 and supplied, in the case of a jet propulsion engine, with air from a compressor of the engine. An element 11 may carry both a plate 15 and fluid and a fluid injector (23).