Method and apparatus for suppressing the noise of a fan-jet engine

Claim 1

In a jet propulsion plant having a fan-jet engine issuing fan air and exhaust gas separately, the combination comprising: a casing for said engine having a downstream and a tubular housing having a downstream end and disposed in spaced relation around the casing to form an annular passage therebetween, the downstream ends of said casing and housing being substantially in the same transverse plane and the fan air of said engine being discharged to the surrounding atmosphere from said annular passage, a lobed thrust nozzle mounted on said downstream end of said casing and extending rearwardly therefrom in coaxial relation therewith, said nozzle being corrugated to form internal lobes therein for the passage of the engine exhaust gas therethrough and into the surrounding atmosphere in separate streams spaced apart circumferentially of the downstream end of the nozzle, the external surface of the corrugated nozzle being exposed to the surrounding atmosphere and having valleys therein between said lobes, said lobes and said valleys extending axially of the nozzle, said valleys increasing in depth in the downstream direction and said lobes increasing in radial dimension in the downstream direction whereby a portion of said discharged fan air flows through said valleys and thence between said streams of exhaust gas.