Ducted fan engine exhaust mixer

#My invention relates to improvements in exhaust systems for engines of the turbofan or bypass type in which a gas turbine engine drives a fan which propels a substantial volume of air past the turbine engine and in which the exhaust from the turbine and the air flowing through the bypass duct are mixed and supplied to a common propulsive jet nozzle.

#It is desirable for maximum efficiency of such engines to accomplish efficiently thorough mixing of the turbine exhaust and bypass flow upstream of the jet nozzle. Various types of mixers for this purpose have been proposed, one being described and claimed in my U.S. Pat. No. 3,273,345 issued Sept. 20, 1966.

#It may be desirable in turbojet engines of any type, including turbofan engines, to minimize infrared radiation from the hot parts of the turbine through the propulsive nozzle. The reasons for this, and one arrangement for accomplishing such a result, are explained in Smale U.S. Pat. No. 3,210,934, issued Oct. 12, 1965.

#Referring to the drawings, FIG. 1 is a schematic illustration of a typical turbofan engine incorporating a mixer according to my invention.

#FIG. 2 is an enlarged sectional view of the mixer structure taken on a plane containing the axis of the engine.

#FIG. 3 is a partial transverse sectional view of the same taken on the plane indicated by the line 3--3 in FIG. 2.

#Referring first to FIG. 1, a jet propulsion engine 2 of the turbofan type includes an outer case 3 defining, sequentially from the air inlet 4 of the engine, the case 6 of a fan, the outer wall 7 of a bypass duct 8, and the wall 10 of an engine outlet type or tailpipe. The tailpipe terminates in a propulsion nozzle 11 which ordinarily is of a variable convergent or convergent-divergent type. A double inner wall structure 12 defines the inner boundary of the bypass duct 8 and the outer case of a gas turbine. Air flows from the air inlet 4 to the gas turbine through a fan 14, a compressor 15, combustion apparatus 16, and an axial-flow turbine 18. It is to be understood, of course, that the compressors and turbine may involve separate rotating members, the engine then being of a two- or three-spool type. Such matters are immaterial to my invention.

#The exhaust gases from the turbine 18 and the air flowing through duct 8 are mixed prior to flow through the tailpipe 10 and the propulsion nozzle 11. A burner to heat the air in duct 8 might be provided, and an afterburner might be provided in the tailpipe 10. These also are immaterial to my invention.

#Referring to FIG. 2, the final stage 19 of the turbine is shown as embodying a rotor structure 20 mounted in a bearing 22 supported from the wall 12 by a plural number of radiating struts 23. Six struts are preferred in this embodiment.