US 4,077,206 A · Gas turbine mixer apparatus for suppressing engine core noise and engine fan noise

Abstract

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.

Claims12

Dependent claims

In a gas turbine engine mixer including a plurality of axially extending circumferentially spaced lobes of increasing radial dimension relative to the longitudinal dimension of said mixer, wherein turbine exhaust gases flowing through the interior of said mixer are mixed with secondary gaseous flow passing along the exterior of said mixer to suppress jet noise, improved suppression means for at least partially dissipating the core noise energy contained within said turbine exhaust gases comprising:

first sound absorbing means for absorbing said core noise energy contained within said turbine exhaust gases, said first sound absorbing means axially mounted along the crest of each of said axially extending lobes, each of said axially extending lobes characterized in that the cross-sectional geometry of each lobe defines a convex exponential acoustic impedance matching horn, each of said convex acoustic impedance matching horns for matching the characteristic impedance of said first sound absorbing material to the characteristic impedance of the turbine exhaust flow containing said core noise energy, each of said convex exponential horns having a mouth region opening inwardly toward said flowing turbine exhaust gases and a throat region located radially outward of said mouth region, each of said convex exponential acoustic matching horns maximizing the outward radial transfer of core noise to said first sound absorbing material.

In a gas turbine engine having a rearwardly extending engine plug centrally located relative to the cross-sectional geometry of said gas turbine engine, a mixer assembly for mixing the turbine exhaust gases of said engine with a secondary gaseous flow of a lower temperature and velocity than that of said turbine exhaust gases, said mixer assembly comprising:

a generally tubular mixer section having a plurality of axially extending corrugations spaced about the cross-sectional periphery thereof, said corrugations of increasing radial dimension relative to the length of said mixer section, the cross-sectional area of each of said corrugations decreasing exponentially relative to the outward radial direction to impart a convex cross-sectional geometry to each of said corrugations, the outermost terminating portion of each of said corrugations being formed of a gas permeable sound absorbent material, said mixer section coaxially mounted about said engine plug for forming a generally annular flow duct between said engine plug and said mixer section for the flow of said turbine exhaust gases;
and
a generally circular exhaust duct, said exhaust duct coaxially mounted about said coaxially arranged mixer section and engine plug, said exhaust duct and said mixer section defining a generally annular flow duct for said secondary gaseous flow.

Dependencies are inferred from the claim text.

Gas turbine mixer apparatus for suppressing engine core noise and engine fan noise

Life of this patent

Gas turbine mixer apparatus for suppressing engine core noise and engine fan noise

Life of this patent

Abstract

Claims12