Aircraft engine noise suppression

Claim 2

Noise suppression apparatus for use in combination with an aircraft engine exhaust passageway comprising: at least 20 generally rectangular corrugated lobes, each having the same average width W and spaced in a uniform array around said exhaust passageway such that the same pitch distance P exists between adjacent lobe centerlines, said distance P being at least 2W but less than 4W; centrally located means for directing the exhaust gas flow outwardly through said lobes; an ejector shroud means surrounding said lobes at the lobe exit plane and spaced outwardly from the outer surfaces of said lobes by a distance S which is greater than W/4 but less than 3W; secondary air passageway means located at the forward end of said shroud means for inducing flow of ambient secondary air along the outside of said lobes; said shroud means extending from said lobe exit plane longitudinally aft a distance L2 at least 10P to a shroud exit plane defined by the aft end of said shroud means; wherein the exhaust gases exiting from said lobes creates pressures acting to entrain secondary air along the outeR surfaces of said lobes to increase the mass flow within said shroud means while reducing the velocity of said exhaust gases.

Claim 3

The apparatus of claim 1 wherein said centrally located means is provided with a valve means for optionally either blocking flow through the center of the lobe array thereby forcing all flow outwardly through the lobes for sound suppression, or allowing flow through the center of the lobe array for increased efficiency during cruise flight.

Claim 4

The apparatus of claim 1 wherein the inside of said ejector shroud means is lined with an acoustic material substantially along its length for attenuation of high frequency sound associated with the mixing of said exhaust gases and said ambient secondary air.

Claim 5

The apparatus of claim 3 wherein said ejector shroud means comprises forward and aft shroud portions divided by slot means for entraining ambient air for boundary layer control and cooling along the inside surface of said aft shroud portion.

Claim 6

The apparatus of claim 1 wherein said centrally located means comprises an aft surface having a recess therein to create an aerodynamic flow patterns simulating those associated with a boattail fairing.

Claim 7

The apparatus of claim 2 wherein said secondary air passageway means includes blow-in doors opened by negative pressures acting on the inside of said doors.

Claim 8

The apparatus of claim 6 wherein said corrugated lobes are arranged around said valve means in an annular array and said shroud means defines a cylindrical section at said shroud exit plane.

Claim 9

The apparatus of claim 6 wherein said valve means is generally rectangular in shape and said corrugated lobes are arranged on opposite sides of said valve means, and wherein said shroud means define a generally rectangular shape at said shroud exit plane.

Claim 10

The apparatus of claim 8 wherein said engine exhaust passageway comprises bifurcated duct means for conveying fan air from a forwardly positioned fan to positions located adjacent to opposite sides of said generally rectangular shape at said shroud exit plane while keeping said fan air isolated from said corrugated lobes and said valve means.

Claim 11

Noise suppression apparatus for use in combination with an aircraft engine circular exhaust passageway comprising: an annular array of at least 20 generally rectangular corrugated fluted lobes closely surrounding and communicating with said circular exhaust passageway; each of said lobes having an average width W, a height H of at least 4W, a longitudinal length L1 of at least 1.5H extending to a common lobe exit plane, and being spaced apart a pitch distance P having a value less than 4W measured circumferentially between adjacent lobe centerlines; centrally located means for directing all of the exhaust gas flow outwardly from said circular exhaust passageway into the inside of said lobes for discharge at said lobe exit plane, said centrally located means including valve means for optionally allowing flow straight through the center of said annular array for improved efficiency during cruise flight; a shroud means closely surrounding said lobe array and radially spaced apart from the outer surfaces of said lobes by a distance S having a value less than 3W; and a secondary air passageway means located at the forward end of said shroud means; wherein in a sound suppression mode of operation said valve means directs exhaust gas flow outwardly through said lobe array to thereby induce flow from said secondary air passageway means for mixing with said exhaust gases within said shroud means to increase the mass flow through said shroud.

Claim 12

Noise suppression apparatus for use in combination with an aircraft engine circular exhaust passageway comprising: an annular array of at least 20 generally rectangular corrugated fluted lobes closely surrounding and communicating with said circular exhaust passageway; each of said lobes having an average width W, a height H of at least 4W, a longitudinal length L1 of at least 1.5H extending to a common lobe exit plane, and being spaced apart a pitch distance P having a value less than 4W measured circumferentially between adjacent lobe centerlines; centrally located means for directing all of the exhaust gas flow outwardly from said circular exhaust passageway into the inside of said lobes for discharge at said lobe exit plane, said centrally located means including valve means for optionally allowing flow straight through the center of said annular array for improved efficiency during cruise flight; a shroud means closely surrounding said lobe array and radially spaced apart from the outer surfaces of said lobes by a distance S having a value less than 3W; and a secondary air passageway means located at the forward end of said shroud means; wherein in a sound suppression mode of operation said valve means directs exhaust gas flow outwardly through said lobe array to thereby induce flow from said secondary air passageway means for mixing with said exhaust gases within said shroud means to increase the mass flow through said shroud.

Claim 13

The apparatus of claim 10 wherein said shroud means is radially spaced apart from the outer surfaces of said lobes by a distance S of at least W/4.

Claim 14

The apparatus of claim 11 wherein said forward end of said shroud means is located in close proximity to said lobe exit plane and extends longitudinally aft a distance L2 haviNg a value of at least 10P.

Claim 15

The apparatus of claim 12 wherein said shroud means is lined with an acoustic material for attenuation of noise associated with the mixing of said exhaust gases and said secondary air.

Claim 16

The apparatus of claim 13 wherein said secondary air passageway means includes blow-in doors actuated by differential pressures acting on said doors and said shroud means comprises forward and aft shroud portions divided by slot means for entraining ambient air for boundary layer control and cooling along the inside surface of said aft shroud portion.

Claim 17

The apparatus of claim 14 wherein said slot means comprises blow-in doors and said aft shroud comprises variable area nozzle means for improved engine efficiency throughout the flight regime.