AIRCRAFT ENGINE NOISE SUPPRESSION

• US 3,710,890 A
• Filed: 09/27/1971
• Issued: 01/16/1973
• Est. Priority Date: 09/27/1971
• Status: Expired due to Term

• Current Assignee: Harold C. True, Richard D. Fitzsimmons
• Original Assignee: Harold C. True, Richard D. Fitzsimmons
• Inventors: True, Harold C., Fitzsimmons, Richard D.
• Primary Examiner(s): Wilkinson, Richard B.
• Assistant Examiner(s): Gonzales, John F.
• Application Number:
  US05/184,137
• Time in Patent Office: 477 Days
• Field of Search: 181/33HB,33HC,33HD 239/265.13,265.17,265.19,265.23 60/262,264
• US Class Current: 181/215
• CPC Class Codes: F02K 1/36 having an ejector
• CPC Class Codes: F02K 1/386 mixing devices in the jet pipe, e.g. for mixing primary and secondary flow

Abstract

An exhaust nozzle noise suppression apparatus adapted for attachment to existing aircraft jet engines. The exhaust flow is directed by a centerbody plug into the inside of a series at least 20 corrugated lobes spaced around the existing exhaust passageway. An ejector shroud is closely spaced around the lobes to entrain large quantities of ambient air along the outside of the lobes by ejector action to increase the mass flow within the shroud while decreasing the velocity of the exhaust gases. The decreased velocity results in substantially attenuated jet noise levels. Total thrust output is maintained despite the decreased velocity because of the increased mass flow. Preferred embodiments utilize a centerbody valve means for either forcing all flow outwardly through the lobes for sound suppression or allowing flow through the center of the lobe array for cruise flight.

Claims

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.