Power plants – Reaction motor – Method of operation
Reexamination Certificate
2003-01-23
2004-09-07
Yu, Justine R. (Department: 3746)
Power plants
Reaction motor
Method of operation
C060S262000, C060S770000, C279S110000, C181S206000
Reexamination Certificate
active
06786037
ABSTRACT:
FIELD OF THE INVENTION
Jet engines can produce a high noise level if the velocity of the mass flow exiting the engine is non-uniform and high. For performance considerations, jet engines often have multiple nozzles with the mass flow exiting each nozzle at a different velocity. Since noise radiating from a jet's exhaust increases with the intensity and non-uniformity of the exhaust velocity, jet noise reduction concepts have historically focused on methods for rapidly mixing the flows and achieving a uniform velocity within a short distance of the nozzles.
BACKGROUND OF THE INVENTION
Various flow-mixing devices have been employed in the past to achieve a uniform velocity within a jet's exhaust and to reduce the noise radiated from the exhaust flow. While those devices have been successful at reducing jet noise, the thrust, drag, and weight penalty associated with those devices have often been of a magnitude that the noise at constant aircraft performance has not been reduced. During the NASA Advanced Subsonic Transport (AST) Program (reference
1
) sharp pointed, triangular shaped, extensions added to the sleeve of an external plug primary nozzle were tested and were found to reduce jet noise. A. D. Young et al (U.S. Pat. No. 3,153,319, reference
2
) also developed extensions that when added to the trailing edge of nozzles reduced jet noise. Brausch et al. (U.S. Pat. 6,360,528 B1 shows nozzle extensions having a planform with semi-round intersections with the baseline nozzle and semi-round trailing edges.
The primary difference between the above-described prior art and the hereinafter described, invention is the rounding of the upstream intersection of the extensions with the nozzle and the rounding of the extension's trailing edge with differing root radii and tip radii. Rounding has as hereinafter described been found to enhance the reduction of low and mid-frequency noise (frequencies below 2000 Hz) by inhibiting an increase in high (frequencies above 2000 Hz) frequency noise and to reduce the thrust loss of sharp-pointed segmented nozzles. Increased high frequency noise has been a characteristic of the previous sharp edged devices even though they have reduced low and mid-frequency noise and have had a net acoustic benefit.
REFERENCES:
patent: 4311291 (1982-01-01), Gilbertson et al.
patent: 4576002 (1986-03-01), Mavrocostas
patent: 5222359 (1993-06-01), Klees et al.
patent: 5771681 (1998-06-01), Rudolph
patent: 5924632 (1999-07-01), Seiner et al.
patent: 6082635 (2000-07-01), Seiner et al.
patent: 6360528 (2002-03-01), Brausch et al.
Belena John F.
Gardner Conrad O.
The Boeing Company
Yu Justine R.
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