Power plants – Internal combustion engine with treatment or handling of... – Material from exhaust structure fed to engine intake
Reexamination Certificate
1999-06-16
2001-11-20
Freay, Charles G. (Department: 3746)
Power plants
Internal combustion engine with treatment or handling of...
Material from exhaust structure fed to engine intake
Reexamination Certificate
active
06318072
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for reducing noise generated by a supersonic jet.
2. Description of Related Art
For a supersonic jet airplane, the thrust force is generated by the reaction of the exhausting of supersonic jet issuing from supersonic jet engines. When a silencer is not provided to the jet engine installed on the supersonic jet airplane, there is fear that very high level noise, which is called screech tone, is generated outside a nozzle of the jet engine by a supersonic jet exhausted from the nozzle. The screech tone causes high level noise in an airport and its surrounding, and when a structure of the airplane is exposed to the strong screech tone for a long time, there is fear that metallic aircraft structure can be destroyed. As is known in the art, the screech tone is generated by a self-sustained oscillation of jets caused by a feedback loop consisting of downstream-convecting large scale coherent eddies around the supersonic jet and upstream-propagating acoustic waves in the ambient.
Recently, several investigations in reduction of supersonic jet noise have been carried out. As a result, it is known that providing small projection within nozzle exit of a jet engine is effective to reduce the screech tone. However, this apparatus for supersonic jet engine reduces the screech tone by merely regulating or fairing a supersonic jet flow utilizing the small projection at the exit of the supersonic jet nozzle, and therefore sufficiently noise reduction could not be obtained. Thus, inventors have studied to develop a new type apparatus for reducing the screech tone on the basis of the entirely different principle from the prior art.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a noise reduction apparatus which is capable to reduce a screech tone generated by a supersonic jet efficiently by means of a simple structure.
According to one aspect of the present invention, an apparatus for reducing a screech tone generated by a supersonic jet, comprises:
a cavity tone generator provided at a neighborhood of an outlet of a supersonic jet nozzle.
In the screech tone reducing apparatus according to the invention, said cavity tone generator is provided near the exit of the supersonic jet nozzle such that a supersonic jet is passed through the cavity tone generator, and therefore the cavity tone is generated from the cavity tone generator. By suitably designing a configuration and a size of the cavity tone generator, it is possible to generate the cavity tone which interferes with the screech tone. As the result, the undesired screech tone can be reduced efficiently. The inventors have conducted various experiments, and have found that in a whole supersonic region, sound pressure level of the screech tone can be reduced than that when a silencer is not provided on the supersonic jet nozzle.
In a preferable embodiment of the screech tone reducing apparatus according to the present invention, the cavity tone generator is a cavity formed in an inner wall of the nozzle exit, said cavity having a lateral cross-sectional shape similar to a lateral cross-sectional shape of the inner wall of the nozzle exit.
In this embodiment, the cavity tone generator is constructed by the cavity formed in the inner wall of the exit of the nozzle, and a cross-sectional shape of the cavity is similar to a cross-sectional shape of the exit of the nozzle.
According to the present invention, it is preferable that the cavity and the nozzle outlet are formed to have a rectangular lateral cross-sectional shape. Also in this case, the screech tone can be sufficiently reduced.
The present invention also relates to a supersonic jet nozzle for ejecting a supersonic jet.
According to the invention, a supersonic jet nozzle for ejecting a supersonic jet comprises:
a nozzle main body having formed therein a passage for ejecting a supersonic jet; and
a cavity tone generator composed of a cavity formed in an inner wall of the nozzle main body defining said passage.
REFERENCES:
patent: 4044203 (1977-08-01), Swinbanks
patent: 4494625 (1985-01-01), Mathes
patent: 5520459 (1996-05-01), Yu et al.
patent: 5530214 (1996-06-01), Morehead et al.
patent: 5821475 (1998-10-01), Morehead et al.
patent: A-49-97601 (1974-09-01), None
patent: A-51-126437 (1976-11-01), None
Ishii Ryuji
Umeda Yoshikuni
Freay Charles G.
Kyoto University
Oliff & Berridg,e PLC
Rodriguez W.
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