超音速/極超音速エンジンの低騒音化技術(<特集>次世代航空機エンジンの基盤技術)

概要

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Noise reduction technologies for supersonic/hypersonic engines are reviewed. The new aircraft noise regulation (Annex 16 Volume 1 Chapter 4) of ICAO (International Civil Aviation Organization) came into effect in 2006, which requires 10 dB quieter takeoff and landing for civil aircrafts when compared with the previous Chapter 3. For subsonic aircrafts, jet noise reduction has been achieved by reducing their jet velocities, which is realized by high-bypass turbofan engines. On the contrary, for supersonic/hypersonic vehicles, which employ turbojet or low-bypass turbofan engines, this strategy is not available because of the increase in the frontal area and the decrease in the jet velocity. It is challenging to realize sufficiently quiet takeoff and landing without the penalty of the cruise velocity. In this review, several strategies for reducing the jet noise from supersonic/hypersonic engines, such as a mixer-ejector nozzle, an eccentric nozzle, a tabbed nozzle, and a nozzle with gas injection, are introduced. Still it seems to be difficult to meet the new strict regulation, and it is necessary to take into account not only the combination of these methods but also the optimization of the flight trajectory using noise prediction methods at early stage of the engine design.
2014-03-20