Conceptual Development of Quiet Turbofan Engines for Supersonic Aircraft

This is a joint thermodynamicand acoustic study of engines for next-generation supersonic aircraft. It explores Ž xed-cycle concepts with potential for quiet takeoff and efŽ cient cruise. The  owpath is simple, withoutmechanical suppressors.The strategy is to takearepresentative state-of-the-artmilitary turbofanengineandincrease its bypass ratio to a moderate value. The engine core stays the same. Three exhaust conŽ gurations are considered: mixed  ow, coaxial separate  ow, andeccentric separate  ow. Engine-cycleanalysispredicts thermodynamicperformance and nozzle exhaust conditions at takeoff and Mach 1.6 cruise. Subscale experiments duplicate the static exhaust conditionsat takeoff power andmeasure the far-Ž eld sound.Flyoverperceived noise levels are estimated for a twinengine aircraft in the 120,000-lbclass. In terms of effective perceived noise level (EPNL), the eccentric arrangement is 6.5 dB quieter than the mixed- ow arrangement and 5 dB quieter than the coaxial conŽ guration. Spectraland time-domainanalyses indicate that the eccentric exhaust is free of strongMachwave radiation.The acousticbeneŽ t of the eccentric arrangement, combined with faster climb afforded by the modiŽ ed engine, leads to a reduction of 14 dB in EPNL. Compared to the baseline engine, the speciŽ c fuel consumption of the modiŽ ed engine is about 13% less at subsonic climb and 3% less at supersonic cruise.