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 xed-cycle concepts with potential for quiet takeoff and ef 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 con 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- eld sound.Flyoverperceived noise levels are estimated for a twin-engine 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 con guration. Spectral- and time-domainanalyses indicate that the eccentric exhaust is free of strongMachwave radiation.The acousticbene t of the eccentric arrangement, combined with faster climb afforded by the modi ed engine, leads to a reduction of 14 dB in EPNL. Compared to the baseline engine, the speci c fuel consumption of the modi ed engine is about 13 % less at subsonic climb and 3 % less at supersonic cruise. Nomenclature D = diameter