Acoustics and Thrust of Quiet Separate-Flow High-Bypass-Ratio Nozzles

TheNASAGlennResearchCenterrecentlycompletedanexperimentalstudytoreducethejetnoisefrommodern turbofan engines. The study concentrated on exhaust nozzle designs for high-bypass-ratio engines. These designs modie ed the core and fan nozzles individually and simultaneously. In comparison with chevrons, tabs appeared to be an inefe cient method for reducing jet noise. Data trends show that interaction between fan e ow and the core cowl could strongly impact noise and cruise performance irrespective of the mixing device installed. The study demonstrates that modie cations of the core nozzle are generally more advantageous than of the fan nozzle. Even greater advantage in noise reduction and associated cruise thrust penalties is demonstrated through simultaneous modie cation of both nozzles. Thebestnozzledesign had a 0.06% cruisethrustlossand, corrected fortakeoff thrust loss, a 2.7-EPNdB reduction for the effective perceived noise level metric. This design simultaneously employed chevrons on the core and fan nozzles. Last, e ve nozzle cone gurations with cruise thrust loss of less than 0.5% and noise reductions of over 2.5 EPNdB are identie ed as candidates for full-scale engine and e ight demonstrations.