Jet Noise Reduction by Notched Nozzle on Japanese ECO Engine Project

Abstract

J et noise r eduction capability of a new nozzle concept (hereinafter “Notched nozzle”) has been investigated thr ough feasibility studies such as small basic model testing in a static anechoic chamber , also anechoic wind tunnel testing using a subscale jet noise r ig of a high bypass engine. The paper dr aws these r esults as noise r esear ch fr om a pr oject for Resear ch and Development of Envir onmentally Compatible Engine for Small Air cr aft, which is named for ECO engine. The objective of investigations is to ver ify noise r eduction effects of the Notched nozzle, of which a plur ality of tr iangular pyr amid-shaped bodies along the tr ailing edge of the exhaust nozzle is positioned in a cir cumfer ential dir ection. By changing Reynolds str ess and tur bulence kinetic ener gy in the shear layer between exhaust jet and exter nal ambient air or mitigation of jet velocity by r apid mixing enhancement, noise r eduction char acter istics can be contr olled. Of the feasibility study with a single str eam basic configur ation, that how much notches contr ibute to changing physical phenomenon in jet str eam in other wor ds r educing far -field noise, ar e investigated for a number of diagnostic builds; a datum base nozzle, thr ee types of Notched nozzles in addition to a chevr on nozzle. Fr om the quantitative assessment of their r elative levels, useful r esults of notches for tr adeoff between low fr equency benefit and high fr equency noise disadvantage compar ing to the chevr on ar e obtained. It is also anticipated that putting notches even the ver y simple build will be possibly a pr omising design. Of the subscale jet noise r ig study with a double str eam configur ation, the Notched cor e nozzle is designed based on r esults fr om feasibility study together with CFD analysis. Far -fields noise measur ements ar e conducted by simulating exhaust nozzle conditions such as pr essur e and temper atur e of the ECO engine, exter nal flow Mach number dur ing air cr aft take-off. Fr om EPNL pr ojection based on far -field noise measur ements, the noise r eduction effects for the Notched nozzle compar ed to the base nozzle wer e 1.2 and 1 EPNdB at the later al and the flyover point r espectively, making a total of 2.2EPNdB dur ing take-off. Cur r ently fur ther investigations of the notch builds getting compar ative advantage to the chevr on ar e examined by the use of LES into the jet flow field or exper imentally.