AEROACOUSTIC CHARACTERISTICS OF A RECTANGULAR MULTIELEMENT SUPERSONICJET MIXER-EJECTOR NOZZLE

This paper provides a unique, detailed evaluation of the acoustics and aerodynamics of a rectangular multi-element supersonic jet mixer-ejec tor noise suppressor. The performance of such mixer-ejectors is import ant in aircraft engine applications for noise suppression and thrust a ugmentation. In contrast to most prior experimental studies on ejector s that reported either aerodynamic oi acoustic data, the present work documents both types of data. Information on the mixing, pumping, ejec tor wall pressure distribution, thrust augmentation and noise suppress ion characteristics of four simple, multi-element, jet mixer-ejector c onfigurations is presented. The four configurations included the effec t of ejector area ratio (AR = ejector cross-sectional area/total prima ry nozzle area) and the effect of non-parallel ejector walls. The conf iguration that produced the best noise suppression characteristics has also been studied in detail. The present results show that ejector co nfigurations that produced the maximum pumping (secondary (induced) fl ow normalized by the primary flow) also exhibited the lowest wall pres sures in the inlet region, and the maximum thrust augmentation. When c ases having the same total mass flow were compared, one found that noi se suppression trends corresponded with those for pumping (per unit se condary area). Surprisingly, the mixing (quantified by the peak Mach n umber, and flow uniformity) at the ejector exit exhibited no relations hip to the noise suppression at moderate primary jet fully expanded M- j (the Mach number that would have been attained under isentropic expa nsion). However, the noise suppression dependence on the mixing was ap parent at M-j = 1.6. The above observations are justified by noting th at the mixing at the ejector exit is not a strong factor in determinin g the radiated noise when noise produced internal to the ejector domin ates the noise field outside the ejector. (C) 1997 Academic Press Limi ted.