Thrust augmentation using mixer-ejector-diffuser systems

Abstract

Forced nlixers have been incorporated into ejector systems to provide short, cfficient devices for improved pumping aid noise suppression on jet engines and other power devices. Such ejector schemes provide a simple means of reducing jet noise by mixing high velocity primary flow with cool ambient air. Ideally, the lower mizd exhaust velocities provide a thrust gain while reducing jet noise. The thrust increase associated with such mixcr/cjector devices arc still well bclowthose associated with an ideal thrust augmentor. The maximum thrust of an ideal ejector is lower than that of an ideal augmentor primarily due to m i ~ g losses associated with the viscous energy transfer process. ‘This paper describes recent developments using mixcr/cjector/diffuser (MED) concepts which allow ejectors to become more competitive for thrust gencration. Analytical cal~vlations are presented which demonstrate that diffusers decrease mixing losses in ejectors, and can significantlyincrease the ideal ejector thrust augmentation. These same analyses demonstrate that such diffusers also decrease ejector mixing rates. Experimental results are presented which demonstrate that forced mixers can be uscd to overcome the slower ejector mixing rates associated with diffusers. Data is presented shwving that forced mixcr lobes, in wnibination with diffusers, can provide improved ejector thrust augmcntation. The diffuser reduces mixing losses while the forced mixcr lobes increase mixing rates. Resulting mixcr/ejector/diffuser (MED) systems can provide a compact exhaust device for noise suppression and/or thrust augmentation. .-i