Further development of supersonic jet noise reduction using nozzle fluidic inserts

The noise produced in the jet plume of high performance military aircraft is of serious concern, particularly to the US Navy. Penn State is working on the development of a noise reduction method using fluidic inserts in the diverging section of the exhaust jet nozzle. Fluidic inserts are derived from the original hard-wall corrugation method. The goal of the fluidic insert method is to develop a practical active noise reduction technique for low bypass ratio turbofan engines that will not sacrifice engine performance. When activated, these fluidic inserts blow air into the divergent section of the converging-diverging nozzle. The concept is that the on-demand noise reduction would be turned off or modified for all flight regimes other than take-off. This method has successfully reduced noise in both the peak mixing noise and broadband shock associated noise in scale model studies, at Penn State and GE Aviation. This paper seeks to further the understanding of the fluidic insert flow field and noise reduction. Previously three fluidic corrugations, equally spaced around the nozzle with two or three fluidic inserts per corrugation, have been used to test this method. The experiments described here implement a strongly asymmetric geometry of fluidic corrugations with three injectors per corrugation. The azimuthally asymmetric nozzle geometry with two fluidic corrugations is derived from the three evenly spaced fluidic corrugations with one of the corrugations inactive. This is the first set of experiments using such strong azimuthal asymmetry with the goal of better understanding how azimuthal variations in sound level can be used beneficially in practical applications. This approach is in preparation for future asymmetric experiments with more complicated combinations of fluidic corrugations in larger scale experiments at GE Aviation.