Prediction, experiments and optimization of High-Speed jet noise reduction using fluidic inserts

This paper describes several components of a study examining noise reduction in high speed heated jets using fluidic inserts. This noise reduction technology is based on the ideas developed by Seiner and his colleagues at NASA Langley Research Center and the University of Mississippi¹. That approach was based on the introduction of corrugated seals into the diverging section of a convergent divergent nozzle. These corrugations change the effective area ratio so that the jet operates closer to an on-design condition and reduces broadband shock-associated noise. In addition, the corrugations generate streamwise vorticity that breaks up the large scale structures in the jet and reduces mixing noise. The idea behind fluidic inserts, described by Morris et al.² is to generate an equivalent effect with low levels of flow injection in the diverging section of the nozzle. This has the considerable advantage that the fluidic inserts can be controlled actively for maximum noise reduction and performance benefits. The present paper describes recent developments in the optimization of the fluidic insert concept. Flow and noise experiments, including the effect of forward flight are described. Numerical simulations are performed to characterize the flow features generated by the fluidic inserts as well as to develop measures of flow characteristics that can be related to the observed noise changes. These measures can be used to develop a cost function in a design optimization procedure.