Book Description

The subject research program sought to explore a novel method for achieving passive flow field control, with applications to mixing enhancement and noise reduction, through the interaction of the flow with flexible filaments. The filament was attached to a jet centerline where it was allowed to interact with and modify the large-scale structures in the flow. This flow control resulted in improved mixing, lower noise, and a more stable flow. The filament was shown to be particularly effective in suppressing screech in underexpanded supersonic jets. The study was successful in identifying an optimal filament configuration, which was used to obtain attenuation levels as high as 32dB. An investigation of temperature effects indicated that the filament performance was actually enhanced with moderate temperature increase. Sound field mappings revealed that the filament created dramatic changes in the sound field. Finally, flow field analysis of the supersonic jet revealed that the filament was successful in extensively modifying the structures in the exhaust plume, which can provide a physical explanation for the measured noise reduction. The researchers feel that this program was successful, as the results prove that the filament effectively attenuated jet noise in both supersonic and subsonic flows.