Reduction of supersonic jet noise using micro-jets in the diverging part of a conical CD-nozzle

Reducing the radiated noise from supersonic jets with maintained thrust is a major challenge. An LES/CAA method and experiments are uti- lized to investigate the flow field and the far-field acoustics of a supersonic jet emitted from a circular CD-nozzle with a sharp throat. Air is injected into the divergent section of the nozzle using 12 evenly distributed micro-jets around the nozzle circumference and the change in total thrust and acoustic signa- ture is investigated. The micro-jets are shown to decrease shock-strength with increased injection until an optimum point where further increase in injection mass flow caused increased shock-strength. As a consequence of the reduced shock strength, the far-field shock-noise was decreased. The net thrust was shown to increase with increased injection mass flow, whereas the specific thrust was slightly decreased. Micro-jet injection into the divergent section of a CD-nozzle appears, therefore, to be an effective configuration for reduced shock-noise radiation from supersonic jets