Acoustics and Flow Field of Slotted Air-Injection Nozzles

Abstract

Experiments investigating the noise and flow-field characteristics of dual-stream jets with fluidic injectors were performed. Air was delivered to the core stream of a bypass-ratio-five nozzle system via slots in the core-nozzle trailing edge. For dual-subsonic-stream jets, up to 3 dB noise reduction was achieved in the peak-jet-noise direction with an injection total pressure roughly equal to 1.5 times that of the core stream and an injection-to-core mass-flow ratio equal to 2.5%. Particle Image Velocimetry (PIV) studies showed fluidic injection reduced turbulent-kinetic-energy levels downstream of the pylon. Flow asymmetries introduced by the pylon were shown to impact streamwise development of vorticity generated by the injectors which limited the ability of the injectors to enhance jet mixing. For dual-transonic-stream jets, fluidic injection significantly reduced broadband-shock-associated noise but had limited impact on turbulent mixing noise. For single-supersonic-stream jets, fluidic injection reduced broadband-shock-associated noise and turbulent mixing noise over a range of frequencies in the peak-jet-noise direction.