Active control of noise from hot, supersonic turbulent jets

We report on an experimental and reduced-order modeling study aimed at reducing mixing noise in hot supersonic jets relevant to military aircraft. A spinning valve is used to modulate four injection nozzles near the main jet nozzle lip over a range of frequencies and mass flow rates. Diagnostics include near-, mid-, and far-field microphone arrays aimed at measuring the effect of actuation on the near-field turbulent wavepacket structures and their correlation with mixing noise. The actuators provide more than 4 dB noise reduction at peak frequencies in the aft arc, and up to 2 dB reduction in OASPL. Experiments are performed to contrast the performance of steady and unsteady blowing with different amplitudes. The results to date suggest that the noise reduction is primarily associated with attenuated wave packet activity associated with the rapidly thickened shear layers that occur with both steady and unsteady blowing. Mean flow surveys are also preformed and serve as inputs to reduced-order models for the wave packets based on parabolized stability equations. These models are in turn used to corroborate the experimental evidence suggesting mechanisms of noise suppression in the actuated flow