Noise Reduction in Supersonic Jets Exhausting over a Simulated Aircraft Carrier Deck

An innovative noise reduction method for supersonic exhaust jets was studied in a model-scale aircraft carrier environment. Acoustic measurements of model exhaust jets with (and without) distributed blowing, producing "fluidic inserts," were performed. The model carrier environment consisted of a ground plane of adjustable distance below the jet, and a simulated jet blast deflector similar to those found in practice. The noise reduction of fluidic insert jets, above a ground plane, with steering of the "quiet planes" was examined with heat-simulated jets using near-and far-field pressure measurements. For jets exhausting over a ground plane, the fluidic inserts reduced the overall sound pressure level by 3-5 dB in the direction of maximum noise radiation. Upstream and sideline angles showed very little or no increase in sound level. Jets impinging on a modeled jet blast deflector were tested in addition to jets solely in the presence of a ground plane. The deflector resulted in downstream acoustic shielding and an increase in low-frequency noise. The region of maximum noise radiation for heat-simulated jets from nozzles with fluidic inserts impinging on the jet blast deflector was reduced in level by 4-7 dB. This region includes areas where carrier personnel are located.