Abstract
Acoustic shielding benefits for CTOL over-the-wing (OTW) applications were obtained experimentally with various multitube nozzles using a simple board to represent a wing. Six nozzles consisting of two to thirteen 0.93-in.-diam tubes were tested. Shielding surface lengths of 5.9 to 21.4 in. were used with each nozzle. In addition, the effect of spacing between tubes on jet noise shielding was studied using a six-tube nozzle. Farfield noise data were obtained at 90° from the jet axis and with a jet exhaust velocity of 660 ft/sec. The jet noise shielding benefits obtained with the various nozzle-surface configurations are discussed in terms of sound-pressure-level spectra. These data are then correlated in terms of a parameter that includes consideration of the number of tubes and the local peak velocity in the flow field near the trailing edge of the shielding surface. In addition, the sound-pressure-level amplification trends caused by jet-surface interaction noise at low frequencies are discussed for the various configurations.
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