This paper proposes a variable nozzle that reduces the jet mixing noise of supersonic aircraft. The proposed variable nozzle uses divergent flaps and provides jet noise reduction and nozzle exit area setting in one mechanism. In the take-off condition, the nozzle has a lobe shape separated by triangular teeth in order to enhance mixing in the mixing layer without additional devices. On the other hand, in supersonic cruise, the nozzle forms a conventional convergent-divergent shape in order to reduce thrust loss. Scale model tests in a jet noise test facility and a model engine test were performed to examine the potential of the concept It was found that the proposed nozzle led to an acoustic benefit of 1.7 dB in the side direction and 2.4 dB downstream in terms of overall sound pressure levels in the model engine test Results suggest that the proposed nozzle has the potential to provide acoustic benefits relative to the thrust loss. It was also found that the relation between nozzle geometry and the spectrum of the proposed nozzle is similar to that of a chevron nozzle; therefore, similar design parameters are anticipated.
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