This paper discusses a parametric study conducted of a variable folding nozzle concept that enables noise reduction and changing of the exit cross-sectional area with a single mechanism for supersonic aircraft. In the study, the effect of the nozzle exit shape, which is determined by the number of divergent flaps and length ratio of the folding edge to the total flap edge, was examined while the exit cross-sectional area was kept constant. Ten test nozzles with an equivalent diameter of 28.8 mm were manufactured by rapid prototyping, and response surface models for noise reduction were experimentally developed. It was found that increasing both the number of flaps and length ratio of the edges increased the noise reduction effect. In the best case, acoustic benefit in terms of an overall sound pressure level (OASPL) of approximately 1.8 dB for a polar angle between 90° and 140°, and 1.1 dB downstream was observed compared with an axisymmetric reference nozzle at a jet Mach number of 0.98. Numerical analyses supported the experimental results and suggest that the best shape can enhance the mixing performance of the jet without generating a high-turbulent kinetic energy region near the nozzle exit. In addition, the results of a demonstration conducted using the DGEN380 engine to confirm the feasibility of the proposed nozzle concept indicate that an acoustic benefit of approximately 1 dB in OASPL was achieved without significant thrust loss under experimental uncertainty.
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