Noise Source Characteristics of Supersonic Plug Nozzles

Plug nozzles have emerged as a promising alternative to traditional converging-diverging configurations for future commercial supersonic aircraft. However, the presence of an external plug can lead to new noise generation mechanisms that are not yet fully understood. In this study, we investigate the near-field acoustics of Mach 1.5 plug nozzles using high-fidelity large eddy simulations (LES). We employ two plug configurations consisting of 10-degree (P10) and 16-degree (P16) half-angle cones to support recent NASA experiments. The LES data is decomposed into its hydrodynamic and acoustic components using Doak’s momentum potential theory (MPT). Spectral proper orthogonal decomposition applied to the MPT-derived hydrodynamic and acoustic components reveals that the Kelvin–Helmholtz (K–H) instability in the jet shear layer is modulated by out-of-phase hydrodynamic structures arising from shock-induced flow separation on the plug surface. As a result, the amplitude of near-field acoustic wavepackets deviates from the traditional Gaussian envelope typically observed in turbulent compressible jets. These findings provide insight into the noise source characteristics of supersonic plug nozzles and serve as a foundation for developing targeted noise reduction strategies for future commercial supersonic transport.