Search

The plug architecture replaces traditional solid exhaust plugs with an elongated design characterized by a hollow interior and a uniformly porous surface. By positioning the plug's crown inside the nozzle, the exhaust travels through a convergent passage up to the crown and a divergent passage past it. In standard solid plugs, shock waves become unsteady at off-design pressure ratios, causing severe acoustic resonance. The porous skin stabilizes localized flow separation and disrupts unsteady shock formation. By doing so, the technology alters complex aerodynamic interactions providing the noise reduction. Translation of the plug provides variable design condition without requiring heavy, maintenance-intensive mechanisms. Sub-scale acoustic testing demonstrates superior noise suppression without sacrificing aerodynamic efficiency. While existing aerodynamic treatments (such as tabs or boundary layer tripping) only mitigate screech or transonic tones, the porous plug represents a breakthrough by eliminating BBSN and EBBN as well as other aberrant noise. Additionally, thrust measurement data indicates this dramatic noise reduction is achieved with minimal impact on the gross thrust coefficient, preserving engine performance within <1% of conventional plugs. While NASA originally developed this porous plug nozzle to help next-generation commercial supersonic aircraft meet strict LTO noise regulations, the technology offers broader aerospace utility. The design can be implemented in high-speed military aircraft to mitigate operational acoustics, or integrated into aerospace inlets and internal ducts to suppress flow noise originating from center-bodies.