Investigation on noise and flow characteristics of supersonic dual-stream co-axial convergent-divergent jets

This paper investigates the aeroacoustic properties of dual-stream co-axial supersonic jets, focusing on sound generation at the engine nozzle exit, which significantly contributes to cabin noise in supersonic civil aviation. The study delves into three primary noise-generating mechanisms present in supersonic jets: broadband shock-associated noise, jet screech, and turbulent mixing noise. While single-stream jet studies are abundant, the understanding of these mechanisms in dual-stream configurations, particularly with co-axial convergent-divergent nozzles, is limited. A dual-jet nozzle was designed with the method of characteristics in combination with a RANS simulation. Background-oriented Schlieren imaging is used to provide insight into the typology of shock-cell structures at varying nozzle pressure ratios. Results showed that nozzle geometry and Mach number significantly influence shock wave generation and interaction mechanisms. Overexpanded and underexpanded conditions led to the emergence of shock-associated noise, while perfectly expanded conditions for the single-jet case exhibited dominance of turbulent mixing noise. Dual-stream configurations introduced additional complexities, such as shock reflections and interactions between primary and secondary streams. Acoustic measurements revealed distinct noise spectra patterns corresponding to different Mach numbers of primary and secondary streams. Tonal peaks were observed in underexpanded and overexpanded conditions, indicating resonant phenomena and shock-associated noise. This study provides a database of experimental data that can be used in the future to deepen our comprehension of the complex phenomena that underpin sound generation in dual-stream co-axial nozzles.