Shock-Cell Structure and Associated Broadband Noise in Supersonic Dual-Stream Jets

Broadband shock-associated noise (BBSAN) in supersonic dual-stream jets was investigated, with emphasis on the role of interstream shock-cell interactions in shaping the acoustic response. A coannular dual-stream nozzle was designed and tested over a range of nozzle pressure ratios. Steady Reynolds-averaged Navier–Stokes simulations, validated by background-oriented schlieren imaging, were used to characterize the shock-cell structure of the coupled jet system, demonstrating that the two supersonic streams merged shortly downstream of the nozzle exit into a single, internally complex shock-cell system. Far-field acoustic measurements revealed rich spectral behavior, with BBSAN dominating the high-frequency range. Multiple broadband spectral humps were consistently identified. These humps were shown to arise from the coupled shock-cell system by relating the measured peak frequencies to the spatial wave numbers of the shock-cell patterns extracted from the flowfield. The results demonstrate that simplified descriptions of BBSAN based on independent shock structures are generally inadequate for dual-stream jets. Instead, the findings highlight that the essential physics of BBSAN generation in such configurations is governed by the coupled shock-cell organization of the flow, which must be accurately captured to interpret and predict the observed acoustic behavior.