Broadband noise reduction under grazing flow via coupled interference and resonance mechanisms

Achieving stable broadband noise reduction under grazing flow using a structurally simple configuration remains a challenge. To address this issue, a broadband noise control design based on the coupling of interference and resonance mechanisms is proposed. In this study, side branch ducts generate destructive interference, whereas internally extended neck resonators provide resonant damping. The acoustic behavior of the structure was elucidated through analysis of the flow field and phase distribution using the k-ε turbulence model and the linearized Navier-Stokes equations. An analytical model formulated using the transfer matrix method was developed and validated against numerical simulations and experimental measurements conducted in a custom-designed grazing flow duct facility. The results demonstrate that the broadband performance originates from the interaction between interference and resonance effects. Specifically, the side-branch ducts generate stable broadband destructive interference that remains robust under grazing flow, whereas the extended-neck resonators introduce resonant dissipation at discrete frequencies. Notably, at a grazing flow velocity of 60 m/s and a sound pressure level of 140 dB, noise reduction is maintained over the frequency range of 700-2000 Hz. The proposed strategy therefore provides a practical design framework for broadband flow-noise control, with potential for implementation in complex duct systems.