Perturbation solution for jet noise reduction via an air–water curtain

The attenuation of jet-generated noise through multiphase curtains offers a promising passive mitigation strategy. This study develops a perturbation-based framework to quantify the interaction of acoustic waves with an air–water droplet curtain placed around a jet. Starting from the volume-averaged multiphase equations, linearized perturbation solutions are derived for two configurations: (i) suspended droplets in quiescent air and (ii) dispersed droplets subjected to the influence of ambient flow. For the suspended case, both asymptotic and numerical solutions are obtained, showing that attenuation increases with droplet volume fraction and that there exists an optimal droplet to jet nozzle diameter ratio for maximum reduction. Comparisons with previous experimental data confirm the ability of the model to capture frequency-dependent absorption trends. The dispersed case reveals that interphase slip reduces peak attenuation and shifts it toward higher frequencies. Parametric studies highlight the roles of volume fractions, Strouhal number, droplet size, and slip velocity in the regulation of attenuation. The results demonstrate that a curtain on the order of one jet nozzle diameter can provide significant noise reduction without affecting thrust.