Low-frequency sound absorptive properties of dual perforated plates under bias flow

Abstract

The low-frequency sound absorptive properties of dual perforated plates with fixed cavity lengths under bias flow is investigated in this paper. The modulus and phase of the reflection coefficient are predicted by the Luong model in the wide range of Strouhal number (0.01–12). The high-pressure amplitude effect is described by the Impedance Describing Function (IDF) nonlinear model. The porosity of the plate varies from 0.15 to 1.23%. The frequency range is 40–400 Hz. The bias flow greatly influences the sound absorptive performance of dual perforated plates both in the linear and nonlinear regime. The comparison between model predictions and measurements show a good agreement. The matching between the bias flow velocity of two plates is the key parameter to determine the sound absorptive performance of dual perforated plates configuration under bias flow. To extend the low-frequency absorption capability by dual perforated plates configuration when lower porosity plate installed with short cavity length, the ratio limit between the two bias flow velocities is given by 0.25–4. Beyond the limitation, the dual perforated plates only work on each absorption frequency with each cavity length. The expressions derived in this study can be used to improve the design of dual perforated plates acoustic dampers.