Low-frequency sound absorptive properties of double-layer perforated plate under grazing flow

The sound absorptive properties of double-layer perforated plate with large back-cavity depth under grazing flow are investigated in this paper. The specific resistance and reactance are measured in a flow duct using the straightforward method presented by Jing. Then the sound absorption coefficient is calculated using the results of measured impedance. The sound absorption coefficient is also predicted by a theoretical model, in which the impedance of the layer of perforated plate under grazing flow is estimated by an empirical model. The predicted results agree well with the measured results. The influences of flow speed and the parameters of double-layer perforated plate on the sound absorptive properties are also investigated. Most notably, an interesting phenomenon is revealed that different from the case without flow, the sound absorption performance of a perforated plate under grazing flow is insensitive to the aperture of perforation and plate thickness.