Experimental investigations of perforated liners with bias flow

It has been found that the presence of a bias flow can enhance the low-frequency sound absorption of a perforated liner. Therefore it is important to understand the acoustic characteristics of a liner with bias flow for practical applications. This paper presents experimental investigations of the acoustic properties of a perforated liner with bias flow. First, the experimental results show that the presence of a bias flow markedly increases both the absorption coefficient and effective bandwidth of a perforated liner. Second, it is shown in the present experiment that plate thickness has a major influence on the acoustic properties of a liner with bias flow. A simple model is presented to consider this behavior; the model gives good agreement with the measured data. Considering that blowing and suction will have a different effect on the mean shear flow over the surface of a perforated liner, comparative experimental results between blowing and suction are also included in the present investigation. (C) 1999 Acoustical Society of America. [S0001-4966(99)04410-0].