Effect of plate thickness on impedance of perforated plates with bias flow

A numerical model is presented of the Rayleigh conductivity of a square-edged orifice in the presence of finite plate thickness and bias Row Particular attention is paid to the evaluation of the effect of finite plate thickness on its acoustic impedance. In the presence of bias Row, the acoustic impedance of a kind of perforated plate, which is constructed with square-edged orifices in a plate of finite thickness, is calculated from the Rayleigh conductivity on the assumption that the orifices are well separated. The numerical analysis shows that, although the acoustic resistance increases with the increasing bias flow speed on most occasions, it decreases in a certain range of low bias Row speed, and it can even decrease to negative values fur certain combinations of Strouhal number and plate thickness. When the bias flow speed is near zero, increasing plate thickness leads to an increase of the acoustic reactance. However, the acoustic reactance decreases as the bias flow speed is increasing. As a result, the effect of plate thickness on the acoustic reactance will disappear at high bias Row speed. Experimental data are also presented. Qualitatively, the experimental and theoretical results are in good agreement.