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