Acoustic impedance of rectangular panels

The modal radiation impedance of a rectangular panel simply supported in an infinite baffle in the presence of an inviscid, uniform, subsonic flow is determined. The analysis is based on an expansion in normal modes of the transverse vibration displacement field of the panel and the use of wavenumber-frequency transforms. Integral expressions for the modal radiation impedance and the cross-modal coupling impedance are formulated. A Gaussian quadrature with reusable abscissas is developed to evaluate these modal radiation impedances. Changes with respect to flow speed in modal radiation damping of a rectangular membrane are measured. For the first observable low order mode the change is significant and agrees with the theory. For higher order modes non-significant changes are predicted and measured. The computed modal radiation reactances of the membrane are compared with the best available experiments. Significant discrepancies exist. Their causes are discussed.