A model of acoustic impedance of perforated plates with bias flow considering the interaction effect

A numerical model of the acoustic impedance of perforated plates under bias flow conditions was derived, with consideration given to the interaction effect between orifices. The normalized impedance divided by the mean flow Mach number of an orifice was expressed as a function of the Strouhal number varying the porosity and thickness-to-radius ratio. The prediction model was accomplished by solving the incompressible Euler equation for an orifice in a finite-thickness partition that spans a tube. The acoustic impedance was also measured experimentally using an error-controlled setup. As porosity increased, the reactance tended to decrease because the attached mass on the orifices is decreased by the interaction effect. The acoustic impedance predicted by the proposed model shows reasonable agreement with measured data over the wide range of porosity values tested, except where nonlinear effects are observed. For comparison of the performance of the new impedance model against two previous models that did not consider the interaction effect, each was used in the evaluation of the transmission loss of perforated baffles. The predicted transmission losses using the new impedance model agree better with the measured data than those using the previous models, in particular at high porosities and at high frequencies.