Experimental Study of the Impedance of Perforated Plates at High Sound Pressure Amplitudes and Grazing Flow

Abstract

In this investigation, the impedance of perforated plates subjected to a combination of high amplitude acoustic excitation and a grazing flow is studied experimentally. During the experimental program, the acoustic pressure amplitude is increased stepwise up to approximately 150 dB while the grazing flow speed is varied up to a maximum Mach number of 0.2. Dimensionless variables are used to correlate the change of impedance with the variation of the acoustic excitation amplitude and the grazing flow velocity. Results show that the acoustic excitation only has an effect on the impedance of the perforated plate if the root mean square amplitude of the particle velocity in the holes of the perforate exceeds the threshold of approximately two times the skin friction velocity. For the resistance, an additive relation between the contributions of grazing flow and high-level acoustic excitation can be assumed in case the particle velocity in the orifices exceeds the threshold level. For the reactance, the influence of high-level acoustic excitation above the threshold level is small compared to the influence of the grazing flow.