Orifice impedance under grazing flow measured with a single microphone method

The effect of one-sided grazing mean ow on the acoustical impedance of rectangular orifices is measured at low Mach number and low Helmholtz number by means of a single microphone method. The results are fairly consistent with previous experimental results obtained by means of a two-microphone impedance tube. Furthermore no significant in- uence of the aperture aspect ratio and aperture wall thickness on the non-dimensional scaled impedance is found, at least for the qualitative trend. Comparison with an existing theoretical model shows reasonable agreement for the resistance, provided that the exper- imental results are tentatively corrected for boundary layer- and induced ow effects. For the reactance no agreement is found.