INVESTIGATION OF THE REASON FOR THE DIFFERENCE IN THE ACOUSTIC LINER IMPEDANCE DETERMINED BY THE TRANSFER FUNCTION METHOD AND DEAN´S METHOD

Abstract

The article considers the reason for the difference in the results of determining the impedance of the single-layer acoustic
liner samples by different methods during the operation in a normal incidence impedance tube. The operation of the normal incidence impedance tube was simulated by numerical solution of the Navier-Stokes equations. The data obtained from the numerical simulation were processed by the transfer function method and Dean’s method. A direct determination of the liner impedance, based on the ratio of the acoustic pressure to the acoustic normal velocity, was used to find out the reasons for the difference in impedance values. The analysis was carried out in the frequency range close to the resonance. It was shown that the transfer function method determines the impedance of the sample face, and the Dean’s method determines the impedance of the one cell only.