Comparison of Semi-Empirical Impedance Models for Locally-Reacting Acoustic Liners in a Wide Range of Sound Pressure Levels

Abstract

A comparison is considered of the experimentally obtained impedance of locally reacting acoustic liner samples with the impedance calculated using semi-empirical Goodrich, Sobolev and Eversman models. The semi-empirical impedance models are outlined. In the experiment, the impedance is synchronously measured on a normal incidence impedance tube by the transfer function method and Dean’s method. A modification of the conventional normal incidence impedance tube is proposed to obtain these measurements. To automate the measurements, a program code is developed that controls sound generation and the recording of signals. The code includes an optimization procedure for selecting the voltage on an acoustic driver, providing the required sound pressure level on the face of the sample at different frequencies. The geometry of acoustic liner samples and specifics of synchronous impedance measurements by the aforementioned methods are considered. Experiments are performed at sound pressure levels from 100 to 150 dB in the frequency range of 500–3500 Hz. A comparative analysis of semi-empirical models with the experimental results at different sound pressure levels is carried out.