Numerical investigation on acoustic energy flux distribution in a lined duct

Acoustic impedance is the most frequently used parameter to represent the acoustic performance of liners. For a locally reacting liner composed by arrays of Helmholtz resonators with same geometric parameters, it is assumed the impedance values are identical over the liner panel under specific operating circumstance. Nearly all the impedance eduction methodologies deploy this assumption to derive acoustic impedance in a grazing incident flow tube by measuring sound pressure along the duct wall. However, in practice, different parts of the liner panel are apparently operating on different sound environment. For instance, the sound pressure level decreases over the liner length gradually due to the absorption and reflection of the acoustic energy. It holds true for real nacelle liners as well. Therefore, the impedance and acoustic performance are varied along the liner panel. In this paper, a liner of eight slit resonators are investigated by a two-dimensional numerical simulation to estimate the acoustic performance of each resonator. An analysis of acoustic energy flux at given positions in the duct is performed. Numerical results show that the resonators exhibit different acoustic behavior especially with intense incident sound waves.