Numerical study on scattering and absorption by periodically arranged acoustical treatment at oblique incidence

Abstract

The propagation of sound over an impedance strip has been a topic of interest in sound abatement design. Excess absorption by the periodical arrangement of two or more distinct impedance conditions has been shown by various theoretical and experimental studies. It is believed that the scattering by the impedance discontinuities can enhance the absorption in some designs. This gives motivation to design a more elaborate set of impedance distribution within one periodic module. In this study, the scattering and absorption by periodically-arranged acoustical treatment at oblique incidence is investigated using the spectral method of Chebyshev collocation. The effects on the sound absorption and reflection by the length of the repeating unit, the angle of incidence and scattering characteristics due to the discontinuities of the acoustical impedance are analyzed. Central to the method is the derivation of out-going waves which allows scattered sound of all directions to leave the computational domain without reflection. The full picture of scattering is captured and analyzed using a rather coarse set of grid suitable for further optimization studies.