A numerical and experimental investigation of the dissipation mechanisms of resonant acoustic liners

In a recent investigation, it was found by direct numerical simulation that sound waves at high intensity can induce vortex shedding at the mouths of the resonators of an acoustic liner. Measurements from their numerical simu lations indicate that the rate at which kinetic energy is transferred to th e shed vortices can be much higher than the viscous dissipation rate. Thus vortex shedding is a dominant dissipation mechanism of resonant acoustic li ners. This paper reports the results of a co-ordinated investigation aiming at validating the observations and measurements of direct numerical simula tion experimentally. The experiment uses a normal incidence impedance tube. Good agreements are found between the measured absorption coefficients of the physical experiment and direct numerical simulation over a broad range of frequencies and sound pressure levels. A separate visualization experime nt confirms the observation of shed vortices at high incident sound intensi ty. (C) 2001 Academic Press.