Numerical and Experimental Study of Resonant Liners Aeroacoustic Absorption Under Grazing Flow

Abstract

Resonant liners such as perforated honeycomb panels are used to reduce fan noise in the inlet nacelles. In a previous paper (Roche et al ., AIAA paper 2009-3146), the results of Direct Numerical Simulations (DNS), performed with the Onera CEDRE CFD code, enabled us to identify the viscous wall friction and the vortex s hedding as their main dissipation mechanisms. The impact of a rise of Sound Pressure Level (SPL) on their acoustic properties was pointed out. In this paper, 3D Navier-Stokes and Euler computations are performed, so that the relative efficiencies of these dissipation mechanisms can be evaluated. The distinction between “linear” and “nonlinear” absorption is found to be less obvious than commonly admitted. In order to estimate the effect of the sound waves incidence, an admittance is locally defined from the acoustic fie lds over the resonator opening inlet section. The coupling of acoustics with a stationar y 0.1 Mach number grazing air flow is ultimately discussed. The additional nonlinearities introduced by the flow are highlighted with DNS computations and Laser Doppler Velocimetry (LDV) experiments. The evolution of the local admittance is studied as well.