Noise Dissipation Mechanisms in a Multi-Cavity Acoustic Liner Grazed by Turbulent Flow and Acoustic Waves

High-fidelity lattice-Boltzmann very-large-eddy simulations are used to analyse the acoustic energy dissipation mechanisms over a 22-cavities single-degree-of-freedom liner with chamfered orifices, subjected to grazing turbulent flow and acoustic plane wave at 145 dB. The analysis extends previous single-cavity investigations by accounting for the streamwise development of the grazing flow and the associated decay of the sound pressure level (SPL) along the liner. The results show that, in the absence of grazing flow, acoustic dissipation is dominated by vortex shedding in the upstream cavities, where the SPL is sufficiently high, and by viscous effects downstream as the SPL decreases. The dissipation is concentrated in the first portion of the liner, where nonlinear effects are strongest. When grazing flow is introduced, the flow topology inside the orifice is significantly modified. A quasi-steady vortex forms in the upstream portion of the orifice, redistributing the acoustic-induced velocity and concentrating viscous dissipation on the downstream lip during the inflow phase. At the same time, vortex shedding becomes phase dependent, contributing to dissipation during inflow and to acoustic energy generation during outflow, resulting in a net negative contribution. The combined effect leads to a redistribution of dissipation along the liner, with an approximately uniform streamwise behaviour arising from the balance between enhanced viscous dissipation and vortex-shedding generation. These results explain the reduced liner performance in the presence of grazing flow and highlight the importance of accounting for grazing flow in liner analysis and design.