Numerical investigation of the acoustic behavior of a multi-perforated liner

The acoustic response of a turbulent flow through an aperture in a multi-perforated liner is computed with incompressible large-eddy simulation (LES). The effect of a large array of apertures is accounted for by simulating a single jet with periodic conditions in both directions tangential to the liner. Turbulent grazing flows are included in the regions above and below the aperture, which is tilted in the tangential flow direction as in practical film cooling liners. The mass flow through the aperture is modulated with a small sinusoidal perturbation superposed on a mean component. The acoustic response is determined by measuring the fluctuating pressure difference across the aperture that results from forcing at a range of different frequencies. The Rayleigh conductivity of the aperture, which is related to the acoustic impedance of the liner, is calculated at each frequency. Good agreement is found when compared with existing theory, when the latter is modified in ad hoc fashion for the thickness and tilting of the aperture. The behavior of the flow inside the aperture and its relationship to the acoustic response are discussed.