On the Impact of the Acoustic Wave Direction on the In-Orifice Flow Dynamics of an Acoustic Liner Grazed by a Turbulent Flow

This study investigates the aerodynamic and acoustic response of a multi-orifice acoustic liner grazed by a planar acoustic wave and turbulent flow, at centerline Mach number equal to 0.32. High-fidelity flow simulations are carried out using a Lattice-Boltzmann Very-Large- Eddy-Simulation solver and the in-situ technique is used to calculate impedance. The triple decomposition technique is adopted to separate the mean-flow effects from those due to grazing tonal acoustic waves with different frequencies and amplitudes. This study highlights the sensitivity of in-situ measurements on the position of the face-sheet probe used to sample the unsteady pressure fluctuations. It is found that the resistance changes up to a factor of three along each cavity. The acoustic-induced velocity field reveals the intricate interaction between the acoustic waves and the turbulent flow. It is shown that the wake shed by the upstream cavity impacts the downstream one, affecting the spatial distribution and the amplitude of the acoustic-induced velocity within the orifice. Furthermore, a vortex within the hole is observed; it is found that its impact on resistance depends on the acoustic wave propagation with respect to the mean flow. In the case of downstream acoustic wave propagation, a smaller area of the orifice is associated with the passage of the grazing acoustic wave, which translates into higher values of resistance compared to the upstream case.