Lattice-Boltzmann Numerical Investigation of a Realistic Multi-Cavity Acoustic Liner with Grazing Flow

Scaled-resolved numerical simulations using the lattice-Boltzmann Very Large Eddy Simulation method are performed to compute the acoustic impedance of a realistic multi-cavity single degree of freedom liner grazed by a turbulent boundary layer. Numerical results are assessed against experimental impedance measurements carried out in grazing flow impedance test facility at the Federal University of Santa Catarina (UFSC), with three different approaches: the in-situ technique, the mode matching method and a Prony-like algorithm. Both experiments and numerical simulations are carried out with and without turbulent grazing flow at Mach number equal to 0.3 and with grazing acoustic tonal plane wave. Acoustic waves with amplitude equal to 130 dB and 145 dB are analyzed. For each amplitude, six frequencies are investigated in the range between 800 Hz and 2300 Hz. For each case, the acoustic wave propagates both in the same direction and opposite to the grazing turbulent flow. Numerical results show very good agreement with experimental data for the no-flow case. In the presence of grazing flow, preliminary numerical results show an overestimation of the resistance with respect to the experimental data. It has been found that using a less dissipative solver for the acoustic simulations and increasing the resolution lead to better agreement. Nevertheless, the numerical database predicts well the different trends between the impedance measurement methods. The presented database, after being recomputed with the less dissipative solver, will be used to understand the physical reasons behind the different impedance measurement results obtained with different eduction methods and clarify the physics of the flow-acoustic interaction