Numerical Investigation of Acoustic Liners Experimental Techniques using a Lattice-Boltzmann Solver

Abstract

The physics behind acoustic liners attenuation in the presence of flow and high sound pressure level is still a matter of debate. Similarly, discrepancies between experimental results and numerical data have been linked to the boundary conditions used to model the liner and boundary layer effects, and the reasons behind these discrepancies are still not clear. In this sense, to avoid the limitations of the boundary condition approach, fully resolved high fidelity computation models of the liner and its dissipation mechanisms may be an important tool to improve understanding. The present study carries out a numerical analysis using a code based on the Lattice-Boltzmann method, and special focus is given on replicating the results from different experimental techniques used to evaluate the liner impedance: the in-situ method and an impedance eduction method based on the mode-matching technique. The study is conducted with a model including a single degree of freedom liner with multiple cavities based on a real geometry. The model considers high sound pressure level, grazing plane acoustic waves without flow in order to replicate the experimental setup. A mesh convergence analysis is performed, and the liner impedance obtained numerically is compared with experimental results from the in-situ method and the impedance eduction technique. The numerical pressure and velocity fields are also analyzed in detail to better understand the damping mechanisms and physics involved.

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

“…It is worth mentioning that, in the experiments, results from the in-situ technique are obtained for the most upstream cavity. For such a configuration, local resistance decreases as reactance increases at downstream cavities [17]. Since the numerical results are averaged over all cavities, this could affect the numerical results' agreement to the experimental ones.…”

“…In this paper, we present a follow-up of the work presented by Schroeder et al [17], where the same multi-cavity SDOF liner is investigated in the presence of flow, and the comparison between eduction methods is extended by including the Prony-like Kumaresan-Tufts (KT) technique [21]. Numerical results are presented for acoustic plane wave with tonal frequency equal to 800, 1100, 1400, 1700, 2000 and 2300 Hz (i.e., above and below the resonant frequency) and amplitude equal to 130 dB and 145 dB.…”

“…In this study, the same liner geometry and computational approach presented by Schroeder et al [17] are considered. As shown in Fig.…”

“…The implementation of this technique in LBM has already been proven effective and capable of delivering good results [9]. A recent study has shown that, in the abscence of grazing flow, the resistance and SPL tend to decrease along the liner's length, as the acoustic wave interacts with successive cavities in a row, and this behavior is more noticeable near the resonant frequency [17]. Meanwhile, the reactance tends to increase along the liner's length [17].…”

“…Recently, a realistic multi-cavity SDOF liner was simulated by Schroeder et al [17] through a LB solver. They analyzed the same liner experimentally investigated by Spillere et al [18].…”