Design of a single degree of freedom acoustic liner for a fan noise test rig

Abstract

Acoustic liners are an essential part of noise reduction technologies commonly applied in aircraft turbofan engines. Fan noise suppression can be achieved by selecting an appropriate liner design with optimal acoustic impedance at the blade passing frequency. Great efforts have been made not only to improve experimental characterization and numerical methods for acoustic liners, but also to understand noise generation mechanisms, which ultimately impacts on the liner design itself. To gain confidence in the liner design process, a liner barrel was developed and fabricated for the Fan Noise Test Rig located at the University of São Paulo. To this end, analytical methods were used to determine the optimal acoustic impedance for the Fan Noise Test Rig, and a flat test sample was fabricated for experimental characterization with flow using both in-situ and impedance eduction techniques at the Federal University of Santa Catarina. A liner barrel of same nominal geometry was fabricated and placed at the Fan Noise Test Rig, and a modal decomposition indicated that the Tyler-Sofrin mode has been successfully suppressed at the first blade passing frequency. Numerical predictions of liner transmission loss considering the flat sample impedance showed good agreement with experimental results.

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

“…Also shown in Fig. 5 are the experimental data obtained by Spillere et al [13]. Frequency, Hz It can be seen from Fig.…”

“…However, the numerical domain is much more precise in this regard, yielding results closer to the in-situ method, as this method is more precise in this region of the spectrum. A similar analysis is also presented by Spillere et al [13], where the differences in impedances educed and calculated by in-situ is explored for experimental data in the context of a fan noise test rig.…”

“…The following section presents the results obtained with both methods, and we analyze the results for different SPL and different cavities (in the case of the in-situ method) for the no flow case. The experimental data was obtained by Spillere et al [13] in the UFSC liner test rig, for both the in-situ and eduction methods.…”

“…Therefore, this study can also be seen as a cross-validation of both techniques. Results are compared with the experimentally educed impedance of a typical low-porosity single-degree-of-freedom liner sample, as well as the impedance measured with in-situ technique, as published in Spillere et al [13]. As a means to save computational resources, the total liner length is reduced, but the relevant design parameters i.e.…”

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

“…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]. Simulations were performed without grazing flow and the impedance was obtained with both the in-situ [19] and the mode matching method [20].…”