Lattice-Boltzmann Very Large Eddy Simulation of a Multi-Orifice Acoustic Liner with Turbulent Grazing Flow

Abstract

A lattice-Boltzmann Very Large Eddy simulation of a multi-orifice acoustic liner, grazed by a turbulent flow at Mach number equal to 0.3 and a planar acoustic wave with amplitude equal to 130 dB and frequency equal to 1800 Hz, is carried out. The geometry of the liner replicates the experiments carried out in the Grazing Flow Impedance Tube (GFIT) facility at NASA Langley. It is found that the impedance, obtained from numerical simulations using the Dean's method, is a function of the orifice location. This is attributed to two phenomena: the interaction between the wake behind the upstream orifices and the downstream ones; and the interaction between the flow fields in the cavity induced by the ejected vortices. Results show that, for the investigated configuration, two vortical structures are generated in the orifice: one, formed along the downstream inner wall of the orifice, weakly penetrates into the cavity; the second, formed at the bottom downstream corner of the orifice, is ejected into the cavity up to three orifice diameters. The direction along which the latter is ejected varies with the orifice location. The ejected vortices are characterized by an annular vortex and a trailing vortex similarly to what found for synthetic jets. In the cavity, large scale vortical structures are found. On the face sheet, it is found that the turbulent wakes behind the upstream orifices increases the vertical velocity component within the orifices. These findings suggest that local measurement techniques, such as the Dean's method, might be affected by the sampling location in realistic configurations.

Acoustic-induced velocity in a multi-orifice acoustic liner grazed by a turbulent boundary layer

“…The commercial software 3DS Simulia PowerFLOW 6-2019 is used. The solver has been already validated for SDOF liner [13][14][15][16]. The same solver has been also used to simulate the effect of a SDOF liner installed on the nacelle of the NASA Source Diagnostic Test engine [17]; the predicted sound attenuation is in agreement with the one obtained with a different high-fidelity flow solver [18].…”

“…The flow field is instead sampled such to have 720 point per wavelength. For each configurations, acoustic waves with 10 acoustic periods are considered based on the findings from previous studies from the authors [15,16] and DNS results by Zhang and Bodony [2]. Data are sampled after convergence of the unsteady field, which is in general after no more than 2 acoustic periods.…”

High fidelity modeling tools for engine liner design and screening of advanced concepts

“…Avallone et al. 17 further extended the work by Manjunath et al. 15 by including a grazing flow at M gf = 0.3.…”

“…The simulations are performed with the LBM code PowerFLOW V6-2019, which is capable of predicting the acoustic wave absorption mechanism by resolving the actual facesheet geometry in the numerical grid. Based on best practices from previous simulations using this approach, 12,15,17 a grid resolution of 30 voxels (i.e., volume elements) per perforation hole diameter was chosen. A cylindrical cut-out of a larger liner geometry is simulated with no-slip hard wall boundary conditions, as shown in Figure 8.…”

“…The following process and procedure is based on the work by Avallone et al. 17 The simulation domain consists of a long rectangular duct with spanwise periodic boundary conditions. A single SDOF liner element (Configuration 1 from Figure 7(a)) is placed inside the domain and is exposed to the grazing flow (Figure 12).…”