Evaluation of Spanwise Variable Impedance Liners with Three-Dimensional Aeroacoustics Propagation Codes

Abstract

Three perforate-over-honeycomb liner configurations, one uniform and two with spanwise variable impedance, are evaluated based on tests conducted in the NASA Grazing Flow Impedance Tube (GFIT) with a plane-wave source. Although the GFIT is only 2" wide, spanwise impedance variability clearly affects the measured acoustic pressure field, such that three-dimensional (3D) propagation codes are required to properly predict this acoustic pressure field. Three 3D propagation codes (CHE3D, COMSOL, and CDL) are used to predict the sound pressure level and phase at eighty-seven microphones flush-mounted in the GFIT (distributed along all four walls). The CHE3D and COMSOL codes compare favorably with the measured data, regardless of whether an exit acoustic pressure or anechoic boundary condition is employed. Except for those frequencies where the attenuation is large, the CDL code also provides acceptable estimates of the measured acoustic pressure profile. The CHE3D and COMSOL predictions diverge slightly from the measured data for frequencies away from resonance, where the attenuation is noticeably reduced, particularly when an exit acoustic pressure boundary condition is used. For these conditions, the CDL code actually provides slightly more favorable comparison with the measured data. Overall, the comparisons of predicted and measured data suggest that any of these codes can be used to understand data trends associated with spanwise variable-impedance liners.

Time-domain simulation of the acoustic nonlinear response of acoustic liners at high sound pressure level

“…which is slightly different from the porosity given in the article [Jones et al, 2017]: ϕ p = 11%. In a first step, the porosity in Table 7 is used.…”

“…In practice, acoustic liners in aircraft engines used for noise reduction are subject to grazing flow. The objective of this section is to model the acoustic behavior of acoustic liner studied by Jones et al [2017] and Diab et al [2022] in a grazing incidence configuration, however without mean flow. To do so, a porous-based modeling of the perforated plate is used with a similar approach to that of Section 7, leading to a volume modeling of the liners (where cavities are meshed).…”

“…Table 7: Geometric properties of the DPP1 and SVC1 liners studied in [Jones et al, 2017, Diab et al, 2022 In [Jones et al, 2017], the 50.8 mm-wide and 406.4 mm-long SVC1 liner consists of a 4 × 30 array of separated square chambers with 22 perforations, each of size 15.748 mm × 15.748 mm, and the cavities of l c = 76.2 mm in depth. Note that the porosity of its perforated plate directly calculated from the geometry of the liner is…”

Broadband and Low-Frequency Acoustic Liner Investigations at NASA and ONERA

“…Variable-depth liners constructed using wide chambers have been tested in the NASA Grazing Flow Impedance Tube (GFIT) in the presence of mean flow. [41,59,60] The wide chambers were covered with conventional perforated facesheets that provided a large portion of the acoustic resistance. As such, the nonlinearity of these facesheets caused a corresponding nonlinearity for the full liners.…”

Broadband Inlet Liner Design for the DGEN Aero-propulsion Research Turbofan

“…As part of a continuing effort to add to the prediction tools available to the Langley Liner Physics Team, the COMSOL code 19,20 was used to confirm selected in-duct CDL propagation predictions. Similar to CDL, COMSOL solves the convected Helmholtz equation with the acoustic potential as the unknown variable.…”