Impedance Eduction for Multisegment Liners

Abstract

This paper explores the validity of an indirect method for impedance eduction of multisegment liners. This is accomplished via results obtained with two uniform liners and one two-segment liner, where each segment is constructed to match the geometry of one of the uniform liners. Each uniform liner is evaluated using direct and indirect impedance eduction methods. An indirect impedance eduction method is used to educe the impedance for each segment of the two-segment liner, and the results are compared with those educed for the uniform liners. These impedance spectra are shown to compare favorably for the majority of test conditions. Poorer comparisons are achieved for those test conditions where one segment of the two-segment liner provides little attenuation. Poor attenuation is a wellknown cause for impedance eduction difficulties. Overall, this multisegment impedance eduction method offers the potential to study complicated liners in a more efficient manner (i.e., without the requirement to build and test separate liners to duplicate each unique segment of the multisegment liner). More detailed studies are required to further validate this tool, and are intended to be the focus of future research.

Overview of Liner Activities in Support of the International Forum for Aviation Research

“…Data were acquired at two flow conditions (Mach 0.0 and 0.3) and two source levels (120 and 140 dB). The resultant data were used to investigate a multizone impedance eduction approach 19 (see Section II.C). For the purposes of this challenge, the acoustic pressure data acquired at 95 microphone locations in the GFIT, along with the test environment information will be included in the comparison database based on collaboration with the respective IFAR participants.…”

“…The results presented herein are confined to mid-range frequencies for which the largest effects (greatest attenuation) were observed at Mach 0.3 and a source level of 140 dB. The earlier paper 19 provides impedances educed for each of these liners using methods designed for uniform and two-zone liners. Results for the Mach 0.3 flow condition and a source level of 140 dB are presented in Figure 5.…”

IFAR Liner Benchmark - Challenge #1 - DLR

“…The second is a two-segment liner, where the only difference between the two axial segments is the depth of the liner cavity. First measurement results from these liner configurations have been published by NASA in Jones et al 1 .…”

“…Since the calculation is purely analytic and iteration-free, this eduction method is referred to as the straightforward method by Jing et al 18 . The corresponding values from the NASA GFIT test rig 1 are also plotted in figure 11 for the no flow case (green triangles) and for the case with a centerline Mach number of M = 0.3 (orange triangles). It should be noted that even with the same measured centerline Mach number the average Mach number in the duct is probably different between the GFIT test rig and the DUCT-R due to different cross-sectional dimensions and hence, different flow profiles.…”

IFAR liner benchmark challenge #1 – DLR impedance eduction of uniform and axially segmented liners and comparison with NASA results

“…The second is a two-segment liner, where the only difference between the two axial segments is the depth of the liner cavity. Measurement results from these liner configurations have been published by NASA in Jones et al 1,2 The goal of Challenge #1 is to gather data from multiple test rigs with the same liner configurations manufactured using 3D printing. By sharing the data with each participant, it will be possible to evaluate dependence of these results on fabrication, data acquisition and analysis (e.g., impedance eduction) approaches.…”