A review of variable-impedance acoustic liner concepts developed at NASA

2021 ◽  
Vol 263 (5) ◽  
pp. 1633-1644
Author(s):  
Michael Jones
Keyword(s):  
Prediction Models ◽  
Normal Incidence ◽  
Wide Frequency Range ◽  
Acoustic Properties ◽  
Surface Porosity ◽  
Acoustic Liner ◽  
Impedance Tubes ◽  
Flow Impedance ◽  
Grazing Flow ◽  
Langley Research Center

This paper presents results attained in the NASA Langley Research Center test rigs using concepts for which the impedance varies over the surface of the liner. These liners are typically designed for significant sound absorption over a wide frequency range, but it is also possible to tune the design to achieve increased absorption at selected frequencies. A brief review is provided regarding a number of variable-impedance concepts. The first is a modified version of a conventional two-layer liner, in which the embedded septum location and acoustic properties are different for adjacent core chambers. Two concepts employ core chambers with different lengths, one with bent chambers to allow packaging within a limited volume, and the other with shared inlet ports to reduce the surface porosity. The last employs a perforated facesheet in which the hole diameter and porosity are varied over the surface of the liner. Data acquired in the NASA normal incidence and grazing flow impedance tubes are used to demonstrate the capabilities of these concepts. Impedance prediction models are also presented for comparison with these measured data.

Impedance eduction for uniform and multizone acoustic liners

2021 ◽  
pp. 1475472X2110238
Author(s):  
Michael G Jones ◽  
Douglas M Nark ◽  
Brian M Howerton
Keyword(s):  
Impedance Spectra ◽  
International Forum ◽  
Acoustic Liners ◽  
Prony Method ◽  
Research Challenges ◽  
Test Conditions ◽  
Acoustic Liner ◽  
Flow Impedance ◽  
Grazing Flow ◽  
Computationally Expensive

This paper presents results for five uniform and two multizone liners based on data acquired in the NASA Langley Grazing Flow Impedance Tube. Two methods, Prony and CHE, are used to educe the impedance spectra for each of these liners for many test conditions. The Prony method is efficient and generally provides accurate results for uniform liners, but is not well suited for multizone liners. The CHE method supports assessment of both uniform and multizone liners, but is much more computationally expensive. The results from these liners demonstrate the efficacy of both eduction methods, but also clearly demonstrate that sufficient attenuation is required to support accurate impedance eduction. For the liners considered in this study, the data indicate approximately 3 dB attenuation is needed for each zone of a multizone liner in order to ensure quality impedance eduction results. This study was conducted in response to two acoustic liner research challenges in support of a collaboration of multiple national laboratories under the International Forum for Aviation Research.

Numerical Analysis of Acoustic Liner Performance in grazing flow

2019 ◽  
Author(s):  
Shunji Enomoto ◽  
Tatsuya Ishii ◽  
Toshio Nishizawa ◽  
Hidemi Toh
Keyword(s):  
Numerical Analysis ◽  
Acoustic Liner ◽  
Grazing Flow

scholarly journals Design and optimization of acoustic liners with a shear grazing flow: OPAL software platform description

2021 ◽  
Vol 263 (6) ◽  
pp. 508-518
Author(s):  
Frank Simon ◽  
R. Roncen ◽  
P. Vuillemin ◽  
P. Klotz ◽  
Fabien Méry ◽  
...  
Keyword(s):  
Transmission Loss ◽  
Low Frequency ◽  
Total Sample ◽  
Software Platform ◽  
Linearized Euler Equations ◽  
Design And Optimization ◽  
Acoustic Liners ◽  
Acoustic Liner ◽  
Frequency Regime ◽  
Grazing Flow

In the context of aircraft noise reduction in varied applications where a cold or hot shear grazing flow is present (i.e., engine nacelle, combustion chamber, jet pump, landing gear), improved acoustic liner solutions are being sought. This is particularly true in the low-frequency regime, where space constraints limit the efficiency of conventional liner technology. Therefore, liner design must take into account the dimensional and phenomenological characteristics of constituent materials, assembly specifications and industrial requirements involving multiphysical phenomena. To perform the single/multi-objective optimization of complex meta-surface liner candidates, a software platform coined OPAL (OPtimisation of Acoustic Liners) was developed. Its first goal is to allow the user to assemble a large panel of parallel/serial elementary acoustic layers along a given duct. Then, the physical properties of this liner can be optimized, relatively to weighted objectives, for a given flow and frequency range: impedance target, maximum absorption coefficient or transmission loss with a total sample size and weight... The presentation will focus on the different elementary bricks and assembly of a problem (from 0D analytical coarse designs in order to reduce the parameter space, up to 2D plan or axisymmetric high-order Discontinuous Galerkin simulations of the Linearized Euler Equations).

INVESTIGATION OF THE REASON FOR THE DIFFERENCE IN THE ACOUSTIC LINER IMPEDANCE DETERMINED BY THE TRANSFER FUNCTION METHOD AND DEAN´S METHOD

Akustika ◽  
2021 ◽  
pp. 224
Author(s):  
Igor Khramtsov ◽  
Oleg Kustov ◽  
Vadim Palchikovskiy ◽  
Victor Ershov
Keyword(s):  
Transfer Function ◽  
Function Method ◽  
Stokes Equations ◽  
Direct Determination ◽  
Normal Incidence ◽  
Normal Velocity ◽  
Impedance Tube ◽  
Transfer Function Method ◽  
Acoustic Liner ◽  
The Difference

The article considers the reason for the difference in the results of determining the impedance of the single-layer acoustic liner samples by different methods during the operation in a normal incidence impedance tube. The operation of the normal incidence impedance tube was simulated by numerical solution of the Navier-Stokes equations. The data obtained from the numerical simulation were processed by the transfer function method and Dean’s method. A direct determination of the liner impedance, based on the ratio of the acoustic pressure to the acoustic normal velocity, was used to find out the reasons for the difference in impedance values. The analysis was carried out in the frequency range close to the resonance. It was shown that the transfer function method determines the impedance of the sample face, and the Dean’s method determines the impedance of the one cell only.

3D printed multifunctional, load-bearing, low-frequency sound absorbers

2021 ◽  
Vol 263 (1) ◽  
pp. 5605-5610
Author(s):  
William Johnston ◽  
Pulitha Godakawela Kankanamalage ◽  
Bhisham Sharma
Keyword(s):  
Mechanical Performance ◽  
Low Frequency ◽  
Normal Incidence ◽  
Acoustic Properties ◽  
Low Frequencies ◽  
Load Bearing ◽  
Fibrous Network ◽  
Size Limitation ◽  
Porous Architecture ◽  
3D Printed

Cellular porous materials are an attractive choice for lightweight structural design. However, though their open porous architecture is ideally suited for multifunctional applications, their use is typically limited by the pore sizes achievable by traditional as well as advanced fabrication processes. Here, we present an alternative route towards overcoming this pore size limitation by leveraging our recent success in printing fibrous structures. This is achieved by superimposing a fibrous network on a load-bearing, open-celled porous architecture. The multifunctional structure is 3D printed using a novel technique that enables us to simultaneously print a load-bearing scaffold and the necessary fibrous network. The acoustic properties of the printed structures are tested using a normal-incidence impedance tube method. Our results show that such structures can provide very high absorption at low frequencies while retaining the mechanical performance of the underlying architected structure.

ON CONTROL OF A PRESSING FORCE APPLIED TO ACOUSTIC LINER SAMPLE IN A NORMAL INCIDENCE IMPEDANCE TUBE

Akustika ◽  
2021 ◽  
pp. 277
Author(s):  
Oleg Kustov ◽  
Vadim Palchikovskiy ◽  
Igor Khramtsov ◽  
Roman Bulbovich
Keyword(s):  
Control System ◽  
Control Unit ◽  
Normal Incidence ◽  
Pressure Control ◽  
Pneumatic Cylinder ◽  
Acoustic Characteristics ◽  
Impedance Tube ◽  
Pressing Force ◽  
Acoustic Liner

The study considers the influence of control of the pressing force applied to an acoustic liner sample in a normal incidence impedance tube on the spread of acoustic characteristics of the tested sample. The design of a normal incidence impedance tube with a control system of a sample pressing force is presented. This system is implemented as a piston in a pneumatic cylinder with a pressure control unit. The measurements were taken on days when the characteristics of the environment were different from each other. This made it possible to better track the influence of the pressing force on reducing the spread of acoustic characteristics. In total, 10 measurements of the acoustic liner sample were carried out on a normal incidence impedance tube with and without control of the pressing force. The measurements were carried out for six months. As a result, the study has shown that the control of the pressing force applied to the acoustic liner sample provides a smaller spread of the obtained acoustic characteristics.

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