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Keywords = locally reacting acoustic liners

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17 pages, 2854 KiB  
Article
Comparison of Semi-Empirical Impedance Models for Locally-Reacting Acoustic Liners in a Wide Range of Sound Pressure Levels
by Vadim Palchikovskiy, Aleksandr Kuznetsov, Igor Khramtsov and Oleg Kustov
Acoustics 2023, 5(3), 676-692; https://doi.org/10.3390/acoustics5030041 - 14 Jul 2023
Cited by 3 | Viewed by 2538
Abstract
A comparison is considered of the experimentally obtained impedance of locally reacting acoustic liner samples with the impedance calculated using semi-empirical Goodrich, Sobolev and Eversman models. The semi-empirical impedance models are outlined. In the experiment, the impedance is synchronously measured on a normal [...] Read more.
A comparison is considered of the experimentally obtained impedance of locally reacting acoustic liner samples with the impedance calculated using semi-empirical Goodrich, Sobolev and Eversman models. The semi-empirical impedance models are outlined. In the experiment, the impedance is synchronously measured on a normal incidence impedance tube by the transfer function method and Dean’s method. A modification of the conventional normal incidence impedance tube is proposed to obtain these measurements. To automate the measurements, a program code is developed that controls sound generation and the recording of signals. The code includes an optimization procedure for selecting the voltage on an acoustic driver, providing the required sound pressure level on the face of the sample at different frequencies. The geometry of acoustic liner samples and specifics of synchronous impedance measurements by the aforementioned methods are considered. Experiments are performed at sound pressure levels from 100 to 150 dB in the frequency range of 500–3500 Hz. A comparative analysis of semi-empirical models with the experimental results at different sound pressure levels is carried out. Full article
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28 pages, 10996 KiB  
Article
Suppression of the Spatial Hydrodynamic Instability in Scale-Resolving Simulations of Turbulent Flows Inside Lined Ducts
by Mikhail Shur, Mikhail Strelets and Andrey Travin
Fluids 2023, 8(4), 134; https://doi.org/10.3390/fluids8040134 - 17 Apr 2023
Viewed by 1781
Abstract
This paper addresses one of the major obstacles arising in the high-fidelity scale-resolving simulations of turbulent flows inside ducts with the walls covered by acoustic liners in order to attenuate the sound radiated from the duct. It consists of the development of spatial [...] Read more.
This paper addresses one of the major obstacles arising in the high-fidelity scale-resolving simulations of turbulent flows inside ducts with the walls covered by acoustic liners in order to attenuate the sound radiated from the duct. It consists of the development of spatial hydrodynamic (convective) instability over the treated walls at the low values of the acoustic resistance of the liner. For reasons that remain unclear, the growth rate of this instability and its effect on sound propagation through the duct is strongly overestimated by the CFD simulations using the macroscopic concept of the locally reacting acoustic impedance. A new damping volume source term (“body force”) is proposed, whose introduction into the momentum equation resolves this issue by means of artificially suppressing the instability while remaining within the framework of the computationally efficient model of the impedance wall, i.e., without trying to simulate the liner microscopically. Examples are presented of the application of the developed methodology to the flows in the grazing impedance tubes with two different liners. They suggest that the proposed form of the damping source term can be considered universal and that the suppression of the hydrodynamic instability ensured by this term is not accompanied by any significant distortion of the propagation of the sound waves and the turbulence statistics, except for a very narrow near-wall region. Full article
(This article belongs to the Special Issue Next-Generation Methods for Turbulent Flows)
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