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Frequency Domain Linearized Navier-Stokes Equations Methodology for Aero-Acoustic and Thermoacoustic Simulations
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aeroacoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. SDB Aerodynamic.
2015 (English)Licentiate thesis, monograph (Other academic)
Abstract [en]

The first part of the thesis focuses on developing a numerical methodology to simulate the acoustic properties of a hybrid liner consisting of a perforated plate, a porous layer and a Helmholtz cavity. Liners are always a standard way to reduce noise in today’s aeroengines, e.g. the fan noise can be reduced effectively through the installation of acoustic liners as wall treatments in the ducts. In order to optimize a liner in the design phase, an accurate and efficient prediction tool is of interests. Hence, a unified Linearized Navier-Stokes equations(LNSE) approach has been implemented in the thesis, combining the LNSE in frequency domain with the fluid equivalent model. The LNSE is applied in the vicinity of the perforated plate to simulate sound propagation including viscous damping effect, and the fluid equivalent model is used to model the sound propagation in the porous material including absorption.

The second part of the thesis focuses on the prediction of thermoacoustic instabilities. Thermoacoustic instabilities arise when positive coupling occurs between the flame and the acoustics in the feedback loop, i.e. the flame acts as an amplifier of the disturbances (acoustic or fluid) at a natural frequency of the combustion system. Once the thermoacoustic instabilities occur, it will lead to extremely high noise levels within a relatively narrow frequency range, resulting in a huge damage to the structure of the combustors. Hence, a solution must be found, which breaks the link between the combustion process and the structural acoustics. The numerical prediction of thermoacoustic instabilities in the thesis is performed by two different numerical methodologies. One solves the Helmholtz equation in combination of the flame n − tau model with the low Mach number assumptions, and the other solves the Linearized Navier-Stokes equations in frequency domain with mean flow. The result show that the mean flow has a significant effect on the thermoacoustic instabilities, which is non-negligible when the Mach number reaches to 0.15.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , 69 p.
TRITA-AVE, ISSN 1651-7660 ; 2015:98
Keyword [en]
Linearized Navier-Stokes Equations, frequency domain, fluid equivalent model, hybrid liner, thermoacoustic instabilities, Rijke-tube
National Category
Mechanical Engineering
Research subject
Engineering Mechanics
URN: urn:nbn:se:kth:diva-179677ISBN: 978-91-7595-800-2OAI: diva2:885566
2015-12-15, D2, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
EU, FP7, Seventh Framework Programme, 26766

QC 20151221

Available from: 2015-12-21 Created: 2015-12-18 Last updated: 2015-12-21Bibliographically approved

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Na, Wei
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